Jeffrey B. Casady

Normally-Off SiC VJFETs for 800 V and 1200 V Power Switching Applications

This paper reports on the development of a normally- off 4H-SiC VJFET power switch technology suitable for drop in replacement in switching-mode power supplies (SMPS). The fabricated devices exhibited a low specific on-resistance (Ron-sp) measured at V_DS=1 V and V_Gs=2-5 V. The transistors designed for 800 V applications had R_ON-SP < 2.9 mOmegaldrcm² and R_ON-SP < 6.6 mOmegaldrcm² at 25degC and 200degC, respectively. The devices designed for 1200 V application had R_ON-SP < 4.3 mOmegaldrcm² at 25degC and R_ON-SP < 12.8 mOmegaldrcm² at 200degC. The total delay time of 73 ns was measured on a 1200 V device when switching from 600 V to 4.9 A with the gate bias ranging from 0 V to 2.75 V. The highest measured off-state drain voltage blocked by a 1200 V device at V_GS=0 V exceeded 1800 V with the total drain leakage of 1 mA.

Cryogenic and high temperature performance of 4H-SiC vertical junction field effect transistors (VJFETs) for space applications

In this paper, we present an investigation on the different aspects of the performance of a 600V, 3A 4H-SiC vertical-trench junction field effect transistor (VJFET) at cryogenic and high temperatures. Some critical device physics related factors that affect the DC characteristics and switching performance of the device are explored. In particular, the experimental low-temperature performance of 4H-SiC VJFETs (down to 30K or -243/spl deg/C) is presented for the first time to our knowledge.

A review of SiC static induction transistor development for high-frequency power amplifiers

Abstract An overview of silicon carbide (SiC) static induction transistor (SIT) development is presented. Basic conduction mechanisms are introduced and discussed, including ohmic, exponential, and space charge limited conduction (SCLC) mechanisms. Additionally, the impact of velocity saturation and temperature effects on SCLC are reviewed. The small signal model, breakdown voltage, power density, and different gate structures are also discussed, before a final review of published SiC SIT results. Published S-band (3–4 GHz) results include 9.5 dB of gain and output power of 120 W, and L-band (1.3 GHz) results include 400 W output power, 7.7 dB of gain, and power density of 16.7 W/cm.

On development of 6H-SiC LDMOS transistors using silane-ambient implant anneal

Abstract 6H-SiC lateral double implanted metal oxide semiconductor field effect transistors have been fabricated on four p-type wafers with p-type epitaxial layers doped with Al at 2–7×10 16 cm −3 . Each of the wafers received two nitrogen implants of heavy and light doses for drain/source and drift regions, respectively. The wafers had the implants activated at 1600°C in an Ar ambient (one wafer) or a silane overpressure ambient (three wafers). The subsequent characterization confirmed a much smoother surface for the silane-annealed wafers, with step bunching reduced from 25 nm peak steps with periodicity of 1 μm to undetectable steps. Near optimal breakdown voltages of 600 V were obtained for a 9 μm drift region length devices, and threshold voltage ranged from 9 to 12 V. Average values for effective channel mobility μ eff were in the range 35.2–44.1 cm 2 /Vs for the three silane-annealed wafers, and 30.0 cm 2 /Vs for the argon-annealed wafer.

Processing of Silicon Carbide for Devices and Circuits

Publisher Summary Most traditional integrated circuit technologies using silicon devices are not able to operate at temperatures above 250°C especially when high operating temperatures are combined with high-power, high-frequency, and high-radiation environments. Much attention has been given to SiC, currently the most mature of the wide-bandgap semiconductors, as a material well-suited for high-temperature and efficient high-power operation. SiC has potential for use in numerous other high-power, high-frequency, and radiation-resistant applications. Silicon carbide (SIC), aluminum nitride (A1N), gallium nitride (GaN), boron nitride (BN), diamond, and zinc selenide (ZnSe) are the primary wide bandgap semiconductors, now being developed for use in various applications. An overview of the electronic properties of SiC as relating to high-temperature electronics, as well as significant achievements involving high-temperature SiC electronics prior to 1996 has been given in the chapter. A broad overview of some of the high-temperature applications using SiC electronics has also been discussed. Devices such as high-frequency Metal Semiconductor Field Effect Transistors (MESFETs), which do not rely on large area or a high-quality dielectric may be the first SiC electronic devices (excluding optical devices) to reach the commercial market.

High-voltage (600 to 3 kV) silicon carbide diode development

The design, fabrication and testing of silicon carbide rectifiers are examined. Both Schottky (600 V to 1 kV) and junction barrier Schottky (JBS) (1 kV to 3 kV) diodes are investigated in terms of practical design, manufacturing and cost issues. Emphases on material quality and edge termination techniques for large scaleable devices are discussed. Using high quality epitaxial layers and both implanted guard ring, and implanted single-zone junction termination extension (JTE) edge termination techniques, 1 kV Schottky and 2.5 kV JBS diodes are demonstrated.

High-temperature Characterization of a 1200 V Power Module with 36 mm2 of SiC VJFET Area

This is the first high-temperature static and dynamic characterization of a half-bridge power module using 1200 V, 45 mΩ depletion-mode vertical JFETs. With only 36 mm2 of JFET area, the peak pulsed current is measured to be nearly 500 A at room temperature (transistors not saturated), decreasing to 230 A at 250 °C (transistors saturated). Total switching losses are less than 3.2 mJ from 25 °C to 250 °C and show negligible dependence on junction temperature. The achievement of this level of performance with such a small SiC transistor area is important, since die area directly impacts achievable module footprint (system-level power density and cost), device capacitance (switching losses), and semiconductor cost.

Silicon carbide junction field effect transistors applied to solid-state power modulators

A new generation of power semiconductor devices is emerging based on the maturation of semiconducting silicon carbide. In this paper, alternatives to the divider resistors are presented using newly available 600-V, 2-A SiC JFETs. Two configurations are possible. The first employs a series combination of JFETs with shorted gate-source terminals operating as current limiting diodes. This allows a greater voltage to be blocked by the IGBT than can be blocked by currently available SiC JFETs. The superior thermal properties of SiC JFETs permit the larger bias currents required to drive the large IGBT gate capacitance at high repetition rates to be sourced. The second configuration is highly efficient and avoids thermal loading of the SiC JFET. The SiC current limiting diodes are replaced by a single SiC JFET switched concurrently with the IGBT. This configuration requires the SiC JFET to block the full voltage blocked by the IGBT, a capability expected in later generations of SiC JFETs. The gate drivers demonstrated in this paper are also applicable to power modulators using large arrays of silicon power MOSFETs. The near-term prospect for very fast SiC JFETs as replacements for silicon MOSFETs in power modulators is also discussed