Insulated-gate bipolar transistor

An insulated-gate bipolar transistor (IGBT) is a three-terminal power semiconductor device primarily forming an electronic switch. It was developed to combine high efficiency with fast switching. It consists of four alternating layers (NPNP)<ref name=":0">Template:Cite book</ref><ref name=":2">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=":3">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=":4">Template:Cite journal</ref> that are controlled by a metal–oxide–semiconductor (MOS) gate structure.

Although the structure of the IGBT is topologically similar to a thyristor with a "MOS" gate (MOS-gate thyristor), the thyristor action is completely suppressed, and only the transistor action is permitted in the entire device operation range. It is used in switching power supplies in high-power applications: variable-frequency drives (VFDs) for motor control in electric cars, trains, variable-speed refrigerators, and air conditioners, as well as lamp ballasts, arc-welding machines, photovoltaic and hybrid inverters, uninterruptible power supply systems (UPS), and induction stoves.

Since it is designed to turn on and off rapidly, the IGBT can synthesize complex waveforms with pulse-width modulation and low-pass filters, thus it is also used in switching amplifiers in sound systems and industrial control systems. In switching applications modern devices feature pulse repetition rates well into the ultrasonic-range frequencies, which are at least ten times higher than audio frequencies handled by the device when used as an analog audio amplifier. Template:As of, the IGBT was the second most widely used power transistor, after the power MOSFET.Template:Citation needed

IGBT comparison table<ref>Basic Electronics Tutorials.</ref>

Device characteristic	Power BJT	Power MOSFET	IGBT
Voltage rating	High <1 kV	High <1 kV	Very high >1 kV
Current rating	High <500 A	Low <200 A	High >500 A
Input drive	Current ratio hFE ~ 20–200	Voltage VGS ~ 3–10 V	Voltage VGE ~ 4–8 V
Input impedance	Low	High	High
Output impedance	Low	Medium	Low
Switching speed	Slow (μs)	Fast (ns)	Medium
Cost	Low	Medium	High

Device structure

File:IGBT Cross Section.jpg

Cross-section of a typical IGBT showing internal connection of MOSFET and bipolar device

An IGBT cell is constructed similarly to an n-channel vertical-construction power MOSFET, except the n+ drain is replaced with a p+ collector layer, thus forming a vertical PNP bipolar junction transistor. This additional p+ region creates a cascade connection of a PNP bipolar junction transistor with the surface n-channel MOSFET. The whole structure comprises a four layered NPNP.<ref name=":0" /><ref name=":2" /><ref name=":3" /><ref name=":4" />

Difference between thyristor and IGBT

Difference between thyristor and IGBT<ref>Difference Between IGBT and Thyristor.</ref>

Aspect	Thyristor	IGBT
Definition	A four-layer semiconductor device with a P-N-P-N structure	An insulated-gate bipolar transistor combining features from bipolar transistors and MOSFETs
Terminals	Anode, cathode, gate	Emitter, collector, gate
Layers	Four layers	Three layers
Junction	PNPN structure	NPN(P) structure
Modes of operation	Reverse blocking, forward blocking, forward conducting	On-state, off-state
Design structure	Coupled transistors (PNP and NPN)	Combined bipolar and MOSFET features
Carrier source	Two sources of carriers	One source of carriers
Turn-on voltage	N/A	Low gate voltage required
Turn off loss	Higher	Lower
Plasma density	Higher	Lower
Operating frequency range	Suitable for line frequency, typically lower	Suitable for high frequencies, typically higher
Die size and paralleling requirements	Larger die size, can be manufactured as monolithic devices up to 6" (15 cm) in diameter	Smaller die size, often paralleled in a package
Power range	Suitable for high-power applications	Suitable for medium-power applications
Control requirements	Requires gate current	Requires continuous gate voltage
Value for money	Cost-effective	Relatively higher cost
Control method	Pulse triggering	Gate voltage control
Switching speed	Slower	Faster
Current switching capability	High	Moderate
Control current	High current drive	Low current drive
Voltage capability	High voltage handling	Lower voltage handling
Power loss	Higher power dissipation	Lower power dissipation
Application	High voltage, robustness	High-speed switching, efficiency

