I. Introduction
Thin-film transistors (TFTs) with polycrystalline-silicon (poly-Si) channel material have been widely used as a driving device for controlling liquid crystal and pixels in a display panel [1], [2]. In addition to display industry, static random-access memory circuit, dynamic random-access memory circuit, and nonvolatile memory are also implemented by the poly-Si TFTs to realize 3-D integrated circuits in the very large-scale integration industry [3]–[6]. However, there are many grain boundaries in the poly-Si channel film, resulting in high trap state density among the energy bandgap. The trap state density would seriously degrade the carrier field-effect mobility (), threshold voltage (), and subthreshold swing (SS) of poly-Si TFT [7]–[10]. In addition, the trap state density would also seriously degrade the short-channel effect (SCE) of poly-Si TFT when the channel length is decreased [11], [12]. In order to improve the electrical characteristics of poly-Si TFT, plasma treatment process is widely used to passivate the trap state density and improve the performance and reliability of poly-Si TFT [13]–[17]. Among various gas plasma treatments, the ammonia gas (NH3) plasma is the most widely used to perform the defect passivation process because the ammonia plasma can improve the device performance and reliability of poly-Si TFT simultaneously [13], [15]. Recently, the poly-Si TFT with junctionless (JL) structure has been extensively studied because there are many advantages of JL structure, such as better SCE, higher on-state current, simple fabrication process, and low cost [18]–[23]. Moreover, the electrical behavior of a poly-Si film with a high doping concentration will be close to that of a single crystal silicon film [7]. This is because the trap state inside the poly-Si is easily filled with a large number of majority carriers, which greatly reduces the impacts of trap state on the carrier transport. However, the impacts of plasma passivation method on the poly-Si JL-TFT are less discussed. In this work, the ammonia gas plasma treatment on poly-Si JL-TFT with high-/metal-gate structure is studied. The trap state passivation effect of plasma treatment could further enhance the performance of poly-Si JL-TFT and improve the reliability behavior. The results would be helpful for the development of nonvolatile memory and 3-D integrated circuits.