ELECTROMECHANICAL COUPLING-CONSTANT EXTRACTION OF THIN-FILM PIEZOELECTRIC MATERIALS USING A BULK ACOUSTIC-WAVE RESONATOR

Thin-film piezoelectric materials such as ZnO and AIN have great poten tial for on-chip devices such as filters, actuators and sensors. The e lectromechanical coupling constant is an important material parameter which determines the piezoelectric response of these films. This paper presents a technique based on the Butterworth Van-Dyke (BVD) model wh ich, together with a simple one-mask over-moded resonator, can be used to extract the bulk, one-dimensional electromechanical coupling const ant K-2 of any piezoelectrically active thin-film. The BVD model is us ed to explicitly define the series resonance, parallel resonance, and quality factor Q of any given resonating mode. Common methods of defin ing the series resonance, parallel resonance, and Q are shown to be in accurate for low coupling, lossy resonators such as the over-moded res onator. Specifically, an electromechanical coupling constant K2 of (2. 6 +/- 0.1)% was measured for an (002) c-axis textured AIN film with an x-ray diffraction rocking curve of 7.5 degrees using the BVD based ex traction technique.