the Invention and Demonstration of the IgBt

A Look Back

by Krishna Shenai

The Invention and Demonstration of the IGBT

M

uch of the credit for 20th-century advances in computing and communication goes to the silicon transistor and the integrated circuit. The same may be said for the silicon insulated gate bipolar transistor (IGBT) with respect to the impending revolution taking place in energy technology. The silicon IGBT offers unprecedented energy efficiency when switching electrical power in the range of few hundred kilowatts to multimegawatts at a low manufacturing cost. It is transforming the electric utility, transportation, telecommunication, manufacturing, and medical infrastructures in a manner never seen before. This article pertains to the discovery and demonstration of early IGBT devices. The IGBT is a three-terminal power semiconductor switch primarily used in electrical power switching applications that demand high efficiency and fast switching. It switches electrical power in many modern appliances, such as automobiles, trains, air conditioners, and refrigerators. Figure 1(a) represents the cross section of a vertical IGBT device with a double-diffused MOSFET gate structure, and Figure 1(b)

Digital Object Identifier 10.1109/MPEL.2015.2421751 Date of publication: 24 June 2015

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Gate (G) Emitter (E) CGE

RG

n+ RW

p-Body CGC RD

n-epi

CCE n Buffer p+Substrate Collecter (C) (a) Main Bipolar Transistor

C

RD

CGC C G

CCE

RG RW

CGE

E (b) fig 1 The schematics of (a) a cross section and (b) the circuit model of a vertical IGBT device with planar DMOSFET gate structure.

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shows the circuit model of the device [1]. The main powerswitching device in this structure is the vertical p-n-p bipolar transistor, which is triggered into on-state conduction by the base electron current supplied from the MOS channel. The holes injected from the p+ substrate into the lightly doped n-type epitaxial drift region cause electrical conductivity modulation of the drift region and, thus, reduce the collector series resistance when the device is fully turned on. The IGBT can carry a much higher current than the MOSFET, but in the on state, a minimum forward voltage drop VF equivalent to the junction built-in potential of the p-n junction formed by the p+ collector and n-type buffer region is present. The typical on-state and reverse-blocking current– voltage (I–V) characteristics of an IGBT are shown in Figure 2 with an enhancement-mode MOSFET gate. The underlying device concept in an IGBT is the triggering of a bipolar transistor action by the base current injected from a MOS channel. When the supply of base current is removed by turning off the MOS channel, the bipolar transistor comes out of conduction and the IGBT turns off. The IGBT turn-off process is much slower than that of a MOSFET because it takes time

to remove the stored charge IGBT shown in Figure 1(a) in the quasi-neutral base reconsists of four alternating pIF Active Region and n-type semiconductor gion. Typically, the turn-off process is accelerated by layers that are controlled by Increasing Gate a MOS gate structure withintroducing carrier traps in Voltage out regenerative action. The the base region. The IGBT current tail is largely due to MOS-controlled regenerative VR mode of operation was first the residual minority carrier Reverse Forward VF observed by Yamaguchi in stored charge in the vicinCharacteristics Characteristics his Japanese patent S47ity of the junction between 21739, which was filed in the p+-type substrate and 1968 [2] with reference to the n-type buffer. CMOS latch-up induced by a As shown in Figure 1(a) MOS channel current. A Japand (b), the IGBT has severIR anese patent was subseal parasitic devices inherent quently issued to Mitsubishi in the structure. The most fig 2 The typical I–V characteristics of an IGBT device with an in 1972. The four-layer important among these de- enhancement-mode MOSFET gate. p-n-p-n gate turn-off thyrisvices is the parasitic p-n-p-n tor itself was first proposed by F.E. IGBT device. Figure 3 shows two comthyristor between the collector and Gentry in 1963, and a U.S. patent was mon circuit symbols used to represent emitter. If the thyristor is turned on issued for this device structure in 1967 an IGBT device in electronic circuits. during the electrical power switching [3]. Plummer also found the MOS-conprocess, the IGBT may not be easily trolled regenerative mode of operation turned off using the MOS gate. The The Discovery and Demonstration in a four-layer lateral monolithic semiparasitic thyristor action places a of the IGBT Device Concept conductor switching device for which limit on the maximum current density The IGBT is a fairly recent concept in he had first filed a patent application that can be reliably switched in an comparison with the transistor. The

