Search Results (12)

Metal oxide semiconductor (MOS)-based chemiresistive gas sensors, attributable to their low cost, compact structure, and long operational lifetime, have been widely employed for the detection and monitoring of trace ozone (O₃) in environmental air. Moreover, as ozone is a highly reactive oxidizing species extensively used in medical device sterilization, hospital disinfection, and food processing and preservation, accurate monitoring of ozone concentration is also essential in medical sanitation and food safety inspection. However, their practical applications are often limited by insufficient sensitivity and the requirement for elevated operating temperatures. In this study, Au-modified indium oxide (Au-In₂O₃) nanocomposite sensing materials were synthesized via a hydrothermal route followed by surface modification. Structural and morphological characterizations confirmed the uniform dispersion of Au nanoparticles on the In₂O₃ surface, which is expected to enhance the interaction between the sensor and target gas molecules. The resulting Au-In₂O₃ sensor exhibited excellent O₃ sensing performance under room-temperature conditions. Compared with pristine In₂O₃, the Au-In₂O₃ sensor with 1.0 wt% Au modification demonstrated a remarkably enhanced response of 1398.4 toward 1 ppm O₃ at room temperature. Moreover, the corresponding response/recovery times were shortened to 102/358 s for Au-In₂O₃. The outstanding O₃ sensing performance can be attributed to the synergistic effects of Au nanoparticles, including the spillover effect and the formation of a Schottky junction at the Au-In₂O₃ interface. These results suggest that Au-modified In₂O₃ cauliflower represents a highly promising candidate material for high performance O₃ sensing at low operating temperatures. Full article

Designing metal–semiconductor-based core–shell nanostructures with strong interactions is emerging as a unique component for chemiresistor applications. Here, we have developed an effective hydrogen (H₂) gas sensor based on Au-In₂O₃ core–shell nanostructures, which were synthesized through a short-time microwave hydrothermal process. At an optimal temperature of 375 °C, the device based on Au-In₂O₃ displays a high sensitivity of ~42, which is five times greater than that of the In₂O₃ toward 100 ppm of H₂ gas. Moreover, the Au-In₂O₃ sensor showed higher selectivity toward H₂ gas and stability over a long period. The excellent H₂ gas-sensing performance of Au-In₂O₃ core–shell nanoparticles can be credited to the sensitization and Au catalytic effect core, and their strong interaction with the In₂O₃ component. Our work not only accounts for a facile synthesis approach for Au-In₂O₃ core–shell nanoparticles by synergistic properties of Schottky heterojunctions, but also offers a new insight into how strong metal–semiconductor interactions (SMSIs) play a dynamic role in developing high-performance gas-sensing devices. Full article

Indium oxide-based gas sensors have been proven to be a promising material for detecting nitrogen dioxide (NO₂) gas because of its wide bandgap and stability. In this paper, the enhancement mechanism for the sensitivity of indium oxide NO₂ gas sensors was systematically investigated using density functional theory (DFT) calculations and experimental validation with noble metals like Au, Ag, Pt, Pd, and Cu. We have fabricated a GaN nanowire-based NO₂ gas sensor functionalized with In₂O₃ and decorated with noble metals using a standard fabrication technique. Experimental tests showed that Au/In₂O₃ sensors exhibited the highest response of 38.9% followed by bare In₂O₃ with 10% for 10 ppm NO₂ at room temperature. The sensing properties were mainly attributed to a spillover effect or catalytic performance of Au with In₂O₃. The adsorption energies, charge transfers, and band gap confirm the enhanced sensing capability of Au-decorated Indium oxide for a NO₂ gas sensor. Full article

This paper introduces a cost-effective, high-performance approach to achieving wafer level vacuum packaging (WLVP) for MEMS-based uncooled infrared sensors. Reliable and hermetic packages for MEMS devices are achieved using a cap wafer that is formed using two silicon wafers, where one wafer has precise grating/moth-eye structures on both sides of a double-sided polished wafer for improved transmission of over 80% in the long-wave infrared (LWIR) wavelength region without the need for an AR coating, while the other wafer is used to form a cavity. The two wafers are bonded using Au-In transient liquid phase (TLP) bonding at low temperature to form the cap wafer, which is then bondelectrical and Electronics d to the sensor wafer using glass frit bonding at high temperature to activate the getter inside the cavity region. The bond quality is assessed using three methods, including He-leak tests, cap deflection, and Pirani vacuum gauges. Hermeticity is confirmed through He-leak tests according to MIL-STD 883, yielding values as low as 0.1 × 10⁻⁹ atm·cc/s. The average shear strength is measured as 23.38 MPa. The package pressure varies from 133–533 Pa without the getter usage to as low as 0.13 Pa with the getter usage. Full article

