Ultraviolet pulsed laser crystallization of Ba0.8Sr0.2TiO3 films on LaNiO3-coated silicon substrates

Abstract

In this work, Ba 0.8 Sr 0.2 TiO 3 (BST) films on LaNiO 3-buffered SiO 2 /Si (LNO/SiO 2 /Si) substrates were crystallized by pulsed laser irradiation. Solution-derived amorphous barium-strontium-titanate precursor layers were crystallized with a KrF excimer laser in oxygen ambient at fluences ranging from 50 to 75 mJ cm-2. With the substrate temperature set to 500 ºC, the number of pulses and film thickness were varied until high-quality crystallinity could be achieved. It was found that films with a thickness of 40 nm are fully crystallized with a uniaxial {00l} orientation which is predetermined by the LaNiO 3 orientation. On the other hand, for 160 nanometer thick films, crystallization was observed after 12000 pulses in the 70 nm close to the surface, while the rest of the film remained amorphous. The large temperature difference between the film surface and interface due to the low thermal conductivity of the amorphous BST is suggested as the origin of this behavior. Films thicker than 80 nm cracked on crystallization due to the stress caused by the different thermal expansion coefficients of film and substrate, as well as the large temperature variations within the BST film.

Laser Irradiation of Metal Oxide Films and Nanostructures: Applications and Advances

“…In this context, laser irradiation appears as a potential alternative because laser irradiation exhibits a significantly fast and localized thermal effect without any interference with the underlying substrates or surrounding circuitry. Many studies have been conducted on the laser irradiation of dielectric, ferroelectric, and piezoelectric ceramic films for different purposes . Representative findings of some of these studies on laser irradiated electroceramic films are discussed below.…”

“…Laser‐induced transformation of amorphous to crystalline phase has been demonstrated in many studies to stimulate the functional activity of electroceramic perovskite films . The degree of crystallization of the amorphous film and the fraction of functionally active material resulting from laser irradiation was found to significantly influence the properties of the film.…”

“…The degree of crystallization of the amorphous film and the fraction of functionally active material resulting from laser irradiation was found to significantly influence the properties of the film. The limited laser‐absorption depth and the temperature inhomogeneity across the thickness, coupled with extremely short heating times during laser irradiation have been considered the main sources for the partially crystallized layers . In the case of laser‐annealed Ba 0.6 Sr 0.4 TiO 3 films, Kang et al observed a strong dependence of out‐of‐plane dielectric properties of the film on the residual amorphous phase.…”

“…Despite the promising benefits of using laser radiation for crystallization and densification of amorphous precursor films, careful control over different laser processing parameters is required to avoid damage to the constitutive materials . Therefore, specific thermophysical and photothermal parameters should be considered in the design of the laser‐irradiation process.…”

Ultrafast Epitaxial Growth Kinetics in Functional Oxide Thin Films Grown by Pulsed Laser Annealing of Chemical Solutions

“…[15][16][17][18] Laser crystallization of CSD precursor films has been mostly investigated for a broad range of polycrystalline oxides such as ZrO 2 , TiO 2 , undoped and Sn-doped In 2 O 3 , Ba 1-x Sr x TiO 3 (x=0.2 and 0.3) and (Pb,La)(Zr,Ti)O 3 using diode, excimer and Nd:YAG lasers in the IR, Vis and UV ranges. [17][18][19][20][21][22][23][24] In addition, some works have grown polycrystalline Al-doped ZnO from sputtered amorphous films with IR diode and UV excimer lasers in CW and pulsed modes. 25,26 Nevertheless, UV lasers are the best choice for oxide crystallization due to their large absorption at those wavelengths.…”