Effects of A.C. Stress on Charge and Voltage Decay Rates of PZT Thin Film Capacitors for DRAM Applications

Abstract

ABSTRACTA PZT thin film capacitor displays a reduction in the charge storage density (Qc') after the device has undergone pulsed electrical stress. This changes the charge-voltage relationship for the devices. The effect of this change in the Q-V relationship on the DRAM READ time is described. Measurements of the charge and voltage decay rates have been previously identified as ideal techniques for characterizing signal loss. For the first time the effects of electrical stress on these rates have been studied. While the charge decay rate decreases with an increase in the number of stress cycles for both the bipolar and unipolar stress, the voltage decay rate decreases after unipolar stress but it increases for bipolar stress at lower stress voltages. The implications of these results on the DRAM performance shall be discussed.