Multiple layer acoustical structures for thin-film resonator based circuits and systems

• US 5,864,261 A
• Filed: 01/29/1997
• Issued: 01/26/1999
• Est. Priority Date: 05/23/1994
• Status: Expired due to Term

• Current Assignee: Iowa State University Research Foundation Incorporated (Iowa State University)
• Original Assignee: Iowa State University Research Foundation Incorporated (Iowa State University)
• Inventors: Weber, Robert J.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Bettendorf, Justin P.
• Application Number:
  US08/789,404
• Time in Patent Office: 727 Days
• Field of Search: 333/187, 333/188, 333/189, 333/190, 333/191, 333/192, 310/321, 310/324, 310/334
• US Class Current: 333/187
• CPC Class Codes: H03H 9/02078 the vibration mode being overmoded
• CPC Class Codes: H03H 9/02133 of stress
• CPC Class Codes: H03H 9/175 Acoustic mirrors
• CPC Class Codes: H03H 9/583 comprising a plurality of piezoelectric layers acoustically coupled
• CPC Class Codes: H03H 9/585 Stacked Crystal Filters [SCF]
• CPC Class Codes: H03H 9/589 Acoustic mirrors

Abstract

A stacked thin film device structure grown on a substrate, the resonator structure comprising a thin film device comprising at least one piezoelectric crystal layer sandwiched between metallic electrodes, and constructed to have an acoustic response in a given frequency range, and an acoustical stack disposed between and joining the thin film device and the substrate and comprising multiple layers of material, each layer having a characteristic thickness and impedance and being composed of a non-lossless material, the characteristic thicknesses and impedances of the layers being adjusted to determine the input impedance presented to the thin film device, and thereby determining the acoustical coupling between the thin film device and the substrate.

Claims

1. A thin film resonator device, comprising:

a thin film resonator;

a substrate underlying and mechanically supporting the resonator, and

an acoustical isolator disposed between and joining the resonator and the substrate and comprising layers of non-lossless material having characteristic impedances and thicknesses selected to present a nominal impedance to the thin film resonator such as would be found if the thin film resonator were coupled to air.

2. A stacked thin film device structure grown on a substrate, comprising;

a thin film device comprising at least one piezoelectric crystal layer sandwiched between electrodes, and constructed to have an acoustic response and a given frequency range;

an acoustical stack disposed between and joining the thin film device and the substrate and comprising multiple layers of material, each layer having a characteristic thickness and impedance and being composed of a non-lossless material, the characteristic thickness and impedances of the layers being adjusted to determine the input impedance presented to the thin film device, and thereby determining the acoustical coupling between the thin film device and the substrate; and

wherein the acoustical stack is an acoustical isolator presenting a nominal input impedance to the thin film device mimicking an acoustical short circuit such as would be found if said thin film resonator were coupled to air, the isolator comprising a sufficient number of layers having characteristic thicknesses and impedances adjusted to cause the isolator to present an iterative impedance to the thin film device which meets an isolation condition in the given frequency range, thereby isolating the thin film device from the substrate.

3. The stacked thin film device structure according to claim 2, wherein the sufficient number is at least six.

4. The stacked thin film device structure according to claim 2, wherein the acoustical isolator is a cascaded stack of stack pairs, each stack pair constituent having a thickness equal to one quarter the wavelength of an acoustical wave in the given frequency range of the thin film device.

5. The stacked thin film device structure according to claim 4, wherein each stack pair is comprised of a first constituent having a relatively higher characteristic impedance, and a second constituent having a relatively lower characteristic impedance.

6. The stacked thin film device structure according to claim 5, wherein the first stack pair constituent is chromium, and the second stack pair constituent is aluminum.

7. The stacked thin film device structure according to claim 5, wherein the first stack pair constituent is copper, and the second stack pair constituent is aluminum.

8. The stacked thin film device structure according to claim 5, wherein three or more stacked pairs are cascaded to form the acoustical isolator.

9. The stacked thin film device structure according to claim 5, wherein the acoustical stack includes an uppermost stack pair, the top constituent of the uppermost stack pair also forming a bottom electrode for the thin film device.

10. The stacked thin film device of claim 4, wherein each stack pair is composed of different materials.

11. The stacked thin film device structure according to claim 2, wherein the thin film device is a thin film resonator.

12. The stacked thin film device structure according to claim 2, wherein the constituent material of the layers is selected to provide temperature compensation to the thin film device.

13. A thin film resonator device, comprising:

a thin film resonator;

a substrate underlying and mechanically supporting the resonator, and

an acoustical isolator disposed between and joining the resonator and the substrate and comprising at least six layers of non-lossless material having characteristic impedances and thicknesses adjusted to present a nominal input impedance to the resonator which acoustically isolates the resonator and substrate.

14. A method for fabricating a thin film resonator device, comprising:

a) providing a substrate;

1) for receiving an acoustical stack to be formed by sequentially depositing individual layers of non-lossless material on the substrate, each layer having a characteristic impedance and thickness; and

2) for receiving a thin film device to be formed by sequentially depositing a first electrode, a piezoelectric layer, and a second electrode, the properties of the electrodes and piezoelectric layer being chosen to give the thin film device an acoustic response in a given frequency range;

b) determining the required characteristic thicknesses and impedances of each stack layer by determining the stack input impedance required to achieve acoustical isolation between the substrate and the thin film device in the given frequency range, the stack input impedance being nominal such as would be found if the thin film resonator device were coupled to air, and calculating the characteristic thicknesses and impedances to achieve that nominal input impedance;

c) depositing the layers of the acoustical stack according to the determination of step b); and

d) depositing the layers of the thin film device on the acoustical stack.