The Advanced Trench HiGT with Separate Floating p-layer for Easy Controllability and Robustness

Transcription

1 The with Searate Floating -Layer for Easy Controllability and Robustness Tiger Arai, S. Watanabe*, K. Ishibashi, Y. Toyoda, T. Oda, K. Saito and M. Mori*. Power & Industrial Systems Division, Power Systems Comany, Hitachi, Ltd. *Hitachi Research Laboratory, Hitachi, Ltd. Hitachi-shi, Ibaraki-ken, Jaan, Abstract In this aer, we roose an advanced (High conductivity IGBT) chi structure and show the new 170 advanced module characteristics. The concet of the advanced is to allow easier dv/dt control while maintaining low losses and robustness. The feature of the new structure is the dee and searate floating -layer which has less influence on the trench gate by the floating -layer through the switching term, so the gate controllability is greatly imroved. This new module exerimentally shows a 25% reduction in turon dv/dt with the same level losses as a conventional. In addition, we confirmed a reduction in turoff dv/dt, sufficiently wide SOA (Safety Oeration Area) and strength against tye-3 short-circuits. 1. Introduction Insulated Gate Biolar Transistors (IGBTs) are widely used in various inverter systems, such as ower sulies and motor drives. With the trend in ower electronics demands, IGBTs have been imroved. IGBTs have laner MOS gates and trench MOS gates, and the latter are used in miniature rocesses and are mainly roduced with mid-range voltages and high current density. Fig. 1 shows the different generations of Hitachi s trench IGBT. We firstly develoed the s to reduce losses while maintaining robustness[1]. This IGBT has the trench MOS gate arrangement with different intervals and formed the floating -layers without connecting to the emitter electrode between the trench MOS gates. The MOS channel reduction from this structure reduces the saturation current density Jc(sat) to retain the short-circuit caability. Furthermore, the ostate voltage of this IGBT is lower to reduce ower dissiation because the active carriers remain more in the drift region. Device structure (cross-section) Features + IGBT Miniaturized IGBT IGBT Low loss Robust + + Floating current Lower Saturation Current Planar IGBT Lower OState Voltage loss Lower loss + -emitter voltage Static outut characteristic Fig. 1 The different generations of Hitachi s trench IGBT and the advanced

2 Easy controllability Lower loss with LiPT + LiPT structure + LiPT structure Floating n Searate floating n current recovery LiPT high injection structure Shorter Tail Current Turn off waveform Lower dv/dt controllable Rg bigger Eon Trade-off of Eon vs. dv/dt Fig. 1(continued) The different generations of Hitachi s trench IGBT and the advanced Secondly, we released s with a LiPT (Low injection Punch Through) structure for lower losses[2]. The low hole carrier injection from the -layer on the collector side shortens the tail current during turoffs to reduce losses without any conventional lifetime controls. Currently, easy dv/dt controllability is demanded to reduce losses, EMIs, voltage surges, and other causes of damage to the main circuits. For examle high dv/dt causes insulation degradation of the motor coils. Because IGBTs could be used under an uer limit dv/dt condition, it can be useful to design the devices with IGBTs to allow easy dv/dt control over a wide range of conditions with lower losses. Some investigations and countermeasures on this matter have been reorted[3][4]. Now we are roducing the advanced s which have a new chi structure to realize high dv/dt controllability while maintaining low losses. 2. Device structure The advanced chi structure is shown in Figs. 1 and 2. The floating -layer of a conventional is moderately searated from the trench gate to allow easy control of turon dv/dt. It is also formed deeer to retain robustness with low losses. Through IGBT switching terms, the floating -layer voltage fluctuation is caused by the collector voltage change. This directly causes gate uncontrollability esecially in the case of the conventional in which the floating -layer contacts the trench gate. On the other hand, in the case of the advanced, the trench gates are searate from the floating -layers so that this floating -layer voltage fluctuation does not affect the + Gate Searate floating A Fig. 2 The advanced structure

