Electrothermal Simulation of the Hot-Spot and Its Countermeasures in Cellular Bipolar Power Transistors

• Published in: IEEE transactions on components and packaging technologies Vol. 32; no. 2; pp. 493 - 500
• Main Authors: Bagnoli, P.E., Stefani, F.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.06.2009; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Analytical models; Assembling; Ballasting resistors; Cellular; copper heat spreader; Devices; Electric power generation; Electrothermal effects; electrothermal modeling; hot spot; Performance analysis; power bipolar transistors; Power transistors; Proximity effect; Silicon; Simulation; Steady-state; Surface resistance; Thermal factors; Thermal resistance
• DOI: 10.1109/TCAPT.2008.2001193
• ISSN: 1521-3331

This paper deals with a theoretical study of the hot-spot onset (HSO) in cellular bipolar power transistors. This well-known phenomenon consists of a current crowding within few cells occurring for high power conditions, which significantly decreases the forward safe operating area (FSOA) of the device. The study was performed on a virtual sample by means of a fast, fully analytical electrothermal simulator operating in the steady state regime and under the condition of imposed input base current. The purpose was to study the dependence of the phenomenon on several thermal and geometrical factors and to test suitable counter measures able to impinge this phenomenon at higher biases or to completely eliminate it. The power threshold of HSO and its localization within the silicon die were observed as a function of the electrical bias conditions as for instance the collector voltage, the equivalent thermal resistance of the assembling structure underlying the silicon die, the value of the ballasting resistances purposely added in the emitter metal interconnections, and the thickness of the copper heat spreader placed on the die top just to the aim of making more uniform the temperature of the silicon surface.