Drop-on-demand inkjet printers are commonly categorized according to one of two mechanisms of drop formation within an inkjet printhead. Thermal bubble inkjet printers use thermal inkjet printheads with heating element actuators that vaporize ink (or other fluid) inside ink-filled chambers to create bubbles that force ink droplets out of the printhead nozzles. Piezoelectric inkjet printers use piezoelectric inkjet printheads with piezoelectric ceramic actuators that generate pressure pulses inside ink-filled chambers to force droplets of ink (or other fluid) out of the printhead nozzles.
Piezoelectric inkjet printheads are favored over thermal inkjet printheads when using jettable fluids whose higher viscosity and/or chemical composition prohibit the use of thermal inkjet printheads, such as UV curable printing inks. Thermal inkjet printheads are limited to jettable fluids whose formulations can withstand boiling temperature without experiencing mechanical or chemical degradation. Because piezoelectric printheads use electromechanical displacement (not steam bubbles) to create pressure that forces ink droplets out of nozzles, piezoelectric printheads can accommodate a wider selection of jettable materials. Accordingly, piezoelectric printheads are utilized to print on a wider variety of media.
Piezoelectric inkjet printheads are commonly formed of multilayer stacks having pressure chambers, piezoelectric actuators, ink channels, etc., configured for controlled ejection of ink drops through printhead nozzles. Ongoing efforts to improve piezoelectric inkjet printheads involve reducing fabrication and material costs of piezoelectric stacks while increasing their performance and robustness. As part of this ongoing trend, multiple silicon die are increasingly used for many of the layers in the stack since finer, more densely packed features can be etched into silicon.
The present embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:
As noted above, efforts to improve piezoelectric inkjet printheads have lead to an increased use of multiple silicon die for many of the layers in piezoelectric stacks. One benefit realized is the ability to etch finer, more densely packed features into the silicon of such multilayer silicon die stacks. Such die stacks also present an opportunity to improve electrical trace routing within the limited space that exists along and between different die layers in the piezoelectric stack. More efficient trace routing enables smaller die sizes which reduces cost by helping to maximize the number of die available from each wafer.
Prior solutions for routing electrical traces on the exposed surface of the diaphragm not covered with piezoceramic include having traces that all emanate from bond pads along the outside edges of the die and run between the piezoceramic actuators. In some solutions traces are routed over the walls separating the chambers and/or over the diaphragm. In some solutions the ground layer extends over the walls and/or diaphragm. In some cases the ground layer or ground traces extend under drive signal traces (i.e., hot traces). Such solutions generally involve electrical traces that cover more die area (increasing production costs and decreasing production yield), because traces that emanate from the edge for both ground and drive signals are crowded into the space between piezoceramics. Solutions that include ground and drive signal traces that cross over and under one another can reduce reliability due to the potential for short circuits and adverse electrical interactions (i.e., capacitive coupling between traces). Such solutions also increase production costs due to the additional photo-etch and deposition process steps, as well as the additional insulating layer between the traces.
Embodiments of the present disclosure improve routing for electrical traces through a piezoelectric drop ejector (printhead) that includes a multilayer MEMS die stack having an efficient electrical trace layout to route drive signals and ground to thin film piezoelectric actuators. An actuator die within the die stack includes wire bond pads at the perimeter of the die that run along both side edges (i.e., both long edges) of the die. The area toward the center of the actuator die that lies in between the bond pads includes rows of piezoelectric actuators (e.g., 4, 6, 8, or more rows) that extend from bond pads at one side edge of the die to bond pads at the other side edge of the die. Electrical drive traces emanate from the bond pads at the side edges of the die and extend inward between piezoelectric actuator rows toward the center of the die to carry actuator drive signals to piezoelectric actuators in the rows of actuators. A ground bus runs along the center of the actuator die, parallel to the side edges of the die, and extends lengthwise between both end edges of the die. Ground traces emanate from the central ground bus and extend outward between piezoelectric actuator rows toward the side edges of the die to carry ground connections to piezoelectric actuators in the rows of actuators. Thus, the efficient electrical trace layout includes “outside-in” drive signal traces that begin at bond pads on the outside edges of the actuator die and travel inward to connect to piezoelectric actuators, and “inside-out” ground traces that begin at a central ground bus and travel outward from the center of the actuator die to connect to the piezoelectric actuators.
