Effects of mechanical stresses on the reliability of low-temperature polycrystalline silicon thin film transistors for foldable displays

Abstract

This paper investigates the mechanical reliability of low temperature polycrystalline silicon (LTPS) thin film transistors (TFTs) for foldable display. Both compressive and tensile directions of mechanical stresses were applied for different types of mechanical stresses, such as dynamic and static mechanical stresses. The electrical characteristics of tested n-channel TFTs under mechanical stress conditions were analyzed based on several key parameters, including the threshold voltage (Vth), field effect mobility (μFE), maximum drain current (ID.MAX) and subthreshold swing (Ssub). For both cases of dynamic and static mechanical stresses, increase of Vth and decrease of μFE and ID.MAX were observed in the compressive direction. This trend was inversed when tensile stress was applied. The degradation of electrical characteristics originates from the change of lattice constant after mechanical stress. However, Ssub increases under dynamic tensile stress while it remains unchanged within 5% under static tensile stress. Transient analysis while bent condition was conducted to investigate the change of parameters in time.