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IGBT Module: Structure,Working Principle,Pros and Cons

IGBT Module

IGBT Module Introduce

An Insulated Gate Bipolar Transistor (IGBT) module is a sub-type of transistor that is commonly used in power electronics applications such as inverter and converter systems. It has the output switching and conduction characteristics of a bipolar junction transistor (BJT), but with the simple gate-drive characteristics of a MOSFET (Metal Oxide Semiconductor Field-Effect Transistor).

The IGBT is designed to turn on and off rapidly (in the microseconds or faster range) to handle high voltage and high current. The ‘insulated gate’ refers to the voltage-controlled input, which is physically separated from the other parts of the transistor by an insulating layer—this separation enables the transistor to handle high energies without damage or interference.

These properties make IGBTs common in appliances and industrial equipment, like motor drivers, induction heating systems, switched-mode power supplies, electric vehicles, and trains. The IGBT modules often include several IGBT devices, diodes and driving circuits together in a single compact package, which can be easier to use than discrete IGBTs.

Type of IGBT Module

Difference IGBT Module
Different types of IGBT modules

IGBT modules can be classified into different types based on several factors such as circuit configuration, power rating, switching speed, etc. A few common types include:

  • Standard Modules: These are the most basic IGBT modules and are usually available in a variety of voltage and current ratings. They are found in many commonplace applications such as AC and DC motor drives, induction heating systems, etc.
  • PIM (Power Integrated Module): These modules integrate several different components into one package, such as IGBTs, diodes, and possibly other components, depending on the specific module. They provide higher density and simplify system design.
  • IPM (Intelligent Power Module): These modules go a step further than the PIM modules by incorporating not just power components, but also control circuits to handle tasks such as signal processing, protection functions, and system control. They are meant to function as a complete, standalone power electronics system.
  • NH/HP (Neutral Point Clamped / Half Bridge) IGBT Modules: These modules are designed for specific applications like three-level inverter systems. They can be used to achieve greater efficiency and better power factor correction than standard two-level inverters.
  • Six-Pack Configuration Module: This is an IGBT module that is built with the equivalent of six IGBT transistors. They are arranged in a three-phase bridge configuration which is commonly used in motor control applications.

Each type of module is designed to optimize certain factors, such as power density, ease of use, or system control capabilities, and the best one for a given application will depend on the specific needs of that application.

IGBT Structure

The following diagram shows the structure of an N-channel enhancement type Insulated Gate Bipolar Transistor (IGBT). The N+ region is called the source region, and the electrode attached to it is called the source electrode. The other N+ region is known as the drain area. The control area of the device is the gate region, and the electrode attached to it is called the gate electrode. The channel is formed close to the boundary of the gate area.

Structure of IGBT
Structure of IGBT(Image Source:electricaltechnology.org)

Between the drain and source there is a study-type region (including both P+ and P- region) where the channel is formed, commonly referred to as the subchannel region. The P+ region on the other side of the drain is known as the drain injector. This is a unique functional area of IGBT, and, along with the drain area and the subchannel region, forms a PNP Bipolar Junction Transistor (BJT). It plays the role of an emitter, injecting holes to the drain electrode to conduct modulation conduction, reducing the on-state voltage of the device. The electrode attached to the drain-injecting region is known as the drain electrode.

The switching operation of an IGBT is performed by applying a positive gate voltage to form a channel, providing a base current for the PNP transistor, causing the IGBT to turn on. Conversely, by applying a reverse gate voltage, the channel is eliminated, letting the reverse base current flow, making the IGBT turn off. The driving method of the IGBT and MOSFET are basically the same, requiring only control of the input electrode of the N-type MOSFET channel, so it has high input impedance characteristics. After the channel of the MOSFET is formed, holes injected from the P+ base to the N-layer (minority carriers) can modulate the conduction of the N-layer. This reduces the resistance of the N-layer, enabling the IGBT to maintain a low on-state voltage even at high voltages.

