Mechanically Robust and Highly Flexible Nonvolatile Charge‐Trap Memory Transistors Using Conducting‐Polymer Electrodes and Oxide Semiconductors on Ultrathin Polyimide Film Substrates

Abstract

Flexible charge‐trap memory thin‐film transistors (CTM‐TFTs) are fabricated and characterized for next‐generation highly functional consumer electronics. Poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and 1.2‐µm‐thick polyimide (PI) films are introduced as source/drain electrodes and plastic substrates, respectively, to realize highly flexible CTM‐TFTs with conducting polymers. A uniquely structured sacrificial layer is suggested for the lithography‐compatible transfer and patterning processes of PEDOT:PSS on inorganic Al2O3 barrier layers are prepared on the PI substrates. The CTM‐TFTs show significantly improved device performance compared with those of the previous proto‐type devices, including a memory window (MW) of 16.8 V and program speed of 100 µs at a program pulse amplitude of ±20 V. Furthermore, the MWs and on/off current ratio do not shown remarkable degradation, and total variations within a range of less than 7.5% are observed even under harsh bending strains with a curvature radius of 1 mm. Additionally, the mechanical robustness of the fabricated CTM‐TFTs is quantitatively discussed based on the contributions of the conducting polymer electrode and the ultrathin PI film to further improve device performance of the flexible CTM‐TFTs.

Experimental and theoretical evidence for hydrogen doping in polymer solution-processed indium gallium oxide

“…Thus, the carrier concentration in IGZO can be manipulated and stabilized by adjusting the Ga concentration (15), with manufactured sputtered IGZO devices having a Ga content of more than 30 atomic percent (at. %) (In:Ga:Zn ∼ 1:1:1) for optimal thin-film transistor (TFT) switching (16,17). Nevertheless, while Ga incorporation is essential for stable IGZO TFT operation, it comes at the cost of lower In 2 O 3 matrix mobility (13).…”

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

“…These results clearly demonstrate that the V th shift obtained in the CTM-TFT originated from the charge-trap/detrap events rather than unstable charge injection caused by interface defect sites. 15,16,34 For further investigations on memory operations, the transfer curves were measured at various V GS sweep ranges of ±10, ± 15, and ±20 V, as shown in Figure 2c. The chargetrap-assisted MW could be clearly obtained even at ±10 V. The MW values monotonously increased with the amplitude of program voltages, reflecting the fact that the concentration of trapped electrons can be controlled during the program operations.…”

“…The chargetrap-assisted MW could be clearly obtained even at ±10 V. The MW values monotonously increased with the amplitude of program voltages, reflecting the fact that the concentration of trapped electrons can be controlled during the program operations. 15,16 In other words, considering that the MW linearly increased with increasing the program V GS , the on-and off-program operations could be effectively modulated by changing the amplitude of program voltages, as shown in Figure S3a. Figure 2d shows the variations in the on-and offprogrammed I DS 's for the CTM-TFT when the program pulse widths were varied from 1 μs to 1 s at fixed program voltages of −20 and +20 V, respectively.…”

“…A charge-trap memory thin-film transistor (CTM-TFT) employing oxide channel and charge-trap layer (CTL) can be a promising candidate for highly functional stretchable memory device. However, oxide-based memory devices have a critical limitation in mechanical stretching operations due to the intrinsic brittleness of oxides, whereas stronger robustness against mechanical stress is quite demanding for practical applications. − Therefore, the device structure should be more sophisticatedly designed to realize the mechanically stretchable nonvolatile memory.…”

Analysis of Mechanical and Electrical Origins of Degradations in Device Durability of Flexible InGaZnO Thin-Film Transistors

“…In this work, we fabricated InGaZnO (IGZO)-channel TFTs on flexible PEN substrates with various thicknesses of 25, 50, and 125 μm and characterized the mechanical and electrical performance under various mechanical deformation conditions. Although there have been some previous works mentioning the importance of substrate thickness, there have rarely been detailed analyses on the effects of substrate thickness on the mechanical durability of the IGZO TFTs fabricated on plastic flexible substrates. ,− Thus, we systematically investigated the relationships between the PEN substrate thickness and critical R for guaranteeing sound TFT operations by numerical calculation and measurement data from the bending tests under various mechanically strained conditions, which include static bending states, dynamic bending tests, and PBS tests in bending states. In addition, the physical origins for performance degradation of flexible IGZO TFTs with variations in the magnitude of applied strain should be clearly addressed.…”