# Patent

## Title
Ink jet printing module

## Abstract

A method of manufacturing an ink jet printing module can include forming a piezoelectric element having a stiffened surface.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part application of and claims priority under 35 U.S.C.§120 to U.S. application Ser. No. 10/020,217, entitled “LOW VOLTAGE INK JET PRINTING MODULE,” filed on Dec. 18, 2001, now U. S. Pat. No. 6,824,253, the entire contents of which are hereby incorporated by reference.


TECHNICAL FIELD
This invention relates to a method of manufacturing a low voltage ink jet printing module.
BACKGROUND
An ink jet printing module ejects ink from an orifice in the direction of a substrate. The ink can be ejected as a series of droplets generated by a piezoelectric ink jet printing module. An example of a particular printing module can have 256 jets in four groups of 64 jets each. A piezoelectric ink jet printing module can include a module body, a piezoelectric element, and electrical contacts that drive the piezoelectric element. Typically, the module body is a rectangular member into the surfaces of which are machined a series of ink chambers that serve as pumping chambers for the ink. The piezoelectric element can be disposed over the surface of the body to cover the pumping chambers in a manner to pressurize the ink in the pumping chambers to eject the ink.
SUMMARY
In general, an ink jet printing module includes a stiffened piezoelectric element. The stiffened piezoelectric element improves jetting of ink when a low voltage is applied to the element compared to non-stiffened piezoelectric element. This can also allow ink jet modules to be smaller because the piezoelectric element has been strengthened. The stiffened piezoelectric element has a rigidity in at least one dimension that is higher than a flat piezoelectric element. The stiffened piezoelectric element can have a curved surface to strengthen the element. The module can jet ink when driven with a voltage of less than 60 volts.
In one aspect, a method of manufacturing an ink jet printing module includes injection molding a precursor into a mold to form a stiffened piezoelectric element, and positioning the piezoelectric element over an ink chamber to subject ink within the chamber to a jetting pressure upon applying a jetting voltage.
In another aspect, a method of depositing ink includes delivering ink to an ink chamber, and applying a jetting voltage across a first electrode and a second electrode on a face of a stiffened piezoelectric element to subject ink within the chamber to a jetting pressure, thereby depositing ink from an exit orifice of the ink chamber.
In another aspect, an ink jet printing module includes an ink chamber, a stiffened piezoelectric element having a region exposed to the ink chamber, and electrical contacts arranged on a surface of the piezoelectric element for activation of the piezoelectric element when a jetting voltage is applied to the electrical contacts. The piezoelectric element is positioned over the ink chamber to subject ink within the chamber to jetting pressure. The region of the stiffened piezoelectric element exposed to the ink chamber can have a curved surface.
In another aspect, the invention features an ink jet printhead module including an ink chamber, a stiffened piezoelectric element having a region adjacent to the ink chamber, the piezoelectric element being positioned over the ink chamber to subject ink within the chamber to jetting pressure, wherein the region of the stiffened piezoelectric element adjacent the ink chamber has a curved surface that substantially spans the ink chamber along a first direction and a second direction, wherein the curved surface has a substantially constant radius of curvature along the first direction and a substantially constant radius of curvature along the second direction, and wherein the first and second direction are orthogonal.
Embodiments may include one or more of the following features.
The curved surface can be concave relative to the ink chamber. The ink jet printhead module can further include a membrane positioned between the stiffened piezoelectric element and the ink chamber. The membrane can include an electrically insulating material (e.g., kapton or SiO2). The ink jet printhead module can further include one or more electrical contacts positioned between the membrane and the stiffened piezoelectric element. The membrane can be a piece of flex print and the flex print extends beyond the stiffened piezoelectric element. In some embodiments, the ink jet printhead further includes electrical contacts arranged relative to the piezoelectric element for activation of the piezoelectric element. At least one of the electric contacts can be on an opposite side of the piezoelectric element to other electrical contacts.
The radius of curvature along the first direction can be substantially the same as the radius of curvature along the second direction. The first radius of curvature can be equal to or greater than the second radius of curvature. The first radius of curvature can be about 5 millimeters or less (e.g., about 3 millimeters or less). In some embodiments, the first radius of curvature is from about 500 to about 3000 microns (e.g., from about 1000 to about 2800 microns, from about 1500 to about 2600 microns). The piezoelectric element can have a thickness of about 5 to about 300 microns (e.g., of about 10 to about 250 microns, of about 100 microns or less). The ink chamber can have a width along the first direction of about 1200 microns or less (e.g., from about 50 to about 1000 microns).
The ink jet printing module can include a series of ink chambers. Each of the ink chambers can be covered by the piezoelectric element. The ink chamber can include a wall contacting the piezoelectric element exposed to the ink chamber at an angle of greater than ninety degrees.
Printhead modules can include piezoelectric elements with relatively high stiffness. For example, piezoelectric elements can include a curved region, having a constant radius of curvature in both directions. The curvature can increase the elements stiffness by reducing its ability to deform when activated.
Details are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.



