Abstract To enhance the sound pressure level (SPL) and reduce the total harmonic distortion (THD) of piezoelectric micro-electro-mechanical system (MEMS) speakers, a nested cantilever piezoelectric MEMS speaker is proposed. It primarily consists of a PZT functional layer and a mica supporting layer. Measurements of the packaged device demonstrate that, compared with many reported piezoelectric MEMS speakers, the proposed nested cantilever piezoelectric MEMS speaker exhibits higher SPL in the mid-frequency range and lower THD within a continuous wider frequency range. When the driving voltage is 1 V rms , the SPL exceeds 89 dB in the frequency range of 4.3 kHz–14.1 kHz, demonstrating its potential in improving the SPL. The THD of the device remains below 1.4% within 160 Hz–20 kHz frequency range, demonstrating it features a wide applicable frequency range. The proposed piezoelectric MEMS speaker shows excellent resistance to fracture and fatigue by dropping from 5 m and playing music for 5 h. This study provides new insights into further improving SPL and reducing THD in piezoelectric MEMS speakers.

Abstract Mechanical property characterization of microstructures plays a critical role in determining the precise design and superior performance of MEMS devices. This work presents an on- wafer compression test method that enables quantitative characterization of the critical buckling stress of microbeams and efficient assessment of etching process quality. The proposed test structure features a self-compensating mechanical mechanism, facilitating robust and reliable extraction of the critical buckling stress. Both compressive loading and subsequent measurement are accomplished in situ on the wafer, eliminating the need for external actuation or high-precision equipment. Furthermore, process-induced geometric non-idealities are incorporated into a defined effective linewidth, providing a comprehensive metric for evaluating etching quality. The experimental results show that the microbeams exhibit a critical buckling stress of 150-200 MPa with less than 5% variation, indicating stability-governed failure rather than material strength limits. Moreover, the extracted linewidth loss reveals geometric non-idealities introduced during etching, highlighting a direct link between mechanical response and process quality. These characteristics highlight the method’s potential for characterizing the compressive mechanical properties of microstructures, and hold promise for evaluating process quality in MEMS manufacturing.

Abstract We describe a single-piece 3D-printed aqueous two-phase system (ATPS) spinneret that eliminates the glass capillaries, alignment steps, and bonding required in polydimethylsiloxane (PDMS)-glass devices, collapsing multi-step fabrication into one print. The printed geometry preserves the coaxial flow needed for forming hydrogel fibers, including Janus structures, maintaining full functionality while removing fabrication complexity.

Abstract In optical systems, where miniaturization is the dominant trend, flat optical components capable of active aberration correction are increasingly required. SmartLens enables tunable wavefront control by locally modifying the refractive index of a transparent thermo-optic polymer using a microscale heater. However, such heaters are typically fabricated through complex multistep photolithography. In this study, we designed and simulated a Fresnel zone plate (FZP)-based microheater geometry to optimize optical efficiency and aberration control. The optimized FZP-shaped heater is fabricated by direct laser writing on a 70 nm-thick chromium (Cr) film and coated with a 1.1 mm-thick polydimethylsiloxane layer to enable thermo-optic modulation. A pronounced coma aberration was generated under off-axis conditions and subsequently compensated through electrically induced thermo-optic wavefront modulation. The fabricated SmartLens demonstrated correction of the off-axis coma aberration, which was quantitatively verified using point spread function and modulation transfer function analyses, including the reduction of directional anisotropy and the convergence of orthogonal full width at half maximum values.

Abstract This study presents a self-tuning optical MEMS microscanner based on a low-cost polyimide structure integrated with a piezoresistive feedback mechanism. The system automatically detects and tracks the torsional resonance frequency (≈ 81 Hz), compensating for spring softening effects that otherwise degrade scan performance. A custom frequency sweep algorithm, combined with a closed-loop control, dynamically adjusts the actuation signal to maintain resonance-locked operation, enabling stable mechanical scan angles of 10–12 ∘ ( ≈ 42 ∘ total optical scan angle (TOSA)) at drive levels of 8–10 V pp and 60–80 mA ( ≈ 0.5 z − 0.8 W ). This approach ensures stable displacement and total optical scan angle over time, even under frequency drift. In high-power characterization sweeps, the device demonstrates optical scan angles up to 100 ∘ TOSA. The proposed architecture offers a practical and scalable solution for energy-efficient, high-resolution optical scanning using inexpensive and easily manufacturable polymer-based MEMS devices.

Abstract Microfluidic devices for chemical and biological processes are commonly constructed of glass. However, glass substrates bonded together by conventional thermal fusion or anodic processes are difficult to detach and reuse. Also, repeated bonding and separation after low-temperature processing has not been sufficiently investigated, and cracks are sometimes observed following substrate separation. This work demonstrates a simple, quick bonding method producing weakly bonded, detachable substrates on the basis of hydrophilic interactions. Leakage tests indicated that such bonds were able to withstand pressures up to 200 kPa, which is sufficient for typical microfluidic experiments. Flow rate measurements confirmed an absence of leakage and the thin bonding layers (approximately 50 nm or less) were found not to affect the channel depth or flow rate in microfluidic channels. The water-based bonding used in this study is applicable to microfluidic devices using organic solvents and could lead to the fabrication of reusable microfluidic devices allowing repeated bonding and detachment.

