JP5564794B2 - Circuit board, active matrix circuit board, and image display device - Google Patents

Description

  The present invention relates to a circuit board having an upper electrode connected to a lower electrode through a through hole provided in an interlayer insulating film, and more particularly to an active matrix circuit board for driving a display having the upper electrode as a pixel electrode and the active matrix thereof The present invention relates to an image display device having a circuit board.

  In recent years, a technical field called printing electronics has attracted attention. In this method, a fine circuit is formed by a printing method, so that the cost is reduced with respect to a conventional semiconductor process by general photolithography. Printing techniques used for printing electronics include inkjet printing, gravure printing, screen printing, and the like.

  Among these, the screen printing method has an advantage that a thick film patterned in a wide area can be easily formed. In a circuit board having fine wiring, leakage occurs between layers during high-frequency operation due to the capacitance between the stacked circuit wirings. Therefore, it is necessary to reduce the capacitance, and it is required to reduce the dielectric constant and increase the thickness of the interlayer insulating film. Here, if the screen printing method is used, it has a through hole (opening including a contact hole, a via hole, etc.) through which a through wiring for ensuring conduction between the laminated circuit wirings is provided, and is a thick film. A certain interlayer insulating film can be easily formed. Patent Document 1 discloses a technique for forming a thick film using a screen printing method. Patent Document 2 discloses a technique for forming an interlayer insulating film using a screen printing method.

  Further, the screen printing method has an advantage that printing can be stably performed with high throughput when the printing area is large. A scanning printing method such as an ink jet printing method has a drawback that the number of scans increases when the area is large and the density is high, and the printing time increases in proportion to the number of scans. Further, a scanning printing method such as an inkjet printing method has a drawback that it is difficult to ensure stability due to overlapping reproduction errors in each scanning. On the other hand, if the screen printing method is used, printing can be performed with good reproducibility if the printing is performed under the condition that the screen shape is stable, that is, the condition that the screen shape is not deformed. In the screen printing method, if the area is the same, it is possible to produce with almost the same throughput regardless of the printing pattern.

  Furthermore, it is also an advantage of the screen printing method that printing can be easily performed on a base having an uneven surface. By scanning a squeegee made of rubber, it is possible to print without being affected by the surface shape of the ground, if the unevenness is about several tens of μm.

Screen printing having the above-described advantages is employed in phosphor printing for plasma displays, electrode printing for multilayer ceramic capacitors, and the like, and has attracted attention as a technique for fine wiring. Patent Document 3 discloses a technique for forming pixel electrodes of an active matrix circuit substrate for driving a display by a screen printing method.
JP 2007-95783 A JP 2007-103913 A JP 2007-148333 A

  However, when the pixel electrodes of the active matrix circuit substrate are formed by using the screen printing method, there are the following problems.

  When the screen printing method is used, patterning is performed by discharging a highly viscous paste-like material from the opening of the screen. For this reason, there is a problem in that the amount of paste to be ejected varies depending on the size of the pattern when it becomes a fine pattern of 100 μm or less. FIG. 12 shows the relationship between the line width and film thickness when forming a wiring pattern by screen printing. As shown in FIG. 12, the film thickness increases as the line width increases. This is because as the line width of the wiring increases, the amount of paste to be discharged increases and the film thickness of the wiring also increases.

  Further, when the screen printing method is used, patterning is performed using a paste that is a fluid. Therefore, when the pattern is fine, the cross-sectional shape of the pattern to be formed becomes a “kamaboko” shape that is a part of the cylinder cut out, and it is difficult to make the surface shape of the pattern flat. There was a problem that there was. For example, Patent Documents 2 and 3 disclose a method of forming pixel electrodes by screen printing on an interlayer insulating film of a display driving circuit. However, when the matrix-like pixel electrodes arranged at a high density by the screen printing method are formed, there is a problem that the surface of the pixel electrode is not flat.

  Furthermore, when an active matrix circuit substrate having a pixel electrode (upper electrode) having such a pixel electrode is bonded to a display panel to form an image display device, there is a problem that display becomes non-uniform. Specifically, a counter electrode using a transparent conductive material is formed on the side of the display panel that faces the active matrix circuit substrate, and a voltage is applied between the pixel electrode and the counter electrode via the switching element, thereby displaying the display panel. Is controlled. At this time, if the distance between the lowermost surface of the display panel and the surface of the pixel electrode is non-uniform, there is a problem that the electric field applied to the display panel becomes non-uniform and display unevenness occurs.

  The present invention has been made in view of the above points, and provides a circuit board having an upper electrode excellent in flatness and size uniformity using a screen printing method with many cost advantages, An object of the present invention is to provide an active matrix circuit board and an image display device for driving a display with high density and high display uniformity.

The first invention includes a substrate, a plurality of lower electrodes formed on the substrate, an interlayer insulating film formed on the substrate and having an opening on each of the plurality of lower electrodes, and the plurality of the plurality of lower electrodes. In the circuit substrate having a flat surface that fills each of the openings, and an upper electrode that is electrically connected to each of the plurality of lower electrodes, the interlayer insulating film includes one opening, Having a curved surface shape having a maximum point at which the height from the substrate surface is a maximum height d at a substantially middle point between the opening closest to the one opening or the next closest opening; A height t from the substrate surface to the surface of the upper electrode at one opening is smaller than the maximum height d of the maximum point.

  In addition, the height from the substrate surface means a height from the substrate surface or a height from the same surface at a predetermined height from the substrate surface. Therefore, the maximum height d and the height t of the upper electrode may be a height from the substrate surface or a height from a surface having the same height from the substrate surface.

  When the maximum height d varies, the height t from the substrate surface of the upper electrode only needs to be smaller than the maximum value dmax of the maximum height d at all the maximum points. That is, instead of the maximum height d, the maximum value dmax of the maximum height d at all the maximum points may be used.

  According to a second invention, in the circuit board according to the first invention, the upper electrode is provided at an intersection of the matrix, is provided corresponding to each of the upper electrodes, and has a pixel region having a predetermined area S0. When the cross-sectional area of the upper electrode at a height d / 2 that is ½ of the maximum height d of the maximum point from the substrate surface is S1, S1 / S0 ≧ 0.2 is satisfied. To do.

  According to a third invention, in the circuit board according to the second invention, when the area of the one opening is S2, S2 / S1 ≦ 0.3 is satisfied.

  According to a fourth invention, in the circuit board according to any one of the first to third inventions, the height t is not less than 0.8 times the maximum height d.

  A fifth invention is characterized in that, in the circuit board according to any one of the first to fourth inventions, a curvature radius of the curved surface shape is not less than 30 times and not more than 200 times the maximum height d. .

  According to a sixth invention, in the circuit board according to any one of the first to fifth inventions, the upper electrode has a convex curved surface shape.

  A seventh invention is an active matrix circuit board including the circuit board according to any one of the first to sixth inventions, wherein the lower electrode is connected to a switching element, and the upper electrode is for display driving. It is characterized by being a pixel electrode.

  An image display device according to an eighth invention includes the active matrix circuit substrate according to the seventh invention, and a display unit and a counter electrode formed on the active matrix circuit substrate.

According to a ninth aspect of the present invention, there is provided a circuit board manufacturing method, comprising: an opening on each of the plurality of lower electrodes on a substrate on which the plurality of lower electrodes are formed; An interlayer insulating film having a curved surface shape having a maximum point where the height from the substrate surface is a maximum height d at a substantially middle point between the opening closest to the opening and the next closest opening; An interlayer insulating film forming step formed by printing, a partial electrode printing step for printing the upper electrode by screen printing so as to fill each of the plurality of openings, and an upper electrode for temporarily curing the upper electrode by heat treatment A pre-curing step, an upper electrode pressing step of pressing and flattening the pre-cured upper electrode, and a main surface of the upper electrode through the heat treatment , and the substrate surface of the upper electrode at the one opening Height from The method of the circuit board, characterized by chromatic and said maximum height upper electrode main curing step you less than d of the maximum point.

  ADVANTAGE OF THE INVENTION According to this invention, the circuit board which has the upper electrode excellent in planarity and the uniformity of size can be provided using the screen printing method with many cost advantages.

Next, the best mode for carrying out the present invention will be described with reference to the drawings.
(First embodiment)
A circuit board and an active matrix circuit board according to a first embodiment of the present invention will be described with reference to FIGS.

  First, the structure of the circuit board and the active matrix circuit board according to the present embodiment will be described with reference to FIGS.

