Charge capacity analysis of the charge-coupled RAM cell

Abstract

The charge (or storage) capacity of the dynamic charge-coupled (CC) random access memory (RAM) cell is analyzed. Theoretical expressions for the capacity are developed which provide excellent agreement between theory and experiment. Test devices were operated with typical dynamic metal-oxide-semiconductor (MOS) RAM voltages, and exhibited charge capacities (per unit area) up to 52 and 86 percent of that of the conventional one-transistor cell for substrate bias voltages of -5 and -1 V, respectively. A simplified model of the CC RAM cell is used to illustrate the dependence of the charge capacity on the device and operating parameters. This model is useful for defining the limitations on capacity and for comparing the capacities of the CC and the one-transistor cells for a variety of conditions. In general, the CC RAM cell charge capacity per unit area ranges from 50 to over 100 percent of that of the one-transistor cell for conventional device parameters. A somewhat higher range applies for projection to low-voltage and very high-density RAM's.