Piezoelectric micromachined ultrasonic transducer and method of fabricating the same

Patent metadata

Field	Value
Publication number	US-11498097-B2
Application number	US-202016880956-A
Country	US
Kind code	B2
Filing date	May 21, 2020
Priority date	May 21, 2020
Publication date	Nov 15, 2022
Grant date	Nov 15, 2022

Abstract

A piezoelectric micromachined ultrasonic transducer (PMUT) includes a substrate, a stopper, and a membrane, where the substrate and the stopper are composed of same single-crystalline material. The substrate has a cavity penetrating the substrate, and the stopper protrudes from a top surface of the substrate and surrounds the edge of the cavity. The membrane is disposed over the cavity and attached to the stopper.

First claim

What is claimed is:

1. A piezoelectric micromachined ultrasonic transducer (PMUT), comprising:
a substrate having an cavity penetrating the substrate;
a stopper protruding from a top surface of the substrate and surrounding an edge of the cavity, wherein the stopper is formed by etching the substrate; and
a membrane disposed over the cavity and attached to the stopper,
wherein the substrate and the stopper are composed of same material comprising single-crystalline silicon, poly-crystalline silicon, amorphous silicon, glass, or ceramic.

2. The PMUT of claim 1 , wherein the edge of the cavity is in proximity to the membrane.

3. The PMUT of claim 1 , wherein the stopper is a ring-shaped, polygon-shaped, or arc-shaped structure disposed along an edge of the membrane.

4. The PMUT of claim 1 , wherein the membrane is a multilayer structure.

5. The PMUT of claim 4 , wherein the multilayer structure comprises:
a base layer;
a dielectric layer disposed on the base layer;
two conductive layers stacked on the base layer; and
a piezoelectric layer disposed between the conductive layers.

6. The PMUT of claim 5 , wherein a material of the base layer is different from the piezoelectric layer.

7. The PMUT of claim 1 , further comprising an interrupted portion penetrating the membrane.

8. The PMUT of claim 7 , wherein the stopper is disposed along a perimeter of the interrupted portion.

9. The PMUT of claim 1 , further comprising a sacrificial layer disposed on a top surface of the substrate and surrounding the stopper, and the etch selectivity of sacrificial layer over the stopper and the base layer is greater than 10 when vapor fluoric acid (VHF) is used as etchant.

10. The PMUT of claim 9 , wherein a top surface of the sacrificial layer is level with a top surface of the stopper.

11. A method of fabricating a piezoelectric micromachined ultrasonic transducer (PMUT), comprising:
providing a substrate;
etching the substrate to form a stopper protruding from the substrate;
forming a sacrificial layer on the substrate, wherein the stopper is exposed from the sacrificial layer;
forming a membrane layer on the stopper and the sacrificial layer;
forming a cavity penetrating the substrate to expose portions of the sacrificial layer; and
removing the portions of the sacrificial layer exposed from the cavity using the stopper as an etch stop structure.

12. The method of claim 11 , wherein the stopper is a ring-shaped, polygon-shaped, or arc-shaped structure disposed along an edge of the membrane.

13. The method of claim 11 , wherein the substrate and the stopper are composed of same single-crystalline material.

14. The method of claim 11 , wherein the step of forming the sacrificial layer on the substrate comprises:
depositing a sacrificial material on the substrate and the stopper; and
planarizing the sacrificial material to expose the stopper.

15. The method of claim 11 , wherein the membrane layer is a multilayer structure comprising:
a base layer;
a dielectric layer disposed on the base layer;
two conductive layers stacked on the base layer; and
a piezoelectric layer disposed between the conductive layers.

16. The method of claim 11 , further comprising forming an interrupted portion penetrating the membrane layer.

17. The method of claim 16 , wherein the stopper is disposed along a perimeter of the interrupted portion.

18. The method of claim 11 , wherein, when the step of forming the sacrificial layer on the substrate is completed, the sacrificial layer comprises:
a first portion surrounded by the stopper; and
a second portion spaced apart from the first portion by the stopper.

19. The method of claim 18 , wherein the second portion of the sacrificial layer remains on the substrate when the step of removing the portions of the sacrificial layer exposed from the cavity is completed.

20. The method of claim 11 , wherein an etch selectivity of the sacrificial layer to the stopper is greater than 10 during the step of removing the portions of the sacrificial layer exposed from the cavity.

Assignees

• Vanguard Int Semiconduct Corp

Inventors

• Kumar Rakesh
• Xia jia jie
• Qian You

Classifications

• B06B1/0651

  of circular shape · CPC title

• B81B2203/0315

  Cavities · CPC title

• B06B1/0666 Primary

  used as a diaphragm · CPC title

• B81B2203/0127

  Diaphragms, i.e. structures separating two media that can control the passage from one medium to another; Membranes, i.e. diaphragms with filtering function · CPC title

• B81C2201/0133

  Wet etching · CPC title