DESCRIPTION OF DRAWINGS
FIGS. 1A and 1B are schematic diagrams depicting an ink jet printing module.
FIG. 2 is a schematic diagram depicting a portion of an ink jet printing module.
FIG. 3 is a schematic diagram depicting a piezoelectric element.
FIG. 4 is a graph depicting pressure generated in an ink chamber as the thickness of the piezoelectric element and curvature is varied.
FIG. 5 is a graph depicting the change in volume generated in an ink chamber as the thickness of the piezoelectric element and curvature is varied.
FIG. 6 is a schematic diagram depicting a piezoelectric element.
FIG. 7 is a graph depicting pressure generated in an ink chamber as the thickness of the piezoelectric element and curvature is varied.
FIG. 8 is a graph depicting the drop volume generated by an ink chamber as the thickness of the piezoelectric element and curvature is varied.
FIG. 9 is a graph depicting the drop volume generated by an ink chamber as the thickness of the piezoelectric element and curvature is varied.
FIG. 10 is a graph depicting pressure generated in an ink chamber as the thickness of the piezoelectric element and curvature is varied.
FIG. 11 is a graph depicting the drop volume generated by an ink chamber as the thickness of the piezoelectric element and curvature is varied.
FIG. 12A and FIG. 12B are schematic diagrams depicting a piezoelectric element through two orthogonal sections.



