Bulk acoustic wave resonator with piezoelectric layer comprising lithium niobate or lithium tantalate

• US 10,164,605 B2
• Filed: 01/26/2016
• Issued: 12/25/2018
• Est. Priority Date: 01/26/2016
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Inventors: Burak, Dariusz, Grannen, Kevin J., Choy, John
• Primary Examiner(s): Dougherty, Thomas
• Application Number:
  US15/006,724
• Publication Number:
  US 20170214387A1
• Time in Patent Office: 1,064 Days
• Field of Search: 310311, 310324, 310328, 310348, 310358, 310364
• CPC Class Codes: H03H 2003/0428 of an electrode
• CPC Class Codes: H03H 3/04 for obtaining desired frequency or temperature coefficient
• CPC Class Codes: H03H 9/02118 of lateral leakage between adjacent resonators
• CPC Class Codes: H03H 9/173 Air-gaps
• CPC Class Codes: H03H 9/175 Acoustic mirrors

Abstract

A bulk acoustic wave (BAW) resonator includes a substrate defining a cavity, a bottom electrode disposed over the substrate and the cavity, a piezoelectric layer disposed on the bottom electrode, and a top electrode disposed on the piezoelectric layer. The piezoelectric layer includes polycrystalline lithium niobate (LN) material or polycrystalline lithium tantalite (LT) material. The BAW resonator may further include an encapsulant layer formed on side and top surfaces of the piezoelectric layer. The encapsulant layer is configured to protect the LN material or the LT material of the piezoelectric layer from a release solvent previously applied to sacrificial material within the cavity in the substrate.

Claims

1. A bulk acoustic wave (BAW) resonator, comprising:

a substrate defining a cavity;

a bottom electrode disposed over the substrate and the cavity;

a piezoelectric layer disposed over the bottom electrode, the piezoelectric layer comprising polycrystalline lithium niobate (LN) material;

a top electrode disposed over the piezoelectric layer; and

an encapsulant layer formed over side and top surfaces of the piezoelectric layer, the encapsulant layer being configured to protect the LN material from a release solvent previously applied to sacrificial material within the cavity in the substrate.

2. The BAW resonator of claim 1, wherein the polycrystalline LN is formed of crystal columns substantially aligned in parallel to each other.

3. The BAW resonator of claim 2, wherein each of the LN crystal columns has a c-axis oriented substantially perpendicular to a top surface of the bottom electrode.

4. The BAW resonator of claim 1, wherein at least one of the bottom electrode and the top electrode comprises multiple conductive layers, a first conductive layer being disposed adjacent to the piezoelectric layer and having a first acoustic impedance, and a second conductive layer being disposed adjacent to the first conductive layer and having a second acoustic impedance greater than the first acoustic impedance.

5. The BAW resonator of claim 1, further comprising:

at least one lateral performance enhancement feature in at least one of the bottom electrode or the top electrode.

6. The BAW resonator of claim 5, wherein the at least one lateral performance enhancement feature comprises at least one of an air-bridge or an air-wing.

7. The BAW resonator of claim 5, wherein the at least one lateral performance enhancement feature comprises one of an inner frame or an outer frame.

8. A bulk acoustic wave (BAW) resonator, comprising:

a substrate defining a cavity;

a bottom electrode disposed over the substrate and the cavity;

a piezoelectric layer disposed over the bottom electrode, the piezoelectric layer comprising polycrystalline lithium tantalate (LT) material; and

a top electrode disposed over the piezoelectric layer; and

an encapsulant layer formed over side and top surfaces of the piezoelectric layer, the encapsulant layer being configured to protect the LT material from a release solvent previously applied to sacrificial material within the cavity in the substrate.

9. The BAW resonator of claim 8, wherein each of the polycrystalline LT is formed of crystal columns substantially aligned in parallel to each other.

10. The BAW resonator of claim 9, wherein each of the LT crystal columns has a c-axis oriented substantially perpendicular to a top surface of the bottom electrode.

11. The BAW resonator of claim 8, wherein at least one of the bottom electrode and the top electrode comprises multiple conductive layers, a first conductive layer being disposed adjacent to the piezoelectric layer and having a first acoustic impedance, and a second conductive layer being disposed adjacent to the first conductive layer and having a second acoustic impedance greater than the first acoustic impedance.

12. The BAW resonator of claim 8, further comprising:

at least one lateral performance enhancement feature in at least one of the bottom electrode or the top electrode.

13. The BAW resonator of claim 12, wherein the at least one lateral performance enhancement feature comprises at least one of an air-bridge or an air-wing.

14. The BAW resonator of claim 12, wherein the at least one lateral performance enhancement feature comprises one of an inner frame or an outer frame.

15. A bulk acoustic wave (BAW) resonator, comprising:

a substrate defining a cavity;

a bottom electrode disposed over the substrate and the cavity;

a piezoelectric layer disposed over the bottom electrode, the piezoelectric layer comprising one or polycrystalline lithium niobate (LN) material or polycrystalline lithium tantalate (LT) material;

a top electrode disposed over the piezoelectric layer; and

an encapsulant layer formed on the piezoelectric layer, the encapsulant layer comprising a dielectric material resistant to release solvent for releasing sacrificial material.

16. The BAW resonator of claim 15, where the dielectric material comprises one of silicon carbide (SiC) or non-etchable boron-doped silicon glass (NEBSG).

17. The BAW resonator of claim 15, where the dielectric material is resistant to release solvent comprising hydrofluoric acid.

18. The BAW resonator of claim 15, wherein at least one of the bottom electrode and the top electrode comprises multiple conductive layers, a first conductive layer being disposed adjacent to the piezoelectric layer and having a first acoustic impedance, and a second conductive layer being disposed adjacent to the first conductive layer and having a second acoustic impedance greater than the first acoustic impedance.

19. The BAW resonator of claim 15, further comprising:

at least one lateral performance enhancement feature in at least one of the bottom electrode or the top electrode.