Fabrication And Characteristics Of Ferroelectric Thin Film Transistors With SnO₂Channels

The thin film transistor (TFT) as switching element of active array drivingdisplays was a leading in flat panel displays. Transparent oxide semiconductors as thechannel materials in the TFT are more and more attention. Compared with theamorphous silicon, polycrystalline silicon and organic semiconductor, transparentoxide semiconductors have many advantages, such as high optical transmittance, lowpower consumption, low requirements of the substrate, and so on. More and morewide forbidden band gap of the transparent oxide semiconductors that satisfy theabove requirements are widely studied. At the same time, ferroelectric thin filmtransistor (FeTFT) based on the structure of TFT because of the ease of large areaintegrated, ferroelectric thin films and the channel layer interface characteristics,non-volatile and other characteristics, aroused great interest in the study. Theferroelectric-gate thin-film transistor with tin oxide (SnO2) as a channel andferroelectric (Bi,Nd)4Ti3O12(BNT) as a gate insulator was fabricated by sol-geltechnique on the different substrate and compared to the device performance beforeand after annealing. And it was studied the change annealing temperature of SnO2thinfilms that effect on the performance of TFT. Finally it was investigated that the SnO2thin films doped with different concentrations of Sb element as the active layer effectson the TFT. Detailed contents and results are as follows:(1) The ferroelectric-gate thin-film transistor with SnO2as a channel andferroelectric BNT as a gate insulator was fabricated by sol-gel technique on the n-typeSi(100) substrate and compared to the device performance before and after annealing.Experimental results show that the performance can be improved significantly afterannealing, the leakage decreases obviously., The defect states in the film interface aredecreased that devices after annealed, and the surface contact gates and wires wereimproved by annealing. At the same time, some grain defects of SnO2film wasimproved, the film quality has been improved. The channel layer makes theconductive channel formed in the device, and the state current improved. Thetransistors exhibit N-type transistor characteristics operating in an enhancement-modewith the “on” current of25μA and a field-effect mobility of0.3cm2V-1s-1.(2) SnO2thin films were investigated respectively at450℃,550℃,650℃annealing effect of the TFT. The experimental results show that properly increasingthe annealing temperature(550℃) can reduce the defects in structure. But with increased of the annealing temperature, the grain will gradually increase. The carrierby the grain boundary scattering in migration resulted mobility decreases. Theimpurity ions under high temperature easily into the lattice, thus increasing the latticescattering, resulting inreduced mobility, and decrease the output current.(3) Studied of Sb doped concentration for0%,5%,10%of SnO2thin films as theactive layer which influence the performance of TFT was preparaed on differentsubstrate of n-type Si(100) and Pt/Ti/SiO2/Si. Experimental results show that the TFTshave leakage phenomenon. Analysis of reasons may be large number of structuraldefects after Sb doped of the SnO2films. The doping concentration is0%on then-type Si(100) substrates prepared TFT that showed an obvious tendency ofsaturation.