R & D Activities for Power Semiconductor Devices in South Korea

Eun-Dong Kim and Pill-Hwan Park*

Power Semiconductor Research group, Korea Electrotechnology Research Institute
P. O. Box 20 Changwon, 641-120 Gyungnam, Republic of Korea

* Machinery and Electronics Technology Devision, Ministry of Science and Technology
1st, Jungan-dong, Kwacheun, 427-715 Kyungki, Republic of Korea


Nation-wide research and development activities for power semiconductor devices in South Korea have been promoted by sponsorship of the Government, the Ministry of Science and Technology, since 1997. The activities have covered a wide range of devices including insulated gate bipolar transistors and their intelligent modules. The sponsorship is expected to advance the realization of ¡®Power System on Chip¡¯ through intelligent power integrated circuits. Our efforts have given very positive effects for the domestic companies to penetrate the conservative power semiconductor market with new devices and to expand their market shares. Help of national research institutes and universities has certainly encouraged for emerging companies to introduce their products to the market.


1. Introduction
The history of power semiconductor devices started with the invention of the all solid-state amplifier structure, so-called ¡®transistor¡¯, in 1949. Strictly speaking, the first controllable power semiconductor switch was commercialized by GE Co. Ltd., USA, with the trade name of SCR (Silicon Controlled Rectifier) in 1957. The International Electrotechnical Committee (IEC) defined its engineering name as ¡®thyristor¡¯, exactly ¡®reverse-blocking triode thyristor¡¯ in 1968. The development was deeply indebted to the purification technology of silicon, so-called ¡®floating-zone (FZ) refining technology¡¯ developed in early 1950¡¯s, because the earlier germanium has the severe thermal instability problem in its device application in spite of its high carrier mobility. We have still used FZ Si wafers of high resistance for high-voltage power semiconductor devices while general IC industries are using Czochralski Si wafers.
Development of different power semiconductor devices opened a new engineering field called ¡®power electronics¡¯ and has led it technologically. But recently the technology advance in power electronics has stimulated to develop new higher-performance power devices, resulted in MOS-gated bipolar-mode devices. Efforts for the development of ideal switches having the infinite voltage-blocking capability with no leakage currents, no on-state voltage drop, and no switching time during on and off transitions will be continued.
On the other hand, user¡¯s demand for the power system on a chip has promoted the development of so-called ¡®Smart Power IC¡¯ by aid of the Ultra-Large Scale Integrated-Circuit (ULSI) technology.
The technology level in power semiconductor devices is certainly behind that in ULSI as much as one or two generations, although the beginning of the IC industry was greatly indebted to the power device technology. Engineers for power electronics, especially in the industry field, have not willingly used new power devices untill others, especially competitors, verify their reliability by field application. Also the long lifetime of the heavy industries¡¯ equipments using power devices might be an obstackle against the market explosion of new devices because lots of investment are required to substitute a new system with the new devices for an old system with old-fashioned devices. 
The world market of the power devices has steadily grown and the growth rate (about 10 - 15%/year) will be lasted during early 2000¡¯s. But the share in the total semiconductor market has decreased year by year because of the rapid growth of microprocessor and memory devices. Although the market portion of power devices will go down below 10% of the total if the market price of memory devices maintains as predicted, the importance of power semiconductor devices can never been ignored.
Korean domestic semiconductor companies started to show their interests to power semiconductor devices since late 1980¡¯s by high-voltage bipolar transistors for television sets. At that time, imported products, even power diodes, covered almost of the domestic market. Until now more than 60% of the domestic diode market should be covered by the imported. But domestic goods have actively substituted the imported in field of high value-added devices such as power MOSFETs.

2. Definition of Power Semiconductor Devices
Since power semiconductor devices can be classified with several sorts, it is not easy to define them in a few words. In Table 1, definitions of current and voltage ratings for different kinds of the devices are summarized. But it is noted that these definitions are not formally established.