The disclosed piezoelectric printhead trace layout has several advantages over prior solutions for routing electrical traces. For example, the trace layout minimizes the number of traces that run in the crowded space between the wire bond pads at the side edges of the actuator die. This is particularly beneficial in printheads having four or more rows of actuators, and/or printheads implementing split actuators that have multiple drive signal connection points. The lengthwise, central ground bus avoids having a continuous ground bus along each of the two outer side edges of the die. The central bus also allows for connections to system ground via pads at both end edges of the die. These features enable a reduced bus width and a corresponding reduction in the width of the die, and they further reduce the number of traces that run in the crowded space between the bond pads at the side edges of the actuator die. They also enable larger bond pads and/or higher bond pad densities on the die.
In addition, each die in the stack is narrower than the die below, to enable straightforward alignment and interconnection during assembly. This facilitates proper vertical fitting of manifold compliances, drive electronics, multiple ink feeds, and so on. The die stack design enables reduced widths of the more expensive die layers in the stack such as the piezoelectric actuator die and nozzle plate, which results in reduced costs. The die stack design allows the piezo-actuators to be located on the same side of the pressure chamber as the nozzle. This in turn allows for chamber ink inlets and outlets to be directly below the chamber, enabling shorter chamber lengths. Control circuitry (e.g., an ASIC) to control piezo-actuator drive transistors is located on the chamber floor of the pressure chamber and includes the inlet and outlet holes through which ink enters and exits the chamber.
In one embodiment, a piezoelectric printhead trace layout includes an actuator die, bond pads along two side edges of the actuator die, rows of piezoceramic actuators between the two side edges, drive traces emanating from the bond pads and extending inward toward the center of the actuator die to carry drive signals to the actuators, a ground bus extended along the center of the actuator die between two end edges of the actuator die, and ground traces emanating from the ground bus and extending outward toward the two side edges to provide ground connections to the actuators.
In another embodiment, a piezoelectric printhead trace layout includes a multilayer die stack where each die in the stack is narrower than the die on which it is stacked, an actuator die in the die stack, drive signal traces emanating from side edges of the actuator die toward the center of the actuator die to piezoelectric actuators, and ground traces emanating from the center of the actuator die toward the side edges of the actuator die to the piezoelectric actuators.
Ink supply assembly 104 supplies fluid ink to printhead assembly 102 and includes a reservoir 120 for storing ink. Ink flows from reservoir 120 to inkjet printhead assembly 102. Ink supply assembly 104 and inkjet printhead assembly 102 can form either a one-way ink delivery system or a recirculating ink delivery system. In a one-way ink delivery system, substantially all of the ink supplied to inkjet printhead assembly 102 is consumed during printing. In a recirculating ink delivery system, however, only a portion of the ink supplied to printhead assembly 102 is consumed during printing. Ink not consumed during printing is returned to ink supply assembly 104.
In one embodiment, ink supply assembly 104 supplies ink under positive pressure through an ink conditioning assembly 105 to inkjet printhead assembly 102 via an interface connection, such as a supply tube. Ink supply assembly 104 includes, for example, a reservoir, pumps and pressure regulators. Conditioning in the ink conditioning assembly 105 may include filtering, pre-heating, pressure surge absorption, and degassing. Ink is drawn under negative pressure from the printhead assembly 102 to the ink supply assembly 104. The pressure difference between the inlet and outlet to the printhead assembly 102 is selected to achieve the correct backpressure at the nozzles 116, and is usually a negative pressure between negative 1″ and negative 10″ of H2O. Reservoir 120 of ink supply assembly 104 may be removed, replaced, and/or refilled.
Mounting assembly 106 positions inkjet printhead assembly 102 relative to media transport assembly 108, and media transport assembly 108 positions print media 118 relative to inkjet printhead assembly 102. Thus, a print zone 122 is defined adjacent to nozzles 116 in an area between inkjet printhead assembly 102 and print media 118. In one embodiment, inkjet printhead assembly 102 is a scanning type printhead assembly. As such, mounting assembly 106 includes a carriage for moving inkjet printhead assembly 102 relative to media transport assembly 108 to scan print media 118. In another embodiment, inkjet printhead assembly 102 is a non-scanning type printhead assembly. As such, mounting assembly 106 fixes inkjet printhead assembly 102 at a prescribed position relative to media transport assembly 108. Thus, media transport assembly 108 positions print media 118 relative to inkjet printhead assembly 102.
Electronic printer controller 110 typically includes a processor, firmware, software, one or more memory components including volatile and no-volatile memory components, and other printer electronics for communicating with and controlling inkjet printhead assembly 102, mounting assembly 106, and media transport assembly 108. Electronic controller 110 receives data 124 from a host system, such as a computer, and temporarily stores data 124 in a memory. Typically, data 124 is sent to inkjet printing system 100 along an electronic, infrared, optical, or other information transfer path. Data 124 represents, for example, a document and/or file to be printed. As such, data 124 forms a print job for inkjet printing system 100 and includes one or more print job commands and/or command parameters.
