POLYCRYSTALLINE BISMUTH TITANATE THIN FILMS FOR MICROELECTRONIC APPLICATIONS

摘要

This program has established that polycrystalline films of bismuth titanate, rf-sputtered from a dielectric target, possess electrical and chemical properties allowing their use in solid state circuits. When used in the context of large area micro-strip circuits, the films yield low effective loss (approximately 1%) and provide an effective relative dielectric constant of 190 + or - 30 for the 1 to 12 GHz frequency range. Extension of these results suggests that the material could be used for microwave circuit by-pass capacitors in which extremely low loss is not required. A major achievement of the present effort has been the improvement of both dielectric withstanding voltage and etching behavior by annealing in oxygen. Such treatment appears to suppress conduction thought to occur along metal-rich grain boundaries. Annealing increases the etch ratio in HCl of as-prepared polycrystalline films by factors of 4 to 10 to values like those for epitaxial material. This relieves, but does not obviate, the problem of undercutting of protected regions which is a peculiarity of the titanate films. As a demonstration of the applicability of sputtered Bi4Ti3O12 films in silicon integrated technology, insulated gate field effect transistors were fabricated using the material as the gate dielectric. In these devices, a thin layer of chemical vapor deposited SiO was used to improve the adhesion of aluminum to the titanate. (Author)