Table 1. Definition of power semiconductor devices
Sort Definition
Discrete Blocking voltage ³ 100V orCurrent rating ³ 1A
Power IC Blocking voltage ³ 50V orCurrent rating ³ 0.5A

In the late 1980¡¯s power bipolar transistors of multi-stage amplification structure, so-called Darlington structure with high-current gain, were developed. For fast switching and protection of the device, diodes and resistors were needed but their integration on a chip was not easy because of their high power dissipation. High-voltage insulation between power chips necessary for inverter circuit was also an obstacle for the integration. These difficulties for the integration resulted in a ¡®module¡¯ structure. In the module devices, power chips, freewheeling diodes and passive components of chip or SMD (Surface Mount Device) types are assembled on ceramic insulators with high thermal conductivity such as AlN, and finally encapsulated with polymer materials.
Recently modules having a driving circuit and protection circuits against over-heating, over-voltages, over-currents, and short-circuit with protection function against voltage shortage in the gate drive circuit have been commercially available. In general these devices are called ¡®intelligent modules.¡¯ For all types of modules, the definition of voltage and current rating for discrete power devices is still adaptable.
Before 1990¡¯s, the power IC (Integrated Circuit) market was mainly covered with general linear power ICs such as analog-type voltage regulators. In late 1990¡¯s analog/digital mixed mode power ICs such as MOSFETs¡¯ and IGBTs¡¯ gate driver ICs appeared in the market. Nowadays user¡¯s demand and the integration technology push a trend for ¡®system on a chip. This trend presents us portable information equipments such as very compact and quite smart PCS (personal communication system) phones.

3. Advances in Power Semiconductor Devices and Their Applications
The development of highly pure Si in 1950¡¯s rapidly substituted the mercury rectifiers with solid-state pn-Si diodes through Ge diodes. Shortly after the invention of SCR, power bipolar transistors were appeared in market and resulted in stimulation of technology innovation for electric home appliances.
The development of power bipolar transistor modules with high current gain by the Darlington structures accelerated to develop highly functional systems such as numerically controlled machines. Commercialization of gate-turn-off (GTO) thyristor in late 1970¡¯s gave chances to find the capability of Japan and to establish the actual history of power electronics. Nowadays, GTO thyristor technology is still important in mass transportation system such as high-speed electric trains although novel voltage-triggering high-speed-switching MOS-gate structures markedly increases their application fields.
Because of long incubation time for confirmation of their reliability by users, it takes a long time for innovative electric systems employing new power devices to develop their market. It is also very difficult and takes long time even for new systems made by a new theory to penetrate the well-organized market by the same reason. In other words the lifetime of power devices and systems are long enough as much as 20 - 30 years. But their life cycle has recently been shortened since the development of power MOFETs and IGBTs of which technology developments have proceeded very rapidly. Such rapid progresses had been never experienced in older devices such as thyristors. The progresses have been deeply indebted to the expansion of their application range. Applications for power semiconductor devices are depicted in Fig. 1, where the boxes indicate the device voltage and current ratings required to meet the system needs.


Fig.1 The power semiconductor devices and their application according to switching power capability and operation frequency.

At voltages lower than 100V, two important applications are found in (1) switching-mode power supplies for computer, telecommunications and home/office automation systems, and (2) automotive electronics. Since the maximum current rating is about 30A(for defrosting) in car electronics, power MOSFET devices are the most suitable for them.
The lighting application supplies a relatively big market for power semiconductors, especially for power MOSFET. A report said the sales of power semiconductor devices for lighting application amount up to 12-16% of worldwide power semiconductor sales. Power semiconductor ballast system becomes commonly being used in home for florescent lamps. A domestic company has a relatively large share in the world market 
Since factory automation and industrial motor control systems are usually operated at voltages between 100 - 440V, device voltage rating is lower than 1,500V, therefore their power bipolar transistor systems have been replaced by MOSFET and IGBT ones.
Inverter traction systems for electric trains are ordinarily made in a operating voltage rage from 700 to 1,500V from which the device voltage rating must increase up to 4.5kV.
Recently FACTS (flexible AC transmission system) becomes no more a future technology, which will offer a huge market for high-power devices such as GTO thyristor. In such very high power system applications, thyristors will still play a major rule because voltage blocking and current handling capability of MOS-gate devices such as IGBT cannot reach to the thyristor¡¯s. Present maximum current and voltage ratings of a IGBT chip are 100A and 4.5kV, respectively. Although IGBT devices with a current capability higher than 1kA are now available, those have a module structure with several IGBT chips, which may results in lower reliability in comparison with high-current single-chip devices.
Table 2 shows historical relationships among developments of power devices, circuits, and electric system. 
The motivation energy for the development of power semiconductor devices was user¡¯s demands as follows:
1. High-voltage blocking capability
2. High-current switching capability
3. Rapid switching characteristics
4. Low power loss
5. High-temperature withstand capability
6. Easy (voltage) driving
7. High reliability
8. Intellectualization
9. High productivity for system assembly

