Electrical charge injection and storage in off-stoichiometric SiO2 films

Abstract

The injection and storage characteristics of electrical charge in off-stoichiometric SiO2 films have been studied using two types of capacitor structures: (A) a simple capacitor formed with an off-stoichiometric SiO2 film deposited on either p- or n-type silicon substrate and a metallic (Al) contact, and (B) a structure similar to (A) but with a thin (100 Å or 500 Å) SiO2 layer between the Si substrate and the off-stoichiometric SiO2. The flat band voltage shifts measured from high frequency capacitance versus voltage curves of these devices were used to study the accumulation of charge in the off-stoichiometric SiO2 layer induced by applied voltage pulses. The width of these pulses was in the range of 10 ms to 100 μs and the amplitude was in the range of 0 to 80 volts. The role of the SiO2 layer in the (B) type structures is to inhibit or reduce charge injection to or from the Si substrate at low applied voltage amplitudes. This effect originates initial shifts of the flat band voltage of opposite polarity to those observed in the case of (A) type structures. The relaxation of the stored charges was monitored by measuring the shifts of the flat band voltage as a function of time when both electrical contacts were connected to ground potential.