Surface Engineering of Polycrystalline Silicon for Long-Term Mechanical Stress Endurance Enhancement in Flexible Low-Temperature Poly-Si Thin-Film Transistors

Abstract

The surface morphology in polycrystalline silicon (poly-Si) film is an issue regardless of whether conventional excimer laser annealing (ELA) or the newer metal-induced lateral crystallization (MILC) process is used. This paper investigates the stress distribution while undergoing long-term mechanical stress and the influence of stress on electrical characteristics. Our simulated results show that the nonuniform stress in the gate insulator is more pronounced near the polysilicon/gate insulator edge and at the two sides of the polysilicon protrusion. This stress results in defects in the gate insulator and leads to a nonuniform degradation phenomenon, which affects both the performance and the reliability in thin-film transistors (TFTs). The degree of degradation is similar regardless of bending axis (channel-length axis, channel-width axis) or bending type (compression, tension), which means that the degradation is dominated by the protrusion effects. Furthermore, by utilizing long-term electrical bias stresses after undergoing long-tern bending stress, it is apparent that the carrier injection is severe in the subchannel region, which confirms that the influence of protrusions is crucial. To eliminate the influence of surface morphology in poly-Si, three kinds of laser energy density were used during crystallization to control the protrusion height. The device with the lowest protrusions demonstrates the smallest degradation after undergoing long-term bending.

Scalable Approach for Amorphous Thin Silicon Films Near‐IR Laser‐Induced Crystallization Using Nickel Absorption Layer

“…Due to necessity of Ni ablation from silicon surface, single laser pulse fluence was chosen to be higher (2 J cm −2 ) than commonly utilized 0.1–0.6 J cm −2 …”

“…Here we propose an approach for preparing thin pc‐Si films on isolating substrates that combines advantages of LIC and MILC methods. Particularly, high radiation absorption in amorphous silicon (a‐Si) is needed for LIC, therefore excimer and UV lasers are utilized, which forces search for less complicated and expensive systems. Recent study utilized near‐IR laser irradiation for a‐Si films crystallization .…”

Novel Electronics for Flexible and Neuromorphic Computing

“…Low‐temperature polycrystalline‐silicon (LTPS) TFTs are one of the most promising technologies that can be employed for next‐generation electronics due to their high carrier mobility, stability, and CMOS compatibility . Figure a shows the photographic and schematic (inset) images of TFTs on plastic demonstrated by LTPS . Appropriate energy density (560 mJ cm −2 ) of excimer laser was applied to completely melt the silicon while minimizing the protrusion of poly‐Si created during LTPS process, resulting in flexible TFTs with high mobility (over 45 cm 2 V −1 s −1 ) and flexibility.…”

“…The inset shows the optical image of the electrode area (left), and the active region of the device (right). (a) Reproduced with permission . Copyright 2017, American Chemical Society.…”

Remarkable Improvement in Foldability of Poly‐Si Thin‐Film Transistor on Polyimide Substrate Using Blue Laser Crystallization of Amorphous Si and Comparison with Conventional Poly‐Si Thin‐Film Transistor Used for Foldable Displays

“…Another important merit of BLA poly‐Si is no protrusion in the TFT channel . The grain boundary defects at the protrusion can degrade the TFT performance, and also affect the bias stability and mechanical bending stability . The flexibility of the ELA TFTs on PI substrates can be a big issue for the foldable and rollable AMOLED displays …”