Curved micromachined ultrasonic transducer membranes

Patent metadata

Field	Value
Publication number	US-11383269-B2
Application number	US-202016896310-A
Country	US
Kind code	B2
Filing date	Jun 9, 2020
Priority date	Jun 10, 2019
Publication date	Jul 12, 2022
Grant date	Jul 12, 2022

Abstract

A method of forming an ultrasonic transducer device includes forming a curved membrane over a transducer cavity. A center portion of the curved membrane is closer to a bottom surface of the transducer cavity than with respect to radially outwardly disposed portions of the curved membrane.

First claim

What is claimed is:

1. A method of forming an ultrasonic transducer device, the method comprising:
forming a curved membrane over a transducer cavity, wherein a center portion of the curved membrane is closer to a bottom surface of the transducer cavity than with respect to radially outwardly disposed portions of the curved membrane;
forming a curved sacrificial cavity material, over a transducer bottom electrode, by chemical mechanical polishing (CMP);
forming one or more membrane layers over the curved sacrificial cavity material and the transducer bottom electrode;
removing the sacrificial cavity material to form the curved membrane,
wherein forming the curved sacrificial cavity material by CMP includes:
forming a sacrificial cavity material layer and patterning the sacrificial cavity material layer over the transducer bottom electrode;
forming a dielectric layer over the patterned sacrificial cavity material layer;
patterning the dielectric layer disposed over the patterned sacrificial layer; and
performing the CMP on the patterned dielectric layer and patterned sacrificial cavity material layer to induce dishing of the patterned sacrificial cavity material layer such that more sacrificial cavity material layer is removed at a center location than with respect to outer locations.

2. The method of claim 1 , wherein
the patterned dielectric layer includes dielectric material that protrudes above a surface of the patterned sacrificial cavity material to induce dishing of the patterned sacrificial cavity material layer during CMP.

3. A method of forming an ultrasonic transducer device, the method comprising:
forming a curved membrane over a transducer cavity, wherein a center portion of the curved membrane is closer to a bottom surface of the transducer cavity than with respect to radially outwardly disposed portions of the curved membrane;
forming a curved sacrificial cavity material over a transducer bottom electrode, by grayscale lithography;
forming one or more membrane layers over the curved sacrificial cavity material and the transducer bottom electrode; and
removing the sacrificial cavity material to form the curved membrane,
wherein the grayscale lithography includes:
forming a sacrificial cavity material layer over the transducer bottom electrode;
forming a photoresist layer over the sacrificial cavity material layer;
performing spatially modulated patterning of the photoresist layer to create a curved profile in the patterned photoresist layer;
developing the patterned photoresist layer so as to form a photoresist structure having the curved profile above the transducer bottom electrode; and
etching the curved profile of the photoresist structure and the sacrificial cavity material to transfer the curved profile into the sacrificial cavity material layer.

4. The method of claim 3 , further comprising:
using a etch recipe selected for a low etch selectivity between the photoresist and the sacrificial cavity material layer.

5. A method of forming an ultrasonic transducer device, the method comprising:
forming a curved membrane over a transducer cavity, wherein a center portion of the curved membrane is closer to a bottom surface of the transducer cavity than with respect to radially outwardly disposed portions of the curved membrane,
wherein forming the curved membrane includes:
forming the transducer cavity on a CMOS wafer;
bonding a membrane wafer to the CMOS wafer to seal the transducer cavity; and
performing an anneal to collapse the bonded membrane wafer into the transducer cavity and induce a curvature in the membrane wafer.

6. The method of claim 5 , further comprising:
patterning layers in the membrane wafer to induce film stress that biases the membrane wafer to curve toward the transducer cavity.

7. The method of claim 5 , wherein
after bonding the membrane wafer, a gas is pressurized on an exterior of the transducer cavity such that the annealing is performed at a gas pressure that induces the membrane wafer to collapse into the transducer cavity.

Assignees

• Bfly Operations Inc

Inventors

• Schmid Gerard
• Hosali Sharath
• Beach James
• Zahorian Jaime Scott
• Satir Sarp

Classifications

• B81C2201/0105

  Sacrificial layer · CPC title

• B81C1/00158

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

• B81B2201/0271

  Resonators; ultrasonic resonators · 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

• B06B1/0292 Primary

  Electrostatic transducers, e.g. electret-type · CPC title