Patent Publication Number: US-8523328-B2

Title: Flow-through liquid ejection using compliant membrane transducer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly-assigned, U.S. patent application Ser. No. 13/089,541, entitled “MEMS COMPOSITE TRANSDUCER INCLUDING COMPLIANT MEMBRANE”, Ser. No. 13/089,532, now U.S. Pat. No. 8,409,900, entitled “FABRICATING MEMS COMPOSITE TRANSDUCER INCLUDING COMPLIANT MEMBRANE”, Ser. No. 13/089,563, entitled “FLOW-THROUGH EJECTION SYSTEM INCLUDING COMPLIANT MEMBRANE TRANSDUCER”, Ser. No. 13/089,610, entitled “FLOW-THROUGH EJECTION SYSTEM INCLUDING COMPLIANT MEMBRANE TRANSDUCER”, Ser. No. 13/089,632, entitled “FLOW-THROUGH LIQUID EJECTION USING COMPLIANT MEMBRANE TRANSDUCER”, all filed concurrently herewith. 
     FIELD OF THE INVENTION 
     This invention relates generally to the field of digitally controlled fluid dispensing systems and, in particular, to flow through liquid drop dispensers that eject on demand a quantity of liquid from a continuous flow of liquid. 
     BACKGROUND OF THE INVENTION 
     Ink jet 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 transfer and fixing. Ink jet printing mechanisms can be categorized by technology as either drop on demand ink jet (DOD) or continuous ink jet (CIJ). 
     The first technology, “drop-on-demand” (DOD) ink jet printing, provides ink drops that impact upon a recording surface using a pressurization actuator, for example, a thermal, piezoelectric, or electrostatic actuator. One commonly practiced drop-on-demand technology uses thermal actuation to eject ink drops from a nozzle. A heater, located at or near the nozzle, heats the ink sufficiently to boil, forming a vapor bubble that creates enough internal pressure to eject an ink drop. This form of inkjet is commonly termed “thermal ink jet (TIJ).” 
     The second technology commonly referred to as “continuous” ink jet (CIJ) printing, uses a pressurized ink source to produce a continuous liquid jet stream of ink by forcing ink, under pressure, through a nozzle. The stream of ink is perturbed using a drop forming mechanism such that the liquid jet breaks up into drops of ink in a predictable manner. One continuous printing technology uses thermal stimulation of the liquid jet with a heater to form drops that eventually become print drops and non-print drops. Printing occurs by selectively deflecting one of the print drops and the non-print drops and catching the non-print drops. Various approaches for selectively deflecting drops have been developed including electrostatic deflection, air deflection, and thermal deflection. 
     Printing systems that combine aspects of drop-on-demand printing and continuous printing are also known. These systems, often referred to as flow through liquid drop dispensers, provide increased drop ejection frequency when compared to drop-on-demand printing systems without the complexity of continuous printing systems. 
     Micro-Electro-Mechanical Systems (or MEMS) devices are becoming increasingly prevalent as low-cost, compact devices having a wide range of applications. As such, MEMS devices, for example, MEMS transducers, have been incorporated into both DOD and CIJ printing mechanisms. 
     MEMS transducers include both actuators and sensors that convert an electrical signal into a motion or they convert a motion into an electrical signal, respectively. Typically, MEMS transducers are made using standard thin film and semiconductor processing methods. As new designs, methods and materials are developed, the range of usages and capabilities of MEMS devices is be extended. 
     MEMS transducers are typically characterized as being anchored to a substrate and extending over a cavity in the substrate. Three general types of such transducers include a) a cantilevered beam having a first end anchored and a second end cantilevered over the cavity; b) a doubly anchored beam having both ends anchored to the substrate on opposite sides of the cavity; and c) a clamped sheet that is anchored around the periphery of the cavity. Type c) is more commonly called a clamped membrane, but the word membrane will be used in a different sense herein, so the term clamped sheet is used to avoid confusion. 
     Sensors and actuators can be used to sense or provide a displacement or a vibration. For example, the amount of deflection  8  of the end of a cantilever in response to a stress a is given by Stoney&#39;s formula
 
δ=3σ(1−ν) L   2   /Et   2   (1),
 
where ν is Poisson&#39;s ratio, E is Young&#39;s modulus, L is the beam length, and t is the thickness of the cantilevered beam. In order to increase the amount of deflection for a cantilevered beam, one can use a longer beam length, a smaller thickness, a higher stress, a lower Poisson&#39;s ratio, or a lower Young&#39;s modulus. The resonant frequency of vibration is given by
 
ω 0 =( k/m ) 1/2 ,  (2),
 
where k is the spring constant and m is the mass. For a cantilevered beam, the spring constant k is given by
 
 k=Ewt   3 /4 L   3   (3),
 
where w is the cantilever width and the other parameters are defined above. For a lower resonant frequency one can use a smaller Young&#39;s modulus, a smaller width, a smaller thickness, a longer length, or a larger mass. A doubly anchored beam typically has a lower amount of deflection and a higher resonant frequency than a cantilevered beam having comparable geometry and materials. A clamped sheet typically has an even lower amount of deflection and an even higher resonant frequency.
 
     Thermal stimulation of liquids, for example, inks, ejected from DOD printing mechanisms using a heater or formed by CIJ printing mechanisms using a heater is not consistent when one liquid is compared to another liquid. Some liquid properties, for example, stability and surface tension, react differently relative to temperature. As such, liquids are affected differently by thermal stimulation often resulting in inconsistent drop formation which reduces the numbers and types of liquid formulations used with DOD printing mechanisms or CIJ printing mechanisms. 
     Accordingly, there is an ongoing need to provide liquid ejection mechanisms and ejection methods that improve the reliability and consistency of drop formation on a liquid by liquid basis while maintaining individual nozzle control of the mechanism in order to increase the numbers and types of liquid formulations used with these mechanisms. There is also an ongoing effort to increase the reliability and performance of flow through liquid drop dispensers. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the invention, a method of ejecting liquid includes providing a liquid dispenser including a substrate and a diverter member. A first portion of the substrate defines a liquid dispensing channel including an outlet opening and a second portion of the substrate defines an outer boundary of a cavity. Other portions of the substrate define a liquid supply channel and a liquid return channel. The diverter member includes a MEMS transducing member. A first portion of the MEMS transducing member is anchored to the substrate. A second portion of the MEMS transducing member extends over at least a portion of the cavity and is free to move relative to the cavity. A compliant membrane is positioned in contact with the MEMS transducing member. A first portion of the compliant membrane covers the MEMS transducing member. A second portion of the compliant membrane is anchored to the substrate such that the compliant membrane forms a portion of a wall of the liquid dispensing channel. The wall is positioned opposite the outlet opening. A continuous flow of liquid is provided from a liquid supply through the liquid supply channel through the liquid dispensing channel through the liquid return channel and back to the liquid supply. The diverter member is selectively actuated to divert a portion of the liquid flowing through the liquid dispensing channel through outlet opening of the liquid dispensing channel when drop ejection is desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which: 
         FIG. 1A  is a top view and  FIG. 1B  is a cross-sectional view of an embodiment of a MEMS composite transducer including a cantilevered beam and a compliant membrane over a cavity; 
         FIG. 2  is a cross-sectional view similar to  FIG. 1B , where the cantilevered beam is deflected; 
         FIG. 3  is a top view of an embodiment similar to  FIG. 1A , but with a plurality of cantilevered beams over the cavity; 
         FIG. 4  is a top view of an embodiment similar to  FIG. 3 , but where the widths of the cantilevered beams are larger at their anchored ends than at their free ends; 
         FIG. 5  is a top view of an embodiment similar to  FIG. 4 , but in addition including a second group of cantilevered beams having a different shape; 
         FIG. 6  is a top view of another embodiment including two different groups of cantilevered beams of different shapes; 
         FIG. 7  is a top view of an embodiment where the MEMS composite transducer includes a doubly anchored beam and a compliant membrane; 
         FIG. 8A  is a cross-sectional view of the MEMS composite transducer of  FIG. 7  in its deflected state; 
         FIG. 8B  is a cross-sectional view of the MEMS composite transducer of  FIG. 7  in its deflected state; 
         FIG. 9  is a top view of an embodiment where the MEMS composite transducer includes two intersecting doubly anchored beams and a compliant membrane; 
         FIG. 10  is a top view of an embodiment where the MEMS composite transducer includes a clamped sheet and a compliant membrane; 
         FIG. 11A  is a cross-sectional view of the MEMS composite transducer of  FIG. 10  in its deflected state; 
         FIG. 11B  is a cross-sectional view of the MEMS composite transducer of  FIG. 10  in its deflected state; 
         FIG. 12A  is a cross-sectional view of an embodiment similar to that of  FIG. 1A , but also including an additional through hole in the substrate; 
         FIG. 12B  is a cross-sectional view of a fluid ejector that incorporates the structure shown in  FIG. 12A ; 
         FIG. 13  is a top view of an embodiment similar to that of  FIG. 10 , but where the compliant membrane also includes a hole; 
         FIG. 14  is a cross-sectional view of the embodiment shown in  FIG. 13 ; 
         FIG. 15  is a cross-sectional view showing additional structural detail of an embodiment of a MEMS composite transducer including a cantilevered beam; 
         FIG. 16A  is a cross-sectional view of an embodiment similar to that of  FIG. 6 , but also including an attached mass that extends into the cavity; 
         FIG. 16B  is a cross-sectional view of an embodiment similar to that of  FIG. 16A , but Where the attached mass is on the opposite side of the compliant membrane; 
         FIGS. 17A to 17E  illustrate an overview of a method of fabrication; 
         FIGS. 18A and 18B  provide addition details of layers that can be part of the MEMS composite transducer; 
         FIGS. 19A and 19B  are schematic cross sectional views of example embodiments of a liquid dispenser made in accordance with the present invention; 
         FIGS. 20A and 20B  are a schematic plan view and a schematic cross sectional view, respectively, of another example embodiment of a liquid dispenser made in accordance with the present invention; 
         FIGS. 20C and 20D  are schematic cross sectional views of the liquid dispenser shown in  FIG. 20A  showing additional example embodiments of a liquid dispenser made in accordance with the present invention; 
         FIGS. 21A and 21B  are a schematic cross sectional view and a schematic plan view, respectively, of another example embodiment of a liquid dispenser made in accordance with the present invention; 
         FIGS. 22A and 22B  are a schematic cross sectional view and a schematic plan view, respectively, of another example embodiment of a liquid dispenser made in accordance with the present invention; 
         FIGS. 23A and 23B  are partial schematic cross-sectional views of a portion of the diverter member shown in  FIGS. 19A and 19B ; 
         FIG. 24A  is a schematic cross-sectional view of another example embodiment of a liquid dispenser made in accordance with the present invention; 
         FIG. 24B  is a schematic cross-sectional view of another example embodiment of a liquid dispenser made in accordance with the present invention; 
         FIG. 24C  is a schematic cross-sectional view of another example embodiment of a liquid dispenser made in accordance with the present invention; 
         FIG. 25A  is a schematic cross-sectional view of another example embodiment of a liquid dispenser made in accordance with the present invention; 
         FIG. 25B  is a schematic cross-sectional view of another example embodiment of a liquid dispenser made in accordance with the present invention; 
         FIG. 25C  is a schematic cross-sectional view of another example embodiment of a liquid dispenser made in accordance with the present invention; 
         FIG. 25D  is a schematic cross-sectional view of showing actuation of the diverter member of the liquid dispenser shown in  FIG. 25C ; 
         FIG. 25E  is a schematic plan view of the diverter member of the liquid dispenser shown in  FIG. 25C ; 
         FIGS. 26A and 26B  are schematic plan views of a diverter member of another example embodiment of a liquid dispenser made in accordance with the present invention; and 
         FIG. 27  shows a block diagram describing an example embodiment of a method of ejecting liquid using the liquid dispenser described herein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. In the following description and drawings, identical reference numerals have been used, where possible, to designate identical elements. 
