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EP0772525A1 - Procedes de construction et de fabrication pour des tetes d'impression activees thermiquement - Google Patents

Procedes de construction et de fabrication pour des tetes d'impression activees thermiquement

Info

Publication number
EP0772525A1
EP0772525A1 EP96911651A EP96911651A EP0772525A1 EP 0772525 A1 EP0772525 A1 EP 0772525A1 EP 96911651 A EP96911651 A EP 96911651A EP 96911651 A EP96911651 A EP 96911651A EP 0772525 A1 EP0772525 A1 EP 0772525A1
Authority
EP
European Patent Office
Prior art keywords
heater
ink
drop
nozzle
nozzles
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP96911651A
Other languages
German (de)
English (en)
Inventor
Kia Silverbrook
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Eastman Kodak Co
Original Assignee
Eastman Kodak Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AUPN2305A external-priority patent/AUPN230595A0/en
Priority claimed from AUPN2303A external-priority patent/AUPN230395A0/en
Application filed by Eastman Kodak Co filed Critical Eastman Kodak Co
Publication of EP0772525A1 publication Critical patent/EP0772525A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/14—Structure thereof only for on-demand ink jet heads
    • B41J2/14451—Structure of ink jet print heads discharging by lowering surface tension of meniscus
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/1623—Manufacturing processes bonding and adhesion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/1626—Manufacturing processes etching
    • B41J2/1628—Manufacturing processes etching dry etching
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/1626—Manufacturing processes etching
    • B41J2/1629—Manufacturing processes etching wet etching
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/1631—Manufacturing processes photolithography
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/1632—Manufacturing processes machining
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/1635—Manufacturing processes dividing the wafer into individual chips
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/164—Manufacturing processes thin film formation
    • B41J2/1642—Manufacturing processes thin film formation thin film formation by CVD [chemical vapor deposition]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/164—Manufacturing processes thin film formation
    • B41J2/1645—Manufacturing processes thin film formation thin film formation by spincoating

Definitions

  • the invention provides a drop on demand printing including a plurality of nozzles, being characterized in that at least one of the nozzle includes an electrothermal actuator, and further characterized that the heater is located at the tip of the nozzle.
  • a preferred feature of the invention is that the heater is situated on a rim which protrudes from the surface of the printing head in the immediate vicinity of the rim.
  • Figure 3(e) shows the power pulses which are applied to the nozzle heater to generate the temperature curves of figure 3(c)
  • Figure 5 shows projected manufacturing yields for an A4 page width color print head embodying features of the invention, with and without fault tolerance.
  • Figure 6 shows a generalized block diagram of a printing system using a print head
  • Figure 30 shows dimensions of the layout of a single ink channel pit with 24 main nozzles and 24 redundant nozzles.
  • Figure 31 shows an arrangement and dimensions of 8 ink channel pits, and their corresponding nozzles, ink a print head.
  • Figure 32 shows 32 ink channel pits at one end of a four color print head.
  • Figure 34 shows the full complement of ink channel pits on a 4" (100 mm) monolithic print head module.
  • the invention constitutes a drop-on-demand printing mechanism wherein the means of selecting drops to be printed produces a difference in position between selected drops and drops which are not selected, but which is insufficient to cause the ink drops to overcome the ink surface tension and separate from the body of ink, and wherein an alternative means is provided to cause separation of the selected drops from the body of ink.
  • the drop selection means may be chosen from, but is not limited to, the following list: 1) Electrothermal reduction of surface tension of pressurized ink
  • Electrothermal Low temperature Requires ink pressure reduction of surface increase and low drop regulating mechanism.
  • Ink tension of selection energy Can be surface tension must reduce pressurized ink used with many ink substantially as temperature types. Simple fabrication. increases CMOS drive circuits can be fabricated on same substrate
  • Electrothermal Medium drop selection Requires ink pressure reduction of ink energy, suitable for hot oscillation mechanism. Ink viscosity, combined melt and oil based inks. must have a large decrease with oscillating ink Simple fabrication. in viscosity as temperature pressure CMOS drive circuits can increases be fabricated on same substrate
  • the preferred drop selection means for water based inks is method 1: "Electrothermal reduction of surface tension of pressurized ink”. This drop selection means provides many advantages over other systems, including; low power operation (approximately 1% of TU), compatibility with CMOS VLSI chip fabrication, low voltage operation (approx. 10 V), high nozzle density, low temperature operation, and wide range of suitable ink formulations. The ink must exhibit a reduction in surface tension with increasing temperature.
  • the preferred drop selection means for hot melt or oil based inks is method 2: ' ⁇ lectrothermal reduction of ink viscosity, combined with oscillating ink pressure".
  • Proximity with Useful for hot melt inks Requires print medium to be oscillating ink using viscosity reduction very close to print head pressure drop selection method, surface, not suitable for reduces possibility of rough print media. Requires nozzle clogging, can use ink pressure oscillation pigments instead of dyes apparatus
  • FIG. 1 A simplified schematic diagram of one preferred printing system according to the invention appears in Figure 1(a).
  • This type of nozzle may be used for print heads using various techniques for drop separation.
  • Printing apparatus and methods of this invention are suitable for a wide range of applications, including (but not limited to) the following: color and monochrome office printing, short run digital printing, high speed digital printing, process color printing, spot color printing, offset press supplemental printing, low cost printers using scanning print heads, high speed printers using pagewidth print heads, portable color and monochrome printers, color and monochrome copiers, color and monochrome facsimile machines, combined printer, facsimile and copying machines, label printing, large format plotters, photographic duplication, printers for digital photographic processing, portable printers inco ⁇ orated into digital 'instant' cameras, video printing, printing of PhotoCD images, portable printers for 'Personal
  • An optimum temperature profile for one print head embodiment involves an instantaneous raising of the active region of the nozzle tip to the ejection temperature, maintenance of this region at the ejection temperature for the duration of the pulse, and instantaneous cooling of the region to the ambient temperature.
  • This optimum is not achievable due to the stored heat capacities and thermal conductivities of the various materials used in the fabrication of the nozzles in accordance with the invention.
  • improved performance can be achieved by shaping the power pulse using curves which can be derived by iterative refinement of finite element simulation of the print head.
