Simulation Of Dual-channel A-IGZO Thin Film Transistors

Nowadays,the flat panel display technology is rapidly developing,and thin film transistor(TFT)as its core components of the device is more concerned by many researchers.In the previous,amorphous silicon TFT and polysilicon TFT have been widely used as pixel switches.the amorphous-indium gallium-zinc oxide thin film transistor(a-IGZO TFT)has been widely used since the stability and the low-temperature preparation performance is good and the uniformity is good and the light transmittance is high)Was developed,it quickly occupied the market.However,since the amorphous indium gallium zinc oxide thin film transistor(a-IGZO TFT)was developed,it quickly occupied the market because of its many advantages such as the good stability,good low temperature preparation performance,uniformity good,high transmittance and other advantages.However,with the development of technology,video formats are becoming more advanced,so the equipment resolution and the clarity are drived to become better,and the existing equipment has been unable to meet the strong demand of the majority of users.And then the double-layer active layer TFT was constantly being studied out.The United States Dehuff research team developed amorphous-indium-zinc oxide thin film transistor(a-IZO TFT)in 2005.The mobility of the a-IZO TFT is much higher than that of the a-IGZO TFT,and its open-state current is high and the low-temperature preparation performance is also good,and its disadvantages is that the stability is not good enough.Therefore,this paper is based on this basis,I use the double-layer active layer structure,and use a-IZO material as the front channel because its high mobility can improve the TFT device on-state current;I also use a-IGZO material as the back channel because its low off current can improve the switching current ratio of the TFT device.And the focus of this paper is as follows:1)The composition of the two materials of the active layer of the TFT device is studied,that is,the total thickness of the active layer of the double-layer active layer TFT is set to a certain value,and the front channel is a-IZO material,The conductivity of the dual active layer TFT and the influence of the carrier concentration of the active layer on the electrical characteristics of the TFT device were investigated according to the change in the thickness ratio of the a-IGZO material.And in contrast to discuss the thickness of these two materials in what state can the TFT device performance to achieve the best.It has been found that when the thickness of the front channel material a-IZO of the double-layer active layer TFT device is 5 nm(the thickness ratio of a-IZO to a-IGZO is 5/35),the switching current ratio of the TFT device reaches the maximum Value,the threshold voltage is closest to 0,and the subthreshold swing is also the minimum value among all the thickness ratios TFTs studied,and the stability stability is also good.And during the research,we can found that the double layer active layer TFT electrical characteristics generally better than the characteristics of single-layer active layer TFT.2)The density of states(DOS)of a-IGZO semiconductors is an important characterization of their electrical properties.The parameters of the DOS model are studied in a number of simulation studies of their properties.Since a-IZO is a-IGZO semiconductor lacking Ga elements,this paper studies the state density model parameters of two active layer materials in combination with the existing a-IGZO DOS model.We mainly to discuss the impact of its specific parameters on the impact of TFT devices.The simulation results show that: a)the increase of the concentration of nta at E = EC of the pre-channel a-IZO leads to the decrease of the open-state current of the dual active layer TFT device and the increase of the threshold voltage.The increase of the characteristic slope wta of the conduction band tail results in an increase in the area of the conduction band and the decrease in the open-state current of the TFT device,and the increase in the threshold voltage and the decrease in the sub-threshold swing.b)The change of the oxygen vacancy state of the a-IGZO material has a great influence on the characteristics of the TFT device,and the relative position of the oxygen vacancy state and the Fermi level can also affect the TFT device.Therefore,the conduction band tail of the pre-channel(the empty orbit of the cation)has a great influence on the TFT device,and the influence of the defect state of the back-channel on the TFT device is more negligible.