Cecilia Codreanu

Peaks in temperature distribution over the area of operating power semiconductor junctions related to the surface leakage current

The surface component of reverse current of operating power PN junctions at high temperature, is a source of power dissipation concentrated in a very thin layer at the junction periphery. The resulted heat in this thin layer is removed towards the heat sink only through the peripheral part of the semiconductor die area. Typical commercial rectifier diodes exhibiting surface leakage current are considered to illustrate non-uniform junction temperature distribution. At higher applied reverse voltage, the surface component of reverse current flows non-uniformly around the junction perimeter. It is shown that the thermal resistance for the heat transfer from the junction periphery is significant higher than the corresponding one for the heat removal from the junction bulk. A simple evaluation indicates that the temperature of local hot spots near the junction peripheral surface may be at least 10 /spl deg/C higher than in the junction bulk. Junction temperature peaks were observed by infrared imaging microscopy. Influence on device reliability is possible.

A designing roule for a pressure sensor with PZT layer

In the pressure sensors domain, the SOI structures bring some advantages: electrical insulation, high temperature sensors, an excellent etch stop layer (buried oxide), compatibility with microelectronic technology, lowering in thermal noise. The goal of this paper is to highlight a pressure sensor based on a coupling between piezoelectric effect in PZT and an /spl Psi/-MOSFET. The analytical models, that will be presented, stand for a useful tool at a first iteration of the sensor designing.

Free carrier lifetime reduction in silicon by electron-beam irradiation

Point defects induced by electron-beam irradiation introduce new recombination centers in the band-gap determining the free carrier lifetime reduction. This effect is successfully used in reduction the switching time of semiconductor devices. Our work presents a model for the free carrier lifetime in silicon that takes into account the influence of concentration and energy level of the recombination centers induced by electron-beam irradiation. The irradiation was made on silicon diodes in a 7 MeV accelerator, in different does and temperature conditions. The simulation procedure consists in modeling the primary defect generation and rescaling the primary defect profile as a function of irradiation temperature. Then carrier lifetime is deduced by using the Shockley-Read-Hall statistics and an experimental database.

Experiments on behaviour of power silicon PN junctions under reverse bias voltage at high temperature

By suitable change of the junction-base (heatsink) thermal resistance for commercially available power diode dice, it has been found out that at high temperature internal overheating is induced at the junction edge by the surface component of the reverse current. To change the junction-base thermal resistance, thin aluminium pellets of different dimension or shape have been used, which were pressed between the silicon die and base for a good thermal and electric contact. The surface component of reverse current as a non-negligible source of dissipated power, localized at the junction periphery, can produce hot spots followed by device failure. Due to the effect of the surface component on the junction temperature distribution over the junction area, the maximum permissible operation temperature has specified values up to 200/spl deg/C for standard recovery junctions and up to 150/spl deg/C for fast recovery junctions.

An Experimental Approach of the Hot Wire Method for Measurement of the Thermal Conductivity

The paper describes an in house made experimental set-up that measures the thermal conductivity in liquids on the basis of the transient hot wire method. The theoretical principle is firstly presented, and then our original experimental approach is described. The hardware as well as the software implementation of the measurement method reveals the simple design configuration of the measurement set-up that contains high performance inexpensive components. It is also simple to use and well suited for research laboratories, data being stored either in text, or in graphical files. Finally, based on experimental results, the measurement accuracy and sensibility performances are discussed and compared with other instruments in literature

Experimental Investigation on the Leakage Reverse Current Component Flowing at the Semiconductor PN Junction Periphery

Due to high level of the leakage reverse current, commercial power silicon diodes available at this time have no specification in the data sheets for operation above 200 degC junction temperature. An experimental method is presented to extract information about the uniformity of the reverse current flow over the silicon die area. The power diode with copper attached heat sink is placed in a hot chamber where the temperature is set, so that the level of reverse current to be enough for heat generation. For the same applied power dissipation at reverse and forward bias, the additional junction temperature increase is monitored by the level of reverse current or by the level of the forward current at constant voltage. Experiments have been performed on commercial silicon diode samples in metallic package. It has been found that the additional junction temperature increase is significantly different, when the same power dissipation is applied at reverse bias and then at forward bias voltage, with the device placed in hot chamber at 200degC or 250 degC, depending on the current level

I-V reverse characteristic instability of high voltage silicon PN junctions at high temperature

Typical experimental results are presented for silicon (Si) PN junctions with a potential reverse voltage higher than 1000 V, revealing reverse current-voltage (I-V) characteristic instability at temperature higher than 125/spl deg/C. High levels of the reverse current reached on behalf of the surface leakage current cause I-V characteristic instability accompanied by a looping effect when this is displayed by means of a curve tracer. For standard recovery silicon diodes stable I-V characteristics are possible up to 200/spl deg/C if enough reduction in the level of the reverse current is provided. For fast recovery high voltage junctions stable characteristics above 150/spl deg/C have not been found for commercial available devices. Although the surface current component is the secondary one for these diodes, it may have some contribution to characteristic instability.

Experimental Drain I-V Characteristics of Power MOS Transistors and the Nature of Reverse Leakage Current of Oxide Passivated PN Junctions

Drain electrical characteristics for a 10 A and 400V MOS transistor have been measured and analyzed. At junction temperature as high as 200 degC and above this value, accentuated rise of the drain reverse (blocking) current takes place before the specified voltage of 400 V is reached, due to current leakage at the cells junction edge. Observed constant drain current, attributed to a primary diffusion current component is not undoubted evidence for the location of this current in the junction bulk. Similar behavior is observed when bias voltage below the threshold voltage is applied on the gate. Oxide-passivated junctions from bipolar devices may behave like those from MOSFETs at high temperature

Application of GAs to optimization of heat transfer in micro-channels

The present work proposes a genetic algorithm (GA) based method for the optimization of geometrical parameters to obtain maximum heat transfer in a micro-channel structure. The works were directed to the specific problems related to thermal transfer performances of micro-cooling systems on chip. Silicon etched micro-channels and water as cooling fluid are considered in the analysis. The results are in good agreement with those in numerical simulations, analytical models, and experimental available data.

Silicon diode electrical characteristics under electron-beam irradiation conditions - experiments and theoretical interpretation

The results of an experimental study on the effects of the electron-beam irradiation on electrical characteristics of silicon diodes having different technological profiles are presented. Experimental results are correlated with theoretical approaches to conclude on efficiency of using the irradiation method to decrease lifetimes in different types of diodes.