3 gate controllability. Furthermore, the advanced secures low ostate voltages as in the conventional s because of the comosition of the floating -layers. We designed the deth of the floating -layers and the length between the trench gate and the searate floating -layer to maintain a high blocking voltage and guard against the damage of the trench gate. 3. dv/dt controllability We show the measurement data related to the controllability of the advanced s dv/dt for turon, reverse recovery, and turoff Turon and reverse recovery Fig. 3 shows the trade-off between maximum reverse recovery dvak/dt at 25C, =0~15/chi and Eon at 125C, =15/chi. (The chi is rated at 15.) It is exerimentally confirmed the advanced offers a better trade-off than a conventional as shown by the simulation results. The advanced rovides a 25% reduction in turon dv/dt comared to the conventional one with the same level-low losses. Furthermore, the advanced can be controlled down to 13kV/μs, less than the conventional s 19kV/μs. Fig. 4 shows the chi-switching waveforms of the conventional and the advanced. The diode reverse recovery waveform at Max. recovery dvka IC = 0 ~ Simulation Mesurment E on (mj/cm 2 )@125, 15 Fig. 3 Trade-off relationshi between maximum reverse recovery dvak/dt@25c, =0 ~ 15/chi and turon loss Eon@125C, = 15/chi. (The chi is rated at 15.) IGBT = Rated current (15/chi) Diode reverse = Maxium dv/dt current 90 6A 55mJ/cm2 dv/dt=20ka/us Vak Ia mJ/cm dv/dt=14ka/us Vak Ia Fig. 4 Chi switching waveforms of the conventional and the advanced

4 low current with the conventional is a maximum dv/dt of 20kV/μs with voltage ringing, but for the advanced, it is a maximum dv/dt of14kv/μs without voltage ringing. Fig. 5 shows the advanced s turon waveform with various gate resistances at = 15/chi, 125C. From this result, the advanced is dv/dt controllable between 0.3k and 2.5kV/μs using gate resistance. From these results we exerimentally confirmed that the advanced is easily and widely dv/dt controllable for turon and reverse recovery using gate resistance., 90 (10/div) VCE IC ~-2.5kV/us 0./div (50/div) Fig. 5 The turon waveforms with various gate resistances for the = 15/chi. (The chi is rated at 15.) 3.2. Turoff dv/dt controllability Figs. 6 (a) and (b) show the turoff waveform of the 170, 360 advanced module at Vcc=125, =360,. We tuned the drift layer to 20μm thicker with the simulation results. The tuned module waveform (b) is without voltage ringing. And Fig. 6 (c) shows the turoff waveform of the advanced measured at 40C. From this result we exerimentally confirmed that the tuned module is 3.8kV/μs dv/dt without voltage ringing at 40C., kV/us (ΔV=42) 125 (50/div), kV/us (ΔV=42) 125 (50/div) 0.5us/div (10/div) 0.5us/div (10/div) (a) The conventional module mounted on a 20μm thinner chi, (b) The advanced module,, kV/us (ΔV=519V) 125 (50/div) 0.5us/div (100/div) (c) The advanced module, -40C Fig. 6 Turoff waveform of the 170, 360 advanced =360, Ls=55nH, Vge=15V/-15V, Rg(off)=1.5Ω.

