1、附录 A Fuji IGBT Modules Application Manual Power converters, such as variable-speed motor drives and uninterruptible power supplies forcomputers, were revolutionized with the introduction of bipolar power transistor modules and powerMOSFETs. The demand for compact, lightweight, and efficient power co
2、nverters has consequentlyalso promoted the rapid development of these switching devices.Bipolar transistor modules and MOSFETs however, cannot fully satisfy the demands of these powerconverters. For example, while bipolar power transistor modules can withstand high voltages andontrol large currents,
3、 their switch -ing speed is rather slow. Conversely, power MOSFETs switch fast, but have a low withstand voltage and current capacity. Therefore, to satisfy these requirements, the insulated gate bipolar transistor (IGBT) was developed.The IGBT is a switching device designed to have the high-speed s
4、witching performance and gatevoltage control of a power MOSFET as well as the high-voltage / large-current handling capacity of abipolar transistor. Compares the basic structure of an IGBT and a power MOSFET.The IGBT is characterized by a p+-layer added to the drain side of the power MOSFET structur
5、e.It is this p+-layer that enables the various IGBT features explained in this manual. As shown in Fig.1-2,the ideal IGBT equivalent circuit is a monolithic Bi-MOS transistor in which a pnp bipolar transistor and a power MOSFET are darlington connected.Applying a positive voltage between the gate an
6、d the emitter,awitches on the MOSFET and produce a low resistance effect between the base and the collector of pnp transistor,thereby switching it on. When the applied votage between the gaate and the emitter is set to”0”,the MOSFET will switch odd, causing the supply of base current to the pnp tran
7、sistor to stop and thereby switching that off as well. This means that an IGBT can be switched on and off using voltage signals in the same way as a power MOSFET. Like the power MOSFET, a positive voltage between the gate and the emitter produces a current flowthrough the IGBT, switching it on. When
8、 the IGBT is on, positive carriers are injected from the p+-layeron the drain side into the n-type bases layer, thereby precipitating conductivity modulation. Thisenables the IGBT to achieve a much lower on-resistance than a power MOSFET. The IGBT has a very low on resistance for the following reaso
9、ns:A power MOSFET becomes a single-layer semiconductor (n-type in the diagram) when it is in theon-state, and has resistor characteristics between the drain and the source. The higher the breakdownvoltage and the device, the thicker the n-layer has to be, but this results in an increaseddrain-to-sou
10、rce resistance. Thus, as the breakdown voltage increases so does the on-resistance,making it difficult to develop large capacity power MOSFETs. Unlike the power MOSFET, the n-base layer resistance of the IGBT becomes negligible due to theeffect of the pn diode formed by the junction of the added p+-
11、layer and n-type base layer when viewed from the drain side. As the ideal equivalent circuit in Fig. 1-2 shows, the IGBT is a monolithiccascade-type Bi-MOS transistor that consists of a pnp bipolar transistor and a power MOSFET connected in Darlington form. The device can be compared to a hybrid cas
12、cade-type Bi-MOS transistor that consists of a bipolartransistor chip and a power MOSFET chip. The major difference is the on-resistance of the powerMOSFET. The on-resistance is extremely small in the IGBT. Considering the chip for inter-chip wiring,the IGBT is superior to the hybrid cascade-type Bi
13、-MOS transistor. Fuji Electric Device technology (FDT) began producing and marketing IGBTs (insulated gate bipolartransistors) in 1988 and has been supplying them to the market ever since. Fig. 1-3 is an overview ofthe development of, and technologies implemented in the first five IGBT generations.
