Large anisotropy of ferroelectric and pyroelectric properties in heteroepitaxial oxide layers

Abstract

Epitaxial PbZr0.52Ti0.48O3 (PZT) layers were integrated on Si(001) with single PZT {001} orientation, mosaïcity below 1° and a majority of a-oriented ferroelectric domains (∼65%). Ferroelectric and pyroelectric properties are determined along both the out-of-plane and in-plane directions through parallel-plate capacitor and coplanar interdigital capacitor along the <100>PZT direction. A large anisotropy in these properties is observed. The in-plane remnant polarization (21.5 µC.cm−2) is almost twice larger than that measured along the out-of-plane direction (13.5 µC.cm−2), in agreement with the domain orientation. Oppositely, the in-plane pyroelectric coefficient (−285 µC.m−2.K−1) is much lower than that measured out-of-plane (−480 µC.m−2.K−1). The pyroelectric anisotropy is explicated in term of degree of structural freedom with temperature. In particular, the low in-plane pyroelectric coefficient is explained by a two-dimensional clamping of the layers on the substrate which induces tensile stress (from thermal expansion), competing with the decreasing tetragonality of a-domains (shortening of the polar c-axis lattice parameter). Temperature-dependent XRD measurements have revealed an increased fraction of a-domains with temperature, attesting the occurrence of a partial two-dimensional clamping. These observed properties are of critical importance for integrated pyroelectric devices.

Sensing Ability of Ferroelectric Oxide Nanowires Grown in Templates of Nanopores

“…The pyroelectric voltage, which is a link between the polarization degree and the temperature change, is higher at the longest KNbO 3 nanowires of 10 µm, which could be a reason for a greater voltage drop. It should be also noted that the maximum of the curve is shifted toward the higher temperature (~42 • C) as compared to the shortest nanowire, where the maximum is situated at 36 • C. This may be ascribed to the higher nanowire polarizable volume at the longer length [33].…”

“…It should be also noted that the maximum of the curve is shifted toward the higher temperature (~42 °C) as compared to the shortest nanowire, where the maximum is situated at 36 °C. This may be ascribed to the higher nanowire polarizable volume at the longer length [33].…”

Pyroelectric Properties of BaxSr(1−x)TiO3/PVDF-TrFE Coating on Silicon

“…For the pyroelectric sensors’ performance, the position of the electrical contacts in regard to the polarization axes, unknown in advance, is also important. Reports of the anisotropy of this effect are available in the literature [ 8 , 9 ]; therefore, it is of great importance to locate the electrodes in such way so as to maximize collection of the generated charge carriers. Therefore, it is not sufficient to prepare a parallel plate structure for detail and correct study of pyroelectric structures.…”