We improved biometric authentication security using dual recognition based on fingerprint image detection and skin-temperature-change sensing under quantum dot light-emitting diode (QLED) displays. ...QLEDs are more advantageous than organic light-emitting diodes (OLEDs) in terms of the contrast classification of patterns such as those in fingerprint recognition, owing to their narrow full-width-half-maximum. In this work, scattered, transmitted, and reflected light was captured from the top of the QLED, improving the digital luminance by 25%, as compared with that of OLEDs, because the electroluminescence spectra of the QLED were sustained, whereas those of the OLED were distorted by the generated noise peaks. A QLED with eight apertures sized up to tens of micrometers, mimicking the actual wiring structure of commercialized smartphones, was implemented to detect human fingerprints. The QLED using reduced graphene oxide as the temperature sensor detected temperature changes instantaneously upon finger touch, showing a 2% temperature response based on the human body temperature; however, the temperature change was less than 0.1% for spoof fingerprints printed on paper. Thus, this study successfully enhanced biometric authentication security, through fingerprint recognition based on image sensing using an optical system with micrometer-sized apertures and skin-temperature detection under QLED displays.
Bright, low‐voltage driven colloidal quantum dot (QD)‐based white light‐emitting devices (LEDs) with practicable device performances are enabled by the direct exciton formation within quantum‐dot ...active layers in a hybrid device structure. Detailed device characterization reveals that white‐QLEDs can be rationalized as a parallel circuit, in which different QDs are connected through the same set of electrically common organic and inorganic charge transport layers.
Microdisplays have been used in various applications such as beam projectors, view finders of digital cameras, projection TVs, night vision for military use, and augmented reality/virtual reality ...(AR/VR) devices. Organic light-emitting diode (OLED) microdisplays have attracted much attention as main displays of glass-type and head-mounted-type AR/VR devices due to their rich colors, high contrast ratio, fast response time, small form factor, and high resolution. This review investigates the device, process, pixel circuit, and panel technologies for OLED microdisplays. In addition, the technology status and issues of OLED microdisplays are discussed.
Thin-film transistor (TFT)-driven full-color organic light-emitting diodes (OLEDs) with vertically stacked structures are developed herein using photolithography processes, which allow for ...high-resolution displays of over 2,000 pixels per inch. Vertical stacking of OLEDs by the photolithography process is technically challenging, as OLEDs are vulnerable to moisture, oxygen, solutions for photolithography processes, and temperatures over 100 °C. In this study, we develop a low-temperature processed Al
O
/SiN
bilayered protection layer, which stably protects the OLEDs from photolithography process solutions, as well as from moisture and oxygen. As a result, transparent intermediate electrodes are patterned on top of the OLED elements without degrading the OLED, thereby enabling to fabricate the vertically stacked OLED. The aperture ratio of the full-color-driven OLED pixel is approximately twice as large as conventional sub-pixel structures, due to geometric advantage, despite the TFT integration. To the best of our knowledge, we first demonstrate the TFT-driven vertically stacked full-color OLED.
The recently reported laser pyrolytic jetting process enables facile generation of highly porous, free-standing graphene fiber from polyimide film upon the scanning of tightly focused continuous-wave ...laser. As a follow-up study, we claim that the corresponding laser pyrolytic jetting process is favorable for the fabrication of relevant energy device applications compared to the conventional LIG process in both energy-saving and material-saving perspectives. Moreover, the volume of the pyrolysis product is substantially increased in the case of pyrolytic jetting compared to conventional LIG, resulting in an extended surface area for storing more electric charges. At the same time, material characterization by Raman measurement validates that the exfoliated product from pyrolytic jetting is analogous to the conventional LIG and therefore suitable for supercapacitor application. As a result, supercapacitor created by the pyrolytic jetting allows substantial enhancement in the capacitance compared to the conventional LIG for both with and without manganese oxide layer coating, proposing the potential of pyrolytic jetting for the efficient fabrication of carbon-based energy devices.
Fermented red ginseng (FRG) has been used as a general stimulant and herbal medicine for health promotion in Asia for thousands of years. Few studies have investigated the effects of FRG containing ...prebiotics on the gut microbiota. Here, 29 Korean women aged ≥ 50 years were administered FRG for three weeks to determine its effect on stool characteristics, biochemical parameters, and gut microbiome. Gut microbial DNA was subjected to 16S rRNA V3-V4 region sequencing to assess microbial distribution in different stages. Additionally, the stool consistency, frequency of bowel movements, and biochemical parameters of blood were evaluated. We found that FRG intake improved stool consistency and increased the frequency of bowel movements compared to before intake. Biochemical parameters such as glucose, triglyceride, cholesterol, low-density lipoprotein cholesterol, creatinine, alkaline phosphatase, and lactate dehydrogenase decreased and high-density lipoprotein cholesterol increased with FRG intake. Gut microbiome analysis revealed 20 specific bacteria after three weeks of FRG intake. Additionally, 16 pathways correlated with the 20 specific bacteria were enhanced after red ginseng intake. In conclusion, FRG promoted health in elderly women by lowering blood glucose levels and improving bowel movement frequency. The increase in bacteria observed with FRG ingestion supports these findings.
