Insulated gate bipolar transistor (IGBT) is a widely used semiconductor device in the field of power electronics, which combines the advantages of metal oxide semiconductor field-effect transistor (MOSFET) and bipolar junction transistor (BJT), and has the characteristics of high input impedance and low on voltage drop. Despite the increasing application of wide bandgap semiconductors such as SiC and GaN, before the rise of these new technologies, IGBT had already become an ideal choice for many high-power applications due to its high efficiency and reliability, and is still suitable for various application scenarios.

This article will provide an in-depth interpretation of device structure, loss calculation, parallel design, reliability testing, and other key knowledge points of IGBT, providing a one-stop solution for everyone.

IGBT device structure

IGBT is a power semiconductor transistor composed of four alternating layers (P-N-P-N), controlled by the voltage applied to the gate of metal oxide semiconductor (MOS). After gradual adjustment and optimization, this basic structure can reduce switch losses and achieve thinner device thickness. The IGBT developed by onsemi combines trench gate with field stop structure, aiming to suppress inherent parasitic NPN behavior. This method helps reduce the saturation voltage and on resistance of the device, thereby improving overall power density.

Figure 1: Trench Field Cut off IGBT Structure

IGBT loss calculation

Accurate calculation of losses is crucial for IGBT to operate efficiently in the system! The losses of IGBT can be decomposed into conduction losses and switch (on and off) losses, while diode losses include conduction and off losses. Accurately measuring these losses typically requires the use of an oscilloscope to monitor the waveform during device operation through voltage and current probes. Measuring energy requires the use of mathematical functions. After determining the total energy of a switching cycle, the power consumption can be obtained by dividing it by the switching cycle time.

IGBT parallel design

Facing loads of tens or even hundreds of kilowatts, a single IGBT device is often unable to handle them, and in this case, "parallel design" has become the core solution for high-power systems. Parallel devices can be discrete packaged devices or bare chips assembled in modules. This design can not only achieve higher rated current and improve heat dissipation, but also achieve system redundancy. It should be noted that process and layout changes between components can affect the static and dynamic current distribution of parallel devices. System design engineers need to understand these in order to design reliable systems. Therefore, system design engineers need to focus on these key points: static changes, dynamic changes, thermal coefficient, gate resistance, empirical data, etc.

IGBT reliability

As the "core component" of power electronic systems, the reliability of IGBT is crucial for ensuring the safe operation of the entire system. IGBT needs to undergo a series of extensive reliability tests to verify consistency, which aim to accelerate the fault mechanisms encountered in practical applications and ensure satisfactory reliability performance in "real-world" applications.

The reliability tests routinely conducted on IGBTs include: high temperature reverse bias (HTRB), high temperature gate bias (HTGB), high temperature storage life (HTSL) test, high humidity high temperature reverse bias (H3TRB), high acceleration stress free test (UHAST), intermittent operating life (IOL), temperature cycling (TC), low temperature storage life (LTSL) test, steady-state operating life (SSOL) test, etc.

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