In one embodiment, electronic printer controller 110 controls inkjet printhead assembly 102 for ejection of ink drops from nozzles 116. Thus, electronic controller 110 defines a pattern of ejected ink drops that form characters, symbols, and/or other graphics or images on print media 118. The pattern of ejected ink drops is determined by the print job commands and/or command parameters from data 124. In one embodiment, electronic controller 110 includes temperature compensation and control module 126 stored in a memory of controller 110. Temperature compensation and control module 126 executes on electronic controller 110 (i.e., a processor of controller 110) and specifies the temperature that circuitry in the die stack (e.g., an ASIC) maintains for printing. Temperature in the die stack is controlled locally by on-die circuitry that includes temperature sensing resistors and heater elements in the pressure chambers of fluid ejection assemblies (i.e., printheads) 114. More specifically, controller 110 executes instructions from module 126 to sense and maintain ink temperatures within pressure chambers through control of temperature sensing resistors and heater elements on a circuit die adjacent to the chambers.
In one embodiment, inkjet printing system 100 is a drop-on-demand piezoelectric inkjet printing system with a fluid ejection assembly 114 comprising a piezoelectric inkjet (PIJ) printhead 114. The PIJ printhead 114 includes a multilayer MEMS die stack, where each die in the die stack is narrower than the die below. The die stack includes a thin film piezoelectric actuator ejection element and control and drive circuitry configured to generate pressure pulses within a pressure chamber that force ink drops out of a nozzle 116. In one implementation, inkjet printhead assembly 102 includes a single PIJ printhead 114. In another implementation, inkjet printhead assembly 102 includes a wide array of PIJ printheads 114.
The layers in the die stack 200 include a first (i.e., bottom) substrate die 202, a second circuit die 204 (or ASIC die), a third actuator/chamber die 206, a fourth cap die 208, and a fifth nozzle layer 210 (or nozzle plate). There is also usually a non-wetting layer (not shown) on top of the nozzle layer 210 that includes a hydrophobic coating to help prevent ink puddling around nozzles 116. Each layer in the die stack 200 is typically formed of silicon, except for the non-wetting layer and sometimes the nozzle layer 210. In some embodiments, the nozzle layer 210 may be formed of stainless steel or a durable and chemically inert polymer such as polyimide or SU8. The layers are bonded together with a chemically inert adhesive such as epoxy (not shown). In the illustrated embodiment, the die layers have fluid passageways such as slots, channels, or holes for conducting ink to and from pressure chambers 212. Each pressure chamber 212 includes two ports (inlet port 214, outlet port 216) located in the floor 218 of the chamber (i.e., opposite the nozzle-side of the chamber) that are in fluid communication with an ink distribution manifold (entrance manifold 220, exit manifold 222). The floor 218 of the pressure chamber 212 is formed by the surface of the circuit die 204. The two ports (214, 216) are on opposite sides of the floor 218 of the chamber 212 where they pierce the circuit die 204 and enable ink to be circulated through the chamber by external pumps in the ink supply system 104. The piezoelectric actuators 224 are on a flexible membrane that serves as a roof to the chamber and is located opposite the chamber floor 218. Thus, the piezoelectric actuators 224 are located on the same side of the chamber 212 as are the nozzles 116 (i.e., on the roof or top-side of the chamber).
Referring still to
Circuit die 204 is the second die in die stack 200 and is located above the substrate die 202. Circuit die 204 is adhered to substrate die 202 and it is narrower than the substrate die 202. In some embodiments, the circuit die 204 may also be shorter in length than the substrate die 202. Circuit die 204 includes the ink distribution manifold that comprises ink entrance manifold 220 and ink exit manifold 222. Entrance manifold 220 provides ink flow into chamber 212 via inlet port 214, while outlet port 216 allows ink to exit the chamber 212 into exit manifold 222. Circuit die 204 also includes fluid bypass channels 232 that permit some ink coming into entrance manifold 220 to bypass the pressure chamber 212 and flow directly into the exit manifold 222 through the bypass 232. As discussed in more detail below with respect to
Circuit die 204 also includes CMOS electrical circuitry 234 implemented in an ASIC 234 and fabricated on its upper surface adjacent the actuator/chamber die 206. ASIC 234 includes ejection control circuitry that controls the pressure pulsing (i.e., firing) of piezoelectric actuators 224. At least a portion of ASIC 234 is located directly on the floor 218 of the pressure chamber 212. Because ASIC 234 is fabricated on the chamber floor 218, it can come in direct contact with ink inside pressure chamber 212. However, ASIC 234 is buried under a thin-film passivation layer (not shown) that includes a dielectric material to provide insulation and protection from the ink in chamber 212. Included in the circuitry of ASIC 234 are one or more temperature sensing resistors (TSR) and heater elements, such as electrical resistance films. The TSR's and heaters in ASIC 234 are configured to maintain the temperature of the ink in the chamber 212 at a desired and uniform level that is favorable to ejection of ink drops through nozzles 116. In one embodiment, the set temperature of the TSR's and heaters in ASIC 234 is specified by the temperature compensation and control module 126 executing on controller 110 to sense and adjust ink temperature within pressure chambers 212. If the ink is to be at an elevated temperature entering the printhead assembly 102, the temperature control module 126 will engage the pre-heater within the ink conditioning assembly 105.
