# US 2025/0096772 A1 · Microacoustic Filter with an Acoustically-Decoupled Electrode Structure

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- Number: US 2025/0096772 A1
- Document ID: US20250096772A1
- Status: Published application
- Kind: A1
- Application number: 18/470,200
- Filed: 2023-09-19
- Published: 2025-03-20
- Earliest claimed: 2023-09-19
- Assignees: RF360 Singapore Pte. Ltd.
- Applicants: RF360 Singapore Pte. Ltd.
- Inventors: Soeren Zimmermann; Marc Konstantin Dietrich; Willi Aigner; Benno Blaschke; Matthias Knapp
- Web page: https://patentgrep.com/patent/US20250096772A1

## CPC

- H03H 9/02228: {Guided bulk acoustic wave devices or Lamb wave devices having interdigital transducers situated in parallel planes on either side of a piezoelectric layer}
- H03H 9/205: having multiple resonators (crystal tuning forks H03H9/21)
- H03H 3/02: for the manufacture of piezoelectric or electrostrictive resonators or networks (H03H3/08 takes precedence)
- H03H 9/02015: {Characteristics of piezoelectric layers, e.g. cutting angles}
- H03H 9/02125: {of parasitic elements}
- H03H 9/131: {consisting of a multilayered structure}
- H03H 9/132: {characterized by a particular shape}
- H03H 9/564: {implemented with thin-film techniques}
- H03H 9/566: {Electric coupling means therefor (H03H9/0095 takes precedence)}
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)

## Abstract

An apparatus is disclosed for implementing a microacoustic filter with an acoustically-decoupled electrode structure. In an example aspect, the apparatus includes the microacoustic filter with a piezoelectric layer, a substrate, and an electrode structure. The piezoelectric layer has a crystalline structure operative to laterally excite a plate mode. The electrode structure is positioned between the piezoelectric layer and the substrate and has a has a first surface that faces the piezoelectric layer. The microacoustic filter also includes at least one spacer extending from the substrate past a plane defined by the first surface of the electrode structure and towards the piezoelectric layer to form a cavity between the electrode structure and the piezoelectric layer.

## Claims

### Claim 1

An apparatus comprising:
a microacoustic filter comprising:
a piezoelectric layer having a crystalline structure operative to laterally excite a plate mode;
a substrate;
an electrode structure positioned between the piezoelectric layer and the substrate, the electrode structure having a first surface that faces the piezoelectric layer; and
at least one spacer extending from the substrate past a plane defined by the first surface of the electrode structure and towards the piezoelectric layer to form a cavity between the electrode structure and the piezoelectric layer.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein a distance between the first surface of the electrode structure and the piezoelectric layer is between approximately 2 and 200 nanometers.

### Claim 3 (depends on 2)

The apparatus of claim 2, wherein the distance between the first surface of the electrode structure and the piezoelectric layer is between approximately 50 and 75 nanometers.

### Claim 4 (depends on 1)

The apparatus of claim 1, wherein the cavity is formed within at least an acoustically-active resonator area of the microacoustic filter.

### Claim 5 (depends on 4)

The apparatus of claim 4, wherein the at least one spacer is positioned within the acoustically-active resonator area of the microacoustic filter.

### Claim 6 (depends on 5)

The apparatus of claim 5, wherein:
the electrode structure comprises multiple fingers; and
the at least one spacer comprises multiple spacers positioned between different sets of fingers of the multiple fingers.

### Claim 7 (depends on 6)

The apparatus of claim 6, wherein:
the electrode structure comprises two busbars; and
each spacer of the multiple spacers is positioned between two fingers of the multiple fingers that are connected to a same busbar of the two busbars.

### Claim 8 (depends on 6)

The apparatus of claim 6, wherein:
the electrode structure comprises two busbars; and
each spacer of the multiple spacers is positioned between two fingers of the multiple fingers that are connected to different busbars of the two busbars.

### Claim 9 (depends on 5)

The apparatus of claim 5, wherein the at least one spacer comprises at least one wall spacer having a longitudinal axis that extends across at least a portion of the acoustically-active resonator area of the microacoustic filter.

### Claim 10 (depends on 5)

The apparatus of claim 5, wherein the at least one spacer comprises at least one column spacer.