These market demands have accelerated developing different kinds of power semiconductor devices.
Reverse blocking thyristors are still used in very high power systems such as high-voltage DC power transmission system but for easy parallel and series connection, light-activated(LA) thyristors are preferred. In 1996 a Japanese company developed 8kV/3kA LA - thyristor and thyristor valve blocks with them for HVDC connection in consociation with other two companies.
Bi-directional thyristor, so-call Triac, is also the cheapest device until now for direct AC control even though its blocking voltage and switching current are restricted to several hundreds volts and a few ten amperes, respectively. The reverse-conducting thyristors is no more produced now because of their device instability but reverse-conducting GTO devices with an isolation structure between GTO and diode parts are necessary for Integrated Gate Commutation Thyristors (IGCTs).
General thyristors have a critical disadvantage that they cannot be switched-off by a gate signal. In Japan the GTO thyristor with the switch-off capability by a pulse gate current was world-first commercialized. Increase rate of GTO thyristor production in Japan in 1994 recorded about 15% in comparison with 1993. It is undeniable that Japanese companies such as Toshiba, Mitsubishi, and Fuji have the world-top technology compatibility in high-power devices. Now they can make 6kV/6kA GTO device with 6-inch NTD (neuron transmutation doping) wafer. In the device proton irradiation technology is applied for improvement of the trade-off characteristic between power loss and switching time. In Korea a VVVF inverter systems with 4.5kV/3kA GTO have been used for the subway traction systems after the 4th line of Seoul.
IGCTs with hybrid integration of driver circuit have been used for development of high voltage inverters such as steel mill systems in Korea. Also we are developing an IGCT inverter for the traction system of Korean next-generation high-speed train system. Recent efforts for improving high-current switching capability of MOS-gate thyristors may open a new prospect for very high power systems like FACTS in this century.
Bipolar power transistors have been widely used until late 1980¡¯s but rapidly replaced by power MOSFETs in low-voltage systems because of easy constructing its drive circuit with low cost and high frequency operation resulting in a low audible noise and compact-size system. They has continuously replaced by IGBTs in systems of higher voltages. Now bipolar power transistor systems are hardly developed for new generation systems. We looked through the brief history of power semiconductor devices. Now the trend of technology improvement for each device is more carefully described.


Table 2. Brief chronological table for power devices, electric circuits, and electric systems. 
Period Power Devices Electric Circuits Electric Systems
-1899 l DC motorl Induction Motor
1900-1949 l Vacuum devicesl Mercury rectifierl Thyratronl Ignitronl Transistorl Amplifiers l Rectification circuit theoryl Cyclo-converterl Resonance-type inverter l Thyratron 
1950¡¯s l Junction transistorl Ge rectifierl Si rectifierl Thyristor l Jones circuit l Ignitron electric train
1960¡¯s l FET, SITl MOSETl Triacl Light-activated thyristorl GTO thyristorl ICs and HICs l McMurray circuitl PWM inverterl VVVF inverterl Multiphase chopperl Impulse current circuits l Thyristor Leonardl VVVF inverter for AC motorl CVCF power supplyl Chopper-type electric trainl DC power transmission system
1970¡¯s l Microprocessorl Power transistors and modulesl High-power GTO thyristor l Switching regulatorl High-efficiency converter l Active filterl AC servo-motorl Vector controller forinduction motorl Static VAR compensator
1980¡¯s l Inverter modulesl Power BiCMOS devicesl IGBT and MCTs Zero-voltage switching theory l Inverter air conditionerl Inverter elevatorl Inverter electric trainl Linear motor controller
1990¡¯s l IGCTsl Smart Power ICs l Capacitive buck/bust circuits l Inverter power supply for solar power generator and SMESl Magnetic levitation trainl FACTSl DC/DC converters on chip

