EP0771272A1 - Tetes d'impression monolithiques et leurs procedes de fabrication - Google Patents

Tetes d'impression monolithiques et leurs procedes de fabrication

Info

Publication number
EP0771272A1
EP0771272A1 EP96913782A EP96913782A EP0771272A1 EP 0771272 A1 EP0771272 A1 EP 0771272A1 EP 96913782 A EP96913782 A EP 96913782A EP 96913782 A EP96913782 A EP 96913782A EP 0771272 A1 EP0771272 A1 EP 0771272A1
Authority
EP
European Patent Office
Prior art keywords
ink
nozzles
drop
die
printing
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Withdrawn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
EP96913782A
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 AUPN2301A external-priority patent/AUPN230195A0/en
Priority claimed from AUPN2302A external-priority patent/AUPN230295A0/en
Application filed by Eastman Kodak Co filed Critical Eastman Kodak Co
Publication of EP0771272A1 publication Critical patent/EP0771272A1/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Withdrawn legal-status Critical Current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
    • B41J2/164—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
    • 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
    • B41J2/1646—Manufacturing processes thin film formation thin film formation by sputtering

Definitions

  • the present invention is in the field of computer controlled printing devices.
  • the field is constructions and manufacturing processes for thermally activated drop on demand (DOD) printing heads which integrate multiple nozzles on a single substrate.
  • DOD thermally activated drop on demand
  • Inkjet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing.
  • ink jet printing mechanisms have been invented. These can be categorized as either continuous inkjet (CIJ) or drop on demand (DOD) inkjet.
  • Continuous inkjet printing dates back to at least 1929: Hansell, US Pat. No. 1,941,001.
  • Sweet et al US Pat. No. 3,373,437, 1967 discloses an array of continuous ink jet nozzles where ink drops to be printed are selectively charged and deflected towards the recording medium. This technique is known as binary deflection CU, and is used by several manufacturers, including Elmjet and Scitex. Hertz et al US Pat. No.
  • 3,416,153, 1966 discloses a method of achieving variable optical density of printed spots in CIJ printing using the electrostatic dispersion of a charged drop stream to modulate the number of droplets which pass through a small aperture.
  • This technique is used in ink jet printers manufactured by Iris Graphics.
  • Kyser et al US Pat. No. 3,946,398, 1970 discloses a DOD ink jet printer which applies a high voltage to a piezoelectric crystal, causing the crystal to bend, applying pressure on an ink reservoir and jetting drops on demand.
  • Many types of piezoelectric drop on demand printers have subsequently been invented, which utilize piezoelectric crystals in bend mode, push mode, shear mode, and squeeze mode.
  • Piezoelectric DOD printers have achieved commercial success using hot melt inks (for example, Tektronix and Dataproducts printers), and at image resolutions up to 720 dpi for home and office printers (Seiko Epson). Piezoelectric DOD printers have an advantage in being able to use a wide range of inks. However, piezoelectric printing mechanisms usually require complex high voltage drive circuitry and bulky piezoelectric crystal arrays, which are disadvantageous in regard to manufacturability and performance.
  • Endo et al GB Pat. No. 2,007,162, 1979 discloses an electrothermal DOD ink jet printer which applies a power pulse to an electrothermal transducer (heater) which is in thermal contact with ink in a nozzle.
  • the heater rapidly heats water based ink to a high temperature, whereupon a small quantity of ink rapidly evaporates, forming a bubble.
  • the formation of these bubbles results in a pressure wave which cause drops of ink to be ejected from small apertures along the edge of the heater substrate.
  • BubblejetTM trademark of Canon K.K. of Japan
  • Thermal Ink Jet printing typically requires approximately 20 ⁇ J over a period of approximately 2 ⁇ s to eject each drop.
  • the 10 Watt active power consumption of each heater is disadvantageous in itself and also necessitates special inks, complicates the driver electronics and precipitates deterioration of heater elements.
  • U.S. Patent No. 4,275,290 discloses a system wherein the coincident address of predetermined print head nozzles with heat pulses and hydrostatic pressure, allows ink to flow freely to spacer-separated paper, passing beneath the print head.
  • U.S. Patent Nos. 4,737,803; 4,737,803 and 4,748,458 disclose inkjet recording systems wherein the coincident address of ink in print head nozzles with heat pulses and an electrostatically attractive field cause ejection of ink drops to a print sheet
  • one object of the invention is to provide a printing head wherein a plurality of nozzles are fabricated into a single structure.
  • the printing head is monolithic.
  • the substrate of the printing head is a single crystal of silicon.
  • the print nozzles can be formed using semiconductor fabrication processes including photolithography and chemical or plasma etching. In a further preferred form, nozzles are formed simultaneously. In a further preferred mode, the nozzles are formed by fabricating holes through the substrate material of the head.
  • a further preferred fo ⁇ n of the invention is that drive circuitry is fabricated on the same substrate as the print head nozzles.
  • a further preferred aspect of the invention is that the substrate is composed of single crystal silicon.
  • a further preferred aspect of the invention is that the dielectric layer is composed of silicon dioxide.
  • a further preferred aspect of the invention is that the nozzle tip hole is fabricated with a radius less than 50 microns.
  • the heating element is fabricated in the form of an annulus, with connecting electrodes at opposite sides of the annulus.
  • a further preferred aspect of the invention is that the barrel hole is substantially coaxial with the nozzle tip hole.
  • the passivation layers include a layer of silicon nitride.
  • the passivation layers include a layer of tantalum.
  • a further preferred aspect of the invention is that the conducting electrodes are fabricated from metals which are substantially or entirely composed of either molybdenum or aluminum.
  • a further preferred aspect of the invention is that the drive circuitry is fabricated on the same substrate as the nozzles.
  • the present invention constitutes an apparatus having (a) manifold means for supplying ink to a print head, (b) means for applying over atmospheric pressure to ink in said manifold means and (c) means for uniformly attracting ink from a print head toward a print region, a printir g head comprising a plurality of nozzles fabricated into a monolithic structure and a plurality of drop selection means formed on said structure for respectively addressing such nozzles to produce a difference in the menisci positions of uniformly pressurized ink in selected and non-selected nozzles.
  • the present invention constitutes a process for manufacturing a thermally activated drop on demand printing head, said process including the steps of: (a) forming a layer of dielectric material on a substrate; (b) forming at least one conducting electrode on said substrate; (c) forming a nozzle tip hole through said dielectric layer; (d) forming at least one electrically resistive heating element on a surface of said nozzle tip hole, said heating element being connected via said conducting electrodes to a drive circuit; and (e) forming an aperture through said substrate to provide communicable passage with said nozzle tip hole.
  • Figure 1 (a) shows a simplified block schematic diagram of one exemplary printing apparatus according to the present invention.
  • Figure 1(b) shows a cross section of one variety of nozzle tip in accordance with the invention.
  • Figures 2(a) to 2(f) show fluid dynamic simulations of drop selection.
  • Figure 3(a) shows a finite element fluid dynamic simulation of a nozzle in operation according to an embodiment of the invention.
  • Figure 3(b) shows successive meniscus positions during drop selection and separation.
  • Figure 3(c) shows the temperatures at various points during a drop selection cycle.
  • Figure 3(d) shows measured surface tension versus temperature curves for various ink additives.
  • Figure 3(e) shows the power pulses which are applied to the nozzle heater to generate the temperature curves of figure 3(c)
  • Figure 4 shows a block schematic diagram of print head drive circuitry for practice of the invention.
  • Figure 5 shows projected manufacmring 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 7 shows a single silicon substrate with a multitude of nozzles etched in it.
  • Figure 8(a) shows a possible layout of a small section of a print head.
  • Figure 8(b) is a detail of figure 8(a).
  • Figures 9(a) to 9(r) show simplified manufacturing steps for the processes added to a standard integrated circuit fabrication.
  • Figure 10 shows a nozzle layout for a small section of the print head.
  • Figure 11 shows a detail of the layout of two nozzles and two drive transistors.
  • Figure 12 shows the layout of a number of print heads fabricated on a standard silicon wafer
  • Figures 13 to 24 show cross sections of the print head in a small region at the tip of one nozzle at various stages during the manufacturing process.
  • Figure 25 shows a perspective view of the back on one print head chip.
  • Figures 26(a) to 26(e) show the simultaneous etching of nozzles and chip separation. These diagrams are not to scale.
  • Figure 27 shows dimensions of the layout of a single ink channel pit with 24 main nozzles and 24 redundant nozzles.
  • Figure 28 shows an arrangement and dimensions of 8 ink channel pits, and their corresponding nozzles, ink a print head.
  • Figure 29 shows 32 ink channel pits at one end of a four color print head.
  • Figure 30(a) and figure 30(b) show the ends of two adjacent print head chips (modules) as they are butted together to form longer print heads.
  • Figure 31 shows the full complement of ink channel pits on a 4"
  • 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 separation of drop selection means from drop separation means significantly reduces the energy required to select which ink drops are to be printed. Only the drop selection means must be driven by individual signals to each nozzle.
  • the drop separation means can be a field or condition applied simultaneously to all nozzles.
  • the drop selection means may be chosen from, but is not limited to, the following list:
  • Electrothermal reduction of surface tension of pressurized ink 2) Electrothermal bubble generation, with insufficient bubble volume to cause drop ejection
