Investigation of Temperature Characteristics and Substrate Influence on AlScN-Based SAW Resonators

It has been found that introducing Sc into AIN to form Al
_1-x
Sc
_x
N can lead to a significant increase in piezoelectric response, making Al
_1-x
Sc
_x
N a promising material for electroacoustic devices, such as frequency filters for mobile communications. 1 μm thick highly c-axis oriented Al
_1-x
Sc
_x
N thin films were deposited on 100 mm Si(001)(x = 0, 0.14, 0.23, and 0.32)and on Al
₂
O
₃
(0001)(x = 0.14 and 0.23)substrates using reactive pulsed-DC magnetron sputtering and SAW resonators with wavelengths λ = 2-24 μm were fabricated. The effective electromechanical coupling k
_eff
²
of the resonators improved with increasing Sc concentration, for instance, the λ = 2 μm AIN (f
_s
= 2.08 GHz)and Al
_0.68
Sc
_0.32
N (f
_s
= 1.83 GHz)resonators exhibited coupling of 0.6 % and 2.6 %, respectively. Furthermore, 3 % increase in resonant frequency and 9.6 % increase in coupling were observed when comparing λ = 2 μm resonators based on Al
₂
O
₃
to those based on Si substrates. The temperature coefficient of frequency (TCF)was found to reach up to -27.4 ppm/K at x = 0.23 using Si substrates, while the equivalent resonators based on Al
₂
O
₃
substrates exhibited lower TCF of -26.1 ppm/K. Thermal hysteresis errors were calculated to be ~1%. Employing Al
₂
O
₃
substrates for λ = 2 μm Al
_0.77
Sc
_0.23
N-based resonators showed reduced TCF, higher resonant frequency, and higher coupling coefficient when compared to the same design resonators on Si substrates.