  FIG. 1 is a cross-sectional view schematically showing the structure of the circuit board according to the present embodiment. FIG. 2 is a top view schematically showing the structure of the active matrix circuit substrate according to the present embodiment. 2A shows a state where a switching element is formed, and FIG. 2B shows a state where an interlayer insulating film having a through hole (opening) is formed on the switching element. FIG. 2C shows a state in which the pixel electrode (upper electrode) is formed on the through hole (opening). FIG. 3 is a cross-sectional view schematically showing the structure of the active matrix circuit substrate according to the present embodiment in comparison with the structure of a conventional active matrix circuit substrate. 3A is a cross-sectional view taken along line AA in FIG. 2B, and FIGS. 3B and 3C show a conventional pixel electrode (upper electrode) for comparison. It is a figure which shows the state in which the display panel and the opposing board | substrate are formed on the formed board | substrate.

  Referring to FIG. 1, a circuit board 20 according to the present embodiment includes a substrate 1, a lower electrode 4, an interlayer insulating film 6, and an upper electrode 7. That is, the substrate 1, the plurality of lower electrodes 4 formed on the substrate 1, and the interlayer insulation formed on the substrate 1 and having a plurality of through holes (openings) 9 on each of the plurality of lower electrodes 4. The film 6 includes an upper electrode 7 formed so as to fill each of the plurality of through holes (openings) 9 and electrically connected to each of the plurality of lower electrodes 4. In other words, the lower electrode 4, the interlayer insulating film 6, and the upper electrode 7 are formed on the substrate 1, and the upper electrode 7 and the lower electrode 4 are electrically connected through the through hole (opening) 9. .

  As shown in FIG. 1, the interlayer insulating film 6 includes a through hole (opening) 9 and a through hole (opening) 9 closest to the through hole or a through hole (opening) next to the through hole. 9 has a curved surface shape having a maximum point C at which the height from the substrate surface is a maximum height d at a substantially middle point with respect to 9. Further, the height t from the substrate surface of the upper electrode 7 in the through hole (opening) 9 is smaller than the maximum height d of the maximum point C.

  Hereinafter, in the present embodiment, an active matrix circuit substrate 30 for driving a display is exemplified as the best mode of the circuit substrate 20 having the substrate 1, the lower electrode 4, the interlayer insulating film 6, and the upper electrode 7 as described above. . The circuit board 20 according to the present invention is similar to the active matrix circuit board 30 for driving a display, and is used for various devices that require uniformity of the electric field distribution on the upper electrode 7 as will be described later. It can be used as a drive circuit board and is not limited to display driving. When the circuit board according to the present embodiment is used as an active matrix circuit board for driving a display, the output terminals of switching elements arranged in a matrix form correspond to the lower electrode of the present invention, and a display panel ( The pixel electrode that applies an electric field to the display portion) corresponds to the upper electrode of the present invention.

  In the present embodiment, any substrate can be used as long as it can output a predetermined voltage from the output terminal of the switching element as the substrate in which the switching elements are arranged at the intersections of the matrix (arranged in a matrix). . An example of such an active matrix circuit substrate 30 is one using a general TFT (Thin Film Transistor) as a switching element. As an example, FIGS. 2A and 2B are top views of the active matrix circuit substrate, and FIG. 3A is a cross-sectional view of the active matrix circuit substrate. A gate electrode 2 and a gate insulating film 3 are sequentially stacked on the substrate 1, and a source electrode 5 and a drain electrode 4 are formed on the gate insulating film 3. The drain electrode 4 corresponds to the lower electrode of the present invention. A semiconductor 8 is formed in the channel region 10 on the gate insulating film 3 and between the source electrode 5 and the drain electrode 4.

  As the substrate 1, any substrate can be used as long as it has a function of holding a patterned circuit, and a substrate having high adhesion to the material of the gate electrode 2 and the gate insulating film 3 in contact with the substrate 1 is preferable. . Examples include inorganic resins such as glass and silicon, and arbitrary resins such as polyethylene naphthalate, polyethylene terephthalate, polycarbonate, and acrylic. A surface treatment or a coating layer for improving the adhesion to the adjacent layer may be formed on these materials.

  As the material for the gate electrode 2, the source electrode 5, and the drain electrode 4, any material having high conductivity can be used, and metals and alloys are preferable. As the film formation method and formation method of the gate electrode 2, the source electrode 5, and the drain electrode 4, any method can be used, and a combination of a vacuum film formation method such as sputtering or vacuum evaporation and photolithography, An example is a printing method using an ink in which a conductive filler is dispersed. However, the printing method is preferable from the viewpoint that the material used can be reduced and the manufacturing cost can be reduced. Examples of the printing method include an ink jet method, a gravure printing method, and a screen printing method. About these printing methods, a suitable method can be selected corresponding to a required resolution.

  As the material of the gate insulating film 3, any insulator material can be used. However, in consideration of forming the source electrode 5 and the drain electrode 4 on the gate insulating film 3, it is preferable to use a highly flat material and a film formation method.

  In this embodiment, as shown in FIG. 2A, a switching element can be formed by patterning the semiconductor 8 in the channel region 10 to form a transistor. As shown in FIG. 2A, the active matrix circuit board 30 can be formed by arranging switching elements in a matrix.

  As the material of the semiconductor 8, any known inorganic semiconductor material / organic semiconductor material can be used. The method for forming the semiconductor 8 is preferably a method of patterning an organic semiconductor by a printing method because the manufacturing cost can be reduced. In the active matrix circuit substrate 30 illustrated in FIG. 2A, the gate electrode 2 corresponds to a selection line, and the source electrode 5 corresponds to a signal line. The output from the switching element is taken out from the drain electrode 4.

  The active matrix circuit board 30 is an example of the embodiment and does not limit the contents of the present invention. As long as the output for driving the display is possible, a plurality of switching elements may be combined, and an electrode for correcting capacitance and low efficiency may be formed by an arbitrary method.

  Next, with reference to FIGS. 4 to 5, the structure and manufacturing method of the interlayer insulating film in the circuit board according to the present embodiment will be described.

  FIG. 4 is a top view schematically showing the pattern of the interlayer insulating film of the active matrix circuit substrate according to the present embodiment. FIG. 5 is a diagram for explaining the method of manufacturing the circuit board according to the present embodiment, and is a diagram schematically showing how the interlayer insulating film is formed by screen printing.

  In order to drive a display using the active matrix circuit board 30 according to the present embodiment, as shown in FIGS. 2B and 3A, an interlayer insulating film having a through hole (opening) 9 is used. 6 and the pixel electrode (upper electrode) 7 needs to be formed on the through hole (opening) 9 as shown in FIG. Thereby, the area of the pixel electrode (upper electrode) 7 for driving the display can be increased. At this time, a leakage current is generated during high-frequency operation due to the capacitance between a certain pixel electrode (upper electrode) 7 and another electrode not connected to the pixel electrode (upper electrode) 7. Therefore, it is necessary to reduce the capacitance generated between the pixel electrode (upper electrode) 7 and another electrode not connected to the pixel electrode (upper electrode) 7 of the active matrix circuit board 30. Therefore, the interlayer insulating film 6 is preferably formed of a thick film made of a material having a low dielectric constant.

  The pattern of the interlayer insulating film 6 can be formed by printing a plurality of times using screens having different patterns. FIG. 4 schematically shows the pattern of the interlayer insulating film. As shown in FIG. 4A, a first interlayer insulating film 61 having a line pattern is formed, and a second interlayer insulating film 62 having a discrete dot pattern is formed thereon. A through hole (opening) 9 can be formed. Further, as shown in FIG. 4B, a first interlayer insulating film 61 having a line-shaped pattern is formed, and a line-shaped pattern rotated 90 degrees on the first interlayer insulating film 61 is formed. By forming the second interlayer insulating film 63, the through hole (opening) 9 can be formed. By these methods, it is possible to compensate for the disadvantages of screen printing that is not suitable for so-called “blank printing” in which the surrounding area is printed and only a small area is not printed.

  At this time, as shown in the cross-sectional view of FIG. 3A, the surface shape of the interlayer insulating film 6 is a convex curved surface shape that is a convex curved surface, and the apex thereof is an adjacent through hole (opening). Located near the midpoint. That is, there is a feature that there is no flat portion on the interlayer insulating film. The curvature radius is preferably in the range of 30 times to 200 times the maximum film thickness (film thickness at the apex). By making the cross-sectional shape of the interlayer insulating film a gentle curved surface structure, the surface of the pixel electrode material can be flattened. Thereby, the electrode surface can be kept parallel to the counter electrode, and the dissipation of the electric lines of force can be suppressed, and the display quality can be improved.

  In the case of FIG. 4 (a), the cross section having the convex curved surface shape shown in FIG. 3 (a) is a cross-sectional view taken along the lines AA and BB in FIG. 4 (a). In this case, as shown in FIG. 3A, the interlayer insulating film 6 is an abbreviation of a through hole (opening) 9 and a through hole (opening) 9 closest to the through hole (opening). It has a curved surface shape having a maximum point C at which the height from the surface of the substrate 1 is a maximum height d at an intermediate point.