History

File:1957(Figure 7)-Gate oxide transistor by Frosch and Derrick.png

Diagram of NPNP transistor made by Frosch and Derrick at Bell Labs, 1957<ref name="iopscience.iop.org">Template:Cite journal</ref>

The bipolar point-contact transistor was invented in December 1947<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> at the Bell Telephone Laboratories by John Bardeen and Walter Brattain under the direction of William Shockley. The junction version known as the bipolar junction transistor (BJT), invented by Shockley in 1948.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Later the similar thyristor was proposed by William Shockley in 1950 and developed in 1956 by power engineers at General Electric (GE). The metal–oxide–semiconductor field-effect transistor (MOSFET) was also invented at Bell Labs.<ref name="iopscience.iop.org"/><ref>Template:Cite journal</ref><ref>Template:Cite book</ref> In 1957 Frosch and Derick published their work on building the first silicon dioxide transistors, including a NPNP transistor, the same structure as the IGBT.<ref name=":5">Template:Cite journal</ref> The basic IGBT mode of operation, where a pnp transistor is driven by a MOSFET, was first proposed by K. Yamagami and Y. Akagiri of Mitsubishi Electric in the Japanese patent S47-21739, which was filed in 1968.<ref>Template:Cite book</ref>

File:IvsV IGBT-en.svg

Static characteristic of an IGBT

In 1978 J. D. Plummer and B. Scharf patented a NPNP transistor device combining MOS and bipolar capabilities for power control and switching.<ref name=":7">Template:Cite book</ref><ref name=":8">Template:Cite patent</ref> The development of IGBT was characterized by the efforts to completely suppress the thyristor operation or the latch-up in the four-layer device because the latch-up caused the fatal device failure. IGBTs had, thus, been established when the complete suppression of the latch-up of the parasitic thyristor was achieved. Later, Hans W. Becke and Carl F. Wheatley developed a similar device claiming non-latch-up. They patented the device in 1980, referring to it as "power MOSFET with an anode region" for which "no thyristor action occurs under any device operating conditions".<ref name="U. S. Patent No. 4,364,073">U. S. Patent No. 4,364,073, Power MOSFET with an Anode Region, issued December 14, 1982 to Hans W. Becke and Carl F. Wheatley.</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

A. Nakagawa et al. invented the device design concept of non-latch-up IGBTs in 1984.<ref name="Nakagawa Ohashi Kurata et al 1984">Template:Cite book</ref><ref name="patents.google.com">A. Nakagawa, H. Ohashi, Y. Yamaguchi, K. Watanabe and T. Thukakoshi, "Conductivity modulated MOSFET" US Patent No. 6025622 (Feb. 15, 2000), No. 5086323 (Feb. 4, 1992) and No. 4672407 (Jun. 9, 1987).</ref> The invention is characterized by the device design setting the device saturation current below the latch-up current, which triggers the parasitic thyristor. This invention realized complete suppression of the parasitic thyristor action, for the first time, because the maximal collector current was limited by the saturation current and never exceeded the latch-up current.

In the early development stage of IGBT, all the researchers tried to increase the latch-up current itself in order to suppress the latch-up of the parasitic thyristor. However, all these efforts failed because IGBT could conduct enormously large current. Successful suppression of the latch-up was made possible by limiting the maximal collector current, which IGBT could conduct, below the latch-up current by controlling/reducing the saturation current of the inherent MOSFET. This was the concept of non-latch-up IGBT. "Becke’s device" was made possible by the non-latch-up IGBT.