DETAILED DESCRIPTION
An ink jet printing module includes a piezoelectric element positioned over jetting regions of a body. The jetting regions can be portions of pumping chambers within the body. The pumping chambers can be sealed. Electrical contacts, such as electrodes, can be positioned on a surface of the piezoelectric element. The piezoelectric element spans each jetting region. When a voltage is applied to an electrical contact, the shape of the piezoelectric element changes in a jetting region, thereby subjecting the ink within the corresponding pumping chamber to jetting pressure. The ink is ejected from the pumping chamber and deposited on a substrate.
One example of a piezoelectric ink jet printing module is a shear mode module, such as the module described in U.S. Pat. No. 5,640,184, the entire contents of which is incorporated herein by reference. The electrical contacts in a shear mode module can be located on the side of the piezoelectric element adjacent to the ink chamber. Referring to FIGS. 1A, 1B and 2, piezoelectric ink jet head 2 includes one or more modules 4 which are assembled into collar element 10 to which is attached manifold plate 12 and orifice plate 14. Ink is introduced into module 4 through collar 10. Module 4 is actuated to eject ink from orifices 16 on orifice plate 14. Inkjet printing module 4 includes body 20, which can be made from materials such as sintered carbon or a ceramic. A plurality of chambers 22 are machined or otherwise manufactured into body 20 to form pumping chambers.
Ink passes through ink fill passage 26, which is also machined into body 20, to fill the pumping chambers. Opposing surfaces of body 4 include a series of electrical contacts 31 and 31′ arranged to be positioned over the pumping chambers in body 20. Electrical contacts 31 and 31′ are connected to leads, which, in turn, can be connected to integrated circuits 33 and 33′. The components are sealed together to form the print module.
Referring to FIG. 2, piezoelectric element 34 has electrodes 40 on one surface of the piezoelectric element 34. Electrodes 40 register with electrical contacts 31, allowing the electrodes to be individually addressed by a driver integrated circuit. Electrodes 40 can be formed by chemically etching away conductive metal that has been deposited onto the surface of the piezoelectric element. Suitable methods of forming electrodes are also described in U.S. Pat. No. 6,037,707, which is herein incorporated by reference in its entirety. The electrode can be formed of conductors such as copper, aluminum, titanium-tungsten, nickel-chrome, or gold. Each electrode 40 is placed and sized to correspond to a chamber 22 in body 4 to form a pumping chamber. Each electrode 40 has elongated region 42, having a length and width slightly narrower than the dimensions of the pumping chamber such that gap 43 exists between the perimeter of electrodes 40 and the sides and end of the pumping chamber. These electrode regions 42, which are centered on the pumping chambers, are the drive electrodes that cover a jetting region of piezoelectric element 34. A second electrode 52 on piezoelectric element 34 generally corresponds to the area of body 20 outside chamber 22, and, accordingly, outside the pumping chamber. Electrode 52 is the common (ground) electrode. Electrode 52 can be comb-shaped (as shown) or can be individually addressable electrode strips. The film electrodes and piezoelectric element electrodes overlap sufficiently for good electrical contact and easy alignment of the film and the piezoelectric element.
The piezoelectric element can be a single monolithic lead zirconium titanate (PZT) member. The piezoelectric element drives the ink from the pumping chambers by displacement induced by an applied voltage. The displacement is a function of, in part, the poling of the material. The piezoelectric element is poled by the application of an electric field. A poling process is described, for example, in U.S. Pat. No. 5,605,659, which is herein incorporated by reference in its entirety. The degree of poling can depend on the strength and duration of the applied electric field. When the poling voltage is removed, the piezoelectric domains are aligned. The piezoelectric element can have a thickness of 5 to 300 microns, 10 to 250 microns, 15 to 150 microns, less than 100 microns, or less than 50 microns.
Subsequent applications of an electric field, for example, during jetting, can cause a shape change proportional to the applied electric field strength.
The piezoelectric element can be stiffened, for example, by introducing a curved surface in a portion of the element that covers the ink chamber. The curved surface can have a substantially constant curvature, such as a spherical or cylindrical shape. Referring to FIG. 3, a region 100 of piezoelectric element 34 is curved. The curvature of the piezoelectric element 34 is concave relative to ink chamber 102. The concave curvature of the surface can reduce buckling that otherwise may occur during jetting. Walls 104 of the chamber 102 can be oriented to contact the stiffened piezoelectric element 34 at an angle of greater than ninety degrees. The chamber can have a width of less than 1200 microns, a width of 50 to 1000 microns, or a width of 100 to 800 microns. Electrodes 42 and 52 are on surface 106 of the piezoelectric element 34. By applying a jetting voltage across the electrodes, ink within the chamber is subjected to a jetting pressure, which deposits ink from an exit orifice of the ink chamber. For example, the jetting voltage can be less than 60 volts.
The curved surface can have a substantially constant radius of curvature. The degree of curvature, or radius of curvature, affects the stiffness and jetting characteristics of the module. The radius of curvature is the radius of a circle drawn to encompass the curved surface. The curved surface can have a radius of curvature of less than 5 millimeters, or less than 3 millimeters. The curved surface can have a radius of curvature of 500 to 3000 microns, 1000 to 2800 microns, or 1500 to 2600 microns. The curved surface can be a cylindrical section or a spherical section.
