Yuji Nishibe

Giant magneto-impedance effect in layered thin films

Giant Magneto-Impedance (GMI) of films with a layered structure has been studied. They are Co-Si-B/Cu/Co-Si-B, Co-Si-B/Ag/Co-Si-B, and Fe-Co-Si-B/Cu/Fe-Co-Si-B with a magnetic closed-loop structure. They also have a certain magnetic configuration, for which the uniaxial anisotropy is perpendicular to both the driving current and the external field. Consequently, both reactance X and resistance R of the films change remarkably due to the external field in the frequency range from 100 kHz to 10 MHz, at which the GMI effect hardly appears in the single layer films of the same thickness. The conductivity difference between the outer and inner layers is important in order to achieve a high impedance change ratio in this frequency range. As a result, the ratios /spl Delta/Z/|Z/sub 0/|=(Z/sub maximum/-Z/sub [Hext=0]/)/Z/sub [Hext=0]/ of Co-Si-B/Ag/Co-Si-B films are 440% for a field of 9 Oe at 10 MHz, and the average sensitivity is 49%/Oe. Furthermore, /spl Delta/Z/|Z/sub 0/| of Co-Si-B/Cu/Co-Si-B and Co-Si-B/Ag/Co-Si-B films at 1 MHz is as much as 140%, and the average sensitivity reaches 15%/Oe. The sensitivity at 1 MHz is higher than that of single-layer magneto-impedance films of the same thickness by three orders of magnitude.

Enhancement of giant magneto-impedance in layered film by insulator separation

Giant Magneto-Impedance (MI) effect of CoSiB/SiO/sub 2//Cu/SiO/sub 2//CoSiB films with line structures have been studied. Easy axes have been induced in perpendicular direction to the driving current, and the insulating SiO/sub 2/ layers have prevented the driving current from penetrating into the CoSiB layers. This structure has enabled the effective occurrence of resistance change at a frequency as low as several MHz. As a result, impedance change ratios /spl Delta/Z/Z/sub 0/=(Z/sub maximum/-Z(H/sub ext/=0))/Z(H/sub ext/=0) are much higher than that of any other layered film without insulating layers. The /spl Delta/Z/Z/sub 0/ at 20 MHz is as high as 700% at 11 Oe, and the maximum slope is 300%/Oe.

Pb-free high temperature solders for power device packaging

Abstract Reliabilities of joints for power semiconductor devices using a Bi-based high temperature solder has been studied. The Bi-based solder whose melting point is 270 °C were prepared by mixing of the CuAlMn particles and molten Bi to overcome the brittleness of Bi. Then, joined samples using the solder were fabricated and thermal cycling tests were examined. After almost 2000 test cycles of −40/200 °C test, neither intermetallic compounds nor cracks were observed for CTE (Coefficient of Thermal Expansion) matched sample with Cu interface. On the other hand, certain amount of intermetallic compound such as Bi 3 Ni was found for a sample with Ni interface. In addition, higher reliability of this solder than Sn-Cu solder was obtained after −40/250 °C test. Furthermore, an example power module structure using double high temperature solder layers was proposed.

Extraction of Accurate Thermal Compact Models for Fast Electro-Thermal Simulation of IGBT Modules in Hybrid Electric Vehicles

Abstract An optimized thermal management is of paramount importance when developing efficient and reliable converters for automotive applications. In this paper, we present a new approach to extract accurate compact models for fast electro-thermal simulations of IGBT modules used in hybrid electric vehicles. It is shown that the proposed methodology brings advantages in terms of increased reliability, reduction of the costs, and shortening of the design cycle.

Thin film magnetic field sensor utilizing Magneto Impedance effect

Abstract Recently, the Magneto Impedance effect found in amorphous wires with soft magnetic properties is noticeable as a new principle for sensing magnetic filed. According to this effect, the impedance of the wire in the range of high frequencies over 10 MHz changes remarkably with the external magnetic field. This effect is expected to be promising for magnetic field sensor with high sensitivity. Therefore, we have attempted to introduce this effect into amorphous thin films to extend application fields, and a novel thin film sensor sensitive to small magnetic field based on the Magneto Impedance effect has been proposed. The sensor consists of half bridge of the individual detecting element with FeCoSiB/Cu/FeCoSiB multi-layer, which exhibits the large impedance change ratio more than 100% when an external magnetic field is applied. By the optimization of the operating point due to bias field and the signal processing with a synchronous rectifier circuit, no hysteresis, good linearity and good stability against temperature variation as well as high sensitivity in the sensor characteristics have been achieved. The variation of the sensor output with the temperature is largely reduced to one-third, compared to the conventional thin film sensor we developed formerly. The detection resolution of 10−3 Oe order higher than those of any other conventional thin film sensors is obtained.

