U.S. patent application number 11/869874 was filed with the patent office on 2008-07-24 for microelectromechanical systems contact stress sensor.
Invention is credited to Jack Kotovsky.
Application Number | 20080173960 11/869874 |
Document ID | / |
Family ID | 36061751 |
Filed Date | 2008-07-24 |
United States Patent
Application |
20080173960 |
Kind Code |
A1 |
Kotovsky; Jack |
July 24, 2008 |
MicroElectroMechanical Systems Contact Stress Sensor
Abstract
A microelectromechanical systems stress sensor comprising a
microelectromechanical systems silicon body. A recess is formed in
the silicon body. A silicon element extends into the recess. The
silicon element has limited freedom of movement within the recess.
An electrical circuit in the silicon element includes a
piezoresistor material that allows for sensing changes in
resistance that is proportional to bending of the silicon
element.
Inventors: |
Kotovsky; Jack; (Oakland,
CA) |
Correspondence
Address: |
Eddie E. Scott
P.O. Box 808, L-703
Livermore
CA
94551
US
|
Family ID: |
36061751 |
Appl. No.: |
11/869874 |
Filed: |
October 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11143543 |
Jun 1, 2005 |
7311009 |
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11869874 |
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60629271 |
Nov 17, 2004 |
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Current U.S.
Class: |
257/419 ;
257/E21.001; 257/E29.001; 438/53 |
Current CPC
Class: |
G01L 1/18 20130101 |
Class at
Publication: |
257/419 ; 438/53;
257/E21.001; 257/E29.001 |
International
Class: |
H01L 29/00 20060101
H01L029/00; H01L 21/00 20060101 H01L021/00 |
Goverment Interests
[0002] The United States Government has rights in this invention
pursuant to Contract No. DE-AC52-07NA27344 between the United
States Department of Energy and Lawrence Livermore National
Security, LLC.
Claims
1. A microelectromechanical systems stress sensor, comprising: a
microelectromechanical systems body, a recess in said body, a
silicon element that extends into said recess, said silicon element
having limited freedom of movement within said recess, and an
electrical circuit in said silicon element, said electrical circuit
including a piezoresistor material.
2. The stress sensor of claim 1 wherein said silicon member is a
silicon beam.
3. The stress sensor of claim 1 wherein said silicon member is a
silicon diaphragm.
4. The stress sensor of claim 1 wherein said microelectromechanical
systems body comprises a silicon body.
5. The stress sensor of claim 1 wherein said microelectromechanical
systems body comprises a compliant material body.
6. The stress sensor of claim 1 wherein said microelectromechanical
systems body comprises a silicone body.
7. The stress sensor of claim 1 wherein said microelectromechanical
systems body comprises a silicone rubber body.
8. The stress sensor of claim 1 wherein said microelectromechanical
systems body comprises a body made of fabric.
9. The stress sensor of claim 1 wherein said recess is an
indentation in said microelectromechanical systems body.
10. The stress sensor of claim 1 wherein said recess is an
indentation in said microelectromechanical systems body with said
indentation having a floor.
11. The stress sensor of claim 1 wherein said recess is a hole that
extends through said microelectromechanical systems body.
12. The stress sensor of claim 1 wherein said recess is a grove in
said microelectromechanical systems body.
13. The stress sensor of claim 1 wherein said
microelectromechanical systems body has a thickness, wherein said
silicon element has a thickness, and wherein said thickness of said
silicon element is less than said thickness of said
microelectromechanical systems body.
14. The stress sensor of claim 1 wherein said electrical circuit
comprises a piezoresistor material that extends along said silicon
element.
15. The stress sensor of claim 1 wherein said electrical circuit
includes legs comprised of a piezoresistor material that extend
along said silicon element.
16. The stress sensor of claim 1 wherein said electrical circuit
comprises a piezoresistor material that allows for sensing changes
in resistance that is proportional to bending of said silicon
element.
17. The stress sensor of claim 1 including a material encapsulating
said microelectromechanical systems body.
18. The stress sensor of claim 1 including a polyimide film
encapsulating said microelectromechanical systems body.
19. The stress sensor of claim 1 including a measuring unit for
measuring changes in electrical property of said silicon
element.
20. The stress sensor of claim 1 including at least one additional
recess in said body, at least one additional silicon element that
extends into said additional recess, and at least one additional
electrical circuit in said additional silicon element, said
additional electrical circuit including a piezoresistor
material.
21. The stress sensor of claim 1 including at least one additional
recess in said body, at least one additional silicon element that
extends into said additional recess, at least one additional
electrical circuit in said additional silicon element, said
additional electrical circuit including a piezoresistor material,
and at least one spring element connecting said silicon element and
said additional silicon element.
22. A stress sensor, comprising: microelectromechanical systems
body means for providing a base, recess means in said body means
for forming an open area, silicon element means that extends into
said recess means for limited movement, and electrical circuit
means in said silicon element means for sensing movement of said
silicon element means.
23. The stress sensor of claim 22 wherein said silicon element
means is a silicon beam.
24. The stress sensor of claim 22 wherein said silicon element
means is a silicon diaphragm.
25. The stress sensor of claim 22 wherein said
microelectromechanical systems body means comprises a silicon
body.
26. The stress sensor of claim 22 wherein said
microelectromechanical systems body means comprises a compliant
material body.
27. The stress sensor of claim 22 wherein said
microelectromechanical systems body means comprises a silicone
body.
28. The stress sensor of claim 22 wherein said
microelectromechanical systems body means comprises a silicone
rubber body.
29. The stress sensor of claim 22 wherein said
microelectromechanical systems body means comprises a body made of
fabric.
30. The stress sensor of claim 22 wherein said recess means is an
indentation in said microelectromechanical systems body means.
31. The stress sensor of claim 22 wherein said recess means is an
indentation in said microelectromechanical systems body with said
indentation having a floor.
32. The stress sensor of claim 22 wherein said recess means is a
hole that extends through said microelectromechanical systems body
means.
33. The stress sensor of claim 22 wherein said recess means is a
grove in said microelectromechanical systems body means.
34. The stress sensor of claim 22 wherein said
microelectromechanical systems body means has a thickness, wherein
said silicon element means has a thickness, and wherein said
thickness of said silicon element means is less than said thickness
of said microelectromechanical systems body.
35. The stress sensor of claim 22 wherein said electrical circuit
means comprises a piezoresistor material that extends along said
silicon element means.
36. The stress sensor of claim 22 wherein said electrical circuit
means includes legs comprised of a piezoresistor material that
extend along said silicon element means.
