Thin film ZT characterization using transient Harman technique

Thin-film thermoelectric materials offer great potential for improving the thermoelectric figure of merit ZT due to the freedom of tailoring the electron and heat transport. The characterization of these thin films is difficult because of the coexistence of the substrate, non-ideal contact, and asymmetric three-dimensional device structure. We have investigated theoretically and experimentally the transient Harman method for measuring the ZT of a thin film Si/SiGe superlattices on a silicon substrate. 3D electrothermal simulations allow us to identify the contribution of the thin film and the substrate to the transient response. On the measurement side, ringing at short times and noise can be significantly improved by using high-speed packages and electrical impedance matching. The Joule heating contribution to the thermoelectric EMF is separated from the Peltier one by the bipolar measurement. The parasitic non-ideal effects of contacts and substrate can be removed by variable thickness superlattice method.