FR2678102A1 - MATRIX FLAT SCREEN WITH ITS CONTROL METHOD AND ITS APPLICATION TO IMAGE DISPLAY. - Google Patents

Abstract

The invention relates to a matrix flat screen, the two faces of which respectively comprise an array of N row electrodes 3 and an array of K column electrodes 4. Between these two faces, an electron source 10 provides sufficient electrons to illuminate. the selected image points, a confinement electrode 13, as well as a blocking electrode 12 respectively ensure the confinement of the electrons on the column electrodes and the control of the charge of electrons sent from the column electrodes to the row electrode selected, in order to illuminate the image points located at the intersection of said selected row 3 and columns 4. Application to all the fields requiring the display on screen of still or moving images.

Description

MATRIX FLAT SCREEN WITH ITS CONTROL METHOD

  AND ITS APPLICATION TO IMAGE DISPLAY

DESCRIPTION

  The present invention relates to a matrix flat screen allowing in particular the display of high definition images. It finds many applications in the fields requiring a screen display of still or moving images,

in color or black and white.

  There are today several types of flat screens, including cathodoluminescent screens using the guidance of electrons emitted by a known electron source. Such a device is described in the patent application.

  French published under number FR-A-2 647 580.

  FIG. 1 diagrammatically shows a section of the screen according to the prior art, previously mentioned. The device comprises two substrates 1 and 2, at least one of which is transparent, and on which are deposited two gratings. electrodes. A first network of N electrodes 3 is deposited on a first substrate 1, called a substrate-line. The electrodes-lines 3 are covered in large part with a layer 5 of a cathodoluminescent material. The ends of the electrodes 3 are not covered with said cathodoluminescent layer, thus allowing a contact zone, not shown in the figure, and through which is ensured an electrical contact with control means external to the device and

not shown in the figure.

  A second network of K electrodes-columns 4 is deposited on a second substrate 2, called a column-substrate. The column electrodes 4 are largely covered with an electrically insulating layer 6 consisting, for example, of Si O 2 or Si 3 N 4 The ends of the column electrodes 4 are not covered with said insulating layer, thus allowing a contact zone 8 through which is ensured the electrical contact with the control means mentioned above. The array of row electrodes 3 and the array of column electrodes 4 are crossed, their points of intersection, N x K, defining the elementary points of the image, also called points.

image or pixels.

  Throughout the rest of the description,

  for example, a screen made up of four line electrodes and four column electrodes, thus allowing a screen of

4 x 4 = 16 image points.

  The column substrate 2 and the line substrate 1 are assembled by a tight sealing bead 9 so as to form a vacuum enclosure. This enclosure comprises, in the vicinity of the sealing bead 9, an electron source 10 of known type. for example, a source consisting of microfilaments or a single filament also externally supplied. The screen is addressed sequentially line

by line.

  The unselected line electrodes 3 are brought to a potential of identical value to that of the potential Vs of the electron source, while the selected line electrode 3a is brought to a potential VL higher than the potential Vc of the electrodes. columns 4 (Vc being greater than or equal to the potential Vs of the electron source 10) Moreover, in order to adjust the brightness of each pixel, each column-electrode receives a determined potential Vc making it possible to attract more or fewer electrons by From the source 10 In other words, depending on the desired brightness on the pixels of the same selected line, the columns associated with these pixels may have different potentials Vc but still greater than or equal to Vs. Thus, from the electron source 10 at the electrodes-columns 4, the electrons, represented by points, are accelerated in the direction of the arrow 11a Blocked by the insulating layer 6, the electrons accumulate t in its vicinity, forming in the void of the enclosure of the charge zones 7 (a charge zone 7 is associated with each electrode-column) allowing

  drive the electrons to the selected line.

  The electrons accumulated in the vicinity of the insulator 6 then strike the cathodoluminescent layer 5 of the selected line electrode 3a in a direction as indicated by the arrows

11b and 11c.

