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This paper introduces novel driving methods of the pull-down unit in a gate driver circuit for enhancement- and depletion-mode a-IGZO thin-film transistors (TFTs). The proposed gate driver circuit can achieve uniform output characteristics and effectively reduce the $\text{V}_{\mathrm{ OUT}}$ ripple voltage because the threshold voltage ( $\text{V}_{\mathrm{ TH}}$ ) of the pull-down units is compensated regardless of the a-IGZO TFT operation characteristics (enhancement mode: positive value of $\text{V}_{\mathrm{ TH}}$ , depletion mode: negative value of $\text{V}_{\mathrm{ TH}}$ ). Many groups proposed the $\text{V}_{\mathrm{ TH}}$ compensation method for pull-down TFTs in the gate driver circuit using a diode connection structure. However, the diode connection structure to extract the $\text{V}_{\mathrm{ TH}}$ value cannot be applied in the depletion-mode oxide TFTs because TFT enters the turn-on state even when the $\text{V}_{\mathrm{ GS}}$ value is 0 V. To solve this problem, we adopted the $\text{V}_{\mathrm{ TH}}$ extraction period only once in one frame time. As a result, our circuit can compensate for $\text{V}_{\mathrm{ TH}}$ of the pull-down unit in the enhancement mode and can be normally operated in the depletion mode. Adjunctively, two low signals (VGL1 and VGL2) and QC node were designed to prevent the leakage current path for Q and $\text{V}_{\mathrm{ OUT}}$ nodes. To verify the threshold voltage tolerance for various stress conditions, we demonstrated the reliability of the circuit according to the threshold voltage change of the TFTs. The simulation result shows that all the $\text{V}_{\mathrm{ OUT}}$ waveforms are maintained at +28 V (VGH) under the $\text{V}_{\mathrm{ TH}}$ shift conditions from −7 V to +11 V; further, the rising time and falling time are less than $0.62~{\mu }\text{s}$ and $0.96~{\mu }\text{s}$ , respectively. Based on a 120-Hz ultra-high definition (UHD) graphics ( $3840{\times }2160$ ) display panel, the proposed circuit has uniform $\text{V}_{\mathrm{ OUT}}$ characteristics compared to previous $\text{V}_{\mathrm{ TH}}$ compensation circuit when $\Delta \text{V}_{\mathrm{ TH}}$ changes from −3 V to +11 V. When $\Delta \text{V}_{\mathrm{ TH}}$ changes from −4 V to −7 V, there is also no circuit malfunction, even with slight increase in the falling time and power consumption.

We demonstrate a novel structure for a quantum-dot light-emitting diode (QD-LED) with wide-range colour-tuneable pixels, fabricated via full solution processing. The proposed device has a symmetrical structure produced via stacking of an inverted-structure diode with a green QD emission layer (EML) and normal-structure diode with a red QD EML. It is an electron-only device; however, a charge generation layer in the middle of the device generates holes for the formation of excitons. Depending on the polarity of the applied voltage, either the bottom inverted unit or the top normal unit is operated, thereby emitting green or red light, respectively. The working mechanism of the device is investigated via analysis of the charge generation mechanism and carrier transport path. In addition, the colour tunability is verified using a simple alternating current (AC) driving scheme; the duty cycle modulation of the AC signal enables fine colour adjustment over a broad range, from pure green to pure red. Thus, our colour-tuneable QD-LED with vertically stacked independently operated sub-pixels can open a promising pathway towards cost-effective ultra-high-resolution displays.

Graphene-based transistors are promising devices in the evaluation of carrier density in biological analytes. We report on the design and fabrication of a graphene-based field-effect transistor for monitoring and assessing the interaction between the coagulation factors based on the charge carrier density in a blood sample. When biochemical reactions occurred during the coagulation cascade process, a dopant effect was noticed on the graphene surface by the change in Dirac point voltage values. Additional experiments were performed using blood samples treated with activators (vitamin K, calcium chloride, and thromboplastin reagent) and inhibitors (heparin drugs) to evaluate the selectivity of the graphene field-effect transistor devices. Since the transfer characteristic curves presented divergent behaviours for different levels of procoagulants and anticoagulants, the measurements showed that the devices can assess changes in the concentrations of factors that inhibit or accelerate the cascade process when using untreated and treated samples. Reproducibility was verified by testing samples from different sources. To the best of our knowledge, this study is the first to demonstrate the potential of graphene in monitoring the hemostasis process through the analysis of the electrical properties of human whole blood.

