SiC Power Device｜Basic

Summary

2018.12.06

This final section ends by summarizing the key points of the physical properties of SiC, SiC-SBDs (Schottky barrier diodes), SiC-MOSFETs and full-SiC power modules.

＜Introduction＞

▶Introduction

Key Points

・SiC power devices are next-generation, low-loss elements that are excellent for reducing power loss and for operating in high-temperature environments.

・Although these are new semiconductor devices, they have already been widely used even in automotive markets that require high quality and reliability.

＜What is SiC (silicon carbide)?＞

▶What is silicon carbide?

Key Points

・The physical properties of SiC are well-suited to power devices.

・Compared with Si semiconductors, losses are low, and dynamic characteristics in high-temperature environments are excellent.

▶Development Background and Advantages of SiC Power Devices

Key Points

・SiC has been developed as one solution to energy-related problems.

・In addition to reducing losses, SiC offers the major advantage of miniaturization.

＜SiC Schottky Barrier Diode (SiC-SBD)＞

▶What are SiC-SBDs? – Features of SiC-SBDs and Comparison with Si Diodes

Key Points

・Features of SiC-SBDs are excellent high-speed operation combined with a high voltage.

・Compared with Si PN diodes having high voltages, SiC devices afford excellent reverse recovery times and other high-speed characteristics, and so make possible lower losses and more compact equipment.

▶What are SiC-SBDs? – Reverse Recovery Characteristics of SiC-SBDs and Si-PNDs

Key Points

・An SiC-SBD has a faster trr and much smaller reverse recovery current compared with a Si-PND (FRD), and so losses are small.

・The reverse recovery characteristic (trr and reverse recovery current) of an SiC-SBD exhibits almost no temperature dependence.

▶What are SiC-SBDs? – Forward Voltages of SiC-SBD and Si-PND

Key Points

・The VF of an SiC-SBD rises with temperature, whereas the VF of an Si-PND (FRD) falls.

・The increase in the VF of an SiC-SBD at high temperatures causes the IFSM to decline, but there is no thermal runaway, such as occurs in Si-PNDs (FRDs), the VF of which declines.

・In second-generation SiC-SBDs, the VF falls, and at present they can be called the power diodes that are best able to help reduce losses.

▶Evolution of SiC-SBDs

Key Points

・ROHM SiC-SBDs have already evolved to the third generation.

・Third-generation products offer improved TFMS and reduced leakage currents, and further reduce the low VF values achieved in the second generation.

▶Advantages of using SiC-SBDs

Key Points

・The trr is fast, so that recovery losses can be dramatically reduced, for higher efficiency

・For a similar reason, the reverse current is small so that noise is low, and the number of noise/surge suppression components can be reduced, enabling enhanced miniaturization

・High frequency operation enables miniaturization of inductors and other peripheral components

▶What are SiC-SBDs? – Reliability Tests

Key Points

・At ROHM, tests conforming to industry standards for semiconductor devices are conducted to evaluate the reliability of SiC-SBDs.

＜SiC-MOSFET＞

▶What are SiC-MOSFETs? ? SiC-MOSFET Features

Key Points

・SiC-MOSFETs can contribute to reduced losses and smaller application size relative to Si-MOSFETs and IGBTs.

▶What are SiC-MOSFETs? – Comparison of Power Transistor Structures and Features

Key Points

・The features of power transistors differ depending on the materials and structures.

・There are various advantages and disadvantages where characteristics are concerned, but SiC-MOSFETs exhibit excellent characteristics overall.

▶What are SiC-MOSFETs? – Differences with Si-MOSFET

Key Points

・In order to obtain a low on-resistance for a SiC-MOSFET, the Vgs must be set higher than that for a Si-MOSFET, to around 18 V or so.

・The internal gate resistance of a SiC-MOSFET is higher than that of a Si-MOSFET, and so the external resistance Rg is set low; but surge protection should also be considered.

▶What are SiC-MOSFETs? – Differences with IGBTs

Key Points

・The on-resistance characteristic of SiC-MOSFET Vd-Id characteristics changes linearly, and SiC-MOSFETs have an advantage over IGBTs at low currents.

・Switching losses of SiC-MOSFETs can be greatly reduced compared with IGBTs.

▶What are SiC-MOSFETs? – Body Diode Characteristics

Key Points

・The forward characteristic Vf of the body diode of a SiC-MOSFET is high compared with that of an Si-MOSFET.

・The trr of a SiC-MOSFET body diode is fast, and the recovery loss can be reduced relative to that of an Si-MOSFET.

▶What are SiC-MOSFETs? – Trench-structure SiC-MOSFETs and Actual Products

Key Points

・ROHM has achieved mass production of SiC-MOSFETs that adopt an original double-trench structure.

・Trench-structure SiC-MOSFETs have an ON-resistance lower by about 50%, and an input capacitance lower by about 35%, compared with DMOS-structure products.

▶What are SiC-MOSFETs? – SiC Application Examples

Key Points

・The effectiveness of SiC-MOSFETs should be considered carefully, taking hints from case studies that utilize SiC-MOSFETs.

▶What are SiC-MOSFETs? – Reliability of SiC-MOSFETs

Key Points

・The reliability of ROHM SiC-MOSFETs is equivalent to that of Si-MOSFETs currently in use.

＜Full-SiC Power Modules＞

▶What are Full-SiC Power Modules?

Key Points

・Full-SiC power modules are configured using SiC-MOSFETs and SiC-SBDs developed and manufactured by ROHM.

・Faster switching and greatly reduced losses can be achieved compared with Si-IGBT power modules.

・Full-SiC power modules continue to evolve, adopting the most advanced third-generation SiC-MOSFETs.

▶Switching Losses in Full-SiC Power Modules

Key Points

・Full-SiC power modules are capable of dramatic cuts in switching losses compared with IGBT modules.

・The difference is particularly stark at higher switching frequencies.

・SiC power modules can perform rapid switching even while greatly reducing losses.

▶Tips for Practical Use: Gate Driving–Part 1

Key Points

・”False gate turn-on” is one issue requiring consideration in relation to gate driving in a full-SiC power module.

・False gate turn-on arises due to the fast dV/dt during high-side switch-on and the low-side parasitic gate capacitance and gate impedance.

▶Tips for Practical Use: Gate Driving–Part 2

Key Points

・Methods for suppressing false gate turn-on include ① setting Vgs to a negative voltage when turned off, ② adding an external capacitor CGS, and ③ adding a mirror clamp MOSFET.

・By optimizing the gate driving of a full-SiC power module, clean operation with still lower losses is possible.

▶Tips for Practical Use: Snubber Capacitors

Key Points

・In order to exploit high-speed switching performance, parasitic inductances in electric wiring must be suppressed insofar as possible.

・Capacitors are connected near power terminals to reduce wiring inductance.

▶ Tips for Practical Use： The Effects of Specialized Gate Drivers and Snubber Modules

Key Points

・Surges and ringing can be dramatically suppressed by using a specialized gate driver and a snubber module.

・Where losses are concerned, there is an increase in Eon and a decrease in Eoff. When comparing overall losses (Eon+Eoff), losses are reduced.

【Download Documents】 Basics of SiC Power Devices

This handbook explains the physical properties and advantages of SiC, the differences in characteristics and usage of SiC Schottky barrier diodes and SiC MOSFETs with a comparison to Si devices, and includes a description of full SiC modules with various advantages.

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