The effects of high electric field transients on MOSFETs with gate oxide thicknesses ranging from 55 Angstrom to 200 Angstrom were studied to determine the new requirements for future ESD protection circuits. The oxide breakdown field for a 1 mu sec constant voltage pulse increased as the gate oxide thickness decreased. 200 Angstrom and 85 Angstrom oxides had breakdown fields of 14 MV/cm and 22 MV/cm, respectively. For shorter pulses, the breakdown field increased as expected. A simple and accurate method to determine oxide breakdown for an arbitrary voltage waveform was developed. At electric fields below that of oxide breakdown, threshold shifts occured. A 100 nsec 15 Mv/cm pulse caused a shift of minus 14 mV for a 100 Angstrom oxide and even larger shifts for thicker oxides. Quasi-static CV measurements showed negligible interface states generation at this field, therefore the threshold shifts are due to the trapping of holes in the oxide. Present-day input protection circuits may have to be modified to provide adequate voltage clamping for these thin oxides.
|Number of pages||6|
|Journal||Electrical Overstress/Electrostatic Discharge Symposium Proceedings|
|State||Published - 1 Dec 1987|