Vipindas Pala

Silicon carbide power MOSFETs: Breakthrough performance from 900 V up to 15 kV

Since Cree, Inc.s 2^nd generation 4H-SiC MOSFETs were commercially released with a specific on-resistance (R_{ON, SP}) of 5 mΩ·cm² for a 1200 V-rating in early 2013, we have further optimized the device design and fabrication processes as well as greatly expanded the voltage ratings from 900 V up to 15 kV for a much wider range of high-power, high-frequency, and high-voltage energy-conversion and transmission applications. Using these next-generation SiC MOSFETs, we have now achieved new breakthrough performance for voltage ratings from 900 V up to 15 kV with a R_{ON, SP} as low as 2.3 mΩ·cm² for a breakdown voltage (BV) of 1230 V and 900 V-rating, 2.7 mΩ·cm² for a BV of 1620 V and 1200 V-rating, 3.38 mΩ·cm² for a BV of 1830 V and 1700 V-rating, 10.6 mΩ·cm² for a BV of 4160 V and 3300 V-rating, 123 mΩ·cm² for a BV of 12 kV and 10 kV-rating, and 208 mΩ·cm² for a BV of 15.5 kV and 15 kV-rating. In addition, due to the lack of current tailing during the bipolar device switching turn-off, the SiC MOSFETs reported in this work exhibit incredibly high frequency switching performance over their silicon counter parts.

10 kV and 15 kV silicon carbide power MOSFETs for next-generation energy conversion and transmission systems

Advanced high-voltage (10 kV-15 kV) silicon carbide (SiC) power MOSFETs described in this paper have the potential to significantly impact the system performance, size, weight, high-temperature reliability, and cost of next-generation energy conversion and transmission systems. In this paper, we report our recently developed 10 kV/20 A SiC MOSFETs with a chip size of 8.1 × 8.1 mm2 and a specific on-resistance (RON, SP) of 100 MΩ-cm2 at 25 °C. We also developed 15 kV/10 A SiC power MOSFETs with a chip size of 8 × 8 mm2 and a RON, SP of 204 mQ cm2 at 25 °C. To our knowledge, this 15 kV SiC MOSFET is the highest voltage rated unipolar power switch. Compared to the commercial 6.5 kV Silicon (Si) IGBTs, these 10 kV and 15 kV SiC MOSFETs exhibit extremely low switching losses even when they are switched at 2-3× higher voltage. The benefits of using these 10 kV and 15 kV SiC MOSFETs include simplifying from multilevel to two-level topology and removing the need for time-interleaving by improving the switching frequency from a few hundred Hz for Si based systems to ≥ 10 kHz for hard-switched SiC based systems.

27 kV, 20 A 4H-SiC n-IGBTs

In this work, we report our recently developed 27 kV, 20 A 4H-SiC n-IGBTs. Blocking voltages exceeding 24 kV were achieved by utilizing thick (210 μm and 230 μm), lightly doped N-drift layers with an appropriate edge termination. Prior to the device fabrication, an ambipolar carrier lifetime of greater than 10 μs was measured on both drift regions by the microwave photoconductivity decay (μPCD) technique. The SiC n-IGBTs exhibit an on-state voltage of 11.8 V at a forward current of 20 A and a gate bias of 20 V at 25 °C. The devices have a chip size of 0.81 cm2 and an active conducting area of 0.28 cm2. Double-pulse switching measurements carried out at up to 16 kV and 20 A demonstrate the robust operation of the device under hard-switched conditions; coupled thermal analysis indicates that the devices can operate at a forward current of up to 10 A in a hard-switched environment at a frequency of more than 3 kHz and a bus voltage of 14 kV.

22 kV, 1 cm 2 , 4H-SiC n-IGBTs with improved conductivity modulation

In this paper, we report our recently developed large area 4H-SiC n-IGBTs that have a chip size of 1 cm2 and an active conducting area of 0.37 cm2. A blocking voltage of 22.6 kV has been demonstrated with a leakage current of 9 μA at a gate bias of 0 V at room-temperature. This is the highest breakdown voltage of a single MOS-controlled semiconductor switch reported to date. To improve the conductivity modulation and lower the conduction losses during the on-state, a thermal oxidation process was applied to enhance the carrier lifetime prior to the device fabrication. Compared to the devices that did not receive this lifetime enhancement process, the lifetime enhanced devices displayed nearly 1 V lower forward voltage drop with little increase in switching energy and no degradation of static blocking characteristics. A specific differential on-resistance of 55 mΩ-cm2 at 20 A and 125 °C was achieved, suggesting that bipolar power devices with thick drift regions can benefit from further enhancement of the ambipolar carrier lifetime.

