A Characterization of Endurance in 64 Mbit Ferroelectric Random Access Memory by Analyzing the Space Charge Concentration

概要

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Space charge concentration due to fatigue cycles was examined with an adequate modeling in order to expect read/write endurance of a 64 Mbit one-transistor and one-capacitor (1T1C) ferroelectric random access memory (FRAM). For monitoring the change in space charge concentration according to fatigue cycles, we assumed that our ferroelectric capacitor is governed by a partially depleted Schottky conduction model. With this, the space charge concentration at the each decade of the fatigue cycles was calculated by measuring the current–voltage characteristics. The space charge concentration at the initial stage was evaluated into $1.95 \times 10^{20}$ and $2.16 \times 10^{20}$/cm3 after the $10^{11}$ cycles. The concentration of $2.29 \times 10^{20}$/cm3 was expected at the fatigue cycles of $10^{16}$ through a linear regression of the concentration plot against fatigue cycles. Accordingly, it could be said that our ferroelectric capacitor has few problems of endurance up to the $10^{16}$ cycles considering the concentration of ${\sim}10^{20}$ and the film thickness of 80 nm. Other empirical data obtained in the capacitor level after full integration are supporting this expectation as well.
2008-04-25