Hexagonal 4H-silicon carbide (4H-SiC) is a transversely isotropic substrate garnering interest for precision MEMS devices such as resonant gyroscopes. This paper investigates the elastic anisotropy of 4H-SiC by utilizing capacitive bulk acoustic wave (BAW) resonators with ultra-high mechanical quality factors (Q) enabled by phononic crystals. We directly measure the value of C66 using Lamé mode resonators for the first time and numerically fit the values of C11 and C12 using BAW elliptical modes in center-supported solid disk resonators. We compare (00 01) 4H-SiC to (111) Si, another in-plane isotropic material and validate (0 001) 4H-SiC's superior robustness to fabrication and design variations. Measurement of in-plane BAW elliptical modes in multiple disk resonators with as-born frequency splits as low as 3 ppm reveal (00 01) 4H-SiC's transverse isotropy across process corners. Lamé mode resonators display a temperature coefficient of frequency (TCF) three times lower compared to its Si counterpart. Finally, this paper provides a modified set of elastic constants for 4H-SiC with a view towards monocrystalline SiC MEMS devices.

中文翻译：

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使用超高 Q 体声波谐振器研究 4H-SiC 的弹性各向异性


六方 4H 碳化硅 (4H-SiC) 是一种横向各向同性基板，引起了谐振陀螺仪等精密 MEMS 器件的兴趣。本文利用电容体声波 (BAW) 谐振器研究 4H-SiC 的弹性各向异性，该谐振器具有由声子晶体实现的超高机械品质因数 (Q)。我们首次使用 Lamé 模式谐振器直接测量 C66 的值，并使用中心支撑固体盘谐振器中的 BAW 椭圆模式对 C11 和 C12 的值进行数值拟合。我们将 (00 01) 4H-SiC 与另一种面内各向同性材料 (111) Si 进行比较，并验证 (0 001) 4H-SiC 对制造和设计变化的卓越鲁棒性。对多个盘式谐振器中的面内 BAW 椭圆模式的测量（初始频率分裂低至 3 ppm）揭示了 (00 01) 4H-SiC 跨工艺角的横向各向同性。 Lamé 模式谐振器的频率温度系数 (TCF) 比 Si 谐振器低三倍。最后，本文针对单晶 SiC MEMS 器件提供了一组修改后的 4H-SiC 弹性常数。