Impact of Grain Size on The Q-Factor of Poly-Crystalline Diamond Mems Resonators

This paper reports on the impact of grain size on the quality factor of poly-crystalline-diamond (PCD) MEMS resonators. For this purpose, the grain size of each PCD thin film is tuned from tens of nm to several µm via the methane flow rate during the chemical vapor deposition process on silicon substrates. In addition, a PCD stack, where the growth regime is changed during the deposition run, is studied. From these thin films purely mechanical plate-type resonators were fabricated and photo thermally actuated. The resonance characteristics are studied with Laser-Doppler vibrometry. Measurements are performed in a regime where material losses are the dominant dissipation mechanism and others like gas damping and thermo-elastic damping can be neglected. Furthermore, the resonator devices are assumed to have similar anchor losses across all thin films. It is shown, that quality factors of PCD MEMS-resonators can be increased by more than one order of magnitude when increasing the grain size in the investigated range.