Real time degradation monitoring system for high power IGBT module under power cycling test

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, Franc

Electron beam induced radio emission from ultracool dwarfs

We present the numerical simulations for an electron-beam-driven and loss-cone-driven electron-cyclotron maser (ECM) with different plasma parameters and different magnetic field strengths for a relatively small region and short time-scale in an attempt to interpret the recent discovered intense radio emission from ultracool dwarfs. We find that a large amount of electromagnetic field energy can be effectively released from the beam-driven ECM, which rapidly heats the surrounding plasma. A rapidly developed high-energy tail of electrons in velocity space (resulting from the heating process of the ECM) may produce the radio continuum depending on the initial strength of the external magnetic field and the electron beam current. Both significant linear polarization and circular polarization of electromagnetic waves can be obtained from the simulations. The spectral energy distributions of the simulated radio waves show that harmonics may appear from 10 to 70$\nu_{\rm pe}$ ($\nu_{\rm pe}$ is the electron plasma frequency) in the non-relativistic case and from 10 to 600$\nu_{\rm pe}$ in the relativistic case, which makes it difficult to find the fundamental cyclotron frequency in the observed radio frequencies. A wide frequency band should therefore be covered by future radio observations.Comment: 10 pages, 19 figures, accepted for publication in the Astrophysical Journa

Failure Analysis of Power Devices Based on Real-Time Monitoring

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, Franc

Magnetic phase diagram of the frustrated S=1/2 chain magnet LiCu_2O_2

We present the results of the magnetization and dielectric constant measurements on untwinned single crystal samples of the frustrated S=1/2 chain cuprate LiCu_2O_2. Novel magnetic phase transitions were observed. A spin flop transition of the spiral spin plane was observed for the field orientations H||a,b. The second magnetic transition was observed at H~15 T for all three principal field directions. This high field magnetic phase is discussed as a collinear spin-modulated phase which is expected for an S=1/2 nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic chain system

A power cycling degradation inspector of power semiconductor devices

We have proposed a failure analysis based on a real-time monitoring of power devices under acceleration test. The real-time monitoring enables to visualize the mechanism that leads to a failure by obtaining the change of structure inside the device in time domain with high spatial resolution. In this paper, we presented a new analytical instrument based on the proposed failure analysis concept. The essential functions of this instrument are (1) power stress control, (2) non-destructive inspection and (3) water circulation. An original design power-stress control system and a customized scanning acoustic microscopy system enable us a non-destructive inspection inside the device under power cycling test. This instrument exhibits a great advantage especially to monitor failure mechanisms without having to open the module

Real Time Failure Imaging System under Power Stress for Power Semiconductors using Scanning Acoustic Tomography (SAT)

Failure mechanism of power semiconductors is captured as a movie image under power stress to the device in non-destructive way. The new technique is realized by combining a high speed Scanning Acoustic Tomography (SAT/SAM) and electrical power supply circuit for applying the power stress to the device. Water as acoustic wave couplant in SAT system, which has been a major disadvantage of the system, is utilized as coolant for stressed power to the device. Major barriers to accomplish this system are a severe noise due to a local convection with the heat and a formation of tiny bubbles on the observation surface. These problems are solved by introducing water jet along the scanning interface. This technique enables “real-time” failure analysis.23rd European Symposium on Reliability of Electron Devices,. Failure Physics and Analysis, October 1-5, 2012, Cagliari, Ital

DYNAMICS ANALYSIS OF PEDALING MOTION IN RACING CYCLE WITH COMPUTER SIMULATION

This paper reports the new method based on the computer simulation for the dynamics analysis of the pedaling motion in a racing cycle. At first, we describe three-dimensional mathematical models of lower limbs and the cycle, and then explain the formulation as the systems of Lagrange equations. Time-series angular displacements of each joint, the crank arm, and each pedal were obtained by capturing actual human pedaling motions. The 'ideal' pedal forces were computed by using the model of the cycle. The method for solving the 'inverse kinematics problem' is also proposed. As the results of the dynamic simulation, we obtained several dynamic properties of the three-dimensional pedaling motion. And the differences between the three-dimensional pedaling motion and the two dimensional motion were also described

Real-time imaging of temperature distribution inside a power device under a power cycling test

The analysis of temperature distribution in a power device package is essential to increase the reliability of power devices, because the temperature swing during the operation creates mechanical stress at the interfaces between these materials. However, the temperature distribution is difficult to obtain under operating conditions because of the limitation in the use of non-destructive methods to measure the inside temperature of the device. In this paper, we propose a method of real-time imaging of temperature distribution inside a DUT. This method is based on a “real-time simulation”. The real-time simulation was realized by combining surface temperature monitoring and high-speed thermal simulation. The thermal simulator calculates temperature distribution inside the package by using the monitored surface temperature as a parameter. We demonstrate our system with a TO-220 package device under a power cycling test. The system indicated a temperature distribution change in the package with a frame rate of less than 1 s and the temperature difference at the Si chip was within 2 °C by a comparison with that estimated from forward voltage drop

New high magnetic field phase of the frustrated S=1/2S=1/2 chain compound LiCuVO4_4

Magnetization of the frustrated $S=1/2$ chain compound LiCuVO$_4$, focusing on high magnetic field phases, is reported. Besides a spin-flop transition and the transition from a planar spiral to a spin modulated structure observed recently, an additional transition was observed just below the saturation field. This newly observed magnetic phase is considered as a spin nematic phase, which was predicted theoretically but was not observed experimentally. The critical fields of this phase and its dM/dH curve are in good agreement with calculations performed in a microscopic model (M. E. Zhitomirsky and H. Tsunetsugu, preprint, arXiv:1003.4096v2).Comment: 5 pages, 4 figure