  This type of known screen has the following drawbacks: the almost zero potential difference existing between the charging zones 7 is generally a significant cause of electron leakage from a column electrode 4 towards its neighbor, which makes it impossible to apply different luminosities on the pixels of the same line; electron leaks, common in such screens, can also come from the action of a magnetic field external to the screen such as, for example, the terrestrial field; and when the selected line electrode 3a is taken to the potential VL, which is greater than the potential Vc of the column electrodes 4 and therefore greater than the potential Vs of the electron source, the electrons emitted by the source 10 go directly to the selected line electrode 3a through the charging zones 7, which

  include here as electrical conductors.

  As a result, the amount of energy striking the cathodoluminescent layer at the addressed image points depends on the bit rate of the source 10 and is not precisely controllable. The displayed image therefore risks being

very inhomogeneous.

  The subject of the present invention is precisely a matrix flat screen which makes it possible, in a simple manner, to precisely control the electron charge supplied respectively to the addressed image points, as well as to avoid the leakage of electrons from a

  electrode-column 4 to its neighbors.

  More specifically, the invention relates to a matrix flat screen used, in particular, for displaying high definition images comprising: a first and a second substrate, assembled by a sealing bead, constituting a vacuum chamber; a first network of N line electrodes constructed on the first substrate and covered with at least one cathodoluminescent material; a second network of K electrodes-columns built on the second substrate and covered with an electrically insulating layer, this second network being crossed with the first network so as to define, by their intersections, N x K pixels image; and at least one electron source for injecting electrons into the vacuum chamber, characterized in that it comprises means for confining the injected electrons on the column electrode of each addressed image point, as well as that means to control the electron charge provided to each

addressed image point.

  Advantageously, the means for controlling the charge of electrons comprise at least one blocking electrode located between the electron source and the row electrodes, said blocking electrode being able to be brought to a negative potential with respect to the potential of the source, to prevent electrons from the electron source

  to reach the electrode networks.

  According to the invention, the means for confining the electrons comprise a confining electrode having a comb shape, each tooth of which is inserted between two column electrodes in order to prevent, when said electrode is brought to a negative potential with respect to the potential. from the source, any coupling

  between two adjacent column electrodes.

  In addition, each line-electrode of the screen is controlled by a line-control circuit, this circuit comprising a single transistor whose first electrode is brought to a constant voltage V1, a second electrode of which is connected to said line-electrode. and a third electrode of which is connected to means for controlling the conduction state of the transistor. According to a preferred embodiment of the invention, the screen comprises two electron sources with which are associated two locking electrodes, each source / blocking electrode assembly being

  disposed on either side of said screen.

  The screen according to the invention implements a control method in which one uses: line electrodes brought to a potential VL; column electrodes brought to a potential Vc which is a function of the image to be displayed and crossed with the row electrodes so as to define, by their intersections, image dots; and at least one electron source brought to a potential Vs, characterized in that it consists, on the one hand, in using a blocking electrode and a confinement electrode, the latter being brought to a negative constant voltage Vp by relative to the potential Vs and, on the other hand, to perform for each selected electrode-line and for the blocking electrode successively the following commands: carry the row electrodes and the blocking electrode to the potential Vs of the source, the potential Vs being lower than the potential Vc of the column electrodes; bringing the blocking electrode to the potential Vb lower than the potential Vs of the source; bring the selected line electrode to its potential

  Vl higher than the potential Vs of the source.

  This screen can be used for displaying color images. Each image point is then divided into at least three image-covered subpoints.

  each of a different cathodoluminescent material.

  Other features and benefits

  will emerge more clearly from the description that follows,

  given as an illustration and not a limitation, with reference to the figures in which: FIG. 1, already described, schematically represents a section of the screen according to the art

prior; -

  Figure 2 schematically shows a section of the matrix flat screen according to the present invention; FIG. 3 represents the chronogram of the voltages and luminances encountered during operation of the screen according to the invention; Figure 4 shows the screen according to the invention in a partially cutaway top view; FIG. 5 very schematically represents a section of a flat matrix screen comprising two electron sources; and FIG. 6 represents the line control circuit as implemented in the screen

according to the invention.

