Electrocaloric temperature change in ferroelectric Si-doped hafnium oxide (HfO2) thin films: Presentation held at 37th Spring Meeting of the European Materials Research Society, E-MRS 2019, 27-31 May 2019, Nizza

Ferroelectric HfO2-based thin films receive extensive research interest due to their large spontaneous polarization, scalability, and CMOS compatible manufacturing. As in ferroelectrics, the remnant polarization exhibits a temperature dependence, one can observe a strong pyroelectric response in such films. Recently, the pyroelectric effect of doped HfO2 films has been observed [1]. The electrocaloric effect is closely related to it, as describing a temperature change of the material due to the application of an electric field. First published results indicate rather large electrocaloric coefficients, making doped HfO2 a promising candidate for on-chip solid-state cooling [2]. In this work, a specialized test structure is used to directly assess the strength of the electrocaloric effect in a 20 nm Si-doped HfO2 nano-laminate. A thin-film temperature sensor is formed on the metal-ferroelectric-metal structure, enabling excitation frequencies of up to 60 kHz. Measurement with respect to an electric bias field provides insight into the nature of thermal-electric energy conversion in HfO2 thin films. Additionally, bias dependent pyroelectric measurements are employed to assess the role of defect dipoles, which may have important implications for electrocaloric applications