Ref.) 
FET: Field-Effect Transistor
SIT: Static Induction Transistor
PWM: Pulse Width Modulation
CVCF: Constant-Voltage Constant-Frequency
ICs: Integrated Circuits
HICs: Hybrid ICs
Triac: Bi-directional triode thyristor
BiCMOS: Bipolar-Complement Metal-Oxide-Semiconductor
IGBT: Insulated-Gate Bipolar Transistor
MCTs: MOS-Controlled Thyristors
SMES: Superconducting Magnetic Energy Storage
VVVF: Variable-Voltage Variable-Frequency

FACTS: Flexible AC Transmission System




3.1. Power Rectifiers
Power rectifiers are necessarily needed for all power electronics. During the 1950¡¯s, P-I-N rectifier was commercially introduced for power electronics applications. After then the demand for high power application such as the electro-decomposition of salt has promoted improvement in the ratings. In addition new device structures have been invented in order to improve the switching performance.
In Korea power diodes with 600V blocking voltages are made. Two companies are producing fast recovery diodes. Higher voltage diodes have been developed but not produced until now. But power diodes of VB 1,200V will be produced soon or late. Recently many companies have great interests in low-voltage high-current diodes for low-voltage DC/DC converters.

Low voltage power rectifiers
The reverse blocking capability of power rectifiers is usually less than 100V for their applications such as switching mode power supplies (SMPS) and automotive electronics. Silicon p-i-n structure has been widely used after a short germanium era. The doping concentration and thickness of the i-region limit the reverse blocking voltage. The high concentrations of p+ and n+ emitter suitable for high current injection yield a low on-state voltage drop close to 1V.
For high speed switching of the p-i-n diodes, excess carriers in the i-region should be rapidly removed. The reduction of reverse recovery time can increase their service frequency, which can reduce the transformer volume in SMPSs. 
For improvement of the reverse recovery characteristic, the Schottky barrier diode (SBD) was developed in the 1970¡¯s. This structure sustains the reverse blocking voltage within the n-drift region. The forward current flow is controlled only by the majority carrier, which yields a faster switching characteristic. The blocking voltage is limited by Schottky barrier lowering due to applied reverse voltage, accompanying high leakage currents. To suppress the Schottky barrier lowering in reverse bais condition, the junction barrier controlled Schottky (JBS) rectifier with a junction grid integrated under the MS contact was designed. VLSI technology could produce JBS rectifiers with an on-state voltage drop (VTM) of 0.35V though a recovery transient problem attributed to the auxiliary p-n junction remains.
In universities, different kinds of diode structures have been studied but the companies give attention to p-i-n and SBD structures. They are trying to apply the carrier lifetime control methods by electron or proton irradiation to make fast recovery diodes. Production of new devices such as JBS and MPS (Merged p-i-n/Schottky) diodes in Korea are interfered with patent problem.
A company has a great interest in power synchronous rectifiers with high current handling capability for low-voltage power supply application, which would be based on the VD (vertical double-diffused)-MOS structures.

