U.S. patent application number 11/343395 was filed with the patent office on 2006-06-29 for micromechanical getter anchor.
Invention is credited to Edward Carl Fisher, Joyce Wong Holton, Jwei Wien Liu, Roger A. Robbins, Jack C. Smith.
Application Number | 20060138642 11/343395 |
Document ID | / |
Family ID | 26677572 |
Filed Date | 2006-06-29 |
United States Patent
Application |
20060138642 |
Kind Code |
A1 |
Robbins; Roger A. ; et
al. |
June 29, 2006 |
Micromechanical getter anchor
Abstract
One embodiment provides an anchor to hold getter materials in
place within a micromechanical device package substrate, said
anchor comprising: a first cavity face; and a second cavity face.
The cavity faces define an anchor cavity and mechanically retain a
getter away from a region holding the micromechanical device.
Another embodiment provides an anchor to hold a getter in place
within a micromechanical device package. The anchor comprises: a
package substrate; and a member attached to the package substrate,
the member shaped to provide mechanical retention of the getter
material formed over said member. Another embodiment provides a
micromechanical device package comprising: a package substrate; a
package lid enclosing a package cavity; a micromechanical device in
the package cavity; and a getter anchor in the package cavity.
Other embodiments provide methods of packaging and forming packages
having a getter anchor. One getter anchor is formed in a substrate
906 comprised of at least three layers. The layers form a cavity in
the substrate 906 with a wide bottom portion-formed in the middle
layer 902 and a relatively narrower top portion-formed by the top
layer 904. The narrow portion helps to retain the getter in the
cavity by creating a mechanical lock on the wide portion of getter
in the bottom of the cavity. The preceding abstract is submitted
with the understanding that it only will be used to assist in
determining, from a cursory inspection, the nature and gist of the
technical disclosure as described in 37 C.F.R. .sctn. 1.72(b). In
no case should this abstract be used for interpreting the scope of
any patent claims.
Inventors: |
Robbins; Roger A.;
(McKinney, TX) ; Liu; Jwei Wien; (Plano, TX)
; Smith; Jack C.; (Parker, TX) ; Fisher; Edward
Carl; (Lucas, TX) ; Holton; Joyce Wong;
(Plano, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Family ID: |
26677572 |
Appl. No.: |
11/343395 |
Filed: |
January 31, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10007964 |
Nov 13, 2001 |
6992375 |
|
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11343395 |
Jan 31, 2006 |
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60250913 |
Nov 30, 2000 |
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Current U.S.
Class: |
257/704 ;
257/913; 257/E23.004; 257/E23.137 |
Current CPC
Class: |
H01L 2924/14 20130101;
G02B 26/0833 20130101; H01L 2924/15165 20130101; H01L 2924/01006
20130101; H01L 23/26 20130101; H01L 2224/48227 20130101; H01L
2224/48997 20130101; H01L 2224/484 20130101; H01L 2224/45144
20130101; H01L 2224/05599 20130101; H01L 2224/8592 20130101; H01L
2924/00014 20130101; H01L 2224/85399 20130101; H01L 2924/00014
20130101; H01L 2924/00014 20130101; B81B 2203/0307 20130101; H01L
2924/16195 20130101; H01L 2224/48091 20130101; H01L 2224/45144
20130101; H01L 2924/15153 20130101; H01L 23/13 20130101; H01L
2924/01079 20130101; B81B 7/0038 20130101; H01L 2924/00014
20130101; H01L 24/45 20130101; H04N 5/7458 20130101; H01L 2224/484
20130101; H01L 2224/48091 20130101; H01L 24/48 20130101; H01L
2924/00014 20130101; H01L 2924/00014 20130101; H01L 2924/15787
20130101; H01L 2224/48599 20130101; H01L 2924/01005 20130101 |
Class at
Publication: |
257/704 ;
257/E23.137; 257/913 |
International
Class: |
H01L 23/12 20060101
H01L023/12 |
Claims
1-18. (canceled)
19. An anchor to hold material in place within a micromechanical
device package, said anchor comprising: a package substrate; and a
member attached to said package substrate, said member shaped to
provide mechanical retention of said material formed over said
member.
20. The anchor of claim 19, said member comprising: at least one
elongated member attached to said package substrate.
