IGBT (insulated gate bipolar transistor) knowledge points review

Author | Beiwan Nanxiang

IGBT , full name Insulated Gate Bipolar Transistor, is a semiconductor device widely used in switching control. It combines the high switching speed and high impedance characteristics of MOSFETs with the high gain and low saturation voltage advantages of BJTs. This unique combination makes the IGBT a highly efficient voltage-controlled semiconductor that can achieve large current flow between the collector and the emitter under extremely low gate current drive.

Although the IGBT relies on MOSFETs for control, exhibiting voltage-controlled characteristics similar to standard MOSFETs, it also retains the output transfer characteristics of a BJT. This exceptional combination of properties makes IGBTs a key component in a variety of electronic and power systems, especially where high efficiency and high-performance switching are required.

IGBT, as an advanced semiconductor device, has three key terminals: emitter, collector and gate. Each terminal is equipped with a metal layer, and the metal layer of the gate terminal is covered with a layer of silicon dioxide, which is one of its unique structural features.

From a structural point of view, the inverter IGBT is a complex four-layer semiconductor device, which forms a unique PNPN arrangement by cleverly combining PNP and NPN transistors.

This structural design not only gives the IGBT efficient switching performance, but also makes it excellent in voltage blocking capabilities.

Specifically, the structure of the IGBT starts from the collector side, closest to the (p+) substrate, also called the injection region. Above the injection region is the N drift region, which contains the N layer. The main function of this region is to allow most carriers (hole current) to be injected from (p+) to the N- layer. The thickness of the N-drift region is crucial in determining the voltage blocking capability of the IGBT.

Above the N drift region is the body region, which is composed of the (p) substrate and is close to the emitter. Inside the body region, there is an (n+) layer. The connection point between the injection region and the N-drift region is called the J2 junction, while the connection point between the N region and the body region is the J1 junction.

It is worth noting that the structure of the inverter IGBT is topologically similar to the MOS gated thyristor, but there are significant differences in operation and functionality. Compared to thyristors, IGBTs are more flexible in operation because they only allow transistor operation throughout the entire device operating range, without the need to wait for rapid switching at zero crossing like thyristors. This characteristic makes IGBT more popular in applications such as inverters because it can provide more efficient and reliable switching performance.

An insulated gate bipolar transistor (IGBT) is an advanced semiconductor device that combines the characteristics of a MOSFET and a bipolar transistor (BJT). It takes advantage of the high switching speed of MOSFETs and the low saturation voltage characteristics of BJTs to create a transistor that can both switch quickly and handle large currents. The term "insulated gate" of IGBT reflects that it inherits the high input impedance characteristics of MOSFET. It is also a voltage-controlled device, which is also similar to MOSFET. The term "bipolar transistor" indicates that IGBT also incorporates the output characteristics of BJT.

In the equivalent circuit of an IGBT, you can see that it combines an N-channel MOSFET and a PNP transistor. The N-channel MOSFET is responsible for driving the PNP transistor, where the gate comes from the MOSFET, and the collector and emitter come from the PNP transistor. In a PNP transistor, the collector and emitter form a conduction path that conducts and carries current when the IGBT is switched to the on state.

For a BJT, the gain is calculated by dividing the output current by the input current, expressed as Beta (β): β = output current/input current. However, the MOSFET is a voltage-controlled device whose gate is isolated from the current conduction path, so the gain of the MOSFET is the ratio of the change in output voltage to the change in input voltage. This characteristic also applies to IGBTs, whose gain is the ratio of the change in output current to the change in input gate voltage. Due to the high current capability of the IGBT, the high current of the BJT is actually controlled by the gate voltage of the MOSFET.

The symbol of IGBT includes the collector-emitter part of the transistor and the gate part of the MOSFET. When the IGBT is in conduction or switching "on" mode, current flows from the collector to the emitter. In IGBT, the voltage difference from gate to emitter is called Vge, while the voltage difference from collector to emitter is called Vce. Since the current flow in collector and emitter is relatively the same: Ie=Ic, Vce is very low.

The following are some mathematical formulas for IGBTs. These equations and parameters are fundamental to the analysis and design of circuits containing IGBTs.

1. Collector current (Ic):

   
   

Collector current is the current flowing from the collector to the emitter of the IGBT. It can also be determined using Ohm's law. Here, Vce represents the collector-emitter voltage and Rl is the load resistance. ?????????=?????????/???????