14、FDTsucceeded in enhancing the characteristics of the first three IGBT generations, by using epitaxialwafers, optimizing the lifetime control techniques, and by applying fine patterning technology.Thecompany was able to significantly enhance the characteristics of the fourth and fifth generations bys
15、witching from epitaxial wafers to FZ (floating zone) wafers. This achievement brought about arevolutionary transition in conventional approaches to IGBT design. The basic design concept of epitaxial wafer-based IGBTs (the third and fourth generations rated at upto 600V, called punch-through (PT) IGB
16、Ts) is described below. These IGBTs were injected with acarrier at a high level from the collector side so that they would be filled up with the carrier to reducethe on voltage when they are turned on. In order to obtain this on voltage reduction, an n-buffer layersupporting a higher voltage was bui
17、lt in the FZ wafer to achieve a thinner n-layer. Moreover, alifetime control technique was implemented to remove the carrier filling up the IGBTs so as to lessenthe switching loss (Eoff) when they are turned off. Implementing lifetime control techniques led to increased on voltage because its effect
18、 (reducedcarrier transport efficiency) persisted even in the regular on state. FDT initially worked around thisproblem by pursuing higher-level carrier injection.The basic design concept of epitaxial wafer-basedIGBTs can be simply expressed in the wording higher-level injection and lower transport e
19、fficiency.In contrast, FZ wafer-based IGBTs (fourth-generation 1200V IGBTs and later) implement the oppositeapproach to the basic design concept, such that carrier injection from the collector is suppressed toreduce injection efficiency and thus boost transport efficiency.The aforementioned design c
20、onceptof higher-level injection and lower transport efficiency implemented in epitaxial wafer-based IGBTshad a limited effect in terms of characteristics enhancement as it took the illogical approach of usinglifetime control techniques to suppress a carrier that had already been injected with a carr
21、ier. Moreover, the use of lifetime control resulted in certain effects that were detrimental to addressing thethen growing need for the parallel use of IGBTs. One of these was increased variation in on voltagecharacteristics caused by lifetime control. The new FZ wafer-based non-punch through (NPT)
22、IGBT (implemented from the fourth generation) and field stop (FS) IGBT (implemented from the fifthgeneration) were the result of technologies we developed to deal with these problems.The IGBTsare essentially designed to control the impurity level of the collector (p+ layer), without relying onlifeti
23、me controls, to suppress carrier injection efficiency.Yet, Fuji Electric had to work out an IGBT that withstood voltages as high as 1200V and that was as thin as one hundred and several tens ofmicrons to achieve characteristics superior to those of an epitaxial wafer-based IGBT. (With a FZwafer-base
24、d NPT or FS IGBT, the n-layer would approximate the chip (wafer) in thickness, and lessthickness meant a lower on voltage.) In other words, the development of an FZ-wafer based IGBT has been a constant struggle for ever-thinner wafers. FDT has launched a new line of NPT IGBTs that have evolved out o
25、f the fourth generation of 1200VIGBTs, as the S-series resolve these tasks.The company has made progress in developing 600VIGBTs requiring less thickness to such point that the market release of the 600V U series (fifthgeneration) is just around the corner. The U-series fifth generation of 1200V IGB
26、Ts has advancedfrom the NPT structure to the New FS structure to achieve enhanced characteristics that surpass theS series. The FS structure, while adhering to the basic design concept of the lower-level carrierinjection and higher transport efficiency with a lifetime control-free process, has an n-
27、buffer layersupporting a higher voltage was built in the FZ wafer to achieve an IGBT structure that is thinner thanthe NPT structure. The company has completed reparations for putting on the market the resultantU-series of 1200V IGBTs which has an on voltage that is lower than that of the S-series.T
28、histechnology is also implemented in a high withstand voltage line of 1700V IGBTs, which will soon beput on the market as well. FDT has also pursued a finer-patterned surface structure as a technological prerequisite to enhancingIGBT characteristics.(Because an IGBT is made up of numerous IGBT block
29、s, fine patterningshould allow a lower on voltage to be attained for more IGBT blocks.) FDT was able to realize moreenhanced characteristics with the first four IGBT generations in terms of fine patterning in a planar structure (in which IGBTs are fabricated in a planar pattern).However, the company
30、 was able to dramatically enhance the characteristics with the fifth generation of the 1200V and 1700V lines ofIGBTs, as a result of a technical breakthrough it made in fine pattern technology by drilling trenches inthe Silicon (Si) surface. The most difficult challenge inproducing an IGBT was makin
31、g gatecontrolled protection possible. Differingfrom the ideal equivalent circuit shownin Fig. 1-2, the actual IGBT is acombination of thyristor and MOSFET as shown in Fig. 1-5.The circuit design in Fig. 1-5 has one problem however, if the thyristor istriggered, then the IGBT cannot beturned off. Thi
32、s phenomenon, knownas “latch-up”, may allow an overcurrentto destroy the device. To prevent this “latch-up phenomenon”,the following techniques are used: 1) Reducing the base-emitterresistance makes the device lesssusceptible to latch-up. 2) Optimizing the thickness of the n+-buffer layer and the impurityoncentration, allows the EFh ofthe pnp transistor to be controlled.