21. The anchor of claim 19, said member comprising: at least one
elongated member attached to said package substrate by one
point.
22. The anchor of claim 19, said member comprising: at least one
elongated member attached to said package substrate by one end.
23. The anchor of claim 19, said member comprising: at least one
elongated member attached to said package substrate by at least two
points.
24. The anchor of claim 19, said member comprising: at least one
elongated member attached to said package substrate by at least two
ends.
25. The anchor of claim 19, said member comprising: at least one
elongated member attached to said package substrate though an
intermediate bond pad.
26. The anchor of claim 19, said member comprising: at least one
wire member attached to said package substrate.
27. The anchor of claim 19, said member comprising: at least one
bond wire member attached to said package substrate.
28. A micromechanical device package comprising: a package
substrate; a package lid enclosing a package cavity; a
micromechanical device in said package cavity; and a getter anchor
in said package cavity.
29. The micromechanical device package of claim 28, wherein said
getter anchor comprises at least one member attached to said
package substrate.
30. The micromechanical device package of claim 28, wherein said
member is attached to said package substrate by one point.
31. The micromechanical device package of claim 28, wherein said
member is attached to said package substrate by one end.
32. The micromechanical device package of claim 28, wherein said
member is attached to said package substrate by at least two
points.
33. The micromechanical device package of claim 28, wherein said
member is attached to said package substrate by at least two
ends.
34. The micromechanical device package of claim 28, wherein said
member is attached to said package substrate though an intermediate
bond pad.
35. The micromechanical device package of claim 28, wherein said
member is a wire.
36. The micromechanical device package of claim 28, wherein said
member is a bond wire.
37. The micromechanical device package of claim 28, wherein said
anchor is a cavity anchor.
38. The micromechanical device package of claim 28, wherein said
cavity anchor is formed in said package substrate.
39. The micromechanical device package of claim 28, wherein said
cavity anchor is a slot formed in said package substrate.
40. The micromechanical device package of claim 28, wherein said
slot has a narrow top and a wider bottom portion.
41. The micromechanical device package of claim 28, said cavity
anchor formed to provide mechanical retention of a getter
material.
42. A method of packaging a micromechanical device, said method
comprising: providing a package substrate having a getter anchor;
attaching a micromechanical device to said package substrate;
attaching a getter material to said getter anchor; and attaching a
package lid to said package substrate.
43. The method of claim 42, wherein providing a package substrate
having a getter anchor comprises: providing a ceramic package
substrate having an anchor cavity formed therein.
44. The method of claim 42, wherein providing a package substrate
having a getter anchor comprises: providing a package substrate
having at least one member attached thereto, said member forming
said getter anchor.
45. The method of claim 42, wherein providing a package substrate
having a member attached thereto comprises: attaching at least one
elongated member to said package substrate.
46. The method of claim 42, wherein providing a package substrate
having a member attached thereto comprises: attaching at least one
mushroom shaped member to said package substrate.
47. The method of claim 42, wherein providing a package substrate
having a member attached thereto comprises: attaching at least one
wire to said substrate.
48. The method of claim 42, wherein providing a package substrate
having a member attached thereto comprises: attaching at least one
wire loop to said substrate.
49. The method of claim 42, wherein providing a package substrate
having a member attached thereto comprises: providing a package
substrate having a member attached to a bond pad of said
substrate.
50. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: putting a getter material into an
anchor cavity.
51. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: putting a desiccant material into an
anchor cavity.
52. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: putting a molecular sieve material
into an anchor cavity.
53. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: putting a getter mixed with a carrier
material into an anchor cavity.
54. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: putting a getter mixed with a solvent
material into an anchor cavity.
55. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: putting a getter mixed with a
lubricant into an anchor cavity.
56. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: attaching a desiccant material to
said anchor.
57. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: attaching a molecular sieve material
to said anchor.
58. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: attaching a getter mixed with a
carrier material to said anchor.
59. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: attaching a getter mixed with a
solvent material to said anchor.
60. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: attaching a getter mixed with a
lubricant to said anchor.
61. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: attaching an adhesive to said anchor;
and attaching a getter to said adhesive.
62. The method of claim 42, wherein attaching a getter material to
said getter anchor comprises: attaching an adhesive to said anchor;
and attaching a preformed getter to said adhesive.
