In this paper, the long-term reliability of commercial 1.2-kV 4H-SiC MOFSETs under repetitive unclamped inductive switching stresses is evaluated experimentally. The degradation of device characteristics, including the threshold voltage V_th, drain leakage current I_dss, and on-state resistance R_on, is observed after 80k avalanche cycles. The regular charge pumping (CP) measurements reveal that the failure mechanism characterized by the hot holes injection and trapping into the gate oxide above the channel and JFET region may occur during the aging experiments, which is further ascertained by the succeeding electrothermal simulations and should be responsible for the degradation of V_th and I_dss. After decapping the failed devices, the bond wires lift off due to thermal fatigue is discovered and regarded as the main reason for the degradation of R_on. The poststress high-temperature treatment is also carried out as an approach to indirectly corroborate the aforementioned failure mechanisms. Moreover, the impact of different test conditions on the degradation rate of electrical characteristics is discussed to thereby find ways to relieve these degeneration phenomena.

A novel silicon carbide (SiC) trench MOSFET with floating/grounded junction barrier-controlled gate structure (FJB-MOS/GJB-MOS) is presented and investigated utilizing Sentaurus TCAD simulations. The split P+ region introduced beneath the trench could better shield the gate oxide from the high electric field in the blocking mode, leading to an enhancement in the breakdown voltage while without significant degradation of other characteristics. As a result, the FJB-MOS with floating P+ shielding exhibits a higher figure of merit related to the breakdown voltage and the specific on-resistance ( ${V}_{\textsf {BR}}^{{\,\textsf {2}}}/{R}_{ \mathrm{\scriptscriptstyle ON},\textsf {sp}}$ ), which is improved by 15% and 49%, respectively, with comparison to those of the state-of-the-art double-trench MOSFET and L-shaped gate trench MOSFET. In terms of the GJB-MOS with grounded P+ shielding, it shows great advantage in reducing the switching losses thanks to the lower specific gate–drain charge ${Q}_{{\:\textsf {gd,sp}}}$ and is more conductive to high frequency applications. Additionally, the formation of the P+ region is aided by the Sentaurus Process and the processing implementation of the proposed structure is discussed.

Flexible strain sensors have a wide range of applications in biomedical science, aerospace industry, portable devices, precise manufacturing, etc. However, the manufacturing processes of most flexible strain sensors previously reported have usually required high manufacturing costs and harsh experimental conditions. Besides, research interests are often focused on improving a single attribute parameter while ignoring others. This work aims to propose a simple method of manufacturing flexible graphene-based strain sensors with high sensitivity and fast response. Firstly, oxygen plasma treats the substrate to improve the interfacial interaction between graphene and the substrate, thereby improving device performance. The graphene solution is then sprayed using a soft PET mask to define a pattern for making the sensitive layer. This flexible strain sensor exhibits high sensitivity (gauge factor ~100 at 1% strain), fast response (response time: 400–700 μs), good stability (1000 cycles), and low overshoot (<5%) as well. Those processes used are compatible with a variety of complexly curved substrates and is expected to broaden the application of flexible strain sensors.

The trend to move toward the solid-state and repetitive pulsed power supply requires the high-voltage, high-current, and high-speed semiconductor devices, which makes an insulated gate bipolar transistor (IGBT) preferred for this application. However, as a bipolar device, the IGBT is limited by the switching speed and switching loss. In this paper, the potential of silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) for the pulsed power application is investigated. The surge current capabilities of 1.2-kV, 30-A commercial Si IGBT and SiC MOSFET are characterized and compared by the capacitor discharge experiment. In addition, the effects of various circuit parameters, including gate resistance, dc-link voltage, and dc-link capacitance, on the capacitor discharge process are investigated. It is found that the pulse current of SiC MOSFET is around two times of Si IGBT, which achieves good agreement with the datasheet. Using $di/dt$ to represent the discharging speed, the SiC MOSFET is 10 times faster than the Si IGBT. It is because the SiC MOSFET shows a lower ON-resistance in the saturation region resulted from the short-channel effect. This paper confirms the high-speed and high-current advantages of SiC MOSFET in the pulsed power application.

Traveling-wave ultrasonic micromotor is a promising technology for microactuation and nanopositioning. A special designed annular stator was proposed with the combination of two separate buffer structures to achieve high performance. Traveling-wave propagation with moving antinodes was observed and analyzed. The fabricated stator exhibits large displacement of 4.71 μm at 1 V and high quality factor of 220 with the central frequency of 101.6 kHz. The assembled rotor was actuated, and controllable rotate speed was achieved. The measured maximum torque reached to 2.63 μNm at 1.3 V and 101 kHz. Besides, unconstraint rotation with no lateral slip was found during the entire rotation process, indicating stable, uniform, and highly reliable actuation of the micromotor. [2018-0026]