Abstract:
A fluid injection device integrating a piezoelectric sensor, a fluid injection apparatus and a method for analyzing fluid content in a fluid injection device. The fluid injection device comprises a fluid injector and a piezoelectric sensor. The fluid injector comprises a plurality of fluid chambers formed in a substrate for receiving fluid. A structural layer is disposed on the substrate and the plurality of fluid chambers. At least one fluid actuator is disposed on the structural layer opposing each fluid chamber. A nozzle is adjacent to the at least one fluid actuator and connecting each fluid chamber through the structural layer. The piezoelectric sensor id disposed on the structural layer to analyze fluid content in each fluid chamber.

Description:
BACKGROUND  
       [0001]     The invention relates to fluid injection devices, and more particularly, to fluid injection devices integrating piezoelectric sensors and methods of analyzing fluid in fluid injection devices.  
         [0002]     Fluid injection devices have been applied in information technology industries for decades. As micro-system engineering technologies have progressed, fluid injection devices have typically been employed in inkjet printers, fuel injection systems, cell sorting systems, drug delivery systems, print lithography systems and micro-jet propulsion systems. Among inkjet printers presently known and used, fluid injection devices can be divided into two categories continuous mode and drop-on-demand mode, depending on the fluid injection device.  
         [0003]     According to the driving mechanism, conventional fluid injection devices can further be divided into thermal bubble driven and piezoelectric diaphragm driven fluid injection devices. Of the two, injection by thermally driven bubbles has been most successful due to its reliability, simplicity and relatively low cost. No matter which kind of injection device is selected, in situ analysis of ink in a fluid injection device is an important issue in replacing an ink cartridge. If the amount of ink in the fluid injection device is inadequate, not only does print quality deteriorate, but, the fluid injection device itself, such as a heater, can also be damaged due to a dry firing effect.  
         [0004]     U.S. Pat. No. 5,699,090, the entirety of which is hereby incorporated by reference, discloses a thermal bubble driven ink jet printhead. By measuring the average in resistance dependent on temperature change, the amount of ink in an inkjet printhead can be estimated.  
         [0005]      FIG. 1  is a block diagram of methods for optimizing printing parameters for a conventional inkjet printhead. After a controller  111  receives and processes printing data, operating signals are transmitted to a printhead driver circuit  113 . A voltage control power supply  115  provides a control voltage V S  to the printhead driver circuit  113 . The magnitude of the control voltage V S  is controlled by the voltage control power supply  115 . The printhead driver circuit  113  controlled by the controller  111  provides a driving voltage pulse V P  to heaters  117  of the thermally driven inkjet printhead  119 , thereby triggering inkjet injection. Subsequently, a temperature sensing resistor  123  on the inkjet printhead  119  can be provided as reference for each heater  117  of the thermally driven inkjet printhead  119 . An analog signal is output to analog/digital (A/D) converter  125  according to the comparison between temperature sensing resistor  123  and each heater  117 , thereby optimizing printing parameters for the thermal bubble driven inkjet printhead.  
         [0006]      FIG. 2  sets forth a representative graph of normalized printhead temperature plotted against time. The graph of  FIG. 2  indicates different phases of operation of the heater resistors of a printhead. The control circuit for the inkjet printhead can depend on the graph of  FIG. 2  to optimize printing parameters. The graph of  FIG. 2 , however, can be affected by materials of the temperature sensing resistor, circuit layout, and positions of the temperature sensing resistor. Current passing through the temperature sensing resistor may cause increased temperature, affecting accuracy of the graph of  FIG. 2 . Measurement of ink content in the inkjet printhead using the temperature sensing resistor  123  is intrinsically limited and not applicable to non-thermally driven injection devices.  
       SUMMARY  
       [0007]     A fluid injection device integrating a piezoelectric sensor is provided. The piezoelectric sensor can promptly measure resonating frequencies of a structural layer at which fluid content is insufficient. By employing a fluid injection device integrating a piezoelectric sensor, a cartridge can be immediately replaced as soon as the amount of fluid in the chamber is insufficient.  
         [0008]     The invention provides a fluid injection device integrating a piezoelectric sensor comprising a fluid injector and a piezoelectric sensor. The fluid injector comprises a plurality of fluid chambers formed in a substrate for receiving fluid. A structural layer is disposed on the substrate and the plurality of fluid chambers. At least one fluid actuator is disposed on the structural layer opposing each fluid chamber. A nozzle is adjacent to the at least one fluid actuator and connects each fluid chamber through the structural layer. The piezoelectric sensor is disposed on the structural layer to analyze fluid content in each fluid chamber.  