63. A method of forming a package having an anchor, said method
comprising: forming a first package substrate layer; forming a
second package substrate layer, said second layer having a void;
forming a third package substrate layer; laminating said first,
second, and third layers such that said void forms an anchor cavity
suitable for anchoring a getter.
64. The method of claim 63, further comprising: forming a fourth
package substrate layer, said fourth package substrate layer having
a void, wherein said second and fourth layers are adjacent when
said layers are laminated such that a cavity anchor with a narrow
top and a relatively wide bottom is formed by said voids in said
second and fourth layers.
65. A method of packaging a micromechanical device, said method
comprising: providing a package substrate; attaching a
micromechanical device to said package substrate; attaching bond
wires between said micromechanical device and said package
substrate; attaching a getter material to said bond wires; and
attaching a package lid to said package substrate.
66. The method of claim 65, wherein attaching a getter material to
said getter anchor comprises: attaching an adhesive to said bond
wires; and attaching a getter to said adhesive.
67. The method of claim 65, wherein attaching a getter material to
said getter anchor comprises: attaching an adhesive to said bond
wires; and attaching a preformed getter to said adhesive.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The following patents and/or commonly assigned patent
applications are hereby incorporated herein by reference:
TABLE-US-00001 Patent No. Filing Date Issue Date Title 5,061,049
Sept. 13, 1990 Oct. 29, 1991 Spatial Light Modulator and Method
5,583,688 Dec. 21, 1993 Dec. 10, 1996 Multi-Level Digital
Micromirror Device
FIELD OF THE INVENTION
[0002] This invention relates to the field of
micro-electromechanical systems (MEMS), more particularly to
methods of attaching getters in packages containing lubrication for
the MEMS device.
BACKGROUND OF THE INVENTION
[0003] Micromechanical devices are small structures typically
fabricated on a semiconductor wafer using techniques such as
optical lithography, doping, metal sputtering, oxide deposition,
and plasma etching which have been developed for the fabrication of
integrated circuits.
[0004] Micromirror devices, such as the Digital Micromirror
Device.TM. (DMD.TM.) produced by Texas Instruments, are a type of
micromirror device. Other types of micromechanical devices include
accelerometers, pressure and flow sensors, gears and motors. While
some micromechanical devices, such as pressure sensors, flow
sensors, and micromirrors have found commercial success, other
types have not yet been commercially viable.
[0005] MEMS devices typically have moving mechanical components
that rub against each other. Lubricants are required to prevent the
small components from wearing out prematurely and to reduce
stiction where the components touch. One effective lubricant is
perfluordecanoic acid, or PFDA. PFDA forms a monolayer over the
components leaving a surface that is non-reactive. PFDA is often
applied over the entire interior surface of a package, including
the MEMS device. Unfortunately, once PFDA is applied to the package
interior, it is very difficult to attach other components, such as
moisture and gas getters, to the package. What is needed is a
system and method for providing positive retention of getters to
the package interior that does not rely on adhesion between the
getter and the package.
SUMMARY OF THE INVENTION
[0006] Objects and advantages will be obvious, and will in part
appear hereinafter and will be accomplished by the present
invention which provides a method and system for a micromechanical
getter anchor. One embodiment of the claimed invention provides an
anchor to hold getter materials in place within a micromechanical
device package substrate, said anchor comprising: a first cavity
face; and a second cavity face. The first and second cavity faces
define an anchor cavity and are arranged to mechanically retain a
getter away from a region holding the micromechanical device.
[0007] Another embodiment of the disclosed invention provides an
anchor to hold a getter in place within a micromechanical device
package. The anchor comprises: a package substrate; and a member
attached to the package substrate, the member shaped to provide
mechanical retention of the getter material formed over said
member.
[0008] Another embodiment of the disclosed invention provides a
micromechanical device package comprising: a package substrate; a
package lid enclosing a package cavity; a micromechanical device in
the package cavity; and a getter anchor in the package cavity.
[0009] Another embodiment of the disclosed invention provides a
method of packaging a micromechanical device. The method comprises:
providing a package substrate having a getter anchor; attaching a
micromechanical device to the package substrate; attaching a getter
material to the getter anchor; and attaching a package lid to the
package substrate.
