Solid state force transducer and method of making same

• US RE31,459 E
• Filed: 01/28/1980
• Issued: 12/06/1983
• Est. Priority Date: 02/09/1976
• Status: Expired due to Term

• Current Assignee: Barry Block, Harry E. Aine
• Original Assignee: Barry Block, Harry E. Aine
• Inventors: Block, Barry
• Primary Examiner(s): Albritton, C. L.
• Application Number:
  US06/115,610
• Time in Patent Office: 1,408 Days
• Field of Search: 338/2, 338/4, 338/5, 338/7, 338/47, 357/26, 73/517, 73/518, 73/720, 73/721, 73/726, 73/727, 29/580, 29/592, 29/610 SG, 156/647
• US Class Current: 338/47
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/123 by piezo-resistive elements, e.g. semiconductor strain gauges
• CPC Class Codes: H01L 29/84 controllable by variation of applied mechanical force, e.g. of pressure
• CPC Class Codes: H04R 23/006 using solid state devices solid state devices per se H01L
• CPC Class Codes: Y10T 29/49002 Electrical device making
• CPC Class Codes: Y10T 29/49103 Strain gauge making

Abstract

Solid state folded leaf spring force transducers are fabricated by batch photolithographic and etching techniques from a monocrystalline material, such as silicon. The folded leaf spring structure includes elongated gaps separating adjacent leaf spring leg portions, such elongated gaps being oriented parallel to a crystallographic axis of the monocrystalline material. In a preferred embodiment the monocrystalline material is of diamond cubic type and the leaf spring gaps extend in mutually orthogonal directions parallel to the <011> and <011> crystallographic axes, respectively. In a preferred method of fabricating the spring structure, the structure is etched from a monocrystalline wafer by means of an anisotropic etchant so as to more precisely define angles and dimensions of the resultant spring structure. In one embodiment, the gaps between adjacent leg portions of the spring structure are sealed in a fluid tight manner by means of oxide membranes left intact upon etching of the spring structure. In an accelerometer embodiment, sensing masses of equal weight are affixed to opposite sides of the spring structure for dynamically balancing same. .Iadd.

Claims

1. said leaf spring structure..]. .[.19. In a method for fabricating a solid state force transducer, the steps of:

forming a leaf spring structure in a wafer by recessing a leaf spring pattern at a selected location through a first major face of said wafer;

said recessed leaf spring pattern including a pair of mutually opposed E-shaped leaf spring pattern portions, each E-shaped spring pattern portion including a deflectable central leg portion extending outwardly from a central region of the spring structure and a pair of leg portions on opposite side of and extending outwardly from said central region generally parallel to said central leg portion, said outer leg portions being supported at their inner ends from a portion of the wafer and being interconnected at their outer ends to the outer end of said central leg portion for deflection therewith..]. .[.20. The method of claim 19 wherein said step of recessing said spring structure from a wafer of said monocrystalline material includes etching said spring structure from said wafer so as to leave an unetched web portion spanning the space between adjacent leg portions of said spring structure, said web portion being substantially thinner than said leg portions being spanned by said web..]. .[.21. In a solid state force transducer;

1eaf spring means having a plurality of leg portions angularly separated about an axis of maximum compliance and supported so that said leg portions of said leaf spring means are physically displaced relative to the support structure in response to the application of a force to said leaf spring means;

output sensor means disposed relative to said leaf spring means so as to be responsive to the displacement of at least one of said leg portions in the direction of maximum compliance for deriving an output which is a function of the force applied to the transducer; and

2. wherein said leaf spring means is of a monocrystalline material..]. .[.22. The apparatus of claim 21 wherein said leg portions of said monocrystalline leaf spring means are separated by a slot in said monocrystalline material, and wherein the longitudinal axis of said slot is oriented parallel to a crystallographic axis of said monocrystalline material..]. .[.23. The apparatus of claim 1 wherein said monocrystalline material is nonmetallic..]. .[.24. The apparatus of claim 21 wherein said monocrystalline material is a semiconductive material..]. .[.25. The apparatus of claim 21 including sensing mass means formed on said leaf spring means..]. .[.26. The apparatus of claim 25 wherein said sensing mass means is disposed with approximately equal mass on opposite sides of the plane of the wide dimension of said leaf spring means..]. .[.27. The apparatus of claim 22 wherein said monocrystalline material is of the diamond cubic type and wherein the longitudinal axis of said slot is oriented parallel to one of the <

