ZnO薄膜的制备及其晶体管性能研究

【作者】 陈韬；

【导师】 屈新萍；

【作者基本信息】 复旦大学 ， 微电子学与固体电子学， 2010， 博士

【摘要】 ZnO-TFT具有低温生长、高迁移率以及全透明的优点,具有取代Si基器件成为下一代薄膜晶体管技术的可能,有很大的应用前景。而其材料特性、器件和工艺特性等方面还有很多前沿的科学问题值得研究。本文围绕着“ZnO薄膜的制备”和“ZnO薄膜器件特性研究”两个主题,将全文分成四个部分,对ZnO的薄膜特性和器件性能进行了系统研究。第一部分研究了ZnO薄膜特性与生长条件和后期处理的关系。首先研究了退火条件对离子束淀积ZnO薄膜特性的影响。采用原位XRD方法在100℃到950℃范围研究了ZnO薄膜特性随温度的变化,发现退火特性存在三个温度区间,并根据结果选择了300℃到600℃作为研究区间。在该温度范围内对ZnO薄膜的物相特性、电学特性和光学特性与退火温度和气氛的关系进行了系统研究。实验发现,氧气气氛可以明显减少薄膜内部氧缺陷的含量,从而降低载流子浓度,使薄膜的电学特性由导体向半导体转换。研究了直流磁控溅射淀积的ZnO薄膜特性和生长温度的关系,当衬底温度达到300℃时,薄膜的结晶性明显改善,带边发射增强。而用溶胶凝胶法淀积的ZnO薄膜结晶性能较差,在退火温度低于500℃时,薄膜为非晶形态,但是PL谱中薄膜表现出良好的光学特性,具有较为单一的紫外光发射。第二部分制备了n-ZnO薄膜/p-Si异质结,研究了ZnO薄膜不同气氛和温度的淀积条件对异质结电学特性如开关比和电流传输特性的影响。实验表明,在正向电压下异质结导通电流可以分为线性电流区、隧道-复合电流区和空间电荷限制电流区。通过变温测试,验证了不同的导电机理：隧道-复合电流不依赖于测试温度的变化；空间电荷限制电流随着温度的升高而减小,根据Rose理论反映出缺陷在能带中的分布对载流子输运的影响。在第三部分中用离子束溅射和溶胶凝胶法制备了ZnO薄膜晶体管,并研究了工艺条件对器件性能的影响。实验发现,采用离子束淀积的ZnO薄膜由于载流子浓度较高,必须在氧气条件下进行退火处理,降低薄膜的导电特性。经过氧气退火的样品,晶体管的开关比和场效应迁移率随着温度的升高而增加。但是延长退火时间会造成介质层漏电流增大,引起器件开关比降低。研究了不同后期退火温度、电极材料以及掺杂对溶胶凝胶法制作的ZnO-TFT性能的影响。实验发现,选择与ZnO薄膜有高肖特基势垒的Pt作为源漏电极时晶体管的导通电流明显减小,并且可以迅速进入饱和区。通过对ZnO与Pt接触特性的研究发现,ZnO与Pt之间势垒达到0.89 eV。该类源-栅薄膜晶体管器件在低功耗小尺寸电路的应用中具有一定的潜力。针对溶胶凝胶法易掺杂的特点,研究了不同的In掺杂对器件性能的影响。随着In含量的增加,器件的开关比降低,但是迁移率由未掺杂的0.061 cm2/V·s增加到5%In掺杂的0.246 cm2/V·s,选择合适的掺杂浓度显得非常重要。此外利用日本制备的GIZO薄膜制备了TFT器件,经过500℃空气退火场效应迁移率达到3.48 cm2/V·s。第四部分中我们研究了ZnO纳米结构制备场效应晶体管。通过水热法在低温条件下合成了ZnO纳米棒阵列,采用Pt作为源漏电极,ZnO纳米棒阵列作为导电沟道层制作了背栅结构的场效应晶体管。相比ZnO薄膜场效应晶体管,纳米场效应晶体管由于缺陷的减少具有更高的导通电流。通过纳米棒的图形化生长,减少了纳米棒之间“结”所引入的缺陷,载流子迁移率达到了6.7 cm2/V·s。整个工艺温度控制在300℃以下,与柔性衬底上的应用相兼容。更多还原

【Abstract】 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.更多还原