New 17V IGBT Modules with CSTBT and Improved FWDi John Donlon 1, Eric Motto 1, Shinichi Iura 2, Eisuke Suekawa 2, Kazuhiro Morishita 3, Masuo Koga 3 1) Powerex Inc., Youngwood, PA, USA 2) Power Device Works, Mitsubishi Electric Corp., Fukuoka, Japan 3) Fukuryo Semicon Engineering Corp., Fukuoka, Japan Abstract: This paper presents a new series of 17V IGBT modules using the new trench gate IGBT technology called Light Punch Through Carrier Stored Trench gate Bipolar Transistor - LPT-CSTBT - and a new free-wheel diode design. The current ratings of new 17V IGBT modules now go up to 36A for single switch types and 12A for dual/chopper switch types, which is 5% higher than previous conventional modules. 1. Introduction High voltage, high current IGBT modules are widely used for converters in high power applications such as traction drives. These converters have a continuous trend towards higher output power and smaller equipment size. In response to these market needs, IGBT modules having an increased rated current are necessary. This has led to the development of a novel series of 17V IGBT modules with 5% higher rated current by using a new IGBT/FWDi chip-set. This paper introduces the structure and performance of the newly developed 17V IGBT modules. 2. New 17V module product range In comparison with conventional modules, the features of the new 17V series, which have package compatibility with the conventional modules, are: a) 5% increased current rating in the same package size b) Reduced IGBT losses by using the carrier stored trench gate IGBT chip technology c) Suppressed diode oscillation by new soft reverse recovery FWDi Fig.1 and Table 1 show a comparison between the packages used for the conventional modules and those for the newly developed series. The new packages offer mechanical compatibility with the conventional ones, i.e., the same footprint and terminal outline, in spite of 5% increase in rated current or the equivalent rated current in a significantly smaller package. a) b) Fig.1: Package style comparison of 24A single switch type a) Conventional IGBT module b) New IGBT module Table 1: Line-up of the 17V IGBT module Package size (L x W) Ic Connection Conventional New 6A 8A 12A 12A 16A 18A 24A Dual / Dual Dual / Chopper CM6DY-34H CM8HA-34H CM8DZ-34H CM12HA/HC-34H CM16HC-34H 19 x 14mm 2 CM18HC-34H 19 x 14mm 2 CM24HC-34H 36A CM12E4C-34N CM18HC-34N CM24HC-34N 19 x 14mm 2 CM36HC-34N
The new 17V IGBT series offers a product range from 18A to 36A in single switch modules and 12A in dual/chopper switch modules, as shown in Table 1. G E To take an example, Table 2 shows the specification of the 12A dual/chopper module. p base n+ emitter V MOS Table 2: Specification of 12A Module (/CM12E4C-34N) Maximum ratings: Item Conditions Ratings V CES V GE = V, T jmin T j T jmax 17 V V GES V CE = V, T jmin T j T jmax ± 2 V I C T C = 8 C 12 A I CM Pulse 24 A P C T C = 25 C 64 W T j 4 +15 C V iso f=6hz 4 V rms Mass 8 g (typ.) Electrical/Thermal characteristics: Item Conditions Typical I CES V GE = V GES, T j = 125 C 4 ma V GE(th) V CE = 1V, I C = 12mA, T j = 25 C 7. V V CE(sat) V GE = 15V, I C = 12A, T j = 125 C 2.4 V V EC V GE = V, I C = 12A, T j = 125 C 2.1 V E on E off E rec V CC = 85V, I C = 12A 4 mj/p L S = 1nH, V GE = ±15V R G(on) = 1.3Ω, R G(off) = 3.3Ω 36 mj/p 9% integration 24 mj/p R th(j-c)q IGBT part 19.5 K/kW R th(j-c)r Diode part 42. K/kW R th(c-f) Thermal conductive grease applied 16. K/kW 3. Chip technology 3-1. IGBT chip technology The newly developed 17V IGBT modules are based on our new trench gate chip technology called Light Punch Through Carrier Stored Trench gate Bipolar Transistor or LPT-CSTBT. The features of LPT-CSTBT are as follows. a) Trench gate & Carrier stored structure b) Light punch through structure n- layer n+ buffer layer p + substrate Carrier stored layer C Fig.2: Cross section of LPT-CSTBT a) Trench gate & Carrier stored structure IGBT chips used in modules with high power rating need to be optimized for low losses and higher current density in order to increase the current rating. This reduction of losses is achieved by using the LPT-CSTBT chip technology. The development and features of this chip technology is explained in detail in references [1] and [2]. The cross section of the LPT-CSTBT is