Materials Science Forum Vols. 740-742

Abstract: The design and development of SiC integrated circuits (ICs) nowadays is a necessity due to the increasing demand for high temperature intelligent power applications and intelligent sensors. Due to the superior electrical, mechanical and chemical proprieties of 4H-SiC poly-type, 4H-SiC MESFET transistor is a good compromise for ICs on SiC able to work at higher temperatures (HT) than on Si. This paper presents new experimental results of approaching embedded logic gates with SiC MESFETs and resistors, built in junction-isolated tubs. The P+ implantation isolation technology offers important perspectives regarding the integration density of devices per unit area and wafer surface, being able to use far more complex design geometry for modeling ICs on SiC.

Abstract: The static and dynamic characteristics of Complementary JFET (CJFET) logic inverter are studied across a range of temperatures and supply voltages to assess potential improvements in performance of digital logic functions for operation in extreme environments. The logic inverter is truly the core of all digital designs. The design and analysis of inverter enables the design of more complex structures, such as NAND, NOR and XOR gates. These complex structures in turn form the building blocks for modules, such as adders, multipliers and microprocessors. At 500 deg C and operating at a supply voltage of 1 V, the CJFET inverter have noise margin comparable to that of room temperature silicon and silicon on insulator CMOS inverters. Furthermore, the static power dissipation by CJFET inverter at 500 deg C is 20.6 nW which is six orders of magnitude lower than that by current SiC technologies, making CJFET technology ideal for achieving complex logic functions, far greater than a few-transistors ICs, in the nearer term.

Abstract: 400V/2.5A 4H-SiC JFETs, having a reduced surface field (RESURF) structure have been fabricated. Measurements on the on-resistance, blocking, and switching characteristics were carried out. It was confirmed that the JFET has fast switching characteristics. A demonstration of a Pulse Width Modulation (PWM) decoder using JFETs was carried out. The input waveform, which is pulse width modulated 20.5MHz at 4.1MHz sine wave, as able to be decoded at 4.1MHz sine wave.

Abstract: When using JFETs with a threshold voltage lower than 2 V in a power supply system or inverter system, a high-speed drive circuit capable of precisely controlling the gate current and a mounting method are important to reduce the switching loss. In this paper, a drive circuit of a normally-off SiC-JFET with a separate source terminal is proposed and the effects are evaluated. By dividing the common source inductance and applying the speed-up capacitor, the turn-on time and turn-on energy losses can be decreased by 40% and 60%, respectively. A speed-up capacitor larger than 100 nF greatly decreases the rising time (tr) and turn-on energy losses. By applying the developed normally-off SiC-JFETs and proposed gate driver to PFC circuits and DC/DC circuits, a highly efficient power supply will be achieved.

Abstract: Silicon Carbide devices are capable of operating as a semiconductor at high temperatures and this capability is being exploited today in discrete power components, bringing system advantages such as reduced cooling requirements [1]. Therefore there is an emerging need for control ICs mounted on the same modules and being capable of operating at the same temperatures. In addition, several application areas are pushing electronics to higher temperatures, particularly sensors and interface devices required for aero engines and in deep hydrocarbon and geothermal drilling. This paper discusses a developing CMOS manufacturing process using a 4H SiC substrate, which has been used to fabricate a range of simple logic and analogue circuits and is intended for power control and mixed signal sensor interface applications [2]. Test circuits have been found to operate at up to 400°C. The introduction of a floating capacitor structure to the process allows the use of switched capacitor techniques in mixed signal circuits operating over an extended temperature range.

Abstract: Superior performance of the Silicon Carbide (SiC) semiconductor in high temperature and harsh environment is widely known. However, utilizing the Vertical Channel 4H–SiC JFET (SiC VJFET) for analog circuit design exhibits significant design challenges, even at room temperature. The fundamental challenges are low intrinsic gain, the limitation of the Gate to Source Voltage Range (GSVR), and restrictions on utilizing Channel Length (CL) as a design parameter due to fabrication complexity. These challenges must be successfully overcome at room temperature, before moving forward with high temperature design. After addressing these issues, two operational amplifiers (opamps) with two distinct design topologies are designed and fabricated. The first design (opamp-1) emphasizes on the gain and Common Mode Rejection Ratio (CMRR) performances [1]. The second design (opamp-2) presents a novel opamp [2] with universal applications where the reliability and unity gain frequency performances are also improved. In this paper, the performance parameters of these two opamps along with their design topologies are reported and compared.

Abstract: To fulfill the space and weight requirements of the photovoltaic systems, an all-SiC transformer less dc-dc multilevel converter based on the Cockcroft-Walton voltage multiplier capable of providing high voltage conversion ratios without an extremely high duty cycle has been realised. The evaluation of converter performance utilising SiC devices have been detailed and presented. The converter offers self-balancing which maintains the same output at all output levels, reducing the complexity of the control strategy. SiC Schottky diodes were used to achive lowest reverse recovery and fast switching while evaluating the high voltage and high frequency performance of the SiC MOSFET in the multilevel boost converter.

Abstract: Utilizing a high power discrete SiC-JFET developed by KEK, a switching power supply (SPS) that had a circuit topology of H-bridge was designed and constructed to drive the induction acceleration system for the KEK digital accelerator. The SPS was operated with a 38 Ω dummy resistance load and bipolar outputs of 800V and 21A were successfully demonstrated at 1 MHz. Also, the combination test with an actual accelerator cell is being conducted.

Abstract: We, the R&D Partnership for Future Power Electronics Technology (FUPET), have reported a forced-air-cooled DC 600 V three-phase AC 400 V inverter built with SiC-JFETs and SiC-SBDs and designed to attain an output power density (OPD) of 40 kW/L with a switching frequency (fSW) of 50 kHz. This paper reports the test results of this inverter attaining an OPD of 40 kW/L in operating a 3-phase motor with fSW = 50 kHz, and an OPD of more than 60 kW/L in operating an equivalent circuit with fSW = 20 kHz by adopting specialized high speed drive circuit boards.

Abstract: This paper addresses and evaluates the temperature dependence performance of silicon carbide (4H-SiC) based insulated gate bipolar transistors (IGBTs) using two dimensional numerical computer aided design tool (i.e., Atlas TCAD from Silvaco). Using identical set of device physical parameters (doping, thicknesses), simulated structure was first caliberated with the experimental data. A minority carrier life time in the drift layer of 1.0 – 1.6 µs and contact resistivity of 0.5 - 1.0 x 10-4 Ω-cm2 produces a close match with the experimental device. A set of n type IGBT structures were then numerically simulated to extract the conduction losses for various blocking voltage classes. An on-resistance first decays with temperature (i.e., increased in ionization level, and increase in minority carrier life time), stays nearly constant with further increase in the temperature (may be all carriers are now fully ionized and increase in carrier life time is compensated with decrease in the carrier mobility) and finally increases linearly with temperature (>450 oC) due to decrease in the carrier mobility. Compared with Si based IGBTs, numerical simulation predicts lower VCEON and RON values for 4H-SiC based IGBTs for higher voltage classes and hence potential for achieving smaller conduction losses for SiC based IGBTs.