3.2. Switches
1) Transistors
The name of ¡°transistor¡± is originated from the ¡°transfer resistance¡± which acts as a triode. When the transistor came into the light, in 1948, the transistor stands for the bipolar transistor. After advent of Field Effect Transistor (FET), however, thousands of new transistors have been invented for analogue and digital applications. The bipolar power transistors wired as Dalington configuration in order to enhance the current gain at the expense of high saturation voltage and slow turn-off time. Therefore, the Dalington bipolar transistors are used for high voltage and high current application. Bipolar transistors are one of the most competitive power switches that share more that 30% of the world power semiconductor market, higher market share than power MOSFET until early 1990¡¯s. But inherent drawbacks of bipolar transistor such as difficulty of gate drive and parallel operation, thermal runaway, power losses at driving circuit make the bipolar transistor substituted by power MOSFETs for high speed low power applications, and by IGBTs for high power applications. Therefore the effort to develop the power transistor modules based on bipolar transistors was directly transferred to IGBTs from late 1980¡¯s.
The first FET was invented on 1924 in form of Junction FET (JFET). In Japan, the JFET for power electronic circuit was developed by name of Static Induction Transistor (SIT) on late 1970¡¯s. The SIT is used at high frequencies around 100kHz, high voltage low current switching applications such as power supplies for induction heating system, microwave amplifiers, audio. The devices with ratings up to 1,200V and 300A are commercialized in Japan. In Korea FET devices have been studied only for communication systems in a different R&D program.
More promising FET device is MOSFET than SIT. Even thought the electrical characteristics of power MOSFET are similar to that of JFETs, the MOSFET could be easily build up in enhanced or depleted mode, n-channel or p-channel depending on application. Power MOSFET in trench structure on the Si device originated from VMOS on 1970's. This structure was made on (100) oriented silicon substrates, using wet etching technique to form the notch sloping from the horizontal at 54.7¡ã. The MOSFET channels are formed along the slope of V-groove to conduct current at appropriate bias voltage. The many single VMOS are connected in parallel on the silicon top surface at which the source and gate electrodes are metallized while the bottom of silicon wafer is metallized as common drain. This device provided the vertical high current path from top to bottom of the epi layer instead of lateral current flow at planar DMOS structure. The two scheme of VMOSFET, i.e., vertical current path and parallel connection of many VMOS cells have been adopted to many modern power MOS devices while the V-groove shape, however, was disappeared because of the high electric field and current concentration at vertex of groove showing low voltage blocking capability and thermal instability for blocking and conduction mode, respectively. DMOS structure, the basic processing technique for almost all power MOSFET even so far, was considered as the best alternative besides the VMOS in terms of the on-state resistance. The DMOS structures are utilized not only for MOSFET, but also for IGBT and some kind of MOS gated thyristors. The easy processing and stable operation of DMOSFET make the DMOSFET the most popular commercialized MOSFET. But the presence of JFET resistance under the gate makes the on-resistance of the DMOSFET higher than VMOSFET. Continuous efforts have been made to reduce the on-resistance per unit area for conventional DMOS. For example, the specific on-resistance (on-resistance per cm2) of 60V DMOSFET was 7mW-cm2 based on 10mm design rule in the 1970's. In 1990's, with the development of VLSI fabrication technique, the specific on-resistance of 0.75 mW-cm2 was demonstrated by 1.25mm rules. Even further improvement of the on-resistance with maintaining moderate voltage blocking capability could be possible by UMOS structure. The lower channel resistance in the UMOS due to its high channel density and highest electron mobility of the (100) crystal could result in the smaller on-resistance. In addition, the JFET resistance due to pinching effect from p-base in DMOS does not exist in UMOS structure to reduce on-resistance. Specific on-resistance of 0.58 mW-cm2 for the 60V UMOSFET has been reported.
IGBT is a hybrid MOS-gate transistor that combines the attributes of MOSFET gate and BJT. The device was commercially introduced in 1983, and since then the ratings and characteristics have improved significantly. The device structure shows no difference from MOSFET except n+ layer at the drain added by a p+ layer at the collector. The IGBT has a high input impedance of a MOSFET with BJT-like conduction characteristics. If the gate is positive with respect to emitter and the voltage is beyond the threshold value, an n-channel is induced in the p region. This gives the forward bias on the base/emitter junction of the pnp transistor and holes are injected in the n-region. The holes cross the reverse-biased collector junction and constitute the pnp transistor collector current. The minority carrier injection causes conductivity modulation in the n-region, significantly improving voltage drop over that of a MOSFET. Besides the low conduction drop, the IGBTs suffer from the slow switching time because of stored charge in the n-drift region. The turn-off time of IGBT can be controlled by means of carrier lifetime control techniques. For the power devices, the lifetime control by electron irradiation is widely applied because of reproducibility, precise dosage control, and contamination-free process. Although the electron irradiation was successful in reducing the turn-off time, it was found that the on-state voltage drop of the IGBT increases by the lifetime control. Recently the proton method is actively studied because it gives a smaller increase of the voltage drop.
After successful application of UMOS trench structure to MOSFET, this structure was considered useful to IGBTs. The specific on-resistance can be minimized with UMOS gate structure on IGBTs along with the channel density increase and JFET resistance elimination. With the trench process, the relatively small UMOS cell size can be made in comparison with the DMOS cell (typically 20mm) for same design rules. In addition, the IGBT¡¯s latch-up at high currents could effectively be suppressed by using UMOS gate. The hole current path of UMOS IGBTs is somewhat straight and short compared to in the p-base of DMOS IGBTs. Since wide safe-operating-area(SOA) of UMOS structure has been shown to be superior to that for the DMOS structure, UMOS IGBTs are expected to replace the DMOS IGBT in the future. 
As mentioned before, the ratings of the IGBT have been significantly increased. IGBT modules with rating of 4,500V and 1kA made by Japanese and European companies are in the market. The IGBTs already take place the BJT at medium frequency applications, and even MOSFET at frequency up to 20kHz applications. It is clear that the IGBT will keep extend its application area until invention of better power devices. 
In Korea, Fairchild Semiconductor Korea Co. Ltd. produces 600V IGBT chips including their modules and is developing 1,200V chips. Many companies have developed IPMs (Intelligent Power Modules) based on IGBTs for various applications such as DC power supplies and motor drivers. Now drivers for air-conditioners are commonly using IPMs. The Ministry of Science and Technology (MOST) has sponsored the R&D projects for IGBT chips and modules since 1997.

