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type:Journal Article, Parallel connected power devices such as Insulated Gate Bipolar Transistors (IGBTs) can be used to realize a system with higher current and higher power rating. However, the operation of parallel connected IGBTs is prone to unbalancing due to variation in parameters of the semiconductor devices and asymmetric parallel system. In this paper, feedback control is proposed for peak overshoot minimization as well as current balancing of parallel connected IGBTs. A fully digital feedback control (DFC) is implemented using the universal clock for balanced operation of the two parallel connected IGBTs.

type:Conference Paper, We monitored the current imbalance in a SiC-MOSFET chip under unclamped inductive switching condition by using our printed circuit board Rogowski coils. The current imbalance varied significantly from sample to sample. The SiC-MOSFET with a larger current imbalance was destroyed with lower avalanche current than other samples. It is assumed that the chip was destroyed due to partial temperature rise accompanying current concentration from current distribution and thermal simulation. The result shows that the current monitoring system is effective for analysis of avalanche robustness., 14th International Seminar on Power Semiconductors, August 29-31, 2018, Prague, Czech

type:Journal Article, In this paper, we propose the criteria of bias voltage from parasitic capacitance and demonstrate the criteria in an experiment with the present IGBT. The bias voltage criteria are theoretically predicted for the new generation IGBT based on the scaling principle. For safe switching, the required gate voltage bias is predicted to be −1.2V or less for the present IGBTs and −6V or less is required to completely cancel the gate noise voltage. From the IGBT design, the bias voltage of scaling IGBT requires −2V to completely cancel the gate noise voltage.

type:Journal Article, High reliability is required for power modules because they are increasingly demanded as key devices in an energy-saving society. However, commercially available current sensors like current transformers and Rogowski coils are still of large size. Therefore, it is impossible to measure the current in small parts. In addition, long wiring with large sensors reduces the performance of power modules. In previous studies, we proposed a current sensor of PCB Rogowski coil with a fishbone pattern. The sensor is sufficiently small and thin with high accuracy for power module application. The PCB current sensor can be used as a built-in current sensor in power modules from the viewpoint of size. However, the sensor requires further improvement to be attached to bonding wire from a usability perspective. We propose a new pattern for the clamp-type PCB sensor and fabricate the PCB sensor as a built-in sensor in a power module. With the new pattern, it is possible to move and widen the gap for clamping. The signal error is small even though the sensor is inclinedly attached to the bonding wire. The accuracy is confirmed by a comparison between the clamp-type PCB sensor in the module and a commercially available current sensor outside the module. The clamp-type PCB sensor can be applied for intelligent power modules as well as current measurement for power electronic converters., source:https://doi.org/10.1016/j.microrel.2017.06.026

type:Journal Article, The shoot-through phenomenon has not been fully discussed for high-power inverters with IGBTs. This is because a negative gate voltage is applied to IGBTs during off states. Recently, attention is paid to an improved gate driver with only a positive gate voltage in order to meet demands for simplification, integration, and reduction in power consumption as well as in cost of the gate driver. Moreover, the threshold voltage of the next-generation IGBT will decrease with microfabrication techniques of the gate structure. This will make the shoot-through phenomenon severer and degrade the inverter reliability with the next-generation IGBTs. The influence of the parasitic parameters in both the IGBT and circuit on the shoot-through mechanism has not been investigated so far.This paper clarifies the shoot-through mechanism and investigates the impact of the next generation IGBTs on the inverter reliability. The influence of the internal capacitance of IGBT including stray inductance on inverter reliability is experimentally confirmed., source:https://doi.org/10.1016/j.microrel.2017.06.087

type:Journal Article, We have developed a printed circuit board Rogowski coil for monitoring of current and protection of high-voltage power modules and packages. It is small, thin, and inexpensive current sensor and is almost the ideal Rogowski coil because of its fishbone pattern. For noise reduction under high-voltage/-current conditions in a module, shield layers and coaxial connector are employed. In addition, a new, fast simulation tool was developed to optimize the main coil pattern for realization of arbitrary printed circuit board geometry in specific, limited spaces.