  • the power applied to the heater can be varied in time by various techniques, including, but not limited to:
  • Ink viscosity Global Ink cartridge sensor or Global PFM patterns user selection and/or clock rate
  • Ink dye or pigment Global Ink cartridge sensor or Global PFM patterns concentration user selection
  • FIG. 4 is a block schematic diagram showing electronic operation of an example head driver circuit in accordance with this invention.
  • This control circuit uses analog modulation of the power supply voltage applied to the print head to achieve heater power modulation, and does not have individual control of the power applied to each nozzle.
  • Figure 4 shows a block diagram for a system using an
  • the output of the nand gate 215 drives an inverting buffer 216, which in tum controls the drive transistor 201.
  • the drive transistor 201 actuates the electrothermal heater 200, which may be a heater 103 as shown in figure 1(b).
  • the clock to the shift register is stopped the enable pulse is active by a clock stopper 218, which is shown as a single gate for clarity, but is preferably any of a range of well known glitch free clock control circuits. Stopping the clock of the shift register removes the requirement for a parallel data latch in the print head, but adds some complexity to the control circuits in the Head Control ASIC 400.
  • Data is routed to either the main nozzles or the redundant nozzles by the data router 219 depending on the state of the appropriate signal of the fault status bus.
  • the print head shown in figure 4 is simplified, and does not show various means of improving manufacturing yield, such as block fault tolerance.
  • Drive circuits for different configurations of print head can readily be derived from the apparatus disclosed herein.
  • Digital information representing patterns of dots to be printed on the recording medium is stored in the Page or Band memory 1513, which may be the same as the Image memory 72 in figure 1(a).
  • Data in 32 bit words representing dots of one color is read from the Page or Band memory 1513 using addresses selected by the address mux 417 and control signals generated by the Memory Interface 418.
  • These addresses are generated by Address generators 411, which forms part of the 'Per color circuits' 410, for which there is one for each of the six color components.
  • the addresses are generated based on the positions of the nozzles in relation to the print medium. As the relative position of the nozzles may be different for different print heads, the Address generators 411 are preferably made programmable.
  • the count from the enable counter 404 is then decoded by the decoder 405 and buffered by the buffer 432 to produce the enable pulses for the head 50.
  • the counter 403 may include a prescaler if the number of states in the count is less than the number of clock periods in one enable pulse. Sixteen voltage states are adequate to accurately compensate for the heater thermal lag. These sixteen states can be specified by using a four bit connection between the counter 403 and the dual port RAM 317. However, these sixteen states may not be linearly spaced in time. To allow non-linear timing of these states the counter 403 may also include a ROM or other device which causes the counter 403 to count in a non-linear fashion. Alternatively, fewer than sixteen states may be used.
  • the printing density is detected by counting the number of pixels to which a drop is to be printed ('on' pixels) in each enable period.
  • the 'on' pixels are counted by the On pixel counters 402.
  • the number of enable phases in a print head in accordance with the invention depend upon the specific design. Four, eight, and sixteen are convenient numbers, though there is no requirement that the number of enable phases is a power of two.
  • the On Pixel Counters 402 can be composed of combinatorial logic pixel counters 420 which determine how many bits in a nibble of data are on. This number is then accumulated by the adder 421 and accumulator 422.
  • the clock to the print head 50 is generated from the system clock
  • Printing in accordance with the present invention has many of the advantages of the ⁇ nal ink jet printing, and completely or substantially eliminates many of the inherent problems of thermal inkjet technology.
  • FIG. 5 is a graph of wafer sort yield versus defect density for a monolithic full width color A4 head embodiment of the invention.
  • the head is 215 mm long by 5 mm wide.
  • the non fault tolerant yield 198 is calculated according to
  • Mu ⁇ hy's method approximates the effect of an uneven distribution of defects.
  • Figure 5 also includes a graph of non fault tolerant yield 197 which explicitly models the clustering of defects by introducing a defect clustering factor.
  • the defect clustering factor is not a controllable parameter in manufacmring, but is a characteristic of the manufacmring process.
  • the defect clustering factor for manufacturing processes can be expected to be approximately 2, in which case yield projections closely match Mu ⁇ hy's method.
  • a solution to the problem of low yield is to inco ⁇ orate fault tolerance by including redundant functional units on the chip which are used to replace faulty functional units.
  • redundant sub-units In memory chips and most Wafer Scale Integration (WSI) devices, the physical location of redundant sub-units on the chip is not important However, in printing heads the redundant sub-unit may contain one or more printing actuators. These must have a fixed spatial relationship to the page being printed. To be able to print a dot in the same position as a faulty acmator, redundant actuators must not be displaced in the non-scan direction. However, faulty actuators can be replaced with redundant acmators which are displaced in the scan direction. To ensure that the redundant actuator prints the dot in the same position as the faulty acmator, the data timing to the redundant acmator can be altered to compensate for the displacement in the scan direction.
  • the minimum physical dimensions of the head chip are determined by the width of the page being printed, the fragility of the head chip, and manufacturing constraints on fabrication of ink channels which supply ink to the back surface of the chip.
  • the minimum practical size for a full width, full color head for printing A4 size paper is approximately 215 mm x 5 mm. This size allows the inclusion of 100% redundancy without significantly increasing chip area, when using 1.5 ⁇ m CMOS fabrication technology. Therefore, a high level of fault tolerance can be included without significantly decreasing primary yield.
  • Figure 5 shows the fault tolerant sort yield 199 for a full width color A4 head which includes various forms of fault tolerance, the modeling of which has been included in the yield equation.
  • This graph shows projected yield as a function of both defect density and defect clustering.
  • the yield projection shown in figure 5 indicates that thoroughly implemented fault tolerance can increase wafer sort yield from under 1% to more than 90% under identical manufacmring conditions. This can reduce the manufacturing cost by a factor of 100.
  • fault tolerance is highly recommended to improve yield and reliability of print heads containing thousands of printing nozzles, and thereby make pagewidth printing heads practical.
  • fault tolerance is not to be taken as an essential part of the present invention.
  • FIG. 6 A schematic diagram of a digital electronic printing system using a print head of this invention is shown in Figure 6.
  • This shows a monolithic printing head 50 printing an image 60 composed of a multitude of ink drops onto a recording medium 51.