         [0009]     The invention also provides a fluid injection apparatus comprising a cartridge, a fluid injector chip with a plurality of fluid injectors disposed on the cartridge, and at least one piezoelectric sensor. Each fluid injector comprises a plurality of fluid chambers formed in a substrate connecting the cartridge. A structural layer is disposed on the substrate and the plurality of fluid chambers. At least one fluid actuator is disposed on the structural layer opposing each fluid chamber. A nozzle adjacent to the at least one fluid actuator connects each fluid chamber through the structural layer. The piezoelectric sensor is disposed on the structural layer to analyze fluid content in each fluid chamber.  
         [0010]     The invention further provides a method for analyzing fluid content in a fluid injection device. The fluid injection device has a fluid chamber with a structural layer thereon and at least one actuator disposed on the structural layer. The method comprises measuring a resonant frequency of the structural layer with a piezoelectric sensor, thereby outputting a signal, and receiving the signal and optimizing printing parameters accordingly. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0011]     The invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:  
         [0012]      FIG. 1  shows a block diagram of methods for optimizing printing parameters for a conventional inkjet printhead;  
         [0013]      FIG. 2  shows a representative graph of normalized printhead temperature plotted against time;  
         [0014]      FIG. 3A  shows a plan view of an embodiment of a piezoelectric sensor disposed on a fluid injection device;  
         [0015]      FIG. 3B  shows a cross-section of an embodiment of a piezoelectric sensor disposed on a fluid injection device;  
         [0016]      FIG. 3C  shows a cross-section of an embodiment of a piezoelectric sensor disposed on a fluid injection device with fluid filled in a chamber;  
         [0017]      FIG. 4  shows a perspective view of an embodiment of a fluid injection device;  
         [0018]      FIG. 5  shows a plan view of an embodiment of the fluid injector chip of  FIG. 4 ;  
         [0019]      FIGS. 6A-6B  show cross-sections taken along A-A of  FIG. 5  showing a state of fluid filled in the fluid chamber;  
         [0020]      FIGS. 7A-7B  show cross-sections taken along B-B of  FIG. 5  showing a state of fluid filled in the fluid chamber with a piezoelectric sensor thereon;  
         [0021]      FIG. 8A  show a graphical curve showing relationship between return loss S 11  and the resonant frequency of the piezoelectric sensor in an empty fluid chamber;  
         [0022]      FIG. 8B  shows a graphical curve showing relationship between return loss S 11  and the resonant frequency of the piezoelectric sensor in a filled fluid chamber;  
         [0023]      FIG. 9  shows a plan view of another embodiment of the fluid injector chip;  
         [0024]      FIG. 10  shows a plan view of another embodiment of the fluid injector chip;  
         [0025]      FIG. 11  shows a cross-section taken along C-C of  FIG. 10  showing a state of fluid filled in the fluid chamber; and  
         [0026]      FIG. 12  shows a block diagram of an embodiment of a method for optimizing printing parameters of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0027]      FIG. 3A  is a plan view of an embodiment of a piezoelectric sensor disposed on a fluid injection device.  FIG. 3B  is a cross-section of an embodiment of a piezoelectric sensor disposed on a fluid injection device.  FIG. 3C  is a cross-section of an embodiment of a piezoelectric sensor disposed on a fluid injection device with fluid filled in a chamber.  
         [0028]     Referring to  FIGS. 3A and 3B , a monolithic piezoelectric sensing unit  10 S comprises a substrate  1  such as a single crystalline silicon substrate. A fluid chamber  5  is formed in the substrate  1 . A structural layer  3  is disposed in the substrate  1  and the fluid chamber  5 . The structural layer  3  is preferably a low stress layer, such as low stress Si 3 N 4 .  
         [0029]     A first electrode  22 , such as Au, Al, Pt, alloys, or a combination thereof, is formed on the structural layer  3 . A piezoelectric layer  4  is formed on the first electrode  22 . The piezoelectric layer  4  comprises ZnO, AlN, LiNbO 3 , LiTaO 3 , PbTiO 3 , (Ba x Sr 1-x )TiO 3 , Pb(Zr y T 1-y )O 3 , or a combination thereof. A second electrode  21 , such as Au, Al, Pt, alloys, or a combination thereof, is formed on the piezoelectric layer  4 .  
         [0030]     The first electrode  22 , the piezoelectric layer  4 , and the second electrode  21  are composed of a piezoelectric sensor  2 . A via  23  in the piezoelectric layer  4  is created to measure piezoelectric signals. Since fluid content in the fluid chamber  5  is directly dependent on the elastic wave velocity in the piezoelectric layer  4 , measuring the elastic wave velocity variation in the piezoelectric layer  4  can determine whether fluid is filled in the fluid chamber. An embodiment of the piezoelectric sensor is disclosed in detail in the following.  
