Piezoelectric micromachined ultrasonic transducer and method of fabricating the same

Patent metadata

Field	Value
Publication number	US-2022023915-A1
Application number	US-202016936452-A
Country	US
Kind code	A1
Filing date	Jul 23, 2020
Priority date	Jul 23, 2020
Publication date	Jan 27, 2022
Grant date	—

Abstract

A PMUT includes a substrate, a membrane, and a sacrificial layer. The substrate has a cavity penetrating the substrate. The membrane is disposed over the cavity and includes a first piezoelectric layer, a bottom electrode, a top electrode, and a second piezoelectric layer. The first piezoelectric layer is disposed over the cavity and includes an anchor portion, where the anchor portion of the first piezoelectric layer is in direct contact with the substrate. The top and bottom electrodes are disposed over the first piezoelectric layer. The second piezoelectric layer is disposed between the bottom electrode and the top electrode. The sacrificial layer is disposed between the substrate and the first piezoelectric layer, and a vertical projection of the sacrificial layer does not overlap a vertical projection of portions of the membrane disposed over the cavity.

First claim

What is claimed is:

1 . A piezoelectric micromachined ultrasonic transducer (PMUT), comprising:
a substrate having a cavity penetrating the substrate; a membrane disposed over the cavity, the membrane comprising:
a first piezoelectric layer disposed over the cavity, the first piezoelectric layer comprising an anchor portion, wherein the anchor portion of the first piezoelectric layer is in direct contact with the substrate;
a bottom electrode disposed over the first piezoelectric layer;
a top electrode disposed over the bottom electrode; and
a second piezoelectric layer disposed between the bottom electrode and the top electrode; and
a sacrificial layer disposed between the substrate and the first piezoelectric layer, wherein a vertical projection of the sacrificial layer is not overlapped with a vertical projection of portions of the membrane disposed over the cavity.

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

3 . The PMUT of claim 1 , wherein the anchor portion of the first piezoelectric layer in direct contact with the substrate is a ring-shaped, polygon-shaped, or arc-shaped structure disposed along an opening of the cavity.

4 . The PMUT of claim 1 , further comprising an interface between one end of the sacrificial layer and the first piezoelectric layer, wherein an angle between the interface and a top surface of the substrate is 10°-40°.

5 . The PMUT of claim 1 , wherein the etch selectivity of sacrificial layer to the dielectric layer is greater than 10 when vapor fluoric acid (VHF) is used as etchant.

6 . The PMUT of claim 5 , wherein a material of the first piezoelectric layer is the same as a material of the second piezoelectric layer.

7 . The PMUT of claim 6 , wherein the dielectric layer is in direct contact with the bottom electrode.

8 . The PMUT of claim 5 , further comprising an elastic layer disposed on the membrane.

9 . The PMUT of claim 8 , further comprising at least one contact pad disposed over the sacrificial layer, wherein the elastic layer is spaced apart from the contact pad.

10 . The PMUT of claim 8 , further comprising a passivation layer disposed between the membrane and the elastic layer.

11 . A method of fabricating a piezoelectric micromachined ultrasonic transducer (PMUT), comprising:
providing a substrate; forming a sacrificial layer on the substrate, wherein the sacrificial layer comprises at least one hole exposing the substrate; forming a piezoelectric layer in the at least one hole and on 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 piezoelectric layer as an etch stop structure.

12 . The method of claim 11 , wherein an angle between a sidewall of the at least one hole and a top surface of the substrate is 10°-40°.

13 . The method of claim 11 , wherein the piezoelectric layer comprises an anchor portion in direct contact with the substrate.

14 . The method of claim 13 , wherein the anchor portion of the piezoelectric layer in direct contact with the substrate is a ring-shaped, polygon-shaped, or arc-shaped structure disposed along an opening of the cavity.

15 . The method of claim 11 , further comprising:
forming a plurality of layers on the piezoelectric layer and on the sacrificial layer before the step of forming the cavity penetrating the substrate, wherein the plurality of layers comprises:
a bottom electrode;
a top electrode disposed over the bottom electrode; and
a further piezoelectric layer disposed between the bottom electrode and the top electrode.

16 . The method of claim 15 , further comprising forming an elastic layer on the plurality of layers.

17 . The method of claim 16 , further comprising at least one contact pad disposed on the plurality of layers and electrically coupled to one of the top electrode or the bottom electrode, wherein the elastic layer is spaced apart from the contact pad.

18 . The method of claim 16 , wherein the piezoelectric layer is in direct contact with the bottom electrode.

19 . The method of claim 11 , wherein, when the step of removing the portions of the sacrificial layer exposed from the cavity is completed, other portions of the sacrificial layer remain on the substrate.

20 . The method of claim 11 , wherein an etch selectivity of the sacrificial layer to the piezoelectric layer 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

• Qian You
• Kumar Rakesh
• Xia jia jie

Classifications

• B06B1/0611

  in a pile · CPC title

• B06B1/0666 Primary

  used as a diaphragm · CPC title

• B81B2203/0307

  Anchors · 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

• B81C1/00158

  Diaphragms, membranes (manufacture process for semi-permeable inorganic membranes B01D67/0039) · CPC title