  • the drop separation means may be chosen from, but is not limited to, the following list:
  • DOD printing technology targets shows some desirable characteristics of drop on demand printing technology.
  • the table also lists some methods by which some embodiments described herein, or in other of my related applications, provide improvements over the prior art.
  • Monolithic A4 pagewidth print heads can be manufactured using standard 300 mm (12") silicon wafers
  • Shift registers can be electrical connections integrated on a monolithic print head using standard CMOS processes
  • TD thermal ink jet
  • piezoelectric ink jet systems a drop velocity of approximately 10 meters per second is preferred to ensure that the selected ink drops overcome ink surface tension, separate from the body of the ink, and strike the recording medium.
  • These systems have a very low efficiency of conversion of electrical energy into drop kinetic energy.
  • the efficiency of ⁇ J systems is approximately 0.02%).
  • the drive circuits for piezoelectric inkjet heads must either switch high voltages, or drive highly capacitive loads.
  • the total power consumption of pagewidth ⁇ J printheads is also very high.
  • An 800 dpi A4 full color pagewidth TU print head printing a four color black image in one second would consume approximately 6 kW of electrical power, most of which is converted to waste heat.
  • the difficulties of removal of this amoimt of heat precludes the production of low cost, high speed, high resolution compact pagewid h TU systems .
  • One important feature of embodiments of the invention is a means of significantly reducing the energy required to select which ink drops are to be printed. This is achieved by separating the means for selecting ink drops from the means for ensuring that selected drops separate from the body of ink and form dots on the recording medium. Only the drop selection means must be driven by individual signals to each nozzle.
  • the drop separation means can be a field or condition applied simultaneously to all nozzles.
  • Drop selection means shows some of the possible means for selecting drops in accordance with the invention.
  • the drop selection means is only required to create sufficient change in the position of selected drops that the drop separation means can discriminate between selected and unselected drops.
  • 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
  • Electrothermal Well known technology High drop selection energy, bubble generation, simple fabrication, requires water based ink, with insufficient bipolar drive circuits can problems with kogation, bubble volume to be fabricated on same cavitation, thermal stress cause drop ejection substrate
  • Electrostatic Simple electrode Nozzle pitch must be attraction with one fabrication relatively large. Crosstalk electrode per nozzle between adjacent electric fields. Requires high voltage drive circuits
  • Other drop selection means may also be used.
  • 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".
  • This drop selection means is particularly suited for use with inks which exhibit a large reduction of viscosity with increasing temperature, but only a small reduction in surface tension. This occurs particularly with non-polar ink carriers with relatively high molecular weight This is especially applicable to hot melt and oil based inks.
  • the table “Drop separation means” shows some of the possible methods for separating selected drops from the body of ink, and ensuring that the selected drops form dots on the printing medium.
  • the drop separation means discriminates between selected drops and unselected drops to ensure that unselected drops do not form dots on the printing medium.
  • Transfer Very small spot sizes can Not compact due to size of Proximity (print be achieved, very low transfer roller or transfer head is in close power dissipation, high belt. proximity to a accuracy, can print on transfer roller or rough paper belt
  • 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
  • the preferred drop separation means depends upon the intended use. For most applications, method 1: “Electrostatic attraction”, or method 2: “AC electric field” are most appropriate. For applications where smooth coated paper or film is used, and very high speed is not essential, method 3: “Proximity” may be appropriate. For high speed, high quality systems, method 4: 'Transfer proximity” can be used. Method 6: “Magnetic attraction” is appropriate for portable printing systems where the print medium is too rough for proximity printing, and the high voltages required for electrostatic drop separation are undesirable. There is no clear 'best' drop separation means which is applicable to all circumstances.
  • FIG. 1 A simplified schematic diagram of one preferred printing system according to the invention appears in Figure 1(a).
  • An image source 52 may be raster image data from a scanner or computer, or outline image data in the form of a page description language (PDL), or other forms of digital image representation.
  • This image data is converted to a pixel-mapped page image by the image processing system 53.
  • This may be a raster image processor (RIP) in the case of PDL image data, or may be pixel image manipulation in the case of raster image data.
  • Continuous tone data produced by the image processing unit 53 is halftoned. Halftoning is performed by the Digital Halftoning unit 54.
  • Halftoned bitmap image data is stored in the image memory 72.
  • the image memory 72 may be a full page memory, or a band memory.
  • Heater control circuits 71 read data from the image memory 72 and apply time- varying electrical pulses to the nozzle heaters
  • the recording medium 51 is moved relative to the head 50 by a paper transport system 65, which is electronically controlled by a paper transport control system 66, which in tum is controlled by a microcontroller 315.
  • the paper transport system shown in figure 1(a) is schematic only, and many different mechanical configurations are possible. In the case of pagewidth print heads, it is most convenient to move the recording medium 51 past a stationary head 50. However, in the case of scanning print systems, it is usually most convenient to move the head 50 along one axis (the sub-scanning direction) and the recording medium 51 along the orthogonal axis (the main scanning direction), in a relative raster motion.
  • the microcontroller 315 may also control the ink pressure regulator 63 and the heater control circuits 71.
  • ink is contained in an ink reservoir 64 under pressure.
  • the ink pressure In the quiescent state (with no ink drop ejected), the ink pressure is insufficient to overcome the ink surface tension and eject a drop.
  • a constant ink pressure can be achieved by applying pressure to the ink reservoir 64 under the control of an ink pressure regulator 63.
  • the ink pressure can be very accurately generated and controlled by situating the top surface of the ink in the reservoir 64 an appropriate distance above the head 50. This ink level can be regulated by a simple float valve (not shown).
  • ink is contained in an ink reservoir 64 under pressure, and the ink pressure is caused to oscillate.
  • the means of producing this oscillation may be a piezoelectric actuator mounted in the ink channels (not shown).
  • the ink is distributed to the back surface of the head 50 by an ink channel device 75.
  • the ink preferably flows through slots and/or holes etched through the silicon substrate of the head 50 to the front surface, where the nozzles and actuators are situated.
  • the nozzle actuators are electrothermal heaters.
  • a convenient external field 74 is a constant electric field, as the ink is easily made to be electrically conductive.
  • the paper guide or platen 67 can be made of electrically conductive material and used as one electrode generating the electric field.
  • the other electrode can be the head 50 itself.
  • Another embodiment uses proximity of the print medium as a means of discriminating between selected drops and unselected drops.
  • Figure 1(b) is a detail enlargement of a cross section of a single microscopic nozzle tip embodiment of the invention, fabricated using a modified CMOS process.
  • the nozzle is etched in a substrate 101, which may be silicon, glass, metal, or any other suitable material. If substrates which are not semiconductor materials are used, a semiconducting material (such as amo ⁇ hous silicon) may be deposited on the substrate, and integrated drive transistors and data distribution circuitry may be formed in the surface semiconducting layer.
  • Single crystal silicon (SCS) substrates have several advantages, including:
  • Print heads can be fabricated in existing facilities (fabs) using standard VLSI processing equipment;
  • SCS has high mechanical strength and rigidity
  • SCS has a high thermal conductivity.
  • the nozzle is of cylindrical fo ⁇ n, with the heater 103 forming an annulus.
  • the nozzle tip 104 is formed from silicon dioxide layers 102 deposited during the fabrication of the CMOS drive circuitry.
  • the nozzle tip is passivated with silicon nitride.
  • the protruding nozzle tip controls the contact point of the pressurized ink 100 on the print head surface.
  • the print head surface is also hydrophobized to prevent accidental spread of ink across the front of the print head.
  • Many other configurations of nozzles are possible, and nozzle embodiments of the invention may vary in shape, dimensions, and materials used.
  • Monolithic nozzles etched from the substrate upon which the heater and drive electronics are formed have the advantage of not requiring an orifice plate.
  • the elimination of the orifice plate has significant cost savings in manufacture and assembly.
  • Recent methods for eliminating orifice plates include the use of 'vortex' actuators such as those described in Domoto et al US Pat. No. 4,580,158, 1986, assigned to Xerox, and Miller et al US Pat. No. 5,371,527, 1994 assigned to Hewlett-Packard. These, however are complex to actuate, and difficult to fabricate.
  • the prefe ⁇ ed method for elimination of orifice plates for print heads of the invention is inco ⁇ oration of the orifice into the actuator substrate.
  • This type of nozzle may be used for print heads using various techniques for drop separation. Operation with Electrostatic Drop Separation
  • Figure 2 shows the results of energy transport and fluid dynamic simulations performed using FIDAP, a commercial fluid dynamic simulation software package available from Fluid Dynamics Inc., of Illinois, USA.
  • FIDAP Fluid Dynamics Inc.
  • This simulation is of a thermal drop selection nozzle embodiment with a diameter of 8 ⁇ m, at an ambient temperature of 30°C.
  • the total energy applied to die heater is 276 nJ, applied as 69 pulses of 4 nJ each.
