Thermal effects and analysis of high fequency devices in analog integrated circuit design

The study concentrates on the thermal modeling aspects of the heterojunction bipolar transistors device using the TCAD 3-dimensional thermal simulation. Die concentration and operational speed of transistors are rapidly increasing because of high market a demand, which is leading to thermal runaway complication and current crowding effect. The susceptibility of transistors to temperature change requires a more sensitive and accurate modeling of the thermal effects of the device. The heat source is the junction between base and lightly doped collector, which gets trapped within the device because of the presence of isolation oxide sidewalls and bottom oxide layer. The thermal impedance depends on the position of the heat source, its separation from the sidewalls and bottom oxide, as well as thickness of the oxide wall and bottom. The thickness of the wafer also changes the thermal heating. The spreading resistance from the heat source to the sidewalls and bottom oxide, to the wafer, and then to ambient temperatures has been calculated using heat flow equation. The results are then compared to TCAD simulation. The mathematical model was within 10% when compared to 3D TCAD simulation. The model presented in this work is based on an extension of the constant angle heat spreading, resulting in closed form expressions which can be used for practical applications. The electrical analogy developed from the thermal analysis can used in VBIC, HICUM and MEXTRAM compact models, which are used to model the behavior of HBTs.;Solder bump packaging results to the formation of a thermal equivalent transmission line for the heat flow from the heat source to the ambient temperature at the bumps. This paper analyses the effect of thermal heating when devices are connected using solder bump. TCAD simulation is performed and mathematical model is developed to support the 3-D simulation result. The thermal impedance depends on the length of line from the heat source to the solder bumps, which is modeled by using electrical transmission line. Closer the solder bump to the device the lesser would be thermal resistance but other tactics are discussed which can reduce the thermal resistance. An infinite long line results to a static characteristic impedance for the line. Equivalent electrical analogy for the thermal transmission line is modeled which can be implemented in standard modeling scheme like HICUM, VBIC.