IGBT And Super Junction MOSFET Are Both Advanced Power Semiconductor Devices

 Introduction

IGBT - Structure and Working
An IGBT is a three-terminal power semiconductor device that combines thesimple gate-drive characteristics of the IGBT And Super Junction MOSFET  with the high-current and low-saturation-voltage capability of bipolar junction transistors (BJTs). The basic structure of an IGBT consists of an insulated gate field-effect transistor (MOSFET) and a bipolar junction transistor (BJT) fabricated in a common-emitterconfiguration.

When a positive voltage is applied to the gate terminal with respect to the emitter, the MOSFET gate forms an N-channel between the source and drain. This allows the device to conduct when the gate–source voltage (VGS) exceeds the device's threshold voltage (VTH). Similar to a MOSFET, the current flowing in the channel is directly controlled by the gate. However, unlike a MOSFET, an IGBT utilizes the injection of minority charge carriers to sustain the main current in the channel. When the IGBT is forward biased, holes are injected from the p-type body into the n-type drift region, which sustains the main current flow. This provides a conducting path between the collector and emitter even when the gate signal is removed.

IGBT Characteristics and Applications
Some key characteristics of IGBTs are high input impedance, reduced switching losses, elimination of minority carrier storage time and improved conduction losses compared to BJT. Due to these advantages, IGBTs are widely used in high-power applications such as adjustable-speed motor drives, electric vehicles, solar inverters, wind turbines and uninterruptible power supplies (UPS).

Compared to other power devices, IGBTs have become popular for medium to high power applications rated between 100 W to 6300 W. They provide designers greater design flexibility, reduced component count and size and easier drive requirements than BJTs. Popular automotive applications include starter motors, electric power steering, lighting systems and fuel injection systems. IGBTs are also increasingly been used in photovoltaic and wind generation systems as the main building blocks for efficient solar inverters and wind turbine drive train circuits.

Super Junction MOSFET - Structure and Performance Improvement
Traditional MOSFETs face challenges related to high on-resistance (Ron) for high-voltage applications. Super Junction (SJ) MOSFETs address this issue through a novel highly doped periodic multi-layer structure where n-pillars are alternately connected to either the source or the substrate. This forms a charge-balanced periodic structure that allows very high doping concentrations without increasing leakage current.

The key to achieving high breakdown voltage while maintaining low on-resistance is in the formation of multiple P/N junctions connected in parallel. This results in an optimal tradeoff between operating voltage and on-resistance. SJ MOSFETs have significantly reduced specific on-resistance (Rons) compared to conventional planar MOSFETs, enabling operation at much higher voltages. For example, a 600 V SJ MOSFET can provide 70% lower Rons compared to a conventional MOSFET.

Super Junction MOSFET Characteristics and Applications
Some key characteristics of SJ MOSFETs are simpler gate drive requirements compared to IGBTs,zero reverse recovery losses, lower switching losses and higher switching frequencies. These advantages have made SJ MOSFETs a popular choice for DC-DC converter, point-of-load converter, server/telecom power supply, solar micro-inverter, induction heating and motor control applications in the 25 V to 600 V range.

Compared to IGBTs, SJ MOSFETs provide faster switching speeds, higher efficiencies at light loads and better thermal performance due to lower RDS(on). Their zero reverse recovery also eliminates associated switching losses. As power systems move to higher switching frequencies for size and efficiency benefits, SJ MOSFETs are able to fully leverage this trend with their fast switching capabilities. SJ MOSFETs also replace IGBTs in applications below 100 W due to their simpler drive requirements.

IGBT vs Super Junction MOSFET
Both IGBTs and Super Junction MOSFETs have their own relative advantages for power electronics applications:

- IGBTs are preferred for medium-high power applications above 100 W due to their high current handling capability and simpler drive requirements compared to MOSFETs. However, they have higher switching losses.

- SJ MOSFETs provide zero reverse recovery, lower switching losses and faster switching over IGBTs. They are suitable for power levels below 100 W and higher switching frequency applications.

- IGBTs have higher conduction losses compared to SJ MOSFETs due to the injection of minority carriers. SJ MOSFETs conduct majority carriers only.

- SJ MOSFET drivers require gate voltage overshoot to fully enhance the MOSFET channel during switching transitions. IGBTs have simpler gate drives.

- IGBTs have higher current saturation levels than MOSFETs enabling very high power capabilities up to 6300 W.

In summary, IGBTs are preferred for medium-high power applications above 100 W where conduction losses dominate, while SJ MOSFETs are becoming increasingly popular for power levels below 100 W and higher frequency applications where switching losses take precedence. Application requirements along with power ratings are key factors in selecting between these two important power semiconductor devices.