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 μm 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.

中文翻译：

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GaN/AlN 异质结构多模微弦谐振器从 10°C 到 325°C 的热响应和 TC f


我们报告了氮化镓/氮化铝 (GaN/AlN) 异质结构微弦谐振器在 -10 °C 至宽温度范围内的热响应和谐振频率温度系数 (TC f) 的首次实验表征和分析至 325°C。由于其优异的电气和机械性能以及化学惰性，GaN 最近激发了人们对用于新兴高功率、高温和恶劣环境应用的 GaN 微机电系统 (MEMS) 日益增长的兴趣。 Si晶圆上的GaN薄膜通常需要AlN缓冲层，因此GaN外延层和GaN/AlN异质层中的残余拉应力分布在影响MEMS规格和性能方面发挥着关键作用。在这里，我们设计并制造了长度 L = 100、200 和 300 μm 的 GaN/AlN 异质结构微弦谐振器，以探测应力和热对谐振行为的影响。所有面外弯曲模式都显示出清晰的弦行为，并且随着温度升高至 325 °C，多模谐振频率几乎呈线性下移。 GaN/AlN 异质结构谐振器的线性温度依赖性和 TC f 值可直接用于热传感。不同装置之间的比较表明，较高的拉伸应力水平导致较小的 TC f 值，这表明可以利用应变工程来有意调节 TC f。