Integrated circuit device having electrothermal actuators

An integrated circuit device includes a substrate. Drive circuitry is arranged on the substrate. A plurality of micro-electromechanical devices is positioned on the substrate. Each device includes an elongate electrothermal actuator having a fixed end that is fast with the substrate so that the actuator is connected to the drive circuitry and a free end that is displaceable along a path relative to the substrate to perform work when the actuator receives an electrical signal from the drive circuitry. A heat sink is positioned intermediate ends of the actuator to disperse excessive heat build-up in the actuator.

FIELD OF THE INVENTION

The present invention relates to an integrated circuit device. In particular, this invention relates to an integrated circuit device having electrothermal actuators. The invention has broad applications to such devices as micro-electromechanical pumps and micro-electromechanical movers.

BACKGROUND OF THE INVENTION

Micro-electromechanical devices are becoming increasingly popular and normally involve the creation of devices on the micron scale utilizing semi-conductor fabrication techniques. For a review on micro-electromechanical devices, reference is made to the article “The Broad Sweep of Integrated Micro Systems” by S. Tom Picraux and Paul J. McWhorter published December 1998 in IEEE Spectrum at pages 24 to 33.

One form of micro-electromechanical device is an ink jet printing device in which ink is ejected from an ink ejection nozzle chamber.

Many different techniques on ink jet printing and associated devices have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207 to 220 (1988).

Recently, a new form of ink jet printing has been developed by the present applicant that uses micro-electromechanical technology. In one form, ink is ejected from an ink ejection nozzle chamber utilizing an electromechanical actuator connected to a paddle or plunger which moves towards the ejection nozzle of the chamber for ejection of drops of ink from the ejection nozzle chamber.

The present invention concerns, but is not limited to, an integrated circuit device that incorporates improvements to an electromechanical bend actuator for use with the technology developed by the Applicant.

DEFINITIONS

In this specification, the phrase “electrothermal actuator” is to be understood as an actuator that is capable of displacement upon heating. Such actuators generally use differential thermal expansion to generate movement. For example, such an actuator may incorporate a heating circuit that is positioned such that heating and subsequent expansion of the heating circuit and a region about the heating circuit results in deformation of the actuator. If the actuator is anchored to a substrate, the deformation results in movement of the actuator. The movement is harnessed to perform work.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided an integrated circuit device which comprisesa substrate;drive circuitry arranged on the substrate; anda plurality of micro-electromechanical devices positioned on the substrate, each device comprising:an elongate electrothermal actuator having a fixed end that is fast with the substrate so that the actuator is connected to the drive circuitry and a free end that is displaceable along a path relative to the substrate to perform work when the actuator receives an electrical signal from the drive circuitry, whereina heat sink is positioned intermediate ends of the actuator to disperse excessive heat build-up in the actuator.

The actuator may include a pair of elongate arms that are spaced relative to each other along the path and are connected to each other at each end, with one of the arms being connected to the drive circuitry to define a heating circuit and being of a material that is capable of expansion when heated, such that, when the heating circuit receives the electrical signal from the drive circuitry, that arm expands relative to the other to deform the actuator and thus displace said free end along said path.

The heat sink may be positioned on the arm that defines the heating circuit.

Each micro-electromechanical device may include a fluid ejection member that is positioned on the free end of the actuator, the integrated circuit device including a plurality of fluid chambers positioned on the substrate, with the substrate defining fluid flow paths that communicate with the fluid chambers, each fluid ejection member being positioned in a respective fluid chamber to eject fluid from the fluid chamber on displacement of the actuator.

A sidewall and a roof wall may define each fluid chamber. The roof wall may define an ejection port. The fluid ejection member may be displaceable towards and away from the ejection port to eject fluid from the ejection port.

Each fluid ejection member may be in the form of a paddle member that spans a region between the respective fluid chamber and the respective fluid flow path so that, when the heating circuit receives a signal from the drive circuitry, the paddle member is driven towards the fluid ejection port and fluid is drawn into the respective fluid chamber.

Each paddle member may have a projecting formation positioned on a periphery of the paddle member. The formation may project towards the ejection port so that the efficacy of the paddle member can be maintained while inhibiting contact between the paddle member and a meniscus forming across the ejection port.

