Thermal time constants of thin-film resistors using pulse nonlinearity measurements

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Abstract
A technique of extracting quantitatve information about the thermal relaxation times of thin‐film resistors is described. The procedure is based on a simple method in which a pulse string is applied to an ac‐coupled circuit, and the resulting dc base‐line shift is a direct measure of the resistive nonlinearity. The temperature rise in the resistor, as manifested by the measured nonlinearity, is found to be a function of the ratio of the pulse period and the thermal relaxation time. A linear dependence of the thermal relaxation time on film thickness for a variety of gold films evaporated onto oxidized silicon wafers is demonstrated, and the independent contributions of the effective thermal mass and the the thermal boundary resistance are quantitatively identified. We also discuss an alternative mode of instrumentation in which a symmetrically chopped string of fast and slow pulses, occurring on a time scale comparable to the relaxation time, is used with a synchronous detector to measure the nonlinearity.

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