  • the ink pressure is 10 kPa above ambient air pressure, and the ink viscosity at 30°C is 1.84 cPs.
  • the ink is water based, and includes a sol of 0.1% palmitic acid to achieve an enhanced decrease in surface tension with increasing temperature.
  • FIG. 1 A cross section of the nozzle tip from the central axis of the nozzle to a radial distance of 40 ⁇ m is shown.
  • Heat flow in the various materials of the nozzle including silicon, silicon nitride, amo ⁇ hous silicon dioxide, crystalline silicon dioxide, and water based ink are simulated using the respective densities, heat capacities, and thermal conductivities of the materials.
  • the time step of the simulation is 0.1 ⁇ s.
  • Figure 2(a) shows a quiescent state, just before the heater is actuated. An equilibrium is created whereby no ink escapes the nozzle in the quiescent state by ensuring that the ink pressure plus extemal electrostatic field is insufficient to overcome the surface tension of the ink at the ambient temperature.
  • the meniscus of the ink does not protrude significantly from the print head surface, so the electrostatic field is not significantly concentrated at the meniscus.
  • Figure 2(b) shows thermal contours at 5°C intervals 5 ⁇ s after the start of the heater energizing pulse.
  • the heater When the heater is energized, the ink in contact with the nozzle tip is rapidly heated. The reduction in surface tension causes the heated portion of the meniscus to rapidly expand relative to the cool ink meniscus. This drives a convective flow which rapidly transports this heat over part of the free surface of the ink at the nozzle tip. It is necessary for the heat to be distributed over the ink surface, and not just where the ink is in contact with the heater. This is because viscous drag against the solid heater prevents the ink directly in contact with the heater from moving.
  • Figure 2(c) shows thermal contours at 5°C intervals 10 ⁇ s after the start of the heater energizing pulse.
  • the increase in temperature causes a decrease in surface tension, disturbing the equilibrium of forces.
  • the ink begins to flow.
  • Figure 2(d) shows thermal contours at 5°C intervals 20 ⁇ s after the start of the heater energizing pulse.
  • the ink pressure has caused the ink to flow to a new meniscus position, which protrudes from the print head.
  • the electrostatic field becomes concentrated by the protruding conductive ink drop.
  • Figure 2(e) shows thermal contours at 5°C intervals 30 ⁇ s after the start of the heater energizing pulse, which is also 6 ⁇ s after the end of the heater pulse, as the heater pulse duration is 24 ⁇ s.
  • the nozzle tip has rapidly cooled due to conduction through the oxide layers, and conduction into the flowing ink.
  • the nozzle tip is effectively 'water cooled' by the ink. Electrostatic attraction causes the ink drop to begin to accelerate towards the recording medium. Were the heater pulse significantiy shorter (less than 16 ⁇ s in this case) the ink would not accelerate towards the print medium, but would instead return to the nozzle.
  • Figure 2(f) shows thermal contours at 5°C intervals 26 ⁇ s after the end of the heater pulse.
  • the temperature at the nozzle tip is now less than 5°C above ambient temperature. This causes an increase in surface tension around the nozzle tip.
  • the rate at which the ink is drawn from the nozzle exceeds the viscously limited rate of ink flow through the nozzle, the ink in the region of the nozzle tip 'necks', and the selected drop separates from the body of ink.
  • the selected drop then travels to the recording medium under the influence of the external electrostatic field.
  • the meniscus of the ink at the nozzle tip then returns to its quiescent position, ready for the next heat pulse to select the next ink drop.
  • One ink drop is selected, separated and forms a spot on the recording medium for each heat pulse. As the heat pulses are electrically controlled, drop on demand inkjet operation can be achieved.
  • Figure 3(a) shows successive meniscus positions during the drop selection cycle at 5 ⁇ s intervals, starting at the beginning of the heater energizing pulse.
  • Figure 3(b) is a graph of meniscus position versus time, showing the movement of the point at the centre of the meniscus.
  • the heater pulse starts 10 ⁇ s into the simulation.
  • Figure 3(c) shows the resultant curve of temperature with respect to time at various points in the nozzle.
  • the vertical axis of the graph is temperature, in units of 100°C.
  • the horizontal axis of the graph is time, in units of 10 ⁇ s.
  • the temperature curve shown in figure 3(b) was calculated by FIDAP, using 0.1 ⁇ s time steps.
  • the local ambient temperature is 30 degrees C.
  • Temperature histories at three points are shown:
  • a - Nozzle tip This shows the temperature history at the circle of contact between the passivation layer, the ink, and air.
  • B - Meniscus midpoint This is at a circle on the ink meniscus midway between the nozzle tip and the centre of the meniscus.
  • C - Chip surface This is at a point on the print head surface 20 ⁇ m from the centre of the nozzle. The temperature only rises a few degrees. This indicates that active circuitry can be located very close to the nozzles without experiencing performance or lifetime degradation due to elevated temperatures.
  • Figure 3(e) shows the power applied to the heater.
  • Optimum operation requires a sha ⁇ rise in temperature at the start of the heater pulse, a maintenance of the temperature a little below the boiling point of the ink for the duration of the pulse, and a rapid fall in temperature at the end of the pulse.
  • the average energy applied to the heater is varied over the duration of the pulse.
  • the variation is achieved by pulse frequency modulation of 0.1 ⁇ s sub-pulses, each with an energy of 4 nJ.
  • the peak power applied to the heater is 40 mW, and the average power over the duration of the heater pulse is 11.5 mW.
  • the sub-pulse frequency in this case is 5 Mhz. This can readily be varied without significantly affecting the operation of the print head.
  • a higher sub-pulse frequency allows finer control over the power applied to the heater.
  • a sub-pulse frequency of 13.5 Mhz is suitable, as this frequency is also suitable for minimizing the effect of radio frequency interference (RFI).
  • Figure 3(d) shows the measured effect of temperature on the surface tension of various aqueous preparations containing the following additives: 1) 0.1% sol of Stearic Acid
  • operation of an embodiment using thermal reduction of viscosity and proximity drop separation, in combination with hot melt ink is as follows.
  • solid ink Prior to operation of the printer, solid ink is melted in the reservoir 64.
  • the reservoir, ink passage to the print head, ink channels 75, and print head 50 are maintained at a temperature at which the ink 100 is liquid, but exhibits a relatively high viscosity (for example, approximately 100 cP).
  • the Ink 100 is retained in the nozzle by the surface tension of the ink.
  • the ink 100 is formulated so that the viscosity of the ink reduces with increasing temperature.
  • the ink pressure oscillates at a frequency which is an integral multiple of the drop ejection frequency from the nozzle.
  • the ink pressure oscillation causes oscillations of the ink meniscus at the nozzle tips, but this oscillation is small due to the high ink viscosity. At the normal operating temperature, these oscillations are of insufficient amplitude to result in drop separation.
  • the heater 103 When the heater 103 is energized, the ink forming the selected drop is heated, causing a reduction in viscosity to a value which is preferably less than 5 cP. The reduced viscosity results in the ink meniscus moving further during the high pressure part of the ink pressure cycle.
  • the recording medium 51 is a ⁇ anged sufficiently close to the print head 50 so that the selected drops contact the recording medium 51 , but sufficiently far away that the unselected drops do not contact the recording medium 51. Upon contact with the recording medium 51, part of the selected drop freezes, and attaches to the recording medium.
  • ink begins to move back into the nozzle.
  • the body of ink separates from the ink which is frozen onto the recording medium.
  • the meniscus of the ink 100 at the nozzle tip then returns to low amplitude oscillation.
  • the viscosity of the ink increases to its quiescent level as remaining heat is dissipated to the bulk ink and print head.
  • One ink drop is selected, separated and forms a spot on the recording medium 51 for each heat pulse. As the heat pulses are electrically controlled, drop on demand ink jet operation can be achieved.
  • An objective of printing systems according to the invention is to attain a print quality which is equal to that which people are accustomed to in quality color publications printed using offset printing. This can be achieved using a print resolution of approximately 1 ,600 dpi. However, 1 ,600 dpi printing is difficult and expensive to achieve. Similar results can be achieved using 800 dpi printing, with 2 bits per pixel for cyan and magenta, and one bit per pixel for yellow and black. This color model is herein called CC'MM'YK. Where high quality monochrome image printing is also required, two bits per pixel can also be used for black. This color model is herein called CC'MM' YKK' .
  • 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.
  • 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
  • Figure 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 800 dpi pagewidth print head which prints process color using the CC'MM'YK color model.
  • the print head 50 has a total of 79,488 nozzles, with 39,744 main nozzles and 39,744 redundant nozzles.
  • the main and redundant nozzles are divided into six colors, and each color is divided into 8 drive phases.
  • Each drive phase has a shift register which converts the serial data from a head control ASIC 400 into parallel data for enabling heater drive circuits.
  • Each shift register is composed of 828 shift register stages 217, the outputs of which are logically anded with phase enable signal by a nand gate 215.
  • the output of the nand gate 215 drives an inverting buffer 216, which in turn 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 Address generators 411 normally generate the address corresponding to the position of the main nozzles. However, when faulty nozzles are present, locations of blocks of nozzles containing faults can be marked in the Fault Map RAM 412. The Fault Map RAM 412 is read as the page is printed. If the memory indicates a fault in the block of nozzles, the address is altered so that the Address generators 411 generate the address co ⁇ esponding to the position of the redundant nozzles. Data read from the Page or Band memory 1513 is latched by the latch 413 and converted to four sequential bytes by the multiplexer 414. Timing of these bytes is adjusted to match that of data representing other colors by the FIFO 415.