Each actuator may include at least one strut that is fast with each arm at a position intermediate ends of the arms.

According to a second aspect of the invention, there is provided a mechanical actuator for micro mechanical or micro electromechanical devices, the actuator comprising:a supporting substrate;an actuation portion;a first arm attached at a first end thereof to the substrate and at a second end to the actuation portion, the first arm being arranged, in use, to be conductively heated;a second arm attached at a first end to the supporting substrate and at a second end to the actuation portion, the second arm being spaced apart from the first arm, whereby the first and second arms define a gap between them;at least one strut interconnecting the first and second arms between the first and second ends thereof; andwherein, in use, the first arm is arranged to undergo expansion, thereby causing the actuator to apply a force to the actuation portion.

Preferably the first arm includes a first main body formed between the first and second ends of the first arm. Preferably the second arm includes a second main body formed between the first and second ends of the second arm. A second tab may extend from the second main body. The first one of the at least one strut may interconnect the first and second tabs.

Preferably the first and second tabs extend from respective thinned portions of the first and second main bodies.

Preferably the first arm includes a conductive layer that is conductively heated to cause, in use, the first arm to undergo thermal expansion relative to the second arm thereby to cause the actuator to apply a force to the actuation portion.

Preferably the first and second arms are substantially parallel and the strut is substantially perpendicular to the first and second arms.

Preferably a current is supplied in use, to the conductive layer through the supporting substrate.

Preferably the first and second arms are formed from substantially the same material.

Preferably the actuator is manufactured by the steps of:depositing and etching a first layer to form the first arm;depositing and etching a second layer to form a sacrificial layer supporting structure over the first arm;depositing and etching a third layer to form the second arm; andetching the sacrificial layer to form the gap between the first and second arms.

Preferably the first arm includes two first elongated flexible strips conductively interconnected at the second arm. Preferably the second arm includes two second elongated flexible strips. Preferably the actuation portion comprises a paddle structure.

Preferably the first arm is formed from titanium nitride. Preferably the second arm is formed from titanium nitride.

DETAILED DESCRIPTION OF THE DRAWINGS

InFIGS. 1to3, reference numeral10generally indicates a first embodiment of a nozzle arrangement of an integrated circuit device, in accordance with the invention.

The nozzle arrangement10is one of a plurality that comprises the device. One has been shown simply for the sake of convenience.

The nozzle arrangement10includes a wafer substrate12. A layer of a passivation material20, such as silicon nitride, is positioned on the wafer substrate12. A nozzle chamber wall14and a roof wall16are positioned on the wafer substrate12to define a nozzle chamber18. The roof wall16defines an ejection port22that is in fluid communication with the nozzle chamber18.

An inlet channel24extends through the wafer substrate12and the passivation material20into the nozzle chamber18so that fluid to be ejected from the nozzle chamber18can be fed into the nozzle chamber18. In this particular embodiment the fluid is ink, indicated at26. Thus, the fluid ejection device of the invention can be in the form of an inkjet print-head chip.

The nozzle arrangement10includes a thermal actuator28for ejecting the fluid26from the nozzle chamber18. The thermal actuator28includes a paddle30that is positioned in the nozzle chamber18, between an outlet of the inlet channel24and the ejection port22so that movement of the paddle30towards and away from the ejection port22results in the ejection of fluid26from the ejection port.

The thermal actuator28includes an actuating arm32that extends through an opening33defined in the nozzle chamber wall14and is connected to the paddle30.

The actuating arm32includes an actuating portion34that is connected to CMOS layers (not shown) positioned on the substrate12to receive electrical signals from the CMOS layers.

The actuating portion34has a pair of spaced actuating members36. The actuating members36are spaced so that one of the actuating members36.1is spaced between the other actuating member36.2and the passivation layer20and a gap38is defined between the actuating members36. Thus, for the sake of convenience, the actuating member36.1is referred to as the lower actuating member36.1, while the other actuating member is referred to as the upper actuating member36.2.