  • This medium will typically be paper, but can also be overhead transparency film, cloth, or many other substantially flat surfaces which will accept ink drops.
  • the image to be printed is provided by an image source 52, which may be any image type which can be converted into a two dimensional array of pixels.
  • Typical image sources are image scanners, digitally stored images, images encoded in a page description language (PDL) such as Adobe Postscript Adobe Postscript level 2, or Hewlett-Packard PCL 5, page images generated by a procedure-call based rasterizer, such as Apple QuickDraw, Apple Quickdraw GX, or Microsoft GDI, or text in an electronic form such as ASCII.
  • PDL page description language
  • This image data is then converted by an image processing system 53 into a two dimensional array of pixels suitable for the particular printing system. This may be color or monochrome, and the data will typically have between 1 and 32 bits per pixel, depending upon the image source and the specifications of the printing system.
  • the image processing system may be a raster image processor (RIP) if the source image is a page description, or may be a two dimensional image processing system if the source image is from a scanner.
  • RIP raster image processor
  • a halftoning system 54 is necessary. Suitable types of halftoning are based on dispersed dot ordered dither or error diffusion. Variations of these, commonly known as stochastic screening or frequency modulation screening are suitable.
  • the halftoning system commonly used for offset printing - clustered dot ordered dither - is not recommended, as effective image resolution is unnecessarily wasted using this technique.
  • the output of the halftoning system is a binary monochrome or color image at the resolution of the printing system according to the present invention.
  • Ink drops 60 escape from the nozzles in a pattern which corresponds to the digital impulses which have been applied to the heater driver circuits.
  • the pressure of the ink in the ink reservoir 64 is regulated by the pressure regulator 63.
  • Selected drops of ink drops 60 are separated from the body of ink by the chosen drop separation means, and contact the recording medium 51.
  • the recording medium 51 is continually moved relative to the print head 50 by the paper transport system 65. If the print head 50 is the full width of the print region of the recording medium 51, it is only necessary to move the recording medium 51 in one direction, and the print head 50 can remain fixed. If a smaller print head 50 is used, it is necessary to implement a raster scan system. This is typically achieved by scanning the print head 50 along the short dimension of the recording medium 51 , while moving the recording medium 51 along its long dimension.
  • a printing speed of 60 A4 pages per minute (one page per second) will generally be adequate for many applications.
  • achieving an electronically controlled print speed of 60 pages per minute is not simple.
  • the minimnm time taken to print a page is equal to the number of dot positions on the page times the time required to print a dot divided by the number of dots of each color which can be printed simultaneously.
  • the image quality that can be obtained is affected by the total number of ink dots which can be used to create an image.
  • approximately 800 dots per inch (31.5 dots per mm) are required.
  • the spacing between dots on the paper is 31.75 ⁇ m.
  • a standard A4 page is 210 mm times 297 mm. At 31.5 dots per mm, 61 ,886,632 dots are required for a monochrome full bleed A4 page.
  • High quality process color printing requires four colors - cyan, magenta, yellow, and black. Therefore, the total number of dots required is 247,546,528. While this can be reduced somewhat by not allowing printing in a small margin at the edge of the paper, the total number of dots required is still very large. If the time taken to print a dot is 144 ms, and only one nozzle per color is provided, then it will take more than two hours to print a single page.
  • printing heads with many small nozzles are required.
  • the printing of a 800 dpi color A4 page in one second can be achieved if the printing head is the full width of the paper.
  • the printing head can be stationary, and the paper can travel past it in the one second period.
  • a four color 800 dpi printing head 210 mm wide requires 26,460 nozzles.
  • Such a print head may contain 26,460 active nozzles, and 26,460 redundant (spare) nozzles, giving a total of 52,920 nozzles. There are 6, 15 active nozzles for each of the cyan, magenta, yellow, and black process colors.
  • Print heads with large numbers of nozzles can be manufactured at low cost This can be achieved by using semiconductor manufacturing processes to simultaneously fabricate many thousands of nozzles in a sihcon wafer. To eliminate problems with mechanical ahgnment and differential thermal expansion that would occur if the print head were to be manufactured in several parts and assembled, the head can be manufactured from a single piece of sihcon. Nozzles and ink channels are etched into the silicon. Heater elements are formed by evaporation of resistive materials, and subsequent photolithography using standard semiconductor manufacturing processes.
  • the manufacmre of monohthic printing heads for my above- described systems is similar to standard silicon integrated circuit manufacture.
  • the normal process flow should be modified in several ways to form the nozzles, the barrels for the nozzles, the heaters, and the nozzle tips.
  • the basic process can be modified to fo ⁇ n the necessary structures.
  • the minimum length of a monohthic print head is determined by the width of the required printing capability.
  • the minimum width of a monohthic print head is determined by the mechanical strength requirements, and by the ability to provide ink supply channels to the back of the sihcon chip.
  • the minimum size of a photograph type full width four color head is at least 100 mm long by approximately 5 mm wide. This gives an area of approximately 5 square cm.
  • CMOS complementary metal-oxide-semiconductor
  • VLSI CMOS Low power, high speed process
  • the speeds required are moderate, and the power consumption is dominated by the heater power required for the ink jet nozzles. Therefore, a simple technology such as nMOS is adequate.
  • CMOS is likely to be the most practical production solution, as there is a significant amount of idle CMOS manufacmring capability available with line widths between 1 ⁇ m and 2 ⁇ m
  • nMOS nMOS
  • the choice of the base technology is largely independent of the ability to fabricate nozzles.
  • the method of inco ⁇ oration of nozzle manufacmring steps into semiconductor processing procedures which have not yet been invented is also likely to be obvious to those skilled in the art.
  • the simplest fabrication process is to manufacture the nozzles using sihcon micromechanical processing, without fabricating active semiconductor devices on the same wafer.
  • this approach is not practical for print heads with large numbers of nozzles, as at least one extemal connection to the print head is required for each nozzle.
  • CMOS is currently the most popular integrated circuit process. At present, many CMOS processes are in commercial use, with line widths as small as 0.35 ⁇ m being in common use. CMOS offers the following advantages for the fabrication of print heads:
  • the substrate can be grounded from the front side of the wafer.