011> and

<

011>

crystallographic axes of said monocrystalline material..]. .[.28. The apparatus of claim 21 wherein said output sensor means includes piezoresistive means formed in said spring structure..]. .[.29. The apparatus of claim 21 including base support structure disposed outside of the periphery of said spring structure for supporting said spring structure therefrom..]. .[.30. The apparatus of claim 27 wherein said spring structure includes a pair of mutually opposed E-shaped folded catilever leaf spring portions having a plurality of intersecting elongated rectilinear slots defining said spring structure, and wherein some of said slots have their longitudinal axes oriented parallel to the <

011>

crystallographic axis and other ones of said slots have their longitudinal axes oriented parallel to the <

011>

4. Iadd.38. .Iaddend. 32. The product of the method of claim .[.9..].

5. Iadd.39. .Iaddend. 33. The product of the method of claim .[.12..].

6. Iadd.40. .Iaddend. 34. The product of the method of claim .[.14..].

7. Iadd.42. .Iaddend. 35. The product of the method of claim .[.19..].

8. Iadd.46. .Iaddend. 36. The product of the method of claim .[.18..]. .Iadd.52. .Iaddend. .[.37. The product of the method of claim 20..]. .Iadd. 38. In a method for fabricating a solid state force transducer, the step of:

forming a folded cantilever leaf spring transducer structure in a wafer by removing portions of the wafer at a selected location through at least one of the major faces of said wafer to define the folded cantilever spring transducer structure, said folded cantilever spring structure including a folded portion having first and second generally parallel coplanar leaf spring leg portions joined together at a joined first end region thereof and second ends of said leg portions being displaceable one with respect to the other, in responsive to the applied force to be transduced, along an axis of maximum compliance generally orthogonal to the plane of said folded leaf spring leg portions and passing through said second end of said first leg portion, the second end of said second leg portion forming a point of support for said folded cantilever spring portion with said joined region of said leaf spring also being displaceable relative to said point of support in response to the applied force being transduced. .Iaddend..Iadd. 39. The method of claim 38 wherein the step of removing portions of the wafer to define said leaf spring structure includes removing portions of the wafer through both major faces of said wafer to define said folded cantilever leaf spring structure. .Iaddend..Iadd. 40. The method of claim 38 wherein said folded cantilever leaf spring structure includes a pair of mutually opposed E-shaped leaf spring portions, each E-shaped leaf spring portion including a deflectable central leg portion extending from the axis of maximum compliance of the spring and a pair of outer deflectable leg portions disposed on opposite sides of and adjacent said central leg portion and extending generally parallel thereto, said pair of outer leg portions being supported at their inner ends from a portion of the wafer and being joined together at their outer ends to the outer end of said central leg portion and said joined outer ends of said outer leg portions being free to deflect relative to their supported ends with deflection of said central leg portion in response to the applied force to be transduced. .Iaddend..Iadd. 41. The method of claim 38 wherein said step of forming said folded cantilever leaf spring structure in said wafer includes etching said spring structure from said wafer so as to leave an unetched web portion spanning the space between adjacent leg portions of said folded cantilever spring structure, said web portion being substantially thinner than said leg portions. .Iaddend..Iadd. 42. The method of claim 38 wherein said wafer includes a monocrystalline portion and wherein said leg portions of said folded cantilever leaf spring structure are defined by slots in said wafer material, and including the step of orienting the longitudinal axes of said slots parallel to a crystallographic axis of said monocrystalline portion of said wafer. .Iaddend..Iadd. 43. The method of claim 42 wherein said monocrystalline portion of said wafer is of diamond cubic type material. .Iaddend..Iadd. 44. The method of claim 38 wherein said cantilever leaf spring material is composed of a material containing silicon. .Iaddend. .Iadd. 45. The method of claim 38 including the step of forming a sensing mass structure on said folded cantilever spring structure. .Iaddend..Iadd. 46. The method of claim 45 wherein said step of forming said sensing mass structure on said folded cantilever spring structure includes, forming said sensing mass structure with approximately equal mass on opposite sides of the plane of said folded cantilever leaf spring structure. .Iaddend..Iadd. 47. The method of claim 42 wherein said monocrystalline portion is of diamond cubic type and wherein the longitudinal axes of said slots are oriented parallel to one of the <

