TRANSDUCER DEVICES HAVING DIFFERENT FREQUENCIES BASED ON LAYER THICKNESSES AND METHOD OF FABRICATING THE SAME

• US 20110291207A1
• Filed: 05/28/2010
• Published: 12/01/2011
• Est. Priority Date: 05/28/2010
• 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: CHOY, John, MARTIN, David
• Granted Patent: US 8,357,981 B2
• Time in Patent Office: Days
• US Class Current: 257/416
• CPC Class Codes: G10K 9/125 with a plurality of active elements
• CPC Class Codes: H10N 30/04 Treatments to modify a piezoelectric or electrostrictive property, e.g. polarisation characteristics, vibration characteristics or mode tuning
• CPC Class Codes: H10N 39/00 Integrated devices, or assemblies of multiple devices, comprising at least one piezoelectric, electrostrictive or magnetostrictive element covered by groups H10N30/00 – H10N35/00
• CPC Class Codes: Y10T 29/42 Piezoelectric device making

Abstract

A transducer array on a common substrate includes a membrane and first and second transducer devices. The membrane is formed on the common substrate, and includes a lower layer and an upper layer. The first transducer device includes a first resonator stack formed on at least the lower layer in a first portion of the membrane, the upper layer having a first thickness in the first portion of the membrane. The second transducer device includes a second resonator stack formed on at least the lower layer in a second portion of the membrane, the upper layer having a second thickness in the second portion of the membrane, where the second thickness is different from the first thickness, such that a first resonant frequency of the first transducer device is different from a second resonant frequency of the second transducer device.

Claims

1. A transducer array on a common substrate, the transducer array comprising:

a membrane formed on the common substrate, the membrane comprising a lower layer and an upper layer;

a first transducer device comprising a first resonator stack formed on at least the lower layer in a first portion of the membrane, the upper layer having a first thickness in the first portion of the membrane; and

a second transducer device comprising a second resonator stack formed on at least the lower layer in a second portion of the membrane, the upper layer having a second thickness in the second portion of the membrane, the second thickness being different from the first thickness, such that a first resonant frequency of the first transducer device is different from a second resonant frequency of the second transducer device.

2. The transducer array of claim 1, wherein the first resonator stack is formed between the lower layer and the upper layer in the first portion of the membrane, and the second resonator stack is formed between the lower layer and the upper layer in the second portion of the membrane.

3. The transducer array of claim 1, wherein the first resonator stack is formed on both the lower layer and the upper layer in the first portion of the membrane, and the second resonator stack is formed on both the lower layer and the upper layer in the second portion of the membrane.

4. The transducer array of claim 1, wherein the lower layer and the upper layer of the membrane are formed of the same material having different stresses.

5. The transducer array of claim 4, wherein each of the lower layer and the upper layer comprises boron silicate glass (BSG).

6. The transducer array of claim 1, wherein the lower layer and the upper layer of the membrane are formed of different materials having different stresses.

7. The transducer array of claim 1, wherein the first resonator stack comprises a first piezoelectric layer formed between a first lower electrode and a first upper electrode, and the second resonator stack comprises a second piezoelectric layer formed between a second lower electrode and a second upper electrode.

8. The transducer array of claim 7, wherein the lower layer comprises at least the first lower electrode and the second lower electrode.

9. A method of fabricating a transducer array comprising a plurality of transducer devices on a common substrate, the method comprising:

forming a lower layer of a membrane on the common substrate;

forming a plurality of resonator stacks corresponding to the plurality of transducer devices on the lower layer;

forming an upper layer of the membrane on the lower layer and the plurality of resonator stacks;

forming a mask on the upper layer, the mask defining at least one opening configured to expose a portion of the upper layer on at least one resonator stack;

changing a thickness of the exposed portion of the upper layer through the at least one mask opening to change a resonant frequency of at least one transducer device corresponding to the at least one resonator stack, wherein the changed resonant frequency is different from a resonant frequency of at least one other transducer device on the common substrate corresponding to a resonator stack covered by the mask; and

removing the mask.

