| In the field of active matrix flat panel display,including AMLCD and AMOLED,thin-film transistor as pixel switch,has irreplaceable role.High resolution,large size,and flexible display have become a new direction in the development of display technology,for which the thin film transistor has also been put forward higher requirements.As a metal oxide?compared to traditional a-Si TFT and p-Si TFT?with high migration,excellent stability,high light transmission and low temperature preparation process,Zn O-TFT is considered the most promising candidate for the next generation of high-resolution liquid crystal displays and transparent organic light-emitting diode displays.However,some reports indicate that the undoped Zn O TFT has a low on current,large threshold voltage and high density crystal boundary;in order to improve the performance of Zn O TFT,this paper is divided into the following parts.Firstly,Zn O films were grown on glass substrate at room temperature by rf magnetron sputtering.The effects of working pressure on the crystal structure,optical properties and electrical properties of Zn O films were studied by the Ultra-visible light spectrophotometer?X-ray diffraction?XRD?instrument and the Hall effect test system.The results show that the zinc oxide film is composed of polysemes with the structure of the six-sided fiber-zinc ore and the c-axis orientation,and is highly dense.With the increase of working pressure,the size of the film grain and hall migration rate showed a consistent increase and then decrease;similarly,the carrier concentration of the film increased slowly and then increased exponentially(1010 to1019/cm3);while the resistivity showed a tendency to decrease(10-7 to 10-2 sccm).In addition,the internal pressure stress of the film decreased firstly and then increased as the working pressure increases.The average transmission rate of all films in the visible light area is greater than 80%.The optical band gap of the film is between3.21 and 3.24 e V.Secondly,to optimize the process parameters of zinc oxide thin film transistors,we use Si O2/p+-Si substrate and radio frequency magnetron sputtering to prepare Zn O-TFT,and study the effects of working pressure and channel thickness on TFT performance.The devices with working pressures of 0.3 Pa,0.6 Pa,0.9 Pa,3 Pa,6 Pa and 9 Pa were prepared.By calculating the deposition rate and controlling the sputtering time,the film thickness is 40nm,70nm and 100nm resipectively.The results show that when the working pressure is 0.9 Pa and the film thickness is 40nm,the zinc oxide thin film transistor has the best performance,with a lower off-state current ratio?1.3×108?.Thirdly,in order to further realize the high performance of Zn O-TFT,the continuous gradient channel device is prepared by adjusting the working pressure by using the regulated concentration of Zn O carrier.That is,a layer of ultra-thin high carrier Zn O?H-Zn O?is deposited on the surface of the Si O2 insulation layer and the low carrier concentration of Zn O?L-Zn O?is continued to be deposited without interruption of deposition.We explored the optimal thickness of the H-Zn O ultra-thin layer when the Zn O-TFT has the best electrical performance,it is about 0.6 nm.At the same time,we prepared the graded channel Zn O:N-TFT with the appropriate amount of nitrogen doping,which showed the synergy of electrical performance and stability.Compared with the single-layer Zn O TFT,the switching current ratio of the gradient channel Zn O:N-TFT is increased by 1 order of magnitude??1×109?,the carrier migration rate is increased by 3 times??9.4 cm2/Vs?,and the open current increases by 1 order of magnitude??2 m A?. |
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