Dielectric properties of epitaxial KNbO₃ ferroelectric thin films

Abstract

The dielectric response of KNbO3 epitaxial ferroelectric thin films was measured as a function of bias, frequency, and temperature. Thin films with a thickness of 80 to 350 nm were deposited on spinel substrates by low-pressure metalorganic chemical vapor deposition. Bias dependence measurements showed hysteresis in the dielectric response. The dielectric constant decreased with bias, and the tunability was calculated to be between 35% and 42% for an applied field of 7 MV/cm. The frequency dependence of the dielectric constant followed a power law. A pronounced thickness effect was observed in the dielectric response, especially at the Curie temperature. With decreasing thickness, the dielectric constant and the loss tangent decreased. A diffuse ferroelectric phase transition was observed for films with a thickness less than 350 nm.

Epitaxially grown ferroelectric thin films for agile devices

“…These temperatures of phase transitions are close to data reported for KNbO 3 single-crystals [41,130]. Nevertheless, the transition temperatures are slightly lower for our film than for some samples reported by other groups [87,93,131,132]. The difference can be due to strain or, more likely, to grains size.…”

Synthesis of Potassium Niobiate (KNbO3) Thin Films by Low-Temperature Hydrothermal Epitaxy

“…Subsequently, all essential properties can be tailored in wide ranges by using different combinations of materials, crystallographic orientations (cuts), and microstructures. 15 So far, KNbO 3 thin films can be synthesized by the following methods: metalorganic chemical vapor deposition (MOCVD), [16][17][18][19] pulsed-laser deposition, 10,20-25 sputtering, 26,27 liquid-phase epitaxy, [28][29][30] and solgel. [31][32][33] All these synthesis routes share similar disadvantages of high-temperature processing, requiring temperatures ranging between 600°C and over 900°C to obtain a crystalline KNbO 3 phase.…”

“…So far, KNbO 3 thin films can be synthesized by the following methods: metalorganic chemical vapor deposition (MOCVD), − pulsed-laser deposition, ,− sputtering, , liquid-phase epitaxy, − and sol−gel. − All these synthesis routes share similar disadvantages of high-temperature processing, requiring temperatures ranging between 600 °C and over 900 °C to obtain a crystalline KNbO 3 phase. The high synthesis temperatures cause typical problems such as difficulties to control potassium stoichiometry due to high volatilization of potassium oxide, interdiffusion between film and the substrate, ,, formation of interphase layers (particularly in the case of using MgO substrate), , and multidomain formation during cooling to room temperature. ,− ,,, The presence of pyrochlore and/or amorphous phases, as well as porosity, was reported particularly for the KNbO 3 films synthesized by the sol−gel method. , In addition, liquid-phase epitaxy (LPE) is not well suited for films with thickness under 1 μm …”

Tunability of High-Dielectric-Constant Materials from First Principles

“…Extension to higher order is also of interest for collinear tunability of ferroelectrics, as measurements in films allow the determination of the electric field dependence of χ s up to very high fields, showing strongly nonlinear behavior [9] that cannot be investigated using the relatively low-order expansions of the present work. The development of methods for density functional calculations in finite fields [10] will make it possible to investigate this regime.…”