Charge pumping for DRAM retention diagnostic

Abstract

Charge pumping is an effective technique used extensively to analyze the interface state density of submicron MOSFETs. In essence, charge pumping measures the interface state density by pulsing the gate between inversion and accumulation. By filling traps with minority carriers in the inversion portion of the pulse, and allowing the minority carriers to recombine with majority carriers during the accumulation portion of the pulse, a DC current is generated in the body of the device. The magnitude of the charge-pumping current is then proportional to the number of pulses and the interface state density. We describe the use of charge pumping to diagnose retention behavior of DRAM arrays. This allows in-situ testing of the DRAM array device and, therefore, direct correlation to charge-retention characteristics of the functional 16 Mb DRAM chip. The concept is extendible to any DRAM cell. Our goal here was to correlate the charge-pumping current with retention failures in a DRAM to provide another diagnostic technique for retention learning.