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6,500 V

4,500 V

3,300 V

2,500 V

1,200 V 1,700 V

Vce. on (v)

cal discrete MOS-controlled in 1978. U.S. patent 4,199,774 bipolar transistor switch was subsequently issued in C with the potential for scaling 1980 [4], and a detailed paper to medium- and high-power on the experimental results C levels. This early success in was published in February IGBTs spurred worldwide in1978 at the IEEE InternationG terest in commercializing the al Solid-State Circuits Connew high-power solid-state ference by Scharf and G switching technology. HowPlummer [5]. Interestingly, ever, for IGBT technology the paper by Scharf and to be commercially viable, Plummer also discusses the E E the parasitic thyristor action nonregenerative MOS-con(a) (b) needed to be suppressed, the trolled bipolar transistor opswitching speed needed to eration with reference to be improved, and the devices measured I–V characteristics fig 3 Two commonly used circuit symbols of an IGBT. needed to be operational shown in Figure 3 in this artiat higher junction temperacle. The experimental results 6.0 tures. Many researchers have were adequately supported 5.5 SPT made important contribuwith two-dimensional device 5.0 tions in solving these pracsimulations. Figure 11 in 4.5 tical problems, and there Plummer’s 1980 patent also 4.0 are too many to list in this describes a nonregenerative 3.5 article. Perhaps blanket elecbipolar-mode vertical device SPT+ 3.0 tron irradiation and selecstructure with V-groove MOS 2.5 tive proton implantation are gate control similar to the 2.0 the two techniques that are device structure shown in 1.5 responsible for the success Figure 1(a). U.S. patent B1 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 of today’s commercial IGBT Re33209 was reissued to Voltage Class (v) devices in solving these critiPlummer in 1995 for the cal problems [14]–[19]. At the IGBT mode of operation in fig 4 Power loss reduction achieved with 6.5-kV/750-A SPT1984 IEEE IEDM, Nakagawa the four-layer SCR device [6]. IGBT and diode technology (courtesy of A. Kopta, ABB, Badenet al. presented a 1,200-V/75-A In a 1979 paper [10], Baliga Baden, Switzerland). nonlatch-up bipolar-mode presented the experimental MOSFET with a large safe operating carriers injected from the anode was results for vertical enhancement-mode area at 125 °C, which clearly demondiscussed. The first experimental MOS-gated silicon thyristor device. In strated the potential for efficient and demonstration of a practical discrete the same paper, Baliga also described fast medium- and high-power switchvertical IGBT device was reported by a V-groove MOSFET device with the ing applications [20]. Baliga et al. [12] in a paper presented drain region replaced by a p-type anToday, 6.5-kV IGBT power modat the IEEE International Electron ode region. The detailed modeling and ules capable of switching in excess of Devices Meeting (IEDM) held in Deexperimental results of insulated-gate 900 A are commercially manufactured cember 1982. The paper was titled planar thyristors were published by [21]. Figure 4 shows the efficiency per“The Insulated Gate Rectifier (IGR): Scharf and Plummer in two seminal formance of various types of IGBT A New Power Switching Device.” papers in 1980 [7], [8]. In a parallel depower modules based on soft punchWithin a few months of this developvelopment, Tihanyi [9] also experimenthrough (SPT) device technology. ment, Russell et al. published a paper tally demonstrated the functional [13], “The Conductivity-Modulated integration of power MOS and bipolar Field-Effect Transistor (COMFET): A devices; vertical MOSFET-triggered Summary and Conclusions New High Conductance MOS-Gated thyristors, optically coupled lateral The observations made in this article Device,” which also presented the thyristors with MOS input, and opticalclearly suggest that, between 1978 experimental data for a practical disly coupled MOS triacs were successand 1982, four separate research crete vertical IGBT device; this paper fully implemented in silicon. groups at Stanford University, GE was submitted for publication on 8 On 14 December 1982, Becke Corporate R&D Center, Siemens AG, December 1982. and Wheatley received U.S. patent and RCA Corporation were intensely The papers by Baliga et al. [12] and 4,364,073, filed on 25 March 1980 [11], working on the functional integration Russell et al. [13] perhaps for the first in which drain region conductivity of power MOS and bipolar transistor time provided evidence of a true vertimodulation in a MOSFET by minority concepts. The basic device concept,

