 IGBT module (IGBTs and freewheeling diodes) with a rated current of 1200 A and a maximum voltage of 3300 V | |
| Working principle | Semiconductor |
|---|---|
| Invention year | 1959[dubious –discuss] |
| Electronic symbol | |
 IGBT schematic symbol | |
Aninsulated-gate bipolar transistor (IGBT) is a three-terminalpower semiconductor device primarily forming an electronic switch. It was developed to combine high efficiency with fast switching. It consists of four alternating layers (NPNP)[1][2][3][4] that are controlled by ametal–oxide–semiconductor (MOS)gate structure.
Although the structure of the IGBT is topologically similar to athyristor with a "MOS" gate (MOS-gate thyristor), the thyristor action is completely suppressed, and only thetransistor action is permitted in the entire device operation range. It is used inswitching power supplies in high-power applications:variable-frequency drives (VFDs) for motor control intrains,electric cars, variable-speed refrigerators and air conditioners, as well as lamp ballasts,arc-welding machines, photovoltaic and hybridinverters,uninterruptible power supply systems (UPS), andinduction stoves.
Since it is designed to turn on and off rapidly, the IGBT can synthesize complex waveforms withpulse-width modulation andlow-pass filters, thus it is also used inswitching amplifiers in sound systems and industrialcontrol systems. In switching applications, modern devices featurepulse 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. As of 2010[update], the IGBT was the second most widely used power transistor, after thepower MOSFET.[citation needed]
| Device characteristic | PowerBJT | 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 |
An IGBT cell is constructed similarly to an n-channel vertical-constructionpower MOSFET, except the n+ drain is replaced with a p+ collector layer, thus forming a vertical PNPbipolar junction transistor. This additional p+ region creates a cascade connection of a PNP bipolar junction transistor with the surface n-channelMOSFET. The whole structure comprises a four-layered NPNP.[1][2][3][4]
The bipolar point-contact transistor was invented in December 1947[6] at theBell Telephone Laboratories byJohn Bardeen andWalter Brattain under the direction ofWilliam Shockley. The junction version, known as the bipolar junction transistor (BJT), was invented by Shockley in 1948.[7] Later a similar thyristor was proposed by William Shockley in 1950 and developed in 1956 by power engineers atGeneral Electric (GE). Themetal–oxide–semiconductor field-effect transistor (MOSFET) was later invented at Bell Labs between 1959 and 1960.[8][9]
The basic IGBT mode of operation, where a pnp transistor is driven by a MOSFET, was first proposed by K. Yamagami and Y. Akagiri ofMitsubishi Electric in the Japanesepatent S47-21739, which was filed in 1968.[10]
In 1978 J. D. Plummer and B. Scharf patented a NPNP transistor device combining MOS and bipolar capabilities for power control and switching.[11][12] The development of the IGBT was characterised by an effort to completely suppress the thyristor operation, or thelatch-up, in the four-layer device because the latch-up caused fatal device self-destruction. 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".[13][14]
A. Nakagawa et al. invented the device design concept of non-latch-up IGBTs in 1984.[15][16] The invention is characterised by the device design setting the device saturation current below the latch-up current, which triggers the parasitic thyristor. This invention achieved 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 the IGBT, research was aimed at increasing the latch-up current itself to suppress the latch-up of the parasitic thyristor. However, all these efforts failed because the IGBT could conduct an enormously large current. Successful suppression of latch-up became possible by constraining the maximal collector current to stay below the latch-up current, by controlling or reducing the saturation current of the inherent MOSFET. This was the breakthrough behind the non-latch-up IGBT, which in turn made "Becke’s device" possible.
The IGBT is characterised 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 5×105 W/cm2,[17][18] which far exceeded the value, 2×105 W/cm2, of existing power devices such as bipolar transistors and power MOSFETs. This is a consequence of the largesafe 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 evengate 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 capable of operating over an extended current range were first reported byB. Jayant Baliga et al. in 1982.[19] The first experimental demonstration of a practical discrete vertical IGBT device was reported by Baliga at theIEEE International Electron Devices Meeting (IEDM) that year.[20][19]General Electric commercialized Baliga's IGBT device the same year.[21] Baliga was inducted into theNational Inventors Hall of Fame for the invention of the IGBT.[22]
A similar paper was also submitted by J. P. Russel et al. to IEEE Electron Device Letter in 1982.[23] The applications for the device were initially regarded by thepower 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 usingelectron irradiation.[24][25] This was followed by demonstration of operation of the device at elevated temperatures by Baliga in 1985.[26] 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,[27] 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.[28] 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.[15] The non-latch-up design concept was filed for US patents.[29] 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.[18] 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 byToshiba 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 largesafe operating area. It was demonstrated that the product of the operating current density and the collector voltage exceeded the theoretical limit of bipolar transistors, 2×105 W/cm2 and reached 5×105 W/cm2.[17][18]
The insulating material is typically made of solid polymers, which have issues with degradation. There are developments that use anion gel to improve manufacturing and reduce the voltage required.[30]
The first-generation IGBTs of the 1980s and early 1990s were prone to failure through effects such aslatchup (in which the device will not turn off as long as current is flowing) andsecondary breakdown (in which a localized hotspot in the device goes intothermal 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 rivalingpower MOSFETs and excellent ruggedness and tolerance of overloads.[17] Extremely high pulse ratings of second- and third-generation devices also make them useful for generating large power pulses in areas includingparticle andplasma physics, where they are starting to supersede older devices such asthyratrons andtriggered 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-stateTesla coils andcoilguns.
As of 2010[update], the IGBT is the second most widely usedpower 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 theRF amplifier (11%) andbipolar junction transistor (9%).[31] The IGBT is widely used inconsumer electronics,industrial technology, theenergy sector,aerospace electronic devices, andtransportation.
The IGBT combines the simple gate-drive characteristics ofpower MOSFETs with the high-current and low-saturation-voltage capability ofbipolar transistors. The IGBT combines an isolated-gateFET for the control input and a bipolar powertransistor as a switch in a single device. The IGBT is used in medium- to high-power applications likeswitched-mode power supplies,traction motor control andinduction heating. Large IGBT modules typically consist of many devices in parallel and can have very high current-handling capabilities in the order of hundreds ofamperes with blocking voltages of6500V. These IGBTs can control loads of hundreds ofkilowatts.
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:
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.
Circuits with IGBTs can be developed andmodeled with variouscircuit simulating computer programs such asSPICE,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 likeFETs andBJTs in aDarlington configuration.[citation needed] An alternative physics-based model is the Hefner model, introduced by Allen Hefner of theNational 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 theSaber simulation software.[32]
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.[33]
Failure assessment of IGBTs is becoming a topic of interest forpredictive 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, whereasdata-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.[34][35]
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| International | |
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