Power electronic devices based on new materials

Power electronic devices based on new materials

The power electronic devices introduced in the previous articles all use silicon semiconductor materials. However, because traditional silicon-based power electronic devices have approached the theoretical limit that can be reached due to the constraints of parasitic diodes (although this limit has been repeatedly broken with the continuous innovation of device technology), most scholars believe that the potential of relying on silicon devices to continue to improve and improve the performance of power electronic devices and systems is very limited. Therefore, more and more attention is paid to a new type of semiconductor material-wide bandgap semiconductor material.

Among the wide band gap semiconductor materials, silicon carbide (SiC) and gallium nitride (GaN) are the most promising semiconductor materials. They are called third-generation semiconductor materials and can be used in the manufacture of power semiconductor devices. Taking SiC semiconductor material as an example, it has the advantages of large forbidden band width (close to 3 times that of Si), high critical breakdown electric field (10 times that of Si), high thermal conductivity (over 3 times that of Si), and high device limit operating temperature (up to 600°C). It is suitable for the manufacture of new power electronic devices with high voltage and high current, high operating frequency and high temperature environment.

In SiC-type power electronic devices, common ones are SiC Schottky Barrier Diode (SiC SBD), SiC power PiN (SiC PIN) diode, SiC thyristor, SiC Junction Field Effect Transistor (SiC JFET), and SiC Bipolar Junction Transistor (SiC BJT) and so on. Among them, SiC SBD is the first SiC power electronic device to be commercialized. Its outstanding advantages are extremely small reverse leakage current, extremely short reverse recovery time, and can adapt to a working temperature of 300 ℃. It has been used in the national economy and military, etc. The field is widely used. Compared with SIC SBD, SiC PiN diode is more suitable for high voltage field, it has higher breakdown voltage and low reverse leakage current. At the same time, compared with silicon power diodes, the reverse recovery time of SiC PiN diodes is significantly reduced, and switching losses are reduced.

Because SiC material has the characteristics of higher critical breakdown voltage, higher carrier drift rate and thermal conductivity than Si, thyristors made of SiC have greater performance advantages than Si-based devices. The conduction path of the SiC thyristor largely depends on the width of the withstand voltage (such as the breakdown voltage Vb) of the base region. Figure 1a shows the structure of a P+NPN 4H-SiC thyristor device with a breakdown voltage Vb of 400V, and Figure 1b is a cross-sectional view of the structure of a 2.6kV thyristor.

Power electronic devices based on new materials
Figure 1 – The structure of SiC thyristors with different breakdown voltage levels

Figure 2 shows the volt-ampere characteristics of 2.6kV4H-SiC at different temperatures. It can be seen from the figure that even when the current density reaches several hundred A/cm2, the forward voltage drop of the SiC thyristor is still very small and has a negative temperature coefficient.

Power electronic devices based on new materials
Figure 2 – Volt-ampere characteristics of 2.6kV 4H-SiC thyristor at different temperatures

In addition, compared with Si power MOSFET, SiC power MOSFET has the advantages of low on-resistance, fast switching speed, good gate insulation, high stability, high temperature resistance, and strong working ability, and has received extensive attention from the industry. SiC JFET is a voltage-controlled unipolar device. It has the advantages of fast switching speed, high input impedance, good high-temperature characteristics, and mature preparation technology. It has become one of the fastest growing SiC power devices in recent years and has been commercialized. SiC BJT is a current control device made of SiC material. It has almost no forward bias damage. However, the low current gain (usually <30) of SiC BJT devices limits its application range.

In addition to SiC devices, GaN devices are also typical representatives of wide bandgap power devices. Common GaN devices include GaN transistors and GaN diodes. GN transistors are similar to Si MOSFETs, and can be divided into depletion type and enhancement type according to the different formation mechanism of the conductive channel. GaN diodes have excellent characteristics such as high voltage resistance, high temperature resistance, and low on-resistance, which makes it widely used in power electronics and other fields.

Due to the continuous development of new wide-bandgap semiconductor materials such as SiC and GaN, it is expected that within a few years, power electronic devices using SiC and GaN materials will be widely used in power electronic equipment known for energy saving.