The ink jet printing module can be prepared by forming a stiffened piezoelectric element, and positioning the piezoelectric element over an ink chamber to subject ink within the chamber to a jetting pressure upon applying a jetting voltage. The stiffened piezoelectric element can be prepared by grinding a curved surface into a thin layer of piezoelectric material or by injection molding a precursor into a mold having the curved surface features of the piezoelectric element. For example, a mixture can be prepared from a piezoelectric material powder and an organic binder. The mixture is injection molded to form a green sheet, which can be heated to remove the binder. The green sheet can be a thin film having a thickness of 10 to 50 microns, or 20 to 40 microns. The powder can be sintered, for example, to at least about 95% of theoretical density. Injection molding to form a piezoelectric article is described, for example, in U.S. Pat. No. 5,340,510, which is incorporated by reference in its entirety.
Referring to FIGS. 12A and 12B, in certain embodiments, a printhead module 1201 includes a region 1200 of a piezoelectric element 1234 that is curved in more than one direction. FIG. 12A shows a section of piezoelectric element 1234 along a one direction, while FIG. 12B shows a section of piezoelectric element 1234 along an orthogonal direction. The curvature of piezoelectric element 1234 is concave relative to an ink chamber 1202, and curved region 1200 spans ink chamber 1202 in both directions. Walls 1204 of chamber 1202 can be oriented to contact the stiffened piezoelectric element 1234 at an angle of greater than ninety degrees.
In general, the curvature of region 1200 can be the same or different through both directions. The radius of curvature, for each direction, can be constant or can vary.
Electrical contacts 1242 and 1252 are positioned on opposite sides of stiffened piezoelectric element 1234. Electrodes can be formed from electrically conductive materials, such as gold, aluminum, or other metals. In some embodiments, the electrical contacts can be formed from electrically conductive alloys, such as ‘Ti-tungsten’ (Au/Ti—W), or electrically conductive oxides, such as ITO (Indium-Tin-Oxide).
Printhead module 1201 also includes a membrane 1210 positioned between piezoelectric element 1234 and ink chamber 1202. Membrane 1210 protects electrical contact 1252 from ink in the ink chamber. In general, membrane 1210 is formed from a flexible material so that it can accommodate extension of piezoelectric element 1234 during activation. In some embodiments, membrane 1210 is formed from an electrically conductive material, such as nickel, copper, gold, and/or other metals, or a semiconductor, such as silicon. Alternatively, membrane 1210 is formed from an electrically insulating material, such as silicon dioxide or kapton. Membrane 1210 can also be formed from a polymer, or a mixture of two or more materials, such as a mixture of silicon nitride and silicon dioxide, for example. In certain embodiments, membrane 1210 is a piece of flex print, which carries electrical contact 1252.
In general, the thickness of membrane 1210 can vary as desired. In some embodiments, membrane 1210 can be relatively thin, such as about 10 microns or less thick (e.g., from about 0.5 microns to about 5 microns).
The curvature stiffens the piezoelectric element and improves jetting of ink when a low voltage is applied to the element. A comparable ink jet printing module having a flat piezoelectric element requires application of a higher voltage to jet an ink drop of comparable volume. A concave surface relative to the chamber can lead to higher positive pressure within the chamber than negative pressure during jetting, for example, a pressure during jetting that can be up to two times higher the pressure during chamber filling. Reducing the dimensions of the ink jet printing module can also lead to higher voltage requirements to achieve a given drop volume. Smaller jets can make the printhead more compact. The stiffened element can also allow ink jet modules to be made smaller because the piezoelectric element has a rigidity in at least one dimension that is higher than a flat piezoelectric element. When the piezoelectric element is curved in the resting state, the deflection normal to the piezoelectric element can be amplified relative to a flat plate. Moreover, thinner ink chambers can allow smaller-dimensioned jets having improved performance to be made.
While certain embodiments of ink jet printhead modules have been described, the components of the described modules can be adapted for use in other modules. For example, components such as curved piezoelectric elements can be used in the printhead modules described in U.S. patent application Ser. No. 10/189,947, entitled “PRINTHEAD,” filed on Jul. 3, 2002, the entire contents of which is hereby incorporated by reference.
Finite element analysis modeling of structures having a cylindrical shape (as shown in FIG. 3), a particular radius of curvature, and operated in an extension mode, demonstrated the improved pumping performance of the stiffened piezoelectric element relative to a flat element. In the model, ANSYS multiphysics coupled field analysis (ANSYS Version 5.7, ANSYS Inc. of Canonsburg, Pa.) was employed using the parameters of an ink chamber diameter of 0.102 cm, an ink chamber depth of 0.152 mm, lead zirconium titanate (PZT 5A, Morgan Electro Ceramics, Bedford, Ohio) poled in the thickness direction, a cavity plate constructed of KOVAR® (a low expansion iron-nickel-cobalt alloy available from High Temp Metals, Inc., Sylmar, Calif.), land piezoelectric width (the distance between chambers) of 0.254 mm, an ink density of 1000 kg/m3, a pulse voltage of 50 volts, element thickness ranging from 1 mil (25.4 microns) to 10 mils (254 microns) and a radius of curvature of 30 mils, 40 mils, 50 mils, 100 mils or infinity (flat). The pressures and displacements generated by stiffened piezoelectric elements having particular thicknesses and radii of curvature are listed in Table 1. Pressures and total volume generated by stiffened piezoelectric elements are depicted in FIGS. 4 and 5. A comparative example of a flat piezoelectric element at a jetting voltage of 100 volts in shear mode is included as a comparison.