  • CMOS has, however, some disadvantages over nMOS and other technologies in the fabrication of print heads which include integrated drive circuitry. These include:
  • CMOS is susceptible to electrostatic discharge damage. This can be minimized by including protection circuits at the inputs, and by careful handling.
  • protection circuits at the inputs, and by careful handling.
  • Heater design High quahty printing using print heads of my systems requires consistent size ink drops. To produce consistently sized ink drops, the nozzle diameter must be accurately controlled, as must the thickness, width and length of the heater. Of equal importance is the position of the heater in relation to the nozzle, and the thickness and thermal properties of the materials which isolate the heater from the ink. For best results, these characteristics of a high resolution print head should be controlled to better than 0.5 ⁇ m accuracy. This may be achieved by using modem production semiconductor hthographic equipment However, use of the latest generation of semiconductor equipment is very expensive.
  • the heater element of a monohthic printing nozzle configuration using a self-aligned process, where the thickness of the heater, the width of the heater, and the position of the heater in relation to the nozzle are all determined by deposition and etching steps, instead of lithographic processes. This allows high accuracy and small dimensions to be achieved even when using relatively coarse lithography.
  • Figure 8(a) shows an example layout for a small section of a print head. This shows two columns of nozzles. One of these columns contains the main printing nozzles. The other column contains the redundant nozzles for fault tolerance. The nozzle 200 and drive transistor 201 are shown.
  • FIG 8(b) is a detail enlargement of a section of figure 8(a).
  • the layout is for 2 micron nMOS, though little change is required for CMOS, as the drive transistor of a CMOS design would be fabricated as an nMOS transistor.
  • the layout shows three nozzles 200, with their drive transistors 201 and inverting drivers 216.
  • the three nozzles are in a staggered (zig-zag) pattern to increase the distance between the nozzles, and thereby increase the strength of the sihcon wafer after the nozzles have been etched through the substrate.
  • the large V * and V " currents are carried by a matrix of wide first and second level metal lines which covers the chip.
  • the V * and V terminals can extend along the entire two long edges of the chip.
  • the first manufacturing step is the delivery of the wafers.
  • Sihcon wafers are highly recommended over other materials such as gallium arsenide, due to the availabihty of large, high quahty wafers at low cost the strength of sihcon as a substrate, and the general maturity of fabrication processes and equipment.
  • the wafers must be manufactured with good thickness control. This is because holes must be etched all of the way through the wafer. Variations in wafer thickness will affect relative etch times. To ensure that holes in regions where the wafer is thicker are etched, holes in regions where the wafer is thin must be over-etched. Excessive over-etching will also substantially etch the glass in the heater region, changing the thermal characteristics of the nozzle.
  • the heater element will be etched if the wafer is excessively over-etched.
  • Acmal thickness of the wafer is not critical, as the etching equipment can be automatically configured to detect waste gasses from the etching of sihcon dioxide, and an etch stop can be programmed from this point.
  • the thickness variation of a particular wafer, and thickness variations between wafers in a batch which are to be simultaneously etched are less than 5 ⁇ m.150 mm wafers manufactured to standard Semiconductor Equipment and Materials Institute (SEMI) specifications allow 25 ⁇ m total thickness variation. 200 mm wafers manufactured to SEMI specifications allow 75 ⁇ m total thickness variation. In both cases, the thickness variation on an individual wafer must be reduced to less than 5 ⁇ m.
  • SEMI Semiconductor Equipment and Materials Institute
  • the prior art process may be nMOS, pMOS, CMOS, Bipolar, or other process.
  • the active circuits can be fabricated using unmodified processes.
  • some processes will need modification to allow for the large currents which may flow though a print head.
  • a large head may have in excess of 8 Amperes of cu ⁇ ent flowing through the heater circuits when fully energized, it is essential to prevent electromigration.
  • Molybdenum should be used instead of aluminum for first level metal, as it is resistant to electromigration.
  • the metallization layers should also be thicker than the minimum normally required in a CMOS circuit.
  • the inter-metal dielectric should be increased in thickness.
  • Figure 9(c) shows a cross section of the wafer in the region of a nozzle after this step.
  • Figure 9(d) shows a cross section of the wafer in the region of a nozzle after this step. This step can be performed with the same hthographic accuracy as the main process.
  • the contacts to the heater can overlap the edge of the nozzle tip by several mm.
  • FIG. 5 Application of a resist filler to define the heater width.
  • the heater is deposited on the sidewalls of the nozzle. This is to increase the thermal transfer between the heater and the ink by allowing only thin intermediate layers.
  • the heater is self aligned to the nozzle tip, and the width of the heater is accurately controlled by the depth of RIE etching of the resist. This allows the heater parameters to be controlled to an accuracy beyond that achievable with 2 ⁇ m lithography.
  • Figure 9(e) shows a cross section of the wafer in the region of a nozzle after spin coating a thick layer of resist, and postbaking to planarize.
  • RIBE reactive ion beam etch
  • Figure 9(h) shows a cross section of the wafer in the region of a nozzle after this step.
  • 9) Apply a thick resist to both sides of the wafer.
  • the resist on the front side of the wafer is just to prevent handling damage or stray etching.
  • the resist on the backface of the wafer should be a three level resist as the nozzle barrel is etched all of the way through the wafer. As the wafer is approximately 650 ⁇ m thick, this requires substantially more etching than is normally required in sihcon processing.
  • the relative etch rates over the entire wafer must be tightly controlled to prevent excessive etching of the back surface of the nozzle tip. If the etch rate is controlled to be within 2% over the entire wafer, when the fastest etching portions are etched the slowest will still have 13 ⁇ m of sihcon remaining to etch. When this is combined with 5 ⁇ m variation in wafer thickness, the variation is 18 ⁇ m. This variation can be compensated by an overetch of 20 ⁇ m from first detection of end stop conditions. If the etchant used has a selectivity of 20:1 of sihcon over SiO_>, then the under-surface of the SiO 2 will be etched 1 ⁇ m. This is within the design constraints of the process.
  • the sidewalls of the barrel are substantially vertical.
  • the required radius of the nozzle at the nozzle tip is approximately 7 ⁇ m.
  • the radius of the nozzle barrels must be less than 29 ⁇ m or they will coalesce, making the design of a mask with properly defined nozzle formations impossible.