         [0031]      FIG. 4  is a perspective view of an embodiment of a fluid injection device. A fluid injection device  30  comprises a fluid injector chip  7  and ink cartridge  8 .  
         [0032]      FIG. 5  is a plan view of an embodiment of the fluid injector chip of  FIG. 4 . The fluid injector chip  7  comprises a plurality of injectors  10 A. Fluid is provided from ink cartridge  8  via a filter, a stand pipe into a manifold  11  of the fluid injector chip  7 . The fluid is subsequently filled into each fluid chamber  5  of injectors  10 A for fluid injection. Each fluid chamber  5  is a different distance from the manifold  11  of the fluid injector chip  7 .  
         [0033]     Fluid injector chip  7  is a monolithic structure fabricated by a micro-electro-mechanical system (MEMS) process. For example, the fluid injector chip  7  is formed by lithographic and etching processes in a single crystalline silicon wafer. Piezoelectric sensor  2  is disposed on the fluid chamber farthest from the manifold  11 .  
         [0034]      FIGS. 6A-6B  are cross-sections taken along A-A of  FIG. 5  showing a state of fluid in the fluid chamber. Referring to  FIG. 6A , when the amount of fluid in the ink cartridge is sufficient, and the cartridge does not require refilling. Uniformity and trajectory of triggered droplets  12  are consistent. Referring to  FIG. 6B , when the amount of fluid in the ink cartridge is insufficient, the chamber requires refilling. Uniformity and trajectory of triggered droplets  12 ′ are inconsistent. Moreover, the fluid injector cannot be triggered, resulting in a dry-firing effect.  
         [0035]      FIGS. 7A-7B  are cross-sections taken along B-B of  FIG. 5  showing a state of fluid filled in the fluid chamber with a piezoelectric sensor thereon. A piezoelectric sensor  2  comprising a lower electrode  22 , a piezoelectric layer  4  and an upper electrode  21  is provided to measure the amount of fluid content in the fluid chamber.  
         [0036]     The fluid injector chip  7  is fabricated by providing a single crystalline silicon substrate  1 . A sacrificial layer (not shown), a structural layer  3 , heaters  15  are sequentially formed on the silicon substrate  1 . The silicon substrate  1  is then etched to create a manifold  11 . The sacrificial layer (not shown) is removed to create a fluid chamber  5 . A nozzle  16  is created by etching through the structural layer  3 . If the heaters  15  are replaced by a piezoelectric sensor  2 , a monolithic piezoelectric sensing unit  10 S is provided.  
         [0037]     The piezoelectric sensor  2  is fabricated by forming a lower electrode  22  on the structural layer  3 . A piezoelectric layer  4  is deposited on the lower electrode  22 . An upper electrode  21  is formed on the piezoelectric layer  4 . An opening  13  is created in the piezoelectric layer  4  for measuring electric wave velocity in the piezoelectric layer  4 .  
         [0038]     Referring to  FIG. 7A , a piezoelectric sensor  2  is disposed at the fluid chamber farthest from the center line of the manifold  11 , i.e., D h &lt;D s , where D h  is the distance from the nozzle  16  of the fluid chamber farthest from the center line of the manifold  11 , and D s  is the distance from the piezoelectric sensor  2  to the center line of the manifold  11 .  
         [0039]     Referring to  FIG. 7B , since the piezoelectric sensor  2  is disposed at the fluid chamber  5  farthest from the manifold  11 , the fluid chamber  5  with an inadequate amount of ink under the piezoelectric sensor  2  will be refilled prior to other fluid chambers of the fluid injector chip. The piezoelectric sensor can serve as a thin film bulk acoustic resonator (FBAR), the resonant frequency of which is dependent on the velocity and wavelength of the acoustic wave:  
             f   =       v   γ     =     v     2   ⁢   d                 Eq   .           ⁢   1             
 
         [0040]     where f is a resonant frequency of a piezoelectric sensor on an empty fluid chamber, v is longitudinal wave velocity of a piezoelectric layer on an empty fluid chamber, λ is the wavelength of the acoustic wave, and d is the thickness of the piezoelectric layer.  
         [0041]      FIG. 8A  is a graphical curve showing the relationship between the return loss S 11  and resonant frequency of the piezoelectric sensor on an empty fluid chamber. Indication  41  is the return loss S 11  when the fluid chamber is empty.  
