THIN-FILM BULK ACOUSTIC WAVE DELAY LINE

• US 20130162369A1
• Filed: 06/21/2012
• Published: 06/27/2013
• Est. Priority Date: 06/21/2011
• Status: Active Grant

• Current Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Original Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Inventors: Hunt, William, Munir, Farasat, Wathen, Adam, Davis, Kyle Spencer, Maloney, James Geoffrey, Westafer, Ryan Sloan
• Granted Patent: US 9,473,106 B2
• Time in Patent Office: Days
• US Class Current: 333/141
• CPC Class Codes: H03H 9/30 Time-delay networks

Abstract

A thin-film bulk acoustic wave delay line device providing true-time delays and a method of fabricating same. An exemplary device can comprise several thin-film layers including thin-film transducer layers, thin-film delay layers, and stacks of additional thin-film materials providing acoustic reflectors and matching networks. The layer material selection and layer thicknesses can be controlled to improve impedance matching between transducers and the various delay line materials. For example, the transducer layers and delay layers can comprise piezoelectric and amorphous forms of the same material. The layers can be deposited on a carrier substrate using standard techniques. The device can be configured so that mechanical waves propagate solely within the thin films, providing a substrate-independent device. The device, so constructed, can be of a small size, e.g. 40 μm per side, and capable of handling high power levels, potentially up to 20 dBm, with low insertion loss of approximately 3 dB.

Claims

1. A bulk-acoustic-wave delay line device comprising:

one or more input transducer layers, including a first input transducer layer, for converting input electrical signals to mechanical waves;

one or more output transducer layers, including a first output transducer layer, for converting the mechanical waves to output electrical signals;

wherein each of the one or more input transducer layers and each of the one or more output transducer layers comprises a thin-film piezoelectric medium positioned between two electrode layers, each electrode layer comprising one or more electrodes; and

one or more delay layers, including a first delay layer adjacent to the first input transducer layer and adjacent to the first output transducer layer, each delay layer comprising a thin-film delay medium.

2. The device of claim 1, further comprising a substrate for carrying the one or more input transducer layers, the one or more output transducer layers, and the one or more delay layers.

3. The device of claim 2, wherein the first input transducer layer is the first output transducer layer.

4. The device of claim 2, further comprising a thin-film acoustic reflector stack between the substrate and the first input transducer layer.

5. The device of claim 2, wherein the first delay layer is positioned between the first input transducer layer and the first output transducer layer.

6. The device of claim 2, further comprising a thin-film acoustic matching network between the substrate and the first input transducer layer.

7. The device of claim 2, wherein the substrate is configured to receive and terminate incident energy of the mechanical waves to reduce undesired reflections.

8. The device of claim 1, wherein the thin-film delay mediums and the thin-film piezoelectric mediums primarily comprise a first material that can be deposited as a thin film.

9. The device of claim 8, wherein the thin-film delay mediums are at least as thick as one-fourth the acoustic wavelength of the first material.

10. The device of claim 8, wherein the thin-film delay mediums are a non-piezoelectric form of the first material.

11. The device of claim 1, wherein the one or more delay layers have a same acoustic impedance.

12. The device of claim 1, wherein the thickness of each of the one or more delay layers is selected to compensate for delay incurred by conveyance of the mechanical waves through output transducer layers.

13. The device of claim 1, wherein the device is no more than approximately 100 μ

m on a side, and configured to handle power levels up to approximately 20 dBm with low insertion loss.

14. The device of claim 1, configured to provide delays on the order of nanoseconds.

15. A method of constructing a thin-film bulk-acoustic-wave delay line device comprising depositing on a substrate:

one or more transducer layers, wherein a transducer layer comprises a thin-film piezoelectric medium positioned between a pair of electrode layers, each electrode layer comprising one or more electrodes; and

one or more delay layers, wherein a delay layer comprises a thin-film delay medium.

16. The method of claim 15, further comprising:

selective etching of the transducer layers and delay layers, wherein the transducer layers and delay layers are etched to progressively smaller lateral dimensions as the distance from the substrate increases to expose the input and output electrodes of the transducer layers.

17. The method of claim 15, further comprising:

selective deep anisotropic etching, wherein multiple etching steps are performed at the end of a fabrication process to expose the input and output electrodes of the transducer layers.

18. The method of claim 17, wherein the etching is wet etching using an acoustically lossy etch stop material.

19. The method of claim 17, wherein the etch stop material primarily comprises gold.

20. The method of claim 15, further comprising removing at least part of the substrate.

21. A thin-film bulk-acoustic-wave delay line device comprising:

an upper thin-film transducer layer for converting input electrical signals to mechanical waves;

a lower thin-film transducer layer for converting the mechanical waves to output electrical signals;

wherein a thin-film transducer layer comprises;

a first electrode and a second electrode;

wherein an electrode comprises a plurality of metal layers including;

a metal layer for adhesion;

a metal layer for electrical conductance; and

a metal etch-stop layer on regions of the electrode for forming external electrical contacts; and

a piezoelectric medium of a first chemical composition and with a substantially high coupling coefficient positioned between the first and second electrodes; and

a thin-film delay layer comprising an amorphous material of the first chemical composition and positioned between the upper and lower thin-film transducer layers;

a thin-film acoustic matching network comprising a plurality of additional thin-film layers and positioned between a substrate and the lower thin-film transducer layer; and

the substrate for carrying the thin-film transducer layers, the thin-film delay layer, and the thin-film acoustic matching network.