  • This means that the etch angle must be no greater than 1.9 degrees (this is calculated as arctan ((29 ⁇ m-7 ⁇ m) / 650 ⁇ m)).
  • the etch angle strongly affects the size of the unexposed regions on the backface mask. This design has considerable tolerance of etch angle and backface mask accuracy, as the ahgnment and diameter of the ba ⁇ el at the nozzle tip is not critical.
  • FIG. 9(k) shows a cross section of the wafer in the region of a nozzle after this step.
  • the thermal conductivity of amo ⁇ hous SiO ⁇ (glass) is low.
  • a practical material for present use is sihcon nitride. While the the ⁇ nal conductivity is not as good as other non-conducting materials such as diamond or sihcon carbide, passivation qualities are excellent and the material is well known for semiconductor manufacturing.
  • the 0.5 ⁇ m conformal layer of Si 3 N 4 can be apphed by PECVD.
  • Figure 9(n) shows a cross section of the wafer in the region of a nozzle after this step.
  • Figure 9(0) shows a cross section of the wafer in the region of a nozzle after this step.
  • the effective thickness of the nozzle wall must be very small.
  • a thin 'rim' of tantalum can be fabricated at the nozzle tip by removing the front surface (i.e. the surface from which the drops are ejected, which is normally not in contact with the ink) of the tantalum. Then a small amount of Si 3 N 4 is also removed, leaving the tantalum passivation layer on the inside of the nozzle protruding. The tantalum is anisotropically etched from the front surface of the wafer, leaving tantalum on all surfaces except the front surface.
  • Figure 9(p) shows a cross section of the wafer in the region of a nozzle after this step.
  • the exposed dielectric layer can be treated with a hydrophobizing agent.
  • the device can be treated with dimethyldichlorosilane to make the exposed SiO 2 hydrophobic. This will affect the entire nozzle, unless the regions which are to remain hydrophilic are masked, as dimethyldichlorosilane fumes will affect any exposed SiC ⁇ .
  • the apphcation of a hydrophobic layer is required if the ink is water based, or based on some other polar solvent If the ink is wax based or uses a non- polar solvent then the front surface of the print head should be hpophobic. In summary, the front surface of the print head should be fabricated or treated in such a manner as to repel the ink used.
  • the hydrophobic layer need not be limited to the front surface of the device.
  • the entire device may be coated with a hydrophobic layer (or hpophobic layer is non-polar ink is used) without significantly affecting the performance of the device. If the entire device is treated with an ink repellent layer, then the nozzle radius should be taken as the inside radius of the nozzle tip, instead of the outside radius.
  • Figure 9(q) shows a cross section of the wafer in the region of a nozzle after this step.
  • TAB Tape automated bonding
  • Bonding pads must be opened out from the Si 3 N passivation layer. This can be achieved through standard masking and etching processes. After the bonding pads have been opened, the resist must be stripped, and the wafer cleaned. Then wafer testing can proceed. After wafer testing, solder bumps are apphed. Then the wafer is diced. The wafers should be cut instead of scribed and snapped, to prevent breakage of long print heads, and because the wafer is weakened along the nozzle rows.
  • FIG. 9(r) shows a cross section of the wafer in the region of a nozzle after this step.
  • 100 is ink
  • 101 is sihcon
  • 102 is CVD
  • SiO 2 ,103 is the heater material
  • 104 is the tantalum passivation
  • 106 is the second layer metal interconnect (aluminum)
  • resist 108 is sihcon nitride (Si 3 N 4 ) and
  • the above manufacturing process is not the simplest process that can be employed, and is not the lowest cost practical process. However, the above process has the advantage of simultaneous fabrication of high performance devices on the same wafer. The process is also readily scalable, and 1mm line widths can be used if desired.
  • data phasing circuits can be inco ⁇ orated on chip, and the LIFT head can be supphed with a standard memory interface, via which it acquires the printing data by direct memory access.
  • the nozzle ba ⁇ els are formed using a single anisotropic etch through the full 650 ⁇ m of the wafer thickness. This etch must be accurately controlled with respect to both sidewall angle and evenness of etch rate over the entire wafer.
  • the tolerance requirements of this step can be reduced by using two major steps. In the first step a large channel is etched most of the way through the wafer, leaving a thickness of approximately 50 ⁇ m in the region of the nozzles.
  • a multi-level resist is then apphed to the base of this channel, and the nozzle barrels are imaged using a projection system with optical focus on the resist layer at the base of the channel.
  • the nozzle barrels are then etched through the remaining 50 ⁇ m of sihcon. This process reduces the sidewall angle tolerance requirements from 2 degrees to more than 10 degrees, thus making the process substantially easier to control.
  • the physical strength of the chip is substantially reduced by this process, meaning that very careful mechanical handling is required to prevent breakage in subsequent processing steps.
  • the process described above is one prefe ⁇ ed process for production of printing heads as it allows high resolution, full color heads to inco ⁇ orate drive circuitry, data distribution circuitry, and fault tolerance. Also, the active circuitry of the head is protected from chemical attack by the ink by two passivation layers: sihcon nitride and tantalum.
  • the temperature and duration of the heat pulse apphed to the nozzle tip must also be accurately controlled.
  • Figure 10 shows a simple planar construction in accordance with the invention for a nozzle heater, using hthography capable of resolving 2 ⁇ m line widths.
  • the ink 100 in contained in a circular nozzle of radius 7 ⁇ m.
  • This nozzle is coated with a passivation layer 104 which is 0.5 ⁇ m thick.
  • the heater 103 is fabricated by planar hthography able to resolve 2 ⁇ m line widths.
  • the contacts 106 to the heater are formed by aluminum, and are 2 ⁇ m wide. This heater configuration suffers the foUowing problems:
  • the inimum width of the heater 103 is 2 ⁇ m. This reduces the heater resistance, meaning that higher currents are required to achieve a particular heater power than if the heater width was less. 2)
  • the width of the heater 103 is controlled by hthography, with a typical variation of 0.5 ⁇ m. This variation means that heater resistance, and therefore heater power will vary from head to head.
  • the distance from the heater 103 to the passivation layer 104 must be at least 2 ⁇ m. This limits the efficiency of the thermal coupling between the heater and the ink.
