镨掺杂铟镓氧化物薄膜晶体管的低频噪声特性分析

Analysis of low frequency noise characteristics of praseodymium doped indium gallium oxide thin film transistor

本文研究了镨掺杂铟镓氧化物(PrIGO)薄膜晶体管(thin film transistor, TFT)的低频噪声特性.根据低频噪声测试分析结果得知:IGO-TFT和PrIGO-TFT器件沟道电流的功率谱密度与频率的关系均满足1/fg(g≈0.8)的关系,符合载流子数涨落模型.通过研究不同沟道长度对器件低频噪声的影响,明确了器件的噪声主要来源于沟道区而非源/漏接触区.基于载流子数涨落模型,提取界面处的缺陷态,发现Pr元素掺杂会在IGO体系中诱导出缺陷态.而该缺陷态可以作为电离氧空位和电子的复合中心,进而改善氧化物TFT器件中由氧空位所导致的光照负偏压(negative bias illumination stability, NBIS)稳定性问题.

Metal oxide thin film transistors(MOTFTs)have been extensively investigated in the display industry because of their attractive characteristics,including high performances,low processing temperatures,and simple fabrication.However,under the actual working condition,the characteristics of TFTs are easily affected by the light irradiation caused the negative gate bias stress(NBIS).Therefore,the NBIS stability of MOTFT is a crucial issue that must be solved before their commercialization into an optoelectronic device.In this article,praseodymium-doped indium gallium oxide(PrIGO)is employed as the channel layer of thin film transistor(TFT).The TFTs with Pr doping exhibit a remarkable enhancement in NBIS stability.The structure and chemical composition of PrIGO film are analyzed by X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS),respectively.Besides,to further explore the mechanism for the improvement of NBIS stability,the low-frequency noise characteristics of IGO-TFT device and PrIGO-TFT device are studied.According to the low frequency noise characterization and analysis results,the correspondence between the normalized drain current noise power spectral density(SID/IDS2)and frequency shows 1/fγ(γ≈0.8)low frequency noise behavior for IGO-TFT device and PrIGO-TFT device.In addition,by studying the influences of different channel lengths on the low frequency noise of the IGO-TFT and PrIGO-TFT devices,it can be concluded that the low frequency noise of the device comes mainly from the channel region rather than from the source/drain contact region.In the linear region of the IGO-TFT device and PrIGO-TFT device,according to the linear fitting of the SID/IDS2 versus the overdrive voltage(VGS-Vth),it is proved that the low frequency noise of the IGO-TFT device and the PrIGO-TFT device are mainly affected by the carrier number fluctuation model.Finally,based on the carrier number fluctuation model,the defect state density at the interface between active layer and gate insulating layer is extracted to be 7.76×1017 cm-1·eV-1 and 9.55×1017cm-3·eV-1 for IGO-TFT and PrIGO-TFT devices,respectively.We speculate that the Pr element can induce defect states in the IGO system,and the trap states induced by Pr ions facilitate the capture of free electrons by positively charged oxygen vacancies,which lead the photo-induced carrier in conduction band to be suppressed.