  Moreover, in the case of FIG.4 (b), the cross section which has the convex-surface shape shown to Fig.3 (a) turns into sectional drawing which follows the AA line of FIG.4 (b). In this case, as shown in FIG. 3A, the interlayer insulating film 6 is not a through-hole (opening) 9 and a through-hole (opening) closest to the through-hole (opening). It has a curved surface shape having a maximum point where the height from the surface of the substrate 1 is a maximum height d at a substantially middle point with the adjacent through hole (opening) 9. That is, the vicinity of the center point C of the overlapping portion 64 that is a portion where the first interlayer insulating film 61 and the second interlayer insulating film 63 overlap is a maximum point where the height of the interlayer insulating film is the maximum height d from the substrate surface. Become.

  Further, increasing the film thickness of the interlayer insulating film 6 (the film thickness maximum value at the intermediate point C with the adjacent through hole) reduces the electric capacity between the pixel electrode and the electrode of the underlying switching element. This is preferable. On the other hand, as the film thickness increases, the radius of curvature decreases, which affects the pixel electrode surface shape. The optimum range is from 1 μm to 20 μm, more preferably from 3 μm to 10 μm.

  The size of the through hole (opening) 9 needs to be set to a size that can sufficiently reduce the contact resistance. The optimum size of the through hole (opening) 9 is set according to the pixel electrode material and the output electrode material of the switching element, but is preferably in the range of 5 to 80 μm, more preferably in the range of 20 to 50 μm.

  Although any method can be used as a method for forming the interlayer insulating film, it is preferable to use a screen printing method in this embodiment because a thick interlayer insulating film having a desired shape can be formed. . The screen printing method can easily form a thick film having a thickness of 1 μm or more as compared with the vacuum film forming method or other printing methods. In addition, the screen printing method is more productive than the photolithography forming method, as long as an appropriate screen can be produced, a thick film in a patterned state can be easily formed. It has a great advantage.

  An arbitrary insulator can be used as the material for the interlayer insulating film, but it is necessary to select a material that can be used for screen printing. As these materials, known materials that are commercially available as screen printing pastes may be used. Specifically, polymer materials such as polyvinyl alcohol, cellulose polymer, silicon polymer, polyethylene, polystyrene, polyamide, high molecular weight polyether, polyvinyl butyral, methacrylic ester polymer, and butyl methacrylate resin can be used. A plasticizer may be added to these resin materials, or an arbitrary solvent may be used to adjust the viscosity to good printability. In addition, when it is desired to impart high hardness, high thermal conductivity, and passivation to the interlayer insulating film, an insulating inorganic filler may be mixed with these resins. As the filler, fine particles of metal oxide or metal nitride are preferable. As an example of the insulating inorganic substance, fine particles such as alumina, silica, titania, yttria, zirconia, aluminum nitride, silicon nitride, and titanium nitride used for insulating ceramics can be used.

  Here, the pattern formation process by the screen printing method will be described with reference to FIG.

  When using the screen printing method to form an interlayer insulation film with through-holes, pattern the emulsion that does not transmit paste on the mesh that transmits the paste, provide an emulsion opening, and apply the paste by squeegee scanning over the screen. Patterning can be done through the emulsion openings. That is, the pattern of the emulsion opening formed on the screen becomes the pattern of the interlayer insulating film. Accordingly, if a screen having an emulsion opening pattern in which an interlayer insulating film is not formed in a through hole (opening) portion is prepared, an interlayer insulating film having a through hole (opening) can be formed.

  FIG. 5A is a conceptual diagram (cross section) of general screen printing. Printing is performed on the substrate 1 placed on the stage 28 by placing the paste 23 on the screen 22 stretched in the screen frame 21 and scanning the elastic squeegee 24 from left to right in the figure. . At this time, the screen 22 can limit the paste discharge area by patterning the emulsion 26 through which the paste 23 does not pass below the mesh 25 through which the paste 23 passes.

  Since the screen 22 is elastically deformed, by scanning the squeegee 24 while applying pressure downward in the figure, the screen 22 and the sample come into contact with only the screen contact portion 22a in the vicinity of the portion where the squeegee 24 is located. By scanning the squeegee, the paste 23 is filled in the emulsion opening 27 of the emulsion 26, and the lower surface of the paste 23 comes into contact with the substrate 1 which is the printing object (FIG. 5B). After passing through the squeegee 24, the screen 22 moves upward in the figure due to the tension of the screen 22 (FIG. 5 (c) to FIG. 5 (d)). As a result, the paste 23 remains on the substrate 1. At this time, the amount of paste remaining on the substrate 1 depends on the size of the emulsion opening 27 of the emulsion 26. When there is a sufficiently wide emulsion opening 27a of the emulsion 26, almost the entire amount of the filled paste 23a adheres to the substrate, but when the emulsion opening 27b of the emulsion 26 is small, as shown in FIG. Only a part of the filled paste 23 b remains on the substrate 1. In such a case, when the emulsion opening 27a and the emulsion opening 27b are compared, the height (thickness) of the residual pastes 23a and 23b tends to be lower (thin) in the residual paste 23b. Therefore, in the case of screen printing, it can be seen that it is difficult to make the film thicknesses of the patterns having different sizes the same, but conversely, it is found that they are suitable for printing a uniform pattern of the same size.

  Moreover, as shown in FIG.5 (e), the paste 23 adhering on the board | substrate 1 changes to a stable shape with the viscosity, elasticity, surface tension, and wettability with a board | substrate. Particularly in the case of a size of 100 μm or less, a dome-shaped cross-sectional shape as shown in FIG. Furthermore, there is a tendency to spread more in the plane direction than the emulsion opening due to wettability with the substrate.

  As described above, when printing is performed using the screen printing method, the cross-sectional shape of the printed pattern tends to be a gentle dome shape. Further, the amount of spreading spread depends on the wettability with the substrate and the surface shape.

  The arrangement period for arranging the through holes (openings) needs to match the density of the output electrodes (for example, drain electrodes) of the switching elements that are the underlying layers to be connected. In the present invention, 80 μm or more is a preferable range. When the arrangement period is 80 μm or less, the influence of the screen mesh becomes large and it becomes difficult to maintain a uniform film thickness.

  As described above, a screen obtained by patterning an emulsion on a mesh is used as a screen for forming an interlayer insulating film. Here, when high-resolution screen printing with a size of 100 μm or less is performed, the specification of the mesh greatly affects. In high-resolution screen printing, it is preferable to use a metal mesh made of metal in order to suppress deformation of the pattern on the screen. Examples of metal mesh include knitted metal wires made of metal, those made by electroforming, and imprinted on a film made of metal. Metal wires are used to achieve high aperture ratio and high density. What weaved is preferable. When the aperture ratio is high, the discharge resistance of the paste decreases, so that high speed printing is possible. On the other hand, reducing the aperture ratio of the mesh and increasing the density of the mesh is advantageous when forming a fine pattern. However, since it is necessary to use a fine metal wire, the strength is reduced and the mesh is easily deformed. Therefore, it is necessary to optimize the mesh density in accordance with the mesh strength and the pattern size. Stainless steel screen meshes made of metal wires are commercially available, and high-density meshes (# 500 mesh) having a mesh density of 500 per inch have been put into practical use. In this application, since it aims at printing of a fine pattern, mesh density is # 200 or more, More preferably, it is # 400 or more.

  When such a high-density mesh is used, it is common to use a thin wire in order to increase the aperture ratio. In the mesh used in the present application, the wire diameter is preferably in the range of 10 to 30 μm, and in the above-mentioned # 500 mesh, preferably 20 μm or less. When the wire diameter is reduced, the aperture ratio can be increased, but it is easily deformed. On the other hand, when the wire diameter is increased, the mesh thickness is increased and at the same time the aperture ratio is decreased.

  Since the pattern of the interlayer insulating film formed by screen printing is in a paste form, it is preferable to perform a curing process of a pattern suitable for the paste material. In the case of a paste made fluid with a thermosetting resin or a solvent, the pattern can be cured by heat treatment. In the case of a paste containing a filler, a hardened film having a higher density can be obtained by decomposing part or all of the binder component by heat treatment. When a photocurable resin is used, the pattern can be cured by irradiating light such as ultraviolet rays.

  Next, with reference to FIG. 6 to FIG. 10, the structure and manufacturing method of the pixel electrode in the circuit board according to the present embodiment will be described.

  First, the structure of the pixel electrode in the circuit board according to the present embodiment will be described with reference to FIGS.

  FIG. 6 is a cross-sectional view schematically showing the structure of the active matrix circuit substrate according to the present embodiment. 6A shows an example in which the surface shape of the pixel electrode (upper electrode) is a plane, and FIG. 6B shows an example in which the surface shape of the pixel electrode (upper electrode) is close to a plane. FIG. 7 is a view for explaining the circuit board according to the present embodiment, and is a sectional view schematically showing a sectional shape formed by periodically arranging through holes.

