METHODS OF FORMING AN EMBEDDED CAVITY FOR SENSORS

• US 20110165719A1
• Filed: 03/13/2009
• Published: 07/07/2011
• Est. Priority Date: 03/13/2008
• Status: Abandoned Application

• Current Assignee: University of Utah Research Foundation (State of Utah)
• Original Assignee: University of Utah Research Foundation (State of Utah)
• Inventors: Solzbacher, Florian, Orthner, Michael
• Application Number:
  US12/922,448
• Publication Number:
  US 20110165719A1
• Time in Patent Office: Days
• US Class Current: 438/53
• CPC Class Codes: G01L 9/0042 Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms details about the integration or bonding of piezoresistor in or on the diaphragm G01L9/0052 and G01L9/0057 respectively
• CPC Class Codes: G01L 9/0054 integral with a semiconducting diaphragm
• CPC Class Codes: G01L 9/0055 bonded on a diaphragm
• CPC Class Codes: Y10T 29/49124 On flat or curved insulated base, e.g., printed circuit, etc.
• CPC Class Codes: Y10T 408/03 Processes

Abstract

A method of forming a sensor with an embedded cavity can include forming at least one cavity (50) in a substrate (52). The cavity (50) can include at least one membrane wall (54) having a plurality of holes (64) in the membrane wall (54), the plurality of holes (64) being formed in a two-dimensional array. A piezoresistive system (58) can be mechanically associated with the membrane wall (54). The method can be a front-side or back-side process for forming the cavity (50). The membrane (54) simultaneously acts as a diaphragm and a fluid passage into the cavity (50). Such sensors can be suitable as pressure sensors, chemical sensors, flow sensors and the like.

Claims

1. A method of forming a sensor with an embedded cavity, comprising:

forming at least one cavity in a substrate such that the cavity includes at least one membrane wall having a plurality of holes in the membrane wall, the plurality of holes being formed in a two-dimensional array; and

forming a piezoresistive system mechanically associated with the membrane wall.

2. The method of claim 1, wherein the method is a front-side approach and the forming the cavity further comprises:

attaching a first material on the substrate composed of a second material;

forming the plurality of holes in the first material in the two-dimensional array; and

selectively etching a common cavity in the second material through the plurality of holes in the first material to form the cavity such that the first material forms the membrane wall.

3. The method of claim 2, wherein the step of forming the plurality of holes occurs subsequent to the step of attaching the first material on the substrate.

4. The method of claim 2, wherein the step of attaching the first material on the substrate includes chemical vapor deposition.

5. The method of claim 2, wherein the step of forming the plurality of holes in the first material additionally forms a plurality of canals in the second material, the plurality of canals directly corresponding to the plurality of holes.

6. The method of claim 5, wherein the depth of the canals substantially defines a depth of the cavity.

7. The method of claim 2, wherein the selective etching is performed with an etchant having a selectivity for the second material over the first material of greater than about 10:

1.

8. The method of claim 2, wherein the first material comprises SiC and the second material comprises Si.

9. The method of claim 8, wherein the SiC comprises cubic SiC.

10. The method of claim 1, wherein the method is a back-side approach and the forming the cavity further comprises:

forming the plurality of holes in the substrate on a front side of the substrate;

etching the cavity in the substrate from a back side of the substrate opposite the front side; and

coupling a backing substrate to the back side of the substrate to enclose the cavity.

11. The method of claim 10, wherein the etching includes anisotropic etching of a <

100>

plane of the back side such that side walls form substantially along <

111>

planes.

12. The method of claim 10, wherein the backing substrate is a silicon wafer.

13. The method of claim 2 or 10, wherein the step of forming the plurality of holes includes laser ablation, wet etching, dry etching, DRIE, three-dimensional printing, drilling, or combinations thereof.

14. The method of claim 1, wherein the plurality of holes in the first material are in a non-random pattern.

15. The method of claim 1, wherein the plurality of holes in the first material are in an equidistant pattern.

16. The method of claim 1, wherein the plurality of holes are configured to increase sensitivity of the piezoresistive responsive feature.

17. The method of claim 1, wherein the plurality of holes have a diameter of about 10 μ

m to about 40 μ

m.

18. The method of claim 1, wherein the membrane wall comprises a material selected from ceramics, polymers, metals, and combinations and mixtures thereof.

19. The method of claim 1, wherein the forming the piezoresistive system comprises modifying select regions of the substrate and/or membrane wall to form piezoresistive elements in the select regions.

20. The method of claim 19, wherein the modifying select regions comprises doping and/or ion implanting.

21. The method of claim 1, further comprising substantially filling the cavity with a hydrogel.

22. The method of claim 21, wherein the hydrogel is selected from the group consisting of substituted acrylic or acrylamide copolymers, acrylic or acrylamide copolymers, PVA/PAA, NIPAAm copolymers, and combinations thereof.

23. The method of claim 21, wherein the hydrogel and the membrane wall are configured to be selectively permeable to at least one of glucose, CO₂, and hydrogen ion (pH detection).