Risako Kibushi

Bio: Risako Kibushi is an academic researcher from Toyama Prefectural University. The author has contributed to research in topics: MOSFET & Heat generation. The author has an hindex of 4, co-authored 18 publications receiving 39 citations.

The effect of cooling from surface of power Si MOSFET on hot spot temperature

Abstract: This paper describes the effect of cooling from a surface of power Si MOSFET on hot spot temperature. In traditional thermal design of electronics, the temperature distribution of chips is assumed to be uniform for simplicity of thermal design. However, in recent years, thermal problems of electronics are more serious, because electronics have been downsizing. Therefore, we should consider the temperature distribution of the chips. In a chip, semiconductor devices are mounted, and the generation of hot spots in semiconductor devices is widely known. Therefore, the chip has non-uniform temperature distribution. However, the detail of thermal properties of power Si MOSFET, which is one type of transistor, is not clear. Power Si MOSFET has large thermal problems, because high voltage is applied to power Si MOSFET. Therefore, we should obtain thermal properties of power Si MOSFET. Thus, the objective of this study is investigation of thermal properties of power Si MOSFET for high reliability of electronics. In this paper, as a fundamental study, we investigate the effect of cooling from the surfaces of power Si MOSFET on hot spot temperature using electro-thermal analysis. As a result, it was investigated that the effect of cooling from the top surface of the device on hot spot temperature is small.

Calculation of tempearture distribution of power Si MOSFET with electro-thermal analysis The effect of boundary condition

Abstract: This paper describes the effect of the boundary condition at the bottom surface of the power Si MOSFET on the analysis results of electro-thermal analysis of the power Si MOSFET. In general, the bottom surface of a semiconductor device is assumed 350 K to calculate the temperature distribution. However, in fact, the temperature of the bottom surface of the device is not constant, and the temperature is affected by the ambient surrounding (for example, cooling method, ambient temperature and so on). Additionally, because the boundary condition of the bottom temperature affects to the temperature distribution of the device, the boundary condition of the analysis is important. In this study, we assumed the heat transfer coefficient at the bottom surface of the device in electro-thermal analysis, and investigated the effect of the cooling performance on the bottom temperature and the temperature distribution. From the results, the heat transfer coefficient should be more than 5 × 107 W/(m2·K) to cool the bottom surface at 350 K in the examined calculation condition. Further, when the cooling performance is higher, the temperature distribution of the device is unhomogeneous.

Fundamental study of surface roughness dependence of thermal and electrical contact resistance

Abstract: For thermal management of electrical equipment, thermal contact resistance is one of the important parameters. However, thermal contact resistance is dependent on various factors, for example surface roughness, the contact pressure and the hardness of the material. Therefore, quantitative evaluation is difficult. Nowadays, CFD (Computational Fluid Dynamics) analysis is widely used in thermal design of electronics. However, unknown thermal contact resistance is always a problem for accurate temperature estimation. In this study, we examined surface roughness and material hardness dependence of thermal contact resistance and electrical contact resistance for simple estimation of thermal contact resistance. Measurement of thermal contact resistance takes a long time and electrical resistance measurement is much shorter. If thermal contact resistance can be estimated from electrical contact resistance, thermal contact resistance can be known in short time, and this method can support accurate CFD analysis. The materials to be measured are Al1070 and S45C, and three patterns (Ra = 0.2, 3.2, 12.5 µm) of surface roughness are examined. After the measurement of thermal and electrical contact resistance, we examined the ratio between electrical contact resistance and thermal contact resistance for the faster estimation of thermal contact resistance using the concept of Wiedemann-Franz law and Lorentz number like experimental constant.

Estimation of Heat Generation From Power Si MOSFET Using Electro-Thermal Analysis

Abstract: This paper describes thermal and electrical properties of power Si MOSFET. The problem of hot spot in sub-micron scale Si MOSFET has been widely known. Recently, power Si MOSFET is key device in a lot of area, for example car electronics. In power Si MOSFET, high voltage is applied and high current is generated. Therefore, heat generation becomes higher and thermal management is important. In this paper, thermal and electrical properties of power Si MOSFET is evaluated with Electro-Thermal Analysis and fundamental heat generation phenomenon of power Si MOSFET is discussed. Under high electric field, electron thermal energy becomes much higher than thermal energy of crystal lattice. Therefore, in this paper, non-equiriblium energy state between electron and lattice is considered. Calculated results showed that hotspot appears in power Si MOSFET. Further, drain voltage dependence of hotspot temperature and temperature dependence of drain current are discussed.Copyright © 2013 by ASME