### Claim 11 (depends on 4)

The apparatus of claim 4, wherein the at least one spacer is positioned outside of the acoustically-active resonator area of the microacoustic filter.

### Claim 12 (depends on 11)

The apparatus of claim 11, wherein the at least one spacer comprises at least one wall spacer that at least partially surrounds the electrode structure.

### Claim 13 (depends on 1)

The apparatus of claim 1, wherein:
the substrate comprises a substrate stack comprising an intermediate layer having a surface that faces a second surface of the electrode structure; and
the intermediate layer and the at least one spacer comprise a dielectric material or amorphous silicon.

### Claim 14 (depends on 13)

The apparatus of claim 13, wherein:
the substrate stack comprises a substrate layer; and
the intermediate layer is disposed between the electrode structure and the substrate layer.

### Claim 15 (depends on 14)

The apparatus of claim 14, wherein the substrate layer comprises at least one of the following materials:
silicon;
silicon dioxide;
silicon carbide;
sapphire; or
glass.

### Claim 16 (depends on 1)

The apparatus of claim 1, wherein the microacoustic filter comprises an embedding layer disposed on the substrate between adjacent fingers of multiple fingers of the electrode structure such that the electrode structure is at least partially embedded within the embedding layer.

### Claim 17 (depends on 16)

The apparatus of claim 16, wherein a thickness of the embedding layer is less than or equal to a thickness of the electrode structure.

### Claim 18 (depends on 16)

The apparatus of claim 16, wherein the embedding layer comprises a dielectric material.

### Claim 19 (depends on 1)

The apparatus of claim 1, wherein:
multiple fingers of the electrode structure are positioned across a first axis;
longitudinal axes of the multiple fingers are substantially parallel to a second axis that is perpendicular to the first axis;
a third axis is perpendicular to the first axis and the second axis;
an orientation of the first axis, the second axis, and the third axis is relative to a crystalline structure of the piezoelectric layer as defined by Euler angles lambda, mu, and theta; and
the piezoelectric layer comprises lithium niobate with a value of the Euler angle lambda being approximately 0°, a value of the Euler angle mu being approximately 32°, and a value of the Euler angle theta being approximately 0°, or at least one symmetrical equivalent thereof.

### Claim 20 (depends on 1)

The apparatus of claim 1, wherein:
multiple fingers of the electrode structure are positioned across a first axis;
longitudinal axes of the multiple fingers are substantially parallel to a second axis that is perpendicular to the first axis;
a third axis is perpendicular to the first axis and the second axis;
an orientation of the first axis, the second axis, and the third axis is relative to a crystalline structure of the piezoelectric layer as defined by Euler angles lambda, mu, and theta; and
the piezoelectric layer comprises lithium niobate with the value of the Euler angle lambda being approximately 0°, the value of the Euler angle mu being approximately 0°, and the value of the Euler angle theta being approximately 90°, or at least one symmetrical equivalent thereof.

### Claim 21 (depends on 1)

The apparatus of claim 1, wherein:
multiple fingers of the electrode structure are positioned across a first axis;
longitudinal axes of the multiple fingers are substantially parallel to a second axis that is perpendicular to the first axis;
a third axis is perpendicular to the first axis and the second axis;
an orientation of the first axis, the second axis, and the third axis is relative to a crystalline structure of the piezoelectric layer as defined by Euler angles lambda, mu, and theta; and
the piezoelectric layer comprises lithium tantalate with a value of the Euler angle lambda being approximately 0°, a value of the Euler angle mu being approximately 42°, and a value of the Euler angle theta being approximately 0°, or at least one symmetrical equivalent thereof.

### Claim 22 (depends on 1)

The apparatus of claim 1, wherein:
the cavity is at least partially filled with a gas; and
the gas comprises air.

### Claim 23 (depends on 1)

The apparatus of claim 1, wherein a resonance frequency associated with the plate mode is between approximately 2 and 20 gigahertz.

### Claim 24 (depends on 23)

The apparatus of claim 23, wherein the resonance frequency associated with the plate mode is between approximately 7.5 and 17 gigahertz.

### Claim 25 (depends on 1)

The apparatus of claim 1, wherein:
the microacoustic filter comprises multiple cascaded resonators; and
a resonator of the multiple cascaded resonators comprises the piezoelectric layer, the electrode structure, and the substrate.