37. The stress sensor of claim 22 wherein said electrical circuit
means comprises a piezoresistor material that allows for sensing
changes in resistance that is proportional to bending of said
silicon element means.
38. The stress sensor of claim 22 including a material
encapsulating said microelectromechanical systems body means.
39. The stress sensor of claim 22 including a polyimide film
encapsulating said microelectromechanical systems body means.
40. The stress sensor of claim 22 including a measuring unit for
measuring changes in electrical property of said silicon element
means.
41. The stress sensor of claim 22 including at least one additional
recess means in said microelectromechanical systems body means, at
least one additional silicon element means that extends into said
additional recess means, and at least one additional electrical
circuit means in said additional silicon element means, said
additional electrical circuit means including a piezoresistor
material.
42. A method of producing a stress sensor, comprising the steps of:
microprocessing a silicon body to produce a recess in said silicon
body, microprocessing said silicon body to produce a silicon
element that extends into said recess and has a limited freedom of
movement within said recess, providing an electrical circuit
including a piezoresistor material operatively connected to said
silicon element and providing a measuring unit for measuring
changes in electrical properties of said electrical circuit.
43. The method of producing a stress sensor of claim 42 wherein
said step of microprocessing said silicon body to produce a silicon
element that extends into said recess and has a limited freedom of
movement within said recess comprises forming a section of said
silicon body with a reduced thickness to form said silicon
element.
44. The method of producing a stress sensor of claim 42 wherein
said step of microprocessing said silicon body to produce a silicon
element that extends into said recess and has a limited freedom of
movement within said recess comprises forming hole in said silicon
body that extends only partially through said silicon body leaving
a section of said silicon body with a reduced thickness to form
said silicon element.
45. The method of producing a stress sensor of claim 42 including
the step of encapsulating said silicon body with a polyimide
film.
46. The method of producing a stress sensor of claim 42 including
the step of providing additional silicon bodies and connecting said
silicon body and said additional silicon bodies with flexible
elements.
47. The method of producing a stress sensor of claim 42 including
the step of providing additional silicon bodies and connecting said
silicon body and said additional silicon bodies with spring
elements.
48. The method of producing a stress sensor of claim 42 including
the step of positioning said silicon body in a compliant
material.
49. The method of producing a stress sensor of claim 42 including
the step of positioning said silicon body in a silicone
material.
50. The method of producing a stress sensor of claim 42 including
the step of positioning said silicon body in a fabric.
51. The method of producing a stress sensor of claim 42 including
the steps of positioning said silicon body in a compliant material,
providing additional silicon bodies in said compliant material, and
connecting said silicon body and said additional silicon bodies
with flexible elements.
52. The method of producing a stress sensor of claim 51 wherein
said compliant material is silicone.
53. The method of producing a stress sensor of claim 51 wherein
said compliant material is fabric.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of prior application Ser.
No. 11/143,543 filed Jun. 1, 2005, entitled "MicroElectroMechanical
Systems Contact Stress Sensor", which claims the benefit of U.S.
Provisional Patent Application No. 60/629,271 filed Nov. 17, 2004,
and entitled, "MicroElectroMechanical Systems Contact Stress
Sensor" both of which are incorporated herein by this reference.
Any disclaimer that may have occurred during the prosecution of the
above-referenced application Ser. No. 11/143,543 is hereby
expressly rescinded.
BACKGROUND
[0003] 1. Field of Endeavor
[0004] The present invention relates to stress sensors and more
particularly to a microelectromechanical systems stress sensor.
[0005] 2. State of Technology
[0006] U.S. Pat. No. 6,272,936 issued Aug. 14, 2001 to Boris Oreper
and John Brennenman and assigned to Tekscan, Inc., provides the
following state of technology information: "There are many
applications where a need exists to detect pressure between two
contacting surfaces, either at a single point, or at a plurality of
points so as to provide a pressure profile. Such applications
include detecting pressure at gaskets, seals, and other contacting
surfaces in various industrial equipment for alignment, adjustment,
various other set-up functions, testing, maintenance, and the like;
in research facilities for measurement and testing of various
products; and in medical facilities for measuring and testing such
things as foot pressure distribution, dental occlusion and the
like. While pressure sensors for certain of these applications are
fabricated as a matrix array, many of these applications require
only one or more button sensors, the output or outputs from which
are read locally, are fed to a computer, either directly or
indirectly, or are otherwise utilized."
SUMMARY
[0007] Features and advantages of the present invention will become
apparent from the following description. Applicants are providing
this description, which includes drawings and examples of specific
embodiments, to give a broad representation of the invention.
Various changes and modifications within the spirit and scope of
the invention will become apparent to those skilled in the art from
this description and by practice of the invention. The scope of the
invention is not intended to be limited to the particular forms
disclosed and the invention covers all modifications, equivalents,
and alternatives falling within the spirit and scope of the
invention as defined by the claims.
[0008] Research and industrial groups often need to sense and/or
measure the stress between contacting surfaces. Instrumentation to
perform this measurement is limited and there is a distinct need
for improvement. In general, there are two basic approaches to
directly measure contact stresses. The first replaces a portion of
one of the contacting materials with a sensor at the materials'
interface. Large sensors may be used for this technique but it is
difficult for the sensor to assume the material properties of the
original material it replaces and thus the contact mechanics
change. This limitation poses an enormous limitation to this
technique with the advantage of being able to use a relatively
large sensor. The second approach leaves the original contacting
materials and surfaces intact and attempts to introduce a minimal
sensor at the interface to measure contact stress.
[0009] The sensor must be very small (thin) to not change the
interface stress as introduction of a bulky sensor at the contact
interface will likely change the contact mechanics. A successful
sensor needs to be minimally small and low in stiffness to allow
conformability.
[0010] The present invention provides a microelectromechanical
systems stress sensor. The microelectromechanical systems stress
sensor comprises a microelectromechanical systems body, a recess in
the body, an element that extends into the recess with the element
having limited freedom of movement within the recess, and an
electrical circuit in the element with the electrical circuit
including a piezoresistor material. In one embodiment of the
invention a beam extends into the recess and an electrical circuit
including a piezoresistor material detects stress. The beam in one
embodiment is a cantilevered beam and in another embodiment is a
doubly supported beam. In another embodiment of the invention the
element that extends into the recess is a diaphragm. In another
embodiment of the invention the element that extends into the
recess is a silicon body. In another embodiment of the invention
the element that extends into the recess is a compliant material
body. In another embodiment of the invention the element that
extends into the recess is a silicone body. In another embodiment
of the invention the element that extends into the recess is a body
made of fabric. Another embodiment includes at least one additional
recess in the microelectromechanical systems body, at least one
additional silicon element that extends into the additional recess,
and at least one additional electrical circuit in the additional
silicon element, the additional electrical circuit includes a
piezoresistor material.
