Characterizations Of Multiple Functions And Corresponding Mechanisms Investigations Of Amorphous In-Ga-Zn-O Thin-Film Transistors

The amorphous indium gallium zinc oxide(a-IGZO)has become a typical amorphous oxide semiconductor(AOS)material and has been extensively studied since it was proposed by the Tokyo Institute of Technology in 2004.The a-IGZO is a flexible and transparent material,and it has a relatively high carrier mobility,currently up to?70 cm²/(V·s).Moreover,it has practical applications because of its good surface properties under low-temperature processing and large-scale manufacturing capabilities.The a-IGZO thin-film transistors(TFTs)have the potential to be used in the core components of flat panel displays and in fields like flexible electronic skins and wearable smart devices.It is well known that a-IGZO have subgap density of states(DOS)originating from structural disorders and defects.DOS can significantly affect the electrical characteristics such as the threshold voltage(V_TH)and the drain current(I_DS)of a-IGZO TFTs.At the same time,the amount of DOS varies with the measurement time,so the measurement time of DOS is required to be consistent with the actual working time.Otherwise,the accuracy of the results may be impacted.At present,the methods to extract the DOS should be developed furtherly.Here,we choose the transient dual-pulse method designed independently by our team.This method can extract DOS in a transient way,it has lower noise and uses the electrical field only.The standard Si-based devices DMG301NU and a-IGZO devices fabricated in the laboratory are chosen.The amount of DOS and its distribution along the energy band are measured by the previously reported C-V method and the transient dual-pulse method.The results show that the illumination may affect the distribution of DOS.Besides,compared with the C-V method,the transient dual-pulse method can characterize the DOS distribution in the energy band better.Based on the DOS mechanisms,the relationship of a-IGZO TFTs to temperature is studied,and a-IGZO TFTs are used to characterize the temperature sensing functions.The shift of transfer curves of Si-based a-IGZO TFTs is different from the previously publications.DOS characterization and the activation energy calculation are performed to investigate the mechanisms which have the impact on the threshold voltages(V_TH).DOS experiments also verify that oxygen vacancies in a-IGZO materials decrease with the increase of temperature.However,the decrease of the activation energy(the average energy required for defects to excite trapped electrons to the conduction band)illustrates that there are at least two mechanisms to impact on V_TH:one should be the oxygen defect ionization,which leads to the decrease of V_TH and the negative shift of transfer curves;the other could be that the amount of free electrons decreases due to oxygen adsorbed on the channel surface and combine electrons in the channel,which leads to the increase of V_TH and the positive shift of transfer curves.In addition to the temperature sensing functions mentioned above,this paper realizes the multiple functions of flexible a-IGZO TFTs,based on new structures proposed by our team.To sum up,this paper starts with the characterization of DOS in the a-IGZO.The C-V method is used to investigate the effect of the illumination on DOS,and proves that the amount of DOS and its corresponding distribution along the energy band can be changed by illumination.By comparison between the transient dual-pulse method and the C-V method,we prove that the transient dual-pulse method is more accurate to extract DOS.At the same time,this paper investigates the mechanisms of the transfer curves of the Si-based a-IGZO TFTs which shift differently from previous publications.Furthermore,the multiple functions of flexible a-IGZO TFTs are obtained based on new structures proposed by our team.It provides a new idea to the application of TFTs in the flexible electronics.