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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.