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Pyroelectric coefficients are measured for Si, Sr, La, Al, and Gd doped HfO2 thin films as well as the solid-solution Hf0.5Zr0.5O2 composition from 280 to 440 K. Pyroelectric currents show sensitivity to the dopant used to stabilize ferroelectricity in HfO2. Large pyroelectric coefficients up to 70 μC cm−2 K−1 were measured in films with the largest remanent polarization magnitudes, La-doped HfO2 and Hf0.5Zr0.5O2. A temperature-driven ferroelectric to antiferroelectric-like transition influences the pyroelectric coefficient and is found only in Si-doped HfO2 thin films. The transition is shown to produce a decrease in the Curie constant with temperature and thus deviates from the Curie law, although most ferroelectric films reported here obey the Curie law. Independent measurements of the remanent polarization, relative permittivity, and pyroelectric coefficient are used to extract the Curie constants of the thin films. The fundamental thermodynamic relationship between the dielectric, ferroelectric, and pyroelectric properties of ferroelectric HfO2 thin films are established based on Landau theory with a universal Curie constant of 5.8 × 10−7 ± 0.46 × 10−7 K C V−1 m−1 (Landau coefficient, α0 = 1.72 × 106 ± 0.138 × 106 V m K−1 C−1) for ferroelectric HfO2 independent of doping concentration and dopant type. An electro-thermal coupling factor of 1.9 × 10−3 and a voltage responsivity figure of merit of 0.085 m2/C illustrate the promising potential of ferroelectric HfO2 thin films for use in embedded energy harvesting and infrared sensing circuits.

Perovskite-type transition metal oxides have great potential as storage material in resistive random-access memory (RRAM) devices. Typical non-volatile memory cells are realized in metal-insulator-metal (MIM) stacks with insulator thicknesses of few nanometers. We report on the investigation of single-crystal SrTiO3 to understand the role of volume and interface real structure for the electrical conductivity in such materials. Conductivity in SrTiO3 single crystals was established by a reducing high vacuum (HV) annealing introducing charged oxygen vacancies acting as donor centers. Titanium electrodes are evaporated on both crystal faces to obtain an MIM element.

Resistance switching in metal – insulator - metal (MIM) structures with transition metal oxides as the insulator material is a promising concept for upcoming non-volatile memories. The electronic properties of transition metal oxides can be tailored in a wide range by doping and external fields. In this study SrTiO3 single crystals are subjected to high temperature vacuum annealing. The vacuum annealing introduces oxygen vacancies, which act as donor centers. MIM stacks are produced by physical vapor deposition of Au and Ti contacts on the front and rear face of the SrTiO3 crystal. The time dependent forming of the MIM stacks under an external voltage is investigated for crystals with varying bulk conductivities. For continued formation, the resistivity increases up to failure of the system where no current can be measured anymore and switching becomes impossible.