A method for fabricating a flexible electrical device is provided. The method includes providing a first substrate, providing a second substrate opposed to the first substrate, wherein one of the first and second substrates includes a polyimide polymer of Formula (I) wherein B is a polycyclic aliphatic group, A is an aromatic group containing at least one ether bond, A′ is an aromatic or aliphatic group, and 1≦n/m≦4, directly fabricating a thin film transistor (TFT) on one of the first and second substrates which includes the polyimide polymer of Formula (I), and disposing a medium layer between the first substrate and the second substrate.