Encapsulated packaging for thin-film resonators and thin-film resonator-based filters having a piezoelectric resonator between two acoustic reflectors

• US 6,548,942 B1
• Filed: 05/15/2000
• Issued: 04/15/2003
• Est. Priority Date: 02/28/1997
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Panasik, Carl M.
• Primary Examiner(s): Ramirez, Nestor
• Assistant Examiner(s): GONZALEZ, JULIO CESAR
• Application Number:
  US09/571,097
• Time in Patent Office: 1,065 Days
• Field of Search: 333/195, 333/24.R, 333/186, 333/193, 333/187, 310/313.D, 310/313.B, 310/335, 310/340, 310/344, 310/364, 310/366, 438/51
• US Class Current: 310/364
• CPC Class Codes: H03H 9/174 Membranes
• CPC Class Codes: H03H 9/175 Acoustic mirrors

Abstract

An acoustic reflector (48) is applied over a thin-film piezoelectric resonator (41, 61) which is supported on a semiconductor or semiconductor-compatible substrate (42, 62) of a microelectronic device (40, 60), enabling an encapsulant (49) to be applied over the reflector-covered resonator without acoustically damping the resonator. In one embodiment, alternating high and low acoustic impedance layers (51, 53 . . . 55) of one-quarter wavelength thicknesses constructively reflect the resonating wavelength to make an encapsulant in the form of an inexpensive plastic molding compound appear as a “clamping” surface to a resonator (41) peripherally supported over an opening (43) on a silicon substrate (42). In another embodiment, an encapsulant- and reflector-covered resonator (61) is mechanically supported above a second reflector (68) which eliminates the need for peripheral support, making substrate (68) also appear as a clamping surface. The invention enables low cost plastic packaging of resonators and associated circuitry on a single monolithic structure. A radio frequency transceiver front-end application is given as an exemplary implementation.

Claims

1. A microelectronic device, comprising:

a substrate, and the substrate comprises silicon;

a piezoelectric resonator disposed on the substrate, the piezoelectric resonator comprises a first electrode layer of metal deposited on the silicon, a layer of piezoelectric material deposited over the first electrode layer, and a second electrode layer of metal deposited over the piezoelectric material layer;

an acoustic reflector located over and coupled to the piezoelectric resonator;

an encapsulant comprising a molding compound having a low acoustic impedance, the encapsulant deposited over and encapsulating the piezoelectric resonator and acoustic reflector, the encapsulant making contact with the acoustic reflector;

the acoustic reflector transforms the low acoustic impedance of the encapsulant into a high acoustic impedance at the acoustic resonator/acoustic reflector interface; and

wherein the acoustic reflector comprises alternating acoustic reflecting layers of first and second acoustic impedance materials deposited over the second electrode layer of metal;

the first acoustic impedance being higher than the second acoustic impedance.

2. The device of claim 1, wherein the acoustic resonator has a given resonant frequency;

and wherein the reflecting layers have thicknesses that cause acoustic impedance mismatches with reflections occurring in-phase with the incident waves that occur at the mismatches to provide constructive interference at the resonant frequency.

3. The device of claim 2, wherein the reflecting layers have thicknessses of one-quarter of the resonating wavelength.

4. The device of claim 1, wherein the encapsulant is an encapsulating compound conformally cured in place over the acoustic reflector and piezoelectric resonator.

5. The device of claim 4, wherein the encapsulant comprises an epoxy, polyimide or silicone resin.

6. The device of claim 5, wherein the encapsulant comprises an epoxy novalac-based resin.