Ultra high voltage MOS controlled 4H-SiC power switching devices

Ultra high voltage (UHV, >15 kV) 4H-silicon carbide (SiC) power devices have the potential to significantly improve the system performance, reliability, and cost of energy conversion systems by providing reduced part count, simplified circuit topology, and reduced switching losses. In this paper, we compare the two MOS based UHV 4H-SiC power switching devices; 15 kV 4H-SiC MOSFETs and 15 kV 4H-SiC n-IGBTs. The 15 kV 4H-SiC MOSFET shows a specific on-resistance of 204 mΩ cm2 at 25 °C, which increased to 570 mΩ cm2 at 150 °C. The 15 kV 4H-SiC MOSFET provides low, temperature-independent, switching losses which makes the device more attractive for applications that require higher switching frequencies. The 15 kV 4H-SiC n-IGBT shows a significantly lower forward voltage drop (VF), along with reasonable switching performance, which make it a very attractive device for high voltage applications with lower switching frequency requirements. An electrothermal analysis showed that the 15 kV 4H-SiC n-IGBT outperforms the 15 kV 4H-SiC MOSFET for applications with switching frequencies of less than 5 kHz. It was also shown that the use of a carrier storage layer (CSL) can significantly improve the conduction performance of the 15 kV 4H-SiC n-IGBTs.

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 Alkaline Earth Interface Passivation

Alkaline earth elements Sr and Ba provide SiO2/SiC interface conditions suitable for obtaining high channel mobility metal-oxide-semiconductor field-effect-transistors (MOSFETs) on the Si-face (0001) of 4H-SiC, without the standard nitric oxide (NO) anneal. The alkaline earth elements Sr and Ba located at/near the SiO2/SiC interface result in field-effect mobility (μFE) values as high as 65 and 110 cm2/V.s, respectively, on 5×1015 cm-3 Al-doped p-type SiC. As the SiC doping increases, peak mobility decreases as expected, but the peak mobility remains higher for Ba interface layer (Ba IL) devices compared to NO annealed devices. The Ba IL MOSFET field-effect mobility decreases as the temperature is increased to 150 °C, as expected when mobility is phonon-scattering-limited, not interface-trap-limited. This is in agreement with measurements of the interface state density (DIT) using the high-low C-V technique, indicating that the Ba IL results in lower DIT than that of samples with nitric oxide passivation. Vertical power MOSFET (DMOSFET) devices (1200V, 15A) fabricated with the Ba IL have a 15% lower on-resistance compared to devices with NO passivation. The DMOSFET devices with a Ba IL maintain a stable threshold voltage under NBTI stress conditions of-15V gate bias stress, at 150 °C for 100hrs, indicating no mobile ions. Secondary-ion mass-spectrometry (SIMS) analysis confirms that the Sr and Ba remain predominantly at the SiO2/SiC interface, even after high temperature oxide annealing, consistent with the observed high channel mobility after these anneals. The alkaline earth elements result in enhanced SiC oxidation rate, and the resulting gate oxide breakdown strength is slightly reduced compared to NO annealed thermal oxides on SiC.

High performance, large-area, 1600 V / 150 A, 4H-SiC DMOSFET for robust high-power and high-temperature applications

In this paper, we report our recently developed 2^nd Generation, large-area (56 mm² with an active conducting area of 40 mm²) 4H-SiC DMOSFET, which can reliably block 1600 V with very low leakage current under a gate-bias (V_G) of 0 V at temperatures up to 200°C. The device also exhibits a low on-resistance (R_ON) of 12.4 mΩ at 150 A and V_G of 20 V. DC and dynamic switching characteristics of the SiC DMOSFET have also been compared with a commercially available 1200 V/ 200 A rated Si trench gate IGBT. The switching energy of the SiC DMOSFET at 600 V input voltage bus is > 4X lower than that of the Si IGBT at room-temperature and > 7X lower at 150°C. A comprehensive study on intrinsic reliability of this 2^nd generation SiC MOSFET has been performed to build consumer confidence and to achieve broad market adoption of this disruptive power switch technology.

900V silicon carbide MOSFETs for breakthrough power supply design

Improvements in 900V SiC MOSFET technology have resulted in switches that have extremely low ON resistance in high-speed packages. 900V SiC MOSFETs are promising candidates for hard switched and soft-switched power supply applications due to low ON resistance at higher temperature, a robust low-recovery body diode, avalanche capability and low output stored charge. System designers will be able to use these features to enable novel topologies and achieve large improvements in power density and efficiency. As an example, a 220 W single-stage flyback LED driver is presented, which achieves 40% size reduction over a 650V silicon MOSFET based solution, obtains similar efficiencies and a lower BOM cost.

Next-Generation Planar SiC MOSFETs from 900 V to 15 kV

A family of planar MOSFETs with voltage ratings from 900 V to 15 kV are demonstrated. This family of planar MOSFETs represents Cree’s next generation MOSFET design and process, in which we continue to refine and evolve device design and processing to further shrink die sizes and enhance device performance. At voltage ratings of 3.3 kV and above, the specific on-resistance of the MOSFETs is approaching the theoretical limit. MOSFET switching performance in a clamped inductive switching circuit for the full range of voltage ratings is also demonstrated. Finally, improved threshold voltage and body diode stability under long-term stresses are presented.