     The example embodiments of the present invention are illustrated schematically and not to scale for the sake of clarity. One of the ordinary skills in the art will be able to readily determine the specific size and interconnections of the elements of the example embodiments of the present invention. 
     As described herein, the example embodiments of the present invention provide liquid ejection components typically used in inkjet printing systems. However, many other applications are emerging which use inkjet printheads to emit liquids (other than inks) that need to be finely metered and deposited with high spatial precision. As such, as described herein, the terms “liquid” and “ink” refer to any material that can be ejected by the liquid ejection system or the liquid ejection system components described below. 
     Embodiments of the present invention include a variety of types of MEMS transducers including a MEMS transducing member and a compliant membrane positioned in contact with the MEMS transducing member. It is to be noted that in some definitions of MEMS structures, MEMS components are specified to be between 1 micron and 100 microns in size. Although such dimensions characterize a number of embodiments, it is contemplated that some embodiments will include dimensions outside that range. 
       FIG. 1A  shows a top view and  FIG. 1B  shows a cross-sectional view (along A-A′) of a first embodiment of a MEMS composite transducer  100 , where the MEMS transducing member is a cantilevered beam  120  that is anchored at a first end  121  to a first surface  111  of a substrate  110 . Portions  113  of the substrate  110  define an outer boundary  114  of a cavity  115 . In the example of  FIGS. 1A and 1B , the cavity  115  is substantially cylindrical and is a through hole that extends from a first surface  111  of substrate  110  (to which a portion of the MEMS transducing member is anchored) to a second surface  112  that is opposite first surface  111 . Other shapes of cavity  115  are contemplated for other embodiments in which the cavity  115  does not extend all the way to the second surface  112 . Still other embodiments are contemplated where the cavity shape is not cylindrical with circular symmetry. A portion of cantilevered beam  120  extends over a portion of cavity  115  and terminates at second end  122 . The length L of the cantilevered beam extends from the anchored end  121  to the free end  122 . Cantilevered beam  120  has a width w 1  at first end  121  and a width w 2  at second end  122 . In the example of  FIGS. 1A and 1B , w 1 =w 2 , but in other embodiments described below that is not the case. 
     MEMS transducers having an anchored beam cantilevering over a cavity are well known. A feature that distinguishes the MEMS composite transducer  100  from conventional devices is a compliant membrane  130  that is positioned in contact with the cantilevered beam  120  (one example of a MEMS transducing member). Compliant membrane includes a first portion  131  that covers the MEMS transducing member, a second portion  132  that is anchored to first surface  111  of substrate  110 , and a third portion  133  that overhangs cavity  115  while not contacting the MEMS transducing member. In a fourth region  134 , compliant membrane  130  is removed such that it does not cover a portion of the MEMS transducing member near the first end  121  of cantilevered beam  120 , so that electrical contact can be made as is discussed in further detail below. In the example shown in  FIG. 1B , second portion  132  of compliant membrane  130  that is anchored to substrate  110  is anchored around the outer boundary  114  of cavity  115 . In other embodiments, it is contemplated that the second portion  132  would not extend entirely around outer boundary  114 . 
     The portion (including end  122 ) of the cantilevered beam  120  that extends over at least a portion of cavity  115  is free to move relative to cavity  115 . A common type of motion for a cantilevered beam is shown in  FIG. 2 , which is similar to the view of  FIG. 1B  at higher magnification, but with the cantilevered portion of cantilevered beam  120  deflected upward away by a deflection δ=Δz from the original undeflected position shown in  FIG. 1B  (the z direction being perpendicular to the x-y plane of the surface  111  of substrate  110 ). Such a bending motion is provided for example in an actuating mode by a MEMS transducing material (such as a piezoelectric material, or a shape memory alloy, or a thermal bimorph material) that expands or contracts relative to a reference material layer to which it is affixed when an electrical signal is applied, as is discussed in further detail below. When the upward deflection out of the cavity is released (by stopping the electrical signal), the MEMS transducer typically moves from being out of the cavity to into the cavity before it relaxes to its undeflected position. Some types of MEMS transducers have the capability of being driven both into and out of the cavity, and are also freely movable into and out of the cavity. 
     The compliant membrane  130  is deflected by the MEMS transducer member such as cantilevered beam  120 , thereby providing a greater volumetric displacement than is provided by deflecting only cantilevered beam (of conventional devices) that is not in contact with a compliant membrane  130 . Desirable properties of compliant membrane  130  are that it have a Young&#39;s modulus that is much less than the Young&#39;s modulus of typical MEMS transducing materials, a relatively large elongation before breakage, excellent chemical resistance (for compatibility with MEMS manufacturing processes), high electrical resistivity, and good adhesion to the transducer and substrate materials. Some polymers, including some epoxies, are well adapted to be used as a compliant membrane  130 . Examples include TMMR liquid resist or TMMF dry film, both being products of Tokyo Ohka Kogyo Co. The Young&#39;s modulus of cured TMMR or TMMF is about 2 GPa, as compared to approximately 70 GPa for a silicon oxide, around 100 GPa for a PZT piezoelectric, around 160 GPa for a platinum metal electrode, and around 300 GPa for silicon nitride. Thus the Young&#39;s modulus of the typical MEMS transducing member is at least a factor of 10 greater, and more typically more than a factor of 30 greater than that of the compliant membrane  130 . A benefit of a low Young&#39;s modulus of the compliant membrane is that the design can allow for it to have negligible effect on the amount of deflection for the portion  131  where it covers the MEMS transducing member, but is readily deflected in the portion  133  of compliant membrane  130  that is nearby the MEMS transducing member but not directly contacted by the MEMS transducing member. Furthermore, because the Young&#39;s modulus of the compliant membrane  130  is much less than that of the typical MEMS transducing member, it has little effect on the resonant frequency of the MEMS composite transducer  100  if the MEMS transducing member (e.g. cantilevered beam  120 ) and the compliant membrane  130  have comparable size. However, if the MEMS transducing member is much smaller than the compliant membrane  130 , the resonant frequency of the MEMS composite transducer can be significantly lowered. In addition, the elongation before breaking of cured TMMR or TMMF is around 5%, so that it is capable of large deflection without damage. 
     There are many embodiments within the family of MEMS composite transducers  100  having one or more cantilevered beams  120  as the MEMS transducing member covered by the compliant membrane  130 . The different embodiments within this family have different amounts of displacement or different resonant frequencies or different amounts of coupling between multiple cantilevered beams  120  extending over a portion of cavity  115 , and thereby are well suited to a variety of applications. 
       FIG. 3  shows a top view of a MEMS composite transducer  100  having four cantilevered beams  120  as the MEMS transducing members, each cantilevered beam  120  including a first end that is anchored to substrate  110 , and a second end  122  that is cantilevered over cavity  115 . For simplicity, some details such as the portions  134  where the compliant membrane is removed are not shown in  FIG. 3 . In this example, the widths w 1  (see  FIG. 1A ) of the first ends  121  of the cantilevered beams  120  are all substantially equal to each other, and the widths w 2  (see  FIG. 1A ) of the second ends  122  of the cantilevered beams  120  are all substantially equal to each other. In addition, w 1 =w 2  in the example of  FIG. 3 . Compliant membrane  130  includes first portions  131  that cover the cantilevered beams  120  (as seen more clearly in  FIG. 1B ), a second portion  132  that is anchored to substrate  110 , and a third portion  133  that overhangs cavity  115  while not contacting the cantilevered beams  120 . The compliant member  130  in this example provides some coupling between the different cantilevered beams  120 . In addition, for embodiments where the cantilevered beams are actuators, the effect of actuating all four cantilevered beams  120  results in an increased volumetric displacement and a more symmetric displacement of the compliant membrane  130  than the single cantilevered beam  120  shown in  FIGS. 1A ,  1 B and  2 . 
       FIG. 4  shows an embodiment similar to  FIG. 3 , but for each of the four cantilevered beams  120 , the width w 1  at the anchored end  121  is greater than the width w 2  at the cantilevered end  122 . For embodiments where the cantilevered beams  120  are actuators, the effect of actuating the cantilevered beams of  FIG. 4  provides a greater volumetric displacement of compliant membrane  130 , because a greater portion of the compliant membrane is directly contacted and supported by cantilevered beams  120 . As a result the third portion  133  of compliant membrane  130  that overhangs cavity  115  while not contacting the cantilevered beams  120  is smaller in  FIG. 4  than in  FIG. 3 . This reduces the amount of sag in third portion  133  of compliant membrane  130  between cantilevered beams  120  as the cantilevered beams  120  are deflected. 
       FIG. 5  shows an embodiment similar to  FIG. 4 , where in addition to the group of cantilevered beams  120   a  (one example of a MEMS transducing member) having larger first widths w 1  than second widths w 2 , there is a second group of cantilevered beams  120   b  (alternatingly arranged between elements of the first group) having first widths w 1 ′ that are equal to second widths w 2 ′. Furthermore, the second group of cantilevered beams  120   b  are sized smaller than the first group of cantilevered beams  120   a , such that the first widths w 1 ′ are smaller than first widths w 1 , the second widths w 2 ′ are smaller than second widths w 2 , and the distances (lengths) between the anchored first end  121  and the free second end  122  are also smaller for the group of cantilevered beams  120   b . Such an arrangement is beneficial when the first group of cantilevered beams  120   a  are used for actuators and the second group of cantilevered beams  120   b  are used as sensors. 