  • This data is then buffered by the buffer 430 to form the 48 bit main data bus to the print head 50.
  • the data is buffered as the print head may be located a relatively long distance from the head control ASIC.
  • Data from the Fault Map RAM 412 also forms the input to the FIFO 416. The timing of this data is matched to the data output of the FIFO
  • the programmable power supply 320 provides power for the head 50.
  • the voltage of the power supply 320 is controlled by the DAC 313, which is part of a RAM and DAC combination (RAMDAC) 316.
  • the RAMDAC 316 contains a dual port RAM 317.
  • the contents of the dual port RAM 317 are programmed by the Microcontroller 315. Temperature is compensated by changing the contents of the dual port RAM 317. These values are calculated by the microcontroller 315 based on temperature sensed by a thermal sensor 300.
  • the thermal sensor 300 signal connects to the Analog to Digital Converter (ADC) 311.
  • the ADC 311 is preferably inco ⁇ orated in the Microcontroller 315.
  • the Head Control ASIC 400 contains control circuits for thermal lag compensation and print density.
  • Thermal lag compensation requires that the power supply voltage to the head 50 is a rapidly time- varying voltage which is synchronized with the enable pulse for the heater. This is achieved by programming the programmable power supply 320 to produce this voltage.
  • An analog time varying programming voltage is produced by the DAC 313 based upon data read from the dual port RAM 317. The data is read according to an address produced by the counter 403.
  • the counter 403 produces one complete cycle of addresses during the period of one enable pulse. This synchronization is ensured, as the counter 403 is clocked by the system clock 408, and the top count of the counter 403 is used to clock the enable counter 404.
  • 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.
  • a latch 423 holds the accumulated value valid for the duration of the enable pulse.
  • the multiplexer 401 selects the output of the latch 423 which co ⁇ esponds to the current enable phase, as determined by the enable counter 404.
  • the output of the multiplexer 401 forms part of the address of the dual port RAM 317. An exact count of the number of 'on' pixels is not necessary, and the most significant four bits of this count are adequate.
  • Combining the four bits of thermal lag compensation address and the four bits of print density compensation address means that the dual port RAM 317 has an 8 bit address. This means that the dual port RAM 317 contains 256 numbers, which are in a two dimensional array. These two dimensions are time (for thermal lag compensation) and print density. A third dimension - temperature - can be included.
  • the microcontroller 315 has sufficient time to calculate a matrix of 256 numbers compensating for thermal lag and print density at the cu ⁇ ent temperature. Periodically (for example, a few times a second), the microcontroller senses the current head temperature and calculates this matrix. The clock to the print head 50 is generated from the system clock
  • JTAG test circuits 499 may be included.
  • Invention compares the aspects of printing in accordance with the present invention with thermal ink jet printing technology.
  • thermal inkjet technology A direct comparison is made between the present invention and thermal inkjet technology because both are drop on demand systems which operate using thermal actuators and hquid ink. Although they may appear similar, the two technologies operate on different principles.
  • Thermal inkjet printers use the following fundamental operating principle.
  • a thermal impulse caused by electrical resistance heating results in the explosive formation of a bubble in liquid ink. Rapid and consistent bubble formation can be achieved by superheating the ink, so that sufficient heat is transfened to the ink before bubble nucleation is complete.
  • ink temperatures of approximately 280°C to 400°C are required.
  • the bubble formation causes a pressure wave which forces a drop of ink from the aperture with high velocity. The bubble then collapses, drawing ink from the ink reservoir to re-fill the nozzle.
  • Thermal ink jet printing has been highly successful commercially due to the high nozzle packing density and the use of well established integrated circuit manufacturing techniques.
  • thermal ink jet printing technology faces significant technical problems including multi-part precision fabrication, device yield, image resolution, 'pepper' noise, printing speed, drive transistor power, waste power dissipation, satellite drop formation, thermal stress, differential thermal expansion, kogation, cavitation, rectified diffusion, and difficulties in ink formulation.
  • Printing in accordance with the present invention has many of the advantages of thermal ink jet printing, and completely or substantially eliminates many of the inherent problems of thermal ink jet technology. Comparison between Thermal ink jet and Present Invention
  • Basic ink carrier Water Water, microemulsion, alcohol, glycol, or hot melt
  • Peak heater 400°C to l,000°C (high Approx. 130°C temperature temperature reduces device life)
  • Heater pulse Typically approx. 40V. Approx. 5 to 10V. voltage
  • Heater peak pulse Typically approx. 200 mA Approx. 4 mA per heater. current per heater. This requires This allows the use of small bipolar or very large MOS MOS drive transistors. drive transistors.
  • Constraints on ink Many constraints including Temperature coefficient of composition kogation, nucleation, etc. surface tension or viscosity must be negative.
  • CMOS complementary metal-oxide-semiconductor
  • nMOS complementary metal-oxide-semiconductor
  • bipolar circuitry usually CMOS, nMOS, or bipolar circuitry required due to high drive current
  • yield The percentage of operational devices which are produced from a wafer run is known as the yield. Yield has a direct influence on manufacturing cost. A device with a yield of 5% is effectively ten times more expensive to manufacture than an identical device with a yield of 50%.
  • Figure 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, which is a widely used yield prediction method. With a defect density of one defect per square cm, Mu ⁇ hy's method predicts a yield less than 1%. This means that more than 99% of heads fabricated would have to be discarded. This low yield is highly undesirable, as the print head manufacturing cost becomes unacceptably high. 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 explicidy models the clustering of defects by introducing a defect clustering factor.
  • the defect clustering factor is not a controllable parameter in manufacturing, 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 die 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, die physical location of redundant sub-units on the chip is not important
  • the redundant sub-unit may contain one or more printing actuators. These must have a fixed spatial relationship to the page being printed.
  • redundant actuators To be able to print a dot in the same position as a faulty actuator, redundant actuators must not be displaced in the non-scan direction.
  • faulty actuators can be replaced with redundant actuators which are displaced in the scan direction.
  • the data timing to the redundant actuator can be altered to compensate for the displacement in the scan direction.
  • the minimum physical dimensions of the head chip are determined by the widtii of the page being printed, die 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 significantiy 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 manufacturing 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. However, fault tolerance is not to be taken as an essential part of the present invention. Fault tolerance in drop-on-demand printing systems is described in the following Australian patent specifications filed on 12 April 1995, the disclosure of which are hereby inco ⁇ orated by reference:
  • 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 otiier 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.
  • the binary image is processed by a data phasing circuit 55 (which may be inco ⁇ orated in a Head Control ASIC 400 as shown in figure 4) which provides the pixel data in the correct sequence to the data shift registers 56. Data sequencing is required to compensate for the nozzle a ⁇ angement and the movement of the paper.
  • the driver circuits 57 When the data has been loaded into the shift registers 56, it is presented in parallel to the heater driver circuits 57.
  • the driver circuits 57 will electronically connect the corresponding heaters 58 with the voltage pulse generated by the pulse shaper circuit 61 and the voltage regulator 62.
  • the heaters 58 heat the tip of the nozzles 59, affecting die physical characteristics of the ink.
  • Ink drops 60 escape from the nozzles in a pattern which conesponds 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 d e 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 d e 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. Multiple nozzles in a single monolithic print head
  • 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 minimum time taken to print a page is equal to the number of dot positions on the page times die 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, me 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 die paper, the total number of dots required is still very large. If the time taken to print a dot is 144 ⁇ s, 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 die 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 6,615 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 alignment and differential diermal 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 silicon. Nozzles and ink channels are etched into me silicon. Heater elements are formed by evaporation of resistive materials, and subsequent photolithography using standard semiconductor manufacturing processes.
  • data distribution circuits and drive circuits can also be integrated on die print head.
  • Figure 7 is a simplified view of a portion of a print head, seen from the back surface of the chip, and cut through some of the nozzles.
  • the substrate 120 can be made from a single silicon crystal.
  • Nozzles 121 are fabricated in the substrate, e.g., by semiconductor photolithography and chemical wet etch or plasma etching processes. Ink enters the nozzle at the top surface of the head, passes dirough the substrate, and leaves via die nozzle tip 123. Planar fabrication of the heaters and the drive circuitry is on the underside of the wafer; that is, the print head is shown 'upside down' in relation the surface upon which active circuitry is fabricated.
