Apparatus and method for detecting a target environmental variable that employs film-bulk acoustic wave resonator oscillators

• US 20060232163A1
• Filed: 04/18/2005
• Published: 10/19/2006
• Est. Priority Date: 04/18/2005
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies Wireless IP Singapore Pte Limited (Broadcom, Inc.)
• Inventors: Rudy, Richard C., Larson, John D. III, Unkrich, Mark A., Flower, Graham M.
• Granted Patent: US 7,358,651 B2
• Time in Patent Office: Days
• US Class Current: 310/319
• CPC Class Codes: G01K 11/265 using surface acoustic wave [SAW]
• CPC Class Codes: G01L 1/165 with acoustic surface waves
• CPC Class Codes: G01L 9/0025 with acoustic surface waves
• CPC Class Codes: H03H 9/0542 consisting of a lateral arrangement H03H9/0566 takes precedence

Abstract

An apparatus and method for detecting a target environmental variable (TEV). A first film-bulk acoustic resonator (FBAR) oscillator that includes a first FBAR with a first response to the target environmental variable generates a first frequency. A second film-bulk acoustic resonator (FBAR) oscillator that includes a second FBAR with a second response to the target environmental variable generates a second frequency. A circuit that is coupled to the first FBAR oscillator and the second FBAR oscillator determines the target environmental variable (e.g., changes in the TEV) based on the first frequency and the second frequency.

Claims

1. An apparatus that detects a target environmental variable comprising:

a first film-bulk acoustic resonator (FBAR) oscillator that includes a first FBAR with a first response to the target environmental variable;

wherein the first FBAR oscillator generates a first frequency;

a second film-bulk acoustic resonator (FBAR) oscillator that includes a second FBAR with a second response to the target environmental variable;

wherein the second FBAR oscillator generates a second frequency; and

a circuit that detects changes in the target environmental variable based on the first frequency and the second frequency.

2. The apparatus of claim 1

wherein the first FBAR oscillator and the second FBAR oscillator detect a difference in the response of the first FBAR to the target environmental variable and the response of the second FBAR to the target environmental variable and extinguish effects on the response of the first FBAR and the response of the second FBAR caused by non-target environmental variables to which the first FBAR and the second FBAR are exposed.

3. The apparatus of claim 1 wherein the circuit measures the difference between the first frequency and the second frequency.

4. The apparatus of claim 1 wherein the first FBAR includes

a FBAR wafer;

an acoustic reflector formed in the FBAR wafer that includes a surface;

a first electrode formed on the surface of the acoustic reflector;

wherein the first electrode includes a surface;

a piezoelectric layer formed on the surface of the first electrode;

wherein the piezoelectric layer includes a surface; and

a second electrode formed on the surface of the piezoelectric layer.

5. The apparatus of claim 4 wherein the second FBAR includes

a second acoustic reflector formed in the FBAR wafer that includes a surface;

a third electrode formed on the surface of the second acoustic reflector;

wherein the first electrode includes a surface;

a second piezoelectric layer formed on the surface of the third electrode;

wherein the piezoelectric layer includes a surface; and

a fourth electrode formed on the surface of the second piezoelectric layer.

6. The apparatus of claim 1 wherein the first FBAR and the second FBAR are manufactured with different mass loading;

wherein the different manufacturing causes the first FBAR and the second FBAR to respond differently to a target environmental variable and to generate an offset frequency that is controlled by the mass loading.

7. A method for detecting a target environmental variable comprising:

utilizing a first film-bulk acoustic resonator (FBAR) oscillator that includes a first FBAR with a first response to the target environmental variable to generate a first frequency;

utilizing a second film-bulk acoustic resonator (FBAR) oscillator that includes a second FBAR with a second response to the target environmental variable to generate a second frequency; and

detecting a change in the target environmental variable based on the first frequency and the second frequency.

8. The method of claim 7 further comprising:

employing the first FBAR oscillator and the second FBAR oscillator to detect a difference in the response of the first FBAR to the target environmental variable and the response of the second FBAR to the target environmental variable and to extinguish common effects on the response of the first FBAR and the response of the second FBAR caused by non-target environmental variables to which the first FBAR and the second FBAR are exposed.

9. A method for manufacturing a target environmental variable detecting apparatus comprising:

forming a first film-bulk acoustic resonator (FBAR) oscillator that has a first response to the target environmental variable to generate a first frequency on a first wafer;

forming a second film-bulk acoustic resonator (FBAR) oscillator that has a second response to the target environmental variable to generate a second frequency on the first wafer; and

forming a circuit that receives the first frequency and the second frequency and generates a difference frequency that represents the target environmental variable.

10. The method of claim 9 wherein forming a first film-bulk acoustic resonator (FBAR) oscillator that has a first response to the target environmental variable to generate a first frequency on a first wafer includes

forming a first film-bulk acoustic resonator (FBAR) that has a first response to the target environmental variable;

and

forming a first gain element that is coupled to the first FBAR.

11. The method of claim 10 wherein forming a second film-bulk acoustic resonator (FBAR) oscillator that has a second response to the target environmental variable to generate a second frequency on a first wafer includes

forming a second film-bulk acoustic resonator (FBAR) that has a second response to the target environmental variable;

and

forming a second gain element that is coupled to the second FBAR.

12. The method of claim 10 further comprising:

forming a micro-cap wafer; and

bonding the micro-cap wafer to the first wafer.

13. The method of claim 10 further comprising:

encapsulating the first wafer with an encapsulating wafer.

14. The method of claim 13 wherein at least one of the first gain element, the second gain element, and the circuit that generates a difference frequency is formed on the encapsulating wafer.

15. The method of claim 13 wherein encapsulating the first wafer with an encapsulating wafer includes

forming a micro-cap wafer;

and

bonding the micro-cap wafer to the first wafer.

16. The method of claim 9 wherein the target environmental variable includes one of pressure, acceleration, temperature, humidity, and other environmental variables.