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Measuring Charge Retention Characteristics of Nonvolatile Storage Devices

IP.com Disclosure Number: IPCOM000079249D
Original Publication Date: 1973-Jun-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

James, RP: AUTHOR

Abstract

Retention time of silicon nonvolatile charge-storage devices is usually determined by extrapolation to large time of measurements of stored charge. Such a procedure is inherently unreliable, as it will not detect any small quasiohmic component of insulation leakage current which may prevent long-term charge retention.

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Measuring Charge Retention Characteristics of Nonvolatile Storage Devices

Retention time of silicon nonvolatile charge-storage devices is usually determined by extrapolation to large time of measurements of stored charge. Such a procedure is inherently unreliable, as it will not detect any small quasiohmic component of insulation leakage current which may prevent long- term charge retention.

In this method, the initial charge is not the charge written in normal operation but, rather, the charge a satisfactory device will retain in normal operation after a specified time has elapsed. What is measured is the small change in charge over a relatively short period of time (e.g., a day). This procedure will detect unacceptably large-leakage currents.

In this method, a floating gate device 10 to be tested forms one arm of a bridge circuit. An on-chip reference device 12 forms the second bridge arm. An off-chip operational amplifier 14, fed from the bridge, generates the voltage applied to the gate 16 of the reference device 12 which is equal to the floating gate voltage. In operation, the differential amplifier 14 senses any differential voltage between points 18 and 20, and subsequently adjusts the voltage applied to the gate 16 to equalize the current flowing through test device 10 and reference device 12. The actual voltage on the gate 16 is read by voltmeter 22.

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