  • the substrate thickness 124 can be that of a standard silicon wafer, approximately 650 ⁇ m.
  • the head widtii 125 is related to the number of colors, the arrangement of nozzles, the spacing between the nozzles, and die head area required for drive circuitry and interconnections. For a monochrome head, an appropriate width would be approximately 2 mm. For a process color head, an appropriate width would be approximately 5 mm. For a CC'MM'YK color print head, the appropriate head width is approximately 8 mm. The length of the head
  • 126 depends upon die application. Very low cost applications may use short heads, which must be scanned over a page. High speed applications can use fixed page- widtii monolithic or multi-chip print heads. A typical range of lengths for print heads is between 1 cm and 21 cm, though print heads longer than 21 cm are appropriate for high volume paper or fabric printing.
  • 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.
  • semiconductor processes upon which monohthic print head production can be based.
  • the basic process can be modified to form the necessary structures.
  • the minimum length of a monolithic print head is determined by the widtii of die required printing capability.
  • the minimum widtii of a monolithic print head is determined by die 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.
  • less than 300,000 transistors are required for the shift registers and drive circuitry. It is therefore not necessary to use recent lithographic equipment.
  • the process described herein is based on standard semiconductor manufacturing processes, and can use equipment designed for 2 ⁇ m line widths.
  • the use of lithographic equipment which is essentially obsolete (at the time of writing, the latest production IC manufacmring equipment is capable of 0.25 ⁇ m line widths) can substantially reduce die cost of establishing factories for the production of print heads. It is also not necessary to use a low power, high speed process r uch as VLSI CMOS. The speeds required are moderate, and the power consumption is dominated by die heater power required for the inkjet 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 widtiis between 1 ⁇ m and 2 ⁇ m Suitable basic manufacturing processes
  • TFT Thin Film Transistors
  • 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 silicon 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:
  • 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 latchup. This is of particular concern due to the high cu ⁇ ents at a voltage typically greater than Vdd that are required for the heater circuits.
  • CMOS is susceptible to electrostatic discharge damage. This can be mi-nimized by including protection circuits at the inputs, and by careful handling. There is no absolute 'best' base manufacmring process which is applicable to all possible configurations of printing head for my above-described systems. Instead, die manufacturing steps which are specific to the nozzles should be inco ⁇ orated into the manufacturer's preferred process. In most cases, there will need to be minor alterations to the specific details of nozzle manufacmring steps to be compatible with the existing process flow, equipment used, preferred photoresists, and preferred chemical processes. These modifications are obvious to those skilled in the art, and can be made widiout departing from the scope of the invention. Heater design
  • High quahty printing using print heads of my systems requires consistent size ink drops.
  • die nozzle diameter must be accurately controlled, as must the thickness, widtii and length of the heater.
  • die tiiickness and tiiermal properties of die materials which isolate the heater from the ink.
  • these characteristics of a high resolution print head should be controlled to better than 0.5 ⁇ m accuracy. This may be achieved by using modern production semiconductor lithographic equipment. However, use of the latest generation of semiconductor equipment is very expensive.
  • the heater element of a monolithic printing nozzle configuration using a self-aligned process, where the thickness of the heater, the width of die heater, and the position of die 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.
  • Layout example 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.
  • Figure 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 tiieir drive transistors 201 and inverting drivers 216.
  • the three nozzles are in a staggered (zig-zag) pattern to increase the distance between die nozzles, and thereby increase the strength of die sihcon wafer after the nozzles have been etched dirough the substrate.
  • the large V* and V " cu ⁇ ents 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 line from A to B in figure 8(b) is the line through which the cross section diagrams of figure 9(a) to figure 9(r) are taken.
  • This line includes a heater connection on die "A” side, and goes through a 'normal' section of die heater on the "B" side.
  • the first manufacmring step is the delivery of die wafers.
  • Silicon wafers are highly recommended over other materials such as gallium arsenide, due to the availability of large, high quality wafers at low cost, the strength of sihcon as a substrate, and die general maturity of fabrication processes and equipment.
  • the wafers must be manufactured witii good thickness control. This is because holes must be etched all of die 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. It is also possible that 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 silicon dioxide, and an etch stop can be programmed from this point. However, it is essential that the thickness variation of a particular wafer, and tiiickness 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.
  • SEMI Semiconductor Equipment and Materials Institute
  • 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.
  • the wafer thickness is here assumed to be 650 ⁇ m.
  • the wafers should not be mechanically or laser gettered, as this will affect back surface etching processes. Oxygen gradient gettering can be used.
  • Figure 9(a) shows a cross section of the wafer in the region of a nozzle after this step.
  • 200 mm (8") wafers are in use, and international standards are being set for 300 mm (12") sihcon wafers.
  • 300 mm wafers are especially useful for manufacmring LIFT heads, as pagewidth A4 (also US letter) print heads can be fabricated as a single chip on tiiese wafers.
  • the prior art process may be nMOS, pMOS, CMOS, Bipolar, or other process.
  • the active circuits can be fabricated using unmodified processes. However, some processes will need modification to allow for the large currents which may flow though a print head. As 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. Also, the metallization layers should also be thicker than the minimum normally required in a CMOS circuit. Also, the inter-metal dielectric should be increased in thickness.
  • this dielectric layer will be made of CVD SiO 2 , approximately 1 ⁇ m thick.
  • the dielectric layer should be increased to approximately 3 ⁇ m, for a total SiO 2 thickness in the nozzle region of 4 ⁇ m. The reason for this increase is for mechanical strength in the nozzle region, to increase thermal resistance to the substrate, and to prevent destruction of the heater while back-etching the nozzle chambers.
  • the nozzle tip must be etched tiirough the SiO 2 with high accuracy.
  • the lithographic resolution must be substantially better than 2 ⁇ m, as the nozzle diameter must not vary significantiy.
  • the nozzle tip should be etched witii a highly anisotropic etch, for example an RIE etch using CF - H 2 gas mixmre.
  • the etch is down to molybdenum in the contact vias, and down to silicon in the nozzle region. If the etching process is sufficiently selective against molybdenum, die inter-level vias can be etched using the same processing step. However, as the SiO 2 thickness to be etched in die nozzle tip is approximately 1 ⁇ m thicker than over the first level metal, care must be taken when using the same mask to etch the nozzles and vias.
  • second level metal As with the first level metal, electromigration must be taken into account. However, the difficulty of bonding to molybdenum tiiin films requires tiiat molybdenum is not used for die second level metal where the bonding pads are located. Instead, tiiis level can be formed from aluminum. Electromigration can be minimized by using large line-widtiis for all high current traces, and by using an aluminum alloy containing 2% copper. The step coverage of the second level metal is important, as the inter-level oxide is thicker than normal. Also, via tapering should not be used to improve step coverage, as this will also cause tapering of the nozzle tip.
  • a separate mask and separate processing steps can be used to taper vias without affecting the nozzle tip.
  • adequate step coverage is possible by using low pressure evaporation.
  • Via step coverage can be improved by placing vias only to areas where the first level metal covers field oxide. At tiiese points the tiiickness of the inter-metal oxide is less due to die previous planarization steps.
  • the prefe ⁇ ed process is the deposition by low pressure evaporation of 1mm of 98% aluminum, 2% copper, with 0.5 ⁇ m coverage on sidewalls.
  • 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 widi the same lithographic accuracy as the main process.
  • the contacts to the heater can overlap the edge of die nozzle tip by several mm.
  • FIG. 9(f) shows a cross section of die wafer in the region of a nozzle after this step.
  • 7) Form the heater.
  • the heater is formed by applying a tiiin conformal film of heater material, and anisotropically etching that material. This leaves heater material remaining only on the vertical surfaces.
  • the heater material for example 0.05 ⁇ m of TaAl alloy, or refractory materials such as HfB 2 or ZrB 2
  • Figure 9(g) shows a cross section of the wafer in the region of a nozzle after this step.
  • RIBE reactive ion beam etch
  • Figure 9(h) shows a cross section of d e wafer in the region of a nozzle after this step.
  • the resist on the front side of die wafer is just to prevent handling damage or stray etching.
  • the resist on die backface of the wafer should be a tiiree level resist as the nozzle ba ⁇ el is etched all of the way dirough the wafer.
  • the selectivity of available etchants is typically no more than 25:1 of silicon over resist. This means that the resist layer must be at least 26 ⁇ m thick to avoid dunning the wafer. As some wafer thinning should not cause problems, the resist thickness can be approximately 25 ⁇ m.
  • a multilevel level resist should be used.