Novel RC Compact Thermal Model of HV Inverter Module for Electro-Thermal Coupling Simulation

This paper describes a novel RC compact thermal model which has the capability of representing thermal behavior of multi chip inverter module peculiar to HV. This RC compact thermal model can take into account lateral heat spreading within the modules and thermal interference among Si chips. The thermal model was validated in comparison of temperature transient responses among the results calculated using the proposed model and FEM. The electro-thermal coupling simulation using this RC compact thermal model offers reasonable accuracy for prediction of the Si chip temperature in HV inverter module.

Novel Electro-Thermal Coupling Simulation Technique for Dynamic Analysis of HV (Hybrid Vehicle) Inverter

This paper describes a novel electro-thermal coupling simulation technique mainly focused on the dynamic analysis of the HV inverter during WOT (Wide Open Throttle) operation. This technique can predict the junction temperature of power devices installed within the power module accurately. This simulation technique is composed of an inverter circuit model including power semiconductor device models, a novel compact thermal model suitable for automotive power modules and motor model. Various information and conditions such as motor current, motor rotation speed, switching frequency and variable DC-link voltage are applied to the simulation for carrying out the WOT operation. The comparison between the simulated and measured results indicates that this method offers reasonable accuracy for the IGBT temperature estimation where the worst case error in the IGBT temperature is less than 10 deg-C. It takes 210 min to complete the WOT simulation with duration of 4 seconds.

Sensing of passing vehicles using a lane marker on a road with built-in thin-film MI sensor and power source

In a field test, we demonstrated the sensing of passing vehicles, using onroad lane markers with a built-in magneto impedance (MI) sensor and a self-contained power source. The vehicle-sensing rate was 100% in the field test and we found that the lane marker could detect vehicles with a high degree of accuracy. A thin-film MI sensor, which is very sensitive to small external magnetic fields, an analog circuit for driving/processing, and a digital circuit with EEPROM memory for storing the number of passing vehicles were incorporated into a thin aluminum plate marker. The lane marker also had a self-contained power source, consisting of a secondary battery and a solar battery, which eliminated the need for an external power supply.

Strain-impedance properties of a CoSiB/Cu/CoSiB layered film

A type of strain sensor element utilizing the magnetostrictive effect and the magneto-impedance effect was presented and the strain-impedance properties of the element were evaluated. The strain-impedance (SI) element constructed from a CoSiB/Cu/CoSiB layered film was prepared on a Corning No. 0313 glass substrate by magnetron sputtering under a magnetic field. The element was composed of an inner copper conductive layer and outer magnetostrictive layers which covered the conductive layer. The Co73Si12B15 negative magnetostriction films (λ=−6×10−6) were adopted as magnetostrictive layers and magnetic anisotropy was induced perpendicular to the applied strain direction. Impedance Z drastically changed with applied compressive strain e up to −2×10−3 and exhibited a good reversibility and reproducibility. The impedance change ratios ΔZ/Z0=(Zmax−Z[e=0])/Z[e=0] of the element were 40% at 15 MHz and 24% at 1 MHz. The maximum gauge factor Gmax defined as the maximum fractional change in impedance to strain (ΔZ/Z...

A consistently potential distribution oriented compact IGBT model

With the trend to higher switching speed for IGBTs, the dynamics of the MOS part have increasing impact on device characteristics. In addition, the base-charge distribution of the BJT part has also to be modeled quite accurately to capture the IGBTs overall dynamic behavior adequately. We present a new IGBT model for circuit simulation, where all controlling potentials in the base region are calculated under fully dynamic load conditions, and which includes an advanced surface- potential-based charge-oriented MOSFET model. The approach assures that the dynamic interaction between MOS and BJT part is accurately taken into account. The models abilities to describe the impact of the MOS-gate capacitance on the IGBT output characteristics, and to capture dynamic effects like overshoot under rapid switch- off conditions, are verified.