摘要:
本文针对铟锌氧化物薄膜晶体管(IZO TFT)的低频噪声特性与变频电容-电压特性展开试验研究,基于上述特性对有源层内局域态密度及其在禁带中的分布进行参数提取。首先,基于IZO TFT 的亚阈区I-V 特性提取器件表面势随栅源电压的变化关系。基于载流子数随机涨落模型,在考虑有源层内缺陷态俘获/释放载流子效应基础上,通过γ因子提取深能态陷阱的特征温度；基于沟道电流噪声功率谱密度及平带电压噪声功率谱密度的测量,提取IZO TFT有源层内局域态密度及其分布。试验结果表明,带尾态缺陷在禁带内随能量呈e指数变化趋势,其导带底密度NTA约为3。42×1020 cm?3·eV?1,特征温度TTA约为135 K。随后,将C-V 特性与线性区I-V 特性相结合,对栅端寄生电阻、漏端寄生电阻、源端寄生电阻进行提取与分离。在考虑有源层内局域态所俘获电荷与自由载流子的情况下,基于变频C-V 特性对IZO TFT有源层内局域态分布进行参数提取。试验结果表明,深能态与带尾态在禁带内随能量均呈e指数变化趋势,深能态在导带底密度NDA约为5。4×1015 cm?3·eV?1,特征温度TDA约为711 K,而带尾态在导带底密度NTA约为1。99×1020 cm?3·eV?1,特征温度TTA约为183 K。最后,对以上两种局域态提取方法进行对比与分析。
Abstract:
Density of localized states (DOS) over the band-gap determines the electrical and instability characteristics in the indium zinc oxide thin film transistor (IZO TFT). In order to propose an accurate extraction method for DOS in the bulk region, low frequency noise and multi-frequency capacitance voltage characteristics are measured and analyzed in this paper. Firstly, the relationship between surface potential and gate voltage is extracted based on subthreshold I-V characteristics. The extraction results show that the surface potential increases with the increase of gate voltage in the sub-threshold region. When the Fermi level is close to the bottom of conduction band, the increase of surface potential should be saturated. Secondly, drain current noise power spectral densities in the IZO TFTs under different operation modes are measured. Based on carrier number fluctuation mechanism, the flat-band voltage noise power spectral density is extracted and localized state near IZO/SiO2 interface is then calculated. By considering the emission and trapping processes of carriers between localized states, the distribution of bulk trap density in the band-gap is extracted based on low frequency noise measurement results. The experimental results show an exponential tail state distribution in the band-gap while NTA is about 3.42 × 1020 cm?3·eV?1 and TTA is about 135 K. Subsequently, contact resistances are then extracted by combining capacitance-voltage characteristics with I-V characteristics in the linear region. The extrinsic parasitic resistances at gate, source, drain are separated. By considering charges trapped in the localized states and free carriers, the distributions of deep states and tail states in the active layer of IZO TFT are extracted through multi-frequency capacitance-voltage characteristics. The experimental results also show an exponential deep state and tail state distribution in the band-gap while NDA is about 5.4 × 1015 cm?3·eV?1, TDA is about 711 K, NTA is about 1.99×1020 cm?3·eV?1, and TTA is about 183 K. The above two proposed extraction methods are compared and analyzed. The deviation between two extraction results may relate to the existence of neutral trap in the gate dielectric which is also an important source of low frequency noise in the IZO TFT.
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