[0010] Another embodiment of the disclosed invention provides a
method of forming a package having an anchor. The method comprises:
forming a first package substrate layer; forming a second package
substrate layer, the second layer having a void; forming a third
package substrate layer; laminating the first, second, and third
layers such that the void forms an anchor cavity suitable for
holding a getter. A further embodiment further comprises: forming a
fourth package substrate layer having a void. The second and fourth
layers are adjacent when laminated such that a cavity anchor with a
narrow top and a relatively wide bottom is formed by the voids in
the second and fourth layers.
[0011] Another embodiment of the disclosed invention provides a
method of packaging a micromechanical device. The method comprises:
providing a package substrate; attaching a micromechanical device
to the package substrate; attaching bond wires between the
micromechanical device and the package substrate; attaching a
getter material to the bond wires; and attaching a package lid to
the package substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] For a more complete understanding of the present invention,
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0013] FIG. 1 is a cross section side view of a micromechanical
package of the prior art showing the location of a getter within
the package.
[0014] FIG. 2 is a perspective view of a portion of a micromirror
package substrate showing an anchor mechanism according to one
embodiment of the present invention.
[0015] FIG. 3 is a perspective view of the portion of a micromirror
package substrate of FIG. 2 showing a getter applied to, and held
by, the anchor of FIG. 2.
[0016] FIG. 4 is a perspective view of a portion of a micromirror
package substrate showing and adhesive applied to, and held by, a
getter anchor, and a pre-formed getter being applied to the
adhesive.
[0017] FIG. 5 is a side view of a portion of a package substrate
showing an alternate anchor member configuration.
[0018] FIG. 6 is a side view of a portion of a package substrate
showing an alternate anchor member configuration.
[0019] FIG. 7 is a cross section side view of a micromechanical
device package showing the bond wires used in the prior art.
[0020] FIG. 8 is a cross section side view of a micromechanical
device package showing the result of a novel application of the
getter to the bond wires of FIG. 7.
[0021] FIG. 9 is an exploded perspective view of a portion of a
micromirror package substrate showing an anchor mechanism according
to one embodiment of the present invention.
[0022] FIG. 10 is a perspective view of the portion of a
micromirror package substrate of FIG. 9 showing the anchor of FIG.
9.
[0023] FIG. 11 is a cross section side view of a portion of a
micromechanical package substrate showing a cavity formed in the
substrate to anchor the getter to the substrate.
[0024] FIG. 12 is a cross section side view of the portion of a
micromechanical package substrate of FIG. 11 showing a getter held
by the anchor of FIG. 11.
[0025] FIG. 13 is a cross section side view of a portion of a
micromechanical package substrate showing an alternate cavity
formed in the substrate to anchor the getter to the substrate.
[0026] FIG. 14 is a cross section side view of the portion of a
micromechanical package substrate of FIG. 13 showing a getter held
by the anchor of FIG. 13.
[0027] FIG. 15 is a cross section side view of a portion of a
micromechanical package substrate showing an alternate cavity
formed in the substrate to anchor the getter to the substrate.
[0028] FIG. 16 is a cross section side view of the portion of a
micromechanical package substrate of FIG. 15 showing a getter held
by the anchor of FIG. 15.
[0029] FIG. 17 is a schematic view of a micromirror-based
projection system utilizing an improved micromirror device package
according to one embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] A new package feature has been developed that forms an
anchor to secure getters and other materials within a package. The
anchor overcomes the limitations of the prior art which required
the getter or other material to be adhered to the inside of the
package prior to the application of a lubricant. When an anchor
according to an embodiment of the present invention is used, the
lubricant may be applied prior to, or simultaneously with, the
getter.
[0031] FIG. 1 is a cross section side view of a semiconductor or
micromechanical package 100 of the prior art showing the location
of a getter within the package. In FIG. 1, a package substrate 102
has an interior floor 104 and interior walls 106. The package
substrate 102 typically is formed of layers of ceramic. The layers
of ceramic include metalization regions (not shown) that provide
electrical connection between the device 108 contained in the
package and circuitry external to the package. After patterning the
metalization on the layers, the layers are assembled and the
ceramic package substrate is fired.
[0032] After mounting the micromechanical device in the package, a
window 110 or lid is placed over the package cavity 112 and sealed
to the ceramic base. This hermetic seal provides a controlled
environment within the package cavity. Semiconductor and MEMS
devices typically require protection from moisture and various
gasses or other chemicals that remain on the device or in the
package after the assembly process, or are released by the package
and its contents. Additionally, moisture that penetrates the
packages must be prevented from harming the device.
