Steven D. Traynor

Capacitor test simulation of retention and imprint characteristics for ferroelectric memory operation

Abstract Ferroelectric memory devices are subject to failure due to both a simple loss of retention or due to imprint. The difference between retention and imprint as described here depends on the test history of the device. A pulsed capacitor test has been devised to simulate the signal available to a typical memory cell after time and temperature stress. The test sequence consists of individual pulses used to compare the switched component to the non-switched component with the difference being the signal available for memory operation. It has been found that this signal when plotted versus log time for a fixed bake temperature stress produces a straight line.

The use of voltage to accelerate the endurance degradation of PZT capacitors

Abstract A voltage vs. endurance model was created to predict the performance of PZT from 3 to 8 volts. Capacitors that are part of the street structure on finished wafer products were cycled from 10 to a total of le 12 cycles. The switched charge was measured over 10 to 12 orders of magnitude in order to develop models to predict performance out to 1e15 cycles. The switched charge was found to degrade as a square function of the log of the number of cycles fatigued. The model was found to fit the data with an r2 greater than .95. Utilizing the minimum allowable charge for a sense amplifier, this model could be used to predict part life over operating voltages.

Remanence polarity effects on hydrogen damage of ferroelectric thin film capacitors

Abstract Ferroelectric properties of metal/ferroelectric/metal capacitors can be severely degraded during FRAM® integration in a hydrogen containing ambient. To understand the mechanism of hydrogen damage we characterized ferroelectric capacitors with the configuration of Pt/PLZT/Pt and Pt/SBTN/Pt annealed in the temperature range of 50°C to 200°C using hysteresis and DC pulsing. The capacitors were stored in specific remanent states (negative, positive, and zero) by poling prior to annealing. The annealing was carried out in a forming gas ambient, containing 1% hydrogen and 99% nitrogen. The degradation is strongly dependent on the polarity of the remanent polarization. From the results, we propose an empirical model of the formation of a fixed dipole layer at the top electrode-ferroelectric interface and we confirm that the polarity of this charge is positive.