shown in Fig.2. The on-state voltage of the IGBT, VCE(sat) = V MOS + V diode. The V MOS is the voltage drop of the MOSFET portion between p base and n + emitter and can be reduced by the trench gate structure. The V diode is the voltage drop of the diode portion between p + substrate and n layer. It can be reduced by the carrier stored layer structure. As a result, the rated current of the LPT-CSTBT is increased in spite of decreasing the active chip area compared to the conventional planar IGBT design (see Fig.3) [1,2]. b) Light punch through (LPT) structure V diode VCE(sat) = V MOS + V diode The LPT structure has the advantage of wide SOA and positive temperature coefficient of VCE(sat). The LPT structure is achieved by implementing an n+ buffer-layer between n- bulk and p+ substrate. Another advantage of LPT is its narrow VCE(sat) distribution, since no lifetime control in n- bulk is required. [1,2]
Rated current of chip [A] 2 15 1 5 Planer IGBT LPT-CSTBT The carrier density profile of the conventional diode and that of new one are compared in Fig.4. The hole injection is suppressed by reduced anode surface carrier density in P layer and cathode surface carrier density in N + layer respectively. Typical waveforms of reverse recovery current and voltage of the new diode and those of the conventional one are compared in Fig.5. Oscillation is clearly absent in the waveforms of the new diode. [3] 5 1 15 2 25 Active chip area [mm 2 ] I E Fig.3: Comparison of the relationship between active chip area and rated collector current of LPT-CSTBT versus conventional planar IGBT 3-2. Diode chip technology IGBT modules need an anti-parallel, emitter to collector free-wheel diode to ensure that reverse voltage does not appear across the IGBT chip. Oscillations of current and voltage often can be observed in a conventional diode, especially during reverse recovery at low current. The oscillation may cause EMI problems both for the module itself or for the converter equipment. In order to suppress such oscillation, an optimized soft recovery diode is needed. The newly designed diode has optimized carrier density to soften the reverse recovery behavior. P V R [VCE: 2V/div, IC: 5A/div, time: 5ns/div] Fig.5: Comparison of waveforms of 12A rating current module during reverse recovery (CM12HA-34H & ) [Tj=125 C, Vcc=1V, Ic=1A] 4. Electrical performance The new 17V IGBT modules with LPT-CSTBT and new diode have improved static and dynamic electrical characteristics as described below. 4-1. Static characteristics : conventional : new diode N N + : conventional : new diode The modules use a number of LPT-CSTBT chips having a positive temperature coefficient connected in parallel in order to realize the high module current rating. The positive temperature coefficient of on-state voltage, VCE(sat), is shown in Fig. 6. The positive temperature coefficient prevents temperature and current imbalance between modules connected in parallel as well as between the parallel chips inside the module. Fig.4: Comparison of carrier density profile between conventional diode and new one
The VCE(sat) of the new modules with LPT-CSTBT is about 35% lower than the conventional one. Furthermore, the trade-off characteristic the relationship between VCE(sat) and turn-off switching energy, Eoff of LPT-CSTBT is significantly improved compared with conventional planar 17V IGBT modules as shown in Fig.7. conditions of di/dt and gate drive, turn-on and turn-off switching energy, Eon and Eoff, of the new 17V IGBT modules are about 12% and 45% lower than those of conventional one as shown in Table 2 and Table 3. Fig.8 and Fig.9 show the typical waveforms of the 12A rated current module during turn-on and turn-off switching under test conditions shown in Table 2 and Table 3 respectively. VCE(sat) [V] 5 4 3 2 1 New @25 C New @125 C Conventional @25 C Conventional @125 C 5 1 15 2 25 3 Ic [A] Fig.6: Output characteristics (typical) of 12A (CM12HA-34H & ) [Tj=25/125 C, V GE=15V] Table 2: Turn-on switching characteristics Item Conventional module CM12HA-34H New module di/dt 32 A/µs 32 A/µs Eon 492 mj 44 mj [Tj=125 C, V CC=85V, I C=12A, V GE=±15V, Ls=12nH] Table 3: Turn-off switching characteristics Item Conventional module CM12HA-34H New module di/dt 52 A/µs 52 A/µs Eoff 59 mj 35 mj [Tj=125 C, V CC=85V, I C=12A, V GE=±15V, Ls=12nH] 8 6 Conventional @RG=1.6ohm New@RG=3.3ohm VCE Conventional; CM12HA-34H Eoff [mj/p] 4 IC 2 New; 1 2 3 4 5 VCE(sat) [V] Fig.7: Trade-off characteristics (typical) of 12A (CM12HA-34H & ) [VCEsat: @Tj=125 C, Ic=12A, V GE=15V] [Eoff: @Tj=125 C, Vcc=85V, Ic=12A, V GE=±15V, 9% integration] Fig.8: Comparison of turn-on switching waveform (CM12HA-34H & ) [Tj=125 C, Vcc=85V, Ic=12A] 4-2. Dynamic characteristics The new 17V IGBT module has excellent dynamic performance in comparison with the conventional one. In the same operating
