Microstructure and Dielectric Properties of Textured SrTiO₃ Thin Films

Abstract

We investigate the relationship between microstructure and dielectric properties of textured SrTiO3 thin films deposited by radio‐frequency magnetron sputtering on epitaxial Pt electrodes on sapphire substrates. The microstructures of Pt electrodes and SrTiO3 films are studied by transmission electron microscopy, atomic force microscopy, and X‐ray diffraction. SrTiO3 films grown on as‐deposited and annealed Pt electrodes, respectively, consist of a mixture of (111)‐ and (110)‐oriented grains. Temperature‐dependent dielectric measurements show that differences in texture and microstructure are reflected in the Curie–Weiss behavior of the SrTiO3 films. Phenomenological models that account for the effects of thermal mismatch strain on the dielectric behavior are developed for different film textures. The models predict that at a given temperature, paraelectric (111)‐oriented films of SrTiO3 on tensile substrates will have a higher Curie–Weiss temperature and a greater dielectric constant than (110)‐oriented films or bulk SrTiO3. The experimental dielectric behavior is compared with the predictions from theory, and different contributions, such as interfacial layers, film stress, and microstructure, to the Curie–Weiss behavior are discussed.

Contributions to the dielectric losses of textured SrTiO3 thin films with Pt electrodes

“…The greater permittivity of the (111) oriented film was consistent with our previous estimates obtained from Landau-GinzburgDevonshire models [15]. These models predicted that in the paraelectric phase, the permittivity of a (111) oriented SrTiO 3 film that is under biaxial tensile strain due to the thermal mismatch with the substrate is greater than that of a (110) oriented film [15].…”

“…Substrates for the electron beam evaporated Pt electrodes were covered with ~ 3 nm thick e-beam Ti adhesion layers, which significantly affected the texture of the SrTiO 3 films subsequently grown onto them, as described below. As reported elsewhere [14][15][16] . The epitaxial Pt films showed rotational twinning [14,15,17].…”

“…Figures 1 and 2(a) show XRD spectra and an AFM image of this film, respectively. The elongated grains in the AFM image were (110) textured grains [15], whereas the more equiaxed grains were of either (110) or 7 (111) texture. Some (100) oriented grains could also be detected in XRD.…”

“…Very briefly, these films contained both (111) and (110) oriented grains, with an area ratio of approximately 1:3 [15]. Figures 1 and 2(a) show XRD spectra and an AFM image of this film, respectively.…”

“…The microstructure of SrTiO 3 films on sputtered Pt electrodes (no Ti underlayer) has been described in detail in a previous publication [15]. Very briefly, these films contained both (111) and (110) oriented grains, with an area ratio of approximately 1:3 [15].…”