The study of hot-carrier stress on poly-Si TFT employing C-V measurement

The degradation of n-type and p-type low-temperature polycrystalline silicon (poly-Si) thin-film transistors (TFTs) due to hot-carrier stress was investigated by capacitance-voltage (C-V) measurement. In C-V measurements, the fixed charges in the gate oxide of TFTs are not affected by a small-applied signal, whereas the trap states in the bandgap respond to the applied frequency, so that the dominant degradation mechanism of poly-Si TFTs can be evaluated. The capacitance (C/sub GS/) between the source and the gate, as well as the capacitance (C/sub GD/) between the drain and the gate, were measured. The difference between the C/sub GD/ and the C/sub GS/ indicates the location of degradation in the TFT. Our experimental results showed that the degradation of n-type TFTs was caused by additional trap states in the grain boundary, whereas the degradation of p-type TFTs was caused by electron trapping into the gate oxide.

[1]  Chenming Hu,et al.  Hot-electron-induced MOSFET degradation—Model, monitor, and improvement , 1985, IEEE Transactions on Electron Devices.

[2]  W. Hansch,et al.  The relationship between Oxide charge and device degradation: A comparative study of n- and p- channel MOSFET's , 1987, IEEE Transactions on Electron Devices.

[3]  T.-Y. Huang,et al.  Effects of trap-state density reduction by plasma hydrogenation in low-temperature polysilicon TFT , 1989, IEEE Electron Device Letters.

[4]  D. Schroder.  Semiconductor Material and Device Characterization , 1990 .

[5]  Degradation of polysilicon TFTs during dynamic stress , 1991, International Electron Devices Meeting 1991 [Technical Digest].

[6]  G. Neudeck,et al.  Frequency-dependent capacitance-voltage characteristics for amorphous silicon-based metal-insulator-semiconductor structures , 1992 .

[7]  I. Wu,et al.  Physical models for degradation effects in polysilicon thin-film transistors , 1993 .

[8]  James S. Im,et al.  On the super lateral growth phenomenon observed in excimer laser-induced crystallization of thin Si films , 1994 .

[9]  Carlo Reita,et al.  Hot carrier effects in n-channel polycrystalline silicon thin-film transistors: a correlation between off-current and transconductance variations , 1994 .

[10]  Michael S. Shur,et al.  Threshold voltage, field effect mobility, and gate-to-channel capacitance in polysilicon TFTs , 1996 .

[11]  Navakanta Bhat,et al.  Bias temperature instability in hydrogenated thin-film transistors , 1997 .

[12]  Positive oxide charge from hot hole injection during channel-hot-electron stress , 1998 .

[13]  J. R. Ayres,et al.  Analysis of Drain Field and Hot Carrier Stability of Poly-Si Thin Film Transistors , 1998 .

[14]  Device degradation of n-channel poly-Si TFTs due to high-field, hot-carrier and radiation stressing , 2001, Proceedings of the 2001 8th International Symposium on the Physical and Failure Analysis of Integrated Circuits. IPFA 2001 (Cat. No.01TH8548).

[15]  Jae-Hoon Lee,et al.  Improvement of polycrystalline silicon thin film transistor using oxygen plasma pretreatment before laser crystallization , 2002 .