No abstract

We discuss the contribution of phonon interactions in determining the upper limit of f.Q product in micromechanical resonators. There is a perception in the MEMS community that the maximum f.Q product of a microresonator is limited to a "frequency-independent constant" determined by the material properties of the resonator [1]. In this paper, we discuss that for frequencies higher than τ ω τ 1 = , where τ is the phonon relaxation time, the f.Q product is no longer constant but a linear function of frequency. This makes it possible to reach very high Qs in GHz micromechanical resonators. Moreover, we show that <100> is the preferred crystalline orientation for obtaining very high Q in bulk-acoustic-mode silicon resonators above ~750 MHz, while <110> is the preferred direction for achieving high-Q at lower frequencies.

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The growth of Shockley type stacking faults in p-i-n diodes fabricated on the C-face of 4H-SiC during forward current operation was investigated using Berg-Barrett X-ray topography and photoluminescence imaging. After forward current experiment, Shockley type stacking faults were generated from very short portions of basal plane dislocations lower than the conversion points to threading edge dislocations in the epitaxial layer. The growth behavior of Shockley type stacking faults was discussed. Growth of stacking faults in the substrates was not observed.