A new technique to characterize stress induced low-level leakage current in flash EEPROM cells

• Main Authors: Wang, Chih-Hung, 王智弘
• Other Authors: Tahui Wang
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/72120740893760197961

碩士 === 國立交通大學 === 電子工程學系 === 85 === In this thesis, we proposed a novel two-phase subthreshold transient current measurement method and an analytical model to characterize the stress induced low-level leakage current (SILC) in a flash EEPROM cell. The associated steady-state and transient characteristics of the read-disturb degradation was evoluated. In order to investigate the oxide charge effect on the read-disturb degradation, a specially designed experiment with twoerase methods were performed. The measurement method consists of two alternating phase; one is the read-disturb phase and the other is the subthreshold current measurement phase. By varying the gate bias in the read-disturb phase, the field dependence of the SILC and the read-dsiturb mechanism can be obtained. An analytical model relating a subthreshold current transient to the charge variations in the tunnel oxide and in the floating gate has been derived. Since in the model the subthreshold current exhibits an exponential dependence on oxide charge and floating gate charge, this method can provide a better resolution than the traditional threshold voltage method. Two erase methods, a conventional method and a modified method, were employed in this work. Our study reveals that the transient component of the SILC is attributed to oxide charge trapping/ detrapping while the steady-state component of the SILC is due to trap-assisted sequential tunneling. Threshold voltage shifts resulting from these two components were characterized separately. During read-disturb, in spite of the large initial transient, thethreshold voltage shift is mainly affected by the steady-state component.However, in the application of a low- voltage operation, the transient component may appear to be a dominant read-disturb degradation mechanism. Our study shows that the transient component can be significantly suppressed by using a modified erase method. Furthermore, by using the two- phase subthreshold transient current technique, an extremely low leakage current (about 1E-19 Amp) can be measured.