Abstract:
Systems and apparatus for ejecting fluid. A fluid injection apparatus includes a fluid ejector unit for ejecting a droplet of fluid, an integrated circuit, and a conductive trace electrically coupling the fluid ejector unit and the integrated circuit. A portion of the conductive trace includes a fuse.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/109,880, filed Oct. 30, 2008, and is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The subject matter of this specification is related generally to fluid ejectors, e.g., inkjet printheads. 
         [0003]    An inkjet printhead can have multiple piezoelectrically controlled ink ejectors, each including a pumping chamber connected to a nozzle. The ink ejectors can be driven by an application specific integrated circuit (ASIC). The ASIC applies a voltage to the piezoelectric material, causing the piezoelectric material to deflect. The deflection actuates the pumping chamber and causes ejection of ink from the associated nozzle. 
         [0004]    The piezoelectrically controlled ink nozzles, along with the ASICs, can be packed into a relatively small area. Because of the small area and defects or deterioration of electrical paths in the ASICs and the connections between the ASICs and the piezoelectric materials, electrical shorts, and thus overcurrent conditions, can occur, which can disable the ink nozzles. 
       SUMMARY 
       [0005]    In general, one aspect of the subject matter described in this specification can be embodied in apparatuses that include a fluid ejector unit for ejecting a droplet of fluid, an integrated circuit, and a conductive trace electrically coupling the fluid ejector unit and the integrated circuit, where a portion of the conductive trace includes a fuse. 
         [0006]    Implementations can include one or more of the following features. The fluid ejector unit can include an actuator supported on the substrate. The actuator can include a first electrode, a second electrode, and a piezoelectric material between the first electrode and second electrode. The fuse can be formed on the piezoelectric material. The fluid ejector unit can include a substrate supporting the actuator. The first electrode can be nearer to the substrate than the second electrode, and the conductive trace can be connected to the second electrode. The fuse can be immediately adjacent the second electrode. The fuse can be spaced apart from the second electrode, and a portion of the conductive trace can connect the fuse to the second electrode. The conductive trace, including the fuse, can be made of ti-tungsten. The thickness of the conductive trace, including the fuse, can be about 1000 angstroms. The fuse can have a length of about 28 microns and a width of about 5 microns. The fuse can include a constricted portion of the conductive trace. The apparatus can include a conductive layer laid over the conductive trace, where a portion of the conductive layer over the fuse is omitted. The conductive layer can be made of gold or copper. 
         [0007]    In general, another aspect of the subject matter described in this specification can be embodied in a system that includes a printhead, where the printhead includes a fluid ejector unit for ejecting a droplet of fluid; an integrated circuit for driving the droplet ejector; and an electrode electrically coupling the droplet ejector and the integrated circuit, where the electrode includes a fuse portion; and a flex circuit for transmitting data to the integrated circuit of the printhead. 
         [0008]    Particular embodiments of the subject matter described in this specification can be implemented to realize one or more of the following advantages. Failure of a droplet ejector nozzle caused by overcurrent conditions can be prevented from propagating and disabling further droplet ejectors. The apparatus, combined with an imaging algorithm that compensates for isolated inoperative droplet ejector nozzle, can eliminate the need to replace printheads in some situations. 
         [0009]    The details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is schematic perspective sectional view of a housed fluid ejector. 
           [0011]      FIG. 2  is a schematic cross-sectional view of a die and an interposer. 
           [0012]      FIG. 3  is a schematic perspective view of a die on which integrated circuit elements are mounted. 
           [0013]      FIG. 4  is a schematic view of a trace leading to an actuator. 
           [0014]      FIG. 5  is a plan view of a die with circuitry. 
           [0015]      FIG. 6  is a simplified perspective view of a die with integrated circuit elements. 
           [0016]      FIG. 7  is a schematic diagram of the electric connections between the flex circuit, die and integrated circuit elements. 
           [0017]      FIG. 8A  is a cross-section view of an example trace with a fuse. 
