Fig. 1 The main steps in the fabrication process, carried out on a silicon wafer (gray). a) The process begins with the deposition of the SiO₂ (blue) / Ta₂O₅ (pink) dielectric mirror, which is then etched into discs of the desired size (only 7 of the 33 dielectric layers are shown). b) Si₃N₄ (green) is deposited on both sides of the wafer. c) The front side Si₃N₄ is etched into the resonator geometry and the backside has square holes etched for the Si etch. d) The carrier wafer is etched through with a TMAH anisotropic etch, releasing the resonators. e) A short BHF etch strips the protective SiO₂ layer off the front of the mirror, and the sample is then removed from solution with a critical point dry.

Fig. 2 Three micro-optomechanical resonators, as viewed from the top of the carrier wafer. Left: optical image, diameter d = 80 μm, Si₃N₄ of thickness t = 500 nm, with resonator arms of diagonal length a = 250 μm and width w = 20 μm. Center: optical image, d = 80 μm, t = 300 nm, a = 2000 μm, w = 2 μm. Right: scanning electron microscope image, d = 40 μm, t = 500 nm, a = 500 μm, w = 10 μm. Note that the anisotropic etch profile of TMAH is clearly visible in the silicon at the top of the image.

Fig. 3 The signal from the photodiode monitoring the cavity transmission during a typical optical ringdown measurement, showing the exponential decay of the signal after the pump laser is switched off via the AOM (averaged over 16 runs to reduce noise). Fitting the data starting 0.5 μs after the AOM switch results in an exponential decay time of τ_cav = 2.11 ± 0.02 μs.

Fig. 4 a) The normalized amplitude of the fundamental mechanical resonance of a low frequency (9.174 kHz) resonator after it is excited by moving by one of the alignment motors by a single step. Data from the first minute after the excitation (not shown) is heavily distorted due to the mechanical amplitude becoming larger than the equivalent width of the optical peak (λ/2F ∼ 5 nm). Fitting the data after t = 80 s results in a power decay time of τ = 15.4 ± 0.3 s, or a mechanical quality factor of Q_m = (9.4 ± 0.2) × 10⁵. b) The thermal resonance spectrum of a high frequency (ω_m = 2π × 157.7 kHz) trampoline resonator. A fit to a Lorentzian gives a peak width (FWHM) of δω_m = 2π × 3.64±0.15 Hz, corresponding to Q_m = (4.3 ± 0.2) × 10⁴.