Poly(dimethylsiloxane) has attracted much attention in soft lithography and has also been preferred as a platform for a photochemical reaction, thanks to its outstanding characteristics including ...ease of use, nontoxicity, and high optical transmittance. However, the low stiffness of PDMS, an obvious advantage for soft lithography, is often treated as an obstacle in conducting precise handling or maintaining its structural integrity. For these reasons, a Glass-PDMS-Glass structure has emerged as a straightforward alternative. Nevertheless, several challenges are remaining in fabricating Glass-PDMS-Glass structure through the conventional PDMS patterning techniques such as photolithography and etching processes for master mold. The complicated techniques are not suitable for frequent design modifications in research-oriented fields, and fabrication of perforated PDMS is hard to achieve using mold replication. Herein, we utilize the successive laser pyrolysis technique to pattern thin-film PDMS for microfluidic applications. The direct use of thin film at the glass surface prevents the difficulties of thin-film handling. Through the precise control of photothermal pyrolysis phenomena, we provide a facile fabrication process for perforated PDMS microchannels. In the final demonstration, the laminar flow has been successfully created owing to the smooth surface profile. We envision further applications using rapid prototyping of the perforated PDMS microchannel.
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•A semi-transparent rGO temperature sensor was fabricated for liveness detection and anti-spoofing of mobile phone authentication.•The rGO temperature sensor showed a linear ...resistance change with respect to the initial resistance value at low to high temperature range.•The resistance of the rGO showed a sensitive temperature change even when the finger was touched on the buffer layer of the polyimide film.•The OLEDs irradiated by the laser source showed nearly the same current–voltage characteristics and electroluminescence spectrum.
We report a semi-transparent temperature sensor for fingerprint liveness detection on an organic light-emitting diode (OLED). Solution-processable graphene oxide was coated between two indium tin oxide electrodes on a glass substrate, and a semi-transparent reduced graphene oxide (rGO) temperature sensor was successively fabricated through graphene oxide (GO) reduction using a laser source. The rGO temperature sensor showed a resistance variance characteristic of 80 % compared to the initial resistance when heated from 15 °C to 170 °C. When finger was touched on the rGO temperature sensor, the resistance variation was 0.5 % and 7 % at 35 °C and 50 °C, respectively. In addition, GO was coated on the light-emitting side of green phosphorescent OLEDs to investigate the damage caused by photothermal reduction energy. The OLEDs irradiated by the laser source for GO reduction showed nearly the same current–voltage characteristics and electroluminescence spectrum as the device without laser irradiation, although the luminance of the device decreased due to the absorption of rGO.
The performance of colloidal quantum dot light-emitting diodes (QD-LEDs) have been rapidly improved since metal oxide semiconductors were adopted for an electron transport layer (ETL). Among metal ...oxide semiconductors, zinc oxide (ZnO) has been the most generally employed for the ETL because of its excellent electron transport and injection properties. However, the ZnO ETL often yields charge imbalance in QD-LEDs, which results in undesirable device performance. Here, to address this issue, we introduce double metal oxide ETLs comprising ZnO and tin dioxide (SnO
) bilayer stacks. The employment of SnO
for the second ETL significantly improves charge balance in the QD-LEDs by preventing spontaneous electron injection from the ZnO ETL and, as a result, we demonstrate 1.6 times higher luminescence efficiency in the QD-LEDs. This result suggests that the proposed double metal oxide ETLs can be a versatile platform for QD-based optoelectronic devices.
Organic light-emitting diode (OLED) microdisplays have received great attention owing to their excellent performance for augmented reality/virtual reality devices applications. However, high pixel ...density of OLED microdisplay causes electrical crosstalk, resulting in color distortion. This study investigated the current crosstalk ratio and changes in the color gamut caused by electrical crosstalk between sub-pixels in high-resolution full-color OLED microdisplays. A pixel structure of 3147 pixels per inch (PPI) with four sub-pixels and a single-stack white OLED with red, green, and blue color filters were used for the electrical crosstalk simulation. The results showed that the sheet resistance of the top and bottom electrodes of OLEDs rarely affected the electrical crosstalk. However, the current crosstalk ratio increased dramatically and the color gamut decreased as the sheet resistance of the common organic layer decreased. Furthermore, the color gamut of the OLED microdisplay decreased as the pixel density of the panel increased from 200 to 5000 PPI. Additionally, we fabricated a sub-pixel circuit to measure the electrical crosstalk current using a 3147 PPI scale multi-finger-type pixel structure and compared it with the simulation result.
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