2. Gate current (Ig):

Gate current is the current required to activate or deactivate the IGBT. It can be calculated using gate voltage and gate-source capacitance (Cgs): ?????????=????????????⋅???????????? ????/???????, where dVgs/dt is the rate of change of the gate-source voltage over time.

3. Switching loss (Ps):

Switching losses in IGBTs come from energy dissipation during turn-on and turn-off transitions. These losses are determined by the following formula: ????????=0.5⋅????????????⋅??????????⋅????????? ???⋅(????????????+????????????????)

where Vce is the collector-emitter voltage, Ic is the collector current, fsw is the switching frequency, and Eon and Eoff are the turn-on and turn-off energy.

4. Forward voltage drop (Vf):

The forward voltage drop is the voltage of the IGBT in the on-state, and Vce(sat) represents the saturation voltage: ?????????=????????????+?????? ??????(????????????)

5. Power dissipation (Pd):

It is calculated by the mentioned formula, where Vce is the collector-emitter voltage and Ic is the collector current. ?????????=????????????⋅?????????

6. Gate charge (Qg):

Gate charge is the total charge required to switch the IGBT from off to on. It is related to the gate current and gate-source voltage: Qg=∫(Igdt) where Ig is the gate current and the integration is performed over the entire switching time.

7. Junction temperature (Tj):

The junction temperature of an IGBT can be estimated by considering power dissipation and thermal resistance. Here Ta is the ambient temperature, Pd is the power dissipation, and Rth is the thermal resistance. ?????????=?????????+(???????⋅???????ℎ)

The insulated gate bipolar transistor (IGBT) is a voltage controlled device whose operating principle is similar to that of a MOSFET. In IGBT, only a small voltage is applied to the gate terminal to start the conduction process of current. This design allows the IGBT to control the flow of current efficiently.

A key characteristic of an IGBT is that it can switch current from collector to emitter, but this process can only occur in one direction, forward switching. This unidirectional conduction characteristic makes IGBTs very useful in circuits where precise control of the direction of current flow is required.

In an actual IGBT switching circuit, a small voltage is usually applied to the gate to control the flow of current. For example, in a motor control circuit, an IGBT can be used to switch current from a positive voltage source to the motor. In order to protect the circuit and motor, a resistor is usually included in the circuit to control the current flowing through the motor to prevent excessive current from damaging the equipment.

This design not only improves the efficiency and reliability of the circuit, but also makes IGBTs a key component in power electronics applications, especially in motor control and power conversion systems. By precisely controlling the gate voltage of the IGBT, efficient and precise control of the current can be achieved, thereby optimizing the performance of the entire system.

The figure below shows the input characteristics of IGBT. It is the graph between the voltage applied on the gate pin and the current flowing through the collector pin.

Initially, when no voltage is applied to the gate pin, the IGBT is off and no current flows through the collector pin. When the voltage applied to the gate pin exceeds the threshold voltage, the inverter IGBT starts conducting and the collector current IC starts flowing between the collector and emitter. The increase in collector current relative to gate voltage is shown in the figure below.

In the image above, the transmission characteristics of the IGBT are shown. It is almost the same as PMOSFET. When Vge (gate-emitter voltage) is greater than the threshold specified by the IGBT specification, the IGBT will enter the "on" state.

When no voltage is applied to the gate pin, no current flows through the IGBT. In this case, the transistor will remain off. However, when a voltage is applied across the gate terminal, the current remains zero for some time. When the voltage exceeds the threshold voltage, the device will begin to conduct and current will flow from the collector to the emitter terminal.

When the gate-emitter voltage (VGE) is less than the threshold voltage (VGE(th)), the IGBT is in the off state and the collector current (IC) is close to zero. As VGE increases and exceeds VGE(th), the IGBT starts to conduct and IC increases accordingly. At VGE(sat), the IGBT enters the saturation state, and the IC does not increase much because the transconductance of the IGBT (the slope of the output characteristic line) will decrease.

The input characteristic curve of an IGBT usually shows the switching behavior of the device, including its input impedance and how the collector current is controlled by changing the gate voltage. These characteristics are crucial for designing IGBT drive circuits and predicting their behavior under different load conditions.

The startup process follows these steps:

1. No gate voltage: When there is no voltage on the gate pin of the IGBT, the IGBT does not conduct and no current flows between the collector and emitter.

2. Apply gate voltage: When a positive voltage is applied to the gate pin, but this voltage is lower than the threshold voltage of the IGBT, the IGBT still does not conduct and the collector current (IC) remains zero.