           [0018]      FIG. 8B  is a schematic view of the example trace of  FIG. 8A . 
           [0019]      FIG. 8C  is a cross-section view of another example trace with a fuse. 
       
    
    
       [0020]    Like reference numbers and designations in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0021]    A fluid ejector is described herein. An exemplary fluid ejector is shown in  FIG. 1 . The fluid ejector  100  includes a fluid ejection module, e.g., a quadrilateral plate-shaped printhead module, which can be a die  103 , fabricated using semiconductor processing techniques. Fluid ejection modules are also described in U.S. Pat. No. 7,052,117, which is incorporated by reference herein. The fluid ejected from the fluid ejector  100  can be ink, but the fluid ejector  100  can be suitable for other liquids, e.g., biological liquids or liquids for forming electronic components. 
         [0022]    Each fluid ejector  100  can also include a housing  110  to support and provide fluid to the die  103 , along with other components such as a mounting frame  142  to connect the housing  110  to a print bar, and a flex circuit (not shown in  FIG. 1 ) to receive data from an external processor and provide drive signals to the die  103 . The housing  110  can be divided by a dividing wall  130  to provide an inlet chamber  132  and an outlet chamber  136 . Each chamber  132  and  136  can include a filter  133  and  137 . Tubing  162  and  166  that carries the fluid can be connected to the chambers  132  and  136 , respectively, through apertures  152  and  156 . The dividing wall  130  can be held by a support  140  that sits on an interposer assembly  146  above the die  103 . 
         [0023]    A fluid ejection assembly, that includes the die  103  and the optional interposer assembly  146 , includes fluid inlets  101  and fluid outlets  102  for allowing fluid to circulate from the inlet chamber  132 , through the die  103 , and into the outlet chamber  136 . A portion of the fluid passing through the die  103  is ejected from the nozzles. 
         [0024]    The fluid ejector  100  can include a flexible printed circuit or flex circuit. The flex circuit can be configured to electrically connect the fluid ejector  100  to a printer system (not shown). The flex circuit is used to transmit data, such as image data and timing signals, from an external processor of the printer system to the die  103  for driving fluid ejection elements on the die  103 . The flex circuit can also be used to connect a thermistor for fluid temperature control. 
         [0025]    Referring to  FIG. 2 , the die  103  can include a substrate  122  in which are formed fluid flow paths  124  that end in nozzles  126  (only one flow path is shown in  FIG. 2 ). A single flow path  124  includes an ink feed  170  (the two areas labeled  170  in  FIG. 2  can be connected by a passage extending out of the page), an ascender  172 , a pumping chamber  174 , and a descender  176  that ends in the nozzle  126 . The flow path  124  can further include a recirculation path  178  so that ink can flow through the flow path  124  even when fluid is not being ejected. 
         [0026]    The substrate  122  can further include a flow-path body  182  in which the flow path  124  is formed by semiconductor processing techniques, e.g., etching, a membrane  180 , such as a layer of silicon, which seals one side of the pumping chamber  174 , and a nozzle layer  184  through which the nozzle  126  is formed. The membrane  180 , flow path body  182  and nozzle layer  184  can each be composed of a semiconductor material (e.g., single crystal silicon). The membrane  180  can be relatively thin, such as less than 25 μm, for example about 12 μm. 
         [0027]    The die  103  also includes an actuator structure  400  with individually controllable actuators  401  supported on the substrate  122  for causing fluid to be selectively ejected from the nozzles  126  of corresponding flow paths  124  (only one actuator is shown in  FIG. 2 ). Each flow path  124  with its associated actuator  401  (fluid ejection element) provides an individually controllable MEMS fluid ejector unit. 
         [0028]    In some embodiments, activation of the actuator  401  causes the membrane  180  to deflect into the pumping chamber  174 , forcing fluid out of the nozzle  126 . For example, the actuator  401  can be a piezoelectric actuator, and can include a lower conductive layer  190 , a piezoelectric layer  192 , and a patterned upper conductive layer  194 . The piezoelectric layer  192  can be between e.g. about 1 and 25 microns thick, e.g., about 8 to 18 microns thick. Alternatively, the fluid ejection element can be a heating element. 