2) Thyristors
Thyristors have been one of the most important power semiconductor devices, used extensively in power electronic circuit. The thyristor, switching-on at a specified angle of positive half cycle of power frequency current, makes it possible to deliver the electric power with small ohmic loss that was impossible by mechanical switches Depending on the physical construction, and turn-on and turn-off behavior, thyristors can be classified into several categories such as general phase-control thyristors, Fast-switching thyristor, bidirectional triode thyristor (TRIAC), reverse-conducting thyristor, static induction thyristor (SITH), light-triggered thyristor (LTT), gate turn off thyristor (GTO), and MOS gated thyristors. Each kind of thyristor has its own application. For examples, SCR is for general purpose, TRIAC for bidirectional AC switching, SITH for fast switching and power circuit with high di/dt and dv/dt, and LTT for HVDC systems. As the thyristors are used for diversified applications, the gate-turn-off feature of thyristor became required. The GTOs have advantage over the thyristors: (1) elimination of commutating components in forced commutation, resulting in reduction in cost, weight, and volume; (2) reduction in acoustic and electromagnetic noise due to the elimination of commutation chokes; (3) faster turn-off, permitting high switching frequencies.
A MOS-Gated Thyristor combines the features of regenerative four-layer thyristor and a MOS structure. After the advent of MOS-gated thyristors such as MOS-controlled Thyristor (MCT), Base Resistance controlled Thyristor (BRT), and Emitter Switched Thyristor (EST) they are considered as easy gate drive devices as MOSFET or IGBTs, when it comes with MOS gates on the cathode side. The MCT, the first MOS-gated thyristor shows the low forward voltage drop comparable to GTO, switching time as fast as IGBT, but no forward current saturation characteristic, just like conventional thyristors. It turns on by negative bias voltage at the gate and turns off by positive voltage. Even if the 1,000V/65A MCTs was already commercialized by Harris, the circuit engineers are not willing to use the MCT for certain applications such as hard switching circuits because the turn-on or turn-off speed of MCT are not controlled by gate bias. Harris says that the turn-off capability of MCT will be 400A/cm2 in one or two years. The second generation MCT of Harris is claimed that it would be able to run a resonant circuit at 300kHz - close to switching speed of fast and ultra fast IGBT, as well as only a half of conduction losses compared to that of IGBTs. 
The lack of the FBSOA in MCTs could be overcome by subsequent MOS-gated thyristor named EST. The principle of the EST is to carry the thyristor current through n-channel enhance-ment mode MOSFET integrated into the p-base region of the thyristor. Turn-off can be obtained simply by reducing the gate voltage below the threshold voltage of the two MOS gates. This thyristor contains a parasitic thyristor that can latch-up at high current densities that brings lost of gate control of the device current. The EST with diverter, a lately developed device retaining current saturation feature of the EST, was reported improvement of its maximum gate-controlled turn-off current density of the conventional EST. VTM of EST is about 0.5V higher than that of MCT due to the series MOSFET. Therefore, the trade-off curve of the EST is inferior to MCT. 
One of solutions to keep the current saturation characteristics and wide SOA while providing low VTM can be a Dual-Gated Base Resistance Controlled Thyristor. With the separate gate bias control, it operates as IGBT when it turns-on and as thyristor during forward conduction mode. 
The MCT is the only device commercialized at present among the MOS-gated thyristors. Most device and circuit engineers expect that the MOS-gated thyristors could be soon or late used at power conversion systems in which the IGBTs and GTOs are currently used exclusively. In Korea, therefore, an effort to develop MOS-gate thyristors for future power switches has been conducted by universities.
IGCT (Integrated Gate Commutation Thyristor) is very attractive as one of promising alternatives for high-voltage high-power switches. IGCTs are the integrated hybrid devices with a switch and a driver circuit. In Korea, high-voltage motor driver systems using IGCTs has been developed for applications of steel-making mill driver, pump driver, and traction driver for high-speed train. KERI (Korea Electrotechnology Research Institute) has developed IGCTs. The MOST has sponsored the R&D project since 2000.


