Intrinsically Tunable Laminated Ferroelectric Scandium Aluminum Nitride Extensional Resonator Based on Local Polarization Switching

This paper reports, for the first time, on an intrinsically tunable scandium aluminum nitride (Sc
0.28
Al
0.72
N) width-extensional resonator based on local polarization switching concept. The resonator is created from alternative stacking of two ferroelectric Sc
0.28
Al
0.72
N films with laminated metal layers. This architecture enables independent control over local polarization across transducer thickness and width. Local polarization reversal of the top Sc
0.28
Al
0
.
72
N film, through application of switching pulses between top and middle electrodes, results in a reduction in net polarization and electromechanical coupling. This translates to the stiffening of the transducer and increases the acoustic velocity, which results in a higher resonance frequency. Here, the local polarization switching concept is demonstrated using a 97 MHz laminated ferroelectric Sc
0.28
Al
0
.
72
N resonator operating in its 3
^rd
width-extensional mode, with a Q of 687 and a k
t
²
of 2.26%. A frequency tuning of 0.65% is achieved, without any degradation in Q, through application of fifteen ~78.5V monopolar pulses with a frequency of 20kHz. This tuning range exceeds the overall 0.53% temperature-induced frequency drift in the resonator over -40°C to 80°C range. This highlights the effectiveness of the local polarization switching approach for temperature stabilization of Sc
0.28
Al
0
.
72
N bulk acoustic resonators used in integrated radio-frequency oscillators and spectral processors.