       FIG. 6  shows an embodiment similar to  FIG. 5  in which there are two groups of cantilevered beams  120   c  and  120   d , with the elements of the two groups being alternatingly arranged. In the embodiment of  FIG. 6  however, the lengths L and L′ of the cantilevered beams  120   c  and  120   d  respectively (the distances from anchored first ends  121  to free second ends  122 ) are less than 20% of the dimension D across cavity  115 . In this particular example, where the outer boundary  114  of cavity  115  is circular, D is the diameter of the cavity  115 . In addition, in the embodiment of  FIG. 6 , the lengths L and L′ are different from each other, the first widths w 1  and w 1 ′ are different from each other, and the second widths w 2  and w 2 ′ are different from each other for the cantilevered beams  120   c  and  120   d . Such an embodiment is beneficial when the groups of both geometries of cantilevered beams  120   c  and  120   d  are used to convert a motion of compliant membrane  130  to an electrical signal, and it is desired to pick up different amounts of deflection or at different frequencies (see equations 1, 2 and 3 in the background). 
     In the embodiments shown in FIGS.  1 A and  3 - 6 , the cantilevered beams  120  (one example of a MEMS transducing member) are disposed with substantially radial symmetry around a circular cavity  115 . This can be a preferred type of configuration in many embodiments, but other embodiments are contemplated having nonradial symmetry or noncircular cavities. For embodiments including a plurality of MEMS transducing members as shown in  FIGS. 3-6 , the compliant membrane  130  across cavity  115  provides a degree of coupling between the MEMS transducing members. For example, the actuators discussed above relative to  FIGS. 4 and 5  can cooperate to provide a larger combined force and a larger volumetric displacement of compliant membrane  130  when compared to a single actuator. The sensing elements (converting motion to an electrical signal) discussed above relative to  FIGS. 5 and 6  can detect motion of different regions of the compliant membrane  130 . 
       FIG. 7  shows an embodiment of a MEMS composite transducer in a top view similar to  FIG. 1A , but where the MEMS transducing member is a doubly anchored beam  140  extending across cavity  115  and having a first end  141  and a second end  142  that are each anchored to substrate  110 . As in the embodiment of  FIGS. 1A and 1B , compliant membrane  130  includes a first portion  131  that covers the MEMS transducing member, a second portion  132  that is anchored to first surface  111  of substrate  110 , and a third portion  133  that overhangs cavity  115  while not contacting the MEMS transducing member. In the example of  FIG. 7 , a portion  134  of compliant membrane  130  is removed over both first end  141  and second end  142  in order to make electrical contact in order to pass a current from the first end  141  to the second end  142 . 
       FIG. 8A  shows a cross-sectional view of a doubly anchored beam  140  MEMS composite transducer in its undeflected state, similar to the cross-sectional view of the cantilevered beam  120  shown in  FIG. 1B . In this example, a portion  134  of compliant membrane  130  is removed only at anchored second end  142  in order to make electrical contact on a top side of the MEMS transducing member to apply (or sense) a voltage across the MEMS transducing member as is discussed in further detail below. Similar to  FIGS. 1A and 1B , the cavity  115  is substantially cylindrical and extends from a first surface  111  of substrate  110  to a second surface  112  that is opposite first surface  111 . 
       FIG. 8B  shows a cross-sectional view of the doubly anchored beam  140  in its deflected state, similar to the cross-sectional view of the cantilevered beam  120  shown in  FIG. 2 . The portion of doubly anchored beam  140  extending across cavity  115  is deflected up and away from the undeflected position of  FIG. 8A , so that it raises up the portion  131  of compliant membrane  130 . The maximum deflection at or near the middle of doubly anchored beam  140  is shown as δ=Δz. 
       FIG. 9  shows a top view of an embodiment similar to that of  FIG. 7 , but with a plurality (for example, two) of doubly anchored beams  140  anchored to the substrate  110  at their first end  141  and second end  142 . In this embodiment both doubly anchored beams  140  are disposed substantially radially across circular cavity  115 , and therefore the two doubly anchored beams  140  intersect each other over the cavity at an intersection region  143 . Other embodiments are contemplated in which a plurality of doubly anchored beams do not intersect each other or the cavity is not circular. For example, two doubly anchored beams can be parallel to each other and extend across a rectangular cavity. 
       FIG. 10  shows an embodiment of a MEMS composite transducer in a top view similar to  FIG. 1A , but where the MEMS transducing member is a clamped sheet  150  extending across a portion of cavity  115  and anchored to the substrate  110  around the outer boundary  114  of cavity  115 . Clamped sheet  150  has a circular outer boundary  151  and a circular inner boundary  152 , so that it has an annular shape. As in the embodiment of  FIGS. 1 and 1B , compliant membrane  130  includes a first portion  131  that covers the MEMS transducing member, a second portion  132  that is anchored to first surface  111  of substrate  110 , and a third portion  133  that overhangs cavity  115  while not contacting the MEMS transducing member. In a fourth region  134 , compliant membrane  130  is removed such that it does not cover a portion of the MEMS transducing member, so that electrical contact can be made as is discussed in further detail below. 
       FIG. 11A  shows a cross-sectional view of a clamped sheet  150  MEMS composite transducer in its undeflected state, similar to the cross-sectional view of the cantilevered beam  120  shown in  FIG. 113 . Similar to  FIGS. 1A and 1B , the cavity  115  is substantially cylindrical and extends from a first surface  111  of substrate  110  to a second surface  112  that is opposite first surface  111 . 
       FIG. 11B  shows a cross-sectional view of the clamped sheet  150  in its deflected state, similar to the cross-sectional view of the cantilevered beam  120  shown in  FIG. 2 . The portion of clamped sheet  150  extending across cavity  115  is deflected up and away from the undeflected position of  FIG. 11A , so that it raises up the portion  131  of compliant membrane  130 , as well as the portion  133  that is inside inner boundary  152 . The maximum deflection at or near the inner boundary  152  is shown as δ=Δz. 
       FIG. 12A  shows a cross sectional view of an embodiment of a composite MEMS transducer having a cantilevered beam  120  extending across a portion of cavity  115 , where the cavity is a through hole from second surface  112  to first surface  111  of substrate  110 . As in the embodiment of  FIGS. 1 and 1B , compliant membrane  130  includes a first portion  131  that covers the MEMS transducing member, a second portion  132  that is anchored to first surface  111  of substrate  110 , and a third portion  133  that overhangs cavity  115  while not contacting the MEMS transducing member. Additionally in the embodiment of  FIG. 12A , the substrate further includes a second through hole  116  from second surface  112  to first surface  111  of substrate  110 , where the second through hole  116  is located near cavity  115 . In the example shown in  FIG. 12A , no MEMS transducing member extends over the second through hole  116 . In other embodiments where there is an array of composite MEMS transducers formed on substrate  110 , the second through hole  116  can be the cavity of an adjacent MEMS composite transducer. 
     The configuration shown in  FIG. 12A  can be used in a fluid ejector  200  as shown in  FIG. 12B . In  FIG. 12B , partitioning walls  202  are fanned over the anchored portion  132  of compliant membrane  130 . In other embodiments (not shown), partitioning walls  202  are formed on first surface  111  of substrate  110  in a region where compliant membrane  130  has been removed. Partitioning walls  202  define a chamber  201 . A nozzle plate  204  is formed over the partitioning walls and includes a nozzle  205  disposed near second end  122  of the cantilevered beam  120 . Through hole  116  is a fluid feed that is fluidically connected to chamber  201 , but not fluidically connected to cavity  115 . Fluid is provided to cavity  201  through the fluid feed (through hole  116 ). When an electrical signal is provided to the MEMS transducing member (cantilevered beam  120 ) at an electrical connection region (not shown), second end  122  of cantilevered beam  120  and a portion of compliant membrane  130  are deflected upward and away from cavity  115  (as shown in  FIG. 2 ), so that a drop of fluid is ejected through nozzle  205 . 
     The embodiment shown in  FIG. 13  is similar to the embodiment of  FIG. 10 , where the MEMS transducing member is a clamped sheet  150 , but in addition, compliant membrane  130  includes a hole  135  at or near the center of cavity  115 . As also illustrated in  FIG. 14 , the MEMS composite transducer is disposed along a plane, and at least a portion of the MEMS composite transducer is movable within the plane. In particular, the clamped sheet  150  in  FIGS. 13 and 14  is configured to expand and contract radially, causing the hole  135  to expand and contract, as indicated by the double-headed arrows. Such an embodiment can be used in a drop generator for a continuous fluid jetting device, where a pressurized fluid source is provided to cavity  115 , and the hole  135  is a nozzle. The expansion and contraction of hole  135  stimulates the controllable break-off of the stream of fluid into droplets. Optionally, a compliant passivation material  138  can be formed on the side of the MEMS transducing material that is opposite the side that the portion  131  of compliant membrane  130  is formed on. Compliant passivation material  138  together with portion  131  of compliant membrane  130  provide a degree of isolation of the MEMS transducing member (clamped sheet  150 ) from the fluid being directed through cavity  115 . 
     A variety of transducing mechanisms and materials can be used in the MEMS composite transducer of the present invention. Some of the MEMS transducing mechanisms include a deflection out of the plane of the undeflected MEMS composite transducer that includes a bending motion as shown in  FIGS. 2 ,  8 B and  11 B. A transducing mechanism including bending is typically provided by a MEMS transducing material  160  in contact with a reference material  162 , as shown for the cantilevered beam  120  in  FIG. 15 . In the example of  FIG. 15 , the MEMS transducing material  160  is shown on top of reference material  162 , but alternatively the reference material  162  can be on top of the MEMS transducing material  160 , depending upon whether it is desired to cause bending of the MEMS transducing member (for example, cantilevered beam  120 ) into the cavity  115  or away from the cavity  115 , and whether the MEMS transducing material  160  is caused to expand more than or less than an expansion of the reference material  162 . 
     One example of a MEMS transducing material  160  is the high thermal expansion member of a thermally bending bimorph. Titanium aluminide can be the high thermal expansion member, for example, as disclosed in commonly assigned U.S. Pat. No. 6,561,627. The reference material  162  can include an insulator such as silicon oxide, or silicon oxide plus silicon nitride. When a current pulse is passed through the titanium aluminide MEMS transducing material  160 , it causes the titanium aluminide to heat up and expand. The reference material  160  is not self-heating and its thermal expansion coefficient is less than that of titanium aluminide, so that the titanium aluminide MEMS transducing material  160  expands at a faster rate than the reference material  162 . As a result, a cantilever beam  120  configured as in  FIG. 15  would tend to bend downward into cavity  115  as the MEMS transducing material  160  is heated. Dual-action thermally bending actuators can include two MEMS transducing layers (deflector layers) of titanium aluminide and a reference material layer sandwiched between, as described in commonly assigned U.S. Pat. No. 6,464,347. Deflections into the cavity  115  or out of the cavity can be selectively actuated by passing a current pulse through either the upper deflector layer or the lower deflector layer respectively. 
