# Patent

## Title
Printhead nozzle arrangement with radially disposed actuators

## Abstract

A nozzle arrangement for an inkjet printhead includes a substrate with a layer of drive circuitry, the substrate defining an ink chamber with an ink supply channel etched through the substrate; and a roof structure having a roof layer over the chamber. The roof structure includes a nozzle rim positioned around an ejection port defined in the roof layer above the chamber; a plurality of actuators radially spaced about, and displaceable with respect to, the nozzle rim, each actuator having an internal copper core for receiving therethrough a current, each actuator configured to thermally expand into the chamber upon receiving the current; and a series of struts interspersed between the actuators to support the nozzle rim with respect to the roof layer.

## Background
CROSS REFERENCES TO RELATED APPLICATIONS
The present application is a Continuation of U.S. application Ser. No. 12/101,147 filed on Apr. 11, 2008, now issued U.S. Pat. No. 7,604,323, which is a Continuation of U.S. application Ser. No. 11/525,860 filed on Sep. 25, 2006, now issued U.S. Pat. No. 7,374,695, which is a Continuation of U.S. application Ser. No. 11/036,021 filed Jan. 18, 2005, now issued U.S. Pat. No. 7,156,495, which is a Continuation of U.S. application Ser. No. 10/636,278 filed Aug. 8, 2003, now issued U.S. Pat. No. 6,886,917, which is a Continuation of U.S. application Ser. No. 09/854,703 filed May 14, 2001, now issued U.S. Pat. No. 6,981,757, which is a Continuation of U.S. application Ser. No. 09/112,806, filed Jul. 10, 1998, now issued U.S. Pat. No. 6,247,790, all of which are herein incorporated by reference.
The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, US patent applications identified by their US patent application serial numbers (USSN) are listed alongside the Australian applications from which the US patent applications claim the right of priority.













CROSS-REFERENCED
US PATENT/PATENT



AUSTRALIAN
APPLICATION (CLAIMING



PROVISIONAL
RIGHT OF PRIORITY



PATENT
FROM AUSTRALIAN



APPLICATION NO.
PROVISIONAL APPLICATION)








