AlN/Sapphire-Based SAW Resonators With Q Over 10000 for Temperature Sensors
Yujie Ai, Hongrui Lv, Yinglong Huang, Jiaheng He, Ye Wang, Jiwen Wu, Yun Zhang
Abstract
A surface acoustic wave (SAW) resonator with quality factors ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> ) of 3526/10 205 at the resonant/antiresonant frequencies ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{r}/{f}_{a}$ </tex-math></inline-formula> ) has been fabricated on thick metal-organic chemical vapor deposition (MOCVD)-grown (0002) aluminum nitride (AlN) films ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4~\mu \text{m}$ </tex-math></inline-formula> ) on sapphire. The impact of device parameters on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> of resonators, including aspect ratio of length to width ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}/{W}$ </tex-math></inline-formula> ), number of interdigital transducers (IDTs), and IDT metal thickness, has been investigated. The high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> is obtained due to the large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}/{W}$ </tex-math></inline-formula> value of 12, which can enhance the acoustic energy superimposition of IDTs, and the thick AlN film ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4~\mu \text{m}$ </tex-math></inline-formula> ), 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{r}/{f}_{a}$ </tex-math></inline-formula> with temperatures ranging from −50 °C to 250 °C and a high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> of 4027 at 250 °C of the resonator have been demonstrated for temperature sensor application.