氢化非晶硅薄膜晶体管的低频噪声特性

针对氢化非晶硅薄膜晶体管(hydrogenated amorphous silicon thin film transistor,a-Si:H TFT)的低频噪声特性展开实验研究.由测量结果可知,a-Si:H TFT的低频噪声特性遵循1/f~γ(f为频率,γ≈0.92)的变化规律,主要受迁移率随机涨落效应的影响.基于与迁移率涨落相关的载流子数随机涨落模型(?N-?μ模型),在考虑源漏接触电阻、局域态俘获及释放载流子效应等情况时,对器件低频噪声特性随沟道电流的变化进行分析与拟合.基于a-Si:H TFT的亚阈区电流-电压特性提取器件表面能带弯曲量与栅源电压之间的关系,通过沟道电流噪声功率谱密度提取a-Si:H TFT有源层内局域态密度及其分布.实验结果表明:局域态在禁带内随能量呈e指数变化,两种缺陷态在导带底密度分别约为6.31×10~(18)和1.26×10~(18)cm~(-3)·eV~(-1),特征温度分别约为192和290 K,这符合非晶硅层内带尾态密度及其分布特征.最后提取器件的平均Hooge因子,为评价非晶硅材料及其稳定性提供参考.

Low-frequency noise in hydrogenated amorphous silicon thin film transistor

Low-frequency noise in the hydrogenated amorphous silicon thin film transistor is investigated in this paper. The drain current noise spectral density shows a 1/f^γ (γ ≈ 0.92, f represents frequency) behavior which ascribes to fluctuations of the interfacial trapped charges due to the dynamic trapping and de-trapping of free carriers into slow oxide traps and localized traps. The normalized noise has the power law dependence on overdrive voltage, and the power law coefficient is about -1 which illustrates that the flicker noise is dominated by mobility fluctuation mechanism. By considering the contact resistance, and emission and trapping processes of carriers between localized states in the Si/SiN_x interface, the variation of low frequency noise with drain current is analyzed and fitted by use of the theory of carrier number fluctuation with correlated mobility fluctuation (ΔN-Δμ model). Furthermore, the relationship between surface band-bending and gate voltage is extracted based on subthreshold current-voltage characteristics, and thus the density of localized states is then extracted through the measurement of drain current noise power spectral density. The experimental results show an exponential localized state distribution in the band-gap while densities of two defect modes at the bottom of conduction band N_T1 and N_T2 are about 6.31×10¹⁸ and 1.26×10¹⁸ cm^-3·eV^-1, and corresponding characteristic temperatures T_T1 and T_T2 are about 192 and 290 K, which is similar to the reported distribution of tail states in the amorphous silicon layer. Finally, the average Hooge's parameter is extracted to estimate the quality of devices and materials.