This paper reported the variation in performance of bias stressed low-temperature polycrystalline silicon thin film transistors (LTPS TFTs) fabricated on metal foil substrate for flexible display applications. The mobility, threshold voltage (Vth), and trap density (Nt) of the proposed p-channel poly-Si TFT as a function of curvature radii were investigated. The significant increase in Vth by 9% was observed as the compressive or tensile mechanical strain increases to 0.1%. In addition, the hole mobility increases by 7% due to an increased compressive strain of 0.1%, while hole mobility decreases by 3.5% with the increase in tensile strain of 0.1%. After dc bias stressing, the LTPS TFT with mechanical strain had better performance than that on flat state in both the mobility drop and Vth shift. Mechanical strain influences the lattice arrangement and electric field at the drain electrode region that resisted device degradation in early stressing period.
The effects of the uniaxial mechanical strain stress on hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) were studied in this work. The proposed a-Si TFTs were fabricated on thin steel foil, and all process temperature was wellcontrolled below 200 . The threshold voltage (V th ) metastability was discussed by applying DC bias stress on gate electrode. The tensile strain was imposed on the device parallel to the sourcedrain current path, and all electrical parameters were extracted from saturation region. Our results indicated both outward and inward strain stress can lead to an un-recoverable destruction on aSi:H TFTs at the first time. Even if the TFTs devices were reflattened to plane, the transfer characteristic didn't recover and had larger V th variation than the consequent bending performance. This phenomenon was related to the disorder of amorphous silicon structure. We provide a model and used activation energy to explain this effect.
We investigated the stability of a-Si:H TFTs under mechanical strain with and without silicon nitride (SiNx:H) passivation. The process temperature of these flexibledevice, including the passivation layer, was well-controlled below 200 , and the substrate was using stainless steel foil. The strain stress was applied cylindrically parallel to the active channel path of TFTs. The stability measurement was performed by DC gate bias stress and lasted up to 10 4 seconds. By using electrical parameter fitting, the V th metastability mechanism was dominated by state creation effect. Our result indicated the device with passivation layer was improved, and the V th had less variation under both outward and inward bending. By exerting 190 post -annealing process after SiNx:H deposited, the V th was shifted left and the reliability of flexible TFTs became better than without post-annealing process. That's related to the passivating effect of hydrogen ion under passivation layer and post-annealing process.
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