3. Exceeding the threshold voltage: Once the gate voltage reaches or exceeds the threshold voltage of the IGBT, the channel of the IGBT begins to form, and the charge carriers (electrons) under the gate begin to accumulate, forming a conductive channel.

4. Current begins to flow: As the gate voltage increases, the resistance of the conductive channel decreases, the collector current (IC) begins to flow, and the IGBT enters the conductive state.

5. Maintain the on-state: In order to keep the IGBT on, the gate voltage needs to be maintained above the threshold voltage. If the gate voltage drops below the threshold, the IGBT will turn off and collector current will stop flowing.

A simple understanding is: initially, when no voltage is applied to the gate pin, the IGBT is in an off state and no current flows through the collector pin. When the voltage applied to the gate pin exceeds the threshold voltage, the IGBT starts conducting and the collector current IG starts flowing between the collector and emitter. The collector current increases as the gate voltage increases as shown in the figure below.

This property of the IGBT makes it a very flexible power electronic switch capable of controlling the flow of high currents at low gate drive currents. When designing the IGBT drive circuit, it is necessary to ensure that the gate drive voltage is sufficient to exceed the threshold voltage to ensure reliable conduction of the IGBT. At the same time, the design of the gate drive circuit also needs to be considered to avoid unnecessary voltage spikes or current surges during the switching process, which may affect the performance and life of the IGBT. The control of gate voltage is crucial to the switching operation of IGBT. It allows the use of a small gate current to control a relatively large collector current, which is one of the reasons why IGBT is widely used in high-power applications.

The current and voltage characteristics of IGBT have three main stages: cut-off region, active region and saturation region. The other two stages are avalanche breakdown and reverse breakdown.

In the figure above, the blue line represents the transmission characteristics of the IGBT. The transfer characteristics express the relationship between the collector current IC and the emitter gate voltage VGE. The trajectory of the cut-off voltage is VGE, at which the IGBT can flow the maximum collector current.

1. Cutoff

Initially, when no voltage is applied to the gate, no collector current flows in the IGBT and the transistor is in the off state. When a voltage is applied to the gate terminal but below the threshold voltage, the IGBT remains in the off state, but there is a small forward leakage current. In both cases, the device is considered to be in the cut-off region.

2.Activity area active

When the gate-emitter voltage (VGE) increases to exceed the threshold voltage, the device enters the active region and starts to conduct. In the active region, the IGBT has a low input voltage drop and the output current starts to increase.

3. Saturation Region

As we all know, IGBT only conducts current in one direction, so after a period of time, the collector current will reach a maximum level. With different voltage levels of VGE, the collector current continues to rise, as shown in the figure below. This stage is called the saturation state, or the IGBT is now fully turned on and conducting. Therefore, this region is also called the ohmic region.

4. Avalanche Breakdown

If the applied voltage VCE exceeds a certain limit, the IGBT will experience avalanche breakdown. When VCE becomes very large, junction J1 can no longer provide resistance or block current, and the IGBT will break down and turn on indefinitely.

5. Reverse Breakdown

With a reverse voltage applied to the IGBT, it should not exceed the maximum reverse voltage VRM. When the reverse voltage exceeds VRM, the transistor breaks down and starts conducting because it can no longer block current in the reverse direction.

The specific process is as follows:

The IV characteristics are shown according to different gate voltages or Vge. The X-axis represents the collector-emitter voltage, or Vce, and the Y-axis represents the collector current. In the off state, the current flowing through the collector and the gate voltage are zero. When we change Vge or gate voltage, the device enters the active region. A stable and continuous voltage on the gate provides a continuous and steady flow of current through the collector. The increase in Vge is proportional to the increase in collector current, Vge3 > Vge2 > Vge1. BV is the breakdown voltage of IGBT.

The output characteristics of IGBT are divided into three stages:

Stage 1: When the gate voltage VGE is zero, the IGBT is in the off state, which is called the cut-off region.

Second stage: When VGE increases, if it is less than the threshold voltage, there will be a small amount of leakage current flowing through the IGBT, but the IGBT is still in the cut-off region.

Phase 3: When VGE increases beyond the threshold voltage, the IGBT enters the active region and current begins to flow through the IGBT. As shown in the figure above, the current will increase as the VGE voltage increases.

This figure contains three stages. The first stage is the cut-off region, when no voltage is applied to the gate pin. During this stage, the transistor will remain off and no current will flow through the transistor.