  FIG. 2 represents a screen according to the same section as that of FIG. 1, screen to which the means for controlling the charge of electrons according to the invention have been added. The references which appear in FIG.

  of the description of said figure 2 and figures

following.

  The following description is given

  for the particular case of a screen for displaying high definition images The screen according to the invention may, however, allow many other functions. Thus, in the case where one seeks to display high definition images, it is essential to avoid the risks of obtaining an inhomogeneous image; precise control of the electron charge striking the cathodoluminescent layer of each pixel is

therefore necessary.

  These means for controlling the charge of electrons consist, for example, of a blocking electrode 12. This blocking electrode 12 is placed parallel to the row electrodes, between the electron source 10 and the network.

of electrodes-lines 3.

To facilitate the description of

  operation of the screen of the invention, we consider Vs = O Volt in the rest of the

description.

  The electrode 12 and the line electrodes 3 are advantageously made using the same conductive material. If the image does not have to be observable through the substrate 1, it will be used

  preferably a reflective metal.

  From a more functional point of view, the blocking electrode 12 makes it possible, when it is brought to a negative potential Vb, to block the passage of the electrons emitted by the electron source 10 towards

the column electrodes.

  More precisely, during the charging of the charge zones 7 with the electrons emitted by the electron source 10, the blocking electrode 12 is brought to a potential Vb identical to that of the said electron source. The electrons circulate then normally from the electron source 10 to the column electrodes 4, as previously described

  in the description of the prior art.

  When all the charging zones 7 have reached a charge Q = C Vc, where C is the column capacitance fixed by construction of the column electrodes (Q being specific to each column-electrode), the blocking electrode 12 is brought to a potential

  Vb sufficiently negative, for example -100 volts.

  Under the effect of such a potential Vb, the electrons, emitted by the electron source 10, are pushed back when they arrive at the blocking electrode 12, then returning to said source 10, as shown on FIG. 2 shows the dashed arrow 11 d. Thus, when the selected line electrode 3a is brought to its potential VL, only the electrons in the charge zones 7 strike the layer of the selected line electrode 3a. the electrons coming from the source 10 being repressed towards

  said source 10 thanks to the blocking electrode 12.

  FIG. 3 shows the chronogram of the voltages and luminances encountered when the screen is in operation, that is to say that it describes the control method implemented in the screen. This method has already been used. described through

  the descriptions in Figures 1 and 2, but

  The sequence of commands appears more clearly

  in the timing diagram of Figure 3.

  The addressing of the screen is done line by line, with a time-line T1 comprising the following three phases: from time t 0 to t 1, the line electrodes (of index li) and the column-electrode (of index b) are brought to the potential Vs of the source. Then Vli = Vb = Vs. In FIG. 3, Vs is represented as zero. Meanwhile, the electrodecolumn (indexed cj) is brought to a potential Vcj (of value between 0 and 10

  About Volts), depending on the image to be displayed.

  From t1 to t2, the blocking electrode is brought to its potential Vb, which is lower than the potential of the source Vs. This potential Vb has the value, in

the example, -100 volts.

  From t 2 to t 3, the line electrode li is raised to its potential VL greater than the potential Vs, VL being 100 Volts in the example The energy stored by the column electrode (cj) at times t O and t 2 is then discharged The luminance Lpij of the image point (pij) intersection of the lines li and column cj, is maximum (Lmax) at t 2, decreases progressively until reaching O at time t 3 The voltage Vcj of the electrode column, of value Vmax between t 0 and t 3 (ie 10 volts, in the example) decreases during the duration of the next line-time reaching Vmax / 2 in the example at this voltage Vmax / 2, the luminance

is lower and is worth Lmax / 2.

  During the duration of this next line-time, the next line-electrode (li + 1) is selected

  and the method described above is applied again.