         [0029]    Referring to  FIGS. 2 and 3 , the fluid ejector  100  further includes one or more integrated circuit elements  104  configured to provide electrical signals for control of ejection of fluid from the die  103  through nozzles located on the underside of the die  103 . The integrated circuit element  104  can be a microchip, other than the die  103 , in which integrated circuits are formed, e.g., by semiconductor fabrication and packaging techniques. Thus, the integrated circuits of the integrated circuit element  104  can be formed in a separate semiconductor substrate from the substrate of the die  103 . However, the integrated circuit element  104  can be mounted directly onto the die  103 . 
         [0030]    Referring to  FIG. 2 , in some embodiments, the fluid ejection assembly of the fluid ejector  100  includes a lower interposer  105  to separate the fluid from the electrical components on the die  103  and/or the integrated circuit element  104 . Passage  212  through the lower interposer  105  can allow for routing of fluid from/to a somewhat centralized location of chambers (not shown) in the housing of the fluid ejector  100  to/from fluid inlets and fluid outlets (not shown) that are closer to an edge of the die  103 . 
         [0031]    A plan and perspective partial view of an exemplary die having circuitry is shown in  FIGS. 5 and 6 , respectively. The multiple actuators  401  on the die  103  can be disposed in columns ( FIG. 6  omits many of the actuators for simplicity). The actuators  401  shown in  FIGS. 5 and 6  are piezoelectric elements, e.g., each actuator includes a piezoelectric layer between two electrodes. For each actuator  401 , an electrode, e.g., the top electrode  194  ( FIG. 2 ), can be connected to a corresponding input pad  402  by way of a conductive trace  407  that is also located on the die  103  ( FIG. 6  illustrates only a single trace  407  for simplicity). Portions of the traces  407  can extend between the columns of actuators  401 . 
         [0032]    In some embodiments, a fluid inlet  412  is formed at the end of a column of actuators  401 . At an opposite end of the column, a fluid outlet (not shown) can be formed in the top of the die  103 . A single fluid inlet and fluid outlet pair can serve one, two, or more columns of actuators  401 . The passage  212  through the lower interposer  105  fluidically connects the inlet  101  to the inlet  412  of the die  103 , and the fluid outlet of the die  103  to the outlet  102 . The die  103  further includes conductive input traces  403  arranged along one or more edges of the die  103 . The traces  403  can have a pitch of about  40  microns or less, e.g.,  36  micron pitch or  10  micron pitch. A flex circuit  201  (see  FIG. 2 ) can be bonded into the input traces  403  of the die  103 . For example, the flex circuit  201  can be connected to the distal ends  420  of the traces  403  at the edge of the die  103  (see  FIG. 6 ). The bonding can be performed, for example, with paste, e.g., Non Conductive Paste (NCP) or Anisotropic Conductive Paste (ACP). 
         [0033]    As shown in  FIGS. 2 ,  3  and  6 , the integrated circuit elements  104  can be mounted to the die  103  in a row extending in an elongated area between the input traces  403  and the inlets  412  or outlets. For example, a first row of integrated circuit elements  104  can be mounted to the die  103  in a first row extending in an elongated area between the input traces  403  on one edge of the die  103  and the inlets  412 , and a second row of integrated circuit elements  104  can be mounted to the die  103  in a row extending in an elongated area between the input traces  403  on the opposite edge of the die  103  and the outlets. 