  As described above, the pixel electrode (upper electrode) 7 is formed on the substrate 1 on which the interlayer insulating film 6 is formed so as to fill the through hole (opening) 9 as shown in FIG. The pixel electrode (upper electrode) 7 is electrically connected to the output electrode (the drain electrode 4 in the example of FIG. 2) of the underlying active matrix circuit substrate 30 through the through hole (opening) 9.

  As shown in the cross-sectional views of FIGS. 6A and 6B, in this embodiment, the surface shape of the pixel electrode (upper electrode) 6 is parallel to the lower surface of the display panel 12 formed above the substrate 1. A simple shape, that is, a shape close to a plane is preferable. Specifically, the unevenness on the surface is preferably 5 μm or less, and more preferably 1 μm or less. Since the distance between the surface of the pixel electrode (upper electrode) 7 and the counter electrode 14 can be made uniform by adopting a structure having a surface shape close to a plane, the electric field lines are dissipated by the adjacent pixel electrode (upper electrode) 7. Thus, the display quality of the display panel 12 can be improved by improving the display resolution.

  Further, when the height of the pixel electrode (upper electrode) 7 in the through hole (opening) 9 from the surface of the substrate 1 is t, t is smaller than the maximum height d of the interlayer insulating film 6. Further, when the maximum height d varies between the local maximum points, the height t from the substrate surface of the pixel electrode (upper electrode) 7 is the maximum value dmax of the maximum height d at all the local maximum points. Smaller than that. Here, the height from the surface of the substrate 1 may be a height from a surface having the same height from the surface of the substrate 1 as described above. The height of the surface of the formed gate insulating film 3 may be used.

  Note that, as shown in FIG. 6B, the height of the surface of the pixel electrode (upper electrode) 7 can be set to be the highest right above the through hole (opening) and lower at the outer periphery. . In other words, the thickness of the pixel electrode (upper electrode) 7 can be a shape that is thickest right above the through hole (opening) and thin at the outer periphery.

  The height t of the pixel electrode (upper electrode) 7 from the substrate surface is preferably 0.8 times or more the maximum height d of the interlayer insulating film 6 as will be described later.

  Further, the area S0 of the pixel region is obtained as S0 = Px × Py, where the vertical and horizontal arrangement periods of the pixel electrode (upper electrode) and the through holes are Px and Py, respectively, as shown in FIG. Can do. Further, S1 is a cross-sectional area of the pixel electrode (upper electrode) at a height d / 2 that is ½ of the maximum height d of the maximum point from the substrate surface, as shown in FIG. 7C. S2 is an area of the through hole (opening), and is an area where the drain electrode and the pixel electrode are in contact with each other as shown in FIG. Further, as will be described later in Examples, the ratio of S1 / S0 is preferably 0.2 or more, and the ratio of S2 / S1 is preferably 0.3 or less.

  The material for the pixel electrode is selected from conductive metals, alloys and compounds, such as Au, Ag, Cu, Pt, Al, C (graphite), Ni, indium oxide, zinc oxide, tin oxide, gallium oxide, etc. Examples thereof include a transparent conductor.

  The pixel electrode (upper electrode) 7 can be formed by a known film formation method, and examples thereof include a vapor phase method such as sputtering, vapor deposition, and CVD, an electroforming method, and a printing method. Like the organic semiconductor formation and interlayer insulating film formation, the printing method is preferable because it has high productivity.

  When using the printing method, it is necessary to use conductive ink or conductive paste as the material of the pixel electrode. In particular, when a pixel electrode is formed using a screen printing method, it is necessary to use a paste-like conductive material. As the conductive paste material, a metal filler or a semiconductor filler added with a resin binder is generally used, and a material that enhances conductivity by baking at a high temperature after printing has been put to practical use. In order to adjust the viscosity and firing temperature of these pastes, an appropriate solvent may be added. In general, baking at a high temperature can increase the electrode density and the crystal grain size and decrease the electrical resistance. However, if an organic material is used as the substrate material or semiconductor material, the heat treatment should be 200 ° C. or lower. preferable. Examples of such a conductive paste include an Ag filler.

  Here, when the interlayer insulating film is formed by screen printing, the film thickness tends to vary. This occurs when the wire spacing of the screen mesh and the pattern size become close. FIG. 7A schematically shows the cross-sectional shape of the through-hole arrangement. In order from the left side of the figure, the film thickness (maximum height from the substrate surface) of the first interlayer insulating film 6 is d1, and the film thickness (maximum height from the substrate surface) of the second interlayer insulating film 6 is d2. ..., The film thickness (maximum height from the substrate surface) d1, d2,... Is distributed in a certain range. These variations in film thickness (maximum height from the substrate surface) are caused by the positional relationship between the wires constituting the screen mesh and the emulsion openings. When the wire spacing of the screen mesh is close to the size of the emulsion opening, the portion where there is no wire in the emulsion opening becomes a thick film as shown by d1 and d5 in FIG. In a certain portion, since the discharge of the insulating paste is suppressed, the film thickness (maximum height from the substrate surface) d becomes thin. In particular, when there is an intersection of wires in the emulsion opening, the discharge of the paste is most suppressed, and the film thickness (maximum height from the substrate surface) becomes thin. Variation in these film thicknesses (maximum height from the substrate surface) d can be dealt with by increasing the film thickness of the emulsion, and is preferably ± 2 μm, more preferably ± 0.5 μm. Thereby, it becomes easy to maintain parallelism with the display panel. However, as described above, the portion where the film thickness (maximum height from the substrate surface) d increases due to the positional relationship between the emulsion openings and the screen mesh wires, and thus occurs as a moire between the pattern period and the mesh interval. . The screen mesh is # 500 (500 per inch), the period of the pattern is 130 μm, and the screen is tilted about 30 ° (with a bias angle). Thick film portions in which the film thickness (maximum height from the substrate surface) d is increased at about 20 locations are generated. When variations in the thickness (maximum height from the substrate surface) d of these thick film portions are measured (when only d1 and d5 in FIG. 7A are measured), the variations are very small. When a comprehensive plane is created only with the apex of the thick film portion, a plane P having a height dmax from the substrate surface and parallel to the substrate 1 can be obtained as shown in FIG. As shown in FIG. 7B, when the pixel electrode (upper electrode) 7 is formed on the lower surface from the plane P and the display panel is bonded, the lower surface of the display panel can be substantially the same as the plane P. The positional relationship between the electrode (upper electrode) and the display panel can be made uniform.

  Next, with reference to FIGS. 8 to 10, a method for manufacturing a pixel electrode in the circuit board according to the present embodiment will be described.

  FIG. 8 is a diagram for explaining the method of manufacturing the circuit board according to the present embodiment, and is a flowchart for explaining the procedure of each step when the pixel electrode (upper electrode) is formed. FIG. 9 is a diagram for explaining the circuit board manufacturing method according to the present embodiment, and is a cross-sectional view schematically showing the structure around the pixel electrode (upper electrode) in the step of forming the pixel electrode (upper electrode). FIG. FIG. 10 is a diagram for explaining the circuit board manufacturing method according to the present embodiment, and is a diagram showing a state in which an upper electrode pressing process is performed using a pressure roller.

  As shown in FIG. 8, the method of manufacturing a circuit board according to the present embodiment includes an interlayer insulating film forming step, an upper electrode printing step, an upper electrode temporary curing step, an upper electrode pressing step, and an upper electrode main curing step. Process. The interlayer insulating film forming step includes steps S11 to S14, the upper electrode printing step includes step S15, the upper electrode temporary curing step includes step S16, and the upper electrode pressing step includes step S17. The upper electrode main curing process includes the process of step S18.

  First, an interlayer insulating film forming process including steps S11 to S14 is performed. Step S11 is a step of printing the first interlayer insulating film 61 on the substrate. Step S12 is a step of heat-treating and curing the printed first interlayer insulating film 61. Step S13 is a step of printing the second interlayer insulating film 62 on the substrate on which the cured first interlayer insulating film 61 is formed. Step S14 is a process in which the printed second interlayer insulating film 62 is heat-treated and cured. As described above, as the first interlayer insulating film 61 and the second interlayer insulating film 62, for example, as shown in FIG. 4A, a line-shaped first interlayer insulating film 61 and a dot-shaped first interlayer insulating film 61 are used. The two interlayer insulating films 62 can be formed by printing and curing, respectively. Also, for example, as shown in FIG. 4B, a linear first interlayer insulating film 61 and a linear second interlayer insulating film 63 orthogonal to the first interlayer insulating film 61 are printed and cured. Can be formed.

  Next, an upper electrode printing process including step S15 is performed. FIG. 9A is a cross-sectional view schematically showing the structure around the pixel electrode (upper electrode) after Step S15 is performed.