TABLE 1






PZT
Radius of
Maximum




Thickness
curvature
Displacement
Pressure


Example
(mils)
(mils)
(μm/μin)
(Pa/PSI)







1
8 (203
100 (2.54 mm)
0.0229/0.901
 −73424/−10.6



microns)


2
5 (127
100 (2.54 mm)
0.0655/2.61
−122827/−17.8



microns)


3
8
 50 (1.27 mm)
0.0347/1.36
 −96501/−13.9


4
5
 50 (1.27 mm)
0.0852/3.35
−172939/−25.1









Finite element analysis modeling of structures depicted in FIG. 6 having a spherical shape, a particular radius of curvature, operated in extension mode, and a constant total chamber volume also demonstrated the improved pumping performance of the stiffened piezoelectric element relative to a flat element. In this model, ANSYS multiphysics coupled field analysis was employed using the parameters of an ink chamber diameter of 0.102 cm, lead zirconium titanate (PZT 5A) poled in thickness direction, a cavity plate constructed of KOVAR®, land piezoelectric width (the distance between chambers) of 0.254 mm, an ink density of 1000 kg/m3, a pulse voltage of 50 volts, piezoelectric element thickness ranging from 1 mil (25.4 microns) to 10 mils (254 microns) and a radius of curvature of 20 mils, 30 mils, 40 mils, 50 mils or infinity (flat). The volume of pumping chamber was kept at 3.14×10−10 m3, which is same as the total volume in the comparative case. Since the chamber diameter is also a constant (0.102 cm) and the radius of curvature varies, the chamber depth becomes a variable. The chamber depth for each radius of curvature was: R=20 mil, depth=2 mil; R=30 mil, depth=11.33 mil; R=40 mil, depth=12.59 mil; or R=50 mil, depth=13.22 mil. The pressures and drop volumes generated by stiffened piezoelectric elements having particular thicknesses and radii of curvature are listed in Table 2. Chamber pressures and drop volumes generated by stiffened piezoelectric elements are depicted in FIGS. 7 and 8. A comparative example of a flat piezoelectric element at a jetting voltage of 100 volts in shear mode is included as a comparison.











TABLE 2






PZT
Radius of
Drop
Chamber



Thickness
curvature
Volume
Pressure


Example
(mils)
(mils)
(pL)
(PSI)



