IC Conventional; CM12HA-34H VCE New; 4-3. Short circuit performance In general, modules with trench gate IGBT chips tend to have quite high short circuit currents because of the trench IGBT s large saturation current density. However, the new modules have suppressed such excessive short circuit currents by introducing an optimized trench cell design. [1] The waveform of new 12A rated current modules () in a short circuit test is shown in Fig.11. The peak short circuit current was 82A and the module has no damage in the short circuit test at a pulse width of tw=2µs. Fig.9: Comparison of turn-off switching waveform (CM12HA-34H & ) [Tj=125 C, Vcc=85V, Ic=12A] VGE The total IGBT losses in inverter operation can be estimated from the above electrical (static and dynamic) characteristics and compared with the conventional modules (see Fig.1). The losses are reduced by 25% when using the new modules. VCE IC 3 @ Tj=125 C, Io=85A rms, Vcc=85V, fc=4khz, t ON =5%, p.f.=.9 IGBT losses [W] 25 2 15 1 Static Dynamic 916 25% reduced 714 1275 5 16 CM12HA-34H Fig.1: Comparison of IGBT inverter losses [VCE: 5V/div, IC: 5kA/div, VGE: 5V/div, time: 5µs/div] Fig.11: Short circuit waveforms of 12A rated current module, [Tj=125 C, V CC=12V, V GE=±15V, R G(on)=1.3Ω, R G(off)=27Ω] 5. Package structure One key issue in power module assembly technology is wire bonding. The new modules use LPT-CSTBT IGBTs which have a higher current density due to the increase module current rating. If the conventional wire bonding technique is applied to LPT-CSTBT the wire temperature may become high. Such high wire temperature is a disadvantageous phenomenon for power cycling capability. Therefore, a new wire bonding technique has been introduced to suppress this temperature increase.
Fig.11 shows a compared top view of IGBT chip temperature including bond wires with an infrared camera and includes a simple cross section depiction of the wire bonding: a) is the conventional wire bonding applied to an LPT-CSTBT chip and b) is the new wire bonding technique. As Fig.11 shows, the wire temperature of new IGBT module is about 12K lower than the conventional one under the same loading conditions. The improvement points of the new wire bonding technique are: - lower wire current density due to increased number of bond wires; - non-cutting ( stitch ) bonding technique (see red circle in Fig.11) to shorten the wire length. By using this new stitch wire bonding technique the temperature excursion is reduced and the power cycling capability of new modules is improved. a) b) Wire temperature: 11 C maximum Wire temperature: 98 C maximum 6. Conclusion A new series of high current 17V IGBT modules using new LPT-CSTBT and new FWDi has been introduced. Improved loss performance allows a 5% increase in rated module current while keeping package compatibility with the previous module generation. 7. References [1] K. Nakamura, S. Kusunoki, H. Nakamura, Y. Ishimura, Y, Tomomatsu, T. Minato, Advanced Wide Cell Pitch CSTBTs Having Light Punch-Through (LPT) Structures, ISPSD 22 [2] J. Yamada, S. Sasaki, T. Matsuoka, Y. Ishimura, Y. Tomomatsu, I. Merfert, E. Thal Next Generation High Power Dual IGBT Module with CSTBT Chip and Package Concept, PCIM Europe 22 [3] K. Satoh, T. Nakagawa, K. Morishita, S. Koga, A. Kawakami, 4.5kV Soft Recovery Diode with Carrier Stored Structure, ISPSD 1998 [4] S. Iura, E. Suekawa, K. Morishita, M. Koga, E. Thal, New 17V IGBT Modules with CSTBT, PCIM Europe 24 Fig.11: Comparison of wire temperature between stitch and no stitch technique a) Conventional wire bonding technique on LPT-CSTBT chip (no stitch wire technique) b) New wire bonding technique on LPT-CSTBT chip (with stitch wire technique)