[0011] The present invention also provides a method of producing a
stress sensor. The method comprises the steps of microprocessing a
silicon body to produce a recess in a silicon body, microprocessing
the silicon body to produce a silicon element that extends into the
recess and has a limited freedom of movement within the recess,
providing an electrical circuit including a piezoresistor material
operatively connected to the silicon element, and providing a
measuring unit for measuring changes in electrical properties of
the electrical circuit. In another embodiment, the present
invention includes providing additional silicon bodies and
connecting the silicon body and the additional silicon bodies by
flexible elements.
[0012] The present invention has use for any application that
requires contact stress sensing or measurement. Examples of use of
the present invention include joint contact stress research in
animals and humans (medical applications), oncologic research and
drug monitoring, roller systems, automotive (engine component
stresses, i.e., head gasket loads), robotic tactile sensing,
footwear design, fastener design, etc.
[0013] The invention is susceptible to modifications and
alternative forms. Specific embodiments are shown by way of
example. It is to be understood that the invention is not limited
to the particular forms disclosed. The invention covers all
modifications, equivalents, and alternatives falling within the
spirit and scope of the invention as defined by the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings, which are incorporated into and
constitute a part of the specification, illustrate specific
embodiments of the invention and, together with the general
description of the invention given above, and the detailed
description of the specific embodiments, serve to explain the
principles of the invention.
[0015] FIGS. 1-3 illustrate one embodiment of a
microelectromechanical systems stress senor apparatus constructed
in accordance with the present invention.
[0016] FIG. 4 illustrates another embodiment of a
microelectromechanical systems stress sensor apparatus constructed
in accordance with the present invention.
[0017] FIG. 5 illustrates another embodiment of a cantilevered beam
microelectromechanical systems stress senor apparatus constructed
in accordance with the present invention.
[0018] FIG. 6 illustrates another embodiment of a
microelectromechanical systems stress senor apparatus constructed
in accordance with the present invention in the form of a
doubly-supported beam.
[0019] FIG. 7 illustrates another embodiment of a
microelectromechanical systems stress senor apparatus constructed
in accordance with the present invention in the form of a flexible
diaphragm.
[0020] FIG. 8 illustrates an embodiment of the present invention
with contact stress sensors connected by silicon microsprings.
[0021] FIG. 9 illustrates an embodiment of the present
invention.
[0022] FIG. 10 illustrates another embodiment of a
microelectromechanical systems stress sensor apparatus constructed
in accordance with the present invention.
[0023] FIG. 11 illustrates another embodiment of a
microelectromechanical systems stress sensor apparatus constructed
in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] Referring to the drawings, to the following detailed
description, and to incorporated materials, detailed information
about the invention is provided including the description of
specific embodiments. The detailed description serves to explain
the principles of the invention. The invention is susceptible to
modifications and alternative forms. The invention is not limited
to the particular forms disclosed. The invention covers all
modifications, equivalents, and alternatives falling within the
spirit and scope of the invention as defined by the claims.
[0025] Referring now to FIGS. 1-3, one embodiment of a
microelectromechanical systems stress senor apparatus constructed
in accordance with the present invention is illustrated. The
apparatus is designated generally by the reference numeral 10. As
shown in FIG. 1, the apparatus 10 comprises a thin
microelectromechanical systems silicon body 11. A recess 12 is
formed in the silicon body 11. The recess 12 may be an indentation
12 with a floor 13 as shown in FIG. 1. In other embodiments of the
invention, the recess 12 may be a hole that extends entirely
through the silicon body 11 or the recess may be a groove that
extends from an edge of the silicon body 11. A silicon beam 14
extends into the recess 12. The thickness of the beam 14 is less
than the body 11. This provides for the top surface of the beam
seeing load and the underside of the beam being shielded from load.
With a floor 13 in place, the underside of the beam is protected
from receiving load even if between compliant solids. The silicon
beam 14 has limited freedom of movement within the recess 12 and
above the floor 13 of the recess 12. An electrical circuit 15 is
formed in the silicon beam 14. The electrical circuit 15 is
comprised of a piezoresistor material.
[0026] The silicon beam 14 and the electrical circuit are
illustrated in greater detail in FIG. 2. The silicon beam 14
extends from the thin silicon body 11 and has limited freedom of
movement within the recess. The electrical circuit 15 extends along
the length of the silicon beam 14. The electrical circuit 15
includes legs 16 and 18 that extend along the length of the silicon
beam 14. An end portion 17 of the electrical circuit 15 connects
the legs 16 and 18. The electrical circuit 15 is comprised of a
piezoresistor material that allows for sensing changes in
resistance that is proportional to bending of the silicon beam 14.
This embodiment shown represents the cantilevered form of the beam.
A doubly-supported beam may be used and the doped piezoresistor may
be used in an `out-and-back` geometry as shown for the cantilever.
The piezoresistive trace may also extend across the
doubly-supported beam. For p-type silicon, a heavy and light
implant may be used to avoid offsetting resistance changes with
load (the top center of the beam is in compression when the ends
are in tension). For n-type silicon the positive and negative
stresses formed at the beam's surface with load will not
offset.
[0027] The apparatus 10 allows the measurement of stress between
contacting surfaces. As illustrated in FIG. 3, the apparatus 10 is
positioned between the members 19 and 20. The member 19 has an
upper surface 21 and the member 20 has an tipper surface 22. The
abutting ends of the members 19 and 20 each have end surface. The
apparatus 10 is positioned between the abutting end surfaces of the
members 19 and 20.
[0028] The apparatus 10 allows the measurement of stress between
contacting surfaces. It can be fabricated as a single device or as
an array of microfabricated stress sensors that independently
measure contact stress. The apparatus 10 includes doped
piezoresistors embedded in cantilevered or doubly supported silicon
beams. With applied normal loads, beam bending produces stress in
the beam's surface and a corresponding change in resistance of the
doped material. The change in resistance is calibrated to the
applied load to provide a highly repeatable stress measurement. Due
to silicon's mechanical and electrical properties, the apparatus 10
shows good accuracy, linearity and lack of hysteresis. Multiple
independent apparatus 10 may be interconnected in a flexible and
extensible array to allow conformity to complex and or compliant
surfaces. The apparatus 10 is very thin which minimizes its effect
on the stress distribution it measures. Flexible Kapton and Kapton
cable connects can be used to encapsulate and communicate with the
sensing devices. A technique of layered Kapton packaging produces a
constant thickness device to maintain even load distributions.