The IGBT is characterized by its ability to simultaneously handle a high voltage and a large current. The product of the voltage and the current density that the IGBT can handle reached more than 5Template:E W/cm²,<ref name="A.Nakagawa 1987"/><ref name="A. Nakagawa pp. 150–153"/> which far exceeded the value, 2Template:E W/cm², of existing power devices such as bipolar transistors and power MOSFETs. This is a consequence of the large safe operating area of the IGBT. The IGBT is the most rugged and the strongest power device yet developed, affording ease of use and so displacing bipolar transistors and even gate turn-off thyristors (GTOs). This excellent feature of the IGBT had suddenly emerged when the non-latch-up IGBT was established in 1984 by solving the problem of so-called "latch-up", which is the main cause of device destruction or device failure. Before that, the developed devices were very weak and were easily destroyed by "latch-up".

Practical devices

Practical devices capable of operating over an extended current range were first reported by B. Jayant Baliga et al. in 1982.<ref name="J. Baliga, pp. 264–267">Template:Cite book</ref> The first experimental demonstration of a practical discrete vertical IGBT device was reported by Baliga at the IEEE International Electron Devices Meeting (IEDM) that year.<ref>Template:Cite journal</ref><ref name="J. Baliga, pp. 264–267"/> General Electric commercialized Baliga's IGBT device the same year.<ref name="Baliga">Template:Cite book</ref> Baliga was inducted into the National Inventors Hall of Fame for the invention of the IGBT.<ref name="NIHF">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

A similar paper was also submitted by J. P. Russel et al. to IEEE Electron Device Letter in 1982.<ref name=COMFET>Template:Cite journal</ref> The applications for the device were initially regarded by the power electronics community to be severely restricted by its slow switching speed and latch-up of the parasitic thyristor structure inherent within the device. However, it was demonstrated by Baliga and also by A. M. Goodman et al. in 1983 that the switching speed could be adjusted over a broad range by using electron irradiation.<ref name="J. Baliga, pp. 452–454">Template:Cite journal</ref><ref>Template:Cite book</ref> This was followed by demonstration of operation of the device at elevated temperatures by Baliga in 1985.<ref>Template:Cite journal</ref> Successful efforts to suppress the latch-up of the parasitic thyristor and the scaling of the voltage rating of the devices at GE allowed the introduction of commercial devices in 1983,<ref>Product of the Year Award: "Insulated Gate Transistor", General Electric Company, Electronics Products, 1983.</ref> which could be used for a wide variety of applications. The electrical characteristics of GE's device, IGT D94FQ/FR4, were reported in detail by Marvin W. Smith in the proceedings of PCI April 1984.<ref name="archive1982.web.fc2.com">Marvin W. Smith, "APPLICATIONS OF INSULATED GATE TRANSISTORS", PCI April 1984 PROCEEDINGS, pp. 121–131, 1984.</ref> Smith showed in Fig. 12 of the proceedings that turn-off above 10 amperes for gate resistance of 5 kΩ and above 5 amperes for gate resistance of 1 kΩ was limited by switching safe operating area although IGT D94FQ/FR4 was able to conduct 40 amperes of collector current. Smith also stated that the switching safe operating area was limited by the latch-up of the parasitic thyristor.

Complete suppression of the parasitic thyristor action and the resultant non-latch-up IGBT operation for the entire device operation range was achieved by A. Nakagawa et al. in 1984.<ref name="Nakagawa Ohashi Kurata et al 1984"/> The non-latch-up design concept was filed for US patents.<ref>A. Nakagawa, H. Ohashi, Y. Yamaguchi, K. Watanabe and T. Thukakoshi, "Conductivity modulated MOSFET", US Patent No. 6025622 (Feb. 15, 2000), No. 5086323 (Feb. 4, 1992) and No. 4672407 (Jun. 9, 1987).</ref> To test the lack of latch-up, the prototype 1200 V IGBTs were directly connected without any loads across a 600 V constant-voltage source and were switched on for 25 microseconds. The entire 600 V was dropped across the device, and a large short-circuit current flowed. The devices successfully withstood this severe condition. This was the first demonstration of so-called "short-circuit-withstanding-capability" in IGBTs. Non-latch-up IGBT operation was ensured, for the first time, for the entire device operation range.<ref name="A. Nakagawa pp. 150–153">Template:Cite book</ref> In this sense, the non-latch-up IGBT proposed by Hans W. Becke and Carl F. Wheatley was realized by A. Nakagawa et al. in 1984. Products of non-latch-up IGBTs were first commercialized by Toshiba in 1985. This was the real birth of the present IGBT.

