Emerging trends in wide band gap semiconductors (SiC and GaN) technology for power devices

A sustainable energy future requires power electronics that can enable significantly higher efficiencies in the generation, distribution, and usage of electrical energy. Silicon carbide (4H-SiC) is one of the most technologically advanced wide bandgap semiconductor that can outperform conventional silicon in terms of power handling, maximum operating temperature, and power conversion efficiency in power modules. While SiC Schottky diode is a mature technology, SiC power Metal Oxide Semiconductor Field Effect Transistors are relatively novel and there is large room for performance improvement. Specifically, major initiatives are under way to improve the inversion channel mobility and gate oxide stability in order to further reduce the on-resistance and enhance the gate reliability. Both problems relate to the defects near the SiO2/SiC interface, which have been the focus of intensive studies for more than a decade. Here we review research on the SiC MOS physics and technology, including its brief history, the state-of-art, and the latest progress in this field. We focus on the two main scientific problems, namely, low channel mobility and bias temperature instability. The possible mechanisms behind these issues are discussed at the device physics level as well as the atomic scale, with the support of published physical analysis and theoretical studies results. Some of the most exciting recent progress in interface engineering for improving the channel mobility and fundamental understanding of channel transport is reviewed.

Silicon carbide: A unique platform for metal-oxide-semiconductor physics

The higher voltage blocking capability and faster switching speed of silicon-carbide (SiC) mosfet s have the potential to replace Si insulated gate bipolar transistors (IGBTs) in medium-/low-voltage and high-power applications. In this paper, a state-of-the-art commercially available 325 A, 1700 V SiC mosfet module has been fully characterized under various load currents, bus voltages, and gate resistors to reveal their switching capability. Meanwhile, Si IGBT modules with similar power ratings are also tested under the same conditions. From the test results, several interesting points have been obtained: different to the Si IGBT module, the over-shoot current of the SiC mosfet module increases linearly with the increase of the load current and it has been explained by a model of the over-shoot current proposed in this paper; the induced negative gate voltage due to the complementary device turn- off (crosstalk effect) is more harmful to the SiC mosfet module than the induced positive gate voltage during turn- on when the gate off-voltage is –6 V; the maximum dv / dt and di / dt (electromagnetic interference) during switching transients of the SiC mosfet module are close to those of the Si IGBT module when the gate resistance is larger than 8 Ω but the switching loss of the SiC mosfet module is much smaller; the switching losses of the Si IGBT module are greater than those of the SiC mosfet module even when the gate resistance of the former is reduced to zero. An accurate power loss model, which is suitable for a three-phase two-level converter based on SiC mosfet modules considering the power loss of the parasitic capacitance, has been presented and verified in this paper. From the model, a 96.2% efficiency can be achieved at the switching frequency of 80 kHz and the power of 100 kW.

Performance Evaluation of High-Power SiC MOSFET Modules in Comparison to Si IGBT Modules

Wide bandgap (WBG) device-based power electronics converters are more efficient and lightweight than silicon-based converters. WBG devices are an enabling technology for many motor drive applications and new classes of compact and efficient motors. This paper reviews the potential applications and advances enabled by WBG devices in ac motor drives. Industrial motor drive products using WBG devices are reviewed, and the benefits are highlighted. This paper also discusses the technical challenges, converter design considerations, and design tradeoffs in realizing the full potential of WBG devices in motor drives. There is a tradeoff between high switching frequency and other issues such as high dv/dt and electromagnetic interference. The problems of high common mode currents and bearing and insulation damage, which are caused by high dv/dt , and the reliability of WBG devices are discussed.

Wide Bandgap Devices in AC Electric Drives: Opportunities and Challenges

This silicon-carbide semiconductor device (101) has a silicon-carbide substrate (10), a main electrode (52), a first barrier layer (70a), and a wiring layer (60). The main electrode (52) is provided directly on top of the silicon-carbide substrate (10). The first barrier layer (70a) is provided on top of the main electrode (52) and is made from a conductive material that does not contain aluminum. The wiring layer (60) is provided on top of the first barrier layer (70a), is isolated from the main electrode (52) by the first barrier layer (70a), and is made from a material that does contain aluminum.

