Resonant sensor and method of making same

• US 4,764,244 A
• Filed: 06/11/1985
• Issued: 08/16/1988
• Est. Priority Date: 06/11/1985
• Status: Expired due to Fees

• Current Assignee: Foxboro Company The Foxboro Massachusetts
• Original Assignee: The Foxboro Company (Schneider Electric SE)
• Inventors: Panagou, John G., Zavracky, Paul M., Morrison, Richard H. Jr., Chitty, Gordon W., Olsen, Everett O.
• Primary Examiner(s): Powell, William A.
• Application Number:
  US06/743,255
• Time in Patent Office: 1,162 Days
• Field of Search: 156/628-634, 156/650-653, 156/655, 156/657, 156/656, 156/659.1, 156/662, 156/667, 310/321-325, 310/367-371, 29/25.35, 29/610 SG, 73/570, 73/587, 73/589, 73/649, 73/704, 73/754, 73/DIG. 4, 73/DIG. 1
• US Class Current: 216/20
• CPC Class Codes: H03H 2009/02511 Vertical, i.e. perpendicular to the substrate plane
• CPC Class Codes: H03H 2009/02519 Torsional
• CPC Class Codes: H03H 3/0072 of microelectro-mechanical resonators or networks micromembranes or microbeams B81B2203/01; manufacture of microstructural devices in general B81C
• CPC Class Codes: H03H 9/02259 Driving or detection means
• CPC Class Codes: H03H 9/2405 of microelectro-mechanical resonators
• CPC Class Codes: H03H 9/2473 Double-Ended Tuning Fork [DETF] resonators
• CPC Class Codes: Y10S 73/04 Piezoelectric
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49103 Strain gauge making

Abstract

Microminiature resonant sensor structures are prepared according to micromachining/microfabrication techniques, which structures include thin-film deposits of piezoelectric materials. Such piezoelectric deposits may be excited electrically by including metallized conductive paths during fabrication, or optically. The resonant frequency of the sensor structure is varied by subjecting it to a physical variable, or measurand, such as pressure, temperature, flow rate, etc. Similarly, the resonant frequency of the devices may be detected electrically or optically. The microminiature resonant structures include ribbons and wires, hollow beam and cantilevered hollow beams, and single- and double-ended double beam resonant structures such as tuning forks.

Claims

1. A method of fabricating a laminar resonant structure, comprising the steps of:

(a) preparing a substrate workpiece;

(b) securing a laminar material to said substrate;

(c) cleaning the exposed laminar material surface;

(d) patterning a first resist on the laminar material surface;

(e) descumming the resist;

(f) etching the workpiece to form a resonant structure on the substrate;

(g) cleaning and baking the workpiece;

(h) depositing a piezoelectric layer on the workpiece surface;

(i) patterning and etching the piezoelectric layer to form a piezoelectric slab;

(j) cleaning and rinsing the workpiece;

(k) applying an insulation layer on the workpiece surface and patterning same;

(l) depositing a conductive metallization layer on the workpiece surface and patterning and etching same;

(m) removing the resonant structure from the substrate.

2. The method of claim 1, wherein the laminar material is a metal.

3. The method of claim 1, wherein the substrate is a glass.

4. The method of claim 1, wherein the resonant structure formed is a ribbon.

5. The method of claim 1, wherein the resonant structure formed is a tuning fork.

6. The method of claim 5, wherein the resonant structure formed is a double tuning fork.

7. The method of claim 1, wherein the resonant structure formed is a cantilevered beam.

8. The method of claim 1, wherein the piezoelectric layer is zinc oxide.

9. The method of claim 1, wherein the piezoelectric layer is cadmium-sulfide.

10. The method of claim 1, wherein an anisotropic etchant process is used for step f.

11. A method of preparing a laminar resonant structure, comprising the steps of:

(a) preparing a substrate workpiece;

(b) depositing a metal layer on said substrate;

(c) cleaning the exposed metal layer surface;

(d) patterning a first resist on the metal surface;

(e) descumming the resist;

(f) etching the workpiece to form a resonant structure on the substrate;

(g) cleaning and baking the workpiece;

(h) depositing a piezoelectric layer on the workpiece surface;

(i) patterning and etching the piezoelectric layer to form a piezoelectric slab;

(j) cleaning and rinsing the workpiece;

(k) applying an insulation layer on the workpiece surface and patterning same;

(l) depositing a conductive metallization layer on the insulation layer and patterning and etching same;

(m) removing resonant structure from the substrate.