  • Lithographic equipment capable of resolving 0.35 ⁇ m line widths is used in volume production of semiconductor devices at present.
  • such equipment is expensive compared to hthographic equipment with resolving power between 1 ⁇ m and 2 ⁇ m.
  • Self-aligned means that the ahgnment of the heater to the nozzle tip is a result of the manufacturing process steps, and is not determined by the ahgnment accuracy of hthographic processing steps.
  • the heater dimensions and position are determined by deposition and etching steps, which can be controlled to much greater accuracy than hthographic steps.
  • Figure 11 (a) shows a plan view of the nozzle tip, showing the self- aligned heater strucmre 103.
  • the heater 103 is vertically oriented in relation to the wafer surface.
  • Figure 11(b) shows an isometric view of the same heater strucmre.
  • the thickness of the heater, width of the heater, and position of the heater in relation to the nozzle tip are ah determined by deposition and etching processes, which can readily be controlled very accurately.
  • the fabrication process for this heater configuration also avoids the requirement for a heater mask and lithographic steps.
  • the physical dimensions of the nozzle are very small. It is not practical to manufacture these devices using manufacturing processes such as molding and milling. Instead, processes used in the manufacmre of integrated circuits can be used. These processes are generally used to manufacmre planar devices. However, three dimensional structures can be fabricated if the co ⁇ ect sequence of masks and manufacmring processes are used.
  • the invention is a heater structure which is self-aligned to the nozzle, the dimensions of which are determined by deposition and etching processes.
  • the heater stmcture and heater contacts are formed in the following fundamental steps; a) etching of the nozzle tip; b) isotropically coating the nozzle tip with an electrically conductive material suitable for heater contacts; c) etching the electrically conductive material using a resist which is patterned with an appropriate pattern for heater contacts; d) coating the nozzle tip and heater contact material with a substance; e) etching the substance to a depth below the surface of the nozzle tip equal to the desired width of the heater; f) isotropically coating the nozzle tip with a layer of heater material to a thickness equal to the desired thickness of the heater; and g) anisotropically etching the heater material in a manner as to remove all of the heater material except the required heater material in the nozzle tip.
  • the heater resistance must be known.
  • the heater resistance can be calculated from the geometry of the heater and the thin film resistivity of the heater material.
  • the preferred heater geometry is a circular band which is connected to drive circuitry at opposite sides. The resistance of the heater can therefore be calculated by the equation:
  • R B is the heater resistance p is the thin film resistivity of the heater material r is the radius of the heater W is the width of the heater
  • T the heater thickness
  • LIFT Head Type A4-4-600 is a summary of some of the characteristics of an example process color print head, according to the invention, for printing an A4 page at 600 dpi in one second (see Appendix A).
  • Another embodiment and fabrication process in accordance with the present invention provides advantages as to power dissipation and heater usage and is described in detail with reference to Figures 12-34. Power dissipation in simple LIFT nozzle designs
  • Figure 12 shows a cross section through a simple nozzle constructed in accordance with an embodiment of the present invention.
  • the ink 100 flows into a cylindrical barrel fabricated from the sihcon substrate 101.
  • the nozzle tip includes an electrically activated heater 103 protected by an electrically insulating material
  • the nozzle is protected from co ⁇ osion by the ink with a passivation layer 104, for example tantalum, with a thin oxide coating of tantalum pentoxide (Ta 2 Os).
  • a passivation layer 104 for example tantalum
  • Ta 2 Os tantalum pentoxide
  • Ink is prevented from flowing along the surface of the nozzle by a hydrophobic coating 109.
  • the ink is placed under pressure. The ink pressure is sufficient to cause the memscus to become convex, but insufficient to cause the ink to escape from the nozzle.
  • the meniscus of the ink is shown in the 'equihbrium' state.
  • This nozzle configuration is simple to fabricate, but is inefficient in the amount of energy required to eject a drop.
  • the distance from the heater to the ink is limited by hthographic resolution, resulting in a long thermal path to the ink. This means that all of the -59- material between the heater and region 106 must be raised above the required drop ejection temperature before the ink can reach the drop ejection temperature.
  • the basic geometry of the nozzle indicates that the the ⁇ nal resistance of paths from the heater away from region 106 is lower than that of the path towards region 106, so the majority of the heat energy will not reach region
  • the power requirement of a print head can be divided into two categories: 1) Quiescent power, which is the power that is consumed when no ink is being ejected. This power requirement mostly derived from the shift registers and drive circuitry of the head, as well as leakage cu ⁇ ents of the main drive transistors. Using modem semiconductor processes, quiescent power consumption can be reduced to a level where it becomes insignificant and will be dissipated by normal conduction and air convection around the head. 2) Active power, which is the amount of power consumed when the head is actually printing. This may be expressed as the amount of energy required to eject a single drop of ink, times the number of drops ejected in a specified time period (typically one second). For a four color 'process' head, active power will be zero when printing white, a maximum when printing sohd four color black.
  • the active power is significantly affected by the detailed design of the nozzle, especially the location, size, and materials su ⁇ ounding the heater. Power reduction is achieved by several means as follows:
  • thermally insulating layer between the heater and the substrate.
  • This layer can be the thermal SiO 2 and CVD SiO 2 layers which are normally part of CMOS device fabrication.
  • the passivation layer should be as thin as practical commensurate with providing good protection against co ⁇ osion.
  • a layer thickness of 2,OO ⁇ A is suitable.
  • Each of the above means effects a reduction in power requirements over a system which does not use these means. Using a combination of these effects, the energy required to eject of drop of ink can be reduced to the level where the head becomes self-cooling.
  • FIG 1 (b) shows a simplified cross section through a high efficiency nozzle.
  • the ink 100 flows into a cylindrical ba ⁇ el which is formed of the sihcon substrate material 101.
  • the nozzle tip includes an electrically activated heater 103 su ⁇ ounded by an electrically insulating material 102, for example Chemical Vapor Deposited glass (CVD SiO 2 ).
  • the nozzle is protected from co ⁇ osion by the ink with a passivation layer 104, which is composed of a material with high electrical resistance, high resistance to permeation by hydroxyl ions, and high thermal conductivity.
  • a suitable material is sihcon nitride.