When the voltage on the gate pin increases, and if it remains below the threshold voltage, it will cause a small leakage current to flow through the device, but the device will remain in the cutoff region.

However, when the voltage applied on the gate pin exceeds the threshold voltage, the device will move to the active region, in which case a large amount of current will flow from the collector to the emitter terminal.

At this stage, the voltage applied and the current produced will be directly proportional. A higher voltage will cause more current to flow at the collector terminal.

When designing an IGBT drive circuit, you need to ensure that VGE is high enough so that the IGBT can quickly switch from the off-state to the active state while avoiding entering the undesirable saturation region, which may result in reduced efficiency and increased heat losses.

The turn-on time of IGBT is defined as the time from forward blocking to forward conduction mode. Here, forward conduction means that the device is conducting in the forward direction. Turn-on time (ton) basically consists of two different times: delay time (tdn) and rise time (tr). Therefore, we can say ton=tdn+tr.

The delay time is defined as the time it takes for the collector-emitter voltage (VCE) to drop from VCE to 0.9VCE. This means that during the delay time, the collector-emitter voltage drops to 90%, and therefore the collector current rises to 0.1IC (10%) from the initial drain current. Therefore, the delay time can also be defined as the time interval for the collector current to rise from zero (actually a small drain current) to 10% of the final value of the collector current IC.

Rise time (tr) is the time it takes for the collector-emitter voltage to drop from 0.9V CE to 0.1V CE . This means that during the rise time, the collector-emitter voltage drops from 90% to 10%. Therefore, the collector current increases from 10% to the final value of the collector current I C . After time t on , the collector current becomes I C and the collector-emitter voltage drops to a very small value, called the conduction voltage drop (V CE(sat) ).

The figure below shows a typical IGBT switching characteristic. You can correlate delay time, rise time, and turn-on time with each other.

Now let's focus on the off time. Unlike the turn-on time, the turn-off time consists of three intervals:

• Delay time, t df

• Initial fall time, tf1

• Final fall time, t f2

Therefore, the off time is the sum of the three different time intervals mentioned above, that is, t off =t df +t f1 +t f2 . Please refer to the switching characteristics of IGBT to explain the above time.

The delay time is the time for the gate voltage to drop from V GE to the threshold voltage VGET. When the gate voltage drops to V during tdf , the collector current drops from I to 0.9I . At the end of the delay time, the collector-emitter voltage starts to rise.

The initial fall time tf1 is defined as the time required for the collector current to fall from 90% to 20% of its final value, I C. In other words, it is the time it takes for the collector-emitter voltage to rise from V CES to 0.1V CE .

The final fall time tf2 is the time required for the collector current to fall from 20% to 10% of I C , or the time required for the collector-emitter voltage to rise from 0.1V CE to the final value V CE .

IGBTs are mainly used in power-related applications. Standard power bipolar transistors (BJTs) have very slow response characteristics, while MOSFETs are suitable for fast switching applications, but are a higher-cost option where higher current levels are required. IGBT is suitable to replace power BJT and power MOSFET.

Additionally, IGBTs offer lower "on" resistance compared to BJTs, and due to this characteristic, IGBTs are thermally efficient in high power related applications.

IGBT is widely used in the electronic field. Due to its low on-resistance, very high current levels, high switching speed, and zero gate drive, IGBTs are used in high-power motor controls, inverters, and switch-mode power supplies with high-frequency conversion regions.

In the image above, a basic switching application using IGBT is shown. RL is a resistive load connected from the emitter of the IGBT to ground. The voltage difference across the load is expressed as VRL. The load can also be inductive. A different circuit is shown on the right. The load is connected to the collector and the current protection resistor is connected to the emitter. In both cases, current will flow from collector to emitter.

In the case of Bipolar Transistor (BJT), we need to supply a constant current at the base of the BJT. But in the case of IGBT, just like MOSFET, we need to provide a constant voltage on the gate and maintain saturation in a constant state.

In the case on the left, the voltage difference VIN (the potential difference between the input (gate) and ground/VSS) controls the output current flowing from the collector to the emitter. The voltage difference between VCC and GND is almost identical across the load.

In the circuit on the right, the current flowing through the load depends on the voltage divided by the value of RS. I RL2 = V IN /R S

Insulated-gate bipolar transistors (IGBTs) can switch "on" and "off" states by activating the gate. If we make the gate more positive by applying a voltage across it, the emitter of the IGBT will keep the IGBT in its "on" state; if we make the gate negative or zero, the IGBT will stay in its "off" state . This is the same way bipolar transistors (BJTs) and MOSFETs switch.

