Results

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Plans and objectives

The objective of this project was to study growth and characterization of complex oxide thin films for electro-optic and piezoelectric applications. The materials in the focus were the lead-free family of alkali and earth alkali niobates, which excel in many aspects concerning piezoelectric and electrooptic properties. A central topic was the establishment of a new type of high-vacuum chemical vapor deposition (HVCVD) method that is based on a multitude of individually controllable, directed precursor beams (Chemical Beam Epitaxy, CBE) for optimizing the film uniformity on large wafers, or on the contrary, to produce compositional gradients in order to carry out combinatorial experiments. A further advantage of HVCVD is the possibility to combine chemical precursors with high energetic laser and electron beams, which allows for selective depositions, local microstructure control, or eventually local doping.
Pulsed laser deposition (PLD) - a technique for small samples only - was used as complimentary or back-up method. This method permits a faster advancement in materials and characterization knowledge.
Different test structures or test devices were foreseen: Thin film wave guides (1.5 µm), frequency doubling, and wave trapping in ring oscillators; and piezoelectric properties in bulk acoustic wave resonators. On a microscopic level, Scanning Near-field Optical Microscopy (SNOM) was employed to study optical uniformity and patterned features. The project included industrial partners for CBE hardware development (ABCD), for providing optimized CVD precursors (SAFC Hitech), and state-of-the art substrates of LiNbO3 (LN) and LiTaO3 (LT) (SAES GETTERS). These substrates are ideal to combine the new thin films with existing technology based on LN and LT single crystals.