  • a suitable process is a three level resist using an inorganic intermediate resist level.
  • the thickness of the first level resist is approximately ten times mat commonly used in three level resists, so the intermediate oxide level must also be correspondingly diicker.
  • Suitable processes are a spin-coat of 25 ⁇ m of optical novalak positive poly methyl methacrylate (PMMA) followed by spin coating 1 ⁇ m spin-on-glass (SOG) followed by spin coating of 0.5 ⁇ m of resist (soft and hardbaking cycles are, of course, also required).
  • Figure 9(i) shows a cross section of die wafer in the region of a nozzle after this step (resist thicknesses not shown to scale).
  • the under-surface of die SiO 2 will be etched 1 ⁇ m. This is within die design constraints of the process. It is also essential tiiat the sidewalls of die barrel are substantially vertical.
  • the required radius of the nozzle at the nozzle tip is approximately 7 ⁇ m.
  • the radius of die iiozzle ba ⁇ els 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 (tiiis is calculated as arctan ((29 ⁇ m-7 ⁇ m) / 650 ⁇ m)).
  • 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 alignment and diameter of the barrel at the nozzle tip is not critical.
  • ink may not flow from the ba ⁇ el to the nozzle tip. If the ba ⁇ el is too wide, the strength of the silicon wafer may be compromised.
  • Figure 9(k) shows a cross section of the wafer in the region of a nozzle after this step.
  • FIG. 12 Isotropic RIE etch of all exposed molybdenum to a depth of 1 ⁇ m. This eliminates the residual metal in the bottom of the nozzle tip. If this is not removed, tiiere is some chance that a short circuit may occur between the molybdenum heater contacts and die tantalum passivation layer. If this possibility is eliminated by other means, then this step is not required.
  • Figure 9(1) shows a cross section of the wafer in the region of a nozzle after this step.
  • a desirable passivation layer is tantalum, which forms an extremely durable tiiin layer of Ta 2 Os which rapidly re-establishes itself in the event of surface damage.
  • tantalum is electrically conductive. This means that die circuit must be electrically insulated from the passivation layer. This can be achieved by a layer of SiO 2 or other electrical non-conductor.
  • thermal coupling between the heater and die ink is best when the die ⁇ nal conductivity of the passivation layers is high, and die specific heat capacity is low.
  • the thermal conductivity of tantalum is high. However, the tiiermal conductivity of amo ⁇ hous
  • SiO 2 glass
  • a practical material for present use is sihcon nitride. While the thermal conductivity is not as good as other non-conducting materials such as diamond or silicon carbide, passivation qualities are excellent and die material is well known for semiconductor manufacturing.
  • the 0.5 ⁇ m conformal layer of Si 3 N can be apphed by PECVD.
  • Figure 9(n) shows a cross section of die 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.
  • 'rim' of tantalum can be fabricated at die 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 die 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.
  • a method of applying such a film using plasma enhanced chemical vapor deposition (PECVD) equipment is described in US patent number 5,073,785. It is not essential to apply a separate hydrophobic layer. Instead, die exposed dielectric layer can be treated with a hydrophobizing agent. For example, if SiO 2 is used as die insulation layer in place of Si 3 N 4 , 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 SiO 2 .
  • PECVD plasma enhanced chemical vapor deposition
  • 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, tiien the front surface of the print head should be lipophobic. 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 die front surface of the device. The entire device may be coated witii a hydrophobic layer (or lipophobic layer is non-polar ink is used) without significantiy affecting the performance of the device.
  • Figure 9(q) shows a cross section of the wafer in the region of a nozzle after this step.
  • Bond, package and test The bonding, packaging, and testing processes can use standard manufacmring techniques. Tape automated bonding (TAB) is recommended as a connection means due to the low profile of TAB and die high cu ⁇ ent capability when a large widtii of contiguous connections can be used. Bonding pads must be opened out from the Si 3 N 4 passivation layer. This can be achieved through standard masking and etching processes. After the bonding pads have been opened, die resist must be stripped, and die wafer cleaned. Then wafer testing can proceed. After wafer testing, solder bumps are apphed. Then the wafer is diced.
  • TAB Tape automated bonding
  • 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.
  • the diced wafers are then mounted in die ink channels. For color print heads, die separate ink channels are sealed to die chip at this stage.
  • the TAB leadframes are applied, and dry device tests performed. The device is tiien be connected to die ink supply, ink pressure is apphed, and functional testing can be performed.
  • Figure 9(r) shows a cross section of the wafer in the region of a nozzle after this step.
  • 100 is ink
  • 101 is silicon
  • 102 is CVD SiO 2
  • 103 is the heater material
  • 104 is the tantalum passivation
  • 106 is the second layer metal interconnect (aluminum)
  • 107 is resist
  • resist 108 is silicon nitride (Si 3 N 4 )
  • 109 is the hydrophobic surface coating.
  • manufacmring processes are possible.
  • the above manufacmring process is not the simplest process that can be employed, and is not die lowest cost practical process.
  • 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 die LIFT head can be supplied witii 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 die 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.
  • a large channel is etched most of die way tiirough the wafer, leaving a thickness of approximately 50 ⁇ m in the region of die nozzles.
  • a multi-level resist is tiien applied to die base of this channel, and die 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 tiirough the remaining 50 ⁇ m of silicon.
  • 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 tiiis 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.
  • Another prefe ⁇ ed print head construction and fabrication process for print heads of my above-described systems is described in detail below witii reference to Figures 10-31. However, many simpler head manufacmring processes can be derived. In particular, heads which do not include active circuitry may be manufactured using much simpler processes. Manufacmring process for print heads using plasma etching for nozzle rims
  • the manufacmre of monohthic printing heads in accordance with this preferred embodiment is similar to standard sihcon 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 die nozzle tips.
  • semiconductor processes upon which such monolithic print head production can be based.
  • mere are many different ways d e basic process can be modified to form the necessary structures.
  • This preferred manufacturing process for integrated printing heads uses ⁇ 100> wafers for standard CMOS processing.
  • the processing is substantially compatible widi standard CMOS processing, as the MEMS specific steps can all be completed after the fabrication of die CMOS VLSI devices.
  • 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 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, botii greater than and less tiian 16 ⁇ m.
  • the process uses anisotropic etching on a ⁇ 100> silicon wafer to etch ink channels, followed by and nozzle barrels. High temperamre steps such as diffusion and LPCVD are avoided during any post-CMOS processes.
  • Figure 10 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 die nozzles, and die 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 die 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 die 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 die 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 die regions between pits, no nozzles can be placed. These regions can be used for the data distribution and fault tolerance circuitry.
  • Figure 10 shows a suitable location for main shift registers 2004, redundant shift registers 2005, and fault tolerance circuitry 2006.
  • Figure 11 is a detail layout of one pair of nozzles (a main nozzle and its redundant counte ⁇ art), along with die drive transistors for the nozzle pair.
  • the layout is for a 1.5 micron VLSI process, with 0.5 micron lithography used for the nozzle tip formation process.
  • the layout shows two nozzles, with their co ⁇ esponding drive transistors.
  • the main and redundant nozzles are spaced one pixel widtii apart, in the print scanning direction.
  • the main and redundant nozzles can be placed adjacent to each otiier without electrostatic or fluidic interference, because both nozzles are never fired simultaneously.
  • Drive transistors can be placed very close to the nozzles, as the temperature rise resulting from drop selection is very small at short distances from die heater.
  • 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 two long edges of die chip.
  • a layer of the heater material appears over all of the active circuitry.
  • This layer of heater material is electrically connected to V * , and acts as an ESD (Electrostatic Discharge) shield.
  • the ESD shield is present to protect the CMOS circuitry from electrostatic discharges from die drop acceleration electrode when using electrostatic drop separation. This layer is omitted from Figure 11 for clarity. Alignment to crystallographic planes
  • the manufacturing process described in this chapter uses the crystallographic planes inherent in die single crystal sihcon wafer to control etching.
  • the orientation of die masking procedures to the ⁇ 111 ⁇ planes must be precisely controlled.
  • the orientation of die primary flats on a sihcon wafer are normally only accurate to within ⁇ 1° of the appropriate crystal plane. It is essential that tins angular tolerance be taken into account in the design of die mask and manufacturing processes.
  • the surface orientation of die wafer is also only accurate to ⁇ 1 °.
  • the starting wafer can be a standard 6" sihcon wafer, except that wafers polished on botii sides are required.
  • Figure 12 shows a 6" wafer with 12 full color print heads, each witii a print widtii of 105 mm. Two of these print heads can be combined to form an A4 US letter sized pagewidtii 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:
  • This process uses special wafers with an epitaxial buried layer of high concentration boron. This buried layer is used as an etch stop for the EDP etch process. Other etch stop means can be used.
  • the major manufacturing steps are as follows:
  • CMOS process 1) Complete the CMOS process, fabricating drive transistors, shift registers, clock distribution circuitry, and fault tolerance circuitry according to die normal CMOS process flow.
  • a two level metal CMOS process with line widtiis 1.5 ⁇ m or less is prefe ⁇ ed.
  • the CMOS process is completed up until oxide over second level metal.
  • the second level metal should be copper, or other material suitable for TAB bonding.
  • Figure 13 shows a cross section of wafer in the region of a nozzle tip after the completion of die standard CMOS process flow. This, and subsequent cross sections of the nozzle tip, are along the line A:B in figure 11. On the 'A' side, diis cross section is tiirough a 'normal' part of the nozzle rim. On the 'B' side, d e cross section is through an electrode. Cross sections of active CMOS circuitry are not shown for clarity, as these are fabricated using standard process flows.
  • This diagram shows die 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) Epitaxial buried boron doped layer 2018: 1 ⁇ m. b) Epitaxial sihcon layer 2019: 10 ⁇ m. c) Field oxide 2021: 1 ⁇ m. d) First interlevel oxide 2022: 0.5 ⁇ m. e) First level metal 2023: 1 ⁇ m. f) Second interlevel oxide 2024: 2 ⁇ m, planarized. g) Second level metal 2025: 1 ⁇ m. h) Passivation oxide 2026: 1.5 ⁇ m, not planarized. 2) Open vias in the passivation oxide layer for heater contact with the electrodes. At die same time, vias to V * are opened which connect the bulk area of heater material which is to be used as an ESD shield.
  • Figure 14 shows a cross section of the wafer in the region of a nozzle tip after this step.
  • heater material 2027 Deposit a thin layer of heater material 2027.
  • the layer thickness depends upon die resistivity of die heater material chosen, and die desired heater resistance. Many different heater materials can be used, including tungsten, nichrome, tantalum/aluminum alloy, polysilicon doped witii boron, zirconium diboride, hafnium diboride, and others.
  • the heater resistance is 728 ⁇ .
  • Figure 15 shows a cross section of the wafer in the region of a nozzle tip after this step.
  • Figure 16 shows a cross section of die wafer in the region of a nozzle tip after this step. 5) Deposit 0.1 micron of PECVD Si 3 N 4 (nitride) 2028 on die front of the wafer.
  • Figure 17 is a cross section of the nozzle tip region after this deposition step.
  • the boron concentration in the epitaxial etch stop layer 2018 should be in excess of 6 x 10 19 atoms per cm 3 in order to slow the etch rate by a large amount.
  • An etch rate reduction of 100: 1 in a 1 micron boron doped layer allows a significant latitude in both wafer thickness and EDP etch rate.
  • the etch time should be approximately 5 hours.
  • ink channels 2010 etched most of die way tiirough the wafer, but limited in deptii by the boron doped etch stop 2018, and limited in etch widtii by [111] crystallographic planes in the sihcon substrate.
  • the position of the sidewall of die ink channel 2010 is not to scale.
  • the etch rates for EDP are approximately as per the following table:
  • etch rates are from H. Seidel, "The Mechanism of Anisotropic Sdicon Etching and its relevance for Micromachining," Transducers '87, Rec. of the 4th Int. Conf. on Solid State Sensors and Actuators, 1987, PP. 120-125.
  • Figure 18 shows a cross section of the wafer in the region of a nozzle tip after this step.
  • the mask lithography must be high resolution (0.5 micron) and well aligned to die mask used for the etching of the outside rim of the heater.
  • the etch is a anisotropic plasma etch which etches through the surface nitride 2028, die heater material 2027, the CVD oxide layers 2022, 2024 and 2026, die thermal oxide 2021, the epitaxial sihcon layer 2019, and the boron doped epitaxial sihcon layer 2018. It is preferable that the sihcon be undercut to reduce viscous drag on die ejected drop. This can be achieved by using etchants which etch sihcon at a higher rate than sihcon dioxide.
  • Figure 19 shows a cross section of the wafer in the region of a nozzle tip after this step.
  • 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 pattern can be adjusted so that the chips are still supported by die wafer at the end of die etching step, leaving only thin 'bridges' which are easily snapped widiout damaging die chips. Alternatively, the chips may be completely separated from die wafer at this stage.
  • the mask slots on the front side of die wafer can be much na ⁇ ower than that tiiose on the back side of die wafer (a 10 ⁇ m widtii is suitable). This reduces wasted wafer area between the chips to an insignificant amount 12) TAB bond die chips.
  • the TAB bonding extends along the long edges of die chips, and includes die main V* and V " power supply connections as well as the logic power and ground, and die data connections to the chip. Solder should be sputtered directiy on the TAB film instead of die print head chips, to avoid solder contamination of the nozzles.
  • TAB substrates should be relatively thin (25 ⁇ m), and die edge of the TAB films can be beveled.
  • the beveling of the TAB edge can be achieved after bonding die TAB substrates to the chip, by the use of laser ablation.
  • a defocused eximer laser can be scanned across the edge of die TAB, removing approximately 1 micron of TAB polymer with each pass. This should be done in a vacuum extraction chamber with helium flow to avoid condensation of the ablated TAB polymer on the surface of the chip.
  • the passivation can be l.OOOA of ECRCVD Si 3 N 4 (Electron- Cyclotron Resonance Chemical Vapor Deposition sihcon nitride) 2029, which provides a high density sihcon nitride layer which forms an effective barrier against hydroxyl ion diffusion tiirough the passivation layer.
  • Figure 20 is a cross section of the nozzle tip region after this deposition step.
  • hydrophobizing agents include (in increasing order of preference):
  • a fluorinated surface is preferable to an alkylated surface, to reduce physical adso ⁇ tion of die ink surfactant.
  • Figure 21 shows a cross section of die a nozzle during the hydrophobizing process. 15) Package as the complete print head. The device can then be connected to die ink supply, ink pressure apphed, and functional testing can be performed.
  • Figure 22 shows a cross section of the a nozzle filled witii ink 2031 in the quiescent state.
  • Figure 23 shows a perspective view of a single completed nozzle structure.
  • the nozzle tip 2042 contains the active portion of the heater, which is connected to second level metal in the regions 2041.
  • the region around die nozzle tip 2042 is etched to a depth of 2 ⁇ m in step 4. This provides a rim around die nozzle tip to prevent the spread of the ink drop across the surface of the print head chip.
  • the heater material and underlying oxide layers are not etched.
  • the heater material in the region 2040 provides an ESD shield over all of the active circuitry on the print head chip.
  • the raised surface in the region 2040 also allows the use of wiping blades to clear the nozzle tip 2042 of dried ink, should diis be required.
  • the nozzle barrel is etched in the silicon substrate through to the ink channel 2043.
  • Figure 24 shows a perspective view of the ink channels seen from the back face of a section of a print head chip. This figure shows eighty ink channel pits 2045, each of which contains 48 nozzles. The crenellated edge of die chip 2044 is also shown.
  • Figure 25 shows an exploded perspective view of a print head assembly, consisting of a print head chip 2046, two TAB connectors 2047, and an ink channel chip 2050.
  • the TAB connectors provide power and data connections to the print head 2046.
  • the edges 2048 of the TAB connectors 2047 is beveled by laser ablation to allow smooth airflow over the surface of the print head 2046 and TAB connector 2047 assembly.
  • the ink channel chip 2050 is etched from sihcon, and is approximately 600 ⁇ m thick.
  • the chip has one ink channel 2051 for each ink color. When assembled to die print head chip 2046, the ink channels 2051 fluidically connect all of the ink channel pits in the print head chip which print ink of the selected color.
  • Ink is provided to die ink channels 2051 via ink holes 2052.
  • the ink channel chips 2050 can be manufactured by front-face and back-face masks, followed by a single anisotropic wet etching step, or by anisotropic dry etching from both surfaces of the wafer.
  • the ink channels 2051, ink holes 2052, and edge of die chip 2050 can be etched simultaneously.
  • Figures 26(a) to 26(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 26(a) shows two regions of the chip, the nozzle region and die chip edge region before etching, along with the masked regions for nozzle tips, ink channels, and chip edges.
  • Figure 26(b) shows the wafer after the nozzle tip holes have been etched at die ⁇ 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 d e ink channels proceeds simultaneously.
  • Figure 26(c) shows the wafer at the time that the pit being etched at die chip edge from the front side of the wafer meets the pit being etched from the back side of die wafer.
  • Figure 26(d) shows the wafer at the time that ink channel pit meets the nozzle tip pit The etching of the edges of die wafer has proceeded simultaneously at the ⁇ 100> rate in a horizontal direction.
  • Figure 26(e) shows the wafer after etching is complete, and the nozzles have been formed.
  • Figure 27 shows dimensions of die layout of a single ink channel pit with 24 main nozzles and 24 redundant nozzles manufactured by die method disclosed herein.
  • Figure 28 shows an arrangement and dimensions of 8 ink channel pits, and their corresponding nozzles, in a print head.
  • Figure 29 shows 32 ink channel pits at one end of a four color print head. There are two rows of ink channel pits for each of the four process colors: cyan, magenta, yellow and black.
  • Figure 30(a) and figure 30(b) show the ends of two adjacent print head chips as they are butted togetiier to fo ⁇ n longer print heads. The precise ahgnment of the print head chips, without offsetting the print head chips in the scan direction, allows printing without visible joins (microbanding) between die printed swatiis on the page.
  • Figure 31 shows the full complement of ink channel pits on a 4.25" (108 mm) monohthic print head module.
  • Appendix A is a summary of some desirable characteristics of a color print head for printing A4 sheets at 600 dpi in one second. Modifications, obvious to those skilled in the art, can be made thereto without departing fro'n the scope of die invention.
  • the pnnt bead is fixed, and u the full width of die A4 paper Resolution is 600 dpi bi-level for medium quality output
  • Chips per wafer 36 From chip sue and recommended wafer size
  • Nozzles per phase- _.. 2,480 From page width, resolution and colors