Tests have also been conducted with silicone rubber encapsulants
that offer extensibility in addition to flexibility for the sensor
package.
[0029] The details of one embodiment of an apparatus 10 for
measuring stress constructed in accordance with the present
invention having been described, the operation of the apparatus 10
and manufacture of the apparatus 10 will now be considered.
[0030] The apparatus 10 allows the measurement of stress between
contacting surfaces. It can be fabricated as a single device or as
an array of microfabricated stress sensors that independently
measure contact stress. The apparatus 10 includes doped
piezoresistors embedded in a cantilevered or doubly supported
Silicon beam 14. An alternate embodiment includes doped
piezoresistors embedded in a silicon diaphragm. With applied normal
loads, beam bending produces stress in the beam's surface and a
corresponding change in resistance of the doped material. The
change in resistance is calibrated to the applied load to provide a
highly repeatable stress measurement. Due to silicon's mechanical
and electrical properties, the devices show good accuracy,
linearity and lack of hysteresis. Where multiple apparatus 10 are
utilized, the independent devices are interconnected in a flexible
and extensible array to allow conformity to complex and or
compliant surfaces. The array is very thin to minimize its effect
on the stress distribution it measures. Flexible polyimide
material, such as Kapton.RTM., or Kapton.RTM. cable connects can be
used to encapsulate and communicate with the sensing devices. A
technique of layered Kapton.RTM. packaging produces a constant
thickness device to maintain even load distributions. Tests have
also been conducted with Silicone rubber encapsulates that offer
extensibility in addition to flexibility for the sensor
package.
[0031] The apparatus 10 has use for joint contact stress research
in animals and humans (medical applications), oncologic research
and drug monitoring, roller systems, automotive (engine component
stresses, i.e., head gasket loads), robotic tactile sensing,
footwear design, fastener design, etc. The apparatus 10 also has
use for Stockpile Stewardship testing and will help to assess load
path issues in device performance. The apparatus 10 has use for any
application that requires contact stresses sensing or
measurement.
[0032] Referring now to FIG. 4, another embodiment of a
microelectromechanical systems stress sensor apparatus constructed
in accordance with the present invention is illustrated. The
apparatus is designated generally by the reference numeral 40. The
apparatus 40 allows the measurement of stress between contacting
surfaces. The apparatus 40 has a thickness of only approximately 55
microns. It can be tuned to produce different bending sensitivity,
thus allowing it to be employed between two surfaces in close
proximity. Its low weight is also useful for space or other
applications that demand low weight or high bandwidth measurements
where instrument mass is an issue in second order dynamics.
[0033] Many research and industrial groups need to measure the
stress between contacting surfaces. Instrumentation to perform this
measurement is limited and there is a distinct need for
improvement. In general, there are two basic approaches to
measuring contact stresses. The first replaces a portion of one of
the contacting materials with a sensor at the materials' interface.
Large sensors may be used for this technique but it is difficult
for the sensor to assume the material properties of the original
material it replaces and thus the contact mechanics change. This
limitation poses an enormous limitation to this technique with the
advantage of being able to use a relatively large sensor.
[0034] The second approach leaves the original contacting materials
and surfaces intact and attempts to introduce a minimal sensor at
the interface to measure contact stress. The sensor must be very
small (thin) to not change the interface stress as introduction of
a bulky sensor at the contact interface will likely change the
contact mechanics. A successful sensor needs to be minimally small
and low in stiffness to allow conformability.
[0035] The apparatus 40 has many uses. For example, the apparatus
40 is useful for stewardship testing. It will help to assess load
path issues in device performance. The apparatus 40 has use for
Joint contact stress research in animals/humans (medical
applications), in oncologic research and drug monitoring, in roller
systems, in automotive (engine component stresses, i.e., head
gasket loads), in robotic tactile sensing, in footwear design, in
fastener design, and in athletic measurements such as golf swing
and impact. The apparatus 40 has use in any application that
requires contact stresses to be determined.
[0036] The apparatus 40 includes doped piezoresistors embedded in a
cantilevered or doubly supported silicon beam 41. The silicon beam
41 extends from the body 47 of the apparatus 40 and has limited
freedom of movement within a recess in the body of the apparatus
40. An electrical circuit 42 extends along the length of the
silicon beam 41. The electrical circuit 42 includes legs 44 and 46
that extend along the length of the silicon beam 41. An end portion
48 of the electrical circuit 42 connects the legs 44 and 46. The
electrical circuit 42 is comprised of a piezoresistor material 43
that allows for sensing changes in resistance that is proportional
to bending of the silicon beam 41.
[0037] The apparatus 40 is based on silicon flexibility used as a
displacement sensor. By doping the silicon surface of beam 41 with
piezoresistors 43, the thin silicon beam 41 will produce a
resistance change proportional to its bending. The apparatus 40 can
be arranged like a cantilevered diving board where tip deflection
due to contact with a moving part produces proportional resistance
change.
[0038] The details of one embodiment of an apparatus 40 for
measuring stress constructed in accordance with the present
invention having been described, the manufacture of the apparatus
40 will now be considered. The apparatus 40 allows the measurement
of stress between contacting surfaces. The apparatus 40 can be
fabricated as a single device or as an array of microfabricated
stress sensors that independently measure contact stress. The
apparatus 40 can be produced utilizing a number of methods of
manufacture, particularly MicroElectroMechanical Systems (MEMS)
technology.
[0039] The first method of manufacture involves the formation of
3-dimensional structures in a single-crystal Silicon wafer. The
process employs an anisotropic plasma etch of Silicon in a deep
reactive ion etcher combined with an anisotropic Potassium
Hydroxide (KOH) etch. The resulting shape is an undercut beam or
bridge in Silicon. As MEMS technology is typically constrained to
two dimensions, creation of an undercut, three dimensional
structure in single crystal Silicon offers a variety of advantages
and applications.
[0040] Examples include transducers, resonators, accelerometers,
stress sensors, flow sensors, actuators, atomic force microscopes,
probes/needles, containers, and heaters/coolers.
[0041] Another method of manufacture is to plasma or wet etch a
recess into a silicon chip to form a thinned diaphragm. The etch
can be performed as a timed or measured etch or with use of a
stopping layer like a buried oxide layer in a silicon-on-insulator
wafer or a doped stopping layer. Both anisotropic and isotropic
etchants may be used for this purpose, success has been
demonstrated with a deep reactive ion etch that etches
anisotropically.
