Quartz has been widely used in modern microelectromechanical systems (MEMS) industry, and wet etching is one of the primary techniques used for its manufacturation. There are many reported literatures focused on the study of etched profiles or etching rate of quartz, but few on its surface quality. Inspired by the surface quality improved by using additives in the silicon wet etching process, the effects of isopropyl alcohol (IPA) and acetic acid on the surface roughness of Z‐cut quartz etched by ammonium bifluoride (NH ₄ HF ₂ ) solution were investigated for the first time. Different concentration of IPA or/and acetic acid was added into the NH ₄ HF ₂ solution, and the morphology of the etched surface was observed using scanning electron microscope and measured by a surface profilometer. It was found that the surface roughness of the Z‐cut quartz decreased with the increasing of IPA or acetic acid concentration. Moreover, the etched surface roughness could be further decreased by using the ternary solution containing IPA and acetic acid. The best etched result ( R _a = 0.12 μm) was obtained when the solution is composed of saturated NH ₄ HF ₂ + 15% v/v IPA + 10% v/v acetic acid. This work provides a new method to improve the surface quality of Z‐cut quartz, and it will benefit the future design and manufacturation work of quartz MEMS devices.

Laser self-mixing interferometer has the advantages of simple architecture, compact size, naturally self-aligned optical characteristics, and low cost. It is promising to replace conventional interferometers for physical measurements, such as displacement, distance, velocity, vibration, and so on. In this paper, this interferometer was tried to be used for micro-electromechanical system (MEMS) dynamic measurement. Firstly, its measurement principle based on a three-mirror cavity model was presented, and then the laser self-mixing interferometer for MEMS dynamic measurement was designed, experiments were finally performed as target moves with different forms. Experimental results suggest that self-mixing interferometer is available for MEMS dynamic measurement, and may have wider applications in the future.

It is meaningful to study the surface morphology of monocrystalline material, but there are few studies on the surface roughness of quartz. So, surface roughness of Z-cut quartz etched by pure ammonium bifluoride and ammonium bifluoride mixed with isopropyl alcohol (IPA) solution was investigated for the first time in this paper. Firstly, when etching in pure ammonium bifluoride solutions, the surface roughness change with etching time, etching temperature, and solution concentration were studied. Then, the surface roughness improvement given by isopropyl alcohol solution was analyzed carefully. The experimental results indicated that: the surface roughness of Z-cut quartz (0001) plane increased with etching time, but decreased with etching temperature and solution concentration; the adding of isopropyl alcohol in ammonium bifluoride solution could decrease the roughness and improve the surface quality. This is the first systemic research of the evolution of quartz surface roughness when etching in ammonium bifluoride solution, and will benefit the future design and manufacture of quartz MEMS devices.

Laser's optical output power and frequency are modulated when the optical beam is back-scattered into the active cavity of the laser. By signal processing, the Doppler frequency can be acquired, and the target's velocity can be calculated. Based on these properties, an interferometry velocity sensor can be designed. When target move in time-varying velocity mode, it is difficult to extract the target's velocity. Time-varying velocity measurement by self-mixing laser diode is explored. A mathematics model was proposed for the time-varying velocity (invariable acceleration) measurement by self-mixing laser diode. Based on this model, a Discrete Chirp-Fourier Transform (DCFT) method was applied, DCFT is analogous to DFT. We show that when the signal length N is prime, the magnitudes of all the side lobes are 1, whereas the magnitudes of the main lobe is , And the coordinates of the main lobe shows the target's velocity and acceleration information. The simulation results prove the validity of the algorithm even in the situation of low SNR when N is prime.