Circuit die 204 also includes piezoelectric actuator drive circuitry/transistors 236 (e.g., FETs) fabricated on the edge of the die 204 outside of bond wires 238 (discussed below). Thus, drive transistors 236 are on the same circuit die 204 as the ASIC 234 control circuits and are part of the ASIC 234. Drive transistors 236 are controlled (i.e., turned on and off) by control circuitry in ASIC 234. The performance of pressure chamber 212 and actuators 224 is sensitive to changes in temperature, and having the drive transistors 236 out on the edge of circuit die 204 keeps heat generated by the transistors 236 away from the chamber 212 and the actuators 224.
The next layer in die stack 200 located above the circuit die 204 is the actuator/chamber die 206 (“actuator die 206”, hereinafter). The actuator die 206 is adhered to circuit die 204 and it is narrower than the circuit die 204. In some embodiments, the actuator die 206 may also be shorter in length than the circuit die 204. Actuator die 206 includes pressure chambers 212 having chamber floors 218 that comprise the adjacent circuit die 204. As noted above, the chamber floor 218 additionally comprises control circuitry such as ASIC 234 fabricated on circuit die 204 which forms the chamber floor 218. Actuator die 206 additionally includes a thin-film, flexible membrane 240 such as silicon dioxide, located opposite the chamber floor 218 that serves as the roof of the chamber. Above and adhered to the flexible membrane 240 is piezoelectric actuator 224. Piezoelectric actuator 224 comprises a thin-film piezoelectric material such as a piezo-ceramic material that stresses mechanically in response to an applied electrical voltage. When activated, piezoelectric actuator 224 physically expands or contracts which causes the laminate of piezoceramic and membrane 240 to flex. This flexing displaces ink in the chamber generating pressure waves in the pressure chamber 212 that ejects ink drops through the nozzle 116. In the embodiment shown in
Cap die 208 is adhered above the actuator die 206. The cap die 208 is narrower than the actuator 206, and in some embodiments it may also be shorter in length than the actuator die 206. Cap die 208 forms a cap cavity 244 over piezoelectric actuator 224 that encapsulates the actuator 224. The cavity 244 is a sealed cavity that protects the actuator 224. Although the cavity 244 is not vented, the sealed space it provides is configured with sufficient open volume and clearance to permit the piezoactuator 224 to flex without influencing the motion of the actuator 224. The cap cavity 244 has a ribbed upper surface 246 opposite the actuator 224 that increases the volume of the cavity and surface area (for increased adsorption of water and other molecules deleterious to the thin film pzt long term performance). The ribbed surface 246 is designed to strengthen the upper surface of the cap cavity 244 so that it can better resist damage from handling and servicing of the printhead (e.g., wiping). The ribbing helps reduce the thickness of the cap die 208 and shorten the length of the descender 242.
Cap die 208 also includes the descender 242. The descender 242 is a channel in the cap die 208 that extends between the pressure chamber 212 and nozzle 116, enabling ink to travel from the chamber 212 and out of the nozzle 116 during ejection events caused by pressure waves from actuator 224. As noted above, in the
Also shown in the die stack 200 of
Referring still to
In one embodiment as shown in
The trace layout with the “inside-out” ground traces 500 and “outside-in” drive traces 504 enables a tighter packing scheme for the traces which allows for more rows of actuators 224 in different embodiments. In addition, the trace layout enables the ground traces and drive traces to be on the same fabrication level, or within the same or common fabrication plane. That is, during fabrication, the same patterning and deposition processes used to put down the drive traces are also used to put down the ground traces at the same time. This eliminates process steps as well as eliminating an insulation layer between the drive traces and ground traces.
Also shown on the actuator die 206 of
In the embodiment of
Referring generally to
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US11/42271 | 6/29/2011 | WO | 00 | 11/8/2013 |