Electrothermal Behavior of High-Frequency Silicon-On-Glass Transistors

In this thesis, research is focused on the investigation of electrothermal effects in high-speed silicon transistors. At high current levels the power dissipation in these devices can lead to heating of both the device itself and the adjacent devices. In advanced transistors these effects are becoming so pronounced that they are threatening to form a showstopper for further improvement of the high-frequency performance. It is therefore of paramount importance that the thermal behavior is correctly understood and brought under control. A special technology developed at DIMES, called back-wafer-contacted silicon-on-glass processing, was applied to experimentally and theoretically study electrothermal effects in bipolar and power MOS transistors. Devices were created that had the world-record high thermal resistance values and at the same time extremely low electrical parasitics. These unique experimental silicon-on-glass devices are particularly well-suited for investigation of 'intrinsic' device behavior under very strong electrothermal feedback. A novel analysis of the thermal breakdown and thermal instability in single-finger and multifinger bipolar devices was developed, on the basis of which methods and general guidelines for making both the devices and simple circuits more thermally stable could be established. For the first time, it was demonstrated that in the near future self-heating will be a crucial limiting factor for the speed of silicon transistors. Moreover, new measurement techniques were developed for extraction of self-heating and mutual thermal coupling resistances and impedances, parameters which are of particular importance for accurate analysis and synthesis of high-frequency integrated circuits. In addition to the bipolar devices, novel radio-frequency power MOS transistors were designed and fabricated in the silicon-on-glass technology and they were found to have an electrical performance that competes well with other advanced power transistors. Moreover these transistors can be readily integrated with high-quality passive components and they can be designed to have very low thermal resistance values. This work demonstrates that these devices are serious candidates for application in advanced wireless communication systems