The lower actuating member36.1defines a heating circuit and is of a material having a coefficient of thermal expansion that permits the actuating member36.1to perform work upon expansion. The lower actuating member36.1is connected to the CMOS layers to the exclusion of the upper actuating member36.2. Thus, the lower actuating member36.1expands to a significantly greater extent than the upper actuating member36.2, when the lower actuating member36.1receives an electrical signal from the CMOS layers. This causes the actuating arm32to be displaced in the direction of the arrows40inFIG. 2, thereby causing the paddle30and thus the fluid26also to be displaced in the direction of the arrows40. The fluid26thus defines a drop42that remains connected, via a neck44to the remainder of the fluid26in the nozzle chamber18.

The actuating members36are of a resiliently flexible material. Thus, when the electrical signal is cut off and the lower actuating member36.1cools and contracts, the upper actuating member serves to drive the actuating arm32and paddle30downwardly in the direction of an arrow29, thereby generating a reduced pressure in the nozzle chamber18, which, together with the forward momentum of the drop42results in the separation of the drop42from the remainder of the fluid26.

It is of importance to note that the gap38between the actuating members36serves to inhibit buckling of the actuating arm32as is explained in further detail below.

The nozzle chamber wall14defines a re-entrant portion46at the opening33. The passivation layer20defines a channel48that is positioned adjacent the re-entrant portion46. The re-entrant portion46and the actuating arm32provide points of attachment for a meniscus that defines a fluidic seal50to inhibit the egress of fluid26from the opening33while the actuating arm32is displaced. The channel48inhibits the wicking of any fluid that may be ejected from the opening33.

A raised formation52is positioned on an upper surface of the paddle30. The raised formation52inhibits the paddle30from making contact with a meniscus31. Contact between the paddle30and the meniscus31would be detrimental to the operational characteristics of the nozzle arrangement10.

A stepped formation25is positioned on the passivation material20defining an edge of the inlet channel24. The stepped formation25is shaped and dimensioned so that, when the paddle30is displaced towards the ejection port22, an opening23is defined between the paddle30and the formation25at a rate that facilitates the entry of fluid into the nozzle chamber18in the direction of arrows27in FIG.3.

A nozzle rim54is positioned about the ejection port22.

InFIGS. 4to6, reference numeral60generally indicates a thermal actuator of the type that the Applicant has identified as exhibiting certain problems and over which the present invention distinguishes.

The thermal actuator60is in the form of a thermal bend actuator that uses differential expansion as a result of uneven heating to generate movement and thus perform work.

The thermal actuator60is fast with a substrate62and includes an actuator arm64that is displaced to perform work. The actuator arm64has a fixed end66that is fast with the substrate62. A fixed end portion67of the actuator arm64is sandwiched between and fast with a lower activating arm68and an upper activating arm70. The activating arms68,70are substantially the same to ensure that they remain in thermal equilibrium, for example during quiescent periods. The material of the arms68,70is such that, when heated, the arms68,70are capable of expanding to a degree sufficient to perform work.

The lower activating arm68is capable of being heated to the exclusion of the upper activating arm70. It will be appreciated that this will result in a differential expansion being set up between the arms, with the result that the actuator arm64is driven upwardly to perform work against a pressure P, as indicated by the arrow72.

In order to achieve this, the arms68,70must be fast with the arm64. It has been found that, if the arms68,70exceed a particular length, then the arms68,70and the fixed end portion67are susceptible to buckling as shown in FIG.6. It will be appreciated that this is undesirable.

InFIGS. 7 and 8, reference numeral80generally indicates a further thermal bend actuator by way of illustration of the principles of the present invention. With reference toFIGS. 4to6, like reference numerals refer to like parts, unless otherwise specified.

The thermal bend actuator80has shortened activation arms68,70. This serves significantly to reduce the risk of buckling as described above. However, it has been found that, to achieve useful movement, as shown inFIG. 8, it is necessary for the fixed end portion67to be subjected to substantial shear stresses. This can have a detrimental effect on the operational characteristics of the actuator80. The high shear stresses can also result in delamination of the actuator arm64.