IGBT is a voltage controlled device, so it only needs a small voltage applied to the gate to remain on. Since these are unidirectional devices, they can only switch forward current from collector to emitter. A typical IGBT switching circuit is shown below, the gate voltage VG is applied to the gate pin to switch a motor (M) from a supply voltage V+. Resistor Rs essentially limits the current through the motor.

The switching characteristics of IGBTs make them very popular in power electronics, especially in applications such as frequency converters, electric vehicle traction control and solar inverters. Its unidirectional conductivity means the direction of current flow needs to be considered when designing circuits, while voltage control provides efficient switching control capabilities. In practical applications, it is also necessary to pay attention to the driving and protection of IGBT to ensure the reliability of the device and extend its service life. IGBTs are indispensable in a wide range of applications due to their versatility. They perform critical functions such as regulating voltage and current, controlling motors, powering devices, supporting renewable energy systems and enabling electric vehicle propulsion systems. When it comes to voltage and current regulation, IGBTs are critical to ensuring consistent and controllable power supply. Their ability to handle high voltages and currents makes them ideal for applications that require precision, such as industrial automation and grid-connected systems.

Basically, an IGBT is a switching device that is controlled like a MOSFET but has output characteristics similar to a BJT. It is used in power amplifiers and other switching devices. Its operation is not complicated and only relies on input voltage to turn on and negative or zero input voltage to turn off. IGBT does not have the secondary breakdown problem common in BJT.

The versatility of IGBTs allows them to play a central role in modern power electronics. They combine the high input impedance of MOSFETs with the low on-state voltage drop of BJTs to provide an effective solution in high voltage and current applications. The IGBT's simple switching mechanism and immunity to secondary breakdown problems make it a reliable and efficient power electronics switching option.

IGBTs are divided into two types based on whether they contain an N+ buffer layer. The inclusion of this extra layer divides them into symmetric and asymmetric IGBTs.

The through-type IGBT contains an N+ buffer layer, which is why it is also called an asymmetric IGBT. They have asymmetric voltage blocking capabilities, i.e. their forward and reverse breakdown voltages are different. Their reverse breakdown voltage is less than their forward breakdown voltage. It has faster switching speed.

Penetrating IGBTs are unidirectional and cannot handle reverse voltage. Therefore, they are used in DC circuits such as inverters and chopper circuits.

They are also called symmetric IGBTs because of the lack of an additional N+ buffer layer. The symmetry of the structure provides symmetrical breakdown voltage characteristics, i.e. equal forward and reverse breakdown voltages. For this reason they are used in AC circuits .

1. Conduction loss

For a given switching speed, NPT (non-penetrating) technology generally has a higher VCE(on) (conduction collector-emitter voltage) than PT (penetrating) technology. This difference is further amplified by the fact that the VCE(on) of NPT increases with increasing temperature (positive temperature coefficient), while the VCE(on) of PT decreases with increasing temperature (negative temperature coefficient). However, with any IGBT, whether PT or NPT, switching losses are weighed against VCE(on). High-speed IGBT has higher VCE(on); low-speed IGBT has lower VCE(on). In fact, a very fast PT device may have a higher VCE(on) than an NPT device that switches slowly.

2. Switching losses

For a given VCE(on), PT IGBTs have higher speed switching capabilities and lower total switching energy. This is due to higher gain and reduced minority carrier lifetime, which suppresses the tail current.

3. Robustness

NPT IGBTs are usually short-circuit rated, while PT devices usually are not, and NPT IGBTs can absorb more avalanche energy than PT IGBTs. NPT technology is more robust due to the wider base area and lower gain of PNP bipolar transistors. This is the main advantage gained by exchanging switching speed with NPT technology. Making a PT IGBT with over 600 volt VCES is difficult, but it is easy to do using NPT technology.

4. Temperature Effect

For PT and NPT IGBTs, the turn-on switching speed and losses are practically unaffected by temperature. However, the reverse recovery current of the diode increases with increasing temperature, so the temperature effect of the external diode affects the IGBT turn-on losses. For NPT IGBTs, the turn-off speed and switching losses remain relatively constant over the operating temperature range. For PT IGBTs, the turn-off speed decreases with increasing temperature, so the switching losses increase accordingly. However, the switching losses are inherently low due to tail current suppression.

