Silicon carbide (SiC) power devices have been investigated extensively in the past two decades, and there are many devices commercially available now. Owing to the intrinsic material advantages of SiC over silicon (Si), SiC power devices can operate at higher voltage, higher switching frequency, and higher temperature. This paper reviews the technology progress of SiC power devices and their emerging applications. The design challenges and future trends are summarized at the end of the paper.

https://ieeexplore.ieee.org/ielaam/41/8031005/7815312-aam.pdf

Review of Silicon Carbide Power Devices and Their Applications

Power semiconductor devices are key components in power conversion systems. Silicon carbide (SiC) has received increasing attention as a wide-bandgap semiconductor suitable for high-voltage and low-loss power devices. Through recent progress in the crystal growth and process technology of SiC, the production of medium-voltage (600?1700 V) SiC Schottky barrier diodes (SBDs) and power metal?oxide?semiconductor field-effect transistors (MOSFETs) has started. However, basic understanding of the material properties, defect electronics, and the reliability of SiC devices is still poor. In this review paper, the features and present status of SiC power devices are briefly described. Then, several important aspects of the material science and device physics of SiC, such as impurity doping, extended and point defects, and the impact of such defects on device performance and reliability, are reviewed. Fundamental issues regarding SiC SBDs and power MOSFETs are also discussed.

https://iopscience.iop.org/article/10.7567/JJAP.54.040103/pdf

Material science and device physics in SiC technology for high-voltage power devices

A review of the basic mechanisms affecting the stability of the threshold voltage in response to a bias-temperature stress is presented in terms of the charging and activation of near-interfacial oxide traps. An activation energy of approximately 1.1 eV was calculated based on new experimental results. Implications of these factors, including the recovery of some bias-temperature stress-activated defects, for improved device reliability testing are discussed.

Basic Mechanisms of Threshold-Voltage Instability and Implications for Reliability Testing of SiC MOSFETs

In this paper, we report on 1.2-kV-class vertical GaN-based trench metal–oxide–semiconductor field-effect transistors (MOSFETs) on a free-standing GaN substrate with a low specific on-resistance. A redesigned epitaxial layer structure following our previous work with a regular hexagonal trench gate layout enables us to reduce the specific on-resistance to as low as 1.8 mΩcm2 while obtaining a sufficient blocking voltage for 1.2-kV-class operation. Normally-off operation with a threshold voltage of 3.5 V is also demonstrated. To the best of our knowledge, this is the first report on vertical GaN-based MOSFETs with a specific on-resistance of less than 2 mΩcm2.

http://iopscience.iop.org/article/10.7567/APEX.8.054101/pdf

1.8 mΩ·cm2 vertical GaN-based trench metal–oxide–semiconductor field-effect transistors on a free-standing GaN substrate for 1.2-kV-class operation

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

We have developed SiC trench structure Schottoky diodes and SiC double-trench MOSFETs. We succeeded in improving device performance by the reduction of the electric field through the introduction of the aforementioned trench structures. The threshold voltage of the trench structure Schottky diode is 0.48V smaller than the planar. Also, the lowest on-resistance in SiC MOSFETs was achieved.

High performance SiC trench devices with ultra-low ron

Generation and elimination of mobile ions in thermally grown SiO2 on 4H-SiC(0001) were systematically investigated by electrical measurements of MOS capacitors. In contrast to a SiO2/Si system, intrinsic positive mobile ions were found to exist in as-oxidized SiO2/SiC structures, leading to significant instability of SiC-MOS devices. Post-oxidation annealing in Ar ambient mostly eliminates the mobile ions, but they are generated again by subsequent high-temperature hydrogen annealing despite the improved interface quality. The density of the mobile ions was estimated to be several 1012 cm−2. Possible physical origins of the mobile ions are discussed on the basis of the experimental findings.

Investigation of unusual mobile ion effects in thermally grown SiO2 on 4H-SiC(0001) at high temperatures

The energy band structure of SiO2/4H-SiC fabricated on (0001) Si- and (000-1) C-face substrates was investigated by means of synchrotron radiation x-ray photoelectron spectroscopy (SR-XPS). The band structure was found to be dependent on substrate orientation and oxide thickness due to both intrinsic and extrinsic effects that cause charge transfer at the SiO2/SiC interface. Our SR-XPS analysis revealed that the intrinsic conduction band offset of the SiO2/SiC for the C-face substrate is smaller than that for the Si-face. This means that, whereas C-face substrates exhibit high carrier mobility, a problem that is crucial to gate oxide reliability remains for SiC-based metal-oxide-semiconductor (MOS) devices owing to increased leakage current.

Energy Band Structure of SiO2/4H-SiC Interfaces and its Modulation Induced by Intrinsic and Extrinsic Interface Charge Transfer

The trench gate structure MOSFET, with its lack of JFET resistance, is one of the structures able to achieve low on-state resistance [1,2]. In 2008, this group succeeded in fabricating 790V SiC trench MOSFETs with the lowest Ron,sp (1.7 mΩcm2) at room temperature. However these devices had issues regarding oxide destruction at the trench bottom during high drain-source voltage application. In order to improve this problem, this group developed the double-trench MOSFET structure. This structure has both source trenches and gate trenches. This paper compares two kinds of trench MOSFETs: the conventional, single trench structure and a double-trench structure. Also, the latest characteristics are presented.

690V, 1.00 mΩcm2 4H-SiC Double-Trench MOSFETs

We have developed AlON high-k gate dielectric technology that can be easily implemented into both planar and trench SiC-based MOSFETs. On the basis of electrical characterization and numerical simulation, the thickness ratio of the AlON layer to the SiO 2 interlayer and nitrogen content in AlON film were carefully optimized to enhance device performance and reliability.

Shuhei Mitani

Papers

High performance SiC trench devices with ultra-low ron

Investigation of unusual mobile ion effects in thermally grown SiO2 on 4H-SiC(0001) at high temperatures

Energy Band Structure of SiO2/4H-SiC Interfaces and its Modulation Induced by Intrinsic and Extrinsic Interface Charge Transfer

690V, 1.00 mΩcm2 4H-SiC Double-Trench MOSFETs

Performance and reliability improvement in SiC power MOSFETs by implementing AlON high-k gate dielectrics