Silicon carbide semiconductor device

The present disclosure relates to a silicon carbide (SiC) field effect device that has a gate assembly formed in a trench. The gate assembly includes a gate dielectric that is an dielectric layer, which is deposited along the inside surface of the trench and a gate dielectric formed over the gate dielectric. The trench extends into the body of the device from a top surface and has a bottom and side walls that extend from the top surface of the body to the bottom of the trench. The thickness of the dielectric layer on the bottom of the trench is approximately equal to or greater than the thickness of the dielectric layer on the side walls of the trench.

Enhanced gate dielectric for a field effect device with a trenched gate

Semiconductor devices include a semiconductor layer structure comprising a drift region that includes a wide band-gap semiconductor material. A shielding pattern is provided in an upper portion of the drift region in an active region of the device and a termination structure is provided in the upper portion of the drift region in a termination region of the device. A gate trench extends into an upper surface of the semiconductor layer structure. The semiconductor layer structure includes a semiconductor layer that extends above and at least partially covers the termination structure.

Power semiconductor devices having gate trenches and buried edge terminations and related methods

4H-SiC metal-oxide-semiconductor field-effect transistors have a substantially lower effective channel mobility than silicon-based counterparts. Nitric oxide annealing has been primarily utilized to provide an order of magnitude improvement in the effective channel mobility. Barium interface layers provide an additional doubling of the mobility over nitric oxide anneals. However, barium-based 4H-SiC transistors show more susceptibility to oxide leakage. We have investigated the atomic scale mechanisms of oxide leakage in barium-based devices with electrically detected magnetic resonance. We observe the presence of E’ centers within the oxides of modestly stressed devices. Our measurements directly demonstrate that these E’ centers are important and very likely the dominating cause of these leakage currents. In conventional silicon-based devices, E’ centers are known to be important defects in reliability issues such as bias temperature instabilities and stress-induced leakage currents.

Leakage Currents and E’ Centers in 4H-SiC MOSFETs with Barium Passivation

In this work, we utilize electrically detected magnetic resonance via the bipolar amplification effect to explore the physical and chemical nature of defects at the 4H-SiC/SiO 2 interface in metal-oxide-semiconductor field effect transistors. Defects at and very near the 4H-SiC/SiO 2 interface are involved in bias temperature instabilities in 4H-SiC transistor technology. Of particular relevance to reliability physics, our results indicate that oxygen deficient silicon atoms in the near-interface oxide, known as E’ centers, can be greatly reduced utilizing nitric oxide and barium annealing. E’ centers have been directly linked to bias temperature instabilities in 4H-SiC technology.

Reliability and Performance Issues in SiC MOSFETs: Insight Provided by Spin Dependent Recombination

A Silicon Carbide (SiC) semiconductor device having back-side contacts to a P-type region and methods of fabrication thereof are disclosed. In one embodiment, an SiC semiconductor device includes an N-type substrate and an epitaxial structure on a front-side of the N-type substrate. The epitaxial substrate includes a P-type layer adjacent to the N-type substrate and one or more additional SiC layers on the P-type layer opposite the N-type substrate. The semiconductor device also includes one or more openings through the N-type substrate that extend from a back-side of the N-type substrate to the P-type layer and a back-side contact on the back-side of the N-type substrate and within the one or more openings such that the back-side contact is in physical and electrical contact with the P-type layer. The semiconductor device further includes front-side contacts on the epitaxial structure opposite the N-type substrate.

Daniel J. Lichtenwalner

Papers

Enhanced gate dielectric for a field effect device with a trenched gate

Power semiconductor devices having gate trenches and buried edge terminations and related methods

Leakage Currents and E’ Centers in 4H-SiC MOSFETs with Barium Passivation

Reliability and Performance Issues in SiC MOSFETs: Insight Provided by Spin Dependent Recombination

Semiconductor devices in sic using vias through n-type substrate for backside contact to p-type layer