New Pe Devices Next Tasks

Integration of Power Devices-next tasks Toru Araki Mitsubishi Electnrc Corporation, Power Device Works 1-1-1 Imajukuhigashi, Nishi-ku, Fukuoka-City Fukuoka, 819-0192, Japan Tel.: +81/(92)-805-3330 Fax: +81/(92)-805-3745 E-Mail: arakitgmailloka.melco.cojp

Keywords «EMC/EMIJ>, Environment>>, FWD>>, High voltage IC's»>>, IJGBT>>, IPM>>, Matrix converter»,

«Monolithic power integration>>, Noise>>, Packaging>>, Power semiconductor device>>, Soft switching>>

Abstract This paper presents new power chip concepts such as Reverse Conducting IGBT (RC-IGBT), which are integrated IGBT with Diode and Reverse Blocking IGBT (RB-IJGBT). The RC-IJGBT will have a big impact for conventional Power Modules. Because, by using RC-IGBT, we can save resources such as Silicon Chip (including material itself and production energy) and also save Packaging Materials. By using RB-IGBT, we will able to make new Power Control Systems such as AC Matrix Converter and thus eliminate the large DC link Capacitor. High Voltage IC (HVIC) is used already as simple gate drive circuit in low power area. By using HVIC, a single gate power supply is enough for driving all 6 inverter switches. This paper presents newest HVIC concept and structure. We are developing new module packaging concepts having a new thermal dissipation structure and using transfer-molded package. This allows us to reduce package size and weight. Consequently our newest package will save resources of packaging and logistics and energy of transport. The newest Power Module, whose key concept is called "Environmental Compatibility", will be a combination of RC-IGBT (or RB-IGBT), HVIC and new packaging technologies in order to save resources. The Key Word "Environmental Compatibility" is indicating our new Power Device's Direction.

Introduction The first wave of Power Device was generated with thyristor and triac, which ware uncontrollable latching devices; their maj or applications were traction and high power management equipment. And the second wave had been brought by bipolar transistor, which was controllable un-latching device for industrial inverter system. Recently, the third wave has come with MOS gate controlled devices such as MOS FET and IGBT. Those new Power Devices are expanding their application fields, i.e. home appliance and automobile those are huge volume market [1]. Generally, many customers use Power Device as Power Module, because customer can design Power Control System easily and can reduce any trouble in development stage by using Power Module. So many customers have accepted Power Module so far [1]. Usually Power Module is used for saving energy, but recently Power Module is facing the task to save resources itself. We indicate the Key Word of next generation Power Module as "Environmental Compatibility". In order to save natural resources and to reduce hazardous substances, we are developing new concept technologies.

Power Chip Technology

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The newest Power chip technology is based on thin wafer process technology. At first, the thin wafer process technology is used for the improvement of conventional IGBT's characteristics. The IGBT has trade-off relationship such as "On-state Loss Vce(sat)" versus "Switching Loss (Eoff)j. By using thin wafer process technology, we can improve that trade-off relationship about 20% (see Fig. 1). Fig. 1 shows 1200V IGBT trade-off relationship. The thickness of thin wafer IGBT is about 130 jm. At second, by using thin wafer process technology, we can realize new concept IGBTs. The first one is the Reverse Conducting IGBT (RC-IGBT) [2]. RC-IGBT is integrated trench gate IGBT with Free Wheeling Diode (FWD) in parallel connection. Fig.2 shows the three-dimensional cross-section of the RC-IGBT. Usually, conventional voltage source inverter system is constructed by twelve power elements, six IGBTs and six FWDs (see Fig.3). By using RC-IGBT, number of power elements will be half value, only six RCIGBTs. This fact is having a big impact for packaging of power module, because it is easy to reduce the packaging size or to mount 50% larger chip in the same size of conventional power module package. To use the RC-IGBT is one of the "Environmental Compatibility" concepts. 2.40

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Fig.2 Three-dimensional cross-section of the RC-IGBT

