This paper presents AlScN piezoelectric two-axis MEMS mirrors with gimbal-less and gimbaled designs fabricated in a CMOS-compatible manner. Integrated piezoelectric sensors provided feedback signals of the actual mirror positions. The mirror with a diameter of 1.5 mm possessed adjustable optical tilt angles of up to 22.6° @ 30 V, with a high resonance frequency of about 8.2 kHz, while the 3 mm mirror reached 48.5° @ 41 V. The mirror with the gimbaled structure exhibited an excellent field of view and good mechanical decoupling. Additionally, a significant improvement in mirror scanning performance was observed in a vacuum (4 Pa), proving that the optical field of view was magnified by more than a factor of 10.

Accurate and efficient measurements of the piezoelectric properties of AlN and AlScN films are very important for the design and simulation of micro-electro-mechanical system (MEMS) sensors and actuator devices. In this study, a process control monitor (PCM) structure compatible with the device manufacturing process is designed to achieve accurate determination of the piezoelectric coefficients of MEMS devices. Double-beam laser interferometry (DBLI) and laser Doppler vibrometry (LDV) measurements are applied and combined with finite element method (FEM) simulations, and values of the piezoelectric parameters d₃₃ and d₃₁ are simultaneously extracted. The accuracy of d₃₁ is verified directly by using a cantilever structure, and the accuracy of d₃₃ is verified by in situ synchrotron radiation X-ray diffraction; the comparisons confirm the viability of the results obtained by the novel combination of LDV, DBLI and FEM techniques in this study.

This paper presents a compact and high-performance piezoelectric micro-electro-mechanical system (MEMS) fast steering mirror (FSM) designed for use in laser inter-satellite links (ISLs). The FSM features a large optical aperture of 10 mm and is batch fabricated using an 8-inch wafer-level eutectic bonding process, packaged into a volume of 26 × 22 × 3 mm³. Notably, the piezoresistive (PZR) sensor is integrated on the spring of the FSM to facilitate precise beam control. Furthermore, an intermediate directional defect structure is novelly designed to create a Stress Concentration Region (SCR), effectively improving PZR sensitivity from 3.3 mV/(V∙mrad) to 5.4 mV/(V∙mrad). In this article, various performance metrics of the FSM are tested, including the mechanical characteristics, PZR sensor properties, and mirror optical quality, which all meet the requirements for laser ISLs. Results indicate that the FSM achieves a high resonant frequency (>1 kHz) and a low nonlinearity of 0.05%@ ± 2.1 mrad. A remarkable minimum angular resolution of 0.3 μrad and a repeated positioning accuracy of 1.11 μrad ensure exceptional pointing precision. The open-loop control is driven by the double-step algorithm, resulting in a step response time of 0.41 ms and achieving a control bandwidth over 2 kHz. Additionally, the integrated angular sensor demonstrates a nonlinearity of 0.09%@ ± 1.05 mrad, a sensitivity of 5.1 mV/(V∙mrad), and a minimum angular resolution of 0.3 μrad. Under quasi-static driven conditions (500 Hz @ ± 2 mrad), the maximum dynamic deformation of the mirror surface is merely 2 nm.

In order to obtain high-quality through-silicon via (TSV) arrays for high voltage applications, we optimized the fabrication processes of the Si holes, evaluated the dielectric layers, carried out hole filling by Cu plating, and detected the final structure and electric properties of the TSVs. The Si through-hole array was fabricated in an 8-inch Si substrate as follows: First, a blind Si hole array was formed by the Si deep reactive etching (DRIE) technique using the Bosch process, but with the largest width of the top scallops reduced to 540 nm and the largest notch elimidiameternated by backside grinding, which also opens the bottom ends of the Si blind holes and forms 500-μm-deep Si through holes. Then, the sidewalls of the Si holes were further smoothed by a combination of thermal oxidation and wet etching of the thermal oxide. The insulating capability of the dielectric layers was evaluated prior to metal filling by using a test kit. The metal filling of the through holes was carried out by bottom-up Cu electroplating and followed by annealing at 300 °C for 1 h to release the electroplating stress and to prevent possible large metal thermal expansion in subsequent high-temperature processes. The TSV arrays with different hole diameters and spacing were detected: no visible defects or structure peeling was found by scanning electron microscopy (SEM) observations, and no detectable interdiffusion between Cu and the dielectric layers was detected by energy dispersive X-ray (EDX) analyses. Electric tests indicated that the leakage currents between two adjacent TSVs were as low as 6.80 × 10⁻¹⁰ A when a DC voltage was ramped up from 0 to 350 V, and 2.86 × 10⁻⁹ A after a DC voltage was kept at 100 V for 200 s.

This paper presents a two-axis AlScN-based water-immersible MEMS mirror fabricated in an 8-inch MEMS process. Compared with other studies, this device has a larger optical aperture 10 mm in diameter. The resonant frequencies of the device are 1011 Hz in air and 342 Hz in water. The scanning angle reaches ±5° and ±2° at resonant frequencies in air and water, respectively. The cavitation phenomenon is observed when the device is operating in water, which leads the device to electrical failure. To address this issue, a device with reduced resonant frequencies—246 Hz and 152 Hz in air and water—is characterized, through which the bubbles can be effectively prohibited. This MEMS mirror could potentially be used in ultrasound and photoacoustic microscopy applications.

Micro-electro-mechanical systems (MEMS) cantilever actuators are pivotal in applications ranging from micro-optics to precision manipulation. However, their performance is fundamentally constrained by a trade-off between dynamic response and static deformation. To address this limitation, this paper presents a segmented grid-etched technique for MEMS cantilever actuators that decouples the resonant frequency from the tilting angle and displacement. The proposed approach strategically modulates the stiffness and mass distribution along the cantilever by etching grid patterns on the segment near the free end, thereby creating a compliant zone for large deformation while preserving the stiffness of the segment near the fixed end to maintain a high resonant frequency. The proposed cantilevers were fabricated using a Cavity SOI-based Single Piezoelectric Layer Double Release (C-SSD) process, achieving a 100% increase in tip inclination angle and a 54% increase in tip displacement, while maintaining a resonant frequency equivalent to that of a conventional uniform cantilever. Additionally, the practical application of this approach is demonstrated through its application to a biaxial piezoelectric micromirror that integrates resonant motion for the fast horizontal axis and quasi-static motion for the slow vertical axis. Notably, the grid-etched structure on the slow axis enhances the optical scan angle by 257% and the frequency-angle product by 64%, achieving a field of view (FOV) of 25°. Furthermore, the successful implementation of this grid-etched cantilever structure in a micromirror validates its potential as a general-purpose design strategy for a wide range of MEMS cantilever actuators.