The basic mechanism leading to the morphology change in the active layer was explored systematically. We found that the wrinkles appearing at the cathode surface under post-annealing processes are more prominent than those under pre-annealing processes, which is strongly related to the roughness increase of the active layer. Due to thermal-induced instability from the aluminum (Al) layer with the device under post-annealing processes, a net compressive strain develops from the thermal expansion mismatch between the layers. Furthermore, an analysis of the mechanical properties shows that the enlarged nano-dimension roughness of the active layer is dominated by the final-bottom morphology of the compressed Al layer which depends on the annealing sequence. (C) 2014 Elsevier B.V. All rights reserved.