Epitaxial, electro‐optically active barium titanate thin films on silicon by chemical solution deposition

Abstract

Recent progress in the integration of BaTiO3 thin films with silicon has shown great promise for the development of on‐chip photonic devices. However, the highest performing thin films in the literature are deposited by costly and/or complex vacuum techniques. In this study, epitaxial BaTiO3 thin films are deposited on thin SrTiO3 template layers on Si(001) from an alkoxide‐based chemical solution under atmospheric conditions and yield an effective Pockels coefficient of 27 ± 4 pm/V for an ~85 nm film. Film crystallinity, microstructure, and defect nature are examined by X‐ray diffraction and high‐resolution transmission and scanning electron microscopy techniques and discussed within the context of the growth method as well as the observed electro‐optical response.

Composition and annealing effects on the linear electro‐optic response of solution‐deposited barium strontium titanate

“…However, neither of these films exhibited a measurable δ at a zero‐field offset, even for increasing E AC to increase the response. Our previous work with non‐annealed BTO films prepared by the same solution‐based method showed a lack of optical hysteresis that has been observed in ferroelectric BTO films prepared by other methods 3,5,21,25 . Although the lack of remanent polarization in non‐annealed films can be attributed to de‐polarizing grain boundaries and defects, the high response of the annealed films suggested they may also retain polarization in the absence of an offset field.…”

“…Effective Pockels coefficients were calculated from r eff = 2 δλ / πn 3 tE AC , where n is the refractive index as determined by spectroscopic ellipsometry, is the film thickness, and E AC is the root‐mean‐square AC field. A more detailed description of the measurement can be found in the literature 3‐5,21,24,25 . The coefficients were determined at an offset field of 35 kV/cm, which is in the saturation region of domain‐poled BTO thin films deposited by this method 21 …”

“…A detailed description of the solution preparation and deposition can be found in literature. 21 Briefly, barium acetate and strontium acetate were massed into the same vial at the desired molar ratios and then dissolved with glacial acetic acid to a concentration of ~0.2 mol/L. Titanium isopropoxide was combined with the chelating agent (acetylacetone) to a ratio of 1:2.2 in a separate vial.…”

“…12 Atomic layer deposition has also shown promise in producing ultra-thin BTO and BST films with relatively high dielectric response. [13][14][15][16][17] A number of chemical solution methods have also been explored, [18][19][20][21] and these methods offer some advantages over their vacuum-based counterparts, such as relaxed equipment requirements and improved scalability.…”

Barium Titanate Nanostructures and Thin Films for Photonics

“…[204] Similar EO response was also found in a chemical solution deposited under atmospheric conditions and yield an effective EO coefficient of 27 ± 4 pm V −1 for a ≈85 nm film of BaTiO 3 . [205] By a novel two-step templated growth, a highly ordered Au-BaTiO 3 -ZnO nanocomposite of self-assembled ZnO nanopillars and Au nanopillars in a BaTiO 3 matrix, was realized. [206] They introduced a design of an epitaxial ordered trilayer film (Au-BaTiO 3 -ZnO), by employing the vaporliquid-solid (VLS) mechanism, in combination with pulsed laser deposition, the three-phase ordering was realized via a combined self-assembly and templating method.…”