Novel methods for the reliability testing of ferroelectric DRAM storage capacitors

Abstract

A new technique has been developed for the characterization of dielectric voltage- and charge-decay times (T/sub V/ and T/sub Q/) in sol-gel derived ferroelectric films under open-circuit conditions. Voltage decay potentially poses a limitation on the maximum allowable refresh-time in the DRAM capacitor. This direct measurement of T/sub V/ is preferred to its conventional estimation based on the current-voltage relationship, because of the implicit inclusion of nonlinearities and stress-induced leakage-reduction effects. Undoped and lanthanum-doped lead-zirconate-titanate (PZT) films have also been characterized for frequency-dispersion in large-signal polarization, bit "0" relaxation and a new bit "1" relaxation mechanism using techniques developed recently. It is proposed that any evaluation of high-permittivity dielectrics for DRAM applications must include these measurements.<>