     A second example of a MEMS transducing material  160  is a shape memory alloy such as a nickel titanium alloy. Similar to the example of the thermally bending bimorph, the reference material  162  can be an insulator such as silicon oxide, or silicon oxide plus silicon nitride. When a current pulse is passed through the nickel titanium MEMS transducing material  160 , it causes the nickel titanium to heat up. A property of a shape memory alloy is that a large deformation occurs when the shape memory alloy passes through a phase transition. If the deformation is an expansion, such a deformation would cause a large and abrupt expansion while the reference material  162  does not expand appreciably. As a result, a cantilever beam  120  configured as in  FIG. 15  would tend to bend downward into cavity  115  as the shape memory alloy MEMS transducing material  160  passes through its phase transition. The deflection would be more abrupt than for the thermally bending bimorph described above. 
     A third example of a MEMS transducing material  160  is a piezoelectric material. Piezoelectric materials are particularly advantageous, as they can be used as either actuators or sensors. In other words, a voltage applied across the piezoelectric MEMS transducing material  160 , typically applied to conductive electrodes (not shown) on the two sides of the piezoelectric MEMS transducing material, can cause an expansion or a contraction (depending upon whether the voltage is positive or negative and whether the sign of the piezoelectric coefficient is positive or negative). While the voltage applied across the piezoelectric MEMS transducing material  160  causes an expansion or contraction, the reference material  162  does not expand or contract, thereby causing a deflection into the cavity  115  or away from the cavity  115  respectively. Typically in a piezoelectric composite MEMS transducer, a single polarity of electrical signal would be applied however, so that the piezoelectric material does not tend to become depoled. It is possible to sandwich a reference material  162  between two piezoelectric material layers, thereby enabling separate control of deflection into cavity  115  or away from cavity  115  without depoling the piezoelectric material. Furthermore, an expansion or contraction imparted to the MEMS transducing material  160  produces an electrical signal which can be used to sense motion. There are a variety of types of piezoelectric materials. One family of interest includes piezoelectric ceramics, such as lead zirconate titanate or PZT. 
     As the MEMS transducing material  160  expands or contracts, there is a component of motion within the plane of the MEMS composite transducer, and there is a component of motion out of the plane (such as bending). Bending motion (as in  FIGS. 2 ,  8 B and  11 B) will be dominant if the Young&#39;s modulus and thickness of the MEMS transducing material  160  and the reference material  162  are comparable. In other words, if the MEMS transducing material  160  has a thickness t 1  and if the reference material has a thickness t 2 , then bending motion will tend to dominate if t 2 &gt;0.5t 1  and t 2 &lt;2t 1 , assuming comparable Young&#39;s moduli. By contrast, if t 2 &lt;0.2t 1 , motion within the plane of the MEMS composite transducer (as in  FIGS. 13 and 14 ) will tend to dominate. 
     Some embodiments of MEMS composite transducer  100  include an attached mass, in order to adjust the resonant frequency for example (see equation  2  in the background). The mass  118  can be attached to the portion  133  of the compliant membrane  130  that overhangs cavity  115  but does not contact the MEMS transducing member, for example. In the embodiment shown in the cross-sectional view of  FIG. 16A  including a plurality of cantilevered beams  120  (such as the configuration shown in  FIG. 6 ), mass  118  extends below portion  133  of compliant membrane  130 , so that it is located within the cavity  115 . Alternatively, mass  118  can be affixed to the opposite side of the compliant membrane  130 , as shown in  FIG. 16B . The configuration of  FIG. 16A  can be particularly advantageous if a large mass is needed. For example, a portion of silicon substrate  110  can be left in place when cavity  115  is etched as described below. In such a configuration, mass  118  would typically extend the full depth of the cavity. In order for the MEMS composite transducer to vibrate without crashing of mass  118 , substrate  110  would typically be mounted on a mounting member (not shown) including a recess below cavity  115 . For the configuration shown in  FIG. 16B , the attached mass  118  can be formed by patterning an additional layer over the compliant membrane  130 . 
     Having described a variety of exemplary structural embodiments of MEMS composite transducers, a context has been provided for describing methods of fabrication.  FIGS. 17A to 17E  provide an overview of a method of fabrication. As shown in  FIG. 17A , a reference material  162  and a transducing material  160  are deposited over a first surface  111  of a substrate  110 , which is typically a silicon wafer. Further details regarding materials and deposition methods are provided below. The reference material  162  can be deposited first (as in  FIG. 17A ) followed by deposition of the transducing material  160 , or the order can be reversed. In some instances, a reference material might not be required. In any case, it can be said that the transducing material  160  is deposited over the first surface  111  of substrate  110 . The transducing material  160  is then patterned and etched, so that transducing material  160  is retained in a first region  171  and removed in a second region  172  as shown in  FIG. 17B . The reference material  162  is also patterned and etched, so that it is retained in first region  171  and removed in second region  172  as shown in  FIG. 17C . 
     As shown in  FIG. 17D , a polymer layer (for compliant membrane  130 ) is then deposited over the first and second regions  171  and  172 , and patterned such that polymer is retained in a third region  173  and removed in a fourth region  174 . A first portion  173   a  where polymer is retained is coincident with a portion of first region  171  where transducing material  160  is retained. A second portion  173   b  where polymer is retained is coincident with a portion of second region  172  where transducing material  160  is removed. In addition, a first portion  174   a  where polymer is removed is coincident with a portion of first region  171  where transducing material  160  is retained. A second portion  174   b  where polymer is removed is coincident with a portion of second region  172  where transducing material  160  is removed. A cavity  115  is then etched from a second surface  112  (opposite first surface  111 ) to first surface  111  of substrate  110 , such that an outer boundary  114  of cavity  115  at the first surface  111  of substrate  110  intersects the first region  171  where transducing material  160  is retained, so that a first portion of transducing material  160  (including first end  121  of cantilevered beam  120  in this example) is anchored to first surface  111  of substrate  110 , and a second portion of transducing material  160  (including second end  122  of cantilevered beam  120 ) extends over at least a portion of cavity  115 . When it is said that a first portion of transducing material  160  is anchored to first surface  111  of substrate  110 , it is understood that transducing material  160  can be in direct contact (not shown) with first surface  111 , or transducing material  160  can be indirectly anchored to first surface  111  through reference material  162  as shown in  FIG. 17E . A MEMS composite transducer  100  is thereby fabricated. 
     Reference material  162  can include several layers as illustrated in  FIG. 18A . A first layer  163  of silicon oxide can be deposited on first surface  111  of substrate  110 . Deposition of silicon oxide can be a thermal process or it can be chemical vapor deposition (including low pressure or plasma enhanced CVD) for example. Silicon oxide is an insulating layer and also facilitates adhesion of the second layer  164  of silicon nitride. Silicon nitride can be deposited by LPCVD and provides a tensile stress component that will help the transducing material  160  to retain a substantially flat shape when the cavity is subsequently etched away. A third layer  165  of silicon oxide helps to balance the stress and facilitates adhesion of an optional bottom electrode layer  166 , which is typically a platinum (or titanium/platinum) electrode for the case of a piezoelectric transducing material  160 . The platinum electrode layer is typically deposited by sputtering. 
     Deposition of the transducing material  160  will next be described for the case of a piezoelectric ceramic transducing material, such as PZT. An advantageous configuration is the one shown in  FIG. 18B  in which a voltage is applied across PZT transducing material  160  from a top electrode  168  to a bottom electrode  166 . The desired effect on PZT transducing material  160  is an expansion or contraction along the x-y plane parallel to surface  111  of substrate  110 . As described above, such an expansion or contraction can cause a deflection into the cavity  115  or out of the cavity  115  respectively, or a substantially in-plane motion, depending on the relative thicknesses and stiffnesses of the PZT transducing material  160  and the reference material  162 . Thicknesses are not to scale in  FIGS. 18A and 18B . Typically for a bending application where the reference material  162  has a comparable stiffness to the MEMS transducing material  160 , the reference material  162  is deposited in a thickness of about 1 micron, as is the transducing material  160 , although for in-plane motion the reference material thickness is typically 20% or less of the transducing material thickness, as described above. The transverse piezoelectric coefficients d 31  and e 31  are relatively large in magnitude for PZT (and can be made to be larger and stabilized if poled in a relatively high electric field). To orient the PZT crystals such that transverse piezoelectric coefficients d 31  and e 31  are the coefficients relating voltage across the transducing layer and expansion or contraction in the x-y plane, it is desired that the (001) planes of the PZT crystals be parallel to the x-y plane (parallel to the bottom platinum electrode layer  166  as shown in  FIG. 18B ). However, PZT material will tend to orient with its planes parallel to the planes of the material upon which it is deposited. Because the platinum bottom electrode layer  166  typically has its (111) planes parallel to the x-y plane when deposited on silicon oxide, a seed layer  167 , such as lead oxide or lead titanate can be deposited over bottom electrode layer  166  in order to provide the (001) planes on which to deposit the PZT transducing material  160 . Then the upper electrode layer  168  (typically platinum) is deposited over the PZT transducing material  160 , e.g. by sputtering. 
     Deposition of the PZT transducing material  160  can be done by sputtering. Alternatively, deposition of the PZT transducing material  160  can be done by a sol-gel process. In the sol-gel process, a precursor material including PZT particles in an organic liquid is applied over first surface  111  of substrate  110 . For example, the precursor material can be applied over first surface  111  by spinning the substrate  110 . The precursor material is then heat treated in a number of steps. In a first step, the precursor material is dried at a first temperature. Then the precursor material is pyrolyzed at a second temperature higher than the first temperature in order to decompose organic components. Then the PZT particles of the precursor material are crystallized at a third temperature higher than the second temperature. PZT deposited by a sol-gel process is typically done using a plurality of thin layers of precursor material in order to avoid cracking in the material of the desired final thickness. 
     For embodiments where the transducing material  160  is titanium aluminide for a thermally bending actuator, or a shape memory alloy such as a nickel titanium alloy, deposition can be done by sputtering. In addition, layers such as the top and bottom electrode layers  166  and  168 , as well as seed layer  167  are not required. 
     In order to pattern the stack of materials shown in  FIGS. 18A and 18B , a photoresist mask is typically deposited over the top electrode layer  168  and patterned to cover only those regions where it is desired for material to remain. Then at least some of the material layers are etched at one time. For example, plasma etching using a chlorine based process gas can be used to etch the top electrode layer  168 , the PZT transducing material  160 , the seed layer  167  and the bottom electrode layer  166  in a single step. Alternatively the single step can include wet etching. Depending on materials, the rest of the reference material  162  can be etched in the single step. However, in some embodiments, the silicon oxide layers  163  and  165  and the silicon nitride layer  164  can be etched in a subsequent plasma etching step using a fluorine based process gas. 
