High Figure-of-Merit Lamb Wave Resonators Based on Al0.7Sc0.3N Thin Film

This work reports the Lamb wave resonator based on Al
_0.7
Sc
_0.3
N thin films using magnetron sputtering with a single alloy target. The resonator fabrication process based on high Sc doping concentration is discussed. Al
_0.7
Sc
_0.3
N thin films with a 1.2° (0002) rocking curve were obtained with improved crystalline quality and reduced abnormal orientation grains (AOGs). The etching process has been optimized to achieve an etch rate of 127 nm/min and a profile angle of 72°. The dispersion properties of Lamb waves and the influence of different electrode metals on the coupling coefficient in Al
_0.7
Sc
_0.3
N thin films were simulated. Al
_0.7
Sc
_0.3
N Lamb wave resonators operating at approximately 300 MHz and 600 MHz were fabricated. A high electromechanical coupling coefficient ( k
_t
²
) of 7.74% is reported, with the loaded quality factor of 1119, respectively. A high Figure-of-Merit (FOM) of 86.6 has been achieved for AlScN film based Lamb wave resonators below 1 GHz. The application potential of high scandium concentration (>25%) in resonators and filters is demonstrated.