Study On The Preparation And Performance Of Inkjet-Printed ZnO-Based TFT

In recent years,ZnO-based thin film transistors(TFTs)have been widely studied due to their high carrier mobility,good uniformity and stability,high optical transparency,and suitability of large area fabrication.Compared with the traditional vacuum process,inkjet printing technology is one of the most promising methods for thin film deposition because of direct patterning deposition of functional materials,low cost,and low material waste.In this work,the ZnO-based active layer of TFT was prepared by inkjet printing.The characteristics of the prepared films and the performances of TFT devices were investigated.The main contents and conclusions are shown as follows:The In-Ga-Zn oxide(IGZO)precursor ink was prepared,and the stable and continuous ink droplets were obtained by adjusting the appropriate drive voltage waveform of the piezoelectric inkjet printer.The effects of ink storage time and inkjet pause time on the stability of droplets were studied.The results showed that the ink did not appear turbidity or precipitation phenomena within 15 days,and the shape and size of the droplets did not show significant changes.In the inkjet printing process,the nozzle was not clogged,and the shape and size of the droplets did not show significant changes within 30-min pause.The IGZO-TFT devices were fabricated by inkjet printing.The effects of substrate temperature and concentration of precursor on the uniformity of IGZO thin films were investigated.The effects of active layer thickness and annealing temperature on the performance of IGZO-TFT were evaluated.The results indicated that the IGZO thin film had a better uniformity when the substrate temperature and concentration of precursor solution were 40 ? and 1.5 mol/L,respectively.And the IGZO-TFT had a better performance when the film was annealed at 400 ? for 3 h.The mobility,threshold voltage,subthreshold swing,on/off current ratio were 1.60 cm2V-1s-1,-5 V,0.94 V/dec,and 2.16 × 106,respectively.Low temperature fabrication process of ZnO-based TFT by inkjet printing was studied.The laser spike annealing(LSA)with a wavelength of 1.06 ?m was used to instead of the conventional thermal annealing.The process temperature was reduced to 200 ?.The effects of LSA treatment on the surface morphology and structure of IGZO thin films were studied,and the LSA treatment parameters were optimized.The results showed that LSA treatment promoted the formation of oxygen vacancy in the IGZO thin film so that the carrier concentration was increased.And the surface roughness of IGZO thin film was increased after LSA treatment.The IGZO-TFT had a better performance after laser scanning at the energy density of 2.1 J/cm2 for 40 times.The mobility,threshold voltage,subthreshold swing,and on/off current ratio of the device were 1.50 cm2V-1s-1,-8.5 V,1.66 V/dec,and 1.29 × 106,respectively.Moreover,the ZnO nanoparticle ink with particle size of 3?6 nm was prepared to instead of IGZO ink,and the TFT devices were fabricated using a conventional thermal annealing process at 150 ?.However,the ZnO-nanoparticle TFT revealed poor performance,and its mobility,threshold voltage,subthreshold swing and on/off current ratio were 0.028 cm2V-1s-1,5 V,5.62 V/dec,4.23 X 104,respectively.The flexible IGZO-TFT by inkjet printing was preliminarily studied.The IGZO-TFT devices were fabricated on a polyimide(PI)substrate with conventional thermal annealing process of 300 ?,and on a polyethylene terephthalate(PET)substrate with laser spike annealing of 200 ?,respectively.The results indicated that,the devices on the PI substrate exhibited better performance,and the mobility,threshold voltage,subthreshold swing and on/off current ratio were 0.36 cm2V-1s-1,0 V,1.28 V/dec,7.98×X 105,respectively.