The Preparation And Properties Of ZnO/BNT Ferroelectric Thin Film Transistor Array

Thin film transistor(TFT) has attracted many intensive research efforts because of their potential application in flat-panel liquid crystal display. With the development demands of large-size display, high resolution and high device integration, the fabrication of large-area TFT array has become the key technology which can affect the future application of TFT. Ferroelectric TFT, in which ferroelectric thin film is used to substitute conventional dielectric layer, has attracted a great deal of attention because of their advantages such as non-volatility, fast and nondestructive readable operation, capability of high-density integration, and low power consumption.Ferroelectric TFT can be applied in both liquid crystal display and non-volatile memory. In this thesis, large-area Bi3.15Nd0.85Ti3O12(BNT) thin films have been prepared in 5-inch Si wafers by the rastering pulsed laser deposition(PLD) method,and then the ZnO/BNT TFT arrays have been achieved. The main research contents and results can be summarized as follows:(1) The BNT thin films were prepared on the 1 cm×1 cm Pt/Ti/SiO2/Si substrates by PLD. The microstructures and ferroelectric properties of the BNT thin films deposited with different conditions were studied by the X-ray diffraction(XRD),scanning electron microscope(SEM) and ferroelectric analyzer. The optimized deposition parameters of the laser energy, oxygen pressure and substrate temperature were concluded to be 420 mJ, 200 mTorr and 800 oC, respectively.(2) 5-inch diameter BNT thin films were prepared on Si wafers by the rastering PLD method with the optimized deposition parameters. The homogeneity of the film thickness, element stoichiometry, crystallinity, optical properties and electrical properties were analyzed by the thin-film analyzer, X-ray photoelectron spectroscopy,XRD, ferroelectric analyzer and semiconductor test system. The results show that the maximum film thickness deviation of the prepared large-area BNT film is less than±10%. The prepared thin films have great uniformity in stoichiometry both along radial direction and film depth, and exhibit homogeneous optical properties and electrical properties.(3) Ferroelectric TFT units with BNT film as insulating layer and ZnO film as channel layer were prepared by PLD on 1 cm×1 cm Pt/Ti/SiO2/Si substrates, and their performances were analyzed. The threshold voltage(Vth), channel mobility(μsat),subthreshold swing(SS) and ratio of Ion/Ioff are 1.3 V, 2.4 cm2/Vs, 0.3 V/decade and105, respectively.(4) Large-area ZnO/BNT ferroelectric TFT arrays were prepared on 5-inch Pt/Ti/SiO2/Si substrates and performance of every ferroelectric TFT unit was analyzed. The results show that the homogeneity of arrays is good. In different area,the Vth values are all below 2.5 V, the μsat values are all above 1.84 cm2/Vs, the ratios of Ion/Ioff are about 103.