Study Of Zno Films And The Transistor Performance

ZnO-TFT has several advantages over the tranditional Si-TFT for the low growth temperature, high carrier mobility and transparency properties, which can be widely used in flat panel display as switch arrays or driver in the future. This work has carried out the research on "ZnO thin film properties by different deposition method" and "ZnO based device investigation". The dissertation has four sections as summarized below.In the first part, we investigate the influence of the deposition condition and post annealing treatment on the properties of the ZnO films. For the films grown by the ion beam deposition, the in-situ XRD (X-Ray diffraction) results reveal the existence of three regions during annealing process and proves that most of the improvement for the films' properties occurs in the temperature region of 100℃to 300℃. The effects of post-annealing treatment on the performance of the ZnO thin films in this region have been investigated. For the ZnO films deposited by the DC magnetron sputtering, the relationship between the films'properties and the deposition conditions has been studied. For the films deposited by the sol-gel method, the effects of the annealing temperature on the films' physical and optical properties have been reported.In the second part, we prepared the n-ZnO film/p-Si heterojunction. The effect of the growth condition on the heterojunctions'properties, such as on/off ratio and current transport has been studied. The different carrier transport mechanism for the heterojunctions under forward and reverse bias is systematically studied which has been proved by the high temperatureⅠ-Ⅴmeasurement. With the increasing measurement temperature, the recombination-tunneling current shows temperature insensitive performance. But the space-charge limited current (SCLC) changes with the temperature which results from the trap assistant in the junction.In the third part, we prepared the ZnO-TFTs by the ion beam deposition and sol-gel method. All as-deposited ZnO films prepared by the ion beam sputtering need annealing treatment in the air ambient or O2 ambient to decrease the carrier concentration in the film. The correlation between the TFT's performance and the annealing treatment is studied. For the ZnO film deposited by the sol-gel method, the transistor fabricated with Pt electrode exhibits lower saturation voltage and current, which is due to the Schottky contact between the Pt electrode and the ZnO film. This kind of Source-gate transistor has the advantage of low power consumption. The study on the In-doped ZnO-TFT shows that increasing the In content results in higher carrier mobility but lower on/off ratio. The ZnO-TFT has the carrier mobility of 0.061 cm2/V-s while the one with 5% In doping is 0.246 cm2/V-s. The effects of annealing treatment on the GIZO-TFT's properties have also been studied. For the GIZO-TFT annealed at 500℃in air, the mobility reaches 3.48 cm2/V-s.Finally, the properties of the ZnO nanorods network transistor have been studied. The channel region is defined by selective growth of the ZnO nanorods on the patterned seed layer. The device obeys the n-type depletion mode with the Ion/Ioff ratio of 103 and field effect mobility of 6.7 cm2/Vs. The fabrication temperature of the whole process is below 300℃which has great potential in the application on flexible substrate.