Electrical Characterization of Power Silicon Carbide MOSFETs with Linear and Hexagonal Base Cell Designs

Introduction. The current advancement of 4H-SiC-based power electronics is driven by rapid progress in bulk and epitaxial growth technology of silicon carbide (SiC) crystals. This determines the demand for improved designs and manufacturing technologies of MOS transistors (MOSFET) and Schottky diodes. Research in this field is highly relevant for a widespread implementation of SiC devices in various areas of power electronics and conversion technology for achieving the required levels of energy efficiency.

Aim. Research and comparative analysis of electrical characteristics of 4H-SiC power MOSFET laboratory samples with linear and hexagonal base cell designs.

Materials and methods. The initial objects of the study were laboratory samples of 4H-SiC-MOSFET with two types of cells and a small-size active area, designed for voltages up to 1200 V. At a later stage, 4H-SiC-MOSFET laboratory samples with optimized parameters of a linear-type cell and a larger active area were manufactured and investigated. The transistors were manufactured via a laboratory technological route without applying a self-aligned channel technology. The samples were characterized using optical and scanning electron microscopy (SEM). Electrical parameters were measured by a Keysight B1505A curve tracer.

Results. The comparative analysis of the output characteristics of the samples showed that transistors with a hexagonal cell topology outperform those with a linear topology in terms of higher values of switching currents. However, the maximum current density J_DS = 125 A/cm² is not critical for silicon carbide. Improved transistors with a linear topology with reduced channel dimensions and an increased active area are characterized by a higher current density and a lower channel resistance in the open state (Ron).

Conclusion. Transistor samples with a hexagonal cell topology in comparison with those with a linear topology, under equal R_on, demonstrate higher values of switched currents but lower reproducibility of parameters. Laboratory samples with an improved linear cell topology are characterized by ~ 4 times lower R_on compared to those with a small active area. Nevertheless, the achieved transistor yield in terms of threshold voltage U_th was less than 10 %, which indicates the necessity of implementation of self-aligned channel technologies and high-resolution lithography in their manufacturing route when scaling up their production.

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