Measuring the thermal diffusivity of CMOS chips

This paper describes a new method for determining the effective value of the thermal diffusivity, Deff, of a CMOS chip. Deff is a parameter that describes the rate at which heat diffuses through a chip, and hence its knowledge is essential for the thermal management of systems on chip and the design of thermal sensors. By embedding an electrothermal filter (ETF) in a frequency-locked-loop (FLL), its phase response, which is determined by its (fixed) geometry and Deff, can be measured. Deff can then be accurately determined from the measured phase response. For an ETF implemented in a 0.7µm CMOS process, the resulting values of Deff were 1.405, 0.755, and 0.495 cm²/s at −55, 27, and 125 °C respectively.