Noriyuki Unno

3D measurement of the position of gold particles via evanescent digital holographic particle tracking velocimetry

A new technique based on digital holography and evanescent waves was developed for 3D measurements of the position of gold nanoparticles in water. In this technique, an intensity profile is taken from a holographic image of a gold particle. To detect the position of the gold particle with high accuracy, its holographic image is recorded on a nanosized step made of MEXFLON, which has a refractive index close to that of water, and the position of the particle is reconstructed by means of digital holography. The height of the nanosized step was measured by using a profilometer and the digitally reconstructed height of the glass substrate had good agreement with the measured value. Furthermore, this method can be used to accurately track the 3D position of a gold particle in water.

Three Dimensional Nanoimprint Lithography Using Inorganic Electron Beam Resist

With the advancement in the information technology the need for increasingly complex three-dimensional (3D) structure is eminent. Gray scale lithography can produce 3D structure but it cannot match the resolution of electron beam lithography (EBL). Today the EBL is primarily used for mask making and for making nanoimprint lithography (NIL) molds (Chou

Comparison of hot spot temperature between Si and SiC power MOSFET using electro-thermal analysis

Recently, thermal problem of electronics is becoming more serious, because electronic devices have been downsizing. Especially, since very high electrical field generates in power devices, it is possible that nano-micro scale high temperature hot spots appear in the device. The hot spot temperature has an impact on performance of electronics, and the hot spot has potential of malfunctioning of the device. Therefore, for higher reliability of electronics, accurate thermal design considering nano-micro scale hot spot is important. In recent years, SiC power semiconductor devices are receiving attention as high-voltage semiconductor devices. For accurate thermal design of the SiC power semiconductor devices, accurate thermal properties of SiC power semiconductor devices should be obtained. However, details of thermal properties of SiC device are not clear. Since high electric field generates in power semiconductor devices, energy non-equilibrium state between electron and lattice should be considered to investigate the hot spot, and Electro-Thermal Analysis is attractive to deal with this non-equilibrium state. In this paper, thermal properties of SiC power semiconductor device are discussed using Electro-Thermal Analysis. We focus on heat generation and hot spot temperature of SiC power MOSFET. By comparing thermal properties of Si power MOSFET with that of SiC power MOSFET, difference of thermal properties between these two MOSFETs is discussed.

Subcooled boiling with nano-coating heating surface

In this study, the effect of the nano-coating heating surface was examined to improve boiling heat transfer. A silane coupling agent, which produces self-assembled monolayer (SAM), was used to change the wettability on the heating surface. Since the coated thickness of SAM is very thin, it does not fill the cavity on the heating surface. By means of the nano-coating heating surface, boiling curve of pool boiling was investigated at the liquid subcooling of 50 K. As a result, a hydrophobic surface obtained by SAM improved the heat transfer coefficient in the nuclear boiling regime. Furthermore, it became clear that a heating surface coated with fluorinated silane copling agent did not prevent the occurrence of microbubble emission boiling (MEB).

Heat transfer performance of uni-directional porous heat sink for cooling of next generation on-vehicle inverter

This study evaluates boiling and evaporative heat transfer performance of a heat sink called EVAPORON-4 utilizing uni-directional porous media in order to remove high heat generation of 300–500 W/cm2 from a chip of the next generation SiC-/GaN-based on-vehicle inverter. The unidirectional porous heat sink has three functions such as direct supply of cooling liquid to a heat transfer surface, promotion of evaporation, and passive vapor discharge. The porous medium is made of oxygen free copper and the porosity is 19.6 %. The small pore holes of 0.5 mm in diameter work for the liquid supply and the large holes of 2.6 mm for the vapor discharge. In order to discharge the vapor through the vapor discharge pore holes, the porous heat sink is set onto a grooved heat transfer surface. As a result, the porous heat sink achieves high cooling performance of approximately 850 W/cm2 at the pumping power of 2.6 W in case of the liquid subcooling of 40 K and the flow rate of 2.0 L/min (102 kg/m2/s).

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

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.

Advanced cooling technology via boiling heat transfer considering the wettability of a heating surface

Aiming for the improvement of the boiling heat transfer coefficient, the effect of the nano-coated heating surface was investigated. We used a silane coupling agent to change the wettability of the heating surface. By means of the coated heating surface, we examined boiling curve of subcooled pool boiling. As a result, the boiling curve with the coating agent was drastically changed and microbubble emission boiling (MEB) was observed even if we used the coated heating surface.

Cooling augmentation of subcooled boiling liquid by a nano-particle coated surface

A demand for the high performance cooling technology with low operating power exists for the thermal management of the next generation power electronics, such as the IC inverter of electric vehicle. Boiling heat transfer is a promising candidate for the cooling technology because it can remove a large amount of heat from a heat generating device by phase change of the liquid. However, it is well known that Critical Heat Flux (CHF) restricts the maximum cooling performance of boiling heat transfer. Thus, there is a lot of research to increase CHF. In particular, the boiling heat transfer with the heating surface coated with nanofluid is expected to be used for this purpose. There are some reports that the nanofluid layer coated by boiling concentration method in saturated boiling increases CHF. In this study, we demonstrated boiling concentration method for the heating surface using nanofluid at subcooled boiling. Furthermore, microbubble emission boiling (MEB) was also examined by using the obtained heating surface with nanofluid. As a result, it became clear that MEB was observed even if the surface was coated with the nano-particle layer and the nanoparticle layer coated in subcooled boiling can also improve the maximum heat flux.