5. Conclusion
Changes in the market and technology of power semiconductor devices have very conservatively made but the power semiconductor industry has dramatically changed during a few decades in USA and Europe. In Korea, Fairchid Semiconductor Co. Ltd., USA, could buy the power semiconductor division of Samsung Electronics Co. Ltd. during the foreign currency crisis in Korea. KEC Co. produces power diodes, transistors, and ICs but is specialized with relatively low-power and low-voltage devices, i.e. smaller than 50A and 600V.
Nation-wide research and development activities for power semiconductor devices in South Korea have been promoted by the sponsorship of the Government, the Ministry of Science and Technology, since 1997. From the mid of 1995 to the mid of 1996, KERI conducted the leading feasibility study for the national R&D program for the development of power semiconductor devices.
The R&D activities in the program have covered a wide range of devices including insulated gate bipolar transistors and their intelligent modules. The most promising devices in the program are power MOSFETs, IGBTs, IGBT modules, IGBT IPMs, and IGCTs. Our works are expected to advance the realization of ¡®Power System on Chip¡¯ through intelligent power integrated circuits. Our efforts have given positive effects for the domestic companies to penetrate the conservative power semiconductor market with new devices and to expand their domestic market shares. The help of national research institutes and universities has certainly encouraged for emerging companies to introduce their products to the market.
Acknowledgements: This work was sponsored by the Ministry of Science and Technology, Republic of Korea.
References
1. E. H. Nicollian and J. R. Brews, MOS (Metal Oxide Semiconductor) Physics and Technology, John Wiley & Sons, New York, 1982.
2. B. J. Baliga, Power Semiconductor Devices, PWS Publishing Co., Boston, 1996.
3. E. D. Kim, ¡°Technical Trend of Power Semiconductor Devices,¡± Proc. Semicon Korea ¡¯97, Seoul, 1997.
4. B. K. Bose, ¡°Power electronics and motion control ¨C technology status and recent trends,¡± IEE PESC conference Record, pp. 3-10 (1992).
5. N. Iwamura, B. J. Baliga, R. Kurlagunda, G. Mann, and A. W. Kelley, ¡°Comparison of RBSOAs of ESTs with IGBTs and MCTs,¡± IEEE Int¡¯l Symp. On Power Semicon. Dev. And ICs, Abstr. 5.2, pp. 195-200 (1994).
6. E. D. Kim et al, R&D Planning for Development of Power Semiconductor Technologies, MOST, Rep. of Korea, 1996.

Introduction of Authors
Dr. E. D. Kim was born in South Korea in 1958 and received his Ph. D. degree in 1985 at Dept. Mater. Sci. Eng., Korea Advanced Institute of Science and Technology (KAIST). He worked for KAIST in the field of ZnO varistor for 4 years before joining with KERI in 1986. He has worked to develop power semiconductor devices for more than 10 years in KERI. Now he is the director of Advanced Materials and Application Lab and conducts two national R&D programs on Si power semiconductor devices and SiC devices.
Mr. P. H. Park was born in South Korea in 1960 and received his B. S. degree at Dept. Elect. Eng., Chonbuk Nat¡¯l Univ. and M. S. degree in the field of Sci. Tech. Policy at Univ. of Manchester, U. K. in 1994. He has served as a government officer in MOST since 1988 and now is the Director of Machinery and Electronics Div., MOST, managing the national R&D program on the development of power semiconductor technologies.