Robert George Mertens

Spray Cooling of IGBT Devices

The popularity and increased usage of insulated gate bipolar transistors (IGBTs) in power control systems have made the problem of cooling them a subject of considerable interest in recent years. In this investigation, a heat flux of 825 W/cm 2 at the die was achieved when air-water spray cooling was used to cool IGBTs at high current levels. The junction temperature of the device was measured accurately through voltage-to-temperature characterization. Results from other cooling technologies and other spray cooling experiments were reviewed. A discussion of electrical power losses in IGBTs, due to switching and conduction, is included in this paper. Experiments were conducted on 19 IGBTs, using data collection and software control of the test set. Three types of cooling were explored in this investigation: single-phase convection with water, spray cording with air-water and spray cooling with steam-water. The results of these experiments show clear advantages of air-water spray cooling IGBTs over other cooling technologies. The applications of spray cooling IGBTs are discussed in open (fixed) and closed (mobile) systems. Current and heat flux levels achieved during this investigation could not have been done using ordinary cooling methods. The techniques used in this investigation clearly demonstrate trio superior cooling performance of air-water spray cooling over traditional cooling methods.

Investigation on the reflectance properties on silicon nanowires grown by electroless etching

In this study, silicon nanowires (SiNWs) were fabricated at four different lengths of time and three etching solution concentrations at room temperature using the electroless etching technique in a silver nitrate (AgNO3) and hydrofluoric acid (HF) based solution. The results show that the reflectance of SiNWs can be modulated as a function of the lengths of the nanowires, and that these lengths can be modulated as a function of the chemical etching ratios. Experiments have shown that a reflectance coefficient as low as 1.2% can be achieved at certain visible wavelengths for the prepared SiNW structures.

Recession and Characterization of Patterned Nanowires Grown by Electroless Etching of Silicon

Silicon nanowires (SiNWs) were grown by the electroless etching technique using silver nitrate (AgNO3)/hydrofluoric acid (HF) solution on a patterned p-type Silicon (Si) substrate with varying etching times and concentrations. The various etch times and concentrations produced different recession depths wherever the pattern allowed the etching solution to contact the Si substrate. At the bottom of each recession, SiNWs were produced of varying length and size, according to the depth of the recession. In this type of growth procedure, as SiNWs are grown, the tips are etched away. SiNWs grown by this method tend to agglomerate at their tips. We report that the recession and height of SiNWs grown by the electroless process can be controlled directly by the concentration of HF in the etching solution and by the etching time. Under precise conditions, the recession of SiNWs can be very nearly eliminated or nearly complete. The heights of SiNWs can also be fairly well controlled. We report that the growth of SiNWs is highly dependent on the ratio of volume of etching solution to the exposed surface area.

Spray Cooling of IGBTs Under High Heat Flux

In this investigation, high current levels were applied to an IGBT and, using spray cooling, a heat flux of 825W/cm2 at the die was achieved. Current and heat flux levels achieved during this investigation could not have been done using ordinary cooling methods. The techniques used in this investigation clearly demonstrate the superior cooling performance of spray cooling over traditional cooling methods.Copyright