This study investigated the effects of fluorine (F) diffusion from a CYTOP passivation layer into amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). The F contained in the CYTOP passivation layer was diffused into a-IGZO through 350℃ annealing. The similar ionic radii of F and oxygen (O) allowed the passivation of oxygen vacancy (Vo) and weakly bonded oxygen by F. As a result, the a-IGZO TFTs with CYTOP passivation were highly stable under various stresses. The threshold voltage (Vth) shifts of a-IGZO TFTs without CYTOP passivation and with CYTOP passivation under a negative bias stress (NBS) test for 10,000s were -6.7 V and -2.5 V, respectively. In addition, the Vth shifts of each device under a negative bias illumination stress (NBIS) test for 4,000s were -10.9 V and -5.3 V, respectively. This improvement was caused by a reduction of Vo and a widened band gap of a-IGZO through the F diffusion effect. In addition, the CYTOP passivation layer maintained excellent properties as a barrier against moisture after 350℃ annealing.

Graphene grown on copper foils by chemical vapor deposition can be directly deposited or transferred to the desired substrates. When a CVD-grown graphene sheet is transferred, its surface may be affected by the handling process and environmental conditions. Defects and contamination on the graphene surface induce unstable electrical characteristics, like in the neutrality point, also known as Dirac point. For this reason, it is hard to quantitatively analyze the results due to an inconstant Dirac point. To overcome this fabrication problem, this study proposes a method to reduce the defects and preserve the initial characteristics of the material, minimizing the damage during the graphene transfer. A high-quality graphene sheet was transferred onto several pairs of electrodes to maintain the original electrical properties. In the device structure proposed herein, the error range of the Dirac point was less than ± 1 mV. We confirmed the transfer characteristics of our device by detecting the hybridization of complementary DNAs to probe DNAs immobilized on the graphene active layer. Also, this new structure can be used to analyze biological samples using different bioreceptors in each channel. Maintaining the detection region may guarantee the stability of graphene properties as an active layer.

We fabricated ultrathin flexible thin film transistors with hydrophobic encapsulation layer by debonding process. In the debonding process, to separate the transistors from the carrier glass in deionized (DI) water, a strong hydrophobic material such as CYTOP was used for encapsulation, thus increasing their resistance to moisture. PVA was used as a release layer and the debonding process was optimized to separate the carrier glass and the transistors. It was confirmed that water penetration into the device can be suppressed effectively when the CYTOP thickness is 800 nm. In addition, the electrical characteristics remained almost constant even in the presence of water for 50 min. The total thickness after debonding process was approximately 2 μm. Waterproof experiments and debonding process were performed for a simple inverter circuit as well as a discrete device, and the operation and voltage gain of the inverter did not change when water was placed on the device or after debonding process. Finally, the flexibility was measured by transferring the device to a flexible PI substrate. Consequently, it was confirmed that degradation in the electrical properties was slightly up to a bending radius of 2.5 mm.

We propose a new gate driver circuit, in which the Q node can be operated as a pull-up either as a hold-down controller. The number of transistors for the QB nodes is reduced because the one QB node can be replaced by the pull-up unit of the Q node. With an additional VOUT pull-down unit designed using only two transistors and one capacitance, we can control the discharge interval of the VOUT node to 100% duty ratio. Despite the simplified circuit configuration, the VOUT characteristic is almost the same as that of a conventional circuit with an AC-driven structure using one Q node, and two or more QB nodes. Our simulation results show that the VH voltage operates at +28 V from the 1071st to 1080th VOUT and the rising/falling time is less than 1 μs. To verify the reliability of this circuit, we further confirmed the VOUT according to the change in the threshold voltage (VTH). The proposed circuit can be operated even when the VTH is shifted to +20.5 V from the initial value (VTH = +1.09 V). Further, the VOUT characteristic is not degraded although the VTH was shifted by +18.5 V for the pull-up unit (TFT's ΔVTH except for pull-up unit: +2 V), and the rising/falling time were confirmed to be less than 3.2 μs.