IGBT module internal circuit diagram
IGBT module internal circuit diagram

Recommended reading:IGBT basic know how – Infineon Technologies

Working Principle of IGBT

N-channel IGBTs work by applying a threshold voltage VTH (positive) between the gate and emitter electrodes, forming an inversion layer (channel) on the p-layer directly under the gate electrode, and injecting electrons from the n- layer under the emitter electrode. This electron is the minority carrier of the p+n-p transistor, and holes start to flow from the collector substrate p+ layer, performing conductivity modulation (bipolar operation), so the saturation voltage between the collector and emitter can be reduced. An n+pn- parasitic transistor is formed on the emitter electrode side. If the n+pn- parasitic transistor operates, it becomes a p+n- pn+ thyristor. The current continues to flow until the current supply on the output side is stopped. The control cannot be performed by the output signal. This state is generally called lockout.

IGBT Working Principle Diagram
Working Principle Diagram(Image Source:techweb.rohm.com)

IGBT suppresses the operation of the n+pn- parasitic transistor by minimizing the current gain factor α of the p+n-p transistor as a lockout control measure. Specifically, the current gain factor α of p+n-p is designed to be below 0.5. The lockout current IL of IGBT is more than 3 times the rated current (DC). The driving principle of IGBT is essentially identical to that of power MOSFET, and the turn-on and turn-off are determined by gate-emitter voltage uGE.

Conduction

The structure of the IGBT silicon chip is very similar to the structure of the power MOSFET. The main difference is that the IGBT adds a P+ substrate and an N+ buffer layer (NPT-non-punch through- IGBT technology does not add this part), where one MOSFET drives two bipolar devices. Applying the substrate creates a J1 junction between the P+ and N+ areas of the tube. When a positive gate bias causes the inversion of the P base area under the gate, an N channel forms, an electron current appears, and a current is generated entirely in the manner of a power MOSFET. If the voltage generated by this electron flow is within the range of 0.7V, J1 will be forward biased, some holes are injected into the N- area, and the resistivity between the cathode and anode is adjusted, reducing the total power conduction losses and initiating a second stream of charge. The final result is the appearance of two different current topologies within the semiconductor layer: an electron current (MOSFET current); hole current (bipolar). When uGE is greater than the opening voltage UGE(th), a channel forms inside the MOSFET, providing base current for the transistor, IGBT conducts.

Conductance Voltage Drop

The conductivity modulation effect reduces the resistance RN and reduces the on-state voltage drop.

Turn-off

When a negative bias or gate voltage below the threshold is applied to the gate, the channel is prohibited and no holes are injected into the N- area. In any case, if the MOSFET current is rapidly decreased during the switching phase, the collector current is gradually decreased, because after the commutation starts, there are still a few minority carriers (minority carriers) in the N layer. The reduction of this residual current value (tail current) depends entirely on the density of the charge at shutdown, and the density is related to several factors, such as the number and topology of impurities, layer thickness, and temperature. The decay of the minority carrier causes the collector current to have a characteristic tail current waveform, and the collector current causes the following problems: increased power consumption; cross-conduction problems, especially in devices using freewheeling diodes, the problem is more obvious.

Given that the tail current is related to the recombination of the minority carrier, the current value of the tail current should be closely related to the temperature of the chip, IC and VCE closely related hole mobility. Therefore, it is feasible to reduce the undesirable effects of this action on the current in the end device design according to the temperature reached, and the tail current characteristics are related to VCE, IC, and TC. When a reverse voltage or no signal is applied between the gate and the emitter, the channel inside the MOSFET disappears, and the base current of the transistor is cut off, and the IGBT is turned off.

Reverse Blocking

When a reverse voltage is applied to the collector, J1 is controlled by a reverse bias, and the depletion layer expands towards the N- area. Due to excessively reducing the thickness of this level, an effective blocking ability cannot be obtained, so this mechanism is very important. On the other hand, if this area size is excessively increased, the voltage drop will continuously increase.

Forward Blocking

When the gate and emitter are shorted and a positive voltage is applied to the collector terminal, the P/N junction J3 is controlled by a reverse voltage. At this time, the depletion layer in the N-drift region is still bearing the voltage externally applied.

Latch-up

There is a parasitic PNPN thyristor between the collector and emitter of the IGBT. Under special conditions, this parasitic device can conduct. This phenomenon increases the amount of current between the collector and emitter, reduces the control ability of the equivalent MOSFET, and usually causes device breakdown problems as well. The conduction phenomenon of the thyristor is called the IGBT latch-up. Specifically, the causes of this defect are different and are closely related to the state of the device. Under normal circumstances, static and dynamic latch-ups have the following main differences:

Static latch-up occurs when the thyristor is fully on.