Once the non-latch-up capability was achieved in IGBTs, it was found that IGBTs exhibited very rugged and a very large safe operating area. It was demonstrated that the product of the operating current density and the collector voltage exceeded the theoretical limit of bipolar transistors, 2Template:E W/cm² and reached 5Template:E W/cm².<ref name="A.Nakagawa 1987"/><ref name="A. Nakagawa pp. 150–153"/>

The insulating material is typically made of solid polymers, which have issues with degradation. There are developments that use an ion gel to improve manufacturing and reduce the voltage required.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The first-generation IGBTs of the 1980s and early 1990s were prone to failure through effects such as latchup (in which the device will not turn off as long as current is flowing) and secondary breakdown (in which a localized hotspot in the device goes into thermal runaway and burns the device out at high currents). Second-generation devices were much improved. The current third-generation IGBTs are even better, with speed rivaling power MOSFETs and excellent ruggedness and tolerance of overloads.<ref name="A.Nakagawa 1987">Template:Cite journal</ref> Extremely high pulse ratings of second- and third-generation devices also make them useful for generating large power pulses in areas including particle and plasma physics, where they are starting to supersede older devices such as thyratrons and triggered spark gaps. High pulse ratings and low prices on the surplus market also make them attractive to the high-voltage hobbyists for controlling large amounts of power to drive devices such as solid-state Tesla coils and coilguns.

Applications

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} Template:See also

Template:As of, the IGBT is the second most widely used power transistor, after the power MOSFET. The IGBT accounts for 27% of the power transistor market, second only to the power MOSFET (53%), and ahead of the RF amplifier (11%) and bipolar junction transistor (9%).<ref>Template:Cite news</ref> The IGBT is widely used in consumer electronics, industrial technology, the energy sector, aerospace electronic devices, and transportation.

Advantages

The IGBT combines the simple gate-drive characteristics of power MOSFETs with the high-current and low-saturation-voltage capability of bipolar transistors. The IGBT combines an isolated-gate FET for the control input and a bipolar power transistor as a switch in a single device. The IGBT is used in medium- to high-power applications like switched-mode power supplies, traction motor control and induction heating. Large IGBT modules typically consist of many devices in parallel and can have very high current-handling capabilities in the order of hundreds of amperes with blocking voltages of Template:Nowrap. These IGBTs can control loads of hundreds of kilowatts.

Comparison with power MOSFETs

An IGBT features a significantly lower forward voltage drop compared to a conventional MOSFET in higher blocking voltage rated devices, although MOSFETS exhibit much lower forward voltage at lower current densities due to the absence of a diode Vf in the IGBT's output BJT. As the blocking voltage rating of both MOSFET and IGBT devices increases, the depth of the n- drift region must increase and the doping must decrease, resulting in roughly square relationship decrease in forward conduction versus blocking voltage capability of the device. By injecting minority carriers (holes) from the collector p+ region into the n- drift region during forward conduction, the resistance of the n- drift region is considerably reduced. However, this resultant reduction in on-state forward voltage comes with several penalties:

• The additional PN junction blocks reverse current flow. This means that unlike a MOSFET, IGBTs cannot conduct in the reverse direction. In bridge circuits, where reverse current flow is needed, an additional diode (called a freewheeling diode) is placed in anti-parallel with the IGBT to conduct current in the opposite direction. The penalty isn't overly severe because at higher voltages, where IGBT usage dominates, discrete diodes have a significantly higher performance than the body diode of a MOSFET.
• The reverse bias rating of the N-drift region to collector P+ diode is usually only of tens of volts, so if the circuit application applies a reverse voltage to the IGBT, an additional series diode must be used.
• The minority carriers injected into the N-drift region take time to enter and exit or recombine at turn-on and turn-off. This results in longer switching times, and hence higher Template:Ill compared to a power MOSFET.
• The on-state forward voltage drop in IGBTs behaves very differently from power MOSFETS. The MOSFET voltage drop can be modeled as a resistance, with the voltage drop proportional to current. By contrast, the IGBT has a diode-like voltage drop (typically of the order of 2V) increasing only with the log of the current. Additionally, MOSFET resistance is typically lower for smaller blocking voltages, so the choice between IGBTs and power MOSFETS will depend on both the blocking voltage and current involved in a particular application.

