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An n-channel forms from the N + buffer layer covering the N - drift region and the body region to the emitter. The accumulation of electrons near the gate terminal in the body p-region makes the region lose its “P-type character” and become more “N-type”. The electrons form an n-channel in the IGBT Transistor like a power MOSFET. Electrons accumulate under the gate terminal due to the electric field and attractive force of the positive charge. The electric field applies force on the electron upwards. An electric field forms inside the IGBT Transistor from the emitter to the collector. The positive ions gather near the semiconductor region. The capacitance C creates a potential difference across the gate terminal with negative ion accumulation towards the positive gate terminal. When we connect a voltage between the collector and the emitter V CE, the junction J 1, and J 3 becomes forward-biased and J 2 reverse-biased. The silicon dioxide layer behaves like a dielectric medium to generate a potential difference at V GE greater than the threshold voltage V GET. This mode of IGBT operation is known as the cut-off mode. No current flows through collector to emitter as the J 2 junction is reversed biased. Voltage V CE is the output voltage of the IGBT device.

The voltage drop across the emitter and collector terminal is known as V CE. The collector terminal is connected to the positive of the battery and the emitter terminal is connected to the negative. The collector terminal of the IGBT is connected to the emitter terminal through another battery. Voltage V GE is the controlling entity input voltage of the IGBT that controls the output collector current I C. The voltage drop across the emitter and gate terminal is known as VV GE. The emitter terminal is connected to the negative of the battery and the gate terminal is connected to the positive. The gate terminal of the IGBT is connected to the emitter terminal through a battery. But the physical construction of IGBT is similar to an n-channel Power MOSFET with the addition of an injection layer. Power MOSFETs only drive unipolar current in the device. It is because a bipolar current flows through electrons and holes. The structure of an IGBT is similar to a Power MOSFET but its operation resembles a power BJT. IGBT working principles How does an IGBT work? The N - drift region, P-type substrate from the body region, and N + emitter form the NPN transistor.

The P + injection layer, N - drift region, and P-type emitter form the PNP transistor.A junction J 3 forms inside the body structure/substrate in the IGBT Transistor. A junction J 2 forms between the N - drift region and the P-type body region.īody region (substrate): On the top of the P + injection layer and N - drift region, there is a body region comprising of P substrate and N + layers near the emitter terminal of the device. A junction J 1 forms between the P + injection layer and the N + buffer layer for conduction.ĭrain drift region: Just above the N + Buffer layer, there is an N - drift region in the IGBT structure. We can say that a P + layer is added to a Power MOSFET to design an IGBT Transistor.īuffer layer: Just above the P + layer, there is an N + buffer layer to increase the voltage rating of the IGBT Transistor. Injecting layer: The layer closest to the collector terminal is called the P + drain or injection layer. There are four layers in an IGBT Transistor: The space between Gate Terminal G and the other two terminals E and C denotes the insulating layer of Silicon Dioxide.Ī P-Channel IGBT can be made by reversing the doping layers of the device.

While Emitter E (or Source) and Collector C (or Drain) are in direct contact with a metal coating, Gate Terminal G is insulated with a Silicon Dioxide layer that generates a potential difference. The Gate of MOSFET replaces the Base of BJT and acts as the controlling terminal. Other names of IGBT include Insulated Gate Transistor (IGT), Metal Oxide Insulated Gate Transistor (MOSIGT), Conductively Modulated Field Effect Transistor (COMFET), and Gain Modulated Field Effect Transistor (GEMFET). IGBT in power electronics stands for Insulated Gate Bipolar Transistor. IGBT starts conducting when the internal PNP Transistor turns ON the internal MOSFET. The internal four layers P-N-P-N form a MOSFET, a PNP, and an NPN Transistor inside the structure. IGBT provides a low ON state power loss, and high ratings compared to MOSFET and BJT. IGBT (Insulated Gate Bipolar Transistor) is a four-layer three-terminal power semiconductor device that is a functional integration of Power MOSFET and BJT to obtain fast switching and a higher power rating.