The maximum dielectric strength of thin silicon oxide films

Thin film silicon oxide capacitors with nonshorting breakdowns were investigated. Breakdowns appear in three forms: single hole, self-propagating, and maximum voltage breakdowns. Single hole and self-propagating breakdowns occur at flaws, and self-propagating breakdowns develop only when the resistor to the source is relatively small, less than 10 kΩ in these experiments. After flaws are burned out by single hole breakdowns, with larger source resistors the maximum voltage breakdown can be observed, destroying the whole capacitor simultaneously. Plotting current against voltage, the current increase is quasi-exponential, but prior to maximum voltage breakdown, the current continues to increase while the voltage decreases slightly below a maximum value Vm. Assuming thermal instability as the cause for this change in the I-V relationship, we have derived an expression for the maximum voltage Vm. Calculated results for fields up to 9.5 MV/cm were found to agree well with measurements for temperatures from -145°C to 65°C and for thicknesses from 3000 Å to 50 000 Å. Fmdecreases with increasing temperature and thickness of insulation, and is higher for silicon dioxide than for silicon monoxide films. Maximum voltage breakdown occurs when the quasi-exponential increase of leakage current with field produces thermal instability over the whole capacitor area. The maximum dielectric strength is characteristic of the whole capacitor and is determined by its electrical and thermal conductance.