This paper presents the design, fabrication and characterization of a MEMS piezoelectric hydrophone based on Silicon-On-Insulator (SOI), using Aluminum Nitride (AlN) as the functional piezoelectrical material. The hydrophone has a ${6}\times {6}$ array and a sandwich structure composed of Molybdenum-Aluminum-Molybdenum (Mo-AlN-Mo) films. The three-layered films adhere back cavities that have a radius of $200~ \boldsymbol {\mu }\text{m}$ and a pitch of $400~ \boldsymbol {\mu }\text{m}$ . The hydrophone shows proximal resonance frequencies of 479 kHz and 476 kHz under Impedance and Doppler tests, respectively. The initial deformation of the diaphragm is avoided by using a hollow PCB in the packaging to keep the hydrophone in a pressure-equalizing environment. The hydrophone is characterized in both water and air platforms. In water, the hydrophone has a sensitivity of −172.6 dB in the range of 100-2000 Hz, and a linearity of 99% at 1000 Hz, whereas in air it has a linearity of 98% at 1000 Hz. These results demonstrate the potential of high performance miniaturized hydrophone systems for wide-band and low-frequency applications.

In this work, an enhancement-mode (E-mode) p-channel GaN metal‒oxide‒semiconductor field-effect transistor (p-MOSFET) with a maximum ON-state current ( I _ON ) density of 10.5 mA/mm, threshold voltage ( V _TH ) of −2.45 V, and I _ON / I _OFF ratio of 108 is demonstrated on a commercial GaN wafer designed on a p-GaN HEMT. Furthermore, we present a novel E-mode p-FET featuring an AlN insert I _ON layer within the p-GaN layer. The AlN layer introduces extra capacitance in the conducting channel and decreases the body factor m of devices. The p-GaN/AlN/p-GaN/AlGaN structure reduces the equivalent channel capacitance, achieving a minimum point-by-point subthreshold swing ( SS ) of 60 mV/dec. Compared with that of the convent I _ON al p-GaN channel FET, the SS decreases from 225 to 105 mV/dec over three orders, the V _TH shifts to −3.05 V, the I _ON / I _OFF ratio increases to 2 × 108, and the device also has an ultralow off-state leakage current in the range of 10 ⁻⁸ mA/mm. The proposed structure is compelling for GaN-based complementary metal‒oxide‒semiconductor (CMOS) logic and power devices.

A mathematical model is necessary to analyze sensor performance and optimize its design. However, most of the existing models of piezoelectric micro-machined hydrophones are incomplete and too complex to understand. There has been no mathematical model for the sensitivity of piezoelectric hydrophones. To address this shortcoming, this paper proposes a mathematical model of a piezoelectric micro-machined hydrophone. The stresses in the piezoelectric layer and static displacement of the diaphragm under uniform sound pressure are derived. In addition, the resonant frequency and sensitivity of the hydrophone are analyzed. The finite element simulation is used to verify the validity of the proposed mathematical model. On the basis of the mathematical model and simulation, the diaphragm radius, top electrode area, and piezoelectric film thickness are optimized. Furthermore, the hydrophone is fabricated, and its morphology is observed. The impedance-frequency spectrum of the hydrophone is measured by HIOKI IM3536 LCR impedance analyzer. The tested resonant frequency is 0.5 MHz, which is relatively close to the calculated result of 0.537 MHz, so the validity of the proposed mathematical model is further validated. Also, the reason why the test result is less than the calculated result is explained. The effective electromechanical coupling coefficient derived from the impedance curve is 7.5%. The developed mathematical model can provide a useful guide for designing high performance piezoelectric micromachined hydrophone and make preliminary predictions of its characteristics.

In this paper, nanosheet deformation during channel release has been investigated and discussed in Gate-All-Around (GAA) transistors. Structures with different source/drain size and stacked Si nanosheet lengths were designed and fabricated. The experiment of channel release showed that the stress caused serious deformation to suspended nanosheets. With the guidance of the experiment result, based on simulation studies using the COMSOL Multiphysics and Sentaurus tools, it is confirmed that the stress applied on the channel from source/drain plays an important role in nanosheet deformation during the fabrication process. The deformation of Si nanosheets would cause a serious degradation of the device performance due to an inability to control the work function of the metal gate. This study proposed that the uniformly stacked GAA nanosheets structure could be successfully demonstrated with suitable channel stress engineering provided by fitting S/D size and an appropriate channel length. The conclusions provide useful guidelines for future stacked GAA transistors’ design and fabrication.

This article systematically studies the AlGaN/GaN MIS-HEMTs using the O ₂ plasma alternately treated Al ₂ O ₃ as gate dielectric. The X-ray photoelectron spectroscopy (XPS) analyses and capacitance-voltage (C-V) measurement results show that the density of the border traps originating from the Al-OH bonds in the ALD-Al ₂ O ₃ gate dielectric can be significantly reduced after the O ₂ plasma alternating treatment. Consequently, a low gate leakage current and a high field-effect mobility of 1680cm ² /V·s are achieved. The results also demonstrate that the fabricated AlGaN/GaN MIS-HEMTs with the O ₂ plasma alternating treatment exhibit improved performances, having a high ON/OFF ratio of ~1011, a steep subthreshold slope of 74 mV/dec, a small hysteresis (Δ V _TH ) of 0.1 V and small ON-resistance ( R _ON ) of 6.0 Ω·mm. The device thermal stability was also improved within the tested temperature range. In addition, the pulsed I _D - V _DS measurements with quiescent drain bias ( V _DS0 ) stress of 40 V present negligible current collapse (2%) and low degradation of dynamic R _ON by 1.04 times the static R _ON .