Furthermore, in both the embodiments of the thermal actuator60,80, the temperature to which the lower activation arm can be heated is limited by characteristics of the fixed end portion67, such as the melting point of the fixed end portion67.

Thus, the Applicant has conceived, schematically, the thermal bend actuator as shown inFIGS. 9 and 10. Reference numeral82refers generally to that thermal bend actuator. With reference toFIGS. 4to8, like reference numerals refer to like parts, unless otherwise specified.

The thermal bend actuator82does not include the fixed end portion67. Instead, ends84of the activating arms68,70, opposite the substrate62, are fast with the fixed end66of the actuator arm64, instead of the fixed end66being fast with the substrate62. Thus, the fixed end portion67is replaced with a gap86, equivalent to the gap38described above. As a result, the activating arms68,70can operate without being limited by the characteristics of the actuator arm64. Further, shear stresses are not set up in the actuator arm64so that delamination is avoided. Buckling is also avoided by the configuration shown inFIGS. 9 and 10.

InFIG. 11, reference numeral90generally indicates a schematic layout of a thermal actuator for illustration of a problem that Applicant has identified with thermal actuators.

The thermal actuator90includes an actuator arm92. The actuator arm92is positioned between a pair of heat sink members91. It will be appreciated that when the arm92is heated, the resultant thermal expansion will result in the heat sink members91being driven apart. The graph shown inFIG. 12is a temperature v. distance graph that indicates the relationship between the temperature applied to the actuator arm92and the position along the actuator arm92.

As can be seen from the graph, at some point93intermediate the heat sinks91, the melting point, indicated at89, of the actuator arm92, is exceeded. This is clearly undesirable, as this would cause a breakdown in the operation of the actuator arm92. The graph clearly indicates that the level of heating of the actuator arm92varies significantly along the length of the actuator arm92, which is undesirable.

InFIG. 13, reference numeral94generally indicates a further layout of a thermal actuator, for illustrative purposes. With reference toFIG. 11, like reference numerals refer to like parts, unless otherwise specified.

The thermal actuator94includes a pair of heat sinks96that are positioned on the actuator arm92between the heat sink members91. The graph shown inFIG. 14is a graph of temperature v. distance along the actuator arm92. As can be seen in that graph, that point intermediate the heat sink members91is inhibited from reaching the melting point of the actuator arm92. Furthermore, the actuator arm92is heated more uniformly along its length than in the thermal actuator80.

InFIG. 15, reference numeral98generally indicates a thermal actuator that incorporates some of the principles of the present invention. With reference to the preceding drawings, like reference numerals refer to like parts, unless otherwise specified.

The thermal actuator98is similar to the thermal actuator82shown inFIGS. 9 and 10. However, further to enhance the operational characteristics of the thermal actuator98, a pair of heat sinks100is positioned in the gap86, in contact with both the upper and lower activation arms68,70. Furthermore, the heat sinks100are configured to define a pair of spaced struts to provide the thermal actuator98with integrity and strength. The spaced struts100serve to inhibit buckling as the arm64is displaced.

InFIGS. 55to59, reference numeral110generally indicates a second embodiment of a nozzle arrangement of an integrated circuit device, in accordance with the invention, part of which is generally indicated by reference numeral112inFIGS. 60to62.

The device112includes a wafer substrate114. A fluid passivation layer in the form of a layer of silicon nitride116is positioned on the wafer substrate114. A cylindrical nozzle chamber wall118is positioned on the silicon nitride layer116. A roof wall120is positioned on the nozzle chamber wall118so that the roof wall120and the nozzle chamber wall118define a nozzle chamber122.

A fluid inlet channel121is defined through the substrate114and the silicon nitride layer116.

The roof wall120defines a fluid ejection port124. A nozzle rim126is positioned about the fluid ejection port124.

An anchoring member128is mounted on the silicon nitride layer116. A thermal actuator130is fast with the anchoring member128and extends into the nozzle chamber122so that, on displacement of the thermal actuator130, fluid is ejected from the fluid ejection port124. The thermal actuator130is fast with the anchoring member128to be in electrical contact with CMOS layers (not shown) positioned on the wafer substrate114so that the thermal actuator130can receive an electrical signal from the CMOS layers.

