Retention and endurance effects of 4K and 64K FRAM memories

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Abstract
In the past few years much attention has been directed to the use of ferroelectric materials as storage elements for nonvolatile memory products. All reliability data to date has used capacitors focusing on fundamental materials behavior and not on product performance. This paper will discuss the reliability of the FM1608S 64K and FM1208S 4K FRAM memories. In particular, fatigue performance out to 1012 read/write cycles and retention performance out to 10 years will be presented. Short and long term retention behavior has been studied on product that has received over 1012 read/write fatigue cycles. Short term retention is defined as the ability of the circuit to maintain a data state with no power applied for one second at 80°C. This test ensures the ferroelectric capacitor structure is storing the charge and not being influenced by the underlying CMOS refresh characteristics of the 2T/2C dynamic RAM cell design. Long term retention is defined as the ability of the circuit to maintain a data state with no power applied after having been stored at an elevated temperature (100°C to 150°C) for more than 1,000 hours. This will be shown to translate into use conditions well in excess of 10 years. The effect of voltage and temperature on fatigue read/write cycles has also been characterized and will be presented. Elevated temperature bakes were developed to remove defect populations from production 4K and 64K material. Subsequently, detailed activation energy experiments were done at temperatures ranging from 80°C to 200°C for more than 2,000 hours. An Arrhenius model was fit to the screened population. Calculated acceleration factors and associated failure mechanisms will be reviewed.

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