         [0034]    A perspective view of an exemplary die  103  with integrated circuit elements  104  mounted thereon is shown in  FIG. 3 . As noted above, the integrated circuit element  104  can be a separately fabricated element, e.g., a separate die, that is mounted on the die  103 . In some implementations, the integrated circuit element  104  is an application-specific integrated circuit (ASIC) element. The integrated circuit element  104  can be a chip that can include, for example a die, packaging, and leads. The leads connecting the bond pads of the integrated circuit element  104  to electrical traces on the die  103  can be solder bumps (see  FIG. 2 ) or wire bonds. For example, the leads can be gold bumps electroplated directly onto an aluminum bonding pad of the integrated circuit element  104 . They can also be copper pillar bumps with a solder cap electroplated directly onto electrical pads of the integrated circuit element  104 . 
         [0035]    The integrated circuit element  104  is configured to provide signals to control the operation of the actuators  401 , as shown in  FIG. 7 . For example, integrated switching elements  302 , e.g., transistors, in the integrated circuit element  104  can be connected to actuators  401  on the die  103  with electrical contacts and leads. Thus, when a signal is sent from the flex circuit  201  to the input trace  403  on the die  103 , it can be transmitted to an input pad  301  on the integrated circuit element  104 , processed on the integrated circuit element  104 , such as at the transistor  302 , and output at an output pad  303  to the input pad  402  on the die  103 , which is connected by the input trace  407  to drive the actuator  401 . In some implementations, the integrated circuit element  104  also includes one or more diodes. 
         [0036]    The integrated circuit element  104  shown in  FIG. 6  includes input pads  301  (see  FIG. 7 ) that are connected to the input traces  403  on the die  103 . For example, the input pads  301  on the integrated circuit elements  104  can be connected to the proximal ends  422  of the input traces  403 , which are closer to a center of the die  103  than distal ends  420  of the input traces  403 . The input pads  301  and input traces  403  can be connected using non-conductive paste (NCP), anisotropic conductive paste (ACP), or solder bumps on the integrated circuit elements  104 . The input pads  301  of the integrated circuit element  104  can be on the bottom surface of the integrated circuit element  104  to provide better electrical connection with the input traces  403  of the die  103 . 
         [0037]    As shown in  FIG. 7 , the integrated circuit element  104  also includes output pads  303  that are connected to the input pads  301  of the integrated circuit element  104  through one or more integrated switching elements  302 . Additionally, the output pads  303  on the integrated circuit element  104  are electrically connected to the input pads  402  of the die  103 . The output pads  303  can be connected to the input pads  402  using NCP, ACP, or solder bumps on the integrated circuit elements  104 . The output pads  303  on the integrated circuit element  104  can be on the bottom surface of the integrated circuit element  104  to provide better electrical connection with the input pads  402  on the die  103 . 
         [0038]    As noted, the integrated circuit element  104  includes integrated switching elements  302 . Each switching element acts as an on/off switch to selectively connect the drive electrode of one MEMS fluid ejector unit to a common drive signal source. The common drive signal voltage is carried on one or more integrated circuit input pads  301 , traces  403 , and corresponding traces on flex circuit  201 . The integrated switching elements  302  are connected to the input pads  301  of the integrated circuit element  104  and the output pads  303  of the integrated circuit element  104 . Thus, the integrated circuit element  104  includes connections that are made internally, such as between the input pads  301 , the integrated switching element  302 , and the output pad  303 . 
         [0039]    One integrated circuit element  104  can include multiple integrated switching elements  302 , such as  256  integrated switching elements. The number of integrated switching elements  302  can be the same as the number of actuators on the die  103  or a fraction thereof. Further, in some embodiments, the number of integrated switching elements  302  is equal to the number of input pads  301  on the integrated circuit  104 . In some embodiments, each integrated switching element  302  is in electrical communication with more than one output pad  303 . 
         [0040]    Returning to  FIG. 2 , the fluid ejector includes an interposer  105  to separate the fluid ejection elements  401  from the external environment. The interposer  105  can be made of a material with the same or similar coefficient of thermal expansion as the die  103 , such as silicon, in order to prevent stress between the two components. Although it is not required, the fluid ejector can further include an upper interposer (not shown). 