     Depositing the polymer layer for compliant membrane  130  can be done by laminating a film, such as TMMF, or spinning on a liquid resist material, such as TMMR, as referred to above. As the polymer layer for the compliant membrane is applied while the transducers are still supported by the substrate, pressure can be used to apply the TMMF or other laminating film to the structure without risk of breaking the transducer beams. An advantage of TMMR and TMMF is that they are photopatternable, so that application of an additional resist material is not required. An epoxy polymer further has desirable mechanical properties as mentioned above. 
     In order to etch cavity  115  ( FIG. 17E ) a masking layer is applied to second surface  112  of substrate  110 . The masking layer is patterned to expose second surface  112  where it is desired to remove substrate material. The exposed portion can include not only the region of cavity  115 , but also the region of through hole  116  of fluid ejector  200  (see  FIGS. 12A and 12B ). For the case of leaving a mass affixed to the bottom of the compliant membrane  130 , as discussed above relative to  FIG. 16A , the region of cavity  115  can be masked with a ring pattern to remove a ring-shaped region, while leaving a portion of substrate  110  attached to compliant membrane  130 . For embodiments where substrate  110  is silicon, etching of substantially vertical walls (portions  113  of substrate  110 , as shown in a number of the cross-sectional views including  FIG. 1B ) is readily done using a deep reactive ion etching (DRIE) process. Typically, a DRIE process for silicon uses SF 6  as a process gas. 
     As described above, one application for which MEMS composite transducer  100  is particularly well suited is as a drop generator (also commonly referred to as a drop forming mechanism). Example embodiments of flow-through liquid dispensers  310  that incorporate the drop generator described above are described in more detail below with reference to  FIGS. 19A-26B  and back to  FIGS. 1A-2 . These types of liquid dispensers are also commonly referred to as continuous-on-demand liquid dispensers. 
     Referring to  FIGS. 19A and 19B , example embodiments of a liquid dispenser  310  made in accordance with the present invention are shown. Liquid dispenser  310  includes a liquid supply channel  311  that is in fluid communication with a liquid return channel  313  through a liquid dispensing channel  312 . Liquid dispensing channel  312  includes a diverter member  320 . Liquid supply channel  311  includes an exit  321  while liquid return channel  313  includes an entrance  338 . 
     Liquid dispensing channel  312  includes an outlet opening  326 , defined by an upstream edge  318  and a downstream edge  319  that opens directly to atmosphere. Outlet opening  326  is different when compared to conventional nozzles because the area of the outlet opening  326  does not determine the size of the ejected drops. Instead, the actuation of diverter member  320  determines the size (volume) of the ejected drop  315 . Typically, the size of drops created is proportional to the amount of liquid displaced by the actuation of diverter member  320 . The upstream edge  318  of outlet opening  326  also at least partially defines the exit  321  of liquid supply channel  311  while the downstream edge  319  of outlet opening  326  also at least partially defines entrance  338  of liquid return channel  313 . 
     A wall  340  that defines outlet opening  326  includes a surface  354 . Surface  354  can be either an interior surface  354 A or an exterior surface  354 B. In  FIG. 19A , upstream edge  318  and downstream edge  319 , as viewed in the direction of liquid flow  327  through liquid dispensing channel  312 , of outlet opening  326  are perpendicular relative to the surface  354 . However, either or both of upstream edge  318  and downstream edge  319 , as viewed in the direction of liquid flow  327  through liquid dispensing channel  312 , of outlet opening  326  can be sloped (angled) relative to the surface  354  of wall  340  of liquid dispensing channel  312 . It is believed that providing downstream edge  319  with a slope (angle) helps facilitate drop ejection. In  FIG. 19B  both upstream edge  318  and downstream edge  319 , as viewed in the direction of liquid flow  327  through liquid dispensing channel  312 , of outlet opening  326  are sloped. In  FIGS. 21A and 22A , discussed in more detail below, only downstream edge  319 , as viewed in the direction of liquid flow  327  through liquid dispensing channel  312 , of outlet opening  326  is sloped. 
     Liquid ejected by liquid dispenser  310  of the present invention does not need to travel through a conventional nozzle which typically has a smaller area. This helps reduce the likelihood of the outlet opening  326  becoming contaminated or clogged by particle contaminants. Using a larger outlet opening  326  (as compared to a conventional nozzle) also reduces latency problems at least partially caused by evaporation in the nozzle during periods when drops are not being ejected. The larger outlet opening  326  also reduces the likelihood of satellite drop formation during drop ejection because drops are produced with shorter tail lengths. 
     Diverter member  320 , associated with liquid dispensing channel  312 , for example, positioned on or in substrate  339 , is selectively actuatable to divert a portion of liquid  325  toward and through outlet opening  326  of liquid dispensing channel  312  in order to form and eject a drop  315 . Diverter member  320  includes one of the MEMS composite transducers  100  described above. Extending over a cavity  390  in substrate  339 , the MEMS composite transducer  100  is selectively movable into and out of liquid dispensing channel  312  during actuation to divert a portion of the liquid flowing through liquid dispensing channel  312  toward outlet opening  326 . 
     As shown in  FIGS. 19A and 19B , liquid supply channel  311 , liquid dispensing channel  312 , and liquid return channel  313  are partially defined by portions of substrate  339 . These portions of substrate  339  can also be referred to as a wall or walls of one or more of liquid supply channel  311 , liquid dispensing channel  312 , and liquid return channel  313 . A wall  340  defines outlet opening  326  and also partially defines liquid supply channel  311 , liquid dispensing channel  312 , and liquid return channel  313 . Portions of substrate  339  also define a liquid supply passage  342  and a liquid return passage  344 . Again, these portions of substrate  339  can be referred to as a wall or walls of liquid supply passage  342  and liquid return passage  344 . As shown in  FIGS. 19A and 19B , liquid supply passage  342  and liquid return passage  344  are perpendicular to liquid supply channel  311 , liquid dispensing channel  312 , and liquid return channel  313 . 
     A liquid supply  324  is connected in fluid communication to liquid dispenser  310 . Liquid supply  324  provides liquid  325  to liquid dispenser  310 . During operation, liquid  325 , pressurized by a regulated pressure supply source  316 , for example, a pump, flows (represented by arrows  327 ) from liquid supply  324  through liquid supply passage  342 , through liquid supply channel  311 , through liquid dispensing channel  312 , through liquid return channel  313 , through liquid return passage  344 , and back to liquid supply  324  in a continuous manner. When a drop  315  of liquid  325  is desired, diverter member  320  is actuated causing a portion of the liquid  325  continuously flowing through liquid dispensing channel  312  to be urged toward and through outlet opening  326 . Typically, regulated pressure supply source  316  is positioned in fluid communication between liquid supply  324  and liquid supply channel  311  and provides a positive pressure that is above atmospheric pressure. 
     Optionally, a regulated vacuum supply source  317 , for example, a pump, can be included in the liquid delivery system of liquid dispenser  310  in order to better control liquid flow through liquid dispenser  310 . Typically, regulated vacuum supply source  317  is positioned in fluid communication between liquid return channel  313  and liquid supply  324  and provides a vacuum (negative) pressure that is below atmospheric pressure. 
     Liquid return channel  313  or liquid return passage  344  can optionally include a porous member  322 , for example, a filter, which in addition to providing particulate filtering of the liquid flowing through liquid dispenser  310  helps to accommodate liquid flow and pressure changes in liquid return channel  313  associated with actuation of diverter member  320  and a portion of liquid  325  being deflected toward and through outlet opening  326 . This reduces the likelihood of liquid other than the ejected drop  315  spilling over outlet opening  326  of liquid dispensing channel  312  during or following actuation of diverter member  320 . The likelihood of air being drawn into liquid return passage  344  is also reduced when porous member  322  is included in liquid dispenser  310 . 
     Porous member  322  is typically integrally formed in liquid return channel  313  during the manufacturing process that is used to fabricate liquid dispenser  310 . Alternatively, porous member  322  can be made from a metal or polymeric material and inserted into liquid return channel  313  or affixed to one or more of the walls that define liquid return channel  313 . As shown in  FIGS. 19A and 19B , porous member  322  is positioned in liquid return channel  313  in the area where liquid return channel  313  and liquid return passage  344  intersect. As such, either liquid return passage  344  includes porous member  322  or that liquid return channel  313  includes porous member  322 . Alternatively, porous member  322  can be positioned in liquid return passage  344  downstream from its location as shown in  FIGS. 19A and 19B . 
     Regardless of whether porous member  322  in integrally formed or fabricated separately, the pores of porous member  322  have a substantially uniform pore size. Alternatively, the pore size of the pores of porous member  322  include a gradient so as to be able to more efficiently accommodate liquid flow through the liquid dispenser  310  (for example, larger pore sizes (alternatively, smaller pore sizes) on an upstream portion of the porous member  322  that decrease (alternatively, increase) in size at a downstream portion of porous member  322  when viewed in a direction of liquid travel). The specific configuration of the pores of porous member  322  typically depends on the specific application contemplated. Example embodiments of this aspect of the present invention are discussed in more detail below. 
     Typically, the location of porous member  322  varies depending on the specific application contemplated. As shown in  FIGS. 19A and 19B , porous member  322  is positioned in liquid return channel  313  parallel to the flow direction  327  of liquid  325  in liquid dispensing channel  312  such that the center axis of the openings (pores) of porous member  322  are substantially perpendicular to the liquid flow  327  in the liquid dispensing channel. Porous member  322  is positioned in liquid return channel  313  at a location that is spaced apart from outlet opening  326  of liquid dispensing channel  312 . Porous member  322  is also positioned in liquid return channel  313  at a location that is adjacent to the downstream edge  319  of outlet opening  326  of liquid dispensing channel  312 . As described above, the likelihood of air being drawn into liquid return passage  344  is reduced because the difference between atmospheric pressure and the negative pressure provided by the regulated vacuum supply source  317  is less than the meniscus pressure of porous member  322 . 
     Additionally, liquid return channel  313  includes a vent  323  that opens liquid return channel  313  to atmosphere. Vent  323  helps to accommodate liquid flow and pressure changes in liquid return channel  313  associated with actuation of diverter member  320  and a portion of liquid  325  being deflected toward and through outlet opening  326 . This reduces the likelihood of unintended liquid spilling (liquid other than liquid drop  315 ) over outlet opening  326  of liquid dispensing channel  312  during or after actuation of diverter member  320 . In the event that liquid does spill over outlet opening  326 , vent  323  also acts as a drain that provides a path back to liquid return channel  313  for any overflowing liquid. As such, the terms “vent” and “drain” are used interchangeably herein. 
