Flame-Sprayed Barium Titanate as a Capacitor Dielectric

Barium titanate has been known as a high-dielectric-constant material and used widely in the electronic industry. Therefore many attempts have been made to use this material as thin sheets or coatings~ but its refractory properties and the difficulty involved in vaporizing it have prevented its extensive use. The flame-spraying process has solved this problem in an economical way, requiring no vacuum chamber, no critical materials, and no costly electrodes such as platinum. A film as thin as 30 µm with a dielectric constant of more than 6000 can be made on iron tape 30 mm wide and 0.1 mm thick at a very low cost. The film thus produced shows many favorable characteristics and performance that cannot be expected from other dielectric films of comparable dielectric constant. This includes capacitance change of plus/minus 15 percent over a temperature range of -55 to +125°C for a film having a dielectric constant of 3000. The flame-sprayed coatings consist essentially of crystalline and glassy components. The crystalline component comprises cubic and tetragonal crystallites. The tetragonal crystallites have a variety of axial ratios (c/a). Applications presently considered for this material are fixed capacitors, variable capacitors, chip capacitors for hybrid IC circuits, and substrates for capacitor networks and/or RC networks. As an extension of this research, semiconducting barium titanate is also discussed here.