AlN/Sapphire-Based SAW Resonators With Q Over 10000 for Temperature Sensors

A surface acoustic wave (SAW) resonator with quality factors (
${Q}$
) of 3526/10 205 at the resonant/antiresonant frequencies (
${f}_{r}/{f}_{a}$
) has been fabricated on thick metal-organic chemical vapor deposition (MOCVD)-grown (0002) aluminum nitride (AlN) films (
$4~\mu \text{m}$
) on sapphire. The impact of device parameters on
${Q}$
of resonators, including aspect ratio of length to width (
${L}/{W}$
), number of interdigital transducers (IDTs), and IDT metal thickness, has been investigated. The high
${Q}$
is obtained due to the large
${L}/{W}$
value of 12, which can enhance the acoustic energy superimposition of IDTs, and the thick AlN film (
$4~\mu \text{m}$
), which can reduce the negative impact of seed layer. Moreover, the temperature coefficient of frequency (TCF) values of −46.52/−46.09 ppm/°C for
${f}_{r}/{f}_{a}$
with temperatures ranging from −50 °C to 250 °C and a high
${Q}$
of 4027 at 250 °C of the resonator have been demonstrated for temperature sensor application.