     Liquid dispenser  310  is typically formed from a semiconductor material (for example, silicon) using known semiconductor fabrication techniques (for example, CMOS circuit fabrication techniques, micro-mechanical structure (MEMS) fabrication techniques, or combinations of both). Alternatively, liquid dispenser  310  is formed from any materials using any fabrication techniques known in the art. 
     The liquid dispensers  310  of the present invention, like conventional drop-on-demand printheads, only create drops when desired, eliminating the need for a gutter and the need for a drop deflection mechanism which directs some of the created drops to the gutter while directing other drops to a print receiving media. The liquid dispensers of the present invention use a liquid supply that continuously supplies liquid, for example, ink under pressure through liquid dispensing channel  312 . The supplied ink pressure serves as the primary motive force for the ejected drops, so that most of the drop momentum is provided by the ink supply rather than by a drop ejection actuator at the nozzle. In other words, the continuous pressurized liquid flow through the liquid dispenser provides the momentum needed for drop formation and liquid/drop travel through the outlet opening. The continuous flow of liquid through liquid dispenser  310  is internal relative to liquid dispenser  310  in contrast with a continuous liquid ejection system in which the liquid jet that is ejected through a nozzle is ejected externally relative to the continuous liquid ejection system. 
     Referring to  FIGS. 20A-20D  and back to  FIGS. 19A and 19B , additional example embodiments of liquid dispenser  310  are shown. In  FIG. 20A , a plan view of liquid dispenser  310 , wall  346  and wall  348  define a width, as viewed perpendicular to the direction of liquid flow  327  (shown in  FIG. 20B ), of liquid dispensing channel  312  and a width, as viewed perpendicular to the direction of liquid flow  327  (shown in  FIG. 20B ), of liquid supply channel  311  and liquid return channel  313 . The MEMS transducing member (for example, cantilever beam  120 ) and compliant membrane  130  of diverter member  320  are also included in  FIG. 20A . Additionally, a length, as viewed along the direction of liquid flow  327  (shown in  FIG. 20B ), and a width, as viewed perpendicular to the direction of liquid flow  327  (shown in  FIG. 20B ), of outlet opening  326  relative to the length and width of liquid dispensing channel  312  are shown in  FIG. 20A . 
     In  FIGS. 20B-20D , the location of the MEMS transducing member (for example, cantilever beam  120 ) and compliant membrane  130  of diverter member  320  relative to the exit  321  of liquid supply channel  311  and the upstream edge  318  of outlet opening  326  is shown. In  FIG. 20B , an upstream edge  350  of diverter member  320  is located at the exit  321  of liquid supply channel  311  and the upstream edge  318  of outlet opening  326 . A downstream edge  352  of diverter member  320  is located upstream from the downstream edge  319  of outlet opening  326  and the entrance  338  of liquid return channel  313 . In  FIG. 20C , an upstream edge  350  of diverter member  320  is located in liquid dispensing channel  312  downstream from the exit  321  of liquid supply channel  311  and the upstream edge  318  of outlet opening  326 . The downstream edge  352  of diverter member  320  is located upstream from the downstream edge  319  of outlet opening  326  and the entrance  338  of liquid return channel  313 . In  FIG. 20D , upstream edge  350  of diverter member is located in liquid supply channel  311 , upstream from the exit  321  of liquid supply channel  311  and the upstream edge  318  of outlet opening  326 . The downstream edge  352  of diverter member  320  is located upstream from the downstream edge  319  of outlet opening  326  and the entrance  338  of liquid return channel  313 . Depending on the application contemplated, the relative location of diverter member  320  to exit  321  and entrance  338  is used to control or adjust characteristics (for example, the angle of trajectory, volume, or velocity) of ejected drops  315 . 
     Referring to  FIGS. 21A-22B  and back to  FIGS. 19A and 19B , liquid dispensing channel  312  includes a first wall  340 . Wall  340  includes a surface  354  (either interior surface  354 A or exterior surface  354 B). A portion of first wall  340  defines an outlet opening  326 . Liquid dispensing channel  312  also includes a second wall  380  positioned opposite first wall  340 . Second wall  380  of liquid dispensing channel  312  extends along a portion of liquid supply channel  311  and along a portion of liquid return channel  313 . A liquid supply passage  342  extends through second wall  380  and is in fluid communication with liquid supply channel  311 . Liquid supply passage  342  includes a porous member  322 . A liquid return passage  344  extends through second wall  380  and is in fluid communication with liquid return channel  313 . Liquid return passage includes a porous member  322 . A liquid supply  324  provides liquid that continuously flows from liquid supply passage  342  through the liquid supply channel  311 , through liquid dispensing channel  312 , through liquid return channel  313  to liquid return passage  344  and back to liquid supply  324 . Diverter member  320  selectively diverts a portion of the flowing liquid through outlet opening  326  of liquid dispensing channel  312 . 
     As shown in  FIGS. 21A-22B , porous member  322  is positioned in liquid supply channel  311  in the area where liquid supply channel  311  and liquid supply passage  342  intersect. As such, either liquid supply passage  342  includes porous member  322  or that liquid supply channel  311  includes porous member  322 . Alternatively, porous member  322  can be positioned in liquid supply passage  342  upstream from its location as shown in  FIGS. 21A-22B . Also, as shown in  FIGS. 21A-22B , porous member  322  is positioned in liquid return channel  313  in the area where liquid return channel  313  and liquid return passage  344  intersect. As such, either liquid return passage  344  includes porous member  322  or that liquid return channel  313  includes porous member  322 . Alternatively, porous member  322  can be positioned in liquid return passage  344  downstream from its location as shown in  FIGS. 21A-22B . 
     As shown in  FIGS. 21A and 21B , porous member  322  includes pores that have the same size. Alternatively, porous member  322  includes pores that have variations in size when compared to each other. As shown in  FIGS. 22A and 22B , the pore size varies monotonically along the direction of the liquid flow  327  through liquid dispensing channel  312  to provide distinct liquid flow impedances. Alternatively, the pores of porous member  322  are shaped differently to provide distinct liquid flow impedances in other example embodiments. In  FIGS. 21B-22B , drain  323  has been removed from each “B” figure so that the liquid return passage  344  and porous member  322  can be seen more clearly. 
     Referring to  FIGS. 19A and 20B , wall  340 , defining outlet opening  326 , includes a surface  354 . Surface  354  can be either interior surface  354 A or exterior surface  354 B. The downstream edge  319 , as viewed in the direction of liquid flow  327  through liquid dispensing channel  312 , of outlet opening  326  is perpendicular relative to the surface  354  of wall  340  of liquid dispensing channel  312 . 
     Downstream edge  319  of outlet opening  326  can include other features. For example, as shown in  FIG. 20A , the central portion of the downstream edge  319  of outlet opening  326  is straight when viewed from a direction perpendicular to surface  354  of wall  340 . When central portion of the downstream edge  319  is straight, the corners  356  of downstream edge  319  are rounded in some example embodiments, to provide mechanical stability and reduce stress induced cracks in wall  340 . It is believed, however, that it is more preferable to configure the downstream edge  319  of outlet opening  326  to include a radius of curvature when viewed from a direction perpendicular to the surface  354  of wall  340  as shown in  FIGS. 21B and 22B  in order to improve the drop ejection performance of liquid dispenser  310 . The radius of curvature is different at different locations along the arc of the curve in some embodiments. In this sense, the radius of curvature can include a plurality of radii of curvature. 
     Referring to  FIG. 20A , outlet opening  326  includes a centerline  358  along the direction of the liquid flow  327  through liquid dispensing channel  312  as viewed from a direction perpendicular to surface  354  of wall  340  of liquid dispensing channel  312 . Liquid dispensing channel  312  includes a centerline  360  along the direction of the liquid flow  327  through liquid dispensing channel  312  as viewed from a direction perpendicular to surface  354  of wall  340  of liquid dispensing channel  312 . As shown in  FIG. 20A , liquid dispensing channel  312  and outlet opening  326  share this centerline  358 ,  360 . 
     It is believed that it is still more preferable to configure the downstream edge  319  of the outlet opening  326  such that it tapers towards the centerline  358  of the outlet opening  326 , as shown in  FIGS. 21B and 22B , in order to improve the drop ejection performance of liquid dispenser  310 . The apex  362  of the taper can include a radius of curvature when viewed from a direction perpendicular to the surface  354  of wall  340  to provide mechanical stability and reduce stress induced cracks in wall  340 . 
     In some example embodiments, the overall shape of the outlet opening  326  is symmetric relative to the centerline  358  of the outlet opening  326 . In other example embodiments, the overall shape of the liquid dispensing channel  312  is symmetric relative to the centerline  360  of the liquid dispensing channel  312 . It is believed, however, that optimal drop ejection performance can be achieved when the overall shape of the liquid dispensing channel  312  and the overall shape of the outlet opening  326  are symmetric relative to a shared centerline  358 ,  360 . 
     Referring to  FIGS. 19A ,  21 B, and  22 B, liquid dispensing channel  312  includes a width  364  that is perpendicular to the direction of liquid flow  327  through liquid dispensing channel  312 . Outlet opening  326  also includes a width  366  that is perpendicular to the direction of liquid flow  327  through liquid dispensing channel  312 . The width  366  of the outlet opening  326  is less than the width  364  of the liquid dispensing channel  312 . 
     In the example embodiments of the present invention described herein, the width  364  of the liquid dispensing channel  312  is greater at a location that is downstream relative to diverter member  320 . Additionally, liquid return channel  313  is wider than the width of liquid dispensing channel  312  at the upstream edge  318  of the liquid dispensing channel  312 . Liquid return channel  313  is also wider than the width of liquid supply channel  311  at its exit  321 . This feature helps to control the meniscus height of the liquid in outlet opening  326  so as to reduce or even prevent liquid spills. 
     In the example embodiment shown in  FIG. 20A , the width  366  of outlet opening  326  remains constant along the length of the outlet opening  326  until the downstream edge  319  of the outlet opening is encountered. The width  366  of outlet opening  326  varies in other embodiments, however. For example, in the example embodiments shown in  FIGS. 21B and 22B , the width  366  of outlet opening  326  is greater at a location that is downstream relative to diverter member  320  and upstream relative to the downstream edge  319  of the outlet opening when compared to the width  366  of outlet opening  326  at a location in the vicinity of diverter member  320 . It is believed that this configuration helps achieve optimal drop ejection performance. 
     Referring to  FIGS. 21A and 22A , wall  340 , defining outlet opening  326 , includes a surface  354 . Surface  354  can be either interior surface  354 A or exterior surface  354 B. The downstream edge  319 , as viewed in the direction of liquid flow  327  through liquid dispensing channel  312 , of outlet opening  326  is sloped (angled) relative to the surface  354  of wall  340  of liquid dispensing channel  312 . It is believed that providing downstream edge  319  with a slope (angle) helps facilitate drop ejection. 
