Improvement in Mechanical Durability of Stretchable Charge-Trap Memory Transistors with Engineered Wavy-Dimensional Structures

Charge-trap memory thin-film transistors (CTM-TFTs) were fabricated with wavy-dimensional structures, and their device performances were demonstrated under mechanically stretching conditions. The fabricated CTM-TFTs obtained a wide memory window of 23.8 V, a steep subthreshold swing of 0.31 V/dec, and a large memory margin (10(6)) with program pulses as short as 1 mu s. Furthermore, the total variations in device parameters could be suppressed within a range of <12% even under stretching conditions with a prestrain as large as 60%. The mechanical durability during the cyclic stretching test with a strain of 50% was significantly improved from 2000 to 30000 cycles when the PI film thickness was reduced from 5.0 to 1.2 mu m. The effects of PI thickness on the mechanical stability of the CTM-TFTs were quantitatively discussed from a viewpoint of surface strain. The difference in critical radius of curvature and the influence of the local strain induced by the spatial fluctuations of the wavy structure were suggested to be critical issues, and hence, the neutral mechanical plane was introduced for further improvement. As a result, the stretchable CTM-TFTs exhibited stable operations until 150000 stretching cycles by the contributions of an ultrathin substrate and a neutral mechanical plane.