As mentioned before, NPT IGBTs generally have a positive temperature coefficient, which makes them ideal for parallel connection. A positive temperature coefficient is desirable for parallel devices because hot devices conduct less current than cold devices, so all parallel devices tend to naturally share current. However, it is a misconception that PT IGBTs cannot be connected in parallel due to their negative temperature coefficient. PT IGBTs can be connected in parallel for the following reasons:

Their temperature coefficients tend to be nearly zero and sometimes positive at higher currents. Heat sharing through a heat sink tends to force devices to share current because hot devices heat their neighbors, thereby reducing their turn-on voltage. Parameters affecting temperature coefficients tend to be well matched between devices.

IGBT combines the best characteristics of BJT (Bipolar Transistor) and MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and therefore excels in almost every aspect. Below is a chart comparing the characteristics of IGBT, BJT and MOSFET, where we compare their maximum capabilities.

The above table compares some key characteristics of power BJT (Bipolar Transistor), power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and IGBT (Insulated Gate Bipolar Transistor). IGBTs offer higher performance than BJTs and MOSFETs in both voltage and current levels, especially in high voltage applications.

The low input driving power of the IGBT means that less energy is required to drive the IGBT, which helps reduce the overall system energy consumption. In addition, the input impedance of IGBTs is as high as MOSFETs, which helps reduce the complexity of the driving circuit. Although IGBTs do not switch as fast as MOSFETs, they have lower switching losses, which is an important advantage in high-power applications. However, the cost of IGBTs is generally higher than that of BJTs and MOSFETs, which may affect their adoption in cost-sensitive applications.

IGBT power module is a key technology in the field of power electronics. IGBT modules are advanced components in power electronics technology. They are carefully designed to integrate multiple IGBT single tubes or chips to achieve more complex and powerful electrical control functions. .

Not only are these modules capable of carrying higher currents and voltages, they are also designed in advanced parallel and series configurations to meet the needs of high-power applications. As a highly efficient electronic switching device, it enables current to be flexibly converted between direct current (DC) and alternating current (AC). This capability is critical to the operation of modern power systems because it allows precise control .

In practical applications, the IGBT module can be likened to a highly precise converter. Like a skilled magician, it is able to transform the one-way flow of direct current into alternating bi-directional alternating current, or vice versa, in an instant. This conversion requires not only extremely high speed, but also extremely high precision to ensure the stability and efficiency of the power system.

Imagine if you were a DC power source and now needed to power a device that required AC power. In this case, you may need a switch that can quickly switch the direction of the current. This switch can change the direction of the current in an extremely short period of time (for example, 100 times per second), thus producing alternating current. Such switching speed is unimaginable for humans, but it is a piece of cake for IGBT power modules.

This ability of IGBT modules makes them play a vital role in electric vehicles, industrial inverters, solar inverters, wind power systems, and various occasions where fast switching of current is required. Not only do they increase the efficiency of power conversion, they also extend the life of batteries and other power storage devices, thereby reducing overall operating costs.

Internal structure of IGBT module

After having a preliminary understanding of the external structure and application of the IGBT module, let's explore the internal structure of this high-tech black module.

The picture shows the internal photo of the IGBT module after removing the black casing. It is worth noting that no precious metals are used inside the IGBT module. The gold part is actually copper instead of gold, and the silver part is aluminum instead of silver.

If the black shell and external connection terminals are removed, the IGBT module mainly consists of three parts: the heat dissipation substrate, the DBC (direct bonding copper) substrate and the silicon chip (including IGBT chip and diode chip), and the rest is mainly solder. Interlayer and interconnection lines are used to connect IGBT chips, diode chips, power terminals, control terminals and DBC. Below we briefly introduce each part:

1. Heat dissipation substrate:

The bottom of the IGBT module is a heat dissipation substrate, whose main purpose is to quickly transfer the heat generated during the IGBT switching process. Since copper has better thermal conductivity, the substrate is usually made of copper, and the thickness of the substrate is 3-8 mm. Of course, there are also substrates made of other materials, such as aluminum silicon carbide (AlSiC), each of which has its own advantages and disadvantages.

