A. Saidane

Using microchannels to cool microprocessors: a transmission-line-matrix study

Abstract As microprocessors components density and clock frequency increase, so do heat dissipation. The heat results from Joule effect due to leakage currents in the components area or active region. This region is only few microns thick and can quickly reach destructing temperatures if heat is not quickly removed. On this critical issue depends the system reliability. The active region is separated from the ventilated heat sink by a silicon substrate and a metal integrated heat spreader, both hundreds of microns thick. This interface region is the microprocessors heat transfer plate where heat exchange is achieved by conduction. Because of the localized heat source, the thermal spreading resistance of the interface region can be high. A novel way of spreading heat in that region is the use of microchannel arrays where an appropriate thermal compound or a phase change liquid can be trapped to increase heat transfer by conduction or to create micro-heat-pipes. Traditional cooling methods, with conventional and well optimised heat sinks, can then be used with less burden. In this paper, the Transmission-Line-Matrix (TLM) technique is used to simulate the effect of microchannels on the temperature distribution in the active region. To minimize the interface heat resistance various microchannel and patterns are examined. In this part of the work, the microchannels are filled with the heat spreader material copper or aluminium. The results show an improved thermal transient behaviour and a reduced active region temperature in steady state.

Thermal behavior Spice study of 6H-SiC NMOS transistors

Silicon carbide is a material that is undergoing major advances associated with a broad scope in the field of electronics. The main properties of silicon carbide such as its high thermal conductivity and high band gap make it a material suitable for use in high-temperature and high-power applications. In this Spice study, the thermal behavior of 6H-SiC NMOS transistors is analyzed through their conductance and transconductance changes with temperature in the range -200 to 700^oC. The performances in two basic applications, current mirrors and differential amplifiers, are compared to similar circuits with silicon transistors. The results show that the 6H-SiC NMOS transistors can be used up to 700^oC, while those based on silicon transistors are limited to around 160^oC.

Thermal behaviour of 6H–SiC bipolar transistors: spice simulation and applications

Abstract As material quality improves and growth technology develops, SiC BJTs are regaining interest. They have the advantage of carrier modulation, high current capabilities and lower initial voltage drop. In this work, the thermal behaviour of 6H–SiC bipolar transistors is simulated. The examined figures of merit such as input resistance h 11 , current gain β and transconductance g m show superior performance of 6H–SiC BJTs, at high temperatures, when compared to similar silicon counterparts. In the range of temperatures −20 to 160 °C, drawbacks found in Si BJTs are attenuated or eliminated with the use of SiC BJTs. These advantages are transferred to 6H–SiC based circuits. The built current mirror shows quasi-ideal behaviour while the designed input stage of the amplifier has a voltage gain thermally stabilised up to 140 °C.

Transmission line matrix (TLM) modeling of self-heating in power PIN diodes

Abstract Design of high-performance electronic components with stable static and dynamic characteristics requires a study of self-heating on electrical properties. TLM method is used to model electrothermal behavior of PIN diodes. Simulation results show a non-uniform temperature distribution in the device. TLM simulation results are in good agreement with those obtained by DESSIS-ISE commercial simulator. TLM computational effort is only a fraction of that required by finite element methods. TLM method is useful in dealing with nonlinear problems since it is unconditionally stable. Modeling and analysis results show that device self heating depends very much on material physical parameters and its geometry. In addition, it has been observed that blocking and conduction times influence heat dissipation.