Browsing by Author "Gu, Shaw-Hung"

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Extraction of nitride trap density from stress induced leakage current in silicon-oxide-nitride-oxide-silicon flash memory
(2006-10-16)
Gu, Shaw-Hung
;
Wang, Tahui
;
Lu, Wen-Pin
;
Ku, Yen-Hui Joseph
;
Lu, Chih-Yuan
The authors propose a technique to extract a silicon nitride trap density from stress induced leakage current in a polycrystalline silicon-oxide-nitride-oxide-silicon flash memory cell. An analytical model based on the Frenkel-Poole emission is developed to correlate a nitride trap density with stress induced leakage current. The extracted nitride trap density is 7.0x10(12) cm(-2) eV(-1). They find that nitride trapped charges have a rather uniform distribution in an energy range of measurement (similar to 0.2 eV). (c) 2006 American Institute of Physics.
Numerical simulation of bottom oxide thickness effect on charge retention in SONOS flash memory cells
(2007-01-01)
Gu, Shaw-Hung
;
Hsu, Chih-Wei
;
Wang, Tahui
;
Lu, Wen-Pin
;
Ku, Yen-Hui Joseph
In this paper, bottom-oxide thickness (T-bo) and program/erase stress effects on charge retention in SONOS Flash memory cells with FN programming are investigated. Utilizing a numerical analysis based on a multiple electron-trapping model to solve the Shockley-Read-Hall rate equations in nitride, we simulate the electron-retention behaviour in a SONOS cell with T-bo from 1,8 to 5.0 nm. In our model, the nitride traps have a continuous energy distribution. A series of Frenkel-Poole (FP) excitation of trapped electrons to the conduction band and electron recapture into nitride traps feature the transitions between the conduction band and trap states. Conduction band electron tunneling via oxide traps created by high-voltage stress and trapped electron direct tunneling through the bottom oxide are included to describe various charge leakage paths. We measure the nitride-charge leakage current directly in a large-area device for comparison. This paper reveals that the charge-retention loss in a high-voltage stressed cell, with a thicker bottom oxide (5 nm), exhibits two stages. The charge-leakage current is limited by oxide trap-assisted tunneling in the first stage and, then follows a 1/t time dependence due to the FP emission in the second stage. The transition time from the first stage to the second stage is related to oxide trap-assisted tunneling time but it prolonged by a factor.