In general, high voltage, high current and lower frequencies favor the IGBT while low voltage, medium current and high switching frequencies are the domain of the MOSFET.

Modeling

Circuits with IGBTs can be developed and modeled with various circuit simulating computer programs such as SPICE, Saber, and other programs. To simulate an IGBT circuit, the device (and other devices in the circuit) must have a model which predicts or simulates the device's response to various voltages and currents on their electrical terminals. For more precise simulations the effect of temperature on various parts of the IGBT may be included with the simulation. Two common methods of modeling are available: device physics-based model, equivalent circuits or macromodels. SPICE simulates IGBTs using a macromodel that combines an ensemble of components like FETs and BJTs in a Darlington configuration.Template:Citation needed An alternative physics-based model is the Hefner model, introduced by Allen Hefner of the National Institute of Standards and Technology. Hefner's model is fairly complex but has shown good results. Hefner's model is described in a 1988 paper and was later extended to a thermo-electrical model which include the IGBT's response to internal heating. This model has been added to a version of the Saber simulation software.<ref>Template:Cite journal</ref>

IGBT failure mechanisms

The failure mechanisms of IGBTs includes overstress (O) and wearout (wo) separately.

The wearout failures mainly include bias temperature instability (BTI), hot carrier injection (HCI), time-dependent dielectric breakdown (TDDB), electromigration (ECM), solder fatigue, material reconstruction, corrosion. The overstress failures mainly include electrostatic discharge (ESD), latch-up, avalanche, secondary breakdown, wire-bond liftoff and burnout.<ref>Template:Cite journal</ref>

IGBT failure assessment

Failure assessment of IGBTs is becoming a topic of interest for predictive maintenance in several applications where IGBTs are widely used such as transportation, telecommunication, and computers. It is particularly challenging given the difficult nature of the problem from a physical and a statistical point of view. Physics of failure are yet to be proven to generalize well to IGBTs, whereas data-driven models require high-quality data of IGBT failures that is often costly to obtain. Given these challenges, most state-of-the-art failure assessment models utilise hybrid approaches which combine physics-of-failure and data-driven models.<ref>Template:Cite conference</ref><ref>Template:Cite journal</ref>

IGBT modules

• IGBT 3300V 1200A Mitsubishi.jpg

  IGBT module (IGBTs and freewheeling diodes) with a rated current of Template:Nowrap and a maximum voltage of Template:Nowrap

• IGBT 2441.JPG

  Opened IGBT module with four IGBTs (half of H-bridge) rated for Template:Nowrap Template:Nowrap

• Infineon IGBT-Modul.jpg

  Infineon IGBT Module rated for Template:Nowrap Template:Nowrap

• Igbt.jpg

  Small IGBT module, rated up to Template:Nowrap, up to Template:Nowrap

• CM600DU-24NFH.jpg

  Detail of the inside of a Mitsubishi Electric CM600DU-24NFH IGBT module rated for Template:Nowrap Template:Nowrap, showing the IGBT dies and freewheeling diodes

See also

• Bipolar junction transistor
• Bootstrapping
• Current injection technique
• Floating-gate MOSFET
• Junction-gate field-effect transistor
• MOSFET
• Power electronics
• Power MOSFET
• Power semiconductor device
• Solar inverter
• Gate turn-off thyristor

Further reading

• Template:Cite book

External links

• Device physics information from the University of Glasgow
• Spice model for IGBT
• IGBT driver calculation