  As shown in FIG. 9A, a pixel electrode (upper electrode) 71 is formed on a through hole (opening) 9 formed in the interlayer insulating film 6. Since the pixel electrode (upper electrode) 71 needs to have electrical conductivity and plasticity as described above, the pixel electrode (upper electrode) 71 is preferably a conductive printing paste and is commercially available as an example. A paste is mentioned. When a paste-like material such as an Ag paste is formed, the surface shape is a convex curved surface due to surface tension, wettability with the base material, viscosity, etc., as shown in FIG. 9A. It becomes a shape. In order to obtain such a shape, the volume of the pixel electrode (upper electrode) 71 needs to match the cross-sectional shape of the interlayer insulating film 6. That is, the volume (the plane formed by the apex (maximum point) of the interlayer insulating film) of the portion below the apex (maximum point where the surface height is the maximum) of the adjacent interlayer insulating film 6 adjacent to each other, and the through When the volume of the electrode material is made larger than the volume surrounded by the bottom and side walls of the hole, the electrode surface becomes the thickest portion of the interlayer insulating film (the maximum height d is the maximum value dmax when flattened), that is, the maximum It will be higher than the highest point). In addition, when the number is too large, there is a problem that the flattening of pressure causes a short circuit with an adjacent pixel electrode (upper electrode) and conduction. On the other hand, when the volume of the pixel electrode material is too small compared to the volume below the apex of the adjacent interlayer insulating film 6 described above, the surface area of the pixel electrode (upper electrode) 72 is reduced after the pressure treatment, and the display panel There is a problem that the area of the region where the voltage can be applied in the (display unit) 12 is reduced. From these viewpoints, the volume of the pixel electrode (upper electrode) 71 is the volume surrounded by the plane formed by the apex (maximum point) of the adjacent interlayer insulating film 6 and the bottom and side surfaces of the through hole (opening) 9. And approximately the same. Therefore, the volume of the pixel electrode (upper electrode) 71 is preferably about 80% to 120% of the aforementioned volume.

  Next, an upper electrode temporary curing step including step S16 is performed. FIG. 9A also shows the structure around the pixel electrode (upper electrode) after step S16 is performed.

  Step S <b> 16 is a step of performing a heat treatment to temporarily cure the pixel electrode (upper electrode) 71. The pixel electrode (upper electrode) 71 only needs to have plasticity, and before the next upper electrode flattening step, the conductive paste can be heat-treated to perform a temporary curing process in which only the surface is cured. Instead of performing a temporary curing process by performing a heat treatment, a surface treatment may be performed in order to prevent adhesion between the press plate and the pixel electrode (upper electrode).

  Next, an upper electrode flattening process including step S17 is performed. FIG. 9B is a cross-sectional view schematically showing the structure around the pixel electrode (upper electrode) after Step S17 is performed.

  In step S17, the substrate on which the pixel electrode (upper electrode) 71 is formed is pressed using the press plate 11 to flatten the pixel electrode (upper electrode) 71, and the pixel electrode (upper electrode) 71 is moved to the interlayer insulating film. The pixel electrode (upper electrode) 72 is lower than the plane formed by the thick film portion (the portion where the maximum height is larger than the surrounding maximum point).

  By performing step S17, the surface of the pixel electrode (upper electrode) 71 can be made flat by applying pressure with the press plate 11 as shown in FIG. 9B. As a result, the pixel electrode (upper electrode) 72 pressed by the press plate 11 has a flat surface that is substantially the same height as the thick film portion of the interlayer insulating film 6 (the portion where the maximum height is larger than the surrounding maximum point). can do. At this time, the press plate 11 is brought into contact with the thickest part of the interlayer insulating film 6 so that the surfaces of all the pixel electrodes (upper electrodes) 72 arranged at the intersection of the matrix (arranged in a matrix) are arranged. A uniform shape can be obtained. At that time, there is an advantage that a uniform surface shape can be obtained without forming ribs conventionally used or dispersing spacers.

  The press plate 11 is preferably made of a material that does not adhere to the pixel electrode (upper electrode) 71 or is subjected to a surface treatment. In addition, a material having sufficient hardness so as not to be deformed or broken in the pressurizing process is preferable, and any material may be used as long as these requirements are satisfied. The press plate 11 is preferably a flat surface, but a pressure roller 29 may be used as shown in FIG. When the pressure roller 29 is used, it is necessary to make the roller diameter sufficiently larger than the electrode pattern. Further, the press plate 11 may be heated in order to increase the plasticity of the pixel electrode material during pressurization or to cure the pixel electrode material during pressurization. In this case, the upper electrode temporary curing process in step S16 is performed simultaneously with the upper electrode flattening process in step S17. Further, when a photo-curable material is used, light irradiation or the like may be performed during pressing in the upper electrode flattening step in step S17.

  Here, the method of lowering the pixel electrode (upper electrode) 71 below the plane formed by the thick film portion of the interlayer insulating film (the portion where the maximum height is larger than the surrounding maximum point) is not limited to the pressing method. Any method can be used. There are a method of polishing the outermost surface by forming a thick film and a method of flattening by applying pressure to a plastic conductive material, but the former has low processing accuracy at the time of polishing and at the same time there is concern about circuit damage due to polishing Therefore, it is not preferable. On the other hand, the latter has the advantage that accuracy can be obtained by abutting the flat press plate 11 on the thick film portion of the interlayer insulating film (the portion where the maximum height is larger than the surrounding maximum point), and is a more preferable method. is there.

  Next, an upper electrode main curing process including step S18 is performed as necessary. FIG. 9C is a cross-sectional view schematically showing a structure around the pixel electrode (upper electrode) when Step S18 is performed, and FIG. 9D is a pixel electrode after Step S18 is performed. It is sectional drawing which shows typically the structure of (upper electrode) periphery.

  Step S18 is a step in which the substrate on which the planarized pixel electrode (upper electrode) 72 is formed is heat-treated to be fully cured.

  After the upper electrode flattening step in step S17, the press plate 11 is removed as shown in FIG. 9C, and an upper electrode curing step for the pixel electrode (upper electrode) 72 is performed as necessary. As the upper electrode curing step, any method such as heat treatment or ultraviolet irradiation can be used. For example, when Ag paste is used, heat treatment can be performed. When the heat treatment is performed, the solvent component or the resin component is volatilized or decomposed to increase the density, so that the volume is reduced. As a result, as shown in FIG. 9D, the surface of the pixel electrode (upper electrode) 73 is formed below the thick film portion of the interlayer insulating film 6 (the portion where the maximum height is larger than the surrounding maximum point). It is possible to

  Next, in the circuit board according to the present embodiment, an operation and effect that can form an upper electrode excellent in flatness and size uniformity using a screen printing method will be described.

  When a pattern is formed using a screen printing method, particularly when a thick coating film is formed, it has an advantage of being excellent in high throughput, uniformity, and stability.

  On the other hand, when a pattern is formed using the screen printing method, patterning is performed by discharging a highly viscous paste-like material from the opening of the screen. As described above, when the pattern becomes finer than 100 μm, There is a disadvantage in that the amount of paste discharged varies depending on the size.

  Further, as described above, in the screen printing process, the amount of wet spread of the printed paste depends on the wettability with the substrate and the surface shape, so in many cases, the cross-sectional shape of the printed pattern is a gentle dome shape. Therefore, it is difficult to form a rectangular cross section. As a result, when the pixel electrode is formed on the interlayer insulating film of the display driving circuit by screen printing, the surface of the pixel electrode is not flat.

  FIG. 3A shows a cross-sectional view when the interlayer insulating film is formed by using a conventional screen printing method. As described above, when the screen printing method is used, the cross section of the interlayer insulating film has a gently convex curved surface shape convex upward. The case where a pixel electrode (upper electrode) is formed on such an interlayer insulating film is shown in FIGS. FIG. 3B is an example in which the pixel electrode (upper electrode) 7 is formed by using known photolithography, and FIG. 3C is an example in which the pixel electrode (upper electrode) is formed by a method using a conventional screen printing method. . In either case, the surface of the pixel electrode is not flat.

  In the case of using such a pixel electrode as a display device, the display panel is bonded via an adhesive 13 as shown in FIGS. 3 (b) and 3 (c). A counter electrode using a transparent conductive material is formed on the opposite side of the display panel, and the display panel is driven by applying a voltage between the pixel electrode and the counter electrode via a switching element. At this time, since the distance between the counter electrode and the surface of the pixel electrode varies, the electric field applied to the display panel becomes non-uniform, resulting in display unevenness.