[0042] An advantage of the diaphragm is that a full wheatstone
bridge may be employed on the sensor. The four resistive legs allow
for a closely balanced bridge and optimal thermal compensation.
Various resistor arrangements may be employed to optimize load
response or thermal stability. Aligning to the (110) direction of
p-type silicon allows for maximum sensitivity to radial loads in
the bending diaphragm. Alignment to (100) directions provides no
response to radial loads. Tangential loads cancel to provide a
thermally stable bridge with each resistor appearing identical.
[0043] Another method of manufacture involves a process of
producing flexible silicon devices. A process has been developed
that creates MEMS transducers on very thin substrates. One method
of manufacture provides minimal silicon thickness or mass. The
delicate substrate is a 4'' Silicon wafer thinned to 55 microns or
less by a grinding and polish process. This substrate is mounted
temporarily on a rigid Silicon, quartz or other substrate.
Photoresist is traditionally used to mount thin substrates on
handle wafers. As silicon and MEMS processing place a variety of
demands on the mounted substrates, a temporary glue layer
connecting the thin substrate to its handle is difficult to
achieve. Applicants utilize a wafer saw tape known as Dynatex
Wafergrip for the temporary adhesive. This material was chosen for
its adhesive strength and thermal continuity. MEMS processing
frequently requires deep reactive ion etching. This process
generates significant heat in the etched substrate (the thin
substrate in this case). Cooling of this substrate is important to
the success of the etch and the masking of the etch with
temperature sensitive materials. Cooling is accomplished by a
steady flow of Helium on the back of the substrate in contact with
the machine's chuck. The joining layer between the thinned
substrate and the handle thus provides a limit for the process as
it acts as a thermal barrier. The wafergrip adhesion is the only
reliable adhesive discovered for etching of thin substrates.
Additionally, it withstands other processing such as
photolithography and various short wet chemistry treatments. The
use of Wafergrip offers significant advantages to photoresist
mounting techniques. Other thin adhesives, glues and chemically
resistant stick layers can be used as alternate embodiments to this
concept.
[0044] The apparatus 40 is created based on the silicon flexibility
and can be used as a displacement sensor. By doping the silicon
surface with piezoresistors, the thin silicon beam 41 produces a
resistance change proportional to its bending. The device 40 can be
arranged with the beam 41 like a cantilevered diving board where
tip deflection due to contact with a moving part produces
proportional resistance change. The device 40 has a thickness of
only 55 microns (approximately . . . thickness can be tuned to
produce different bending sensitivity) allowing it to be employed
between two surfaces in close proximity (for gap measurements). Its
low weight also may be interesting for space or other applications
that demand low weight or high bandwidth measurements where
instrument mass is an issue in second order dynamics.
[0045] The contact stress sensor 40 is formed by producing a doped
piezoresistor through the center of the doubly supported three
dimensional beam described above. A more sensitive device can be
formed by a resistive trace embedded in a cantilevered beam.
Mechanical loads on the Silicon surface produce deflection of the
microbeams relative to their supporting frames. The deflections
produce strain in the Silicon and a proportional resistance change.
For the doubly supported beam, two implants may be required to
create a conductive region at the center of the beam and resistors
at its ends. This prevents the positive and negative strains at the
deflected beam's surface from not offsetting in p-type
piezoresistors. The supportive frame is thicker than the microbeam
at its center, the surface of the beam is identical to the surface
of the chip. The underside of the beam is distant from the backside
of the chip. Thus, equal loads on the top and bottom of the chip
produce a differential load across the beam and beam deflection.
The hole beneath the beam can either be a through chip hole or a
blind hole. The design of the shape of the hole may affect
sensitivity and performance of the chip for different applications.
The supporting frame around the beam can be mechanically isolated
from a bending array to insure bending of the array does not
produce beam strain (i.e., that bending the array so that it
conforms to a curved surface does not produce beam signal intended
to measure applied normal loads only). The size of the hole
surrounding the beam may affect shear sensitivity and should be
designed for the application. The hole size may also affect the
beam's sensitivity to normal loads depending on the compliant layer
above it. A compliant layer above the beam helps to transfer load
to the beam's surface and may affect device sensitivity. Thus the
packaging of the sensor may be important.
[0046] Referring now to FIG. 5, another embodiment of a
microelectromechanical systems stress senor apparatus constructed
in accordance with the present invention is illustrated. The
apparatus is designated generally by the reference numeral 50. As
shown in FIG. 5, the apparatus 50 comprises a thin
microelectromechanical systems silicon body 51. A recess 52 is
formed in the silicon body 51. The recess 52 may be an indentation
with a floor, the recess 52 may be a hole that extends entirely
through the silicon body 51, or the recess may be a groove that
extends from an edge of the silicon body 51. A silicon beam 54
extends into the recess 52.
[0047] The silicon beam 54 extends from the silicon body 51 and has
limited freedom of movement within the recess 52. The electrical
circuit 55 extends from the silicon body 51 into and along the
length of the silicon beam 54. The electrical circuit 55 includes
legs 56 and 58 for connection to detection and measuring equipment
and a piezoresistor material 53 section that extends along the
length of the silicon beam 54. The piezoresistor material 53 allows
for sensing changes in resistance of the electrical circuit 55 that
is proportional to bending of the silicon beam 54. The embodiment
shown in FIG. 5 represents the cantilevered form of the beam. In
other embodiments, a doubly-supported beam is used. The doped
piezoresistor 53 can be used in an `out-and-back` geometry as shown
for the cantilever. The piezoresistive material 53 may also extend
across the doubly-supported beam. For p-type silicon, a heavy and
light implant may be used to avoid offsetting resistance changes
with load (the top center of the beam is in compression when the
ends are in tension). For n-type silicon the positive and negative
stresses formed at the beam's surface with load will not
offset.
[0048] The apparatus 50 allows the measurement of stress between
contacting surfaces. It can be fabricated as a single device or as
an array of microfabricated stress sensors that independently
measure contact stress. The apparatus 50 includes doped
piezoresistors 53 embedded in cantilevered or doubly supported
silicon beams 54. With applied normal loads, beam bending produces
stress in the beam's surface and a corresponding change in
resistance of the doped material 53. The change in resistance is
calibrated to the applied load to provide a highly repeatable
stress measurement. Due to silicon's mechanical and electrical
properties, the apparatus 50 shows good accuracy, linearity and
lack of hysteresis. Multiple independent apparatus 50 may be
interconnected in a flexible and extensible array to allow
conformity to complex and or compliant surfaces. The apparatus 50
is very thin which minimizes its effect on the stress distribution
it measures. Flexible Kapton and Kapton cable connects can be used
to encapsulate and communicate with the sensing devices. A
technique of layered Kapton packaging produces a constant thickness
device to maintain even load distributions. Tests have also been
conducted with silicone rubber encapsulants that offer
extensibility in addition to flexibility for the sensor
package.
