Anant K. Agarwal

15-kV single-bias all-optical ETO thyristor

A new all-optical emitter-turn-off (ETO) configuration is proposed in this paper which is operated under 15 kV single bias and a current of 10 A. This ETO is completely controlled by two optical signals, one for the 15 kV SiC gate-turn-off (GTO) thyristor and the other one for a triggering low-voltage optically controlled Si switch. The latter, called optically-triggered power transistor (OTPT), is used in series with the anode contact of the SiC GTO thyristor in order to handle the current switching between anode and gate path of the SiC GTO thyristor. This OTPT is triggered with a 5-W laser of 808-nm wavelength and the main SiC GTO thyristor is triggered with a laser having a low wavelength of 266 nm. The voltage drop on the OTPT during the on-state is controlled by the power of the laser. For an optical power of 5 W, the structure is optimized to have an on-state voltage of 0.2 V at the junction temperature of 200 °C. This is less than 0.002% of the total bias of 15 kV.

Strategic Overview of High-Voltage SiC Power Device Development Aiming at Global Energy Savings

Advanced high-voltage (≥10 kV) silicon carbide (SiC) devices described in this paper have the potential to significantly impact the system size, weight, high-temperature reliability, and cost of modern variable-speed medium-voltage (MV) systems such as variable speed (VSD) drives for electric motors, integration of renewable energy including energy storage, micro-grids, traction control, and compact pulsed power systems. In this paper, we review the current status of the development of 10 kV-20 kV class power devices in SiC, including MOSFETs, JBS diodes, IGBTs, GTO thyristors, and PiN diodes at Cree. Advantages and weakness of each device are discussed and compared. A strategy for high-voltage SiC power device development is proposed.

High-Mobility SiC MOSFETs with Chemically Modified Interfaces

Alkali (Rb, Cs) and alkaline earth elements (Sr, Ba) provide SiO2/SiC interface conditions suitable for obtaining high metal-oxide-semiconductor field-effect-transistor (MOSFET) channel mobility on the 4H-SiC Si-face (0001), without the standard nitric oxide (NO) anneal. The alkali elements Rb and Cs result in field-effect mobility (μFE) values >25 cm2/V.s, and the alkaline earth elements Sr and Ba resulted in higher μFE values of 40 and 85 cm2/V.s, respectively. The Ba-modified MOSFETs show a slight decrease in mobility with heating to 150 °C, as expected when mobility is not interface-trap-limited, but phonon-scattering-limited. The interface state density is lower than that obtained with nitric oxide (NO) passivation. Devices with a Ba interface layer maintain stable mobility and threshold voltage under ±2 MV/cm gate bias stress at 175 °C, indicating no mobile ions.

Development of Low RON,Diff, 12 kV, 4H-SiC GTOs For High-Power and High-Temperature Applications

In this paper, we report our recently developed 1 × 1 cm2, 12 kV SiC GTOs with a very low differential on-resistance (RON,Diff) of 4 mΩ·cm2 with respect to the device active area at high injection level current of 100 A/cm2 or higher, which is more than a 40% reduction from our previously reported work. This significant reduction in the on-resistance was attributed to an improvement of carrier lifetime in the SiC bulk region. The SiC GTO was wire-bonded and attached to a high-voltage package before the high-temperature measurement. Forward characteristics of the device were then measured using a Tektronics 371 curve tracer from room temperature up to 400°C. Over the temperature range, the RON,Diff of the 4H-SiC GTO increased modestly from 4 mΩ·cm2 at 20°C to 4.7 mΩ·cm2 at 400°C, while the forward voltage drop at 100 A decreased slightly from 3.97 V at 20°C to 3.6 V at 400°C. The gate to cathode blocking voltage (VGK) was measured using a customized high-voltage test set-up. The leakage current was measure...

Wide Bandgap power devices and applications; the U.S. initiative

The U.S. offers multiple mechanisms for funding both small and large businesses to promote innovations in science and industry. However, dating back to the 80s many U.S. companies have chosen to take products created domestically and manufacture them overseas. This has been a particularly disturbing trend in the semiconductor business leading to the loss of jobs and technical expertise as students, educated in the U.S., leave for opportunities elsewhere. Efforts to reverse this tendency are being aggressively undertaken through new initiatives funded by the U.S. Department of Energys (DOE) Advanced Manufacturing Office (AMO). Details of some of these activities, in regards to Wide Bandgap (WBG) semiconductor devices and their applications, are discussed in this paper.

Optical Triggering of High Current (1300 A), High-Voltage (12 kV) 4H-SiC Thyristor

A 12 kV class 4H-SiC thyristor with a pilot thyristor (an amplification step) has been triggered to a current Imax = 1310 A in a mixed resistive-inductive load circuit. In order to further increase the Imax, the homogeneity of the initially turned-on region should be improved and/or additional amplification steps introduced

Optical triggering of 4H-SiC thyristors (18 kV class) to high currents in purely inductive load circuit

Optical switch-on of a very high voltage (18 kV class) 4H-SiC thyristor with an amplification step (pilot thyristor) to the current Imax = 1225 A is demonstrated using a purely inductive load and a calibrated air transformer. Increasing the inductance of the transformer primary winding slows down the turn on process. However, the inductance has little effect during the initial stage of the switch-on process when the voltage drop on the thyristor and its internal resistance is high. The results show that a further switch-on current increase can be only achieved by introducing additional amplification steps in the pilot thyristor.

Characterization of a Large Area Silicon Carbide PiN Diode at Temperatures up to 900°C

For the first time, a large area Silicon Carbide (SiC) PiN diode was measured to determine the forward and reverse characteristics at temperatures up to 900°C. The diode characterized had a chip area of 64 mm2 and used a conventional SiC PiN structure with a 75 um N type blocking layer thickness. A normal rating for this device at room temperature would be 50 amps at 100 A/cm2 and 6 kV. Since a package capable of operating at 900°C was not available, methods were developed to heat and verify the temperature of the diode die, provide electrical connections to the die and provide adequate insulation to minimize temperature gradients across the die. Even at this extreme temperature the diode maintained typical diode characteristics and maintained surprisingly good performance.

Invited) SiC Power Devices for Next Generation Energy Efficiency

Silicon carbide (SiC) materials technology has made rapid advances in recent years. While increasing the wafer diameter from 75 mm to 100 mm, the substrate quality has been greatly improved with much reduced defect density, resulting in higher device yields. Cree is poised to increase the wafer diameter to 150 mm in 2012, which will further reduce the cost of SiC devices. SiC Schottky diodes have demonstrated very high reliability in the field and are being extensively used in Switch Mode Power Supplies (SMPS), and solar inverters, and other applications. Cree has also commercially released a 1200 V, 20 A SiC MOSFET which has been used in solar inverter along with SiC Schottky diode to provide an efficiency gain of 2.36%. More recent R&D results at Cree indicate that the on-resistance of the MOSFET can be reduced by 2x, which will further improve performance and reduce cost.