Poly-Si Thin-Film Transistors on Polyimide Substrate for 1 mm Diameter Rollable Active-Matrix Organic Light-Emitting Diode Display

Thin-film transistor (TFT) backplanes on polyimide (PI) substrate are widely used for foldable active-matrix organic light-emitting diode (AMOLED) display. The low-temperature poly-Si (LTPS) TFTs on PI substrate for AMOLED displays use the inorganic interlayer (ITL) of SiO2/SiNx deposited on the poly-Si. Herein, a flexible ITL, very thin SiNx/organic PI layer stack, is introduced to improve both mechanical flexibility and environmental stability of LTPS TFT backplane on PI substrate. The electrical stabilities of LTPS TFT with various ITLs are studied such as positive bias temperature stress (PBTS) and negative bias temperature stress (NBTS). It is found that the LTPS TFTs are stable under PBTS and/or NBTS. However, the results on mechanical stability depend on the ITL used. The LTPS TFTs with hybrid ITL (SiNx/organic PI) and organic ITL(PI) are stable under mechanical stress because these TFTs have much less strain under mechanical bending because of the low Young's modulus of PI material. In addition, environmental stabilities of the LTPS TFTs with hybrid ITL is stable at 85 degrees C and 85% humidity in dark. Therefore, the LTPS TFTs with hybrid ITL are very suitable for rollable active matrix displays.