[0049] The silicon body 51 has a thickness 57. The thickness 59 of
the silicon beam 54 is less than the thickness 57 of the body 51.
This provides for the top surface of the beam seeing load and the
underside of the beam being shielded from load. The silicon beam 54
is produced by etching the silicon body 51 to form the silicon beam
54. The etching process provides a system for producing the
cantilevered beam 54 with the thickness 59 that is less than the
thickness 57 of the body 51.
[0050] The details of one embodiment of an apparatus 50 for
measuring stress constructed in accordance with the present
invention having been described, the operation of the apparatus 50
and manufacture of the apparatus 50 will now be considered.
[0051] The apparatus 50 allows the measurement of stress between
contacting surfaces. It can be fabricated as a single device or as
an array of microfabricated stress sensors that independently
measure contact stress. The apparatus 50 includes doped
piezoresistors 53 embedded in a cantilevered or doubly supported
silicon beam 54. An alternate embodiment includes doped
piezoresistors embedded in a doubly supported beam or a silicon
diaphragm. With applied normal loads, beam bending produces stress
in the beam's surface and a corresponding change in resistance of
the doped material. The change in resistance is calibrated to the
applied load to provide a highly repeatable stress measurement. Due
to silicon's mechanical and electrical properties, the devices show
good accuracy, linearity and lack of hysteresis. Where multiple
apparatus 50 are utilized, the independent devices are
interconnected in a flexible and extensible array to allow
conformity to complex and or compliant surfaces. The array is very
thin to minimize its effect on the stress distribution it measures.
Flexible polyimide material, such as Kapton.RTM., or Kapton.RTM.
cable connects can be used to encapsulate and communicate with the
sensing devices. A technique of layered Kapton.RTM. packaging
produces a constant thickness device to maintain even load
distributions. Tests have also been conducted with Silicone rubber
encapsulates that offer extensibility in addition to flexibility
for the sensor package.
[0052] The apparatus 50 has use for joint contact stress research
in animals and humans (medical applications), oncologic research
and drug monitoring, roller systems, automotive (engine component
stresses, i.e., head gasket loads), robotic tactile sensing,
footwear design, fastener design, etc. The apparatus 50 also has
use for Stockpile Stewardship testing and will help to assess load
path issues in device performance. The apparatus 50 has use for any
application that requires contact stresses sensing or
measurement.
[0053] Referring now to FIG. 6, another embodiment of a
microelectromechanical systems stress senor apparatus constructed
in accordance with the present invention is illustrated. The
apparatus is designated generally by the reference numeral 60. As
shown in FIG. 6, the apparatus 60 comprises a thin
microelectromechanical systems silicon body 61. A recess 62 is
formed in the silicon body 61. The recess 62 may be an indentation
with a floor, the recess 62 may be a hole that extends entirely
through the silicon body 61, or the recess may be a groove that
extends from an edge of the silicon body 61. A series of doubly
supported silicon beams 64 extend into the recess 62.
[0054] The silicon beams 64 extend from the silicon body 61 and
have limited freedom of movement within the recess 62. An
electrical circuit 65 extends from the silicon body 61 into and
along the length of each of the silicon beams 64. The electrical
circuit 65 includes legs 66 and 68 for connection to detection and
measuring equipment and a piezoresistor material 63 section that
extends along the length of each of the silicon beams 64. The
piezoresistor material 63 allows for sensing changes in resistance
of the electrical circuit 65 that is proportional to bending of the
silicon beams 64. The embodiment shown in FIG. 6 represents the
doubly-supported beams is used. The doped piezoresistor 63 is an
`out-and-back` geometry as shown. The piezoresistive material 63
may also extend across the doubly-supported beams. For p-type
silicon, a heavy and light implant may be used to avoid offsetting
resistance changes with load (the top center of the beams is in
compression when the ends are in tension). For n-type silicon the
positive and negative stresses formed at the beam's surface with
load will not offset.
[0055] The apparatus 60 allows the measurement of stress between
contacting surfaces. It can be fabricated as a single device or as
an array of microfabricated stress sensors that independently
measure contact stress. The apparatus 60 includes doped
piezoresistors 63 embedded in the doubly supported silicon beams
64. With applied normal loads, the beams bending produces stress in
the beam's surface and a corresponding change in resistance of the
doped material 63. The change in resistance is calibrated to the
applied load to provide a highly repeatable stress measurement. Due
to silicon's mechanical and electrical properties, the apparatus 60
shows good accuracy, linearity and lack of hysteresis. Multiple
independent apparatus 60 may be interconnected in a flexible and
extensible array to allow conformity to complex and or compliant
surfaces. The apparatus 60 is very thin which minimizes its effect
on the stress distribution it measures. Flexible Kapton and Kapton
cable connects can be used to encapsulate and communicate with the
sensing devices. A technique of layered Kapton packaging produces a
constant thickness device to maintain even load distributions.
Tests have also been conducted with silicone rubber encapsulants
that offer extensibility in addition to flexibility for the sensor
package.
[0056] The details of the embodiment of an apparatus 60 for
measuring stress constructed in accordance with the present
invention having been described, the operation of the apparatus 60
and manufacture of the apparatus 60 will now be considered.
[0057] The silicon body 61 has a thickness 67. The thickness 69 of
each of the silicon beams 64 is less than the thickness 67 of the
body 61. This provides for the top surface of the beams seeing load
and the underside of the beams being shielded from load. The
silicon beams 64 are produced by etching the silicon body 61 to
form the silicon beams 64. The etching process provides a system
for producing the doubly supported beams 64 with the thickness 69
that is less than the thickness 67 of the body 61.
[0058] The apparatus 60 allows the measurement of stress between
contacting surfaces. It can be fabricated as a single device or as
an array of microfabricated stress sensors that independently
measure contact stress. The apparatus 60 includes doped
piezoresistors 63 embedded in the doubly supported silicon beams
64. An alternate embodiment includes doped piezoresistors embedded
in a silicon diaphragm. With applied normal loads, the beams
bending produces stress in the beam's surface and a corresponding
change in resistance of the doped material. The change in
resistance is calibrated to the applied load to provide a highly
repeatable stress measurement. Due to silicon's mechanical and
electrical properties, the devices show good accuracy, linearity
and lack of hysteresis. Where multiple apparatus 60 are utilized,
the independent devices are interconnected in a flexible and
extensible array to allow conformity to complex and or compliant
surfaces. The array is very thin to minimize its effect on the
stress distribution it measures. Flexible polyimide material, such
as Kapton.RTM., or Kapton.RTM. cable connects can be used to
encapsulate and communicate with the sensing devices. A technique
of layered Kapton.RTM. packaging produces a constant thickness
device to maintain even load distributions. Tests have also been
conducted with Silicone rubber encapsulates that offer
extensibility in addition to flexibility for the sensor
package.
