Enhancing the Plasma-Resistance Properties of Li2O-Al2O3-SiO2 Glasses for the Semiconductor Etch Process via Alkaline Earth Oxide Incorporation.

To develop plasma-resistant glass materials suitable for semiconductor etching processes, we introduced alkaline earth oxides (ROs) into a Li2O-Al2O3-SiO2 (LAS) glass. Analysis of glass properties with respect to the additives revealed that among the analyzed materials, the LAS material in which Li2O was partially replaced by MgO (MLAS) exhibited the most favorable characteristics, including a low dielectric constant (6.3) and thermal expansion coefficient (2.302 × 10-6/°C). The high performance of MLAS is attributed to the high ionic field strength of Mg2+ ions, which restricts the movement of Li+ ions under the influence of electric fields and thermal vibrations at elevated temperatures. When exposed to CF4/O2/Ar plasma, the etching speed of RO-doped glasses decreased compared with that of quartz and LAS glass, primarily owing to the generation of a high-sublimation-point fluoride layer on the surface. Herein, MLAS demonstrated the slowest etching speed, indicating exceptional plasma resistance. X-ray photoelectron spectroscopy analysis conducted immediately after plasma etching revealed that the oxidation-to-fluorination ratio of Li was the lowest for MLAS. This observation suggests that the presence of Mg2+ ions in the plasma discharge inhibits the migration of Li+ ions toward the surface, thereby contributing to the excellent plasma resistance of MLAS.

Graphene-coated microballs for a hyper-sensitive vacuum sensor.

Reduced graphene oxide (RGO)-coated microballs of poly (methyl methacrylate) (PMMA) used for fabricating three-dimensional sensor (3D sensor), which are expected to exhibit high sensitivity compared with conventional two-dimensional (2D) sensors, were prepared using a reaction-based assembly process. The sheet resistance and transmittance of the RGO-coated balls decreased with increasing number of coatings, implying that the RGO was well adhered to the ball by the assembly method. Two types of vacuum pressure sensors using multiple balls and a single ball were fabricated using lift-off and air-blowing methods, respectively. At pressures <1 torr, the sensors showed an increased resistance value due to the bending of graphene sheets by the Van der Waals attractive force. Further, the pressure versus resistance values at the logarithmic scale showed a linear relation, with a pressure reading error <6%. Compared with the 2D sensor fabricated using RGO, the multiball sensor exhibited almost 4-5 times higher RRC value. The single-ball sensor showed reasonable reproducibility at various temperatures. Given the size and pressure reading range of the sensor, the sensitivity of the single-ball sensor at 100 °C was approximately 6,000 times greater than that of the sensor with the highest sensitivity reported in the literature. The increase in surface area and the geometric effect of the sensing part of the single-ball sensor appeared to be responsible for its abnormally high sensitivity.

Efficient Solid-State Photoluminescence of Graphene Quantum Dots Embedded in Boron Oxynitride for AC-Electroluminescent Device.

Emerging graphene quantum dots (GQDs) have received much attention for use as next-generation light-emitting diodes. However, in the solid-state, π-interaction-induced aggregation-caused photoluminescence (PL) quenching (ACQ) in GQDs makes it challenging to realize high-performance devices. Herein, GQDs incorporated with boron oxynitride (GQD@BNO) are prepared from a mixture of GQDs, boric acid, and urea in water via one-step microwave heating. Due to the effective dispersion in the BNO matrix, ACQ is significantly suppressed, resulting in high PL quantum yields (PL-QYs) of up to 36.4%, eightfold higher than that of pristine GQD in water. The PL-QY enhancement results from an increase in the spontaneous emission rate of GQDs due to the surrounding BNO matrix, which provides a high-refractive-index material and fluorescence energy transfer from the larger-gap BNO donor to the smaller-gap GQD acceptor. A high solid-state PL-QY makes the GQD@BNO an ideal active material for use in AC powder electroluminescent (ACPEL) devices, with the luminance of the first working GQD-based ACPEL device exceeding 283 cd m-2 . This successful demonstration shows promise for the use of GQDs in the field of low-cost, ecofriendly electroluminescent devices.

Self-assembled and intercalated film of reduced graphene oxide for a novel vacuum pressure sensor.