PO7991
6,750,901



PO8505
6,476,863



PO7988
6,788,336



PO9395
6,322,181



PO8017
6,597,817



PO8014
6,227,648



PO8025
6,727,948



PO8032
6,690,419



PO7999
6,727,951



PO8030
6,196,541



PO7997
6,195,150



PO7979
6,362,868



PO7978
6,831,681



PO7982
6,431,669



PO7989
6,362,869



PO8019
6,472,052



PO7980
6,356,715



PO8018
6,894,694



PO7938
6,636,216



PO8024
6,329,990



PO7939
6,459,495



PO8501
6,137,500



PO8500
6,690,416



PO7987
7,050,143



PO8022
6,398,328



PO8497
7,110,024



PO8020
6,431,704



PO8504
6,879,341



PO8000
6,415,054



PO7934
6,665,454



PO7990
6,542,645



PO8499
6,486,886



PO8502
6,381,361



PO7981
6,317,192



PO7986
6,850,274



PO7983
09/113,054



PO8026
6,646,757



PO8028
6,624,848



PO9394
6,357,135



PO9397
6,271,931



PO9398
6,353,772



PO9399
6,106,147



PO9400
6,665,008



PO9401
6,304,291



PO9403
6,305,770



PO9405
6,289,262



PP0959
6,315,200



PP1397
6,217,165



PP2370
6,786,420



PO8003
6,350,023



PO8005
6,318,849



PO8066
6,227,652



PO8072
6,213,588



PO8040
6,213,589



PO8071
6,231,163



PO8047
6,247,795



PO8035
6,394,581



PO8044
6,244,691



PO8063
6,257,704



PO8057
6,416,168



PO8056
6,220,694



PO8069
6,257,705



PO8049
6,247,794



PO8036
6,234,610



PO8048
6,247,793



PO8070
6,264,306



PO8067
6,241,342



PO8001
6,247,792



PO8038
6,264,307



PO8033
6,254,220



PO8002
6,234,611



PO8068
6,302,528



PO8062
6,283,582



PO8034
6,239,821



PO8039
6,338,547



PO8041
6,247,796



PO8004
6,557,977



PO8037
6,390,603



PO8043
6,362,843



PO8042
6,293,653



PO8064
6,312,107



PO9389
6,227,653



PO9391
6,234,609



PP0888
6,238,040



PP0891
6,188,415



PP0890
6,227,654



PP0873
6,209,989



PP0993
6,247,791



PP0890
6,336,710



PP1398
6,217,153



PP2592
6,416,167



PP2593
6,243,113



PP3991
6,283,581



PP3987
6,247,790



PP3985
6,260,953



PP3983
6,267,469



PO7935
6,224,780



PO7936
6,235,212



PO7937
6,280,643



PO8061
6,284,147



PO8054
6,214,244



PO8065
6,071,750



PO8055
6,267,905



PO8053
6,251,298



PO8078
6,258,285



PO7933
6,225,138



PO7950
6,241,904



PO7949
6,299,786



PO8060
6,866,789



PO8059
6,231,773



PO8073
6,190,931



PO8076
6,248,249



PO8075
6,290,862



PO8079
6,241,906



PO8050
6,565,762



PO8052
6,241,905



PO7948
6,451,216



PO7951
6,231,772



PO8074
6,274,056



PO7941
6,290,861



PO8077
6,248,248



PO8058
6,306,671



PO8051
6,331,258



PO8045
6,110,754



PO7952
6,294,101



PO8046
6,416,679



PO9390
6,264,849



PO9392
6,254,793



PP0889
6,235,211



PP0887
6,491,833



PP0882
6,264,850



PP0874
6,258,284



PP1396
6,312,615



PP3989
6,228,668



PP2591
6,180,427



PP3990
6,171,875



PP3986
6,267,904



PP3984
6,245,247



PP3982
6,315,914



PP0895
6,231,148



PP0869
6,293,658



PP0887
6,614,560



PP0885
6,238,033



PP0884
6,312,070



PP0886
6,238,111



PP0877
6,378,970



PP0878
6,196,739



PP0883
6,270,182



PP0880
6,152,619



PO8006
6,087,638



PO8007
6,340,222



PO8010
6,041,600



PO8011
6,299,300



PO7947
6,067,797



PO7944
6,286,935



PO7946
6,044,646



PP0894
6,382,769











FIELD OF THE INVENTION
The present invention relates to the field of inkjet printing and, in particular, discloses an inverted radial back-curling thermoelastic ink jet printing mechanism.
BACKGROUND OF THE INVENTION
Many different types of printing mechanisms have been invented, a large number of which are presently in use. The known forms of printers have a variety of methods for marking the print media with a relevant marking media.
Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles, has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques of ink jet printing 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 207-220 (1988).
Ink Jet printers themselves come in many different forms. The utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous ink jet printing including a step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al).
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode form of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) which discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 which discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclose ink jet printing techniques which rely on the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction and operation, durability and consumables.
SUMMARY OF THE INVENTION
According to an aspect of the present disclosure, a nozzle arrangement for an inkjet printhead includes a substrate with a layer of drive circuitry, the substrate defining an ink chamber with an ink supply channel etched through the substrate; and a roof structure having a roof layer over the chamber. The roof structure comprises a nozzle rim positioned around an ejection port defined in the roof layer above the chamber; a plurality of actuators radially spaced about, and displaceable with respect to, the nozzle rim, each actuator having an internal copper core for receiving therethrough a current, each actuator configured to thermally expand into the chamber upon receiving the current; and a series of struts interspersed between the actuators to support the nozzle rim with respect to the roof layer.



BRIEF DESCRIPTION OF THE DRAWINGS
Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
FIGS. 1-3 are schematic sectional views illustrating the operational principles of the preferred embodiment;
FIG. 4(a) and FIG. 4(b) are again schematic sections illustrating the operational principles of the thermal actuator device;
FIG. 5 is a side perspective view, partly in section, of a single nozzle arrangement constructed in accordance with the preferred embodiments;
FIGS. 6-13 are side perspective views, partly in section, illustrating the manufacturing steps of the preferred embodiments;
FIG. 14 illustrates an array of ink jet nozzles formed in accordance with the manufacturing procedures of the preferred embodiment;
FIG. 15 provides a legend of the materials indicated in FIGS. 16 to 23; and
FIG. 16 to FIG. 23 illustrate sectional views of the manufacturing steps in one form of construction of a nozzle arrangement in accordance with the invention.



DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS
In the preferred embodiment, ink is ejected out of a nozzle chamber via an ink ejection port using a series of radially positioned thermal actuator devices that are arranged about the ink ejection port and are activated to pressurize the ink within the nozzle chamber thereby causing the ejection of ink through the ejection port.
Turning now to FIGS. 1, 2 and 3, there is illustrated the basic operational principles of the preferred embodiment. FIG. 1 illustrates a single nozzle arrangement 1 in its quiescent state. The arrangement 1 includes a nozzle chamber 2 which is normally filled with ink so as to form a meniscus 3 in an ink ejection port 4. The nozzle chamber 2 is formed within a wafer 5. The nozzle chamber 2 is supplied with ink via an ink supply channel 6 which is etched through the wafer 5 with a highly isotropic plasma etching system. A suitable etcher can be the Advance Silicon Etch (ASE) system available from Surface Technology Systems of the United Kingdom.
A top of the nozzle arrangement 1 includes a series of radially positioned actuators 8, 9. These actuators comprise a polytetrafluoroethylene (PTFE) layer and an internal serpentine copper core 17. Upon heating of the copper core 17, the surrounding PTFE expands rapidly resulting in a generally downward movement of the actuators 8, 9. Hence, when it is desired to eject ink from the ink ejection port 4, a current is passed through the actuators 8, 9 which results in them bending generally downwards as illustrated in FIG. 2. The downward bending movement of the actuators 8, 9 results in a substantial increase in pressure within the nozzle chamber 2. The increase in pressure in the nozzle chamber 2 results in an expansion of the meniscus 3 as illustrated in FIG. 2.
The actuators 8, 9 are activated only briefly and subsequently deactivated. Consequently, the situation is as illustrated in FIG. 3 with the actuators 8, 9 returning to their original positions. This results in a general inflow of ink back into the nozzle chamber 2 and a necking and breaking of the meniscus 3 resulting in the ejection of a drop 12. The necking and breaking of the meniscus 3 is a consequence of the forward momentum of the ink associated with drop 12 and the backward pressure experienced as a result of the return of the actuators 8, 9 to their original positions. The return of the actuators 8, 9 also results in a general inflow of ink from the channel 6 as a result of surface tension effects and, eventually, the state returns to the quiescent position as illustrated in FIG. 1.
FIGS. 4(a) and 4(b) illustrate the principle of operation of the thermal actuator. The thermal actuator is preferably constructed from a material 14 having a high coefficient of thermal expansion. Embedded within the material 14 are a series of heater elements 15 which can be a series of conductive elements designed to carry a current. The conductive elements 15 are heated by passing a current through the elements 15 with the heating resulting in a general increase in temperature in the area around the heating elements 15. The position of the elements 15 is such that uneven heating of the material 14 occurs. The uneven increase in temperature causes a corresponding uneven expansion of the material 14. Hence, as illustrated in FIG. 4(b), the PTFE is bent generally in the direction shown.
In FIG. 5, there is illustrated a side perspective view of one embodiment of a nozzle arrangement constructed in accordance with the principles previously outlined. The nozzle chamber 2 is formed with an isotropic surface etch of the wafer 5. The wafer 5 can include a CMOS layer including all the required power and drive circuits. Further, the actuators 8, 9 each have a leaf or petal formation which extends towards a nozzle rim 28 defining the ejection port 4. The normally inner end of each leaf or petal formation is displaceable with respect to the nozzle rim 28. Each activator 8, 9 has an internal copper core 17 defining the element 15. The core 17 winds in a serpentine manner to provide for substantially unhindered expansion of the actuators 8, 9. The operation of the actuators 8, 9 is as illustrated in FIG. 4(a) and FIG. 4(b) such that, upon activation, the actuators 8 bend as previously described resulting in a displacement of each petal formation away from the nozzle rim 28 and into the nozzle chamber 2. The ink supply channel 6 can be created via a deep silicon back edge of the wafer 5 utilizing a plasma etcher or the like. The copper or aluminium core 17 can provide a complete circuit. A central arm 18 which can include both metal and PTFE portions provides the main structural support for the actuators 8, 9.
Turning now to FIG. 6 to FIG. 13, one form of manufacture of the nozzle arrangement 1 in accordance with the principles of the preferred embodiment is shown. The nozzle arrangement 1 is preferably manufactured using microelectromechanical (MEMS) techniques and can include the following construction techniques:
As shown initially in FIG. 6, the initial processing starting material is a standard semi-conductor wafer 20 having a complete CMOS level 21 to a first level of metal. The first level of metal includes portions 22 which are utilized for providing power to the thermal actuators 8, 9.
The first step, as illustrated in FIG. 7, is to etch a nozzle region down to the silicon wafer 20 utilizing an appropriate mask.
Next, as illustrated in FIG. 8, a 2 μm layer of polytetrafluoroethylene (PTFE) is deposited and etched so as to define vias 24 for interconnecting multiple levels.
Next, as illustrated in FIG. 9, the second level metal layer is deposited, masked and etched to define a heater structure 25. The heater structure 25 includes via 26 interconnected with a lower aluminium layer.
Next, as illustrated in FIG. 10, a further 2 μm layer of PTFE is deposited and etched to the depth of 1 μm utilizing a nozzle rim mask to define the nozzle rim 28 in addition to ink flow guide rails 29 which generally restrain any wicking along the surface of the PTFE layer. The guide rails 29 surround small thin slots and, as such, surface tension effects are a lot higher around these slots which in turn results in minimal outflow of ink during operation.
Next, as illustrated in FIG. 11, the PTFE is etched utilizing a nozzle and actuator mask to define a port portion 30 and slots 31 and 32.