[0059] The apparatus 60 has use for joint contact stress research
in animals and humans (medical applications), oncologic research
and drug monitoring, roller systems, automotive (engine component
stresses, i.e., head gasket loads), robotic tactile sensing,
footwear design, fastener design, etc. The apparatus 60 also has
use for Stockpile Stewardship testing and will help to assess load
path issues in device performance. The apparatus 60 has use for any
application that requires contact stresses sensing or
measurement.
[0060] Referring now to FIG. 7, another embodiment of a
microelectromechanical systems stress sensor apparatus constructed
in accordance with the present invention is illustrated. The
apparatus is designated generally by the reference numeral 70. As
shown in FIG. 7, the apparatus 70 comprises a thin
microelectromechanical systems silicon body 71. A recess 72 is
formed in the silicon body 71. A flexible silicon diaphragm 73 is
located in the recess 72.
[0061] The flexible silicon diaphragm 73 is formed in the silicon
body 71 and has limited freedom of movement within the recess 72.
An electrical circuit 77 is located on one side of the flexible
silicon diaphragm 73. The electrical circuit 77 includes legs for
connection to detection and measuring equipment and a piezoresistor
material section that extends along the flexible silicon diaphragm
73. The piezoresistor material allows for sensing changes in
resistance of the electrical circuit 77 that is proportional to
bending of the flexible silicon diaphragm 73.
[0062] The apparatus 70 allows the measurement of stress between
contacting surfaces. It can be fabricated as a single device or as
an array of microfabricated stress sensors that independently
measure contact stress. The apparatus 70 includes doped
piezoresistors embedded in the flexible silicon diaphragm 73. With
applied normal loads, the diaphragm's 73 bending produces stress in
the diaphragm's surface and a corresponding change in resistance of
the doped piezoresistor material. The change in resistance is
calibrated to the applied load to provide a highly repeatable
stress measurement. The apparatus 70 is very thin which minimizes
its effect on the stress distribution it measures.
[0063] The details of the embodiment of an apparatus 70 for
measuring stress constructed in accordance with the present
invention having been described, the operation of the apparatus 70
and manufacture of the apparatus 70 will now be considered.
[0064] The silicon body 71 has a thickness 75. The thickness 76 of
the flexible silicon diaphragm 73 is less than the thickness 75 of
the body 71. The flexible silicon diaphragm 73 is produced by
etching a hole 74 partially through the silicon body 71. The
portion of the silicon body 71 remaining below the hole 74 produces
the flexible silicon diaphragm 73. The etching process provides a
system for producing the flexible silicon diaphragm 73 with the
thickness 76 that is less than the thickness 75 of the body 71.
[0065] The apparatus 70 allows the measurement of stress between
contacting surfaces. It can be fabricated as a single device or as
an array of microfabricated stress sensors that independently
measure contact stress. The apparatus 70 includes doped
piezoresistors embedded in the flexible silicon diaphragm 73. With
applied normal loads, the beams bending produces stress in the
diaphragm's 73 surface and a corresponding change in resistance of
the doped material. The change in resistance is calibrated to the
applied load to provide a highly repeatable stress measurement. Due
to silicon's mechanical and electrical properties, the devices show
good accuracy, linearity and lack of hysteresis. Where multiple
apparatus 70 are utilized, the independent devices are
interconnected in a flexible and extensible array to allow
conformity to complex and or compliant surfaces. The array is very
thin to minimize its effect on the stress distribution it measures.
Flexible polyimide material, such as Kapton.RTM., or Kapton.RTM.
cable connects can be used to encapsulate and communicate with the
sensing devices. A technique of layered Kapton.RTM. packaging
produces a constant thickness device to maintain even load
distributions. Tests have also been conducted with Silicone rubber
encapsulates that offer extensibility in addition to flexibility
for the sensor package.
[0066] The apparatus 70 has use for joint contact stress research
in animals and humans (medical applications), oncologic research
and drug monitoring, roller systems, automotive (engine component
stresses, i.e., head gasket loads), robotic tactile sensing,
footwear design, fastener design, etc. The apparatus 70 also has
use for Stockpile Stewardship testing and will help to assess load
path issues in device performance. The apparatus 70 has use for any
application that requires contact stresses sensing or
measurement.
[0067] Referring now to FIG. 8, a package is shown that includes
embedded silicon chips that comprise microelectromechanical systems
stress sensors. The package is generally designated by the
reference numeral 80. The package 80 is primarily a three layer
stack of polyimide film, such as Kapton.RTM., with one layer
carrying conductive metal 81 that provides springs connecting
silicon chips 82 that include microelectromechanical systems stress
sensors 83. The package 80 is uniform in thickness everywhere as
the 80 micron thick chips 82 are encased in a polyimide film stack
with matched thickness middle layer. The package 80 that is
illustrated shows four embedded silicon chips 82 with the four
individual microelectromechanical systems stress sensors 83. The
individual microelectromechanical systems stress sensors 83 each
have two, three or four connecting leads 84. The twelve wires can
be accessed by a flex connector at the exposed metal tips. The
individual microelectromechanical systems stress sensors 83 are
stress sensors that independently measure contact stress such as
the stress sensors shown in FIGS. 5, 6, and 7.
[0068] Flex circuits are common and direct mounting of silicon
devices on flex circuits is common. This package 80 is entirely
encased in the polyimide film so that the ensuing package is
uniform in thickness. Maintaining package thickness uniformity is
necessary for contact stress measurement. The first layer of
polyimide film carries thin, patterned metal traces 81 that mate
with metal contact pads on the surface of the chips 82. A second
layer of polyimide film is cut to have holes identical in shape to
the silicon part. It is aligned and adhered to the first polyimide
film layer. The chip 82 is self-aligned to the metal traces 81 on
polyimide film layer 1 (chip oriented metal side against the metal
traces on the Kapton.RTM.) as it is constrained by the patterned
holes through the polyimide film layer 2. Layer 2 is chosen to be
the same thickness as the silicon part (approximately 55 microns).