We report a new method for measuring vacuum pressures using Van der Waals (VDW) interactions between reduced graphene oxide (RGO) sheets. For this purpose, we utilized a reaction-based self-assembly process to fabricate various intercalated RGO (i-RGO) films, and monitored their electrical behavior with changing pressure and temperature. Pumping to remove gas from a vacuum chamber produced a decrease in the sheet resistance of i-RGO. With further pumping, distinctly different sheet resistance behaivors were observed depending on the measurement temperature. With increasing vacuum pressure, the resistance increased at 100 °C, whereas it decreased at 30 °C. Two types of VDW interactions are proposed to explain these features: a local VDW interaction between RGO sheets that resulted in V-shaped curves of sheet resistance with pressure changes and broad VDW interactions that occur between RGO sheets when the elastic force required to bend carbon clusters on an RGO sheet exceeds their vibrational energy at low temperatures. On the basis of the results, we propose that the resistance behavior of i-RGO as a function of vacuum pressure can be interpreted as the sum of the two different VDW interactions.

Preparation of GZO/Pt/GZO Multi-Layered Transparent Electrodes and Their Application to Touch Sensor Devices.

We have proposed, prepared, and characterized Pt-inserted Ga-doped ZnO (GZO) transparent electrodes of GZO/Pt/GZO (GPG) multilayers on glass and flexible plastic substrates. Pt-inserted GZO electrodes showed remarkably decreased resistivity, even though the thickness of the Pt layer was only a few nm. However, the optical transmittance of the GPG electrodes was degraded with increasing thickness of the Pt layer. The structural, optical, and electrical properties of GZO film and GPG multilayered transparent electrodes on glass substrates were largely affected by post- annealing conditions such as the ambient and temperature. Post-annealing in a N2 ambient was the most effective treatment for achieving high optical transmittance and low electrical resistivity of the GZO films and GPG structure. Good optical transmittance of 78% and electrical resistivity of 3.5 x 10(-3) Ω·cm of the GZO electrode were obtained for the 4-nm-thick Pt insertion layer and post-annealing at 400 °C. In addition, touch sensor devices were fabricated by using GPG structures and flexible plastic substrates. The touch sensor devices exhibited a capacitance ratio of 1.4 between the two states before and after fingertip touching.

Preparation and Characterization of SnO2-Nanoparticle-Included Ink Solution and Its Application to the Patterned Pt Films on SiO2/Si Substrates.

Pure SnO2 nanoparticles with a single tetragonal phase were fabricated and characterized for use as ink solution. It was possible to obtain the SnO2 nanoparticles through the calcination process of SnC204 powders prepared by a hydrothermal reaction of an aqueous solution containing SnCl2 x 2H2O and H2C2O4. The SnO2 powder, synthesized at 600 degrees C, showed a single tetragonal phase, while the powders synthesized at 550 degrees C or lower were composed of a mixture of tetragonal and orthorhombic phases. The particle size of the SnO2 powder with single tetragonal phase was as small as 100 nm and its surface specific area was 12.31 m2/g. It was possible to fabricate the SnO2-nanoparticle-included ink solution for nanoparticle printing by adding a small amount of the previously prepared SnO2 powder to an aqueous solution of glycerol. The region of SnO2 nanoparticles formed by dropping the ink solution was able to successfully fill the gaps between Pt electrodes patterned on SiO2/Si substrates; the range of the gap between the electrodes was from 10 to 100 µm.

Effects of a PbTiO3 insertion layer on the morphological and electromechanical characteristics of sol-gel-driven 0.2PZN-0.8PZT piezoelectric films for energy harvesters.

This study investigated the morphological and electromechanical characteristics of 0.2PZN-0.8PZT films fabricated using a PbTiO3 layer. Crack-free 1-microm-thick films with a pure perovskite phase were obtained on Pt/Ti/SiO2/Si substrates using a modified sol-gel deposition method. A highly dense and smooth morphology and a high piezoelectric coefficient (d33) of 230 pC/N were observed in a 0.2PZN-0.8PZT film with a PbTiO3 insertion layer after annealing at 750 degrees C. The as-produced sol-gel-driven 0.2PZN-0.8PZT thin films are attractive for application to piezoelectrically operated microelectronic actuators, sensors, or energy harvesters due to their low facility cost, smooth surface, and excellent electromechanical characteristics.