         [0041]    As shown in  FIG. 2 , the lower interposer  105  can include a main body  430  and flanges  432  that project down from the main body  430  to contact the die  103  in a region between the integrated circuit elements  104  and the actuators  401 , e.g., over the inlets  412  and outlets. In particular, there can be a flange  432  for each inlet  412  and outlet, with one or more passages (e.g., passage  212 ) extending through the flanges  432 . The flanges  432  hold the main body  430  over the die  103  to form a cavity  434 . This prevents the main body  430  from contacting and interfering with motion of the actuators  401 . In some implementations (shown in  FIG. 2 ), an aperture is formed through the membrane layer  180 , as well as the layers of the actuator  401  if present, and an adhesive bond bonds the flange  432  to the flow-path body  182 . Alternatively, the flange  432  can contact the membrane  180  or another layer that covers the substrate  122 . In addition, in some implementations, some flanges extend to contact the die  103  over the traces  407  between the rows of actuators  401 . 
         [0042]      FIG. 4  is a schematic view of a trace leading to an actuator.  FIG. 4  shows a trace  407  leading to an actuator  401  from integrated circuit  104 . In some implementations, the trace  407  can include an upper trace layer  408 , such as a conductive material (e.g., gold, copper), layered above a lower trace layer. The lower trace layer can be an extension of the top electrode  194  extending from the actuator  401 , e.g., the lower trace layer and the top electrode can be formed from the same layer  194  (shown in  FIG. 2 ). 
         [0043]    Along the path of the trace  407  to the actuator  401  is a fuse  502 . The fuse  502  can be located anywhere along the trace  407  between the actuator  401  and the integrated circuit  104 . In some implementations, the fuse  502  can be in close lateral proximity to the actuator  401 , e.g., adjacent or within  200  microns, e.g., within  100  microns, e.g., within  50  microns, of the actuator  401 . In some implementations, the fuse  502  is a constriction of the lower trace layer, e.g., a constriction of an extension of the top electrode  194  that is not layered over by the upper trace layer  408 . The fuse  502  can be exposed (i.e., not have any layer over it). Alternatively, the fuse  502  can be formed of conductive material different than that of the lower trace layer  194 . 
         [0044]    In some implementations (shown in  FIGS. 2 and 8A ), the upper trace layer  408  is deposited on both sides of the fuse  502 . Thus, there is a material, made of the same material as the upper trace layer  408 , on the end of the fuse  502  opposite to the portion of the trace  407  that leads to the integrated circuit  104 . In some implementations (shown in  FIG. 2 ), the upper trace layer  408  is deposited over a portion of the trace  407  between the fuse  502  and the actuator area  401 . In some implementations (not shown), the fuse  502  is adjacent to the actuator area  401  and the upper trace layer  408  extends over the top electrode  194  in the actuator area  401 . 
         [0045]    In some other implementations (shown in  FIG. 2 ) the upper trace layer  408  does not extend over the top electrode  194  in the actuator area  401 , in order to reduce the mass of material over the membrane  180  and thus reduce the drive voltage needed to actuate the membrane  180 . In such implementations, assuming that the fuse  502  is spaced from the actuator area  401 , the upper trace layer  408  can still be deposited over the portion of the trace  407  between the fuse  502  and the actuator area  401 . 
         [0046]    In some implementations (shown in  FIG. 8C ), the upper trace layer  408  is not deposited on the side of the fuse  502  opposite to the portion of the trace  407  leading to the integrated circuit  104 . For example, the fuse  502  can be immediately adjacent the actuator area  401  (that is not covered by the upper trace layer  408 ), or the fuse can be spaced from the actuator area  401  but the portion of the trace  407  between the fuse  502  and the actuator area  401  simply lacks the upper trace layer  408 . 
         [0047]    The fuse  502  can blow if an excessive amount of current flows through the fuse  502  (i.e., an overcurrent condition). For example, if a short circuit between the electrodes  194  and  190  occurs, leading to an excessive current flow through the top electrode  194  and the fuse  502  to the trace  407 , the fuse  502  can blow or open. The blowing of the fuse  502  disables the actuator  401  and can prevent the overcurrent condition from spreading and disabling other actuators. 
