Materials Science Forum Vols. 821-823

Abstract: Trenched-implanted-gate 4H–SiC vertical-channel JFET (TI-VJFET) have been fabricated with self-aligned nickel silicide source and gate contacts using a process sequence that greatly reduces process complexity as it includes only four lithography steps. The effect of the channel geometry on the electrical characteristics has been studied by varying its length (0.3 and 1.2μm) and its width (1.5-5μm). The transistors exhibited high current handling capabilities (Direct Current density 330A/cm²). The output current reduces with the increase of the measurements temperature due to the decrease of the electron mobility value. The voltage breakdown exhibits a triode shape, which is typical for a static-induction transistor operation.

Abstract: In many power electronic inverters, the gate drive failure may put the switch normally-on in short-circuit (SC) risk. The high power density generated thus leads rapidly to the transistor failure. This paper presents our study via electro-thermal simulation of a 1200 V JFET under short circuit. It provides deep insight of physical phenomena present in the JFET during the short-circuit and will allow further improvements and understanding of it.

Abstract: This paper deals with the geometry of a high voltage (1200 V) vertical JFET made with 4H silicon carbide, inspired by SIT or commercial solutions like Semisouth's one (principle exposed in Fig. 1). A first layout was designed allowing an easy integration of a free-wheeling diode. Indeed with the maturity of SiC JFET fabrication process, nowadays' trend is the high integration level of a complete power electronics system. This paper will focus on the distribution of the gate potential or the source current across the device and the relation that could be done with the switching delay. The measurements start with the classical I–V static characterization from room temperature till 225°C. After packaging the best dies, the switching behavior is studied. Gate bias and temperature dependence is also investigated. In order to fully understand the conducting/blocking or switching mechanisms, some further measurements using lock-in infrared thermography (LIRT) technique was led. Thus, with this complete characterization methodology the device layout can be improved.

Abstract: In this study, the electrical performance of Bipolar-Injection Field-Effect-Transistors (BiFET) in dependence on the junction temperature is presented for the first time. Based on these results, the short circuit capability of the BiFET is discussed. Thereby, the saturation current is estimated to be approximately 150mA at 300K and it increases by a factor of 5 by rising the temperature up to 450K as analyzed in this study. Furthermore, the reduction of the gate-voltage window of the BiFET at elevated temperatures is comparable to unipolar JFETs, and indicates a very good controllability over a wide temperature range. Finally, numerical simulations demonstrate the potential to improve the electrical performance of the BiFET drastically by adjusting the doping concentration in the control region and increasing the ambipolar lifetime in the p-doped drift layer without influencing the dependency on the junction temperature.

Abstract: With the commercial availability of SiC power transistors, this decade will mark an important breakthrough in power transistor technology. However, in power electronic systems, disturbances may place them in short-circuit condition and little knowledge exist about their SC capability. This paper presents our study of SiC MOSFETs, JFETs and BJT under capacitive load short-circuit up to 600V.

Abstract: The aim of this study consists in comparing effects of temperature on various Silicon Carbide power devices. Static and dynamic electrical characteristics have been measured for temperatures from 80K to 525K.

Abstract: This paper proposes a new structure of 4H-SiC bipolar junction transistor, which can both achieve high current gain and high open base breakdown voltage. By introducing a groove type of metal-high k dielectric-silicon carbide (MIS) structure into the active region along the base-emitter sidewall which is formed with the process of isolation etching, a large electric field appears at the interface between high-k dielectric and bulk material by analyzing the potential distribution in forward mode, thus accelerating the electron transport. Based on a doping concentration of 4×10¹⁷cm^-3 and thickness of 0.6um base region, current gain of as high as 191 is obtained using TCAD simulation, and that is almost double of the conventional structure in the same simulation setup. Furthermore, a field plate structure is composed combined with the base contact metal simultaneously, and the open base breakdown voltage is obviously increased from 634V to 948V with a 6μm-thick n-SiC collector (N_d=3×10¹⁵cm^-3).

Abstract: SiC Junction Transistors (SJTs) with 1900 V Drain-Source breakdown voltages, current gain (h_FE) higher than 120 and low on-resistance of 22 mΩ (3.5 mΩ-cm²) are reported in this paper. SJTs with a pre-stress h_FE of 90 suffer only a 10% reduction of the h_FE after 190 hours under a 200 A/cm² DC current stress at a T_J of 125°C, while a similar stress on earlier generation SJTs resulted in over 25% h_FE reduction in only 25 hours. SJT die with pre-stress h_FE in the range of 120-125 show absolutely no current gain degradation even after a 300°C/ 2 hour stress at 60 A/cm² DC drain current.

Abstract: Considering the development of faster power electronic switches, especially silicon carbide (SiC) devices, parasitic elements, such as stray inductances and capacitances, become more and more crucial. Overvoltages caused by stray inductances in combination with fast switching transients can destroy the devices at turn-off. In this paper the implementation of the DVRC circuit for silicon carbide bipolar junction transistors (BJTs) is investigated. The DUT was Fairchild`s FSICBH057A120 (V_CES = 1200 V, R_on = 57 mΩ).

Abstract: The characteristics of a 1200 V and 800 A bipolar junction transistor (BJT) power module has been measured, simulated and verified for the first time in the PSPICE platform. The simulation model is based on a silicon carbide (SiC) Gummel-Poon model for high power applications. The implemented model has been extended with temperature dependent equations in order to extend the BJT operating temperature range. PSPICE simulations are performed to extract technology dependent modeling parameters coupled with static and dynamic characteristics of BJTs at different temperatures and validated against the measured data. The performance of the SiC BJT model is fairly accurate and correlates well with the measured results over a wide temperature range.