Determination of the thermopower of microscale samples with an AC method

A modified AC method based on the micro-fabricated heater and resistance thermometers has been developed to measure the thermopower of microscale samples. A sinusoidal current with angular frequency ω is passed to the heater to generate an oscillatory temperature difference across the sample at a frequency 2ω, which simultaneously induces an AC thermoelectric voltage, also at the frequency 2ω. The key step of the method is extraction of the amplitude and phase of the oscillatory temperature difference by probing AC temperature variations at each individual thermometer. The sign of the thermopower is determined by examining the phase difference between the oscillatory temperature difference and the AC thermoelectric voltage. The technique has been compared with the popular DC method by testing both n-type and p-type thin film samples. Both methods yielded consistent results, which verified the reliability of the newly proposed AC method.