Properties of aluminum nitride thin films for piezoelectric transducers and microwave filter applications

Aluminum nitride thin films have been grown by reactive magnetron sputter technique using a pulsed power supply. The highly (002)-textured columnar films deposited on platinized silicon substrates exhibited quasi-single-crystal piezoelectric properties. The effective d(33) was measured as 3.4 pm/V, the effective e(31) as 1.0 C/m(2). The pyroelectric coefficient turned out to be positive (4.8 mu C m(-2) K-1) due to a dominating piezoelectric contribution. Thin-film bulk acoustic resonators (TFBAR) with fundamental resonance at 3.6 GHz have been fabricated to assess resonator properties. The material parameters derived from the thickness resonance were a coupling factor k=0.23 and a sound velocity v(s) = 11 400 m/s. With a quality factor Q of 300, the TFBARs proved to be apt for filter applications. The temperature coefficient of the frequency could be tuned to practically 0 ppm/K. (C) 1999 American Institute of Physics. [S0003-6951(99)01620-4]