The trench gate IGBT is formed on the front side of RC-IGBT and striped n-region and striped p-region are independently formed on the backside of RC-IGBT. While in IGBT operation, striped p-region on backside of RC-IGBT works as collector of IGBT, while in FWD operation, n-region on backside of RCIGBT works as cathode of FWD. RC-IGBT works alternately in IGBT mode and FWD mode, therefore j unction temperature does not swing so much and this fact has an impact for improvement of power cycling lifetime. This new RC-IGBT structure has been realized recently by using thin wafer process technology. Fig.4 shows the image of comparison of power chip bonding area between conventional IGBT with FWD and RC-IGBT. By using RC-IGBT, number of emitter wire is reduced to almost half value, so the wiring inductance is reduced. Because of reducing the area of pn-junction about 40%, also the j unction capacitance is reduced. Thus the resonant frequency of power chip capacitance and wiring

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inductance is getting higher. Due to this increase of switching noise frequency, customer can design noise filter circuit that is smaller than in today's conventional design. This fact brings much better solution for customer side. is'

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(a) RC-IGBT inductive load turm-on (b) RC-IGBT inductive load turn-off Fig. 6 S witchi ng waveform of the RC-IBGT

Fig.6 shows switching waveform of the RC-IGET. It can be seen that the fundamental switching characteristics of the fabricated RC-IGET reached a level conparable to those of conventional IGET with exernal FWD. The turn-off tail current is very small and short, because of short emitter effect by n-region on baclside of RC-IGCT [3]. The RC-IGCT's switching loss is much smaller than conventional Planer IGBT's switching loss. Total inverter loss of RC-IGET is improved more than 20% against loss of conventional Planer IGCT with FVD. By using local lifetime control technology such as He+ irradiation and backside activating technology, it is possible to optimize FWD 's and IGBT's characteristics individually in RC -ICGT. Exactly, fabricated RC-IBGT was used He+ irradiation technology to reduce reverse recov ery current. The RC-IGBT competes with super junction MOS FET, which has also an integrated FWD. However because of production cost issue, the RC-IGCT is superior to super junction MOS FET. We are aiming to mass-product the RC-IGBT, and in the near future, we will replace the c onventional IGBT with externral FWVD by ne w RC-ICB T. The second one is the Reverse Blocling ICB T (RB-ICBT) [4,5]. The RB-IGET is an IGBT in which the junction between collector and n-layer shows a blocking capability. Fig.7 shows cross section of the RBIGCT to block reverse voltage, the pn-junction that exists on the collector side of every IGCT is used to

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block in reverse direction. To get a blocking capability of the backside junction with ajunction termination structure on the topside, a deep diffusion area at the edge of the device is necessary to bring the backside junction to topside (Fig.7). The RB-IGBT is very suitable for AC matrix converter (see Fig.8). Because by using two RB-IGBTs in anti-parallel, it is easy to make bi-directional switch. The equivalent circuit of RB-IGBT shows IGBT and reverse blocking Diode in series (Fig.8), but actual RBIGBT does not has any series Diode to block reverse voltage, but has only deep diffusion isolation area to block reverse voltage. So VCE(sat) of the RB-IGBT is lower than VCE(sat) of conventional IGBT with reverse blocking Diode in series. This is the big advantage of the RB-IGBT against conventional IGBT with reverse blocking diode. The RB-IGBT according to Fig.7 needs deep and wide diffusion area for isolation. This is not acceptable in terms of manufacturing cost. So we are going to develop Trench Isolation RB-IGBT (TI-RB-IGBT) that is using deep trench technology to make isolation area [6]. This technology was applied already for super junction high voltage MOSFET recently. The isolation area of TI-RB-IGBT is much smaller than the deep diffusion RB-IGBT. So we can realize reasonable chip size and the cost structure is comparable with conventional IGBT with reverse blocking Diode. VWhen we use AC matrix converter, we can eliminate the DC link capacitor having a very large capacitance. This brings a big impact for size and reliability of inverter system and is also a contribution to the "Environmental Compatibility" concept. 1pm Planar Gate IGBT

