Toru Izumi

Reliability investigation of SiC bipolar device module in long time inverter operation

The reliability of SiC bipolar device modules consisting of SiC commutated gate turn-off thyristors and SiC pin diodes fabricated on a 4° off-cut SiC substrate is investigated. According to three-phase inverter operation using a Back to Back system at DC bus voltage of 2 kV and effective output power of approximately 120 kW, the SiC module could achieve the worlds first successful inverter operation lasting more than 1000 hours, thereby verifying its reliability in long time inverter operation.

Development of a 100 kVA SiC inverter with high overload capability of 300 kVA

High overload inverters were developed by using SiC devices for the first time, although its realization by using Si devices had been difficult because of Sis low maximum Tj. The newly developed 100 kVA overload SiC inverter provides an overload capability rate of 200 % and can supply 300 kVA for up to 3 seconds. Moreover, the volume was downsized to 1/7.5 of the previous inverter and the 150 hour continuous inverter operation test at 110 kVA was performed successfully.

Insulating Properties of Package for Ultrahigh-Voltage, High-Temperature Devices

Insulating properties of package for ultrahigh-voltage, high-temperature devices have been investigated. While all the packages have enough insulating strength at room temperature, deterioration of the insulating property at high temperature has been found with some packages. The authors have found that this deterioration is attributed to degrade the insulation property of AlN ceramics for DBC substrate at high temperature and that there is a various degree in the deterioration.

4.5 kV 120A SICGT and Its PWM Three Phase Inverter Operation of 100kVA class

4.5 kV 120 A SICGT with a chip size of 8 mm times 8 mm and a new high heat resistive resin capable of 400 degC operations were developed. The SICGT coated with the resin has a low leakage current of less than 5 times 106 A/cm2 at both 4.5 kV and 250 degC, a low VF of 5.0 V at 120 A, and short turn-on and turn-off times of 0.3 mus and 1.7 mus respectively. A SICGT module was built by mounting one SICGT and two 6mm times 6mm SiC pn diodes in a metal can package, and a 110 kVA PWM 3 phase inverter was developed by using six of the SICGT modules. The electric power capabilities of both the developed SICGT and the 3 phase inverter are the largest ones among the reported SiC switching devices and SiC inverters, respectively

4.5 kV 1000 A Class SiC pn Diode Modules with Resin Mold Package and Ceramic Flat Package

4.5 kV 1000 A class high heat resistive SiC pn diode modules of both a resin mold package type using a new mold resin, Nanotec-resin KA 500, and a ceramic flat package type using a new ACTSG technique were developed for the first time. The resin mold module has a much smaller trr and Qrr in addition to higher Tj (max) of 300 degC as compared with Si pn diodes.

13-kV, 20-A 4H-SiC PiN Diodes for Power System Applications

We successfully fabricated 13-kV, 20-A, 8 mm × 8 mm, drift-free 4H-SiC PiN diodes. The fabricated diodes exhibited breakdown voltages that exceeded 13 kV, a forward voltage drop of 4.9–5.3 V, and an on-resistance (RonAactive) of 12 mW·cm2. The blocking yield at 10 kV on a 3-in wafer exceeded 90%. We investigated failed devices using Candela defect maps and light-emission images and found that a few devices failed because of large defects on the chip. We also demonstrated that the fabricated diodes can be used in conducting high-voltage and high-current switching tests.

Electron Irradiation Lifetime Control for SiC Bipolar Devices of 200 kVA High Power SiC Inverters

To reduce the switching power losses of SiC bipolar devices, an electron irradiation lifetime control method was investigated and was successfully applied to the development of 200kVA full SiC inverters, in which SiCGTs and SiC pn diodes irradiated electrons were used at the condition required to minimize inverter power loss.

Behavior of Stacking Faults in TEDREC Phenomena for 4.5 kV SiCGT

The behavior of stacking faults with regard to Vf degradations and TEDREC phenomena for 4.5 kV SiCGT have been investigated through the use of light emission images. Stacking faults, which cause Vf degradations, are expanded when current densities are increased. A novel phenomena of Vf degradation reduction, TEDREC phenomena, was found, which can reduce degradation by increasing operating temperature. It was observed for the first time that stacking faults become inactive by elevating temperatures to more than 150 oC in spite of existing stacking faults, which is a factor that contributes to TEDREC phenomena.

Stability Investigation of High Heat-Resistant Resin under High Temperature for Ultra-High Blocking Voltage SiC Devices

The reliability of three kinds of high heat-resistant resins has been evaluated under high temperatures. These resins were applied to insulation substrates and a high temperature storage test has been carried out. The insulation performance of the resins was evaluated by applying 20 kV between a pair of electrodes on the substrate covered with resin. The insulation performance at 20 kV was maintained in samples with two of the three kinds of resins for 1,000 hours at 225oC. In a higher temperature storage test at 250oC, samples with one of the kinds of resin were not able to maintain insulation of 20 kV for 200 hours, while the two remaining resins were not able to maintain the insulation for 1,000 hours. In most samples that were not able to maintain the insulation, cracks or detachments were seen. Hardening caused by oxidation of the resin and differences in the coefficient of linear thermal expansion (CTE) are considered as causes of the cracks or detachments. It is thought to be necessary to lower the CTE of the resin and inhibit its oxidation in order to use it at more than 250oC for long periods of time.

Lifetime Control of 4.5 kV SiCGT by High-Energy Electron Irradiation

The measured turn-off waveforms of 4.5 kV SiCGTs by using electron irradiation with various electron doses are reported. The turn-off time decreased with an increase in the electron dose. Furthermore, the turn-off characteristics of SiCGTs with p-type drift layer, which assumed the various trap concentrations, are simulated. The relation between the turn-off characteristics and the trap is also investigated. The simulated results show good correlation to measured data and the simulated turn-off times decrease with an increase in the electron dose as well as measured data.