Dynamic latch-up only occurs during turn-off. This special phenomenon severely limits the safe operation area.

To prevent the adverse effects of the parasitic NPN and PNP transistors, the following measures need to be taken: first, prevent the NPN part from turning on, and change the layout and doping level respectively. The second is to reduce the total current gain of the NPN and PNP transistors.

In addition, the latch-up current has a certain influence on the current gain of PNP and NPN devices. Therefore, it is closely related to the junction temperature; as the junction temperature and gain increase, the resistivity of the P-base region will increase and disrupt the overall characteristics. Therefore, device manufacturers must pay attention to maintaining a certain proportion between the maximum collector current value and the latch-up current, usually a ratio of 1:5.

Recommended reading:Principles of Operation of IGBTs

Advantages and Disadvantages of IGBT

IGBT (Insulated Gate Bipolar Transistor) modules offer several advantages but also have some disadvantages:

Advantages:

  • High Power Efficiency: IGBT modules are known for their power efficiency, which can handle high current and high voltage.
  • Fast Switching Times: They have rapid switching times, which makes them suitable for many applications, including those requiring high-frequency switching.
  • Ease of Operation: Due to their insulated gate, IGBT modules can be easily driven on or off by a voltage signal at the gate, similar to MOSFETs.
  • Thermal Stability: They typically have better thermal stability than comparable power electronic devices.
  • Integrated Design: An IGBT module integrates several IGBTs and freewheeling diodes in one package, simplifying circuit design and enhancing reliability.

Disadvantages:

  • Switching Speed: While IGBT modules can switch quickly, the speed is not as fast as some other power electronic devices, such as MOSFETs or newer wide bandgap devices like SiC or GaN transistors.
  • Conduction Losses: While they offer excellent efficiency, there is still some energy loss during the conduction phase.
  • Complex Drive Circuits: The gate drive circuits for IGBT modules can be complex and require proper design to ensure stable operation and prevent destructive failures due to improper gate voltage levels.
  • Cost: High-end IGBT modules, especially those intended for high power operations, can be costly.

In summary, while IGBTs have some significant advantages that make them a preferred choice for various power electronics applications, they do have a few disadvantages that can limit their usage in certain scenarios. It’s essential to understand these qualities to make an informed decision when designing an electronic system.

Application of IGBT modules

Insulated Gate Bipolar Transistor (IGBT) modules are applicable in various fields due to their features like high input impedance, high voltage and current capabilities, and high efficiency. Here are a few important applications:

  • Motor Drives and Control: IGBT modules are extensively employed in variable speed motor drives. They can run electric motors more efficiently and have the ability for speed and torque control, making them useful for applications like electric vehicles, home appliances, and industrial machines.
  • Power Supplies: IGBT modules are used in Uninterruptible Power Supplies (UPS) and Switch Mode Power Supplies (SMPS) due to their high-efficiency operation. They ensure reliable performance even under changing load conditions.
  • Renewable Energy Systems: IGBTs are used in the inverters of renewable energy systems like wind turbines and solar panels to convert DC power into AC.
  • Electric Vehicles (EVs): IGBT modules are being used extensively in EVs and hybrid cars for the motor control in traction. The battery DC power is usually converted to AC for the motor, which requires high-efficiency power electronic converters where IGBTs are invaluable.
  • Heaters and Induction Heating: Fast switching and good control of IGBT modules make them ideal for induction heating equipment and electric heaters.
  • Consumer Electronics: TV sets, air conditioners, and other appliances may employ IGBT modules for efficient operation and energy saving.
  • Railway Traction: IGBT modules help convert the electrical power efficiently for use in electric locomotives.
  • Audio Amplifiers: IGBTs are also used in Class D audio amplifiers where they enable high efficiency, reducing heat and increasing reliability.