the MOS-controlled bipolar power transistor, had several acronyms. It was referred to as IGR in [12], COMFET in [13], insulated-gate transistor in [22], and bipolar-mode MOSFET (BIFET) in [23]. Today, this key device concept is the best known as the IGBT, which clearly describes the true mode of device operation. However, the question that remains unanswered is who should be credited with the invention of the IGBT—perhaps the most important semiconductor device concept conceived and commercialized since the silicon transistor. There have been patent infringement lawsuits, such as that between Stanford University and Harris Corporation and the former RCA Corporation [24]. The true answer may be best left to the decision of informed readers.

About the Author Krishna Shenai (kshenai@yahoo. com) earned his B.Tech. degree in electronics from the Indian Institute of

Technology, Madras, India, in 1979 and his M.S. and Ph.D. degrees in electrical engineering from the University of Maryland, College Park, in 1981 and Stanford University, California, in 1986, respectively. He is the vice president of LoPel Corporation in Naperville, Illinois. He has made seminal contributions to power semiconductor materials and devices for over 30 years. His research has set industry standards for nearly three decades, and products developed based on his research have been generating multibillion-dollar annual sales revenues. In the 1980s, based on the pioneering optimization of silicon power devices, he proposed the use of WBG semiconductors for electrical power switching. He is a Fellow of the IEEE, the American Physical Society, the American Association for the Advancement of Science, and the Institution of Electronics and Telecommunication Engineers (India) and a member of the Serbian Academy of Engineers. He has authored or coau-

thored more than 400 peer-reviewed archival papers, ten book chapters, and three books. He is a named inventor in 13 issued U.S. patents.

References [1] B. J. Baliga, Modern Power Devices. New York: Wiley, 1987. [2] M. Yamaguchi, Japanese patent, Feb. 5, 1968. [3] F. E. Gentry, “Four layer semiconductor switch with the third layer defining a continuous, uninterrupted internal junction,” U.S. Patent 3 324 359, June 6, 1967. [4] J. D. Plummer, “Monolithic semiconductor switching devices,” U.S. Patent 4 199 774, Apr. 22, 1980. [5] B. W. Scharf and J. D. Plummer, “A MOScontrolled triac device,” in IEEE Int. Solid-State Circuits Conf. Dig. Tech. Papers., Feb. 17, 1978, pp. 222–223. [6] J. D. Plummer, “Monolithic semiconductor switching devices,” U.S. Patent Re33 209, 1995. [7] J. D. Plummer and B. W. Scharf, “Insulatedgate planar thyristors: I—Structure and basic operation,” IEEE Trans. Electron Devices, vol. ED-27, no. 2, pp. 380–387, Feb. 1980.

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[8] J. D. Plummer and B. W. Scharf, “Insulated-

[14] V. A. K. Temple and F. W. Holroyd, “Optimiz-

lated-gate transistors by proton implantation,”

gate planar thyristors: II—Quantitative model-

ing carrier lifetime profile for improved trade-off

IEEE Trans. Electron Devices, vol. ED-33, no.

ing,” IEEE Trans. Electron Devices, vol. ED-27,

between turn-off time and forward drop,” IEEE

11, pp. 1667–1671, Nov. 1986.

no. 2, pp. 387–394, Feb. 1980.

Trans. Electron Devices, vol. ED-30, no. 7, pp.

[20] A. Nakagawa, H. Ohashi, M. Kurata, H.

[9] J. Tihanyi, “Functional integration of power

782–790, July 1983.

Yamaguchi, and K. Watanabe, “Non-latch-up

MOS and bipolar devices,” in Proc. IEEE Int.

