Piezoelectric Properties of Aluminum Nitride for Thin Film Bulk Acoustic Wave Resonator

Abstract

A film bulk acoustic wave resonator (FBAR) was fabricated by using RF-sputtered aluminum nitride (AlN) between 400 nm-thick molybdenum (Mo) bottom and top electrodes. To reduce the acoustic loss of FBARs, an air gap cavity is fabricated below the membrane by a silicon deep-etch process. The sputtered 950 nm-thick AlN film was oriented in the (002) direction. The FBARs were measured by using a HP 8510C vector network analyzer in a wide frequency range of 0.5 ∼ 10.5 GHz. A resonance frequency was observed near 2 GHz as well as another, a third mode about 7 GHz. The minimum insertion loss was 0.056 dB at 1858 MHz. An equivalent circuit modeling regarding this FBAR was performed with modified Butterworth Van-Dyke (MBVD) models, wellknown piezoelectric equivalent circuit models. The calculated effective electromechanical coupling coefficient (keff ) was greater than 6.59 %.