Thermal Response and TC f of GaN/AlN Heterostructure Multimode Micro String Resonators From −10 °C Up to 325 °C

• Published in: Journal of microelectromechanical systems 2021-08, Vol.30 (4), p.521-529
• Main Authors: Sui, Wen, Zheng, Xu-Qian, Lin, Ji-Tzuoh, Alphenaar, Bruce W., Feng, Philip X.-L.
• Format: Article
• Language: English
• Subjects: Aluminum nitride; Buffer layers; Gallium nitride; Gallium nitrides; GaN; GaN/AlN heterostructure; Heterostructures; High temperature; Mechanical properties; Microelectromechanical systems; multimode; Residual stress; Resonance; Resonant frequency; resonator; Resonators; Silicon; Stress; string; Strings; Substrates; temperature coefficient of resonance frequency (TC<italic xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">f ); Temperature dependence; Temperature effects; Temperature measurement; Tensile stress; thermal expansion; Thermal response
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2021.3089703

We report on the first experimental characterization and analysis of the thermal response and temperature coefficient of resonance frequency (TC f ) of gallium nitride/aluminum nitride (GaN/AlN) heterostructure micro string resonators, in a wide temperature range from −10 °C up to 325 °C. Thanks to its excellent electrical and mechanical properties and chemical inertness, GaN has recently stimulated growing interests in GaN microelectromechanical systems (MEMS) for emerging high-power, high-temperature, and harsh-environment applications. GaN films on Si wafers often require AlN buffer layers, thus the residual tensile stress profile in the GaN epilayers and GaN/AlN hetero-layers can play a key role in affecting the MEMS specifications and performance. Here we design and fabricate GaN/AlN heterostructure micro string resonators with length L = 100 , 200 and 300 \mu \text{m} to probe the stress and thermal effects on resonance behavior. All out-of-plane flexural modes show clear string behavior, and the multimode resonance frequencies downshift almost linearly with increasing temperature up to 325 °C. The linear temperature dependence and TC f values of GaN/AlN heterostructure resonators can be directly employed for thermal sensing. Comparison among different devices indicates that higher tensile stress levels contribute to smaller TC f values, suggesting strain engineering may be exploited for intentionally regulating the TC f .