Abstract

L'invention concerne des têtes d'impression qui fonctionnent en utilisant les principes de l'impression par transfert adaptable à la demande de gouttes d'encre selon des forces coïncidentes, par l'intermédiaire de buses multiples intégrées dans une structure monolithique unique pouvant être en silicium. Certains procédés de traitement des semiconducteurs tels que la photogravure et l'attaque chimique sont utilisées en vue de fabriquer simultanément une pluralité de buses par intégration sur la tête monolithique. On attaque le substrat en silicium pour réaliser les buses, ce qui permet d'obtenir deux alignements dimensionnels de buses pour l'impression en couleurs. La fabrication peut se poser sur le procédé existant (CMOS, nMOS et semiconducteurs bipolaires), d'où la possibilité d'utiliser les moyens de fabrication existant pour les semiconducteurs. En outre, on est en mesure de fabriquer des transistors d'attaque, des registres à décalage et des circuits tolérants aux défauts sur la plaquette où les buses ont été intégrées. L'alimentation des actionneurs est faible par rapport à celle d'autres systèmes à écoulements des gouttes sur demande comme les systèmes d'impression thermique à jet d'encre, ce qui permet de recourir à des circuits intégrés d'attaque CMOS ou nMOS.
EP96913782A 1995-04-12 1996-04-09 Tetes d'impression monolithiques et leurs procedes de fabrication Withdrawn EP0771272A1 (fr)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
AUPN2301/95 1995-04-12
AUPN2301A AUPN230195A0 (en) 1995-04-12 1995-04-12 A monolithic lift printing head
AUPN2302A AUPN230295A0 (en) 1995-04-12 1995-04-12 A manufacturing process for monolithic lift print heads
AUPN2302/95 1995-04-12
PCT/US1996/004872 WO1996032284A1 (fr) 1995-04-12 1996-04-09 Tetes d'impression monolithiques et leurs procedes de fabrication

Publications (1)

Publication Number Publication Date
EP0771272A1 true EP0771272A1 (fr) 1997-05-07

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Application Number Title Priority Date Filing Date
EP96913782A Withdrawn EP0771272A1 (fr) 1995-04-12 1996-04-09 Tetes d'impression monolithiques et leurs procedes de fabrication

Country Status (3)

Country Link
EP (1) EP0771272A1 (fr)
JP (1) JPH10502030A (fr)
WO (1) WO1996032284A1 (fr)

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US5719605A (en) * 1996-11-20 1998-02-17 Lexmark International, Inc. Large array heater chips for thermal ink jet printheads
FR2775625B1 (fr) 1998-03-06 2000-05-05 Eastman Kodak Co Dispositif de deplacement d'un fluide
FR2785021B1 (fr) 1998-10-09 2002-02-15 Eastman Kodak Co Dispositif pour controler le deplacement d'un fluide sous l'action d'un gaz
FR2795017B1 (fr) 1999-06-21 2001-08-31 Eastman Kodak Co Dispositif de controle de l'atmosphere d'un reservoir d'encre applique a l'impression par jet d'encre
US6491385B2 (en) * 2001-02-22 2002-12-10 Eastman Kodak Company CMOS/MEMS integrated ink jet print head with elongated bore and method of forming same
JP6383629B2 (ja) * 2014-10-15 2018-08-29 エスアイアイ・プリンテック株式会社 ノズルプレート、液体噴射ヘッドおよび液体噴射装置
JP7322521B2 (ja) * 2019-06-05 2023-08-08 ブラザー工業株式会社 液体吐出ヘッド

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JPS5840512B2 (ja) * 1978-10-04 1983-09-06 株式会社リコー インクジェット記録装置
US4164745A (en) * 1978-05-08 1979-08-14 Northern Telecom Limited Printing by modulation of ink viscosity
JPS5579175A (en) * 1978-12-11 1980-06-14 Nec Corp Device for forming ink drop
FR2448979B1 (fr) * 1979-02-16 1986-05-23 Havas Machines Dispositif destine a deposer sur un support des gouttes d'encre
JPS60210462A (ja) * 1984-04-05 1985-10-22 Fuji Xerox Co Ltd インクジエツト記録装置
US4752783A (en) * 1986-03-27 1988-06-21 Fuji Xerox Co., Ltd. Thermal-electrostatic ink jet recording method and apparatus
EP0367303A1 (fr) * 1986-04-28 1990-05-09 Hewlett-Packard Company Tête d'impression à jet d'encre thermique
US4847630A (en) * 1987-12-17 1989-07-11 Hewlett-Packard Company Integrated thermal ink jet printhead and method of manufacture
GB8912245D0 (en) * 1989-05-26 1989-07-12 Pa Consulting Services Liquid jet recording process
DE69214853T2 (de) * 1991-01-30 1997-05-28 Canon Kk Strahldrucker mit Bläschen für Bildaufzeichnungsvorrichtung
JP3384597B2 (ja) * 1992-11-30 2003-03-10 ヒューレット・パッカード・カンパニー インク転移印刷装置及び方法
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Also Published As

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JPH10502030A (ja) 1998-02-24
WO1996032284A1 (fr) 1996-10-17

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