Nanometer-thick oxide films for pyroelectric energy conversion

Pyroelectric energy conversion utilizes the temperature dependence of spontaneous polarization in crystalline materials to convert waste heat into electricity. High-power-density thermal-to-electrical energy conversion is possible using pyroelectric thin films which allow fast thermal cycling and high electric fields. Published studies, however, have not investigated pyroelectric energy conversion in nanometer-thick films. In addition, there is a lack of suitable techniques for characterization of pyroelectric and other related temperature-dependent properties of thin films. This work develops and implements techniques for temperature-dependent piezoelectric and pyroelectric characterization of nanometer-thick films, and investigates pyroelectric energy conversion using high-frequency thermal-electrical cycles.;Phase-sensitive techniques measured high-temperature electromechanical and pyroelectric response in ~100 nm thick PbZr0.2Ti0.8O 3 films deposited using pulsed laser deposition. Piezoresponse force microscopy (PFM), an atomic force microscopy (AFM) based technique, measured the electromechanical response while a doped-silicon resistive micro-heater provided local temperature control up to 400 °C. Three techniques characterized the pyroelectric response using temperature oscillations generated by a hotplate, a microfabricated heater, or a modulated laser. The pyroelectric current was measured from a microelectrode fabricated onto the film over a heating frequency range 0.02 Hz -- 1.3 MHz.;This work investigated pyroelectric energy conversion in ~200 nm thick epitaxial BaTiO3 films using a microfabricated platform that allowed simultaneous thermal and electrical control. The low thermal mass of the active material and precise thermal-electrical control enabled pyroelectric cycles up to 3 kHz frequency and maximum power density of 30 W/cm3. In comparison, earlier studies were typically limited to cycle frequencies less than 1 Hz and the highest reported power density was 0.11 W/cm 3. In addition to studying high frequency thermal-electrical cycles, this dissertation also examined the effect of variations in temperature and electric field with microsecond temporal resolution. This work will facilitate the design and operation of pyroelectric cycles with high energy and power densities.;This dissertation reports advancements in piezoelectric and pyroelectric characterization of thin films, and presents high-power-density solid-state pyroelectric energy conversion which could be useful for future waste heat harvesting applications.