The thermal actuator130includes an actuator arm132that is fast with the anchoring member128and extends towards the nozzle chamber122. A paddle134is positioned in the nozzle chamber122and is fast with an end of the actuator arm132.

The actuator arm132includes an actuating portion136that is fast with the anchoring member128at one end and a sealing structure138that is fast with the actuating portion at an opposed end. The paddle134is fast with the sealing structure138to extend into the nozzle chamber122.

The actuating portion136includes a pair of spaced substantially identical activating arms140. One of the activating arms140.1is positioned between the other activating arm140.2and the silicon nitride layer116. A gap142is defined between the arms140and is equivalent to the gap38described with reference toFIGS. 1to3.

As can be seen inFIG. 59, the actuating portion136is divided into two identical portions143that are spaced in a plane that is parallel to the substrate114.

The activating arm140.1is of a conductive material that has a coefficient of thermal expansion that is sufficient to permit work to be harnessed from thermal expansion of the activating arm140.1. The activating arm140.1defines a resistive heating circuit that is connected to the CMOS layers to receive an electrical current from the CMOS layers, so that the activating arm140.1undergoes thermal expansion. The activating arm140.2, on the other hand, is not connected to the CMOS layers and therefore undergoes a negligible amount of expansion, if any. This sets up differential expansion in the actuation portion136so that the actuating portion136is driven away from the silicon nitride layer116and the paddle134is driven towards the ejection port124to generate a drop144of fluid that extends from the port124. When the electrical current is cut off, the resultant cooling of the actuating portion136causes the arm140.1to contract so that the actuating portion136moves back to a quiescent condition towards the silicon nitride layer116. The actuator arm132is also of a resiliently flexible material. This enhances the movement towards the silicon nitride layer116.

As a result of the paddle134moving back to its quiescent condition, a fluid pressure within the nozzle chamber is reduced and the fluid drop144separates as a result of the reduction in pressure and the forward momentum of the fluid drop144, as shown inFIGS. 57 and 58. In use, the CMOS layers can generate a high frequency electrical potential so that the actuator arm is able to oscillate at that frequency, thereby permitting the paddle134to generate a stream of fluid drops.

A heat sink member146is mounted on the activating arm140.1. The heat sink member146serves to ensure that a temperature gradient along the arm140.1does not peak excessively at or near a centre of the arm140.1. Thus, the arm140.1is inhibited from reaching its melting point while still maintaining suitable expansion characteristics.

A strut148is connected between the activating arms140to ensure that the activating arms140do not buckle as a result of the differential expansion of the activating arms140. Detail of the strut148is shown in FIG.62.

The purpose of the sealing structure138is to permit movement of the actuating arm and the paddle134while inhibiting leakage of fluid from the nozzle chamber122. This is achieved by the roof wall120, the nozzle chamber wall118and the sealing structure138defining complementary formations150that, in turn, with the fluid, set up fluidic seals which accommodate such movement. These fluidic seals rely on the surface tension of the fluid to retain a meniscus that prevents the fluid from escaping from the nozzle chamber122.

The sealing structure138has a generally I-shaped profile when viewed in plan. Thus, the sealing structure138has an arcuate end portion156, a leg portion158and a rectangular base portion160, the leg portion158interposed between the end portion156and the base portion160, when viewed in plan. The roof wall120defines an arcuate slot152which accommodates the end portion156and the nozzle chamber wall118defines an opening into the arcuate slot152, the opening being dimensioned to accommodate the leg portion158. The roof wall120defines a ridge162about the slot152and part of the opening. The ridge162and edges of the end portion156and leg portion158of the sealing structure138define purchase points for a meniscus that is generated when the nozzle chamber122is filled with fluid, so that a fluidic seal is created between the ridge162and the end and leg portions156,158.

As can be seen inFIG. 60, a transverse profile of the sealing structure138reveals that the end portion156extends partially into the fluid inlet channel121so that it overhangs an edge of the silicon nitride layer116. The leg portion158defines a recess164. The nozzle chamber wall118includes a re-entrant formation166that is positioned on the silicon nitride layer116. Thus, a tortuous fluid flow path168is defined between the silicon nitride layer116, the re-entrant formation166, and the end and leg portions156,158of the sealing structure138. This serves to slow the flow of fluid, allowing a meniscus to be set up between the re-entrant formation166and a surface of the recess164.