### Claim 26 (depends on 1)

The apparatus of claim 1, further comprising:
a wireless transceiver coupled to at least one antenna, the wireless transceiver comprising the microacoustic filter and configured to filter, using the microacoustic filter, a wireless signal communicated via the at least one antenna.

### Claim 27

An apparatus comprising:
a microacoustic filter configured to generate a filtered signal from a radio-frequency signal, the microacoustic filter comprising:
a substrate;
means for producing a formed acoustic wave associated with a laterally-excited plate mode;
means for converting the radio-frequency signal to an acoustic wave and converting the formed acoustic wave into the filtered signal; and
means for separating the means for producing from the means for converting by forming a cavity between the means for producing and the means for converting.

### Claim 28 (depends on 27)

The apparatus of claim 27, wherein the microacoustic filter comprises means for bonding the means for converting to the substrate.

### Claim 29 (depends on 27)

The apparatus of claim 27, wherein the microacoustic filter comprises means for compensating for a decrease in a static capacitance associated with a separation distance between the means for producing and the means for converting, the means for compensating at least partially embedding the means for converting.

### Claim 30

A method of manufacturing a microacoustic filter, the method comprising:
providing a piezoelectric layer having a crystalline structure operative to laterally excite a plate mode;
providing a substrate;
providing an electrode structure between the piezoelectric layer and the substrate, the electrode structure having a surface that faces the piezoelectric layer; and
providing at least one spacer extending from the substrate past a plane defined by the surface of the electrode structure and towards the piezoelectric layer to form a cavity between the electrode structure and the piezoelectric layer.

### Claim 31 (depends on 30)

The method of claim 30, further comprising:
providing a dielectric material between the substrate and the piezoelectric layer, the dielectric material at least partially embedding the electrode structure.

### Claim 32

A microacoustic filter comprising:
a piezoelectric layer having a crystalline structure operative to laterally excite a plate mode;
a substrate; and
an electrode structure that is positioned between the piezoelectric layer and the substrate, the electrode structure having a surface that faces the piezoelectric layer and is separated by a gap from the piezoelectric layer.

### Claim 33 (depends on 32)

The microacoustic filter of claim 32, wherein a distance between the surface of the electrode structure and the piezoelectric layer is between approximately 2 and 200 nanometers.

### Claim 34 (depends on 32)

The microacoustic filter of claim 32, further comprising:
an intermediate layer disposed between the electrode structure and the substrate, the intermediate layer comprising amorphous silicon or a dielectric.

### Claim 35 (depends on 34)

The microacoustic filter of claim 34, wherein:
the microacoustic filter comprises at least one spacer disposed on the intermediate layer, the at least one spacer extending past a plane defined by the surface of the electrode structure; and
the at least one spacer comprises the amorphous silicon or the dielectric.

### Claim 36 (depends on 35)

The microacoustic filter of claim 35, wherein:
the electrode structure comprises two busbars and multiple fingers; and
the at least one spacer is positioned between two fingers of the multiple fingers, the two fingers connected to a same busbar of the two busbars.

### Claim 37 (depends on 32)

The microacoustic filter of claim 32, further comprising a dielectric material positioned between the substrate and the piezoelectric layer and at least partially embedding the electrode structure.

### Claim 38 (depends on 32)

The microacoustic filter of claim 32, wherein:
the electrode structure comprises multiple fingers positioned across a first axis;
longitudinal axes of the multiple fingers are substantially parallel to a second axis that is perpendicular to the first axis;
a third axis is perpendicular to the first axis and the second axis;
an orientation of the first axis, the second axis, and the third axis is relative to the crystalline structure of the piezoelectric layer as defined by Euler angles lambda, mu, and theta; and
the piezoelectric layer comprises one of the following:
lithium niobate with a value of the Euler angle lambda being approximately 0°, a value of the Euler angle mu being approximately 32°, and a value of the Euler angle theta being approximately 0°, or at least one symmetrical equivalent thereof;
the lithium niobate with the value of the Euler angle lambda being approximately 0°, the value of the Euler angle mu being approximately 0°, and the value of the Euler angle theta being approximately 90°, or at least one symmetrical equivalent thereof; or
lithium tantalate with a value of the Euler angle lambda being approximately 0°, a value of the Euler angle mu being approximately 42°, and a value of the Euler angle theta being approximately 0°, or at least one symmetrical equivalent thereof.