     Referring back to  FIGS. 19A-22B , liquid return channel  313  is shown having a cross-sectional area that is greater than the cross-sectional area of liquid dispensing channel  312 . This features also helps to minimize pressure changes associated with actuation of diverter member  320  and a portion of liquid  325  being deflected toward and through outlet opening  326  which reduces the likelihood of air being drawn into liquid return channel  313  or liquid spilling over outlet opening  326  following actuation of diverter member  320 . 
     Liquid supply channel  311  includes an exit  321  that has a cross sectional area. Liquid dispensing channel  312  includes an outlet opening  326  that includes an end  319  that is adjacent to liquid return channel  313 . Liquid dispensing channel  312  also has a cross sectional area. The cross sectional area of a portion of liquid dispensing channel  312  that is located at the end  319  of outlet opening  326  is greater than the cross sectional area of the exit  321  of liquid supply channel  311 . This feature helps to minimize pressure changes associated with actuation of diverter member  320  and the deflecting of a portion of liquid  325  toward outlet opening  326  which reduces the likelihood of air being drawn into liquid return channel  313  or liquid spilling over outlet opening  326  during actuation of diverter member  320 . 
     Referring to  FIGS. 23A and 23B  and back to  FIGS. 1A-2  and  19 A- 22 B, a first portion  368  of substrate  339  defines liquid dispensing channel  312  and a second portion  370  of substrate  339  defines an outer boundary of cavity  390 . Other portions  372 ,  374  of substrate  339  define liquid supply channel  311  and liquid return channel  313 . Liquid supply  324  provides a flow of liquid  325  continuously from liquid supply  324  through the liquid supply channel  311  through the liquid dispensing channel  312  through the liquid return channel  313  and back to liquid supply  324 . Diverter member  320  is selectively actuated to divert a portion of the liquid  325  flowing through liquid dispensing channel  312  through outlet opening  326  of liquid dispensing channel  312 . Diverter member  320  is located in liquid dispensing channel  312  opposite outlet opening  326 . 
     Diverter member  320  includes a MEMS transducing member and a compliant membrane  130 . In  FIGS. 1A-2  and  19 A- 23 B, the MEMS transducing member includes cantilevered beam  120 . A first portion  121  of the MEMS transducing member is anchored to substrate  339  and a second portion  122  of the MEMS transducing member extends over at least a portion of cavity  390  formed in substrate  339 . The second portion  122  of the MEMS transducing member is free to move relative to cavity  390 . When actuated, diverter member  320  moves into liquid dispensing channel  312 . Typically, compliant membrane  130  is a compliant polymeric membrane made from one of the polymers described above. However, compliant membrane  130  can be any of the compliant membranes described above depending on the specific application contemplated. 
     A compliant membrane  130  is positioned in contact with the MEMS transducing member. A first portion  131  of compliant membrane  130  covers the MEMS transducing member and a second portion  132  of compliant membrane  130  is anchored to substrate  339  such that compliant membrane  130  forms a portion of a wall  376  of liquid dispensing channel  312  that is opposite outlet opening  326 . 
     In some example embodiments, porous membrane  322  is fabricated in a portion of compliant membrane  130  when compliant membrane  130  extends across substrate  339  to cover liquid supply passage  342  or liquid return passage  344 . 
     The continuous flow of liquid  325  flows in a direction  327 . As shown in  FIG. 23A , the first portion  121  of the MEMS transducing member that is anchored to substrate  339  is an upstream portion  378  of the MEMS transducing member relative to the direction  327  of liquid flow. As shown in  FIG. 23B , the first portion  121  of the MEMS transducing member that is anchored to substrate  339  is a downstream portion  382  of the MEMS transducing member relative to the direction  327  of liquid flow. When positioned as shown in  FIG. 23B , second portion  122  of cantilevered beam  120  should be located downstream from the upstream edge  318  of outlet opening  326  in order to ensure consistent drop ejection. First portion  121  of cantilevered beam  120  can be located either upstream or downstream from the downstream edge  319  of outlet opening  326  depending on the contemplated application. 
     In some example embodiments of liquid dispenser  310 , cavity  390  is filled with a gas, for example, air. When filled with air, cavity  390  can be vented to atmosphere. In other example embodiments of liquid dispenser  310 , cavity  390  is filled with a liquid, for example, the liquid being ejected by liquid dispenser  310  or cavity  390  has a liquid flowing through it. When cavity  390  includes a liquid, it helps equalize the pressure on both sides of diverter member  320 . 
     Referring to  FIGS. 24A-24C  and back to  FIGS. 1A-2  and  19 A- 23 B, cavity  390  is connected in liquid communication with liquid supply channel  311  and liquid return channel  313 . Diverter member  320  is selectively movable into and out of liquid dispensing channel  312  during actuation. Diverter member  320  includes a first side  320 A that faces liquid dispensing channel  312  and a second side  320 B that faces cavity  390 . 
     Diverter member  320  includes a MEMS transducing member and a compliant membrane. In  FIGS. 24A-24C , the MEMS transducing member includes cantilevered beam  120 . Compliant membrane  130  is positioned in contact with the MEMS transducing member. A first portion  131  of compliant membrane  130  covers the MEMS transducing member and a second portion  132  of compliant membrane  130  is anchored to a portion of a wall of substrate  339  that defines liquid dispensing channel  312 . Diverter member  320  is positioned opposite outlet opening  326 . Typically, compliant membrane  130  is a compliant polymeric membrane made from one of the polymers described above. However, compliant membrane  130  can be any of the compliant membranes described above depending on the specific application contemplated. 
     Optionally, an insulating material covers a surface of the MEMS transducing member that is opposite a surface of the MEMS transducing member that contacts the compliant membrane. For example, a compliant passivation material  138  can be included on the side of the MEMS transducing material that is opposite the side that the portion  131  of compliant membrane  130  is formed on, as described above with reference to  FIG. 14 , when cavity  390  is filled with a liquid or has a liquid flowing through it. Compliant passivation material  138  together with portion  131  of compliant membrane  130  provide protection of the MEMS transducing member (for example, cantilevered beam  120 ) from the fluid being directed through cavity  390 . 
     In the example embodiment shown in  FIG. 24A , a second liquid supply channel  331  supplies liquid  325  through cavity  390  to liquid return channel  313  that is common to liquid supply channel  311  and second liquid supply channel  331 . First liquid supply channel  311  and second liquid supply channel  331  are physically distinct from each other. 
     In the example embodiment shown in  FIG. 24B , liquid supply channel  311  is a first liquid supply channel and liquid return channel  313  is a first liquid return channel. Liquid dispenser  310  also includes a second liquid supply channel  331  that is in liquid communication with cavity  390 . First liquid supply channel  311  and second liquid supply channel  331  are physically distinct from each other. A second liquid return channel  334  is in liquid communication with cavity  390 . First liquid return channel  313  and second liquid return channel  334  are physically distinct from each other. Liquid supply  324  provides a continuous flow of liquid  325  from liquid supply  324  through first liquid supply channel  311  through liquid dispensing channel  312  through first liquid return channel  313  and back to liquid supply  324 . Liquid supply  325  also provides a continuous flow of liquid  325  from liquid supply  324  through second liquid supply channel  331  through cavity  390  through second liquid return channel  334  and back to liquid supply  324 . 
     Liquid dispensing channel  312  and cavity  390  are sized relative to each other so that liquid pressure on both sides of diverter member  320  is balanced. Keeping first liquid supply channel  311  and second liquid supply channel  331  physically separated from each other and keeping first liquid return channel  313  and second liquid return channel  334  physically separated from each other helps to facilitate pressure balancing on both sides of diverter member  320 . 
     In the example embodiment shown in  FIG. 24C , liquid supply channel  311  is a first liquid supply channel and liquid return channel  313  is a first liquid return channel. Liquid dispenser  310  also includes a second liquid supply channel  331  that is in liquid communication with cavity  390 . First liquid supply channel  311  and second liquid supply channel  331  are physically distinct from each other. A second liquid return channel  334  is in liquid communication with cavity  390 . First liquid return channel  313  and second liquid return channel  334  are physically distinct from each other. 
     Liquid supply  324  is a first liquid supply. Liquid supply  324  provides a continuous flow of liquid  325  from liquid supply  324  through first liquid supply channel  311  through liquid dispensing channel  312  through first liquid return channel  313  and back to liquid supply  324 . Liquid dispenser  310  also includes a second liquid supply  386  that provides a continuous flow of liquid  325  from second liquid supply  386  through second liquid supply channel  331  through cavity  390  through second liquid return channel  334  and back to second liquid supply  386 . In this embodiment, liquid  325  is a first liquid that is supplied by first liquid supply  324 . Second liquid supply  386  provides a second liquid  384  through cavity  390 . Depending on the application contemplated, first liquid  325  and second liquid  384  have the same formulation properties or have distinct formulation properties when compared to each other. 
     During operation, second liquid  384 , pressurized above atmospheric pressure by a second regulated pressure source  335 , for example, a pump, flows (represented by arrows  388 ) from second liquid supply  386  through second liquid supply channel  331 , cavity  390 , second liquid return channel  334 , and back to second liquid supply  386  in a continuous manner. Optionally, a second regulated vacuum supply  336 , for example, a pump, can be included in order to better control the flow of second liquid  384  through liquid dispenser  310 . Typically, second regulated vacuum supply  336  is positioned in fluid communication between second liquid return channel  334  and second liquid supply  386  and provides a vacuum (negative) pressure that is below atmospheric pressure. 
     First liquid supply  324 , using regulated pressure source  316  and, optionally, regulated vacuum source  317 , regulates the velocity of the first liquid  325  moving through liquid dispensing channel  312  while second liquid supply  386 , using second regulated pressure source  335  and, optionally, second regulated vacuum source  336 , regulates the velocity of second liquid  384  moving through cavity  390  so that liquid pressure on both sides of diverter member  320  is balanced. This helps to minimize differences in liquid flow characteristics that may adversely affect liquid diversion and drop formation during operation. 
     As described above, liquid pressure balancing on both sides of diverter member  320  is also achieved by appropriately sizing liquid dispensing channel  312  and cavity  390  relative to each other. Again, keeping first liquid supply channel  311  and second liquid supply channel  331  are physically separated from each other and keeping first liquid return channel  313  and second liquid return channel  334  are physically separated from each other helps to facilitate pressure balancing on both sides of diverter member  320 . 