  • the wafers can be processed up to oxide on second level metal using the standard CMOS process flow. Some specific process steps then follow which can also be completed using standard CMOS processing equipment. The final etching of the nozzles through the chip can be completed at a MEMS facihty, using a single hthographic step which requires only 10 ⁇ m hthography.
  • the process does not require any plasma etching of sihcon: all sihcon etching is performed with an EDP wet etch after the fabrication of active devices.
  • the nozzle diameter in this example is 16 ⁇ m, for a drop volume of approximately 8 pi.
  • the process is readily adaptable for a wide range on nozzle diameters, both greater than and less than 16 ⁇ m.
  • the process uses anisotropic etching on a ⁇ 100> sihcon wafer to etch simultaneously from the ink channels and nozzle barrels. High temperature steps such as diffusion and LPCVD are avoided during the nozzle formation process.
  • Layout example Figure 13 shows an example layout for a small section of an 800 dpi print head. This shows the layout of nozzles and drive circuitry for 48 nozzles which are in a single ink channel pit The black circles in this diagram represent the positions of the nozzles, and the grey regions represent the positions of the active circuitry.
  • the 48 nozzles comprise 24 main nozzles 2000, and 24 redundant nozzles 2001.
  • the position of the MOS main drive transistors 2002 and redundant drive transistors 2003 are also shown.
  • the ink channel pit 2010 is the shape of a truncated rectangular pyramid etched from the rear of the wafer. The faces of the pyramidical pit follow the ⁇ 111 ⁇ planes of the single crystal sihcon wafer.
  • the nozzles are located at the bottom of the pyramidical pits, where the wafer is thinnest. In the thicker regions of the wafer, such as the sloping walls of the ink channel pits, and the regions between pits, no nozzles can be placed. These regions can be used for the data distribution and fault tolerance circuitry.
  • Figure 13 shows a suitable location for main shift registers 2004, redundant shift registers 2005, and fault tolerance circuitry 2006.
  • V " and V currents are carried by a matrix of wide first and second level metal lines which covers the chip.
  • the V * and V terminals extend along the entire two long edges of the chip. Alignment to crvstallo raphic planes The manufacturing process described in this chapter uses the crystallographic planes inherent in the single crystal sihcon wafer to control etching.
  • the orientation of the masking procedures to the ⁇ 111 ⁇ planes must be precisely controlled.
  • the orientation of the primary flats on a sihcon wafer are normally only accurate to within ⁇ 1 ° of the appropriate crystal plane. It is essential that this angular tolerance be taken into account in the design of the mask and manufacturing processes.
  • the surface orientation of the wafer is also only accurate to ⁇ 1°.
  • the starting wafer can be a standard 6" sihcon wafer, except that wafers pohshed on both sides are required.
  • Figure 15 shows a 6" wafer with 12 full color print heads, each with a print width of 105 mm. Two of these print heads can be combined to form an A4/US letter sized pagewidth print head, four can be combined to provide a 17" web commercial printing head, or they can be used individually for photograph format printing, for example in digital 'minilabs', A6 format printers, or digital cameras.
  • Example wafer specifications are:
  • the major manufacturing steps are as follows: 1) Complete the CMOS process, fabricating drive transistors, shift registers, clock distribution circuitry, and fault tolerance circuitry according to the normal CMOS process flow. A two level metal CMOS process with line widths 1.5 ⁇ m or less is preferred. The CMOS process is completed up until oxide over second level metal.
  • Figure 16 shows a cross section of wafer in the region of a nozzle tip after the completion of the standard CMOS process flow.
  • This diagram shows the sihcon wafer 2020, field oxide 2021, first interlevel oxide 2022, first level metal 2023, second interlevel oxide 2024, second level metal 2025, and passivation oxide 2026.
  • the layer thicknesses in this example are as follows: a) Field oxide 2021: 1 ⁇ m. b) First interlevel oxide 2022: 0.5 ⁇ m. c) First level metal 2023: 1 ⁇ m. d) Second interlevel oxide 2024:1.5 ⁇ m, planarized. e) Second level metal 2025: 1 ⁇ m. f) Passivation oxide 2026: 2 ⁇ m, planarized.
  • interlevel vias at the nozzle tip There are two interlevel vias at the nozzle tip, shown connecting the first level metal 2023 and a small patch of second level metal 2025. 2) Mask the nozzle tip using resist. The nozzle tip hole is formed to cut the interlevel vias at the nozzle tip in half. This is to provide a 'taller' connection to the heater. On the same mask as the nozzle tip holes are openings which delineate the edge of the chip. This is for front-face etching of the chip boundary for chip separation from the wafer. The chip separation from the wafer is etched simultaneously to the ink channels and nozzles.
  • FIG. 17 is a cross section of the nozzle tip region after the nozzle tip has been etched.
  • heater material 2027 Deposit a thin layer of heater material 2027.
  • the layer thickness depends upon the resistivity of the heater material chosen. Many different heater materials can be used, including nichrome, tantalum/aluminum alloy, tungsten, polysilicon doped with boron, zirconium diboride, hafnium diboride, and others.
  • FIG 19 is a cross section of the nozzle tip region after this deposition step. 5) Chemically thin the wafer to a thickness of approximately 300 microns.
  • FIG. 19 is a cross section of the nozzle tip region after this deposition step.
  • 7) Spin-coat resist on the back of the wafer. Mask the back face of the wafer for anisotropic etching of the ink channels, and chip separation (dicing). The mask contains concave rectangular holes to fo ⁇ n the ink channels, and holes which delineate the edge of the chip. As some angles of the chip edge boundary are convex, mask undercutting will occur. The shape of the chip edge can be adjusted by placing protrusions on the mask at convex comers. The mask patterns are aligned to the ⁇ 111 ⁇ planes. The resist is used to mask the etching of the PECVD nitride previously deposited on the back face of the wafer. Etch the backface nitride, and strip the resist
  • the etch time should be approximately 4 hours.
  • the duration of this etch, and resulting sihcon thickness in the nozzle region can be adjusted to control the geometry of the chamber behind the nozzle tip (the nozzle barrel). While the etch is eventually right through the wafer, it is interrupted part way through to start etching from the front surface of the wafer as well as the back. This two stage etching allows precise control of the amount of undercutting of the nozzle tip region that occurs. An undercut of between 1 micron and 8 microns is desirable, with an undercut of approximately 3 microns being prefe ⁇ ed. This etch is completed in step 12.
