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

Abstract

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 (106) with program pulses as short as 1 μs. 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 μm. 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.

Recent Advances in Metal-Oxide Thin-Film Transistors: Flexible/Stretchable Devices, Integrated Circuits, Biosensors, and Neuromorphic Applications

“…Based on the observed result, it is indicated that the organic passivation film enables the reduction of the mechanical stress applied to the inorganic material layer under both bending and stretching conditions. Kim et al fabricated a charge trapping memory thin-film transistor (CTM TFT) with a wavy-dimensional structure using IGZO and zinc oxide (ZnO) (Figure 3h-j) [64]. IGZO was used as the channel layer, and ZnO was used as the channel trap layer.…”

“…Figure 3. (a) Photograph of the IGZO TFT device at strain condition; (b) The evolution of wrinkles at different stretching values is shown (0%); (c) The evolution of the wrinkles at different stretching values is shown (5.1%); (d) Transfer curve during the PBS tests with a lapse of stress time in prestrain of 50% (adapted from[60] with permission from American Chemical Society); (e) Crack formation near its channel region in strain values above 5% (scale bar: 50 µm) (adapted from[62] with permission from American Chemical Society); (f) Stretching simulation without and with an organic passivation layer; (g) Horizontal equivalent (Von Mises) stress distributions in the stretched state (adapted from[63] with permission from American Chemical Society); (h) Photograph of device surface under a mechanically stretching situation; (i) Transfer characteristics of the stretchable TFTs when pre-strain values were varied up to 60%; (j) Variations in MW and SS as a function of pre-strain value (adapted from[64] with permission from American Chemical Society).…”

Fatigue Effect of Stretchable a-InGaZnO TFT on PI/PDMS Substrate under Repetitive Uni/Biaxial Elongation Stress

“…From a structural point of view, prestrain stretchable TFTs were reported to produce a wavy structure. , These TFTs are fabricated by transferring polyimide (PI) with TFTs after prior stretching of the elastic substrate. However, it is difficult to form a uniform wavy structure, and nonuniformly strained TFTs can operate differently depending on the location.…”

Mechanical Durability of Flexible/Stretchable a-IGZO TFTs on PI Island for Wearable Electronic Application

“…However, there is a way to realize stretchable electronics by studying new substrate structures. Representative structural approaches include using a wavy dimensional substrate − and partially forming flexible plastic islands on a stretchable substrate with elastic interconnects. − Some studies have used both wavy elastomeric substrates and partially formed rigid island region to improve elongation. − …”

“…To form a wavy structure on substrate, the flexible/stretchable device is generally fabricated on a prestrained stretchable substrate. ,, The prestrained substrate naturally has a wavy shape after removing the external elongation force following upper circuit fabrication when the transfer process is completed. The circuit is usually fabricated on the PI film and transferred together with PI.…”