[0033] In the case of a MEMS device, moisture is particularly
harmful because a polarized molecule such as water adheres to the
metal surfaces of the MEMS device. If it becomes sufficiently
plentiful to form a meniscus, then it can capture the moving part
of the MEMS by capillary force, causing it to cease moving and
rendering the part nonfunctional.
[0034] To prevent moisture and other contaminants from harming the
packaged device, one or more getters are used to trap the moisture
and other contaminants. These getters include any environmental
control materials such as desiccants and molecular sieves. FIG. 1
shows two getters 114 attached to the inside of the package 100.
The getters 114 of FIG. 1 adhere to the floor 104 of the package
and the glass window 110.
[0035] As mentioned above, the use of a lubricant in the package
100 affects the adhesion of the getters. For example, if the
lubricant is already in place--coating the floor 104, sides 106,
and window 110--the getter 114 will be unable to adhere to the
package. Alternatively, if the getter 114 is adhered to the
interior of the package 100 prior to the use of the lubricant, it
is possible for the lubricant to work its way between the getter
114 and package over a period of time, especially if the package is
operated over a series of extreme temperature cycles, and reduce
the adhesion of the getter 114. Additionally, the lubricant may
react with the substance adhering the getter 114 to the package and
allow the getter to loosen.
[0036] In some circumstances it is desirable to deposit the getter
and lubricant materials simultaneously. For example, mixing the
lubricant and getters allows them to be deposited in one operation.
After depositing the materials, and typically after installing the
window or lid, the lubricant is distributed throughout the package
interior, often by heating the package to distribute a lubricant
vapor. In this case, the lubricant and getter materials are mixed
together, often with a binder or other carrier and a solvent, and
deposited in the package base. Once the package is sealed, it is
heated to distribute the lubricant throughout the package interior
leaving the getter materials in the place they were deposited. This
mixed deposition is thwarted by the lubricant since the getter
materials fail to adhere to the package base when deposited while
mixed with the lubricant.
[0037] A solution to the problem of keeping the getter materials in
place is the use of an anchor in the package. An anchor is a
feature used to mechanically lock the getter materials in the
package and prevent them from moving. FIG. 2 shows on embodiment of
a solution to this problem. FIG. 2 is a perspective view of a
portion of a micromirror package substrate 200 showing an anchor
mechanism according to one embodiment of the present invention. The
anchor mechanism of FIG. 2 comprises members 202 anchored to the
substrate to provide a structure on which the getter can hold
without the use of adhesion. Wire members, in particular bond wires
202--that is, anchors formed from the same material as the
electrically functional bond wires, are particularly well suited
for use in forming the anchor since the typical process flow
includes use of such wires to connect the semiconductor die or MEMS
device with the package substrate.
[0038] In FIG. 2, special bond pads 204 are formed on the substrate
200 to receive the bond wires 202. The bond pads 204 may not be
necessary if the bond wires 202 will adhere to the substrate 200,
but typically are required to provide sufficient attachment between
the gold bond wire 202 and a ceramic substrate 200. Furthermore,
the bond pads may have more than one bond wire attached, and one
bond pad may be used by all of the wires. The bond pads 204
typically are a plated metal bond pad 204 formed from the same
materials, and during the same process steps, forming other
electrical bond pads on the surface of the substrate used to
electrically connect the packaged micromechanical device with
external circuitry via the interconnecting metalization formed in
the ceramic package base.
[0039] The size, shape, and number of the bond wire 202 loops
forming the anchor are determined by several factors including the
material anchored, the mass of the material anchored, and the
vibrational environment to which the device will be exposed. In
some environments, the bond wire loops may be attached merely by
one end. For example, coiled or kinked wires would be able to hold
the getter without being connected to the substrate on both
ends.
[0040] FIG. 3 is a perspective view of the portion of a micromirror
package substrate of FIG. 2 showing a getter material applied to,
and held by, the anchor of FIG. 2. The getter shown can be any
desiccant, molecular sieve, or other absorbing or gettering
material that can be deposited on, and attached to, the anchor.
