Bulk Acoustic Wave Device with a Semiconductor Layer

• US 20090218912A1
• Filed: 02/29/2008
• Published: 09/03/2009
• Est. Priority Date: 02/29/2008
• Status: Active Grant

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies Wireless IP Singapore Pte Limited (Broadcom, Inc.)
• Inventors: Abd Allah, Mohamed, Weber, Werner, Thalhammer, Robert, Kaitila, Jyrki
• Granted Patent: US 7,977,850 B2
• Time in Patent Office: Days
• US Class Current: 310/321
• CPC Class Codes: H03H 2009/02196 operating on the FBAR element, e.g. by direct application of a tuning DC voltage
• CPC Class Codes: H03H 9/174 Membranes
• CPC Class Codes: H03H 9/175 Acoustic mirrors

Abstract

A bulk acoustic wave device includes a first electrode, a second electrode, a piezoelectric layer arranged between the first and second electrodes and a semiconductor layer arranged between the first and second electrodes. The semiconductor layer is electrically isolated from the first electrode.

Claims

1. A bulk acoustic wave (BAW) device, comprising:

a first electrode;

a second electrode;

a piezoelectric layer disposed between the first and second electrodes; and

a semiconductor layer disposed between the first and second electrodes, wherein the semiconductor layer is electrically isolated from the first electrode.

2. The BAW device according to claim 1, wherein the semiconductor layer comprises a doped semiconductor layer with a doping level.

3. The BAW device according to claim 2, wherein the doping level comprises a moderate level.

4. The BAW device according to claim 1, wherein the first and second electrodes are configured to apply a tunable DC voltage to the first and second electrodes.

5. The BAW device according to claim 1, wherein the piezoelectric layer is sandwiched over a resonator region by the first and second electrodes and the piezoelectric layer extends outside the resonator region and the BAW device is formed as a membrane device with an air interface on both sides of the resonator region.

6. The BAW device according to claim 1, wherein the semiconductor layer comprises crystalline silicon.

7. The BAW device according to claim 1, further comprising an acoustic mirror, the acoustic mirror comprising a layer stack of layers of alternating materials of high and low acoustic impedances.

8. The BAW device according to claim 1, further comprising an isolating layer,

the isolating layer being arranged between the second electrode and the semiconductor layer, so that the semiconductor layer is electrically isolated from the first and second electrodes, or

the isolating layer being arranged between the piezoelectric layer and the semiconductor layer.

9. A serial tunable bulk acoustic wave (BAW) device, comprising:

a first electrode;

a second electrode;

a semiconductor layer;

a piezoelectric layer arranged between the first electrode and the semiconductor layer, wherein the semiconductor layer is arranged between the piezoelectric layer and the second electrode.

10. The serial tunable BAW device according to claim 9, wherein the semiconductor layer comprises a p-type doped silicon or an n-type doped silicon.

11. The serial tunable BAW device according to claim 9, further comprising an isolating layer and a substrate,

wherein the serial tunable BAW device is arranged over a region of the piezoelectric layer and, outside the region, the second electrode is separated from the semiconductor layer by the substrate and the isolating layer.

12. The serial tunable BAW device according to claim 9, wherein the first electrode comprises a first terminal and the second electrode comprises a second terminal, the first and second terminals are adaptable to apply a tunable DC voltage.

13. A parallel tunable bulk acoustic wave (BAW) device, comprising:

a first electrode;

a second electrode;

a semiconductor layer sandwiched between the first and second electrode; and

a piezoelectric layer sandwiched between the first and second electrode.

14. The parallel tunable BAW device according to claim 13, further comprising:

an isolating layer arranged between the second electrode and the piezoelectric layer,

wherein the isolating layer is sandwiched between the second electrode and the semiconductor layer.

15. The parallel tunable BAW device according to claim 14, wherein the isolating layer comprises silicon oxide.

16. An apparatus, comprising:

a bulk acoustic wave resonator; and

means for tuning a resonance frequency integral with the bulk acoustic wave resonator.

17. The apparatus according to claim 16, wherein the BAW resonator comprises first and second electrodes sandwiching a piezoelectric layer, and wherein the means for tuning comprises a semiconductor layer arranged between the first and second electrodes, and wherein

the semiconductor layer is electrically isolated from the first electrode.

18. The apparatus according to claim 16,

wherein the BAW resonator comprises first and second electrodes sandwiching a piezoelectric layer, the piezoelectric layer comprising a semiconductor material,

and wherein the means for tuning comprises a doped region of the piezoelectric layer.

19. The apparatus according to claim 18, wherein the doped region extends across the piezoelectric layer from the first to the second electrode.

20. A method of frequency tuning of a bulk acoustic wave device, the bulk acoustic wave device comprising a first electrode, a second electrode, a piezoelectric layer arranged between the first and second electrodes and a semiconductor layer arranged between the first and second electrodes, wherein the semiconductor layer is electrically isolated from the first electrode, th method comprising:

applying a voltage to the first electrode and the second electrode; and

changing the voltage to a value, such that a resonance frequency of the BAW device comprises a target value.

21. The method according to claim 20, wherein applying a voltage is performed such that the semiconductor layer comprises a depletion layer with a voltage dependent depletion thickness, the voltage dependent depletion thickness determining the target value for tuning the frequency of the BAW device.

22. The method according to claim 20, wherein applying a voltage comprise using a DC voltage.