 5
1
50
131.228
87.214


 6
1
40
133.948
89.039


 7
1
30
129.770
86.219


 8
1
20
108.323
71.975


 9
2
50
79.418
52.793


10
2
40
79.210
52.621


11
2
30
74.931
49.938


12
2
20
65.243
43.350


13
3
50
52.607
35.003


14
3
40
53.339
35.462


15
3
30
52.048
34.591


16
3
20
47.289
31.421


17
4
50
37.363
24.844


18
4
40
38.614
25.704


19
4
30
38.713
25.760


20
4
20
37.351
24.817


21
5
50
27.841
18.509


22
5
40
29.173
19.464


23
5
30
30.405
20.245


24
5
20
30.862
20.534


25
6
50
21.410
14.270


26
6
40
22.986
15.312


27
6
30
24.595
16.370


28
6
20
26.384
17.548


29
7
50
17.299
11.529


30
7
40
18.723
12.486


31
7
30
20.271
13.555


32
7
20
23.093
15.371


33
8
50
14.300
9.555


34
8
40
15.564
10.393


35
8
30
16.819
11.274


36
8
20
20.519
13.680


Comparative
10
Flat
46.221
29.008


 37a





a100 V driving voltage






Additional finite element analysis modeling of structures depicted in FIG. 6 having a spherical shape, a particular radius of curvature, operated in extension mode, and a constant total volume demonstrated the improved pumping performance of the stiffened piezoelectric element relative to a flat element. In this model, ANSYS multiphysics coupled field analysis was employed using the parameters of an ink chamber diameter of 0.102 cm, an ink chamber depth of 0.152 mm, lead zirconium titanate (PZT 5A) poled in thickness direction, a cavity plate constructed of KOVAR®, land piezoelectric width (the distance between chambers) of 0.254 mm, an ink density of 1000 kg/m3, a pulse voltage of 50 volts, piezoelectric element thickness ranging from 1 mil (25.4 microns) to 8 mils (203 microns) and a radius of curvature of 20 mils, 30 mils, 40 mils, or 50 mils. Since the chamber diameter is also a constant (0.102 cm) and the radius of curvature varies, the chamber depth becomes a variable. The chamber depth for each radius of curvature was: R=20 mil, depth=2 mil; R=30 mil, depth=11.33 mil; R=40 mil, depth=12.59 mil; or R=50 mil, depth=13.22 mil. The drop volumes generated by stiffened piezoelectric elements having particular thicknesses and radii of curvature are depicted in FIG. 9.
Other finite element analysis modeling of structures depicted in FIG. 6 having a spherical shape, a particular radius of curvature, operated in extension mode, and a constant total chamber volume also demonstrated the improved pumping performance of the stiffened piezoelectric element relative to a flat element. In this model, ANSYS multiphysics coupled field analysis was employed using the parameters of an ink chamber diameter of 0.102 cm, an ink chamber depth of 0.152 mm, lead zirconium titanate (PZT 5A) poled in thickness direction, a cavity plate constructed of KOVAR®, land piezoelectric width (the distance between chambers) of 0.254 mm, an ink density of 1000 kg/m3, a pulse voltage of 15 volts, piezoelectric element thickness of 0.04 mil (1 micron), 0.10 mil (2.5 microns), 0.30 mil (7.5 microns), 0.50 mil (12.5 microns) or 10 mils (254 microns) and a radius of curvature of 30 mils, 40 mils, 50 mils or infinity (flat). Since the chamber diameter is also a constant (0.102 cm) and the radius of curvature varies, the chamber depth becomes a variable. The chamber depth for each radius of curvature was: R=30 mil, depth=11.33 mil; R=40 mil, depth=12.59 mil; or R=50 mil, depth=13.22 mil. The pressures and drop volumes generated by stiffened piezoelectric elements having particular thicknesses and radii of curvature are listed in Table 3. Chamber pressures and drop volumes generated by stiffened piezoelectric elements are depicted in FIGS. 10 and 11. A comparative example of a flat piezoelectric element at a jetting voltage of 100 volts in shear mode is included as a comparison.











TABLE 3






PZT
Radius of
Drop
Chamber



Thickness
curvature
Volume
Pressure


Example
(mils)
(mils)
(pL)
(PSI)



















38
0.04
30
77.121
116.199


39
0.04
40
62.607
94.260


40
0.04
50
51.683
77.890


41
0.10
30
69.069
104.067


42
0.10
40
58.078
87.422


43
0.10
50
48.929
73.738


44
0.30
30
50.714
76.390


45
0.30
40
46.576
70.108


46
0.30
50
41.443
62.445


47
0.50
30
39.929
60.113


48
0.50
40
38.690
58.226


49
0.50
50
35.797
53.901


Comparative


29.008
46.221


 50a





a100 V driving voltage






While the foregoing embodiments refer to jetting ink, in general, embodiments disclosed herein can also be used in the jetting of other fluids as well. For example, printhead modules can be used to deposit materials used in optical or electronic devices, such as organic light emitting polymers during manufacturing of an electronic display and/or conductive materials for use in conducting wires in circuits. As another example, printhead modules can be used to deposit adhesives, particularly in applications where precise application of the adhesive to a substrate is desired. In some embodiments, printhead modules can be used to meter biological materials, such as fluids containing nucleic acids or pharmacologically active compounds.
A number of embodiments have been described. Other embodiments are within the scope of the following claims.