     Referring to  FIGS. 25A-25E  and back to  FIGS. 1A-2  and  19 A- 24 C, additional example embodiments of a flow-through liquid dispenser  310  are shown. A first portion  368  of substrate  339  defines liquid dispensing channel  312  and a second portion  370  of substrate  339  defines a liquid supply channel  311  and a liquid return channel  313 . Liquid dispensing channel  312  includes outlet opening  326 . Liquid supply  324  provides a flow of liquid  325  continuously from liquid supply  324  through the liquid supply channel  311  through the liquid dispensing channel  312  through the liquid return channel  313  and back to liquid supply  324 . Diverter member  320  is selectively actuated to divert a portion of the liquid  325  flowing through liquid dispensing channel  312  through outlet opening  326  of liquid dispensing channel  312 . Diverter member  320  is positioned on a wall  340  of liquid dispensing channel  312  that includes the outlet opening  326 . 
     Diverter member  320  includes a MEMS transducing member and a compliant membrane. In  FIGS. 25A-25D , the MEMS transducing member includes cantilevered beam  120 . A first portion  121  of the MEMS transducing member is anchored to wall  340  of liquid dispensing channel  312  that includes outlet opening  326 . A second portion of the MEMS transducing member extends into a portion of liquid dispensing channel  312  that is adjacent to outlet opening  326 . The second portion of the MEMS transducing member is free to move relative to outlet opening  326 . When actuated, diverter member  320  moves toward liquid dispensing channel  312  or toward outlet  326  depending on where diverter member  320  is positioned. 
     A compliant membrane  130  is positioned in contact with the MEMS transducing member. A first portion  131  of compliant membrane  130  separates the MEMS transducing member from the continuous flow  327  of liquid  325  through liquid dispensing channel  312 . A second portion  132  of compliant membrane  130  is anchored to the wall  340  of liquid dispensing channel  312  that includes outlet opening  326 . Typically, compliant membrane  130  is a compliant polymeric membrane made from one of the polymers described above. However, compliant membrane  130  can be any of the compliant membranes described above depending on the specific application contemplated. 
     Optionally, an insulating material covers a surface of the MEMS transducing member that is opposite a surface of the MEMS transducing member that contacts the compliant membrane. For example, a compliant passivation material  138  can be included on the side of the MEMS transducing material that is opposite the side that first portion  131  of compliant membrane  130  is located, as described above with reference to  FIG. 14 . Compliant passivation material  138  together with first portion  131  of compliant membrane  130  provide protection of the MEMS transducing member (for example, cantilevered beam  120 ) from the fluid being directed through liquid dispensing channel  312  or outlet opening  326 . 
     The continuous flow of liquid  325  flows in a direction  327 . As shown in  FIG. 25A , diverter member  320  is positioned on an upstream side of wall  340  of liquid dispensing channel  312  that includes outlet opening  326  relative to the direction  327  of liquid flow. In this configuration, the free end of the diverter member  320  moves toward outlet  326  when actuated (shown in  FIG. 25D ) causing the diverter member to be curved away from the liquid dispensing channel  312 . At least a portion of the flow of liquid moving through the liquid dispensing channel  312  adjacent to the outward curvature of the diverter member  320  will stay attached to the curved diverter member, diverting a portion of the flow toward the outlet  326  and creating an ejected drop  315 . As shown in  FIG. 25B , diverter member  320  is positioned on a downstream side of wall  340  of liquid dispensing channel  312  that includes outlet opening  326  relative to the direction  327  of liquid flow. In this configuration, diverter member  320  moves toward liquid dispensing channel  312  when actuated (shown in  FIG. 25D ). As the free end of the diverter member dips into the flow of liquid through the liquid dispensing channel, a portion of the flow is sheared off by the diverter member and directed toward the outlet  326 , forming an ejected drop  315 . In the embodiment shown in  FIG. 25D  and  FIG. 25E , the diverter member  320  includes a first MEMS transducing member and a second MEMS transducing member positioned one on the upstream and one on the downstream sides of the outlet opening  326 . The first and second MEMS transducing members can be actuated individually or together to divert a portion of the liquid flow toward the outlet to eject a drop  315 . 
     Referring to  FIGS. 26A and 26B , in some example embodiments, compliant membrane  130  defines a portion of the perimeter  392  of outlet opening  326 . In other example embodiments, compliant membrane includes an orifice  394 . First portion  121  of the MEMS transducing member and second  132  portion of compliant membrane  130  are anchored to the portion (for example, an upstream wall portion or a downstream wall portion) of wall  340  of liquid dispensing channel  312  that includes outlet opening  326 . A third portion  396  of compliant membrane  130  is anchored to another portion (for example, a downstream wall portion or an upstream wall portion, respectively) of wall  340  of liquid dispensing channel  312  that includes outlet opening  326 . In this configuration, orifice  394  of compliant membrane  130  defines the perimeter  392  of outlet opening  326 . Orifice  394  can be located between second portion  132  of compliant membrane  130  and third portion  396  of compliant membrane  130 . 
     In  FIGS. 25C ,  25 D, and  25 E diverter member  320  includes a first MEMS transducing member and a second MEMS transducing member. The second MEMS transducing member is positioned opposite the first MEMS transducing member. A first portion  398  of the second MEMS transducing member is anchored to another portion of wall  340  of liquid dispensing channel  312  that includes the outlet opening  326 . As shown, each of the first and second MEMS transducing members includes cantilevered beam  120  and first portion  398  of the second MEMS transducing member is anchored to a portion of wall  340  (a downstream wall portion) that is opposite the location where first portion  121  of the first MEMS transducing member is anchored to wall  340  (an upstream wall portion). 
     A second portion  400  of the MEMS transducing member extends into a portion of liquid dispensing channel  312  that is adjacent to outlet opening  326 . Second portion  400  of the second MEMS transducing member is free to move relative to outlet opening  326 . Compliant membrane  130  is positioned in contact with the second MEMS transducing member. A fourth portion  402  of compliant membrane  130  separates the second MEMS transducing member from the continuous flow  327  of liquid  325  through liquid dispensing channel  312 . As shown, third portion  396  of compliant membrane  130  is anchored to a downstream wall portion of wall  340  of liquid dispensing channel  312  and second  132  portion of compliant membrane  130  is anchored to an upstream wall portion of wall  340  of liquid dispensing channel  312 . 
     Compliant membrane  130  is initially positioned in a plane. The MEMS transducing member and the second MEMS transducing member are configured to be actuated out of the plane of compliant membrane  130 . As shown in  FIG. 25D , the first MEMS transducing member and the second MEMS transducing member are actuated in opposite directions. The first MEMS transducing member, anchored to an upstream wall portion of wall  340  of liquid dispensing channel  312 , moves toward outlet  326  when actuated. The second MEMS transducing member, anchored to a downstream wall portion of wall  340  of liquid dispensing channel  312 , moves toward liquid dispensing channel  312  when actuated. 
     Referring to  FIG. 27 , an example embodiment of a method of ejecting liquid using the liquid dispenser described above is shown. The method begins with step  500 . 
     In step  500 , a liquid dispenser is provided. The liquid dispenser includes a substrate and a diverter member. A first portion of the substrate defines a liquid dispensing channel including an outlet opening and a second portion of the substrate defines an outer boundary of a cavity. Other portions of the substrate define a liquid supply channel and a liquid return channel. The diverter member includes a MEMS transducing member. A first portion of the MEMS transducing member is anchored to the substrate. A second portion of the MEMS transducing member extends over at least a portion of the cavity and is free to move relative to the cavity. A compliant membrane is positioned in contact with the MEMS transducing member. A first portion of the compliant membrane covers the MEMS transducing member. A second portion of the compliant membrane is anchored to the substrate such that the compliant membrane forms a portion of a wall of the liquid dispensing channel. The wall is positioned opposite the outlet opening. Step  500  is followed by step  505 . 
     In step  505 , a continuous flow of liquid is provided from a liquid supply through the liquid supply channel through the liquid dispensing channel through the liquid return channel and back to the liquid supply. Step  505  is followed by step  510 . 
     In step  510 , the diverter member is selectively actuated to divert a portion of the liquid flowing through the liquid dispensing channel through outlet opening of the liquid dispensing channel when drop ejection is desired. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
     PARTS LIST 
     
         
         
           
               100  MEMS composite transducer 
               110  substrate 
               111  first surface of substrate 
               112  second surface of substrate 
               113  portions of substrate (defining outer boundary of cavity) 
               114  outer boundary 
               115  cavity 
               116  through hole (fluid inlet) 
               118  mass 
               120  cantilevered beam 
               121  anchored end (of cantilevered beam) 
               122  cantilevered end (of cantilevered beam) 
               130  compliant membrane 
               131  covering portion of compliant membrane 
               132  anchoring portion of compliant membrane 
               133  portion of compliant membrane overhanging cavity 
               134  portion where compliant membrane is removed 
               135  hole (in compliant membrane) 
               138  compliant passivation material 
               140  doubly anchored beam 
               141  first anchored end 
               142  second anchored end 
               143  intersection region 
               150  clamped sheet 
               151  outer boundary (of clamped sheet) 
               152  inner boundary (of clamped sheet) 
               160  MEMS transducing material 
               162  reference material 
               163  first layer (of reference material) 
               164  second layer (of reference material) 
               165  third layer (of reference material) 
               166  bottom electrode layer 
               167  seed layer 
               168  top electrode layer 
               171  first region (where transducing material is retained) 
               172  second region (where transducing material is removed) 
               200  fluid ejector 
               201  chamber 
               202  partitioning walls 
               204  nozzle plate 
               205  nozzle 
               310  liquid dispenser 
               311  liquid supply channel 
               312  liquid dispensing channel 
               313  liquid return channel 
               315  drop 
               316  regulated pressure supply source 
               317  regulated vacuum supply source 
               318  upstream edge 
               319  downstream edge 
               320  diverter member 
               320 A first side 
               320 B second side 
               321  exit 
               322  porous member 
               323  vent 
               324  liquid supply 
               325  liquid 
               326  outlet opening 
               327  arrows, flow direction 
               331  second liquid supply channel 
               334  second liquid return channel 
               335  second regulated pressure source 
               336  second regulated vacuum supply 
               338  entrance 
               339  substrate 
               340  wall 
               342  liquid supply passage 
               344  liquid return passage 
               346  wall 
               348  wall 
               350  upstream edge 
               352  downstream edge 
               354  surface 
               354 A interior surface 
               354 B exterior surface 
               356  corners 
               358  centerline 
               360  centerline 
               362  apex 
               364  width 
               366  width 
               368  first portion 
               370  second portion 
               372  other portions 
               374  other portions 
               376  wall 
               378  upstream portion 
               380  second wall 
               382  downstream portion 
               384  second liquid 
               386  second liquid supply 
               388  arrows 
               390  cavity 
               392  outlet opening perimeter 
               394  orifice 
               396  third portion 
               398  first portion 
               400  second portion 
               402  fourth portion