12. The method of claim 11, wherein the laminar material is a metal.

13. The method of claim 12, wherein the substrate is a glass.

14. The method of claim 12, wherein the resonant structure formed is a ribbon.

15. The method of claim 12, wherein the resonant structure formed is a tuning fork.

16. The method of claim 15, wherein the resonant structure formed is a double tuning fork.

17. The method of claim 12, wherein the resonator formed is a cantilevered beam.

18. The method of claim 12, wherein the piezoelectric layer is zinc oxide.

19. The method of claim 12, wherein the piezoelectric layer is cadmium sulfide.

20. A method of preparing a hollow beam resonant structure comprising the steps of:

(a) etching at least one trough in the front face of a first substrate area,

(b) doping a selected trough area of said first substrate area to a predetermined etch-stop depth,

(c) depositing a piezoelectric material in a selected one of said at least one trough area,

(d) depositing a resistive insulation current blocking layer between said first substrate area and said piezoelectric material,

(e) depositing a metallization layer means for communicating drive and sense signals to said piezoelectric material,

(f) etching at least one complementary-image trough in the front face surface of a second substrate area,

(g) doping a selected trough area of said second substrate area to a predetermined etch-stop depth,

(h) aligning the first and second substrate areas in precise registration with their respective front face substrate surfaces joined,

(i) bonding said joined front face substrate surfaces together, and

(j) etching sufficient undoped substrate away from the doped substrate region to relieve the doped portion from the remaining substrate material, and leave a relieved, hollow microstructural cantilever beam.

21. A microfabricated laminar resonant microstructure for use in sensing a measurand, fabricated by the steps of:

(a) preparing a substrate;

(b) releasably securing a laminar material to said substrate;

(c) cleaning the exposed laminar material surface;

(d) patterning a first resist to outline on the laminar material surface the desired resonant microstructure workpiece;

(e) descumming the resist;

(f) etching the workpiece to form a resonant microstructure on the substrate;

(g) cleaning and baking the workpiece;

(h) depositing a piezoelectric layer on the workpiece surface;

(i) patterning and etching the piezoelectric layer to form at least one piezoelectric slab on the resonant microstructure;

(j) cleaning and rinsing the workpiece;

(k) applying an insulation layer on the workpiece surface and patterning same to outline areas for apertures through said insulation layer to the surface of the piezoelectric slab;

(l) etching through the insulating layer to the surface of the piezoelectric slab to provide apertures through said insulation layer and access to contact areas thereon;

(m) depositing a conductive metallization layer on at least a portion of the workpiece surface and patterning and etching same to form desired electrical contact areas through the insulation apertures to the piezoelectric slab underneath;

(n) removing the resonant structure from the substrate.

22. A microfabricated resonant microstructure for use in sensing a measurand, fabricated by the steps of:

(a) preparing a substrate;

(b) releasably depositing a metallization layer on said substrate;

(c) cleaning the exposed metallization layer surface;

(d) patterning a first resist to outline on the metallization surface the desired resonant microstructure;

(e) descumming the resist;

(f) etching the workpiece to form a resonant microstructure on the substrate;

(g) cleaning and baking the workpiece;

(h) depositing a piezoelectric layer on the workpiece surface;

(i) patterning and etching the piezoelectric layer to form at least one piezoelectric slab on the resonant microstructure

(j) cleaning and rinsing the workpiece;

(k) applying an insulation layer on the workpiece surface and patterning same to outline areas for apertures through said insulation layer to contact areas on the surface of the piezoelectric slab;

(l) etching through the insulating layer to the surface of the piezoelectric slab to provide apertures through said insulation layer and access to contact areas thereon;

(m) depositing a conductive metallization layer on at least a portion of the workpiece surface and patterning and etching means to form desired electrical contact areas through the insulation aperture to the piezoelectric slab underneath;

(n) removing the resonant structure from the substrate.