type:Journal Article, Compact model for expressing turn-off waveform for advanced trench gate IGBTs is proposed even under high current density condition. The model is analytically formulated only with device structure parameters so that no fitting parameters are required. The validity of the model is confirmed with TCAD simulation for 1.2 kV to 6.5 kV class IGBTs. The proposed turn-off model is sufficiently accurate to calculate trade-off curve between turn-off loss and saturation collector voltage under extremely high current conduction, so that the model can be used for system design with the advanced trench gate IGBTs., ESREF 2014, 25th EUROPEAN SYMPOSIUM ON RELIABILITY OF ELECTRON DEVICES,FAILURE PHYSICS AND ANALYSIS, Sep 29–Oct 3, 2014, Technische Universität Berlin

type:Journal Article, A “real time” monitoring system which enables to observe internal degradation process to failure of power semiconductors under power cycling test is proposed. The system was realized by combining a scanning acoustic tomography (SAT/SAM), power stress controlling, device cooling, water jet system and chip temperature monitoring. Two contradictory problems, namely, electrically wiring for power cycling and waterproof of device for SAT imaging were compatible with each other by experimental setup with an original water tank. Self-heating of power devices was supressed by controlling temperature of water which is couplant of ultrasonic wave for the SAT. A demonstration of this system was performed by using an IGBT module which maximum rating of collector current was 400 A (DC)., 24th European Symposium on Reliability of Electron Devices, Failure Physics and Analysis. Schedule, September 30-October 4, 2013, Venue, Arcachon, France

type:Conference Paper, This paper proposes a new power module concept that integrates output current measurement function to make inverters compact. The current measurement function is realized by tiny printed-circuit-board (PCB) Rogowski coils. The PCB Rogowski coil picks up a switching current flowing through an IGBT chip, and then a combination of a digital circuit based on a field-programmable-gate-array (FPGA) and an integrator circuit reproduces the output current of the inverter from the switching current. A major concern of the new power module is the effect of reverse recovery current of free-wheeling diodes because the reverse recovery current is superimposed on the switching current. This paper proposes a mitigating method of the reverse recovery current., 2017 29th International Symposium on Power Semiconductor Devices and IC's (ISPSD), May 28 2017-June 1 2017, Sapporo, Japan, source:http://ieeexplore.ieee.org/document/7988911

type:Journal Article, The aim is to provide failure analysis of power devices based on real-time monitoring. The real-time monitoring provides a time-domain data related to a failure mechanism. The data includes important information about primary failure, which is often lost by conventional post-defect failure analysis. Our system monitors interfaces of component material inside the device by scanning acoustic tomography (SAT) under a power cycling test in addition to electrical and thermal condition of the device. A precursor of the failure in an early stage was indicated by the interface image much earlier than a thermal and an electrical technique. Feature identification and extraction from a series of image data by image processing efficiently pointed out the damaged site before the failure was occurred., ESREF 2015, 26th European Symposium on Reliability of Electron Devices, Failure Physics and Analysis, Oct 5-9, 2015, Centre de Congrès Pierre Baudis, Toulouse, France

type:Journal Article, We developed a high-throughput screening tester for DBC-module of IGBT. The tester realizes a new screening test with current distribution in addition to a conventional switching test. It consists of a power circuit, a replaceable test head, sensor array module and digitizer with LabVIEW program. Therefore, all kinds of DBC-modules can be screened by switching the test head. The tester acquires magnetic field signals and displays GO/NOGO judgment automatically after digital calibration and signal processing in 10 seconds. It is expected to be applied for screening in a production line and analysis in order to prevent the failure of power modules., ESREF 2015, 26th European Symposium on Reliability of Electron Devices, Failure Physics and Analysis, Oct 5-9, 2015, Centre de Congrès Pierre Baudis, Toulouse, France

type:Journal Article, This paper proposes a new short-circuit protection method for an IGBT. The proposed method is characterized by detecting not only gate charge but also gate voltage of the IGBT. This results in a shorter protection time, compared to the previous method that detects only the gate charge. A real-time monitoring system using an FPGA, A/D converters, and a D/A converter is used for the proposed protection method. Experimental results verify that the proposed method achieves a protection time of 390 ns, which is reduced by 68% compared to the previous method., ESREF 2014, 25th EUROPEAN SYMPOSIUM ON RELIABILITY OF ELECTRON DEVICES,FAILURE PHYSICS AND ANALYSIS, Sep 29–Oct 3, 2014, Technische Universität Berlin

type:Journal Article, Current crowding of IGBT and power diode in a chip or among chips is a barrier to the realization of highly-reliable power module and power electronics system. Current crowding occurs because of the parasitic inductance, difference of chip characteristics or temperature imbalance among chips. Although current crowding among IGBT or power diode chips has been analysed on numerical simulations, no sensor with sufficiently high special resolution and fast measurement time has yet been demonstrated. Therefore, the author developed and demonstrated 16-channel flat sensitivity sensor array for IGBT current distribution measurement. The sensor array consists of tiny-scale film sensors with analog amps and shield case against noise. The array and digital calibration method will be applied for reliability analysis, designing and screening of IGBT modules., ESREF 2015, 26th European Symposium on Reliability of Electron Devices, Failure Physics and Analysis, Oct 5-9, 2015, Centre de Congrès Pierre Baudis, Toulouse, France