Improved performance of dynamic random access memory

Abstract

Dynamic Random Access Memory (DRAM) will lose its contents due to the leakage current of the capacitor present in it. Charge Retention capacity of DRAM is affected by leakage current.The temperature dependent current-voltage (I-V) characteristics of Ba(0.8)Sr(0.2)TiO(3) (BST) thin-film capacitors with and without ZrO(2) layer were studied in the temperature range of 400 to 450 K. It is observed that the leakage current is reduced for capacitors with ZrO(2) layer compared to those without this layer. The leakage current is dominated by Ohmic conduction mechanism in the low field region whereas space charge limited current (SCLC) mechanism contributes to the leakage current in the medium field region for both films. The activation energy (E(a)) for Ohmic conduction process is 0.5 eV for BST films and 0.56 eV for BST/Zr(O)2 multilayered film. The leakage current density is reduced by an order of magnitude for BST/ZrO(2) multilayered films compared to that of BST films in the whole electric field range. The estimated trap density (N(t)) decreases from 5.1 x 10^(18) to 2.2 x 10^(18) cm^(-3) with the insertion of Zr(O)2 layer. The observed reduced leakage current for capacitor with BST/ZrO(2) multilayer dielectric is due to the increase in the activation energy and decrease in the trap density and hence suitable for increasing the retention capacity of DRAM. Simulated leakage current density (J) versus electric field (E) is calculated for BST thin film capacitor at different temperatures and is compared with the experimental data. It is observed that the measured leakage current density is higher in comparison to simulated current density and is due to the effect of electrodes and dielectric thin film structure in a real capacitor.