Recently, flexible displays based on active-matrix organic lightemitting diode (AMOLED) on polyimide (PI) substrate are of increasing interest for use in foldable displays. PI substrates are not only thin and light, [1,2] but also could be processed at relatively high temperature (≥450 C). To achieve a flexible AMOLED display, thin-film transistor (TFT) array should be manufactured on a plastic substrate. [3][4][5][6][7][8][9][10][11] Popular semiconductor materials used for TFTs are amorphous silicon (a-Si), amorphous indium-gallium-zinc-oxide (a-IGZO), and polycrystalline Si (poly-Si) on PI substrate. Due to its low-temperature process on large glass substrates such as 10.5G (2.2 m  2.5 m), the a-Si:H has been used as a TFT switching element. However, it cannot be used for AMOLED TFT backplanes because of its threshold voltage (V TH ) shift during OLED operation. [12,13] Note that a-IGZO TFT has at least one order of magnitude higher mobility compared to a-Si:H TFT even though the TFT process temperature is similar. The a-IGZO TFT can be manufactured by using G10.5 glass so that manufacturing cost of oxide TFT backplanes for OLED can be much lower than that of low-temperature poly-Si (LTPS) TFT. Therefore, intensive studies on amorphous oxide semiconductors are being carried out for TFT backplanes of OLED displays. However, all smartphone OLED displays are still based on LTPS TFT backplanes because of its high mobility and excellent stability. The LTPS TFTs on PI substrate with high mobility and high stability are very suitable for mobile application. [14] The effects of mechanical strain and electrical reliability of LTPS TFTs have been previously reported (show in Table 1) with the conclusion that the mechanical stability is inferior to oxide TFTs. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Therefore, finding a solution to overcome the performance degradation during mechanical stress is important for more flexible and foldable AMOLED displays.In this article, to improve the reliability under mechanical stress, flexible LTPS TFTs were fabricated using three kinds of interlayers (ITLs): inorganic (SiO 2 /SiN x ), hybrid (SiN x /PI), and organic (PI) layers. Reliability test of the LTPS TFTs is performed using bending and rolling machines until 10 000 cycles. Using low Young's modulus organic material (PI) ITL, the change in electrical performance under mechanical strain could be reduced significantly. Especially, rolling test with rolling radius of 1 mm was examined until 10 000 cycles. The LTPS TFT with inorganic ITL shows the crack generation after rolling with 1 mm radius. However, the performance of the LTPS TFTs with hybrid ITL

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