On the other hand, according to the circuit board manufacturing method using the screen printing method according to the present embodiment, after forming the pixel electrode (upper electrode) by the screen printing method, the upper electrode temporary curing step, the upper electrode pressing step, the upper portion The electrode main curing process is performed. By these steps, the surface of all the pixel electrodes arranged in a matrix is made uniform by allowing the press plate to abut against the thick part of the interlayer insulating film (the part where the maximum height is larger than the surrounding maximum point). It can be a shape. Further, the volume of the pixel electrode (upper electrode) can be reduced by performing heat treatment, and the surface of the pixel electrode is placed below the thick part of the interlayer insulating film (the part where the maximum height is larger than the surrounding maximum point). It is possible to form. Thereby, even if it uses a screen printing method, the upper electrode excellent in planarity and the uniformity of size can be formed, without each pixel electrode short-circuiting and conducting. As a result, by defining the shape of the interlayer insulating film having through holes formed by using the screen printing method and the cross-sectional shape of the pixel electrode for applying an electric field to the display, for example, a display panel such as an electrophoretic display panel can be used. Contrast and resolution can be increased.
(Second Embodiment)
Next, an electrophoretic display, which is an image display device according to the second embodiment, will be described with reference to FIG. FIG. 11 is a cross-sectional view schematically showing the structure of an electrophoretic display which is an image display device according to the present embodiment.

  As shown in FIG. 11, an electrophoretic display 40 as an image display device according to the present embodiment includes an active matrix circuit substrate 30 according to the first embodiment and a display unit formed on the active matrix circuit substrate. 31 and a counter substrate 32 on which a counter electrode is formed. Further, as the display unit 31, a display panel 31 using an electrophoresis method is used.

  A known display panel 31 using the electrophoresis method can be used. For example, an electrophoretic display panel using microcapsules 33 can be used. Colored fine particles 34 dispersed in the dispersion are enclosed in microcapsules 33. The colored fine particles 34 disperse two kinds of white and black, and each has an opposite charge. The microcapsule 33 is sealed between the counter substrate 32 on which the counter electrode is formed and the active matrix circuit substrate 30 for driving. At this time, the microcapsule 33 needs to be substantially one layer on the entire surface of the display panel 31. At that time, a substrate that supports the microcapsules 33 may be sandwiched between the microcapsules 33 and the counter substrate 32 or the active matrix circuit substrate 30, or an adhesive that adheres both may be sealed. Further, the gap of the microcapsule 33 may be filled with a dispersion liquid. The lower surface of the display panel 31 is in contact with a display driving circuit on which the pixel electrode (upper electrode) 7 is formed, and the upper surface of the display panel 31 is in contact with the transparent counter substrate 32. The charged fine particles 34 dispersed in the microcapsule 33 are moved by connecting the counter electrode of the counter substrate 32 to the ground and applying a voltage to the pixel electrode (upper electrode) 7 through the active matrix circuit substrate 30. I can do it. When the white fine particles are positively charged and the black fine particles are negatively charged, when a voltage is applied so that the pixel electrode (upper electrode) 7 is positive with respect to the counter electrode of the counter substrate 32, the positively charged white The fine particles move to the upper surface side of the display panel, and the negatively charged black fine particles move to the lower surface side of the display panel. As a result, white color is generated and white display is performed. On the other hand, when a voltage is applied so that the pixel electrode (upper electrode) 7 is negative with respect to the counter electrode of the counter substrate 32, the positively charged white particles move to the lower surface side of the display panel, and the negatively charged black particles Moves to the upper surface side of the display panel and develops a black color.

  At this time, since the colored fine particles adhere to each wall surface of the microcapsule 33, the display can be maintained without applying a voltage (even when the circuit is opened).

  The movement of the fine particles moves along the lines of electric force generated when a voltage is applied between the pixel electrode (upper electrode) 7 and the counter electrode of the counter substrate 32. However, when the density of the pixel electrode (upper electrode) is increased, adjacent pixels affect display quality. For example, when the voltage applied between adjacent pixels is inverted, the lines of electric force directed in the vertical direction are directed toward the adjacent pixels. As a result, the horizontal direction component of the lines of electric force is generated, so that the display resolution and contrast are lowered. These become prominent when the pixel arrangement period is 200 μm or less. In order to maintain good display quality with an array period (resolution) of 200 μm or less, it is necessary to optimize the surface shapes of the pixel electrode (upper electrode) 7 and the interlayer insulating film 6.

  In the present embodiment, a display panel 31 and a counter substrate 32 as shown in FIG. 11 are provided above the pixel electrode (upper electrode) 7 formed on the active matrix circuit substrate 30 according to the first embodiment of the present invention. By providing the image display device 40, the surface shapes of the pixel electrode (upper electrode) 7 and the interlayer insulating film 6 can be made appropriate, and the display uniformity of the display panel 31 can be improved. it can.

  According to the present invention, an active matrix circuit substrate for driving an active matrix electrophoretic display, a liquid crystal display, an organic EL display, or a photochromic display is driven using a printing technique such as a screen printing method. Can be formed. Therefore, various displays excellent in image display quality can be manufactured at low cost.

  The effect of the circuit board according to the present invention as an active matrix circuit board for driving a display is as described above. However, as a use of the circuit board according to the present invention, it is possible to make the surface height and planar shape of the upper electrode uniform in a plurality of upper electrodes, and to display an image by attaching a display panel on the circuit board. The present invention is not limited to the use as a display driving panel constituting the apparatus, and includes various uses other than the display driving panel. Hereinafter, uses other than the display driving panel will be described.

  The circuit board of the present invention is characterized in that the height of the upper electrode (the surface thereof) from the substrate surface is lower than the height from the substrate surface of the maximum point of the interlayer insulating film. As a result, the distance between the electrode and the element can be made uniform when the element is bonded onto the circuit board. Because of these characteristics, it can be applied as an electrode for a two-dimensional sensor that senses capacitance.

  Specifically, for example, an insulator sheet is bonded onto the circuit board according to the first embodiment, and a counter electrode is formed on the insulator sheet so as to face the upper electrode on the circuit board. Thereby, a predetermined capacitance is generated between the counter electrode and the upper electrode. And it is possible to comprise electrostatic capacitance sensors, such as a pressure sensor, by measuring the voltage between a counter electrode and an upper electrode. Further, if combined with a display panel, a touch panel or the like can be configured.

  Here, in order to configure the above sensor as a two-dimensional sensor such as a touch panel, the capacitance of the electrode pair including a plurality of upper electrodes arranged in a matrix and a counter electrode facing the plurality of upper electrodes is uniform. It is necessary to be. The capacitance is proportional to the area of each electrode pair and the dielectric constant of the insulator between the electrodes of each electrode pair, and inversely proportional to the distance between the electrodes of each electrode pair. That is, the uniformity of the distance between the upper electrode and the counter electrode in each electrode pair is an important factor for the sensitivity of the sensor. Therefore, by using the circuit board according to the present invention, a highly sensitive sensor can be realized.

  Furthermore, since the circuit board according to the present invention is excellent in the uniformity of the electric field distribution within the electrodes, it is also effective in improving the uniformity of the capacitance between the plurality of electrode pairs. Therefore, it can be used as a circuit board for a two-dimensional sensor having high accuracy.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not construed as being limited to the examples.
[Example 1]
An active matrix circuit substrate was prepared in which thin film transistors were arranged in a matrix with an arrangement period of 130 μm on a plastic substrate having a thickness of 120 μm. The number of thin film transistors was 480 × 480, and an active matrix circuit substrate having an active matrix of about 50 mm square was formed.

  An interlayer insulating film having a through hole was formed on the substrate by screen printing. The screen emulsion pattern was formed so that the through hole was located on the drain electrode of the thin film transistor. As described above, the line-shaped first interlayer insulating film 61 and the dot-shaped second interlayer insulating film 62 were printed as shown in FIG. Sample preparation in this example was performed according to the flowchart shown in FIG.

  As a paste for forming an interlayer insulating film, a mixture of a filler made of silica fine particles and a binder made of polyvinyl alcohol resin was used. At that time, an ethylene glycol solvent was added to make a paste. The filler and binder concentrations of the paste were 58 wt%, and the viscosity was 200 Pa · s.

  The screen was obtained by patterning a 25 μm thick emulsion on a # 500 (500 linear density per inch) stainless steel mesh. The mesh wire was made of a stainless steel wire capable of handling high tension, and the wire diameter was 19 μm.

  Two types of emulsion patterns were prepared, a line pattern and a dot pattern, as shown in FIG. In the line pattern, the width of the emulsion openings was 70 μm and the arrangement period was 130 μm. On the other hand, in the dot pattern, the width of the emulsion opening was 45 μm along the direction perpendicular to the line of the line pattern, and 65 μm along the direction parallel to the line. Further, the arrangement period of the emulsion openings was set to the same 130 μm along the direction parallel to the line and the direction perpendicular to the line.