  Thus, on receiving an energy of value C x Vc x V 1, there is light emission at the points

addressed image.

  The luminance L of each image point depends not only on the efficiency r of the cathodoluminescent material, but also on the frame frequency f, namely the display frequency of the image, the area of the image point, the column capacitor C, the potential VL of the selected line electrode 3a, and also the potential Vc of the corresponding column-electrode 4 For each pixel, this luminance L is expressed as: L = rf C VL Vc 7 r S In this equality, only Vc can vary from one pixel to another and thus allow to regulate

the luminosity.

  In FIG. 4, the screen of the invention is shown in a view from above. In this figure, the substrate-line I is partially cut in order to better show the different electrodes.

  between the two substrates 1 and 2.

  The means for confining the electrons appear clearly in this figure under the reference 13 Indeed, said means for confining the electrons comprise a confinement electrode 13 making it possible to avoid any crosstalk, that is to say any coupling between an electrode column 4 and its neighbors. We will talk indifferently coupling between electrodes-columns or electron leakage from a column electrode to the neighboring column electrodes. The confinement electrode 13 is in the form of a comb in which each tooth 13a is interposed between two column electrodes. The confinement electrode 13 is conductive and can be transparent or opaque, so that said confinement electrode 13 or, if possible, in harmony with the array of column electrodes 4 (because they can be made at the same time) The column substrate 2 and, if possible, the column-electrode array 4 are transparent when the substrate line 1 is opaque and / or the network of line electrodes 3 is opaque also, and vice versa. This electrode 13 is capable of being brought to a negative Vp potential generally ranging between -100 and -500 volts, this potential Vp depending on the pitch of the column electrodes 4, the void volume between the two substrates 1 and 2, potentials Vc applied to the column electrodes 4 and the potential Vs. Reached at a sufficiently negative potential Vp, each column electrode 4 keeps in its charge zone 7, the electrons received from the electron source 10 under the action of the negative potential Vp, the electrons can not escape from the charge zone 7 in which they are confined, so there is no electron leak possible from a

  electrode-column 4 to a neighboring electrode 4.

  The present invention, described for the display of black and white images, also applies to the display of color images. For this application, the known method is used.

  division into several parts of each pixel.

  Each pixel portion is then covered with a cathodoluminescent material of different nature for emitting in blue, green or white.

  red according to the nature of said material.

  The pixels can be divided according to several arrangements According to a first arrangement, each pixel is divided in the direction of the row electrodes into three independent parts each covered with a different cathodoluminescent material (in other words, each column electrode is divided into three sub-electrodes). -columns) These materials are: Zn Cd S: Ag, Zn S: Ca, Ac or Zn S: Ag, Ac, to emit, respectively, in red, green or blue According to a second arrangement, each pixel is divided in the direction of the electrodes-columns in three independent parts each covered with a different cathodoluminescent material (that is, each electrode-line is divided into three sub-electrodes-lines) Finally, according to a third arrangement, each pixel is divided at a time in the direction of the row electrodes and the column electrodes, each pixel then consisting of four independent parts, two of which are covered by the same cathodoluminescent material, the other two parts being each covered with a different cathodoluminescent material (that is, each line electrode is divided into two under row electrodes and each column electrode is

  divided into two under electrodes-columns).

  In FIG. 6, the circuit

  line control system which comprises a single transistor.

  The circuit shown is of the "open drain" type.

  It could also be of the "open collector" type. This circuit comprises only one transistor 14 of the MOS type; the first electrode of said transistor is connected to a control logic 15 of the conduction state of the transistor 14, its second electrode to a voltage line VI and its third electrode to the line electrode 3. In fact, the circuits of FIG. Known command-lines generally use two transistors: one to bring the voltage to V 1 and another to bring the voltage back to 0. However, in the absence of voltage applied to the lines, the electrons emitted from the columns have

  tendency to drop the potential of said lines.

