The IGBT (Insulated Gate Bipolar Transistor) is a voltage-controlled power semiconductor device that can be thought of as a high-power version of a CMOS transistor. It combines the advantages of both MOSFETs and BJTs, offering high switching frequency, low conduction losses, and high current handling capabilities. IGBTs are widely used in various applications such as inverter air conditioners, induction cookers, microwave ovens, active PFC circuits, and UPS systems in computer power supplies. In industrial settings, they are primarily used for motor drives. Functionally, IGBTs act as circuit switches capable of handling voltages in the tens to hundreds of volts and currents ranging from tens to hundreds of amps.
Electricity has been a revolution in human history, enabling the release of kinetic energy daily. The demand for electricity is as essential as oxygen for life. Without it, human civilization would remain in darkness. Among all components in power electronics, the IGBT plays a crucial role. Without IGBTs, modern conveniences like high-speed rail would not exist.
When it comes to IGBTs, many in the semiconductor industry consider them not just discrete devices but key elements in advanced manufacturing projects, such as China’s “02 Special Project,†which focuses on developing cutting-edge power electronics technology. This technology has largely replaced traditional Power MOSFETs and is now considered the “CPU†of the power electronics industry. Despite its importance, the IGBT product, including chips, is still dominated by a few global companies like Fairchild, Infineon, and Toshiba.
### 1. What is an IGBT?
IGBT stands for Insulated Gate Bipolar Transistor. It is a hybrid device combining the features of a MOSFET and a BJT. While MOSFETs are single-carrier devices with high input impedance and low gate current, BJTs are dual-carrier devices with higher current capacity but higher gate drive requirements. IGBTs combine these characteristics, offering the high input impedance of a MOSFET and the high current capability of a BJT. This makes them ideal for high-voltage and high-current applications such as AC motor drives, inverters, switching power supplies, and lighting circuits above 600V.
### 2. Traditional Power MOSFET
To understand IGBTs, we must first look at Power MOSFETs. These devices are designed to handle high voltages and currents. They are typically structured as LDMOS (Lateral Double Diffusion MOSFETs), where the drain, source, and gate are placed on the surface. However, this design leads to limitations in terms of chip area and parallel connection complexity. Later, VDMOS (Vertical DMOS) was developed, placing the drain on the back of the wafer, allowing better control over the drift region and improving performance for high-power applications.
### 3. Structure and Principle of IGBT
The IGBT structure is similar to a Power MOSFET but includes an additional P+ layer on the back side, known as the injection layer. This allows for the injection of holes during conduction, making the IGBT behave similarly to a BJT. The structure also creates a PNPN thyristor-like configuration, which can lead to latch-up issues if not properly controlled. To mitigate this, an N+ buffer layer is often added between the P+ and N-drift regions, helping to reduce tailing current and improve switching speed.
### 4. IGBT Manufacturing Process
The front-end process of IGBT manufacturing is comparable to standard BCD processes, but the back-end is more complex. Key steps include back-thinning, back-side implantation, cleaning, metallization, and alloying. Each step presents unique challenges, especially when dealing with thin wafers and high-current implants.
### 5. New Technologies in IGBT
Several new technologies have emerged to improve IGBT performance. Field Stop (FS) IGBTs introduce an N+ field stop layer to reduce the drift region thickness, lowering on-resistance and improving efficiency. Shorted-Anode (SA) IGBTs enhance current characteristics by integrating the anode directly into the field stop layer, reducing the need for anti-parallel diodes.
### 6. Main IV Characteristics of IGBT
IGBTs can be modeled as a MOSFET connected in series with a PiN diode or as a Darlington structure. Their IV curve shows a shift due to the forward voltage drop across the P-N junction. Understanding these characteristics is essential for optimizing their use in power conversion systems.
Over the years, IGBT technology has evolved through multiple generations, each introducing improvements in performance, reliability, and cost. From the early prototypes to the latest trench and field-stop designs, IGBTs continue to play a vital role in modern power electronics.
China is currently investing heavily in IGBT technology, aiming to reduce dependence on foreign suppliers. With the growth of renewable energy and electric vehicles, the demand for efficient power conversion systems continues to rise. As a core component in these systems, IGBTs will remain a critical focus for future technological advancements.
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