Measuring the thermal diffusivity of CMOS chips

This paper describes a new method for determining the effective value of the thermal diffusivity,
D

_eff
, of a CMOS chip.
D

_eff
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
D

_eff
, can be measured.
D

_eff
can then be accurately determined from the measured phase response. For an ETF implemented in a 0.7 ¿m CMOS process, the resulting values of
D

_eff
were 1.405, 0.755, and 0.495 cm
²
/s at -55, 27, and 125°C respectively.