A channel170is defined in the silicon nitride layer116and is aligned with the recess164. The channel170serves to collect any fluid that may be emitted from the tortuous fluid flow path168to inhibit wicking of that fluid along the layer116.

The paddle134has a raised formation172that extends from an upper surface174of the paddle134. Detail of the raised formation172can be seen in FIG.61. The raised formation172is essentially the same as the raised formation52of the first embodiment. The raised formation172thus prevents the surface174of the paddle134from making contact with a meniscus186, which would be detrimental to the operating characteristics of the nozzle arrangement110. The raised formation172also serves to impart rigidity to the paddle134, thereby enhancing the operational efficiency of the paddle134.

Importantly, the nozzle chamber wall118is shaped so that, as the paddle134moves towards the fluid ejection port124a sufficient increase in a space between a periphery184of the paddle134and the nozzle chamber wall118takes place to allow for a suitable amount of fluid to flow rapidly into the nozzle chamber122. This fluid is drawn into the nozzle chamber122when the meniscus186re-forms as a result of surface tension effects. This allows for refilling of the nozzle chamber122at a suitable rate.

InFIGS. 63 and 64, reference numeral180generally indicates an integrated circuit device that incorporates a plurality of the nozzle arrangements110.

The plurality of the nozzle arrangements110are positioned in a predetermined array182that spans a printing area. It will be appreciated that each nozzle arrangement110can be actuated with a single pulse of electricity such as that which would be generated with an “on” signal. It follows that printing by the chip180can be controlled digitally right up to the operation of each nozzle arrangement110.

InFIGS. 16 and 18, reference numeral190generally indicates a wafer substrate192with multiple CMOS layers194in an initial stage of fabrication of the nozzle arrangement110, in accordance with the invention. This form of fabrication is based on integrated circuit fabrication techniques. As is known, such techniques use masks and deposition, developing and etching processes. Furthermore, such techniques usually involve the replication of a plurality of identical units on a single wafer. Thus, the fabrication process described below is easily replicated to achieve the chip180. Thus, for convenience, the fabrication of a single nozzle arrangement110is described with the understanding that the fabrication process is easily replicated to achieve the device180.

InFIG. 17, reference numeral196is a mask used for the fabrication of the multiple CMOS layers194.

The CMOS layers194are fabricated to define a connection zone198for the anchoring member128. The CMOS layers194also define a recess200for the channel170. The wafer substrate192is exposed at202for future etching of the fluid inlet channel121.

InFIGS. 19 and 21, reference numeral204generally indicates the structure190with a 1-micron thick layer of photosensitive, sacrificial polyimide206spun on to the structure190and developed.

The layer206is developed using a mask208, shown in FIG.20.

InFIGS. 22 and 24, reference numeral210generally indicates the structure204with a 0.2-micron thick layer of titanium nitride212deposited on the structure204and subsequently etched.

The titanium nitride212is sputtered on the structure204using a magnetron. Then, the titanium nitride212is etched using a mask214shown in FIG.23. The titanium nitride212defines the activating arm140.1, the re-entrant formation166and the paddle134. It will be appreciated that the polyimide206ensures that the activating arm140.1is positioned 1 micron above the silicon nitride layer116.

InFIGS. 25 and 27, reference numeral216generally indicates the structure210with a 1.5-micron thick layer218of sacrificial photosensitive polyimide deposited on the structure210.

The polyimide218is developed with ultra-violet light using a mask220shown in FIG.26.

The remaining polyimide218is used to define a deposition zone222for the activating arm140.2and a deposition zone224for the raised formation172on the paddle134. Thus, it will be appreciated that the gap142has a thickness of 1.5 micron.

InFIGS. 28 and 30, reference numeral226generally indicates the structure216with a 0.2-micron thick layer228of titanium nitride deposited on the structure216.