Abstract High-performance wideband surface acoustic wave (SAW) devices are essential components for wireless communication systems in the new age, and spurious modes and temperature stability are two important properties for wideband devices. Nevertheless, preparing wideband spurious-free SAW devices with low temperature drift is still a big challenge. To achieve four strengths including large bandwidth, low temperature drift, suppressed Rayleigh mode and suppressed transverse modes in the meantime, this work proposes and theoretically investigates SAW devices based on three structures including SiO2/Cu/Y-X LiNbO3/69°Y-90°X quartz, Cu/Y-X LiNbO3/69°Y-90°X quartz, and Al/41°Y-X LiNbO3/69°Y-90°X quartz. The characteristics of these devices are revealed and some optimized designs based on these structures are provided. Wideband SAW devices with nearly-zero temperature coefficients of frequency and suppressed Rayleigh mode can be achieved when SiO2/Cu/Y-X LiNbO3/69°Y-90°X quartz structure is applied. Transverse modes are weakened by quartz and can be more effectively suppressed if transverse mode suppression designs of interdigital transducers are applied, so the four strengths can be achieved meanwhile. The devices based on the other two structures can have at least two strengths as well as some unique properties such as ultra-large electromechanical coupling factor of 34.20% and suppressed transverse mode generation, which are suitable for different applications. This work provides more possible structures and designs for the engineers in filter design, and promotes the development of high-performance wideband SAW devices.

Abstract We present a novel approach for the fabrication of single pore microcavities in silicon (111) based on Silicon-on-Insulator substrates and a combination of optical and electron-beam lithography, reactive ion etching and anisotropic wet etching techniques. Using a dedicated sequence of physical vapor deposition, electroplating and surface chemical oxidation, a silver/silver chloride (Ag/AgCl) reference bottom electrode was integrated into the cavity. We have fabricated cavities of volume ∼180 fl terminated at their top with silicon-nitride membranes featuring a single access pore of diameter 150–500 nm, each. Scanning electron microscopy revealed the cavity structure to comprise a hexagonal geometry top silicon nitride membrane and a triangular bottom plane. Atomic force microscopy analysis was performed on the AgCl surface, showing a root-mean-square surface roughness of 43.5 nm, hence resulting in a favorable high surface area of the electrode. We fully characterized our cavities filled with potassium chloride electrolyte solutions in electrical measurements to verify functionality of the integrated reference electrodes. Measured ion currents were stable over 1 d and scaled properly with pore diameter and salt concentration. We suggest our device to serve as platform for the controlled investigation of (bio-) electrochemical processes in smallest confined volumes.

Abstract The quality of neutron gratings critically determines the performance of neutron grating interferometers. However, conventional gadolinium-particle filling methods face significant challenges in the fabrication of small-period, high-aspect-ratio neutron absorption gratings. This study proposes a microfluidic particle filling method based on an all-aqueous process for the fabrication of high-aspect-ratio neutron absorption gratings. Liquid-phase pressurization combined with the all-aqueous process effectively addresses particle transport obstruction within high-aspect-ratio grating trenches, thus enhancing the particle filling ratio. The adaptive particle filling mechanism adaptively redistributes the flow rate of particle suspension in response to flow impedance differences caused by variations in geometric parameters and filling conditions in microchannels. This process progressively minimizes impedance differences, enabling uniform particle filling. The effects of pressure, particle suspension flow velocity, and concentration on particle filling were investigated, and the particle filling ratio and uniformity were evaluated using x-ray absorption imaging. Neutron absorption gratings with a period of 4 μ m were successfully fabricated, demonstrating the applicability of this method to small-period, high-aspect-ratio gratings. This work offers a novel and effective strategy to address the challenges associated with fabricating neutron absorption gratings with small periods and high aspect ratios.

Abstract This study proposed a novel ultra-high-density (supporting up to 65,536 channels) 3D microelectrode arrays (MEAs) based on CMOS devices intended for advanced brain-computer interface (BCI) applications. The proposed MEAs structure combines the advantages of traditional models, like the Utah and Michigan type electrodes, offering the ability to precisely record and generate cortical electroencephalography (EEG) signals in 3D space. Through microelectromechanical systems (MEMS) technology, a compact and highly integrated system was fabricated, which effectively reduced losses and noise interference during signal transmission. The electrode design employed a 32 × 32 microprobe array with 64 electrodes in each microprobe shank, enabling high spatial resolution neural signal recording and stimulation. Results from electrochemical analysis suggested that the electrode had an impedance of approximately 620 kΩ at a frequency of 1 kHz and a charge injection capacity of 0.85 mC/cm², indicating its effectiveness for in vivo neurostimulation applications. This advancement in BCI technology provided significant technical support for scenarios requiring highly precise neural control, such as motor rehabilitation for paralyzed patients.