  • FIG. 11 Isotropically etch 1 micron of SiO 2 2026, without using a mask. This can be achieved with a wet etch which has a high selectivity against Si 3 N 4 . This forms a sihcon nitride rim around the nozzle tip.
  • Figure 21 is a cross section of the nozzle tip region after this etching step.
  • etch rates are from H. Seidel, "The Mechanism of Anisotropic Sihcon Etching and its relevance for Micromachining," Transducers '87, Rec. of the 4th Int Conf. on Sohd State Sensors and Actuators, 1987, PP. 120-125.
  • the etch time is critical, as there is no etch stop. As each batch will vary somewhat in etch rate, wafers should be checked periodically near the end of the etch period. The etch is nearly complete when light first begins to shine through the nozzle tip holes. At this stage, the wafer is returned to the etch for another six minutes. It is desirable that the wafers that are processed simultaneously have matched wafer thicknesses.
  • the etch proceeds in three stages: a) During the first 10 minutes, the etch proceeds at the ⁇ 100> etch rate from both the front side (through the nozzle tip) and the back side of the wafer. The depth of the etch from the front side will be the radius of the nozzle tip hole/ ⁇ 2 (approximately 10 ⁇ m for a 7 ⁇ m radius nozzle tip hole). Figure 22 is a cross section of the nozzle tip region at this time. b) During the next approximately 1 hour and 40 minutes, the etch proceeds at the ⁇ 100> rate from the back face of the wafer, but at the ⁇ 111> rate through the nozzle tip holes.
  • Figure 23 is a cross section of the nozzle tip region at this time.
  • Figure 24 is a cross section of the nozzle tip region at this time.
  • the amount of undercut of the nozzle tip can be controlled by altering the relative amount of etching from the front surface and the back surface. This can readily be achieved by starting the back surface etch some time before starting the front surface etch. As the total etch time is measured in hours, it is readily possible to accurately adjust the amount of time that the wafer is initially etched in EDP before removing the nitride from the nozzle tip region. This method can compensate for different wafer thicknesses, different ⁇ 111>/ ⁇ 100> etch ratios of the etchant as well as give a high degree of control of the thickness of the sihcon membrane and the amount of undercut of the heater. At this stage the chip edges have also been etched, as the chip edge etch proceeds simultaneously to the ink channel etch.
  • the design of the chip edge masking pattem can be adjusted so that the chips are still supported by the wafer at the end of the etching step, leaving only thin 'bridges' which are easily snapped without damaging the chips. Alternatively, the chips may be completely separated from the wafer at this stage.
  • the mask slots on the front side of the wafer can be much na ⁇ ower than that those on the back side of the wafer (a 10 ⁇ m width is suitable). This reduces wasted wafer area between the chips to an insignificant amount
  • Figure 25 is a cross section of the nozzle tip region after this deposition step.
  • Suitable hydrophobizing agents include (in increasing order of preference) :
  • 26 shows a cross section of the a nozzle during the hydrophobizing process.
  • FIG. 27 shows a cross section of the a nozzle filled with ink 2031 in the quiescent state.
  • Figures 29(a) to 29(e) are cross sections of the wafer which show the simultaneous etching of nozzles and chip edges for chip separation. These diagrams are not to scale.
  • Figure 29(a) shows two regions of the chip, the nozzle region and the chip edge region before etching, along with the masked regions for nozzle tips, ink channels, and chip edges.
  • Figure 29(b) shows the wafer after the nozzle tip holes have been etched at the ⁇ 100> etch rate, forming pyramidical pits. At this time, etching of the nozzle tip holes slows to the ⁇ 111> etch rate. Etching of the chip edges and the ink channels proceeds simultaneously.
  • Figure 34 shows the full complement of ink channel pits on a 4"
  • Page priming time 1 J seconds Derived from fluid dynamics, number of nozzles, etc.
  • Bitmap memory requirement 16.6 MBytes Memory required when compression is not used
  • Pixels per line 4 4,960 Active nozzles /Number of colors
  • Chips per wafer 36 From chip size and recommended wafer size

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Abstract

La présente invention décrit une tête d'impression monolithique comportant une configuration de buse dans laquelle l'élément chauffant est formé par un procédé d'alignement automatique, et dans laquelle l'épaisseur, la largeur et la position de l'élément chaufant par rapport à la buse sont toutes déterminées par des étapes de sédimentation et d'attaque chimique en lieu des procédés lithographiques. Ainsi, ce procédé permet un meilleur contrôle de ces paramètres que les procédés lithographiques. L'élément chauffant n'a pas besoin de masque. Une configuration de tête d'impression permet de diminuer les besoins d'alimentation en courant et (1) comporte une couche thermiquement isolante entre l'élément chauffant et le substrat; (2) permet de minimiser la masse thermique de l'élément chauffant et du matériau solide environnant; (3) permet de minimiser la distance entre l'élément chauffant et le ménisque d'encre; (4) utilise un matériau possédant une conductivité thermique relativement élevée afin de protéger l'élément chauffant contre la corrosion de l'encre; et (5) permet d'affouiller le substrat dans la zone de l'élément chauffant. L'invention décrit également un procédé de fabrication d'une telle buse et d'une telle configuration d'élément chauffant.
EP96911651A 1995-04-12 1996-04-09 Procedes de construction et de fabrication pour des tetes d'impression activees thermiquement Withdrawn EP0772525A1 (fr)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
AUPN2305A AUPN230595A0 (en) 1995-04-12 1995-04-12 Power requirement reduction in monolithic lift printing heads
AUPN2303A AUPN230395A0 (en) 1995-04-12 1995-04-12 A self-aligned heater design for lift print heads
AUPN2303/95 1995-04-12
AUPN2305/95 1995-04-12
PCT/US1996/004855 WO1996032267A1 (fr) 1995-04-12 1996-04-09 Procedes de construction et de fabrication pour des tetes d'impression activees thermiquement

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JP4323947B2 (ja) * 2003-01-10 2009-09-02 キヤノン株式会社 インクジェット記録ヘッド
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