Proposal of huge-charge-controlled field-effect transistor using ferroelectric gate insulator and its application to next-generation integrated circuits

本研究计划的目标是利用铁电材料实现可控制10-50 μC/cm ^2的巨大电荷密度的新型开关器件。在这项工作中，我们使用铟锡氧化物（ITO）作为沟道材料，而不是与铁电栅绝缘体的Si。首先，我们制备了Pb（Zr，Ti）O_3（PZT）和（Bi，La）_4Ti_3O_<12>（BLT）铁电薄膜以及ITO薄膜，并对其进行了表征。接下来，我们使用ITO/PZT和ITO/BLT结构制作了铁电栅薄膜晶体管（TFT）。漏极电流-漏极电压特性显示正常的n沟道晶体管操作，具有明显的漏极电流饱和。特别是沟道长度为5 μm的ITO/BLT TFT，获得了0.1mA/μm的大导通电流。该值与具有相同沟道长度的Si-MOSFET的导通电流一样大。从这个开电流，电荷密度。器件中所用的最大电流密度为20 μC/cm ^2，验证了本文提出的工作原理。此外，我们研究了器件参数依赖的电气性能的细节。我们还证明了通过机械抛光铁电薄膜的表面，可以大大降低器件的截止电流。研制了ITIO/BLT结构铁电栅TFT，其通断电流为10 <-3>^A，<-11>通断比大于10^7。此外，还在石英衬底上展示了透明铁电栅TFT。

The objective of this research project is to realize new switching device using ferroelectric materials which can control huge charge density of 10-50 μC/cm^2. In this work, we used indium-tin-oxide (ITO) as a channel material instead of Si with ferroelectric gate insulator. First, we fabricated and characterized ferroelectric thin films, Pb(Zr,Ti)O_3 (PZT) and (Bi,La)_4Ti_3O_<12> (BLT), and ITO thin films. Next, we fabricated ferroelectric-gate thin film transistors (TFTs) using ITO/PZT and ITO/BLT structures. Drain current - drain voltage characteristics shows normal n-channel transistor operation with clear drain current saturation. In particular, a large on-current of 0.1 mA/μm was obtained for ITO/BLT TFTs with a channel length of 5 μm. This value is as large as the on-current of Si-MOSFET with same channel length. From this on-current, the charge density. used in the fabricated device is as large 20 μC/cm^2, which proved the operation principle proposed in this work. Furthermore, we examined the details of device parameter dependence of the electrical properties. We also demonstrated that the off-current of the device can be drastically reduced by mechanically polishing the surface of the ferroelectric film. The ITIO/BLT structure ferroelectric-gate TFT with an on-current of 10^<-3> A and an off-current of 10^<-11> A (on/off ratio is more than 10^7) was demonstrated. In addition, transparent ferroelectric-gate TFTs were also demonstrated on quartz substrates.