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In SiO capacitors, deposition rate and thickness interact in their effect on leakage resistance. Slow (2 Å/s) and fast (20 Å/s) deposited films in the 2000-Å thickness range exhibit almost a million-fold difference in leakage, while similar rates, for 10000-Å films, show only a thousand-fold difference. Dissipation factor and temperature coefficient of capacitance (TCC), under the same conditions, also show extreme variation: dissipation factor from 0.003 (slow films) to 0.075 (fast, thin films), and TCC from < 40 ppm/°C (slow films) to 5700 ppm/°C (fast, thin films). Life tests of SiO capacitors were conducted at 85°C for periods up to 14 000 hours. They included capacitors with a thick (about 10 000 Å) dielectric layer and ones with a thin (about 1000 Å) layer. The thicker ones were under a potential of 47 volts dc and the thinner ones 10 volts dc. In addition, a small group of thick capacitors were held at 125°C, 67 volts dc for a much shorter time, about 6000 hours. The test results for thick 85°C capacitors were that no permanent dielectric failures occurred during the test period and dielectric properties were unchanged from those at the start of the test. Among the 60 thin capacitors, four failures (on the same substrate) occurred during the final tenth of the life test period. Visual inspection indicated that aluminum electrode corrosion was responsible. Ten capacitors maintained at 125°C (only three under voltage stress) were in perfect condition at the conclusion of the test. Their capacitance had not changed significantly but the dissipation factor improved from 0.0075 to 0.0034 (average value of ten capacitors). The most significant finding regarding long-term instability is that aluminum electrodes often deteriorate, sometimes causing dielectric failure.
Parts, Materials and Packaging, IEEE Transactions on (Volume:2 , Issue: 1/2 )
Date of Publication: March/June 1966