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This paper reviews the prospects of normally-off (N-off) JFET switch in SiC. The potential of selected vertical JFET concepts and all-JFET cascode solutions for N-off operation is analyzed using simulations. The performance of analyzed concepts is compared in terms of blocking voltage, specific on-state resistance, maximum output current density and switching performance in the temperature range from 25°C to 250°C. The main objective of the analysis is to ascertain consequences of different design and technology options for the total losses and high temperature performance of the devices.

650 V SiC planar MOSFETs with various JFET widths, JFET doping concentrations, and gate oxide thicknesses were fabricated by a commercial SiC foundry on two six-inch SiC epitaxial wafers. An orthogonal P+ layout was used for the 650 V SiC MOSFETs to reduce the ON-resistance. The devices were packaged into open-cavity TO-247 packages for evaluation. Trade-off analysis of the static and dynamic performance of the 650 V SiC power MOSFETs was conducted. The measurement results show that a short JFET region with an enhanced JFET doping concentration reduces specific ON-resistance (Ron,sp) and lowers the gate-drain capacitance (Cgd). It was experimentally shown that a thinner gate oxide further reduces Ron,sp, although with a penalty in terms of increased Cgd. A design with 0.5 μm half JFET width, enhanced JFET doping concentration of 5.5×1016 cm−3, and thin gate oxide produces an excellent high-frequency figure of merit (HF-FOM) among recently published studies on 650 V SiC devices.

A critical issue with the SiC UMOSFET is the need to develop a shielding structure for the gate oxide at the trench bottom without any increase in the JFET resistance. This study describes our new UMOSFET named IE-UMOSFET, which we developed to cope with this trade-off. A simulation showed that a low on-resistance is accompanied by an extremely low gate oxide field even with a negative gate voltage. The low R onA was sustained as V th increases. The R onA values at V G =25 V (E ox =3.2 MV/cm) and V G =20V (E ox =2.5 MV/cm), respectively, for the 3mm × 3mm device were 2.4 and 2.8 mΩcm 2 with a lowest V th of 2.4 V, and 3.1 and 4.4 mΩcm 2 with a high V th of 5.9 V.

Gate oxide reliability of a trench-gate SiC MOSFET can be improved by incorporating a gate protection structure, but the resulting parasitic JFET resistance is one major drawback. For reduction of on-resistance, a new method of localized high-concentration n-type doping in JFET regions (JD) is developed. Utilizing process and device simulation by TCAD, the optimal condition of JD that enables maximum device performance is derived. By fabricating a device with the optimal JD structure, the on-resistance is successfully reduced by 25% compared to a conventional device without JD, while maintaining the withstand voltage and the gate oxide electric field at the same level. As a result, a device exhibiting a specific on-resistance of 1.84 mΩcm2 and a breakdown voltage of 1560 V is obtained. The optimal JD structure maintains the short-circuit safe operation area comparable to that for the structure without JD. Thus, by reducing the JFET resistance while minimizing effects on other characteristics, localized JD is shown to be an effective means of realizing a reliable, low-resistance SiC power device.

The body diode degradation in SiC power MOSFETs has been demonstrated to be caused by basal plane dislocation (BPD)-induced stacking faults (SFs) in the drift region. To enhance the reliability of the body diode, many process and structural improvements have been proposed to eliminate BPDs in the drift region, ensuring that commercial SiC wafers for 1.2 kV devices are of high quality. Thus, investigating the body diode reliability in commercial planar and trench SiC power MOSFETs made from SiC wafers with similar quality has attracted attention in the industry. In this work, current stress is applied on the body diodes of 1.2 kV commercial planar and trench SiC power MOSFETs under the off-state. The results show that the body diodes of planar and trench devices with a shallow P+ depth are highly reliable, while those of the trench devices with the deep P+ implantation exhibit significant degradation. In conclusion, the body diode degradation in trench devices is mainly influenced by P+ implantation-induced BPDs. Therefore, a trade-off design by controlling the implantation depth/dose and maximizing the device performance is crucial. Moreover, the deep JFET design is confirmed to further improve the body diode reliability in planar devices.

In a trench MOSFET structure, p+ trench bottom implant (also called p+ shielding region) is commonly used to protect the gate oxide from high electric field stress, however, if the design and fabrication process are not optimized properly, the p+ shielding region together with n-drift and the p-base region will form a parasitic JFET which severely degrades the on-state performance of the device. This paper presents this parasitic JFET effect with experimental results and the optimization work that has been done to eliminate the parasitic JFET.

In this paper, the structural cell design optimization of 15kV 4H-SiC p-channel IGBT is performed. The effects of the parameters of JFET region on the blocking voltage and the forward characteristics are analyzed by numerical simulations. The results indicate that the JFET width and JFET region concentration have an important effect on the performance of IGBTs. Based on the simulation structure in this paper, the optimum JFET width is 10μm, and the optimum JFET concentration is 7×1015cm−3. Meanwhile, they should be carefully designed to achieve the best trade-off between the blocking voltage and the forward voltage drop.

In order to overcome the limitation of 1/f noise on long-period magnetotelluric sensors, it is necessary to use low-noise chopping technology for signal conditioning. However, the static operating point drift of Junction Field-Effect Transistor (JFET) is difficult to achieve stable amplification with the chopper technology. This paper proposes a low noise amplifier (LNA) with chopper technology based on feedback adjustment. The LNA reduces the turning frequency of the circuit, and maintains the JFET static point. At 375mHz, its noise is 2.55 nV / Hz .

To improve the efficiency of circuits including SiC MOSFET, it is necessary to increase their specific currents and reliability, respectively. One needs it to reduce the transistor on-resistance and to increase its breakdown voltage. To achieve these goals, the influences of the transistor’s electrophysical characteristics on its design and technological features have been studied with Sentaurus TCAD. We showed that for increasing the transistor currents, it is necessary to reduce the channel length – the distance between the p-bases of the transistor sources, and to create a JFET region. For the increasing the breakdown voltage of the device, we proposed to increase the doping level of the drift region, and suggested a new transistor design that will allow one to obtain devices with a breakdown voltage up to 2500 V.

The fabrication and prolonged 500 °C electrical testing of 4H-SiC junction field effect transistor (JFET) integrated circuits (ICs) with two levels of metal interconnect is reported in another submission to this conference proceedings. While some circuits functioned more than 3000 hours at 500 °C, the majority of packaged ICs from this wafer electrically failed after less than 200 hours of operation in the same test conditions. This work examines the root physical degradation and failure mechanisms believed responsible for observed large discrepancies in 500 °C operating time. Evidence is presented for four distinct issues that significantly impacted 500 °C IC operational yield and lifetime for this wafer.