Surface micromachined fabrication of piezoelectric AlN unimorph suspension devices for rf resonator applications

We report a surface micromachining process for aluminum nitride (AlN) thin films to fabricate piezoelectric unimorph suspension devices for actuator applications. Polysilicon is used as a structural layer. Highly c-axis oriented AlN thin films 1 μm thick are deposited by rf reactive sputtering. Thin layers of chromium on either side of the AIN are used as top and bottom electrodes and also used as a mask to etch the AlN layer. Scattering parameters are measured in fabricated samples using a vector network analyzer. Results show resonant frequencies of devices in the range of (1-2) GHz with an effective electromechanical coupling factor K²_eff ≈ 1.7 %.