2.DBC substrate:

Located on top of a heat sink substrate to provide electrical connections and mechanical support, usually made of copper and ceramic composite materials. DBC (Direct Bond Copper), the full name of direct copper clad substrate, is also abbreviated as: DCB (Direct Copper Bond). The two have the same meaning. DBC is a ceramic surface metallization technology that consists of three layers, with a ceramic insulating layer in the middle and copper cladding layers above and below, as shown in Figure 6a. To put it simply, a layer of copper is plated on both sides of the insulating material, and then a pattern that can carry current is etched on the front side. The back side is directly welded to the heat dissipation substrate, so no etching is required.

The main function of the DBC substrate is to ensure good electrical insulation and good thermal conductivity between the silicon chip and the heat dissipation substrate, and it must also meet a certain current transmission capability. The DBC substrate is similar to a double-layer PCB (Printed Circuit Board) circuit board. The insulating material in the middle of the PCB is usually FR4 (FR4 is the common name for fiberglass reinforced epoxy resin board), while the commonly used ceramic insulating materials for DBC are aluminum oxide (Al2O3) and aluminum nitride (AlN).

As shown in the figure, the IGBT module has a total of 6 DBC (direct bonded copper) substrates inside. Each DBC is equipped with 4 IGBT chips and 2 diode chips, of which 2 IGBT chips and 1 diode chip are used as upper tubes. , and the rest serves as the downtube.

3.Silicon chip:

Including IGBT chips and diode chips, they are the core part of the module and are responsible for switching and controlling current.

IGBT chip:

For example, the IGBT chip model is: IGCT136T170, and its manual can be downloaded from the Infineon official website. The figure shows the top view and basic parameters of the IGBT chip. The gate and emitter of the IGBT are located above the chip ( front), and the collector is located below (back). The thickness of the chip is 200 microns. After the IGBT is turned on, the current flows from the bottom to the top, so the IGBT with this structure can also be called a vertical device.

This chip is capable of passing 117.5A DC current at 100°C. As can be seen from Figure 4, a single IGBT device in the module contains a total of 12 IGBT chips, so the total current is: 117.5A * 12 = 1412A, which basically matches the rated current of 1400A in the IGBT module manual.

diode chip

The picture is a top view of a diode chip, with the anode in front and the cathode in the back. The direction of current flow in the diode is from top to bottom, which is completely opposite to the direction of current flow in the IGBT.

The rated current of the diode chip is 235A. Each IGBT is composed of 6 diodes connected in parallel. The total current can reach 1410A, which is basically consistent with the 1400A in the module manual. The thickness of the diode chip is the same as the IGBT, which is also 200 microns.

Seeing this, everyone may be surprised that it is possible to turn on and off high kilovolt voltages and control hundreds of amperes of current on such a small area and such a thin semiconductor material. This is indeed very remarkable and also a high-power One of the reasons why semiconductor devices are very expensive.

In the field of power electronics, semiconductor devices such as IGBTs and diodes can handle extremely large voltages and currents in extremely small sizes, thanks to their exquisite internal structures and advanced manufacturing processes. The design and manufacture of these devices involves complex physical principles and precise engineering techniques to ensure that they can operate stably under extreme operating conditions.

4.Solder:

Used to hold different components together and provide electrical connections.

5. Interlayer and interconnect lines:

These small connecting wires are responsible for connecting the IGBT chip and diode chip to the external power terminals and control terminals to ensure the correct flow of current. The upper copper layer interconnection between the IGBT chip, diode chip and DBC is usually realized through bonding wires. Commonly used bonding wires include aluminum wire and copper wire, as shown in the figure.

Among them, the aluminum wire bonding process is mature and low-cost, but the electrical and thermodynamic properties of aluminum wire bonding are poor and the thermal expansion coefficient mismatch is large, which will affect the service life of IGBT. The copper wire bonding process has excellent electrical and thermodynamic properties, high reliability, and is suitable for modules with high power density and efficient heat dissipation.

6. IGBT internal current trend:

After having a basic understanding of the internal structure of the IGBT module, let's go back and interconnect all the above components to see how the current flows inside the IGBT module. Here we take the upper tube IGBT in a DBC as an example to illustrate the current flow direction. Red represents the current direction of the upper tube IGBT (S1 and S2), and blue represents the current direction of the diode D1. Figure b is a left side cross-sectional view and schematic diagram of the current direction of the module in Figure a.

The current flow of IGBT modules is a complex three-dimensional process involving electron migration and hole flow inside the chip. When the IGBT is working, the current first enters through the gate (Gate), then flows into the interior of the IGBT chip through the emitter (Emitter), and then flows out at the collector (Collector). For the upper-side IGBT, the current flows from the collector to the emitter; while for the lower-side IGBT, the current flows from the emitter to the collector.