Next, as illustrated in FIG. 12, the wafer is crystallographically etched on a <111> plane utilizing a standard crystallographic etchant such as KOH. The etching forms a chamber 33, directly below the port portion 30.
In FIG. 13, the ink supply channel 34 can be etched from the back of the wafer utilizing a highly anisotropic etcher such as the STS etcher from Silicon Technology Systems of United Kingdom. An array of ink jet nozzles can be formed simultaneously with a portion of an array 36 being illustrated in FIG. 14. A portion of the printhead is formed simultaneously and diced by the STS etching process. The array 36 shown provides for four column printing with each separate column attached to a different colour ink supply channel being supplied from the back of the wafer. Bond pads 37 provide for electrical control of the ejection mechanism.
In this manner, large pagewidth printheads can be fabricated so as to provide for a drop-on-demand ink ejection mechanism.
One form of detailed manufacturing process which can be used to fabricate monolithic ink jet printheads operating in accordance with the principles taught by the present embodiment can proceed utilizing the following steps:
1. Using a double-sided polished wafer 60, complete a 0.5 micron, one poly, 2 metal CMOS process 61. This step is shown in FIG. 16. For clarity, these diagrams may not be to scale, and may not represent a cross section though any single plane of the nozzle. FIG. 15 is a key to representations of various materials in these manufacturing diagrams, and those of other cross referenced ink jet configurations.
2. Etch the CMOS oxide layers down to silicon or second level metal using Mask 1. This mask defines the nozzle cavity and the edge of the chips. This step is shown in FIG. 16.
3. Deposit a thin layer (not shown) of a hydrophilic polymer, and treat the surface of this polymer for PTFE adherence.
4. Deposit 1.5 microns of polytetrafluoroethylene (PTFE) 62.
5. Etch the PTFE and CMOS oxide layers to second level metal using Mask 2. This mask defines the contact vias for the heater electrodes. This step is shown in FIG. 17.
6. Deposit and pattern 0.5 microns of gold 63 using a lift-off process using Mask 3. This mask defines the heater pattern. This step is shown in FIG. 18.
7. Deposit 1.5 microns of PTFE 64.
8. Etch 1 micron of PTFE using Mask 4. This mask defines the nozzle rim 65 and the rim at the edge 66 of the nozzle chamber. This step is shown in FIG. 19.
9. Etch both layers of PTFE and the thin hydrophilic layer down to silicon using Mask 5. This mask defines a gap 67 at inner edges of the actuators, and the edge of the chips. It also forms the mask for a subsequent crystallographic etch. This step is shown in FIG. 20.
10. Crystallographically etch the exposed silicon using KOH. This etch stops on <111> crystallographic planes 68, forming an inverted square pyramid with sidewall angles of 54.74 degrees. This step is shown in FIG. 21.
11. Back-etch through the silicon wafer (with, for example, an ASE Advanced Silicon Etcher from Surface Technology Systems) using Mask 6. This mask defines the ink inlets 69 which are etched through the wafer. The wafer is also diced by this etch. This step is shown in FIG. 22.
12. Mount the printheads in their packaging, which may be a molded plastic former incorporating ink channels which supply the appropriate color ink to the ink inlets 69 at the back of the wafer.
13. Connect the printheads to their interconnect systems. For a low profile connection with minimum disruption of airflow, TAB may be used. Wire bonding may also be used if the printer is to be operated with sufficient clearance to the paper.
14. Fill the completed print heads with ink 70 and test them. A filled nozzle is shown in FIG. 23.
The presently disclosed ink jet printing technology is potentially suited to a wide range of printing systems including: color 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 inbuilt pagewidth printers, portable color and monochrome printers, color and monochrome copiers, color and monochrome facsimile machines, combined printer, facsimile and copying machines, label printers, large format plotters, photograph copiers, printers for digital photographic “minilabs”, video printers, PHOTO CD (PHOTO CD is a registered trade mark of the Eastman Kodak Company) printers, portable printers for PDAs, wallpaper printers, indoor sign printers, billboard printers, fabric printers, camera printers and fault tolerant commercial printer arrays.
It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.
Ink Jet Technologies
The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used. However presently popular ink jet printing technologies are unlikely to be suitable.
The most significant problem with thermal ink jet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.
The most significant problem with piezoelectric ink jet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per printhead, but is a major impediment to the fabrication of pagewidth printheads with 19,200 nozzles.
Ideally, the ink jet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new ink jet technologies have been created. The target features include:
low power (less than 10 Watts)
high resolution capability (1,600 dpi or more)
photographic quality output
low manufacturing cost
small size (pagewidth times minimum cross section)
high speed (<2 seconds per page).
All of these features can be met or exceeded by the ink jet systems described below with differing levels of difficulty. Forty-five different ink jet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the table below under the heading Cross References to Related Applications.
The ink jet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems.
For ease of manufacture using standard process equipment, the printhead is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the printhead is 100 mm long, with a width which depends upon the ink jet type. The smallest printhead designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square mm. The printheads each contain 19,200 nozzles plus data and control circuitry.
Ink is supplied to the back of the printhead by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The printhead is connected to the camera circuitry by tape automated bonding.