10. The method of claim 9, further comprising:

measuring a first thickness and a first stress of the lower layer after forming the lower layer;

measuring a second thickness and a second stress of the upper layer after forming the upper layer; and

changing the thickness of the exposed portion of the upper layer based on the measured first and second thicknesses and the measured first and second stresses.

11. The method of claim 10, wherein the changed resonant frequency is substantially equal to a predetermined target resonant frequency, the method further comprising:

determining a target average stress of the membrane corresponding to the target resonant frequency; and

determining a target thickness of the exposed portion of the upper layer using the target average stress of the membrane, wherein changing the thickness of the exposed portion of the upper layer comprises matching the thickness of the exposed portion of the upper layer to the target thickness.

12. The method of claim 9, wherein changing the thickness of the exposed portion of the upper layer comprises:

etching the exposed portion of the upper layer to reduce the thickness of the exposed portion of the upper layer.

13. The method of claim 12, wherein when a first stress of the lower layer is greater than a second stress of the upper layer, reducing the thickness of the exposed portion of the upper layer increases the resonant frequency of the at least one transducer device corresponding to the at least one resonator stack, and

wherein when the first stress is less than the second stress, reducing the thickness of the exposed portion of the upper layer decreases the resonant frequency of the at least one transducer device corresponding to the at least one resonator stack.

14. The method of claim 9, wherein changing the thickness of the exposed portion of the upper layer through comprises:

depositing material on the exposed portion of the upper layer to increase the thickness of the exposed portion of the upper layer.

15. The method of claim 14, wherein when a first stress of the lower layer is greater than a second stress of the upper layer, increasing the thickness of the exposed portion of the upper layer decreases the resonant frequency of the at least one transducer device corresponding to the at least one resonator stack, and

wherein when the first stress is less than the second stress, increasing the thickness of the exposed portion of the upper layer increases the resonant frequency of the at least one transducer device corresponding to the at least one resonator stack.

16. A method of fabricating a transducer array comprising a plurality of transducer devices on a common substrate, the method comprising:

forming a lower layer of a membrane on the common substrate;

forming an upper layer of the membrane on the lower layer;

forming a plurality of resonator stacks corresponding to the plurality of transducer devices on the upper layer;

forming a mask on the upper layer, the mask defining at least one opening configured to expose at least one resonator stack and a corresponding portion of the upper layer;

changing a thickness of the exposed portion of the upper layer through the at least one mask opening to change a resonant frequency of at least one transducer device corresponding to the at least one resonator stack, wherein the changed resonant frequency is different from a resonant frequency of at least one other transducer device on the common substrate corresponding to a resonator stack covered by the mask; and

removing the mask.

17. The method of claim 16, further comprising:

measuring a first thickness and a first stress of the lower layer after forming the lower layer;

measuring a second thickness and a second stress of the upper layer after forming the upper layer; and

changing the thickness of the exposed portion of the upper layer based on the measured first and second thicknesses and the measured first and second stresses.

18. The method of claim 17, wherein the changed resonant frequency is substantially equal to a predetermined target resonant frequency, the method further comprising:

determining a target average stress of the membrane corresponding to the target resonant frequency; and

determining a target thickness of the exposed portion of the upper layer using the target average stress of the membrane, wherein changing the thickness of the exposed portion of the upper layer comprises matching the thickness of the exposed portion of the upper layer to the target thickness.

19. The method of claim 16, wherein changing the thickness of the exposed portion of the upper layer comprises:

etching the exposed portion of the upper layer to reduce the thickness of the exposed portion of the upper layer.

20. The method of claim 16, wherein changing the thickness of the exposed portion of the upper layer through comprises:

depositing material on the exposed portion of the upper layer to increase the thickness of the exposed portion of the upper layer.