Space-Charge Polarization in Glass Films

Abstract
It is shown that electrical polarization effects in glass films can be conveniently studied using a metal‐glass‐silicon dioxide‐silicon double‐layer capacitor. The buildup of a polarization in the glass layer under the application of a voltage at elevated temperatures can be detected from the resulting shift ΔV in the capacitance‐voltage characteristic. Equations are derived on the basis of a simple model which gives ΔV as a function of time, temperature, applied voltage, and the glass and oxide thicknesses. Experimental data for a lead borosilicate glass are presented and shown to be in excellent agreement with this model. The time constant for polarization of the glass has an activation energy of 1.05 eV and is of the order of weeks at room temperature and minutes at 100°C. The diffusion coefficient calculated from this time constant is in agreement with that for lead in glasses of similar composition and hence it is concluded that in this glass the major mobile ion is Pb++. Additional long‐term polarization effects are observed when the metal is biased positively and these are related to the diffusion of sodium contaminant out of the glass layer into the underlying silicon dioxide.