Lithographic fabrication process for a pressure sensor

• US 20130115729A1
• Filed: 10/24/2012
• Published: 05/09/2013
• Est. Priority Date: 10/18/2004
• Status: Abandoned Application

• Current Assignee: Precision Mechatronics Pty Ltd
• Original Assignee: Precision Mechatronics Pty Ltd
• Inventors: Silverbrook, Kia, Mallinson, Samuel George
• Application Number:
  US13/659,808
• Publication Number:
  US 20130115729A1
• Time in Patent Office: Days
• US Class Current: 438/50
• CPC Class Codes: B60C 23/0408 transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver
• CPC Class Codes: G01L 19/0636 using particle filters
• CPC Class Codes: G01L 9/0072 using variations in capacitance
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass
• CPC Class Codes: H01L 29/66007 Multistep manufacturing processes
• CPC Class Codes: Y10T 29/49155 Manufacturing circuit on or in base
• CPC Class Codes: Y10T 29/49156 with selective destruction of conductive paths

Abstract

Lithographic fabrication of a pressure sensor (30) for environments such as vehicle tires is described. The sensor has a first wafer substrate (32) with first and second planar surfaces on opposing sides. CMOS circuitry (34) is deposited on the first planar surface. A layer of passivation material is deposited on the circuitry. Etched openings in the passivation layer expose parts of the circuitry and an aperture is etched through the first wafer to fluidically connect the exposed circuitry with the second planar surface. Sacrificial material is deposited in the aperture and then a flexible membrane (50) is deposited on the sacrificial material and the exposed parts of the circuitry. The sacrificial material is subsequently etched from the aperture from the second surface. A second substrate is sealed to the second planar surface of the first wafer substrate to define a chamber (58) containing a fluid at a reference pressure.

Claims

1. A method of lithographically fabricating a pressure sensor, the method comprising the steps of:

providing a first wafer substrate having first and second opposing planar surfaces;

depositing circuitry on the first planar surface;

depositing a layer of passivation material on the circuitry;

etching openings in the passivation layer to expose parts of the circuitry;

etching an aperture through the first wafer to fluidically connect the exposed parts of the circuitry and the second planar surface;

depositing sacrificial material in the aperture;

depositing a flexible membrane on the sacrificial material and the exposed parts of the circuitry;

plasma cleaning the sacrificial material out of the aperture from the second surface;

providing a second substrate; and

,

sealing the second substrate to the second planar surface of the first wafer substrate to define a chamber containing a fluid at a reference pressure;

wherein during use, the flexible membrane deflects due to pressure differentials between the reference pressure and an external fluid pressure to be sensed such that the circuitry converts the deflection of the flexible membrane into an output signal indicative of the external fluid pressure.

2. A method according to claim 1 further comprising the steps of:

depositing a second layer of sacrificial material over the membrane;

depositing guard material on the second layer of sacrificial material;

lithographically etching an array of apertures in the guard material; and

, plasma cleaning the sacrificial material away through the array of apertures in the guard material.

3. A method according to claim 1 wherein the step of depositing the flexible membrane further comprises:

sequentially depositing a plurality of layers of different material to form a laminate wherein at least one of the different materials is electrically conductive.

4. A method according to claim 3 wherein the different materials are metal ceramics.

5. A method according to claim 4 wherein the metal ceramics are metal nitrides or mixed metal nitrides.

6. A method according to claim 4 wherein the metal ceramics are titanium nitride, titanium aluminium nitride, tantalum silicon nitride, titanium aluminium silicon nitride, or tantalum aluminium silicon nitride.

7. A method according to claim 3 wherein one or more of the layers of the laminate is metal.

8. A method according to claim 7 wherein the metal is titanium, tantalum or vanadium.

9. A method according to claim 1 wherein the membrane is less than 0.1 grams.

10. A method according to claim 1 wherein the pressure sensor is adapted to sense the air pressure within a pneumatic tire.

11. A method according to claim 1 wherein the membrane is non-planar.

12. A method according to claim 11 wherein the membrane is corrugated.

13. A method according to claim 12 wherein the membrane corrugations have a period of between 5 microns and 15 microns.

14. A method according to claim 12 wherein the membrane is substantially circular and the corrugations are annular.

15. A method according to claim 11 wherein the corrugations have a substantially square-shaped cross-sectional profile.

16. A method according to claim 15 wherein the flexible corrugated membrane has a corrugation factor of 8.

17. A method according to claim 16 wherein the sensor has a linear response up to about 1 MPa.

18. A method according to claim 1 further comprising the steps of:

depositing a layer of electrode material adjacent the aperture such that deflection of the flexible membrane varies the distance between the flexible membrane and the electrode material;

wherein during use,

the layer of electrode material and the flexible membrane form a capacitative sensor.