This paper reports on passive temperature compensation techniques for high quality factor (Q) silicon microresonators based on engineering the geometry of the resonator and its material properties. A 105 MHz concave silicon bulk acoustic resonator (CBAR) fabricated on a boron-doped substrate with a resistivity of 10-3 ÃÂÿ-cm manifests a linear temperature coefficient of frequency (TCF) of -6.3 ppm/ÃÂðC while exhibiting a Q of 101,550 (fQ = 1.06ÃÂÃÂ1013). The TCF is further reduced by engineering the material property via a wafer-level aluminum thermomigration process to -3.6 ppm/ÃÂðC while maintaining an fQ of over 4ÃÂÃÂ1012. Such high fQ products with low TCF values are being reported for the first time in silicon and are critical for successful insertion of these devices into low-power low-phase noise frequency references and high performance resonant sensors.
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