         [0048]      FIG. 8A  is a cross-section view of an example a trace with a fuse.  FIG. 8A  is a magnified view of an indicated portion of the cross-sectional view of  FIG. 2 .  FIG. 8B  is a schematic view of the example trace of  FIG. 8A . In  FIG. 8A , for convenience and ease of illustration, only the electrodes (conductive layers)  194  and  190 , piezoelectric layer  192 , and trace  407 , including upper trace layer portions  408 -A and  408 -B on opposite sides of the fuse  502 , are shown. The fuse  502  can be a constriction of a portion of the top electrode  194 . The portion of the upper trace layer  408  that is over the fuse  502  can be removed or omitted. In some implementations, the upper trace layer portions  408 -A and  408 -B extend on opposite sides of the fuse  502 . In some other implementations, as shown in  FIG. 8C , upper trace layer portion  408 -B is omitted; the upper trace layer  408  terminates at the fuse  502 . 
         [0049]    In some implementations, and as shown in  FIGS. 8A-8C , the fuse  502  (being part of top electrode  194 ) is laid over, e.g., deposited directly on, the piezoelectric layer  192 . Thus, the piezoelectric layer  192  can serve as a substrate for the fuse  502 . Piezoelectric material (e.g., lead zirconate titanate) has thermal conductivity properties that allows a fuse of reasonable size to open or blow under excessive currents (e.g., ˜100 mA) and to not heat excessively under operating currents of about 10 mA. Further, the piezoelectric material does not form carbon tracks when the fuse blows and heats the piezoelectric material. In some other implementations, the fuse  502  can be on top of a silicon or polymer layer or substrate, or on top of an insulator layer over a silicon, polymer or piezoelectric layer or substrate. For example, the fuse  502  can be a constricted portion of the top electrode  194  laid over a silicon or polymer material added to an etched die  103  or an etched bottom electrode  190  and piezoelectric layer  192 . 
         [0050]    In some implementations, the top electrode  194  is made of ti-tungsten and has a thickness T of about 1000 angstroms, which gives the top electrode  194  a sheet resistance of about  7  ohms/square. The fuse portion  502  of this top electrode  194  has a width W and a length L. In some implementations, the width W is about 5 microns and the length L is about 28 microns. In some other implementations, width W of the fuse  502  can be more or less than 5 microns (but still less than the width of the top electrode  194 , depending on the desired current at which the fuse  502  is to blow. More generally, the width W and length L can vary depending on the implementation based on one or more parameters, such as operating currents and maximum acceptable current limits, trace electrical conductivity, substrate thermal diffusivity, etc. The trace  407  can be of a thickness that is suited to provide relatively low resistivity. 
         [0051]    As described above, the integrated circuit  104  can include a transistor  302 . In some implementations, the transistor  302  is a field-effect transistor (FET). If an overcurrent condition occurs, the overcurrent can flow thorough the FET. The FET can be used to limit the current that can flow through the integrated circuit  104 , so that the fuse  502  can have sufficient time to blow. For example, the maximum current can be limited to the gate transconductance times the gate voltage. In some implementations, the transistor current limit is about 100 to 150 mA, which the transistor  302  can withstand for several seconds, giving the fuse  502  sufficient time to blow. 
         [0052]    In some implementations, the integrated circuit  104  includes a diode. The diode can be coupled to the source and drain of the transistor  302  and to the output pad  303 . Current can flow through the transistor  302  or the diode. In these implementations, the current can be limited by the resistance of the fuse  502 . For example, for a 10-volt short circuit, a 40 ohm fuse have a current limit of about 0.25 A. Too high of a fuse resistance, however, can reduce the velocity of fluids ejected by the fluid ejector  100 ; the capacitance in the fluid ejector and the fuse resistance can round off the driver waveform. 
         [0053]    Particular embodiments of the subject matter described in this specification have been described. Other embodiments are within the scope of the following claims.