  An open-drain (or open-collector) circuit is thus used which makes it possible to bring the line to the potential + V 1, the return to O being done progressively when the transistor 14 is not conducting. Such a circuit allows a saving, not only of a transistor by image point, but also of the circuitry around this transistor. The control-line circuit of the invention ensures a cost

  much lower than the usual manufacturing cost.

  A preferred embodiment of the invention is shown in FIG. 5, in a section identical to that of FIG. 2. This embodiment consists of introducing, into the vacuum zone, a second electron source 10 a situated at the opposite of the first electron source 10, by

  relative to the electrode-line network 3.

  Like the electron source 10, the second electron source 10a is placed in the vicinity of the sealing bead 9 and parallel to the row electrodes 3. Furthermore, a second blocking electrode 12a is installed between the network. 3 and said second source of electrons 10a This source 10a and its blocking electrode 12a play the same role as that established for the source 10 and the blocking electrode 12 in

the description of Figure 2.

  This second electron source 10 has provided the same amount of electrons as the electron source, which reduces by half the charge time of the charge zones 7, thus allowing an improvement in the display time of an image on the screen - according to the invention.

Claims (6)

  A matrix flat screen comprising: a first and a second substrate (1, 2), assembled by a sealing bead (9) constituting a vacuum enclosure; a first network of N row electrodes (3) constructed on the first substrate and covered with at least one cathodoluminating material (5); a second network of K electrodes-columns (4) built on the second substrate and covered with an electrically insulating layer (6), this second network being crossed with the first network so as to define, by their intersections, N x K points picture; and at least one electron source (10), brought to a potential Vs, for injecting electrons into the chamber under vacuum, characterized in that it comprises means (13) for confining the injected electrons on the column electrode of each addressed image point, as well as means (12) for controlling the load   of electrons supplied to each addressed image point.   2 matrix flat screen according to claim 1, characterized in that the means for controlling the charge of electrons comprise at least one blocking electrode (12) located in parallel between the electron source and the line electrodes, said electrode blocking device capable of being brought to a potential (Vb) negative with respect to the potential of the source, in order to prevent the electrons coming from the electron source   to reach the electrode networks. 3 Flat matrix screen according to one   any of claims 1 or 2, characterized   in that the means for confining the electrons comprises a comb-like confining electrode (13), each tooth (13a) of which is intercalated between two column electrodes to prevent, when said electrode is brought to a potential ( Vp) negative with respect to the potential of the source, any coupling   between two adjacent column electrodes. 4 Flat matrix screen according to one   any of claims 1 to 3, characterized   in that it comprises two electron sources (10, a) to which two blocking electrodes (12, 12 a) are associated, each source / blocking electrode assembly being disposed on either side of said screen. Matrix flat screen according to one   any of claims 1 to 4, characterized   in that each line electrode is controlled by a circuit comprising a single transistor whose first electrode is brought to a constant voltage (VL), a second electrode of which is connected to said line electrode and of which a third electrode is connected to state control means conduction of the transistor.   6 Method of controlling a flat screen   matrix according to any one of the claims   I to 5, in which use is made of: line electrodes brought to a potential VL; column electrodes brought to a potential Vc depending on the image to be displayed and crossed with the row electrodes so as to define, by their intersections, image points; and at least one electron source brought to a potential Vs, characterized in that it consists, on the one hand, in using a blocking electrode and a confinement electrode, the latter being brought to a negative constant voltage Vp by relative to the potential Vs and, on the other hand, to perform, for each selected electrode-line and for the blocking electrode successively, the following commands: carry the row electrodes and the blocking electrode to the potential Vs of the source the potential Vs being lower than the potential Vc of the column electrodes; bringing the blocking electrode to the potential Vb lower than the potential Vs of the source; bring the selected electrode-line to its potential   Vl higher than the potential Vs of the source.   7 Applying the matrix flat screen   according to any one of claims 1 to 6,   displaying color images by dividing each image point into at least three image sub-points each covered with a material different cathodoluminescent.