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Variations of V_{t} Retention Loss in a SONOS Flash Memory Due to a Current-Path Percolation Effect

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9 Author(s)
Chou, Y.L. ; Dept. of Electron. Eng., Nat. Chiao Tung Univ., Hsinchu, Taiwan ; Chung, Y.T. ; Tahui Wang ; Ku, S.H.
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Discrete nitride program charge loss in a small-area SONOS Flash memory cell during retention is observed. Our measurement shows that a retention Vt of a programmed SONOS cell exhibits a stepwise evolution with retention time. Individual single-program charge-loss-induced threshold voltage shifts (ΔVt) are characterized. We find the following: 1) The magnitude of ΔVt exhibits an exponential distribution, which is believed due to a current-path percolation effect caused by random program charges and substrate dopants, and 2) program-state Vt retention loss has large variations in different cells and P/E cycles due to the percolation effect. We develop a Monte Carlo analysis to take into account the distribution of ΔVt and a tunneling front model to study the spread of a retention Vt distribution in a SONOS Flash memory.

Published in:

Electron Device Letters, IEEE  (Volume:32 ,  Issue: 4 )