Highly Reliable Flexible Device With Charge Compensation Layer

Flexible devices fabricated with polyimide (PI) substrate are crucial for foldable, rollable, or stretchable products in various applications. However, inherent technical challenges remain in mobile charge induced device instabilities and image retention, significantly hindering future technologies. We introduced a new barrier material, SiCOH, into the backplane of amorphous indium-gallium-zinc-oxide (a–IGZO) thin-film transistors (TFTs) that were then implemented into production-level flexible panels. We found that the SiCOH layer effectively compensates the surface charging induced by fluorine ions at the interface between the PI substrate and the barrier layer under bias stress, thereby preventing abnormal positive Vth shifts and image disturbance. The a–IGZO TFTs, metal-insulator-metal (MIM), and metal-insulator-semiconductor (MIS) capacitors with the SiCOH layer demonstrate reliable device performance, Vth shifts, and capacitance changes with an increase in the gate bias stress. A flexible device with SiCOH enables the suppression of abnormal Vth shifts associated with PI and plays a vital role in the degree of image sticking phenomenon. This work provides new inspirations to creating much improved process integrity and paves the way for expediting versatile form-factors.

The Influence of Climate Conditions and On-Skin Positioning on InGaZnO Thin-Film Transistor Performance

Thin-film transistors (TFTs) based on amorphous indium-gallium-zinc-oxide (a-IGZO) have proved promising features for flexible and lightweight electronics. To achieve technological maturity for commercial and industrial applications, their stability under extreme environmental conditions is highly required. The combined effects of temperature (T) from −30.0°C to 50.0°C and relative humidity (RH) stress from 0 to 95% on a-IGZO TFT is presented. The TFT performances and the parameters variation were analysed in two different experiments. First, the TFT response was extracted while undergoing the most extreme climate conditions on Earth, ranging from the African Desert (50.0°C, 22%) to Antarctic (−30.0°C, 0%). Afterwards, the device functionality was demonstrated in three parts of the human body (forehand, arm and foot) at low (35%), medium (60%) and high (95%) relative humidity for on-skin and wearable applications. The sensitivity to T/RH variations suggests the suitability of these TFTs as sensing element for epidermal electronics and artificial skin.

Memory Characteristics of Thin Film Transistor with Catalytic Metal Layer Induced Crystallized Indium-Gallium-Zinc-Oxide (IGZO) Channel

The memory characteristics of a flash memory device using c-axis aligned crystal indium gallium zinc oxide (CAAC-IGZO) thin film as a channel material were demonstrated. The CAAC-IGZO thin films can replace the current poly-silicon channel, which has reduced mobility because of grain-induced degradation. The CAAC-IGZO thin films were achieved using a tantalum catalyst layer with annealing. A thin film transistor (TFT) with SiO2/Si3N4/Al2O3 and CAAC-IGZO thin films, where Al2O3 was used for the tunneling layer, was evaluated for a flash memory application and compared with a device using an amorphous IGZO (a-IGZO) channel. A source and drain using indium-tin oxide and aluminum were also evaluated for TFT flash memory devices with crystallized and amorphous channel materials. Compared with the a-IGZO device, higher on-current (Ion), improved field effect carrier mobility (μFE), a lower body trap (Nss), a wider memory window (ΔVth), and better retention and endurance characteristics were attained using the CAAC-IGZO device.

Back-Channel Etched In-Ga-Zn-O Thin-Film Transistor Utilizing Selective Wet-Etching of Copper Source and Drain

The electrical performance of the back-channel etched Indium–Gallium–Zinc–Oxide (IGZO) thin-film transistors (TFTs) with copper (Cu) source and drain (S/D) which are patterned by a selective etchant was investigated. The Cu S/D were fabricated on a molybdenum (Mo) layer to prevent the Cu diffusion to the active layer (IGZO). We deposited the Cu layer using thermal evaporation and performed the selective wet etching of Cu using a non-acidic special etchant without damaging the IGZO active layer. We fabricated the IGZO TFTs and compared the performance in terms of linear and saturation region mobility, threshold voltage and ON current (ION). The IGZO TFTs with Mo/Cu S/D exhibit good electrical properties, as the linear region mobility is 12.3 cm2/V-s, saturation region mobility is 11 cm2/V-s, threshold voltage is 1.2 V and ION is 3.16 × 10−6 A. We patterned all the layers by a photolithography process. Finally, we introduced a SiO2-ESL layer to protect the device from external influence. The results show that the prevention of Cu and the introduced ESL layer enhances the electrical properties of IGZO TFTs.

Sol-Gel Composites-Based Flexible and Transparent Amorphous Indium Gallium Zinc Oxide Thin-Film Synaptic Transistors for Wearable Intelligent Electronics

In this study, we propose the fabrication of sol-gel composite-based flexible and transparent synaptic transistors on polyimide (PI) substrates. Because a low thermal budget process is essential for the implementation of high-performance synaptic transistors on flexible PI substrates, microwave annealing (MWA) as a heat treatment process suitable for thermally vulnerable substrates was employed and compared to conventional thermal annealing (CTA). In addition, a solution-processed wide-bandgap amorphous In-Ga-Zn (2:1:1) oxide (a-IGZO) channel, an organic polymer chitosan electrolyte-based electric double layer (EDL), and a high-k Ta2O5 thin-film dielectric layer were applied to achieve high flexibility and transparency. The essential synaptic plasticity of the flexible and transparent synaptic transistors fabricated with the MWA process was demonstrated by single spike, paired-pulse facilitation, multi-spike facilitation excitatory post-synaptic current (EPSC), and three-cycle evaluation of potentiation and depression behaviors. Furthermore, we verified the mechanical robustness of the fabricated device through repeated bending tests and demonstrated that the electrical properties were stably maintained. As a result, the proposed sol-gel composite-based synaptic transistors are expected to serve as transparent and flexible intelligent electronic devices capable of stable neural operation.

Effects of polyimide curing on image sticking behaviors of flexible displays

Flexible displays on a polyimide (PI) substrate are widely regarded as a promising next-generation display technology due to their versatility in various applications. Among other bendable materials used as display panel substrates, PI is especially suitable for flexible displays for its high glass transition temperature and low coefficient of thermal expansion. PI cured under various temperatures (260 °C, 360 °C, and 460 °C) was implemented in metal–insulator–metal (MIM) capacitors, amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFT), and actual display panels to analyze device stability and panel product characteristics. Through electrical analysis of the MIM capacitor, it was confirmed that the charging effect in the PI substrates intensified as the PI curing temperature increased. The threshold voltage shift (ΔVth) of the samples was found to increase with rising curing temperature under negative bias temperature stress (NBTS) due to the charging effect. Our analyses also show that increasing ΔVth exacerbates the image sticking phenomenon observed in display panels. These findings ultimately present a direct correlation between the curing temperature of polyimide substrates and the panel image sticking phenomenon, which could provide an insight into the improvement of future PI-substrate-based displays.