A modified AC method based on micro-fabricated heater and resistive thermometers has been applied to measure the thermopower of microscale samples. A sinusoidal current with frequency {omega} is passed to the heater to generate an oscillatory temperature difference across the sample at a frequency 2{omega}, which simultaneously induces an AC thermoelectric voltage, also at the frequency 2{omega}. A key step of the method is to extract amplitude and phase of the oscillatory temperature difference by probing the AC temperature variation 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.
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