Often the getter materials are mixed with a carrier material and a
solvent to aid the delivery of the getter material. Once the getter
material is delivered, typically by a pneumatic syringe, it is
allowed to cure and any solvents mixed with the getter are
evaporated.
[0041] Preformed getters can be denser than directly dispensed
getters that are cured in situ. The higher density of pre-cured
getters may benefit the MEMS device by providing a higher capacity
for gettering. The disclosed invention is applied to the attachment
of preformed getters as shown in FIG. 4. In FIG. 4, bond wires 202
attached to a substrate 200 form a getter anchor. An adhesive 400
is applied to the bond wires 202. A preformed getter 402 is then
applied to the adhesive. This embodiment is important in situations
where the adhesive 400 sticks to the getter 402, usually by soaking
into it, but does not stick well to the substrate 200. The use of a
preformed getter 402 and an adhesive 400 is also applicable to all
of the embodiment described below. In the embodiments describing
cavity anchors, the adhesive is placed in the cavity and the getter
is attached to the adhesive.
[0042] FIGS. 5 and 6 are side views of a portion of a package
substrate 502 showing alternate anchor member configurations. In
FIG. 5, a mushroom shaped member 504 is formed on the package
substrate 502 or a bond pad 506 to capture and retain getter
material applied to the member 504. In FIG. 6, one or more
elongated members 508 are provided to capture and retain the getter
material. The elongated members 508 typically are bond wires and
generally are attached to the package substrate through an
intermediate bond pad 506.
[0043] FIG. 7 is a cross section side view of a micromechanical
device package showing the bond wires used in the prior art. In
FIG. 7, a micromechanical device 702 is attached to a package
substrate 704. Bond wires 706 connect the device 702 to electrical
conduits formed in the substrate 704 to enable electrical
communication with circuitry outside the package. These bond wires
are similar to the anchor formed of bond wires shown in FIG. 2. One
aspect of the present invention provides a method of utilizing the
existing bond wires as an anchor for the gretter material.
[0044] FIG. 8 is a cross section side view of a micromechanical
device package showing the result of the novel application of the
getter to the bond wires 706 of FIG. 7. When the micromechanical
device 702 is packaged, it is first attached to the package
substrate 704. Bond wires 706 are then connected between bond pads
on the device 702 and bond pads on the package substrate 704. The
getter 708, mixed with any desired carriers and solvents, is then
deposited over the bond wires 706 as shown in FIG. 8. The getter
mixture is then cured, if necessary, to harden any carriers or
evaporate any solvents.
[0045] Using the existing bond wires as an anchor prevents having
to form a special purpose anchor for the getter and may increase
the resistance of the device to vibration. The use of existing bond
wires, however, also has several disadvantages and limitations. The
getter and carrier used in the embodiment of FIG. 8 must be
non-conductive. Additionally, applying the getter onto the bond
wires risks short circuiting the bond wires, or breaking the bond
wires.
[0046] FIG. 9 is an exploded perspective view of a portion of a
micromirror package substrate showing an anchor mechanism according
to one embodiment of the present invention. In FIG. 9, three layers
of ceramic material are shown. The three layers make up a portion
of a ceramic package substrate similar to those talked about
throughout this patent application. In FIG. 9, the bottom layer 900
is a solid piece of ceramic. The middle layer 902 has a wide strip
removed from the middle of the piece. The top layer 904 has a
narrow strip removed from the middle of the piece. The narrow strip
removed from the middle of the top piece may be widened as shown in
FIG. 9 at one or places.
[0047] FIG. 10 is a perspective view of the portion of a
micromirror package substrate of FIG. 9 showing the anchor of FIG.
9. FIG. 10 shows the assembled ceramic substrate 906 comprised of
the layers of FIG. 9. The layers of FIG. 9 form a cavity in the
ceramic substrate 906 with a wide bottom portion--formed in the
middle layer 902 and a relatively narrower top portion--formed by
the top layer 904. The narrow portion helps to retain the getter in
the cavity by creating a mechanical lock on the wide portion of
getter in the bottom of the cavity.
[0048] The examples shown in these figures merely are illustrative
of simplified applications of the present invention. The number,
materials, shapes and dimensions of the layers are provided for
purposes of illustration and not for purposes of limitation. For
example, the wide portions of the narrow slot are not necessary but
are illustrated to show one structure that reduces the likelihood
of pockets of air being captured in the getter anchor. Under
certain conditions, air trapped beneath the getter may expand and
could potentially force the getter out of the getter anchor.