Firstly, a 0.05-micron thick layer of PECVD silicon nitride (not shown) is deposited on the structure216at a temperature of 572 degrees Fahrenheit. Then, the layer228of titanium nitride is deposited on the PECVD silicon nitride. The titanium nitride228is etched using a mask230shown in FIG.29.

The remaining titanium nitride228is then used as a mask to etch the PECVD silicon nitride.

The titanium nitride228serves to define the activating arm140.2, the raised formation172on the paddle134, and the heat sink members146.

InFIGS. 31 and 33, reference numeral232generally indicates the structure226with 6 microns of photosensitive polyimide234deposited on the structure226.

The polyimide234is spun on and exposed to ultra violet light using a mask236shown in FIG.32. The polyimide234is then developed.

The polyimide234defines a deposition zone238for the anchoring member128, a deposition zone240for the sealing structure138, a deposition zone242for the nozzle chamber wall118and a deposition zone244for the roof wall120.

It will be appreciated that the thickness of the polyimide determines the height of the nozzle chamber122. A degree of taper of 1 micron from a bottom of the chamber to the top can be accommodated.

InFIGS. 34 and 36, reference numeral246generally indicates the structure232with 2 microns of PECVD silicon nitride247deposited on the structure232.

This serves to fill the deposition zones238,240,242and244with the PECVD silicon nitride. As can be seen inFIG. 35, no mask is used for this process.

InFIGS. 37 and 39, reference numeral248generally indicates the PECVD silicon nitride246etched to define the nozzle rim126, the ridge162and a portion of the sealing structure138.

The PECVD silicon nitride246is etched using a mask250shown in FIG.38.

InFIGS. 40 and 42reference numeral252generally indicates the structure248with the PECVD silicon nitride246etched to define a surface of the anchoring member128, a further portion of the sealing structure138and the fluid ejection port124.

The etch is carried out using a mask254shown inFIG. 41to a depth of 1 micron stopping on the polyimide234.

InFIGS. 43 and 45, reference numeral256generally indicates the structure252with a protective layer258of polyimide spun on to the structure252as a protective layer for back etching the structure256.

As can be seen inFIG. 44, a mask is not used for this process.

InFIGS. 46 and 48, reference numeral259generally indicates the structure256subjected to a back etch.

In this step, the wafer substrate114is thinned to a thickness of 300 microns. 3 microns of a resist material (not shown) are deposited on the back side of the wafer114and exposed using a mask260shown in FIG.47. Alignment is to metal portions262on a front side of the wafer114. This alignment is achieved using an IR microscope attached to a wafer aligner.

The back etching then takes place to a depth of 330 microns (allowing for a 10% overetch) using a deep-silicon “Bosch Process” etch. This process is available on plasma etchers from Alcatel, Plasma-therm, and Surface Technology Systems. The chips are also diced by this etch, but the wafer is still held together by 11 microns of the various polyimide layers. This etch serves to define the fluid inlet channel121.

InFIGS. 49 and 51, reference numeral264generally indicates the structure259with all the sacrificial material stripped. This is done in an oxygen plasma etching process. As can be seen inFIG. 50, a mask is not used for this process.

InFIGS. 52 and 54, reference numeral266generally indicates the structure264, which is primed with fluid268. In particular, a package is prepared by drilling a 0.5 mm hole in a standard package, and gluing a fluid hose (not shown) to the package. The fluid hose should include a 0.5-micron absolute filter to prevent contamination of the nozzles from the fluid268.

The integrated circuit device of the invention is potentially suited to a wide range of printing systems including: colour and monochrome office printers, short run digital printers, high speed digital printers, offset press supplemental printers, low cost scanning printers, high speed pagewidth printers, notebook computers with in-built pagewidth printers, portable colour and monochrome printers, colour and monochrome copiers, colour and monochrome facsimile machines, combined printer, facsimile and copying machines, label printers, large format plotters, photograph copiers, printers for digital photographic ‘minilabs’, video printers, PHOTOCD™ printers, portable printers for PDAs, wallpaper printers, indoor sign printers, billboard printers, fabric printers, camera printers and fault tolerant commercial printer arrays.

Further, the MEMS fabrication principles outlined have general applicability in the construction of MEMS devices.