[15] A. M. Goodman, J. P. Russell, L. A. Good-

1200V 75A bipolar-mode MOSFET with large

Electron Devices Meeting, Dec. 1980, pp. 75–81.

man, C. J. Neuse, and J. M. Neilson, “Improved

ASO,” in Proc. IEEE Int. Electron Devices Meet-

[10] B. J. Baliga, “Enhancement- and depletion-

COMFETs with fast switching speed and high-

ing, Dec. 1984, pp. 860–861.

mode vertical-channel m.o.s. gated thyristors,”

current capability,” in IEEE Int. Electron Devic-

[21] A. Kopta, M. Rahimo, and R. Schnell,

Electron. Lett., vol. 15, no. 20, pp. 645–647,

es Meeting Dig., Abstract 4.3, 1983, pp. 79–82.

“Next generation high performance BIGT

Sept. 27, 1979.

[16] B. J. Baliga, “Switching speed enhancement

HiPak modules,” Power Electron. Europe, no.

[11] H. W. Becke and C. F. Wheatley, Jr., “Power

in insulated gate transistors by electron irradia-

5, pp. 22–25, 2010.

MOSFET with an anode region,” U.S. Patent 4

tion,” IEEE Trans. Electron Devices, vol. ED-31,

[22] M. F. Chang, G. C. Pifer, B. J. Baliga, M. S.

364 073, Dec. 14, 1982.

no. 12, pp. 1790–1795, Dec. 1984.

Adler, and P. V. Gray, “25 amp. 500 volt, insulated

[12] B. J. Baliga, M. S. Adler, P. V. Gray, R. P. Love,

[17] B. J. Baliga, M. S. Adler, P. V. Gray, and R.

gate transistors,” in Dig. IEEE Int. Electron

and N. Zommer, “The insulated gate rectifier (IGR):

P. Love, “Suppressing latchup in insulated gate

Devices Meeting (IEDM), Dec. 1983, Abstract 4.4,

A new power switching devices,” in Proc. IEEE Int.

transistors,” IEEE Electron Device Lett., vol.

pp. 83–86.

Electron Devices Meeting, Dec. 1982, pp. 264–267.

EDL-5, no. 8, pp. 323–325, Aug. 1984.

[23] A. Nakagawa et al., in Proc. Extended

[13] J. P. Russell, A. M. Goodman, L. A. Good-

[18] B. J. Baliga, “Temperature behavior of insu-

Abstracts of the 16th Int. Conf. Solid-Sate Devices

man, and J. M. Neilson, “The COMFET—A new

lated gate transistor characteristics,” Solid-

Materials, Kobe, Japan, 1984, pp. 309–312.

high conductance MOS-gated device,” IEEE

State Electron., vol. 28, no. 3, pp. 289–297, 1985.

[24] Stanford Sues Harris Corp., Claims Pat-

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[19] A. Mogro-Campero, R. P. Love, M. F. Chang,

ent Infringement, News Release, Stanford Univ.

63–65, Mar. 1983.

and R. Dyer, “Localized lifetime control in insu-

News Service, Stanford, CA, Mar. 8, 1994.

by B. Jayant Baliga

IGBT: The GE Story

T

The IGBT has become widely accepted as the power device of choice for mediumEmitter Emitter Gate and high-power applications + + + where the circuit operating N N N Gate Gate P-Base voltages exceed 200 V. It has P-Base P-Base enabled the development of highly efficient adjustable N-Drift N-Drift N-Drift speed motor drives for industrial applications, com+ + + pact fluorescent lamps for P P P lighting, and the electronic (a) (b) (c) ignition system for transportation. The benefits of this fig 1 Cross sections of IGBT device structures: (a) the collector technology to society have V-MOS, (b) the collector D-MOS, and (c) the collector U-MOS. been quantified in previous publications [1], [2]. Cross sections of the IGBT structhe crucible for the gestation of Digital Object Identifier 10.1109/MPEL.2015.2421753 ture are shown in Figure 1. They IGBT technology. Date of publication: 24 June 2015 his article describes the events that led to the conception, development, and commercialization of the IGBT at the General Electric (GE) Company. A unique set of circumstances consisting of the diversity of GE product divisions, a corporate edict to maintain businesses leadership using innovations in technology, and a visionary management style from the top of the company formed

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