Impact of self-heating and thermal coupling on analog circuits in SOI CMOS

This paper examines the influence of the static and dynamic electrothermal behavior of silicon-on-insulator (SOI) CMOS transistors on a range of primitive analog circuit cells. In addition to the more well-known self-heating close-range thermal coupling effects are also examined. Particular emphasis is given to the impact of these effects on drain current mismatch due to localized temperature differences. Dynamic electrothermal behavior in the time and frequency domains is also considered. Measurements and analyses are presented for a simple amplifier stage, current mirrors, a current output D/A converter, and ring oscillators fabricated in a 0.7-mu m SOI CMOS process. It is shown that circuits which rely strongly on matching, such as the current mirrors or D/A converter, are significantly affected by self-heating and thermal coupling. Anomalies due to self-heating are also clearly visible in the small-signal characteristics of the amplifier stage. Self-heating effects are less significant for fast switching circuits. The paper demonstrates how circuit-level simulations can be used to predict undesirable nonisothermal operating conditions during the design stage.