Performance of sputtered pb0.92bi0.07la0.01(fe0.405NB0.325Zr0.27)O3 ferroelectric memory films

Abstract

The ferroelectric behavior of sputtered Pb0.92Bi0.07La0.01(Fe0.405Nb0.325Zr0.27)O3 films was evaluated for possible use in a ferroelectric-photoconductor memory. The material was sputtered onto platinum film substrates which also served as the lower electrodes. Gold 'dots' were evaporated through a mask onto the surface of the ferroelectric to form the upper electrodes. Hysteresis loops showed the films could be switched rapidly at very low voltages but loop squareness decreased substantially at lower frequencies. This decrease in P corresponds to spontaneous depoling of the ferroelectric.Switching and depoling were studied with rectangular voltage pulses. The rate and extent of depoling were determined by poling 'dots' and measuring the charge stored after various times. Depoling occurs rapidly during the first few milliseconds and then relatively slowly. Depoling was also monitored with low-voltage, alternating polarity, disturbing pulses applied to the dot. These disturbing pulses were 5% of the switching voltage and should simulate the noise or dark signal that would be repetitively applied to unaddressed bit positions in a ferroelectric-photoconductor memory. These disturb pulses did accelerate depoling but not an intolerable amount.Switching fatigue was evaluated with sine wave and rectangular voltage pulse excitation. Degradation was not significant before about 109 polarization reversals. It is concluded that these ferroelectric films have characteristics suitable for certain memory applications.