A Novel Self-Aligned Etch-Stopper Structure With Lower Photo Leakage for AMLCD and Sensor Applications

In this letter, the authors introduce a novel self-aligned etch-stopper sidewall-contact hydrogenated amorphous silicon (a-Si : H) thin-film transistor (ESSC-TFT), which reduces the photo leakage current by more than one order of magnitude and increases the on-off ratio to seven orders of magnitude under back light illumination. Such a TFT will enable high-resolution and high-brightness liquid-crystal displays (LCDs) for next-generation TV, monitor, notebook, and mobile-phone applications. This ESSC-TFT design reduces the volume of a-Si film in which the active region can totally be shielded by the gate metal resulting in the prevention from direct back light illumination. With the sidewall contact, the hole current is reduced due to the smaller contact area between drain/source and a-Si layer. As well as the source, drain parasitic intrinsic resistance of a-Si can be also lessened by the ESSC-TFT structure. Although the defects between etched a-Si and n⁺ a-Si film may degrade the on current, the ESSC-TFT still exhibits higher on-off ratio and lower leakage than the one in traditional etch-stopper (ES)-TFT structure. The ESSC-TFT structure can be used not only for TFT-LCD application but also for the applications that demand high on-off ratio and low-leakage device, such as X-ray image sensor