  A known screen printing method was used to form the first interlayer insulating film 61 and the second interlayer insulating film 62. The distance between the screen fixing frame and the sample surface shown in FIG. 5 was 2.4 mm, and the squeegee scanning speed was 60 mm / s. The material of the squeegee was a rubber material that was difficult to dissolve and swell with the solvent, and the angle between the squeegee and the sample surface (angle on the squeegee scanning direction side) was set to 70 °. After each interlayer insulating film is formed, heat treatment is performed to vaporize the paste solvent. For both the first interlayer insulating film 61 and the second interlayer insulating film 62, the heat treatment condition was 120 ° C. for 1 hour.

  As a result, an interlayer insulating film having through holes having a square shape of about 30 μm square could be formed. The cross-sectional shapes along the lines AA and BB in FIG. 4A were observed with a commercially available laser microscope. As a result, as shown in FIG. 7, it is confirmed that the shape is a convex curved surface that is convex upward, and the peak height, that is, the maximum height that is the height from the substrate surface of the maximum point where the height is the maximum. d was generally distributed in the range of 4 μm to 6 μm.

  Further, detailed surface shape measurement of the interlayer insulating film was performed using a laser microscope. As a result, the maximum value dmax of the maximum height d was 5.8 μm, the minimum value dmin was 4.6 μm, and the average value davg was 5.0 μm.

  Next, a pixel electrode (upper electrode) was formed on the formed through hole. A commercially available Ag paste for screen printing was used as a material for the pixel electrode (upper electrode). The Ag paste material was obtained by adding an acrylic resin and a solvent to Ag fine particles, and its viscosity was about 300 Pa · s. The screen used for printing was the same # 500 mesh as the above-mentioned interlayer insulating film as a mesh, and was formed in a matrix with an arrangement period of 130 μm so that the square emulsion openings overlapped the through holes on the interlayer insulating film. The opening was a 55 μm square. Considering that the arrangement period of the pixel electrodes (upper electrodes) is 130 μm, an opening having a size of about 40% is provided.

  A pixel electrode (upper electrode) pattern is printed under the same printing conditions as the interlayer insulating film, and heat treatment is performed at a temperature of 70 ° C. for 5 minutes to volatilize a part of the solvent component of the pixel electrode (upper electrode) paste, thereby increasing the plasticity Provided (temporary curing treatment). When the heat treatment is not performed, since the paste has elasticity and fluidity, the shape after pressurization returns to the shape before pressurization. On the other hand, by performing the heat treatment as in the present embodiment, the shape after pressurization does not return to the shape before pressurization.

The sample on which the pixel electrode (upper electrode) was temporarily cured was sandwiched between two glass plates and pressed with a press. The pressure was set to 10 kgf / cm ² and the pressurization time was 3 minutes. Thereafter, the glass plate was removed, heat treatment was performed at 100 ° C. for 1 hour, the remaining solvent was volatilized and the pixel electrode (upper electrode) was cured to obtain an active matrix circuit substrate for display. As a result of measuring the height t of the surface of the pixel electrode (upper electrode) from the substrate surface using a laser microscope, it was 5.2 μm. As a result, it was confirmed that t was lower than the maximum value dmax 5.8 μm of the maximum height d of the interlayer insulating film.

On the circuit board obtained as described above, an electrophoretic display panel and a counter electrode made of an ITO transparent conductive film were formed in the configuration shown in FIG. 6 to obtain an image display device. The counter electrode and the active matrix circuit of the active matrix circuit substrate were connected to a driving device, and an operation test was performed. As a result, uniform display contrast and resolution could be obtained.
[Comparative Example 1]
An interlayer insulating film was formed by the same method as in Example 1. The emulsion openings on the screen used to form the pixel electrode (upper electrode) on the interlayer insulating film are squares of 85 μm, the pixel electrode (upper electrode) is printed, heat-treated and cured without pressure treatment, and the equivalent area A pixel electrode (upper electrode) was formed. The cross section was a pixel electrode (upper electrode) shape having a curved surface on the dome, as shown in FIG. As a result of measuring the surface shape of the pixel electrode (upper electrode) using a laser microscope, the surface of the pixel electrode (upper electrode) had a maximum height immediately above the through hole, and the maximum height was 10 to 11 μm. .

In the same manner as in Example 1, the display panel and the counter electrode were combined to form a display device, which was connected to a driving device to perform an operation test. As a result, the display contrast and resolution became extremely nonuniform. This is considered to have occurred because the surface of the pixel electrode (upper electrode) is curved, and at the same time, the distance from the display panel is not uniform within the electrode and between the electrodes.
[Example 2]
Samples were prepared in the same manner as in Example 1. However, the Ag paste used to form the pixel electrode (upper electrode) was diluted with a solvent to increase the amount of decrease in the thickness of the pixel electrode (upper electrode) after heat treatment, and the pixel electrode (upper electrode) was thinned. . When the height t of the surface of the pixel electrode (upper electrode) from the substrate surface was measured, the cross-sectional shape was slightly recessed immediately above the through hole, and t immediately above the through hole was 4.6 μm. Compared with the maximum value dmax 5.8 μm of the maximum height of the interlayer insulating film, t was about 80% of dmax. When a display test was performed in the same manner as in Example 1, good uniformity could be obtained.
[Comparative Example 2]
A pixel electrode (upper electrode) was formed by an inkjet method using Ag ink in the interlayer insulating film obtained in Example 1. The Ag ink is obtained by uniformly dispersing resin-coated Ag ultrafine particles (nanoparticles) in a solvent, and can form an Ag thin film of about 100 nm.

  Conditions were set so that a pixel electrode (upper electrode) having a diameter of about 100 μm could be formed by an inkjet method, and a pixel electrode (upper electrode) was formed. In addition, since the film formed by the ink jet method is sufficiently thin, it is not necessary to perform pressing in the pressing step.

  The cross-sectional shape of the formed pixel electrode (upper electrode) was such that it was completely along the interlayer insulating film, as shown in FIG. When the surface shape was measured with a laser microscope, the height t from the substrate surface of the surface of the pixel electrode (upper electrode) in the through hole (opening) was 120 nm.

When the same display test as in Example 1 was performed in combination with the display panel, sufficient display contrast was not obtained.
[Example 3]
An interlayer insulating film and a pixel electrode were formed in the same manner as in Example 1. However, four types of samples (sample numbers No. 1 to 4) having different cross-sectional shapes of the interlayer insulating film were prepared by changing the solvent ratio of the insulating paste used for forming the interlayer insulating film. Specifically, the paste used for forming the interlayer insulating film used in Example 1 was added with a solvent in the range of 0 to 10% wt. By increasing the solvent ratio, it is considered that the viscosity decreases, the amount of change in shape during the drying process also changes, and the cross-sectional shape also changes. About the obtained sample, similarly to Example 1, the three-dimensional measurement of the surface shape was performed using the laser microscope. From the result, the shape of the interlayer insulating film was measured. The results are shown in Table 1.

表１は、実施例３で得られたサンプル番号Ｎｏ．１〜４の４種類のサンプルについて、形状パラメータＳ１／Ｓ０、形状パラメータＳ２／Ｓ１、表示テスト結果を示す。Ｓ０は、画素電極（上部電極）の各々に対応して設けられる画素領域の面積である。Ｓ１は、図７（ｃ）に示すように、基板表面から極大点の極大高さｄの１／２の高さｄ／２における画素電極（上部電極）の断面積である。Ｓ２は、スルーホール（開口部）の面積であり、図７（ｃ）に示すように、ドレイン電極と画素電極の接触する面積である。各測定値は、レーザー電子顕微鏡の３次元測定データから、コンピュータを用いた処理により算出した。

Table 1 shows the sample number No. obtained in Example 3. The shape parameter S1 / S0, the shape parameter S2 / S1, and the display test result are shown for four types of samples 1 to 4. S0 is the area of the pixel region provided corresponding to each pixel electrode (upper electrode). S1 is a cross-sectional area of the pixel electrode (upper electrode) at a height d / 2 that is ½ of the maximum height d of the maximum point from the substrate surface, as shown in FIG. 7C. S2 is the area of the through hole (opening), and is the area where the drain electrode and the pixel electrode are in contact as shown in FIG. Each measurement value was calculated from the three-dimensional measurement data of the laser electron microscope by a process using a computer.

  As shown in FIG. 7C, the cross-sectional area S1 is expressed as davg when the average value between the vertices (maximum points) of the maximum height d from the substrate surface of the interlayer insulating film is davg. The cross-sectional area of the interlayer insulating film at a height of davg / 2 that is ½ may be used. Further, the area S0 of the pixel region is obtained as S0 = Px × Py, where the vertical and horizontal arrangement periods of the pixel electrode (upper electrode) and the through holes are Px and Py, respectively, as shown in FIG. Can do. Further, S2 is the area of the through hole (opening), and the ratio S2 / S1 between S1 and S2 is an index indicating how gentle the cross-sectional shape of the interlayer insulating film is.