[0049] FIG. 11 is a cross section side view of a portion of a
micromechanical package substrate 1100 showing two different anchor
cavities 1102, 1104 formed in a substrate to anchor a getter to the
substrate. The first anchor cavity is similar to the cavity of FIG.
10 in that the lower wide portion is centered under the narrow
portion. The second anchor cavity 1104 has the lower wide portion
offset to one side of the narrow portion. Other embodiments include
wide portions that only run a portion of the length of the anchor,
and wide portions with sections that are alternately offset to each
side of the narrow portion. Many alternate anchor cavity
configurations are possible, the only criteria being that the
anchor should be able to receive and hold the getter material.
[0050] FIG. 12 is a cross section side view of the portion of a
micromechanical package substrate 1100 of FIG. 11 showing a getter
1106 held by the anchors of FIG. 11. Each of the getters 1106 in
FIG. 12 extend above the package substrate 1100. This extension
allows a larger quantity of the getter material to be exposed to
the package cavity, but is not a necessary feature of the present
invention.
[0051] FIG. 13 is a cross section side view of a portion of a
micromechanical package substrate showing an alternate anchor
cavity formed in the substrate to anchor the getter to the
substrate. In FIG. 13, the package substrate 1302 has recesses
formed in both the floor 1304 and wall 1306 portions. These
recesses cooperate to form an anchor cavity capable of trapping a
getter as described above. The recesses of FIG. 13 may be formed in
a manner similar to the recesses described above. In FIG. 13, a
first anchor cavity is formed by a recess in only the floor 1304 of
the package substrate 1302, while a second anchor cavity 1310 is
formed by a recess in both the floor 1304 and the wall 1306 of the
package substrate.
[0052] FIG. 14 is a cross section side view of the portion of a
micromechanical package substrate 1302 of FIG. 13 showing getters
1412, 1414 held by the anchor of FIG. 13. As in FIG. 11, each of
the getters 1412, 1414 in FIG. 14 extend above the package
substrate 1302. Not only does this extension allow a larger
quantity of the getter material to be exposed to the package
cavity, but the extension is likely necessary to prevent the getter
material 1414 in the second anchor cavity 1310 from coming out of
the anchor cavity.
[0053] FIG. 15 is a cross section side view of a portion of a
micromechanical package substrate showing an alternate cavity
formed in the substrate to anchor the getter to the substrate. The
cavity anchor of FIG. 15 relies on the package lid or window 1502,
in combination with the package substrate 1504, to capture and
retain the getter materials. The package substrate 1504 of FIG. 15
provides a cavity to limit the motion of the getter in the plane of
the package substrate and lid. The lid 1502 prevents the getter
material from leaving the anchor cavity in a direction
perpendicular to the plane of the package substrate. FIG. 16 is a
cross section side view of the portion of a micromechanical package
substrate of FIG. 15 showing getter material 1506, 1508 held by the
anchor cavities of FIG. 15.
[0054] FIG. 17 is a schematic view of an image projection system
1700 using a micromirror 1702 having an improved package according
to the present invention. In FIG. 17, light from light source 1704
is focused on the improved micromirror 1702 by lens 1706. Although
shown as a single lens, lens 1706 is typically a group of lenses
and mirrors which together focus and direct light from the light
source 1704 onto the surface of the micromirror device 1702. Image
data and control signals from controller 1714 cause some mirrors to
rotate to an on position and others to rotate to an off position.
Mirrors on the micromirror device that are rotated to an off
position reflect light to a light trap 1708 while mirrors rotated
to an on position reflect light to projection lens 1710, which is
shown as a single lens for simplicity. Projection lens 1710 focuses
the light modulated by the micromirror device 1702 onto an image
plane or screen 1712.
[0055] Thus, although there has been disclosed to this point a
particular embodiment of a system and method for a micromechanical
getter anchor, it is not intended that such specific references be
considered as limitations upon the scope of this invention except
insofar as set forth in the following claims. Furthermore, having
described the invention in connection with certain specific
embodiments thereof, it is to be understood that further
modifications may now suggest themselves to those skilled in the
art, it is intended to cover all such modifications as fall within
the scope of the appended claims.
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