## Claims

1. A nozzle arrangement for an inkjet printhead, the nozzle arrangement comprising
a substrate with a layer of drive circuitry, the substrate defining an ink chamber with an ink supply channel etched through the substrate;
a roof structure having a roof layer over the chamber, the roof structure comprises:
a nozzle rim positioned around an ejection port defined in the roof layer above the chamber;
a plurality of actuators radially spaced about, and displaceable with respect to, the nozzle rim, each actuator having an internal copper core for receiving therethrough a current, each actuator configured to thermally expand into the chamber upon receiving the current; and
a series of struts interspersed between the actuators to support the nozzle rim with respect to the roof layer.

2. The roof structure of claim 1, wherein the actuators are constructed from a material having a coefficient of thermal expansion such that the actuators can perform work during thermal expansion.

3. The roof structure of claim 1, wherein the substrate defines a number of vias through which the drive circuitry is connected to the actuators.

4. The roof structure of claim 3, wherein the actuators are manufactured from a polytetrafluoroethylene (PTFE) material and have internal serpentine copper cores connected to the drive circuitry via the vias.

5. The roof structure of claim 1, wherein the struts include both metal and PTFE portions.

6. The roof structure of claim 1, wherein the ink chamber is an inverted pyramidal ink chamber with a vertex thereof terminating at the ink supply channel.

7. The roof structure of claim 1, wherein the ink supply channel is created by means of a deep silicon back etch of the substrate utilizing a plasma etcher.