Preparation and characterization of barium based perovskite dielectrics on different bottom electrodes by chemical solution deposition

Recently, there has been an interest in CSD techniques for the development of barium titanate (BT) based electrolytic capacitors, multi layer ceramic capacitors (MLCC), and embedded passives in printed wiring boards (PWB’s). In order to miniaturize these components further, the dielectric as well as the electrode thickness has to be reduced. Under such circumstances chemical solution deposition methods are increasingly being favoured for deposition of the dielectrics in the near future over other methods due to its simplicity and low precursor costs. While, the commercially available precursors for CSD are cheap, they have certain problems associated with them in terms of residual carbon content (specially under reducing atmospheres with base metal electrodes) and high processing temperatures. Another drawback of CSD based technique is the number of coatings required to achieve mesoscopic thicknesses (500 nm - 800 nm). It is the aim of this thesis to examine new methods of processing at lower temperatures with different bottom electrodes and achieve mesoscopic thicknesses in a few coating steps while maintaining acceptable device properties. The following processing changes were done in order to lower the crystallization temperature of barium-based perovskites. First, a more reactive atmosphere consisting of a mixture of ozone and oxygen was used to crystallize the films. At temperatures around 650oC the amorphous films derived from the carboxylate route were found to crystallize. Though such a process did not lower the crystallization temperature, post-annealing treatments in ozone reduce the leakage of the thin films by three orders of magnitude. In the second method, amorphous thin films of approximately 100 nm thickness were deposited on platinized silicon wafers and were subjected to different KrF laser fluences between 100 and 150 mJ/cm2. Though the crystallinity increased with increased laser fluences, irradiation above 150 mJ/cm2 led to ablation. Even on irradiating with lower fluences the dielectric films developed cracks during crystallization. Cracking was avoided by keeping the substrate at an elevated temperature of 250oC. This method can be used to crystallize thin films on different substrates where the substrate itself cannot be subjected to high temperature processing. Third, new precursor solutions based on aminoethoxides of barium and strontium were synthesized. By use of these carboxylate free precursors the formation of the intermediate oxo-carbonate phase was avoided. This method led to lower the crystallization temperature to 600oC. Both A-site and B-site substituted BT based thin films were fabricated on Ni electrodes. BT, BST and BTZ thin films of thickness around 600 nm were deposited by 12 multiple coatings. The pyrolysis and the crystallization procedures were optimized into 4 consecutive depositions followed by a crystallization step. This procedure was repeated thrice to achieve a thickness of 600 nm in 12 coating steps. Tunability and frequency dispersion for the different compositions was analysed with respect to processing temperature and post annealing treatments. The possibility to use CSD for the deposition of thin film dielectrics for future MLCC’s with thinner dielectric layers was shown. Finally a new method of deposition of hybrid solutions based on a mixture of microemulsions and CSD solutions (µECSD) was developed. The novelty of this method lies in the fact that films of mesoscopic thickness (500 nm - 800nm) can be deposited with only a few deposition steps. With these hybrid solutions such thicknesses can be achieved with only 5-8 steps depending on the amount of the MOD solution present in the hybrid solution.