Referring to Table 1, sample no. 1-3, the results of the display test were good, but sample numbers No. 1 and S1 / S0 were smaller than 0.2 and S2 / S1 was larger than 0.3. In No. 4, the display uniformity was deteriorated. When the shape of the pixel electrode of sample number 4 was observed with an optical microscope, it was found that the size of the pixel electrode (upper electrode) varied within the surface of the sample. In sample number 4, the amount of upward spreading of the through hole (opening) of the interlayer insulating film is small, and each pixel electrode (upper electrode) is pressed and spread in the pressurizing process (upper electrode pressing step). It is considered that the variation among the pixel electrodes (upper electrodes) increases, and the size of each pixel electrode (upper electrode) varies within the surface of the sample. From the results in Table 1, it is considered that the shape parameter S1 / S0 that defines the cross-sectional shape of the interlayer insulating film is in the appropriate range of 0.2 or more and the shape parameter S2 / S1 is 0.3 or less.
[Example 4]
The relationship between the maximum height d from the substrate surface of the interlayer insulating film and the radius of curvature R of the curved surface shape (cross-sectional shape) of the interlayer insulating film was calculated from the sectional shapes of the four types of samples prepared in Example 3. Here, the cross section for evaluating the cross-sectional shape is as follows. In the interlayer insulating film as shown in FIG. 4A, a through hole (opening) and a through hole (opening) closest to the through hole (opening). The cross section of the interlayer insulating film between the two. On the other hand, in the interlayer insulating film as shown in FIG. 4B, the cross-section for evaluating the cross-sectional shape has a through hole (opening) and a through hole (opening) closest to the through hole (opening). Instead, the cross section of the interlayer insulating film between the next adjacent through hole (opening) is used.

  In sample number 4 where the display uniformity was deteriorated in Example 3, the radius of curvature R was distributed in the range of 20 to 30 times the maximum height d, whereas in sample number 3, the radius of curvature was R was distributed in the range of 30 to 50 times the maximum height d.

From the above, it is considered that the range in which the radius of curvature R of the cross-sectional shape of the interlayer insulating film is at least 30 times the maximum height d is an appropriate range.
[Example 5]
By using the same method as in Example 1, an interlayer insulating film having a through hole (opening) was formed on a substrate in which thin film transistors were arranged in a matrix. However, two types of samples were prepared using an insulating paste diluted 1.25 times with an ethylene glycol solvent and a diluted 1.35 times. The film thickness after drying can be reduced by reducing the solid content (filler and binder) ratio simultaneously with decreasing the viscosity. After the formation of the interlayer insulating film, the curvature radius R of the cross-sectional shape was calculated by the same method as in Example 4, and the result normalized with the average value davg of the maximum film thickness d was as follows.

1.25-fold diluted sample: R / davg = 160-200
1.35-fold diluted sample: R / davg = 240-270
When pixel electrodes were formed on these samples in the same manner as in Example 1, in the samples in which through holes were formed with an insulating paste diluted 1.35 times, the pixel electrodes were in contact with the adjacent pixel electrodes, and electrically The result was a short. If the radius of curvature is too large, it is considered that the amount of electrode expansion when pressed is increased. Therefore, by setting R / davg to 200 or less at least, it is possible to cope with a method for manufacturing a circuit board having a step of flattening by pressing a pixel electrode as described in the first embodiment.

  Even when the radius of curvature R of the cross-sectional shape calculated as described above is normalized not by the average value davg of the maximum film thickness d but by the maximum film thickness d, at least R / d should be approximately 200 or less. Thus, it is possible to correspond to a method of manufacturing a circuit board having a step of pressing and planarizing the pixel electrode as described in the first embodiment.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to such specific embodiments, and various modifications can be made within the scope of the gist of the present invention described in the claims. Can be modified or changed.

It is sectional drawing which shows typically the structure of the circuit board which concerns on the 1st Embodiment of this invention. 1 is a top view schematically showing the structure of an active matrix circuit substrate according to a first embodiment of the present invention. It is sectional drawing which shows typically the structure of the active matrix circuit board based on the 1st Embodiment of this invention compared with the structure of the conventional active matrix circuit board. 1 is a top view schematically showing a pattern of an interlayer insulating film of an active matrix circuit substrate according to a first embodiment of the present invention. It is a figure for demonstrating the manufacturing method of the circuit board based on the 1st Embodiment of this invention, and is a figure which shows a mode that an interlayer insulation film is formed by screen printing. 1 is a cross-sectional view schematically showing the structure of an active matrix circuit substrate according to a first embodiment of the present invention. It is a figure for demonstrating the circuit board which concerns on the 1st Embodiment of this invention, and is sectional drawing which shows typically the cross-sectional shape which a through-hole arranges periodically. It is a figure for demonstrating the manufacturing method of the circuit board based on the 1st Embodiment of this invention, and is a flowchart for demonstrating the procedure of each process at the time of forming a pixel electrode (upper electrode). It is a figure for demonstrating the manufacturing method of the circuit board which concerns on the 1st Embodiment of this invention, and shows the structure around a pixel electrode (upper electrode) in the process of forming a pixel electrode (upper electrode) typically It is sectional drawing. It is a figure for demonstrating the manufacturing method of the circuit board which concerns on the 1st Embodiment of this invention, and is a figure which shows a mode that an upper electrode press process is performed using a pressure roller. It is sectional drawing which shows typically the structure of the electrophoretic display which is an image display apparatus which concerns on the 2nd Embodiment of this invention. It is a graph which shows the relationship between the line | wire width and film thickness of the wiring at the time of forming a wiring pattern by the screen printing method.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Gate electrode 3 Gate insulating film 4 Drain electrode 5 Source electrode 6 Interlayer insulating film 7, 71 Pixel electrode (upper electrode)
8 Semiconductor (organic semiconductor)
9 Through hole (opening)
10 Channel region 11 Press plate 12 Display panel 14 Counter electrode 20 Circuit board 21 Screen frame 22 Screen 23 Paste 24 Squeegee 25 Mesh 26 Emulsion 27, 27a, 27b Emulsion opening 28 Stage 29 Pressure roller 30 Active matrix circuit board 31 Display panel (Display section)
32 counter substrate 33 microcapsule 34 charged fine particle 40 electrophoretic display (image display device)
61 First interlayer insulating films 62 and 63 Second interlayer insulating film 64 Overlapping portion

C Maximum point d Maximum height of interlayer insulating film from substrate surface t Height of pixel electrode (upper electrode) from substrate surface

Claims (9)

A substrate,
A plurality of lower electrodes formed on the substrate;
An interlayer insulating film formed on the substrate and having an opening on each of the plurality of lower electrodes;
In a circuit board having a top surface formed so as to fill each of the plurality of openings, and an upper electrode electrically connected to each of the plurality of lower electrodes,
The interlayer insulating film has a maximum height d from the substrate surface at a substantially middle point between one opening and the opening closest to or next to the one opening. Has a curved surface shape with a maximal point
A circuit board , wherein a height t from the substrate surface to the surface of the upper electrode in the one opening is smaller than the maximum height d of the maximum point. The upper electrode is provided at the intersection of the matrix,
A pixel region provided corresponding to each of the upper electrodes and having a predetermined area S0;
When the cross-sectional area of the upper electrode at a height d / 2 that is ½ of the maximum height d of the maximum point from the substrate surface is S1,
S1 / S0 ≧ 0.2
The circuit board according to claim 1, wherein: When the area of the one opening is S2,
S2 / S1 ≦ 0.3
The circuit board according to claim 2, wherein: The circuit board according to any one of claims 1 to 3, wherein the height t is 0.8 times or more the maximum height d. 5. The circuit board according to claim 1, wherein a radius of curvature of the curved surface shape is not less than 30 times and not more than 200 times the maximum height d. The circuit board according to claim 1, wherein the upper electrode has a convex curved surface shape. An active matrix circuit board comprising the circuit board according to any one of claims 1 to 6,
The lower electrode is connected to a switching element;
The active matrix circuit board, wherein the upper electrode is a pixel electrode for driving a display. An active matrix circuit board according to claim 7,
An image display device having a display portion and a counter electrode formed on the active matrix circuit substrate. On a substrate on which a plurality of lower electrodes are formed, an opening is provided on each of the plurality of lower electrodes, and one opening and an opening closest to or adjacent to the one opening Forming an interlayer insulating film having a curved surface shape having a maximum point at which the height from the substrate surface is a maximum height d at a substantially middle point with the opening to be formed by using screen printing;
An upper electrode printing step of printing the upper electrode by screen printing so as to fill each of the plurality of openings;
An upper electrode temporary curing step of temporarily curing the upper electrode by heat treatment;
An upper electrode pressing step of pressing and planarizing the temporarily cured upper electrode;
Wherein by curing the upper electrode by a heat treatment, the height t from the substrate surface of the upper electrode at the one opening, the maximum height upper electrode main curing step you less than d of the maximum point method of manufacturing a circuit board, characterized in that organic and.

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