## Claims

1. An ink jet printhead module comprising:
an ink chamber;
a stiffened piezoelectric element having a curved region adjacent to the ink chamber, the piezoelectric element being positioned over the ink chamber to subject ink within the chamber to jetting pressure,
wherein the curved region of the stiffened piezoelectric element adjacent the ink chamber spans the ink chamber along a first direction and a second direction, the curved region having a substantially constant radius of curvature along the first direction and a substantially constant radius of curvature along the second direction, and wherein the first and second direction are orthogonal.

2. The ink jet printhead module of claim 1, wherein the curved region is concave relative to the ink chamber.

3. The ink jet printhead module of claim 1, further comprising a membrane positioned between the stiffened piezoelectric element and the ink chamber.

4. The ink jet printhead module of claim 1, wherein the membrane comprising an electrically insulating material.

5. The ink jet printhead module of claim 4, wherein the membrane is a kapton membrane.

6. The ink jet printhead module of claim 4, wherein the membrane is a SiO.sub.2 membrane.

7. The ink jet printhead module of claim 4, further comprising one or more electrical contacts positioned between the membrane and the stiffened piezoelectric element.

8. The ink jet printhead module of claim 4, wherein the membrane is a piece of flex print and the flex print extends beyond the stiffened piezoelectric element.

9. The ink jet printhead module of claim 1, further comprising electrical contacts arranged relative to the piezoelectric element for activation of the piezoelectric element.

10. The ink jet printhead module of claim 9, wherein at least one of the electric contacts is on an opposite side of the piezoelectric element to other electrical contacts.

11. The ink jet printhead module of claim 1, wherein the radius of curvature along the first direction is substantially the same as the radius of curvature along the second direction.

12. The ink jet printhead module of claim 1, wherein the first radius of curvature is equal to or greater than the second radius of curvature.

13. The ink jet printhead module of claim 1, wherein the first radius of curvature is about 5 millimeters or less.

14. The ink jet printhead module of claim 1, wherein the first radius of curvature is about 3 millimeters or less.

15. The ink jet printhead module of claim 1, wherein the first radius of curvature is from about 500 to about 3000 microns.

16. The ink jet printhead module of claim 1, wherein the first radius of curvature is from about 1000 to about 2800 microns.

17. The ink jet printhead module of claim 1, wherein the first radius of curvature is from about 1500 to about 2600 microns.

18. The ink jet printhead module of claim 1, wherein the piezoelectric element has a thickness of about 5 to about 300 microns.

19. The ink jet printhead module of claim 1, wherein the piezoelectric element has a thickness of about 10 to about 250 microns.

20. The ink jet printhead module of claim 1, wherein the piezoelectric element has a thickness of about 100 microns or less.

21. The ink jet printhead module of claim 1, wherein the ink chamber has a width along the first direction of about 1200 microns or less.

22. The ink jet printhead module of claim 1, wherein the ink chamber has a width along the first direction from about 50 to about 1000 microns.

23. The ink jet printhead module of claim 1, further comprising a series of ink chambers.

24. The ink jet printhead module of claim 23, wherein each of the ink chambers is covered by the piezoelectric element.

25. The ink jet printhead module of claim 1, wherein the ink chamber includes a wall contacting the piezoelectric element exposed to the ink chamber at an angle of greater than ninety degrees.

26. The ink jet printhead module of claim 1, wherein the ink chamber is defined by opposing walls that contact the curved region at an angle greater than ninety degrees.

27. The ink jet printhead module of claim 1, wherein the curved region entirely spans the ink chamber.