In an IGBT module, each IGBT chip is connected to one or more diode chips to achieve a specific current path. Under normal operating conditions, IGBTs and diodes turn on and off in a predetermined sequence to control the flow of current, thereby realizing energy conversion and transfer.

The internal structure of the IGBT module is designed to achieve efficient thermal management, electrical connections and mechanical stability to meet the high performance requirements in power electronics applications. Through this carefully designed internal structure, the IGBT module can work reliably in a variety of high-power applications, including electric vehicles, industrial drives and energy conversion systems.

In addition, the design and manufacturing of IGBT modules are constantly advancing to accommodate higher power density, smaller size and lower energy consumption. With the continuous development of technology, IGBT modules will be more widely used in the field of power electronics. They will continue to be the core components of power conversion, driving innovation and progress in energy utilization.

As one of the core devices of power electronics technology, IGBT (Insulated Gate Bipolar Transistor) is widely used in new energy vehicles, wind power generation, industrial motors, rail transportation and other fields. The following is an overview of the market competition landscape for IGBT and related modules:

Global market size: According to YOLE data, the global IGBT market size will be approximately US$6.8 billion in 2022, and is expected to reach US$8.4 billion by 2026.

China market size: China is the world's largest IGBT market, accounting for approximately 40% of the global market size. It is expected that China's IGBT market size will reach 52.2 billion yuan by 2025.

International companies: The global IGBT market competition is relatively concentrated, with Infineon, Fuji Electric, Mitsubishi and other companies occupying major market shares.

Domestic enterprises: China's IGBT industry started late, but in recent years domestic enterprises such as Star Semiconductor, New Clean Energy, BYD, Macro Micro Technology, Silan Micro, etc. are rapidly catching up and improving the level of industrialization.

The following is an introduction to domestic and foreign manufacturers in the IGBT industry chain. It is divided into three parts according to the upstream, middle and downstream. Each part lists 10 manufacturers as examples. Please note that the actual number of manufacturers may be higher and the following table only provides partial information.

Upstream - raw material and equipment suppliers

Midstream - IGBT chip design and manufacturing

Downstream - IGBT modules and applications

China's output growth: From 2019 to 2021, the output of China's IGBT industry was 15.5 million, 20.2 million and 25.8 million respectively, and the output is expected to increase to 36.24 million by 2023.

Module output: Considering that the main product of the IGBT industry is modules, and modules mainly use multiple IGBT chips in parallel, if calculated at a ratio of 1:2.5, China's IGBT chip output in 2021 will be approximately 64.5 million pieces.

International competition: The global IGBT market is monopolized by leading foreign companies, such as Infineon, Fuji, Mitsubishi, etc. These companies have obvious advantages in technology and market share.

Domestic competition: China's IGBT chip industry has a low self-sufficiency rate and relies mostly on imports. However, domestic companies are gradually increasing the localization rate through technological innovation and industrialization improvement.

Market potential: The rapid development of new energy vehicles and new energy power generation has provided huge growth space for the IGBT market.

In summary, the IGBT market is currently dominated by international companies and domestic companies are developing rapidly. At the same time, both the market capacity and installed capacity show a positive growth trend. With the continuous advancement of technology and policy support, the IGBT market is expected to continue to grow in the future.

Summarize:

As a power electronic device, IGBT combines the advantages of BJT and MOSFET and has high voltage and current handling capabilities while maintaining high input impedance and low on-state resistance.

The voltage control characteristics of IGBT make the gate drive circuit design simple, and since there is no input current, the input loss is low. In addition, the high current density of IGBT allows for smaller chip size, higher power gain and faster switching speed than BJT. However, IGBTs also have some disadvantages, such as slower switching speeds than MOSFETs and the inability to conduct in the reverse direction due to their unidirectional conductivity. Additionally, IGBTs typically cost more than BJTs and MOSFETs, and due to their structure, may experience latch-up issues, which require special consideration during design.

Nonetheless, IGBTs remain the device of choice in many high-power applications, and their performance advantages largely make up for these shortcomings.

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5. IGBT Transistors: An Introduction & Selection Guide - EE Times

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20. Forecast analysis of global and Chinese IGBT market size and output in 2023 (Figure) (seccw.com)

    
    

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22. Analysis of market size and competition landscape of China's IGBT industry - Intensive report reading - Future Think Tank (vzkoo.com)