5 Fig. 7 shows the turoff dv/dt vs. of the 170, 360 advanced module at Vcc=125,. The advanced with tuned thickness has the desirable trait of lower turoff dv/dt than the conventional with re-tuned thickness over the full measured collector current range. d/dt (V/us) (kv/μs) (*) mounted 20μm thiner chi 125 (*) Lower dv/dt (A) Fig. 7 Turoff dv/dt vs. of the 1700, /360 advanced =360, Ls=55nH, Vge=15V/-15V, Rg(off)=1.5Ω, 4. Robustness This new structure needs to consider the blocking damage around the trench gate. Fig. 8 shows the simulation results of the otential distribution around the trench gate on DC blocking. From the results of the device simulation, the trench bottom (oint A in Fig. 2) is the avalanche oint. Firstly, the deeer floating -layer is effective in reducing the electric field at the trench bottom. Secondly, we designed the width between the trench gate and the searate floating -layer. Fig. 9 shows the simulation result of the relationshi between the static avalanche voltage and the unit cell size of IGBT. The relationshi between the unit cell size of IGBT and the width between the trench gate and floating -layer is linear. From this simulation result, it aears that the advanced can be designed with a higher avalanche voltage than the conventional. We exerimentally confirmed that the advanced module cleared both the collector - emitter DC blocking test and the gate - emitter DC blocking test. (a) (b) Fig. 8 Potential distribution around a trench gate on DC blocking Vge=, 25C

6 Static avalanche =100μA Higher avalanche voltage at the conventional unit sell size Normarized width between trench gate and floating layer The unit cell size of IGBT Fig. 9 Static avalanche voltage vs. the unit cell size of IGBT (Simulation) Fig. 10(a) shows the high-current turoff waveform of the 170, 360 advanced module. Fig. 10(b) shows the high-current reverse-recovery waveform of the 170, 360 advanced module. We exerimentally confirmed that the RBSOA and recovery SOA of the advanced module are large enough. VGE:1/div IG:5A/div 15V Vge Ig VCE:50/divIC:2.5kA/div VCE:50/div IC:2.0kA/div Aeak -15V [μs] (a)turoff [μs] (b)reverse-recovery Fig. 10 High-current switching waveform of the 170/360 advanced Vcc= 125, =720, Ls=55nH, Vge=15V/-15V, Rg(on)=3.3W, Rg(off)=1.5W, 150C Fig. 11 shows the tye-3 short-circuit mode waveform of the 170, 360 advanced module. In a tye-3 short-circuit, while the main current flows back through a free-wheel-diode in a twolevel-inverter circuit with inductances as load, the other arm s IGBT breaks down and the circuit shorts between the uer and lower arms. We exerimentally confirmed that the advanced module turns off safely after 10μs of a tye-3 short-circuit.

7 VGE:2/div IG:1/div VCE:50/div IC:10kA/div 33.6kA/us 1.21kV 1.61kV 10 17kA/us -5.4kA/us [μs] Fig. 11 tye-3 short-circuit mode waveform of the 170/360 advanced =540, Ls=55nH, Vge=15V/-15V, Rg(on/off)=3.3W/1.5Ω, 150C 5.Losses Fig. 12 shows the trade-off relationshi between Eoff and (sat). The advanced has the same low level of losses as the conventional. This is because the advanced has the same structure for the floating -layer as the conventional, and the active carrier density of the drift layer could be as high as the conventional one Eoff [J] (sat) [V] Fig. 12 trade-off relationshi between Eoff and (sat) 6. Conclusion We roosed a chi structure for an advanced with a dee, searate floating -layer and showed the characteristics of the new 170, 360 advanced module. Exerimentally, this new module showed 25% reduction in turon dv/dt with the same low level of losses as the conventional module and ringing free turoff waveform over the full collector current range (0-360) from -40 to 150C. In addition, we confirmed that the SOA is wide enough and the strength against tye-3 shortcircuits is sufficient. Because of these features, this new module can be driven easily and used at the lowest loss conditions. Reference [1] M. Mori, et al. A -Gate High-Conductivity IGBT () With Short-Circuit Caability, IEEE Transact. on Elec. Dev, vol. 54, No.8, Aug. 2007, [2] K. Oyama, et al. with Low-injection Punch-through (LiPT) structure, in Proc. ISPSD, 2004, [3] M. Yamaguchi, et al. IEGT Design Criterion for Reducing EMI Noise, in ISPSD, 2004, [4] Y. Onozawa, et al. Develoment of the next generation 120 trench-gate FS-IGBT featuring lower EMI noise and lower switching loss, in Proc. ISPSD, 2007,