基于垂直薄膜晶体管的高性能柔性射频识别器件

High-performance flexible thin-film transistor (TFTs) is at the heart of flexible display, and the wearable RF electronic devices. However, in the existing flexible TFT fabrication technology, the lower lithography accuracy (> 1 μm) determines the channel length between the source and drain electrodes, which greatly limits the device current density and operating frequency. At the same time, the existing inorganic TFT materials (such as polysilicon, metal oxide) have insufficient mechanical strength and flexibility, which limits the flexible application of the overall device performance. In order to overcome these two key limitations, this project intends to develop a large area vertical high-performance TFT using a metal-oxide-semiconductor vertical structure. In this structure, the channel length of the transistor is dedicated on the thickness of the semiconductor thin film (typically <100 nm) without being limited by the lithographic accuracy. Based on this, it is expected to develop a vertical flexible TFT with a current density larger than 10,000 A/cm2, an operating voltage of less than 1.5 V and an applied mechanical strain over 1.5%. Furthermore, we are targeting on high-speed single device with cut-off frequency fT>200 MHz, and RF flexible ring oscillator with working frequency>20 MHz, which would be the key for further large area, low-power TFT and its practical application.

高性能的柔性薄膜晶体管是新一代可穿戴射频器件及电路的核心基础。然而，在现有的柔性薄膜晶体管印刷制备中，较低的光刻精度（大于1微米）决定了源漏电极间的沟道长度，极大地限制了器件的电流密度和工作频率。同时，现有的薄膜晶体管沟道材料，如多晶硅、金属氧化物等都机械强度及柔性不足，限制了整体电路的柔性应用。为了克服这两个问题，本项目拟采用新型垂直结构研制大面积的纵向高性能薄膜晶体管。在此结构中，晶体管的沟道长度取决于半导体薄膜的厚度（小于100 nm），而不受限于光刻精度。基于此，期望研制出电流密度达到20,000 A/cm2，工作电压小于1.5 V和可施加应力大于1.5%的垂直柔性薄膜晶体管。在此基础上，构筑高性能环形振荡器件（频率达到20 MHz）和高速单管射频器件（工作截止频率达到200 MHz 以上），为进一步制备大面积，低能耗的薄膜场效应晶体管及相应射频器件，并将之推向实用化提供技术支持。

本项目针对传统垂直半导体器件界面不理想的挑战，使用了二维半导体作为表面无悬挂键的半导体，使用范德华金属作为集成金属，克服了传统集成工艺对垂直沟道的接触损伤，降低了界面态和界面无序性，实现了高性能的垂直晶体管。两项主要成果如下：.1）针对垂直二极管尺寸不能微缩的挑战，开发了双面的范德华集成工艺，构建了超短沟道长度的肖特基二极管。通过在超薄二维半导体两侧机械层压预制的金属电极，展示了一种超小尺寸的肖特基二极管，其实际二极管长度低至3 nm，代表了迄今为止最薄的肖特基二极管。此外，通过厚度相关和温度相关的电学测量，他们解释了超小尺度二极管中的载流子传输机制。制备的二极管可以实现20 ns的光电开关速度。这项研究不仅将肖特基二极管的尺寸减小到3 nm 以下的范围，而且还为以前受限于非理想的金属-半导体接触界面的超薄垂直器件提供了一种通用的低能量接触集成方法。 .2）针对垂直晶体管不理想的金属半导体界面问题，提出了使用低能范德华金属集成技术。通过将预制备的金属电极转移到范德华异质结上，实现了沟道长度低至一个原子层的MoS2垂直晶体管。此器件在沟道长度分别为0.65 nm和3.60 nm的垂直场效应晶体管的开/关比为26和103。该方法还可以扩展到其他层状材料，实现低于3 nm的p型和n型垂直晶体管。