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Fig.8 AC matrix converter

Fig.7 Cross-section of the RB-IGBT

Gate drive technology Constant current drive

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The importance of gate drive circuit is same as the importance of power chips. Because EMI noise and surge voltage issue has become major problem of power management system design recently. In some cases, the noise filter size is bigger than inverter drive system itself. So many customers want to reduce the EMI noise and surge voltage as small as possible. Soft switching technology is brought to solve this EMI noise and surge voltage issue. We provide Intelligent Power Modules (IPM). IPM includes special gate drive IC that has soft switching circuit for EMI noise reduction and protection function for power

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element, which is IGBT or diode. When customers use IPM, they can design inverter system easily without any headache issue. Fig.9 shows special gate drive concept to reduce switching noise. The basic concept is that the gate of IGBT is driven by constant current source instead of conventional constant voltage source and the current value is switched by the emitter current value of IGBT that is detected by using sense emitter cell. On the turn-on state, when the emitter current level is low, gate drive current is small to decrease the output dV/dt and the output noise is reduced. When emitter current reaches the half value of rating current, gate drive current is increased to double value. This function is operated in less than 1 Lts. This high speed and complicated operation is realized by using high speed Bi-CMOS IC technology. Bootstrap Circuit

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Fig. 11 HVIC with bootstrap circuit Fig. 10 New gate drive circuit Fig 10 shows the newest gate drive circuit for our 5th generation IGBT that is called Carrier Stored Trench gate Bipolar Transistor (CSTBT). This gate driver is taken soft switching technology to reduce switching noise and special soft turn-off function to decrease surge voltage when CSTBT faces irregular condition such as over current or short circuit operation. High Side Island

Fig. 12 Block diagram of 600V half bridge driver The reduction of number of power supply for gate drive circuit is more important for small power inverter system, such as white goods application. In this case, the customer wants to design the inverter system as small as possible. High voltage IC (HVIC) technology is useful for single power supply concept. Fig. 11 shows HVIC with bootstrap circuit consisting of one resistor, diode and capacitor. By using this topology

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a single 1 5V power supply for both high side and low side gate drive function is enough. The HVIC for gate drive has high side island that include gate drive CMOS circuit for high side IGBT and high voltage level shift transistor to transmit on-off signals from low side island to high side island. Fig. 12 shows block diagram of 600V half bridge driver. This half bridge driver has two input terminals; high side control input and low side control input. They are controlled individually, but the interlock logic disables the chance of both high side and low side to be in on state at the same time in order to protect the IGBTs against arm-shoot-through. The under voltage protection circuits are included in high side island and low side island. This HVIC is fabricated by 600V Bi-CMOS-DMOS wafer process. The HVIC includes NPN transistor, PNP transistor, n-ch MOS transistor, p-ch MOS transistor, high voltage n-ch DMOS and high voltage p-ch DMOS that is used for reverse level shifting function [7]. The newest design rule of 600V HVIC is 1 .3 im. Fig. 13 shows 600V HVIC structure. B E

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Fig. 13 600V HVIC structure The 600V HVIC combines conventional Bi-CMOS structure with some unique structures to sustain such a high electric field. The first one is REduced SURface Field (RESURF) technology. Fig. 14 shows RESURF structure. The RESURF technology is often used for HVIC and super junction MOS FET. The depletion layer between p-substrate and n-epitaxial layer causes the depletion layer of surface pn-j unction to expand, so that the surface electric field is relaxed. It is realized to increase the breakdown voltage. If we take RESURF structure, we can surpass the Si limit of unipolar devices that is the trade-off relationship between breakdown voltage and on-voltage. The case of using RESU RF techn ique

Fig. 14 RESURF structure

Fig. 15 MFFP and Double buried layer structure

The second one is Multiple Floating Field Plate (MFFP) structure, and we have developed this unique structure. One Al layer and one poly Si layer structure MFFP. Al layer is used for conductor on IC, poly Si layer is used for gate conductor of MOS transistor, and therefore no additional layer is necessary to construct MFFP. The third one is double buried layer structure. Fig. 15 shows MFFP and Double buried layer structure. The avalanche position is shifted surface to substrate by the Double buried layer structure,

