Bulk glassy alloy rods of diameters 18 and 20 mm were formed during the tiltcasting of Zr₆₀Al₁₀Ni₁₀Cu₂₀. A further increase in the rod diameter to 22 mm resulted in the formation of a mixed structure with approximately 60 vol% glassy phase and 40 vol% crystalline phase, which comprised the central region of the transverse cross-section of the alloy rod. The glass transition temperature (T_g), onset temperature of crystallization (T_x), and liquidus temperature (T_l) were measured to be 666 K, 768 K, and 1153 K, respectively, and the resultant ΔT_x (=T_x−T_g), T_g⁄T_l, and γ (=T_x⁄(T_g+T_l)) values were 102 K, 0.578, and 0.422, respectively. The high glass-forming ability of supercooled liquids is attributed to the high resistance of the liquids against crystallization due to the large ΔT_x and high T_g⁄T_l and γ values. For the alloy rod of diameter 20 mm, the Young’s modulus, yield strength, elastic strain, and plastic strain under a uniaxial compressive load are 80 GPa, 1820 MPa, 0.022, and 0.060, respectively; the plastic strain of the rod with diameter 20 mm is greater than that (0.04) of the glassy alloy rod of diameter 2 mm, although there exist no appreciable differences between their strength levels and fracture behaviors. The success of formation of the large-sized Zr-based bulk glassy alloy rod, which exhibits large plastic strains in conjunction with high strength levels, is promising with regard to further extension of the applications of such highly functional materials.

This paper reports the experimental estimation of the mechanical quality factor ( $Q_{m})$ of polymer films, which can be used as damping materials for MEMS. Considering the application to MEMS devices, polymer/PZT composite actuators using two thick photoresists (TMMR-NA1000 and SU8) and PDMS were fabricated and the Q factors were evaluated in a vacuum environment. The comparison between the measured and simulated Q factor confirmed a $Q_m$ range of 14-18 for TMMR-NA1000, 13-20 for SU8, and 5-8 for PDMS, indicating the superior damping capability of PDMS. Additionally, it was also found that the PZT thin film used in this study exhibited $Q_m$ of 200-220 under the driving voltage of 2 V $_{\mathrm{pp}}$ with $+$ 1V DC offset. The evaluation approach developed for assessing $Q_m$ of polymer materials is straightforward, easily implementable, and has broad structure applicability, offering a promising tool for assessing a wide array of materials. 2024-0096

This work presents a polydimethylsiloxane (PDMS)-filled silicon honeycomb structure for passive damping in piezoelectric MEMS microspeakers. The honeycomb framework is designed to enhance viscoelastic energy dissipation while maintaining the diaphragm displacement required for acoustic output. Finite-element simulations comparing honeycomb, circular, square, triangular, and fully PDMS-filled cellular configurations showed that the honeycomb geometry provided the most favorable balance between mechanical Q factor and displacement among the silicon-supported designs. The fabricated device exhibited Q factors of 34.4 in vacuum and 29.4 in air; the vacuum Q factor was 49.5% and 75.4% lower than those of the multi-cantilever and Y-spring reference structures, respectively. The similar extracted gas-damping Q factors indicate that these differences arose mainly from structure-dependent non-air losses. At 20 Vpp with a 6 V DC offset, the honeycomb device achieved an SPL of 105.1 dB at 1 kHz while reducing the resonance peak by 8.0 and 12.1 dB relative to the two references. Its maximum THD was 13.4%, corresponding to 51.3% and 22.1% of the respective reference values. These results demonstrate that the silicon-PDMS honeycomb provides effective passive suppression of resonance-enhanced distortion while maintaining off-resonance acoustic output.

This study presents the on-wafer integration of micropatterned polydimethylsiloxane (PDMS) damping layers into piezoelectric MEMS microspeakers to improve total harmonic distortion (THD) with only a limited sound-pressure-level (SPL) penalty. Drum-type and cantilever-type speakers were investigated, with different PDMS coverage configurations. Vibration measurements showed that PDMS integration substantially reduced the Q factor in both vacuum and air, confirming enhanced structural damping through the viscoelastic loss of PDMS. For the drum structure, the Q factor decreased from 1283.4 to 319.3 in vacuum and from 190.5 to 128.3 in air. For the cantilever structure, the Q factor decreased from 617.4 to 231.4 and 20.5 with local and full PDMS coverage in vacuum, respectively, and from 119.7 to 65.1 and 17.3 in air. The fully covered cantilever structure achieved Q-factor reductions of up to 96.7% in vacuum and 85.5% in air. The acoustic measurements at 2 Vpp with a 1 V DC offset showed that, for the drum structure, the low-frequency SPL decreased by only 0.5 dB, while the THD peak was reduced from 128.4% to 100.0%. For the cantilever structure, full PDMS coverage provided the strongest suppression of resonance-related nonlinear distortion, reducing the maximum THD peak from 218.5% to 12.9%, while the low-frequency SPL decreased by 2.3 dB. These results demonstrate that micropatterned PDMS damping layers provide an effective passive approach for reducing the Q factor and nonlinear distortion in piezoelectric MEMS microspeakers.