011> and

<

011>

crystallographic axes of said monocrystalline portion. .Iaddend..Iadd. 48. The method of claim 42 wherein said step of forming said folded cantilever leaf spring structure includes the step of etching said monocrystalline portion of said wafer with an anisotropic etchant for said material so that said slots are preferentially etched along certain predetermined crystallographic planes. .Iaddend..Iadd. 49. The method of claim 38 including the step of etching a base support structure from said wafer, said base support structure being connected to said cantilever leaf spring structure by an unetched portion of said wafer for supporting said folded cantilever spring structure therefrom at said point of support. .Iaddend..Iadd. 50. In a method of claim 42 wherein said monocrystalline wafer portion is of diamond cubic crystal type and wherein said monocrystalline portion has a major face thereof in the (100) crystallographic plane and wherein the plane of said folded cantilever leaf spring structure is in the (100) crystallographic plane. .Iaddend..Iadd. 51. The method of claim 38 wherein the step of forming a folded cantilever spring structure includes forming an array of said folded cantilever leaf spring structures simultaneously from a single wafer. .Iaddend..Iadd. 52. The method of claim 49 wherein the step of etching said base support structure includes, etching said folded cantilever leaf spring structure so as to leave said base support structure outside of the periphery of said spring structure. .Iaddend..Iadd. 53. The method of claim 49 including the step of, mounting said base support structure to the face of a support plate. .Iaddend..Iadd. 54. In a solid state force transducer having an axis of maximum compliance relative to a support;

folded cantilever leaf spring means having a plurality of generally coplanar monolithic leaf spring leg portions for support from the support so that said leg portions of said leaf spring means extended as a cantilever from the support and fold back in a folded region adjacent to each other to the axis of maximum compliance, said leg portions and said folded region being physically displaced relative to the support in response to the application of a force to said leaf spring means to be tranduced and directed along said axis of maximum compliance; and

output sensor means responsive to the displacement of at least one of said leg portions in the direction of maximum compliance for deriving an output which is a function of the force applied to the transducer. .Iaddend. .Iadd. 55. The apparatus of claim 54 wherein said leaf spring leg portions are made of a monocrystalline material. .Iaddend..Iadd. 56. The apparatus of claim 54 wherein said monolithic leaf spring leg portions are made of a material containing silicon. .Iaddend..Iadd. 57. The apparatus of claim 55 wherein said adjacent leg portions of said monocrystalline folded leaf spring structure are separated by an elongated slot in said monocrystalline material, and wherein the longitudinal axis of said slot is oriented parallel to a crystallographic axis of said monocrystalline material. .Iaddend..Iadd. 58. The apparatus of claim 54 including sensing mass means formed on said folded cantilever leaf spring structure at the axis of maximum compliance. .Iaddend..Iadd. 59. The apparatus of claim 58 wherein said sensing mass means is disposed with approximately equal amounts on opposite sides of the plane of said folded cantilever leaf spring structure. .Iaddend..Iadd. 60. The apparatus of claim 57 wherein said monocrystalline material is of the diamond cubic type and wherein the longitudinal axis of said slot is oriented parallel to one of the <

011> and

<

011>

crystallographic axes of said monocrystalline material. .Iaddend..Iadd. 61. The apparatus of claim 54 wherein said output sensor means includes a piezoresistive means disposed relative to said folded cantilever leaf spring structure for detecting bending of said folded cantilever leaf spring structure in response to the applied force to be transduced. .Iaddend. .Iadd.62. The apparatus of claim 54 including a base support structure disposed outside of the periphery of said folded cantilever leaf spring structure for supporting said spring structure therefrom. .Iaddend..Iadd. 63. The apparatus of claim 54 wherein said folded cantilever leaf spring structure includes a pair of mutually opposed E-shaped folded cantilever leaf spring portions having a plurality of intersecting elongated reclinear slots defining said spring structure. .Iaddend..Iadd. 64. The apparatus of claim 63 wherein said folded cantilever leaf spring structure has leg portions made of a diamond cubic type monocrystalline material and wherein some of said slots have their longitudinal axes oriented parallel to the <

011>

crystallographic axis and other ones of said slots have their longitudinal axes oriented parallel to the <

011>

crystallographic axis. .Iaddend.

3. crystallographic axis..]. 31. The product of the method of claim .[.8..].