| Summary: | 碩士 === 國立交通大學 === 電子工程系 === 87 === The mechanisms and transient characteristics of edge FN and uniform FN stress induced leakage current (SILC) in tunnel oxides are investigated. A correlation between stress induced gate current and substrate current in a n-MOSFET is observed. A numercal positive-oxide-charge-assisted-electron tunneling model is proposed. A coulumbic potential caused by a stress created positive oxide charge is included in the model. The positive oxide charge acts as a sequential tunneling center and increases leakage current at a localized spot.The transient component of Edge-FN SILC or -FN SILC and the DC component of +FN SILC are attributed to positive oxide charge assisted tunneling current.The transient component of SILC induced by positive oxide charge is found to have a strong field dependence and follows a power law time dependence. The power factor is determined by the ratio of electron and hole tunneling masses and tunneling barriers. Moreover, we found that the low field substrate current results from positive oxide chaege detrapping and follows a 1/t time dependence.
A strong correlation between SILC and hole trap location is observed. In edge-FN stress, the bans-to-band tunneling generated holes can gain much energy by lateral field heating and inject into gate oxide. SILC and substrate current measured at a positive oxide field are found to decrease as the vertical stress field increases. The reason is that injected holes are driven more towards the gate at a larger oxide field. Thus, positive oxide charge detrapping current (substrate current) and positive oxide charge assisted electron tunnel;ing current (SILC) are smaller at a positive measurement field. By optimizing the operating bias condition (i.e. the hole trap position), SILC can be minimized.
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