Future development trend of IGBT Module

Infineon's latest series of IGBT modules
Infineon’s latest series of IGBT modules

The future development trends of IGBT (Insulated Gate Bipolar Transistor) modules are likely to focus on several key areas:

  1. Material Advancements: Continued research into materials like Silicon Carbide (SiC) and Gallium Nitride (GaN) could lead to IGBT modules that are more efficient, have higher thermal conductivity, and offer better performance at high frequencies and temperatures.
  2. Integration and Miniaturization: There will be a push towards integrating more functionality into smaller packages. This includes integrating drivers and protective circuitry directly with the IGBT modules to reduce size, improve reliability, and decrease system complexity.
  3. Improved Efficiency: Efforts to improve the efficiency of IGBT modules will continue, reducing losses and improving performance in applications such as inverters for renewable energy systems and electric vehicle powertrains.
  4. Enhanced Thermal Management: As power densities increase, managing heat effectively becomes more critical. Advances in module design and materials that improve heat dissipation will be a focus area.
  5. Smart Features: Incorporation of sensors and connectivity within IGBT modules to enable real-time monitoring, diagnostics, and control, enhancing the smart grid capabilities and predictive maintenance strategies.

These trends will help drive the adoption of IGBT modules in new and existing markets, particularly where efficiency and high power handling are critical.

Conclusion

In conclusion, the Insulated Gate Bipolar Transistor (IGBT) has proven itself as a remarkably efficient and reliable device in the realm of power electronics. Its unique blend of features from MOSFETs and BJTs, combined with increasingly innovative designs, has paved the way for its usage in a broad array of applications, from electric vehicles and renewable energy systems to industrial use, and beyond. As research and development continue, future IGBT technology, potentially incorporating advanced materials and new designs, promises even more robust circuit integration, superior performance, and broader application scope. However, the field of power electronics remains highly dynamic, and the interactions between IGBT and competing technologies, like silicon carbide (SiC) and gallium nitride (GaN) devices, will undoubtedly shape the landscape of future developments.

Frequently Asked Questions (FAQs)

What does an IGBT module do?

An Insulated Gate Bipolar Transistor (IGBT) module is a device that’s used in power electronics mainly for switching applications. It functions as a switch to control electrical power and allows voltage and current to move in a particular desired way. It is often used in electric vehicles, inverters, power supplies, and other high power applications.

Why is IGBT module very popular nowadays?

IGBT modules are popular because they provide high power efficiency and fast switching in applications like electric vehicles, renewable energy systems, and motor drives. They’re also versatile, handle heat well, and have integrated design, simplifying system design and enhancing performance. The demand for such power electronic devices is growing with the push for more sustainable technologies.

What is the difference between IGBT and IGBT module?

An IGBT refers to the single semiconductor device, the Insulated Gate Bipolar Transistor itself. On the other hand, an IGBT module is an assembly that contains one or several IGBTs packaged together with other components such as diodes, capacitors, and other passive elements. These modules also often include driving, protection and snubber circuits.

The IGBT module is designed for easy installation into a system without the need to worry about the complexities of the IGBT’s internal design and driving. This makes them convenient for high-power applications since manufacturers can design the modules to handle their specific power and voltage requirements. A module might also offer improved performance through optimized thermal management or integrated drive circuitry.

What is the full name of IGBT Module?

The full name of an IGBT Module is “Insulated Gate Bipolar Transistor Module”.

References:

[1]IGBT – Working, Types, Structure, Operation & Applications. Available from:

https://www.electricaltechnology.org/2021/08/igbt.html

[2]Principles of Operation of IGBTs. Available from:

https://techweb.rohm.com/product/power-device/igbt/11646/

[3]IGBT basic know how – Infineon Technologies. Available from:

https://www.infineon.com/dgdl/Infineon-IGBT_basics_how_does_an_IGBT_work-AdditionalTechnicalInformation-v01_00-EN.pdf?fileId=5546d462700c0ae60170675ed665777f&da=t

[4]What is gallium nitride and GaN power semiconductors? Available from:

https://gansystems.com/gallium-nitride-semiconductor/

[5]What Is Silicon Carbide (SiC)? Uses & How It’s made. Available from:

https://www.arrow.com/en/research-and-events/articles/silicon-carbide-the-future-of-power

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About Jason

Jason Lin is a distinguished electrical engineer and seasoned technical writer with extensive experience in power electronics. He holds both bachelor's and master's degrees in Electrical and Computer Engineering from Xi'an Jiaotong University. Previously, he served as a Senior Electrical Engineer at BYD Company, specializing in the development of Insulated Gate Bipolar Transistor (IGBT) modules and integrated circuit chips. His commitment to innovation and excellence has significantly contributed to advancements in the field of electrical engineering, earning him the trust and respect of industry professionals.

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