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so that the breakdown voltage is stabilized. Our 600V HVIC combines three unique stuctures that have been explained, high voltage DMOS and conventional Bi-CMOS that is used for smal signal conditioning. The technology tend of HVIC is almost the same as that of general IC; the design rule of HVIC has been still mniimized continuously. Our most progressive HVIC process is 0. SIm CD-MOS with One Time Programumable ROM (OTP-ROM) [8]. By using shrink 1. 3pm process, transistor size is reduced 1/4 of using 5pm process. When we use 0 Svtm process, transistor size is about I1/0 of 5pm process. Fig. 16 shows comparison of actual 600 HVIC chip size 5pm process (M63992FP) and shrink 1.3m process (MS1709FP). The characteristics of MS1709FP are almost the same as those of M63992FP. Only propagation delay of MS1709FP is half value as that of M63992FP, The 0.8m process include OTP-ROM, OTP-ROM will be usefful for caihbrating some characteristics by using digital trimTmng technology, i. e. total propagation delay of gate drive IC with JGBT/MOS FET, highly accurate analogue output voltage of output current converting to use the vector control etc. Of course, by using OTP-ROM and a lot of logic circuits, we can fabricate MCU; probably 4bit to Sbit, with gate drive {VJIC, This fact means the probability of realizing an inverter system module in the near future. Concerning the concept of inverter system module, we will prepare general inverter system module that will include the hard ware of inverter control circuits such as MCU, gate drive and protection circuits, output IGBT, and will have soft ware area to write any program in customer side. This module will be very easy to use and modify by customerfs taste. S.0p mBiCDMOS

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These are hig integration solutions, on the other hand we are developing to expand voltage range; 1200V 1{VIC.Fig 17 shows top view and cross-section of 1200V J{VIC. Development of 1200V HVIC has much higer technical hurdle than that of 600V HVIC. Because as for 1200V HVIC, if we take the same structure as 600V HVIC as hig voltage signal wire, we must use double thickness insulating layer between ground substrate and 1200V wire such as up to 2.5 mt SiO2, it is not acceptable for normal IC process. So we take unique structure, this is called "divided RESURF structure " [9]. Fig 18 shows block diagram of 1200V half bridge driver whose top view has been shown already in Fig. 17. This 1200V HVIC has special fimction as short circuit protection and fault signal comuniuication. Usually, three bridges make the inverter system; so that it causes to use three half bridge HVICs. When inverter system faces a failure condition such as short circuit in one bridge, 1200V HVIC detect short circuit condition and shut down own bridge, and it is necessary to shut down the other bridge. So that 1200V HVIC has communuication port of fault signal, which is Fo port. The Fo port of three 1200V half bridge driver are conected directly each other to make "wired OR logic". In normal condition, Fo port, which is connected open drain n-ch MOS transistor in 1200V J{VIC, is high, the condition changes to be failure in one bridge, the Fo port becomes low and the other two 1200V HVIC detect failure condition in

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inverter system through the Fo port and two l200V HVIC shut down own bridge by themselves. This function can guarantee much safety operation; this causes to protect IGBTs.

Fig.l8 Block diagram of 1200V half bridge driver The gate drive technologies are based on IC technology; such as the soft switching technology to reduce surge voltage and EMI noise, HVIC technology to decrease number of power supply and to realize easy using in customer side. The gate driver technologies become important point to realize "Environmental Compatibility" concept.

Packaging technology

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Fig.20 Comparison of case type and transfer-molded type Our newest packaging technology is based on transfer-molded packaging. The transfer-molded packaging technology has been often used for IC package, and we also have used it for low power range IPM, called "Dual-In-Line IPM". Such DIP-IPM is very suitable for home appliance use, such as air conditioner, refrigerator and washing machine. But recently, we are trying to use the transfer-molded packaging technology also for middle/high power applications. A first example of 300A/600V 2in1 package is shown in Fig.20 [10]. Fig. 19 shows the cross-section of new transfer-molded package. This package is using a unique thermal dissipation structure; the key technical element is an insulating sheet. The material of insulating sheet is epoxy resin with filler and its thermal conductivity is very high. By using Cu heat

