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

Abstract

We examine the fatigue effects of repeated elongation stress for a fabricated a-IGZO thin-film transistor (TFT) on an island polyimide (PI)/poly(dimethylsiloxane) (PDMS) substrate. The repeated elongation stress evaluation was performed in both a uniaxial direction with 10, 30, and 50% strain and biaxial direction with 10, 20, and 30% strain for 50 000 cycles. The a-IGZO TFTs on the island PI exhibit the following parameters: Vth : −0.91 ± 0.30 V, μ sat : 26.3 ± 0.61 cm2/(V s), and SS: 0.40 ± 0.02 V/decade. As a result of the repeated elongation stress in the maximum evaluated elongation (uniaxis: 50% and biaxis: 30%), the subthreshold swing (SS) increased by about 0.20 V/decade in all directions, and the saturation mobility decreased only in the x-axis direction (Δμ sat : 26.30 → 21.43 cm2/(V s)). Through XPS analysis and TCAD simulation, it was confirmed that SS deteriorated due to an increase of the oxygen-vacancy-related defects (NGA and NGD ) in the IGZO channel layer after repeated elongation stress. The transmission line method (TLM) confirmed that contact resistance increased when stretched only in the x-axis direction. In addition, the positive bias stress (PBS) test showed abnormal behavior including an additional SS-degradation-induced Vth negative shift after repeated elongation stress in all directions. Consequently, the degradation mechanism of both the electrical properties and bias stability for the stretchable a-IGZO TFT was determined after elongation stresses.

Biaxially Stretchable Active‐Matrix Micro‐LED Display with Liquid Metal Interconnects

“…In general, accumulated tensile stress induces a negative V th shift in TFT, [12,59] however, the micro-LED on the backplane might have been damaged by the biaxial stretching cycles, resulting in the failure of I DD . It was confirmed that there was negligible degradation in the on-state I DD under variations in VDD and V Data , as shown in Figure S12 (Supporting Information).…”

“…In general, the accumulated tensile stress induces a negative V th shift in TFT due to oxygen vacancy generation, resulting in a current increase. [12,59] However, micro-LED on pixel circuit degrades with increasing stretching cycles. Thus, the deterioration could be attributed to the LED/island interfacial bonding reliability.…”

“…To achieve stable electrical performance under stretching, oxide thin‐film transistors (TFTs) on rigid islands/stretchable substrates have been studied. [ 10–13 ] Especially, amorphous indium‐gallium‐zinc oxide (a‐IGZO) TFTs on the plastic substrate are widely used for flexible and stretchable electronics because of large area scalability, high field‐effect mobility (>10 cm 2 V −1 s −1 ) and low off‐state current. [ 14–16 ] Highly stretchable organic TFTs have been extensively studied, however, there still have issues such as high driving voltage, bias stability, and low on‐state current.…”

Strain-Sensor-In-Pixel Technology for Resolution-Sustainable Stretchable Displays

“…As illustrated in Figure , the empty space between the normal pixels is occupied by the activated hidden pixels, thus preventing the loss of resolution and luminance during stretching . Such an idea was conceptually demonstrated in a simple passive-matrix (PM) LED pixel array, where the activation of hidden pixels was controlled by integrating additional strain sensors outside the array. ,, These sensors, which are typically designed with a positive gauge factor (P-GF) that increases resistance upon stretching, inevitably require complex signal processing to facilitate current flow and trigger the activation of the hidden pixels by the elongation of the substrates. − For further advancement, key technologies compatible with pixel circuits arranged with numerous TFTs are essentially required to enable the application of this design concept to commercially available active-matrix (AM) displays …”

“…However, stretchable displays must satisfy stricter requirements than those imposed on existing flexible or foldable displays to maintain their electrical and optical properties under mechanical stretching. , While commercial products with flexible or foldable displays have recently emerged, the absence of commercial products with stretchable displays indicates an even more challenging technological hurdle. This difficulty arises from variations in the net display area, not during folding conditions but during stretching conditions . Therefore, most components of stretchable displays including light-emitting diodes (LEDs), thin-film transistors (TFTs), dielectrics, interconnects, encapsulations, and substrates should all be designed to withstand mechanical strain.…”