         [0042]     Since the oscillation of the piezoelectric layer is caused by longitudinal wave resonation, when the fluid chamber is refilled, mass loading on the piezoelectric layer may cause a damping effect. The longitudinal wave velocity is changed shifting the resonant frequency of the piezoelectric resonator and reducing the quality factor (Q factor). The shifted resonant frequency f′ is represented as follows:  
               f   ′     =         v   ′     γ     =       v   ′       2   ⁢   d                 Eq   .           ⁢   2             
 
         [0043]     where f′ is a resonant frequency of a piezoelectric sensor on a filled fluid chamber, v′ is longitudinal wave velocity of a piezoelectric layer on a filled fluid chamber, λ is the wavelength of the acoustic wave, and d is the thickness of the piezoelectric layer.  
         [0044]      FIG. 8B  is a graphical curve showing the relationship between the return loss S 11  and resonant frequency of the piezoelectric sensor on a filled fluid chamber. Indication  51  is the return loss S 11  when the fluid chamber is empty. Therefore, whether a fluid chamber is filled can be ensured by measuring longitudinal wave velocity, resonating frequency, and quality factor of the piezoelectric sensor accordingly.  
         [0045]      FIG. 9  is a plan view of another embodiment of the fluid injector chip. At least one piezoelectric sensor, such as three piezoelectric sensors  61 ,  62 , and  63 , are separately disposed overlying fluid chambers  91 ,  92 , and  93  with various distances from the center line of the manifold  11 . Fluid chamber  91  is the nearest to the manifold  11 , while fluid chamber  92  is the farthest from the manifold  11 . Fluid chamber  93  is a dummy chamber which is farther from the manifold  11  than the fluid chamber. When frequency variation is detected by piezoelectric sensor  63 , the fluid in the cartridge is insufficient to refill each fluid chamber. Moreover, when frequency variation is detected by piezoelectric sensors  62  and  63 , some of the fluid chambers have not been adequately refilled. Print quality is thus degraded and cartridge replacement is suggested. Moreover, when frequency variation is detected by piezoelectric sensors  61 ,  62  and  63 , none of the fluid chambers have been adequately refilled and the cartridge must be promptly replaced. Signals measured by piezoelectric sensors  61 ,  62  and  63  are processed by feedback loop circuits, for example analog/digital converters, and transmitted to a controller. Nevertheless, the measuring sequences can be inverted from piezoelectric sensor  61  to piezoelectric sensor  63  to detect whether each fluid chamber is has been completely refilled.  
         [0046]      FIG. 10  is a plan view of another embodiment of the fluid injector chip.  FIG. 11  is a cross-section taken along C-C of  FIG. 10  showing a state of fluid filled in the fluid chamber. Referring to  FIG. 10 , a dummy piezoelectric sensor  10 S′ comprises a chamber  94  disconnected from the manifold  15 . The distance from the dummy piezoelectric sensor  10 S′ to the manifold  11  equals or exceeds the distance from the fluid injector  93  farthest from the manifold  11 . A piezoelectric sensor  74  is formed on the chamber  94 . Note that since the chamber  94  is disconnected from the manifold  11 , fluid does not fill the chamber  94  during operation. Therefore, the results measured by piezoelectric sensor  74  serve as reference for other piezoelectric sensors.  
         [0047]     Accordingly, before the fluid injector chip is filled, each chamber is empty and the resonant frequencies measured by piezoelectric sensors  61 ,  62 ,  63 , and  64  are the same. When the fluid injector chip is filled, the amount of fluid in each chamber can be estimated by comparing resonating frequencies measured by each piezoelectric sensor  61 ,  62 ,  63 , and  64 .  
         [0048]     Alternatively, the invention further provides a method for analyzing the amount of fluid in a fluid chamber of the fluid injector chip.  FIG. 12  is a block diagram of an embodiment of a method for optimizing printing parameters of the invention. After a controller  220  receives and processes printing data, operating signals are transmitted to a printhead driver circuit  230 . A voltage control power supply  240  provides a control voltage V S  to the printhead driver circuit  230 . The magnitude of the control voltage V S  is controlled by the voltage control power supply  240 . The printhead driver circuit  230  controlled by the controller  220  provides a driving voltage pulse V P  to actuators  214  of the fluid injection device  210 , thereby triggering inkjet injection.  
         [0049]     Subsequently, a piezoelectric sensor  216  is provided overlying some fluid chambers  212  of the fluid injection device  210  to measure resonance of the structural layer. An analog signal is transmitted to an analog/digital (A/D) converter  250  to transform a digital output to the controller  220 , thereby optimizing printing parameters for the fluid injection device.  
         [0050]     The fluid injection device integrating piezoelectric sensors overlying fluid chambers of the invention is advantageous in that the amount of fluid in fluid chambers are measured in situ to prevent dry firing effect. Since the piezoelectric sensor measure longitudinal wave on the structural layer, both thermal bubble driven and piezoelectric diaphragm driven printing are applicable to the invention.  
         [0051]     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.