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spreader to reduce thermal resistance of this structure; we can realize the same thermal resistance value as that of conventional case type structure, about 0, ldegfW. And we use Pb free solder at die bonding portion, so that we can realize completely Pb free package. The advantages of this transfer-molded power module are small size, lightweight and improvement of power cycle lifetime. Fig.,20 shows comparison of conventional case type and transfer-molded type. Concerning the comparison table of Fig.20, by using transfer-molded packaging technology; weight is reduced to 1/3, volume becomes to 1/5. This fact exactly complies with the key word "Environmental Compatibility" in middle/high range power module. R x

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On the other hand as for the improvement of low power DIP-IPM packaging, we are going to take the same thermal dissipation structure as new transfer-molded package, which is using insulating sheet. We call this new structure "Ver.4". Fig.2 1 shows the trend of packaging structure of DIP-IPM. By using the Ver.4 structure, the thermal resistance will became 60% of conventional full-molded package structure. We have a plan to prepare the Ver.4 structure in all package line-up such as SIP, super-mini DIP, mini DIP, large DIP and to cover 3A to 75A current range. Another direction of future packaging technology will be the direct lead bond structure. Fig.22 shows the cross-section and internal architecture of direct lead bond structure. The first feature of direct lead bond structure is increasing current density; therefore chip size of IGBT can be reduced. The second feature is low resistance of emitter wire, so on-voltage is reduced. The third feature is improvement of power cycling capability compared to conventional Al wire bond structure more than ten times. By using our new transfer-molded packaging technology and direct lead bond structure, we can realize higher reliability, lower cost, smaller size and lighter weight for power module package. This is the "Environmental Compatibility" concept.

Environmental Compatibility concept Table 1 shows the "Environmental Compatibility" concept. The improvement of power loss has been first priority issue in power devices until now, so that "Low Loss" has been the maj or item so far. But recently, the item "Low Noise" has become also much important, because of reduction of noise filter size and to realize easy to use in customer side. The "easy to use"-factor is very important to spread the market of power devices. The items "Small Size" and "Light Weight" cause also easy to use in customer side, but additionally they will allow to save resources of packaging, logistics and energy of transport. The hottest topic today is reducing hazardous substances to fulfill RoHS directive. By using our new transfer-molded packaging technology, it will be easy to realize Pb free packages without additional cost. Finally the "Environmental Compatibility" concept will bring the total cost down both on our side (as manufacturer of power modules) and customer side.

Conclusion Our "Environmental Compatibility" concept is based on new power chip technologies, new gate drive technologies and new packaging technologies. And we are going to combine all of them to save resources, energy and time. This will cause further cost reduction in both of customer side and our side, and will contribute to a further spreading of power control systems.

References [1] G.Majumdar et al. "Novel Intelligent power Modules for Low-Power Inverters", Proc. Of 1998 IEEE Power Electronics Specialists Conf.Vol.2, ppl 173-1179 [2] H.Takahashi et al. " 1200V Reverse Conducting IGBT ", ISPSD'04, ppl 33-1 36 [3] H.Akiyama et al. "Effects of Shorted Collector on Characteristics of GBTS", ISPSD'90, ppl 31-136 [4] H.Takahashi et al. " 1200V class Reverse Blocking IGBT (RB-IGBT) for AC Matrix Converter", ISPSD'04, pp12 1-124 [5] M.Takei, "The reverse Blocking IGBT for Matrix Converter With Ultra Thin wafer Technology", ISPSD'03,

ppl56-159

[6] N.Tokuda et al. "An ultra-small isolation area for 600V class Reverse Blocking IGBT with Deep Trench Isolation process (TI-RB-IGBT)",ISPSD'04, ppl29-132 [7] T.Terashima et al. " Structure of 600V IC and A New Voltage Sensing Device", ISPSD'93, pp224-229 [8] K.Shimizu et al. "A 600V HVIC Process with a built-in EPROM which enables new concept Gate Driving", ISPSD'04, pp379-382 [9] T.Terashima et al. "A New Level-shifting Technique by divided RESURF Structure", ISPSD'97, pp57-60 [10] T.Sakai et al. "Development of High Current Transfer-mold type Power Module with High heat-cycle

Durability", ISPSD'04,pp293-296

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