The metal on the silicon is soldered to the metal traces below
through use of applied solder paste or electroplating solder (i.e.,
Indium or lead-tin or gold-tin) on the Kapton.RTM. metal traces
(before or after polyimide film layer 2 is applied). Once soldered
in place, the chip's surface is flush with the polyimide film layer
2 surface. The third Kapton.RTM. layer is applied to entirely
encase the chip. Polyimide film layer 3 is patterned with through
holes to provide access to the metal on Kapton.RTM. layer 1 (the
same holes exist on polyimide film layer 2) where a connector will
meet those traces.
[0069] Referring now to FIG. 9, another embodiment of a
microelectromechanical systems stress senor apparatus constructed
in accordance with the present invention is illustrated. The
apparatus is designated generally by the reference numeral 90. The
apparatus 90 utilizes a flexible silicon diaphragm 91 as described
in connection with the microelectromechanical systems stress senor
apparatus 70 previously described and illustrated in FIG. 7. The
flexible silicon diaphragm 91 is formed in the thin
microelectromechanical systems silicon body 95. The flexible
silicon diaphragm 91 has limited freedom of movement within the
silicon body 95.
[0070] An electrical circuit is located on the flexible silicon
diaphragm 91. The electrical circuit includes legs 93 for
connection to detection and measuring equipment and a piezoresistor
material section 92 that extends along the flexible silicon
diaphragm 91. The piezoresistor material 92 allows for sensing
changes in resistance of the electrical circuit that is
proportional to bending of the flexible silicon diaphragm 91.
[0071] The apparatus 90 allows the measurement of stress between
contacting surfaces. The apparatus 90 includes doped piezoresistors
93 embedded in the flexible silicon diaphragm 91. With applied
normal loads, the diaphragm's 91 bending produces stress in the
diaphragm's surface and a corresponding change in resistance of the
doped piezoresistor material. The change in resistance is
calibrated to the applied load to provide a highly repeatable
stress measurement. The apparatus 90 is very thin which minimizes
its effect on the stress distribution it measures.
[0072] The apparatus 90 has use for joint contact stress research
in animals and humans (medical applications), oncologic research
and drug monitoring, roller systems, automotive (engine component
stresses, i.e., head gasket loads), robotic tactile sensing,
footwear design, fastener design, etc. The apparatus 90 also has
use for Stockpile Stewardship testing and will help to assess load
path issues in device performance. The apparatus 90 has use for any
application that requires contact stresses sensing or
measurement.
[0073] Referring now to FIG. 10, another embodiment of a
microelectromechanical systems stress senor system constructed in
accordance with the present invention is illustrated. The system is
designated generally by the reference numeral 100. As shown in FIG.
10, the system 100 comprises a thin microelectromechanical systems
silicon body 103.
[0074] The apparatus 100 utilizes a flexible silicon diaphragm 101
as described in connection with the microelectromechanical systems
stress senor apparatus 70 previously described and illustrated in
FIG. 7. The flexible silicon diaphragm 101 is formed in the thin
microelectromechanical systems silicon body 103. The flexible
silicon diaphragm 101 has limited freedom of movement within the
silicon body 103.
[0075] An electrical circuit is connected to the flexible silicon
diaphragm 101. The electrical circuit includes legs 102 for
connection to detection and measuring equipment and a piezoresistor
material section 104 that extends along the flexible silicon
diaphragm as described in connection with the
microelectromechanical systems stress senor apparatus 70 previously
described and illustrated in FIG. 7. The piezoresistor material
allows for sensing changes in resistance of the electrical circuit
that is proportional to bending of the flexible silicon diaphragm
101.
[0076] The microelectromechanical systems stress senor apparatus
100 provides a full Wheatstone bridge chip with 700 um diameter
diaphragm. Thermally compensating resistors are on (100) silicon
axes for no radial load sensitivity but identical thermal response.
Standoff metal disk centered on the diaphragm assures contact
conformity between the device and its package or loading
surface.
[0077] The apparatus 100 allows the measurement of stress between
contacting surfaces. With applied normal loads, the diaphragm's 101
bending produces stress in the diaphragm's surface and a
corresponding change in resistance of the doped piezoresistor
material. The change in resistance is calibrated to the applied
load to provide a highly repeatable stress measurement. The
apparatus 100 is very thin which minimizes its effect on the stress
distribution it measures.
[0078] The apparatus 100 has use for joint contact stress research
in animals and humans (medical applications), oncologic research
and drug monitoring, roller systems, automotive (engine component
stresses, i.e., head gasket loads), robotic tactile sensing,
footwear design, fastener design, etc. The apparatus 100 also has
use for Stockpile Stewardship testing and will help to assess load
path issues in device performance. The apparatus 100 has use for
any application that requires contact stresses sensing or
measurement.
[0079] Referring now to FIG. 11, a package is shown that includes
freestanding metal embodiment of the contact stress sensing array.
The package is generally designated by the reference numeral 110.
Independent islands of silicon round disks 111 are interconnected
by freestanding metal springs 112. The array is supported on a
compliant body 113. The compliant body 113 is made of a compliant
material. For example, the compliant body 113 illustrated is a
silicone rubber body 113. In other embodiments other packaging
materials such as fabric may be employed.
[0080] The package 110 provides springs 111 connecting silicon
chips 112 that include microelectromechanical systems stress
sensors. The springs 111 provide an electrical circuit connected to
the flexible diaphragm 111. The electrical circuit includes a
piezoresistor material section that extends along the flexible
silicon diaphragm 111. The piezoresistor material allows for
sensing changes in resistance of the electrical circuit that is
proportional to bending of the flexible silicon diaphragm 111.
[0081] Since the microelectromechanical systems stress sensors are
supported on a silicone rubber body 113, the package 110 can be
used in locations where there is a contoured surface. The apparatus
110 has use for joint contact stress research in animals and humans
(medical applications), oncologic research and drug monitoring,
roller systems, automotive (engine component stresses, i.e., head
gasket loads), robotic tactile sensing, footwear design, fastener
design, etc. The apparatus 110 also has use for Stockpile
Stewardship testing and will help to assess load path issues in
device performance. The apparatus 110 has use for any application
that requires contact stresses sensing or measurement.
[0082] While the invention may be susceptible to various
modifications and alternative forms, specific embodiments have been
shown by way of example in the drawings and have been described in
detail herein. However, it should be understood that the invention
is not intended to be limited to the particular forms disclosed.
Rather, the invention is to cover all modifications, equivalents,
and alternatives falling within the spirit and scope of the
invention as defined by the following appended claims.
* * * * *