Analysis of Heat Generation from a Power Si MOSFET

Abstract: This paper describes the thermal properties of power Si MOSFETs. Recently, the thermal problems of driving devices have been gaining attention. The thermal design of semiconductor chips is important since the main heat source in a driving device is the semiconductor chips. Power Si MOSFETs, which are widely used as semiconductor devices in car electronics, have serious thermal problems, since they use high voltages. Therefore, the thermal properties of power Si MOSFETs must be studied in order to improve the reliability of the electronics. In this study, the thermal properties of power Si MOSFETs are discussed. To investigate these thermal properties, calculations are performed using electrothermal analysis. From the calculations, a hot spot appears in the power Si MOSFET, and the hot spot temperature rises with increase in the applied voltage. Furthermore, the difference between the hot spot temperature and the average temperature becomes greater with the increase in applied voltage. The results indicate the risk of conventional thermal design with the assumption of uniform heat generation.

The Effect of Electrothermal Nonuniformities on Parallel Connected SiC Power Devices Under Unclamped and Clamped Inductive Switching

Abstract: Nonuniformities in the electrothermal characteristics of parallel connected devices reduce overall reliability since power is not equally dissipated between the devices. Furthermore, a nonuniform rate of operational degradation induces electrothermal variations thereby accelerating the development of failure. This paper uses simulations and experiments to quantitatively and qualitatively investigate the impact of electrothermal variations on the reliability of parallel connected power devices under unclamped inductive switching (UIS) conditions. This is especially pertinent to SiC where small die areas mean devices are often connected in parallel for higher current capability. Measurements and simulations show that increasing the variation in the initial junction temperatures and switching rates between parallel connected devices under UIS reduces the total sustainable avalanche current by 10%. It is seen that the device with the lower junction temperature and lower switching rate fails. The measurements also show that the maximum sustainable avalanche energy for a given variation in junction temperature and switching rate increases with the avalanche duration, meaning that the effect of electrothermal variation is more critical with high power (high current and low inductor) UIS pulses compared with high energy (low current and high inductance) pulses. These results are important for condition monitoring and reliability analysis.

Analysis, Design, and Implementation of Junction Temperature Fluctuation Tracking Suppression Strategy for SiC MOSFETs in Wireless High-Power Transfer

Abstract: In order to improve system reliability and reduce device thermal fatigue failure in multiload wireless power transfer (WPT) systems for electric vehicles, the implementation of the junction temperature fluctuation suppression strategy for SiC MOSFETs is necessary However, current methods are relatively lacking, and active thermal management has not been used in WPT systems In this article, the relationship between circuit parameters and junction temperature of SiC MOSFET is analyzed In particular, a junction temperature fluctuation tracking suppression strategy for SiC MOSFETs is proposed, which consists of a coarse and a fine adjustment stage As for the former, a shunt capacitor bank switching method is implemented In order to compensate for the coarse adjustment defects in the small adjustment range and poor effect, in fine adjustment stage, a changing driving voltage method is used Finally, a 5-kW multiload WPT system is built for verification Experimental results show that the proposed strategy has obvious effect on the suppression of junction temperature fluctuation and keeps temperature near the target temperature Benefiting from this, the maximum 139 °C junction temperature fluctuation is completely eliminated when the power fluctuations are within 361% of the rated power, and the heat load of each SiC MOSFET can be independently adjusted

Research Progress of Thermal Contact Resistance

Abstract: Thermal contact resistance of solid–solid interface is involved in many fields such as aerospace, low-temperature superconductivity and electronic machinery. With the booming of aerospace technology, the requirements for space detectors continue to increase; the research on accurate prediction, measurement and utilization of thermal contact resistance is becoming increasingly serious. This article systematically summarizes and analyzes the research progress of thermal contact resistance. It also comparatively analyzes theoretical prediction models, steady-state and transient-state experimental methods and numerical analysis methods from different angles, and summarizes the advantages and disadvantages of different methods. Moreover, the effects of the influencing factors such as the physical properties, the surface state, the contact pressure, the contact temperature, the heat flux direction and the thermal interface materials on the solid–solid thermal contact resistance are also briefly described. Through this systematic comparative analysis, further development directions are pointed out.

Comparison of thermal properties between Si and SiC power MOSFET using electro-thermal analysis

Abstract: This paper describes comparison of thermal properties between Si power MOSFET and SiC power MOSFET. Conventionally, Si power MOSFET has been widely used in power electronics area. On the other hand, SiC power MOSFET has wide band gap, and is gaining attention as a new generation power device. However, thermal properties of SiC power MOSFET has not been clear. For appropriate thermal management of SiC power MOSFET, heat generation tendency and temperature rise of the device should be investigated. In this paper, we conducted numerical simulation to investigate thermal properties of SiC power MOSFET. Electro-Thermal Analysis was employed as simulation method. We compared temperature between Si power MOSFET and SiC power MOSFET, and discussed difference of heat generation and temperature between these two devices.