In this study, the CALPHAD approach was employed to model the thermodynamics of the Au-Ge-X (X = In, Sb, Si, Zn) ternary systems, leveraging experimental phase equilibria data and previous assessments of related binary subsystems. The solution phases were modeled as substitutional solutions, and their excess Gibbs energies were expressed using the Redlich–Kister polynomial. Owing to the unavailability of experimental data, the solubility of the third elements in the Au-In, Au-Sb, and Au-Zn binary intermetallic compounds was excluded from consideration. Additionally, stable ternary intermetallic compounds were not reported in the literature and, thus, were not taken into account in the present thermodynamic calculations. Calculations of liquidus projections, isothermal sections, and vertical sections for these ternary systems have been performed, aligning with existing experimental findings. These thermodynamic parameters form a vital basis for creating a comprehensive thermodynamic database for Au-Ge-based alloys, which is essential for the design and development of new high-temperature Pb-free solders. Full article

With increasingly serious environmental problems caused by the improvement in people’s living standards, the number of cars has increased sharply in recent years, which directly leads to the continuous increase in the concentration of NO₂ in the air. NO₂ is a common toxic and irritant gas, which is harmful to both the human body and the environment. Therefore, this research focuses on NO₂ detection and is committed to developing high-performance, low detection limit NO₂ sensors. In this study, flower-like Au-loaded In₂O₃ was successfully fabricated using the hydrothermal method and the wet impregnation method. The morphological features and chemical compositions of the as-prepared samples were characterized using SEM, TEM, XRD and XPS. A variety of sensors were fabricated and the gas-sensing properties of sensors were investigated. The results indicate that the sensor based on 0.5 mol% Au/In₂O₃ shows a response value of 1624 to 1 ppm NO₂ at 100 °C, which is 14 times that based on pure In₂O₃. Meanwhile, the detection limit of the sensor based on 0.5 mol% Au/In₂O₃ for NO₂ is 10 ppb, and the response value is 10.4. In addition, the sensor based on 0.5 mol% Au/In₂O₃ also has high selectivity to NO₂ among CO, CO₂, H₂, CH₄, NH₃, SO₂ and H₂S. Finally, the sensitization mechanism of Au/In₂O₃ was discussed, and the reasons for improving the performance of the sensor were analyzed. The above results and analysis demonstrate that the gas-sensing attributes of the sensor based on 0.5 mol% Au/In₂O₃ to NO₂ improved remarkably; at the same time, it has been proved that the composite material has extensive potential in practical applications. Full article

In this paper, based on density functional theory, the structural stability and mechanical properties of AuIn₂ doped with RE (RE = Y, Sc) were investigated. The bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio of the materials were calculated by Viogt−Reuss−Hill approximation. The calculation results show that Sc−S_Au (trace of Au substituted by Sc in AuIn₂), Y−S_Au and Y−S_In have stable structure, and Y−S_Au has obvious effect on the toughness indexes of AuIn₂ alloy. Furthermore, based on Clarke and Cahill modes, the lattice thermal conductivity of the intermetallic compound was calculated and shows the same tendency with the Debye temperature and fast heat transfer rate in the direction of [110]. Full article

Photoactivated gallium nitride (GaN) nanowire-based gas sensors, functionalized with either bare In₂O₃ or In₂O₃ coated with a nanolayer of evaporated Au (Au/In₂O₃), were designed and fabricated for high-sensitivity sensing of NO₂ and low-power operation. The sensors were tested at room temperature under 265 nm and 365 nm ultraviolet illumination at several power levels and in relative humidity ranging from over 20% to 80%. Under all conditions, photoconductivity was lower in the Au/In₂O₃-functionalized sensors compared to that of sensors functionalized with bare In₂O₃. However, when tested in the presence of NO₂, the Au/In₂O₃ sensors consistently outperformed In₂O₃ sensors, the measured sensitivity being greater at 265 nm compared to 365 nm. The results show significant power reduction (×12) when photoactivating at (265 nm, 5 mW) compared to (365 nm, 60 mW). Maximum sensitivities of 27% and 42% were demonstrated with the Au/In₂O₃ sensors under illumination at (265 nm, 5 mW) for 1 ppm and 10 ppm concentration, respectively. Full article

A novel gold catalyst supported by In₂O₃-ZrO₂ with a solid solution structure shows a methanol selectivity of 70.1% and a methanol space–time yield (STY) of 0.59 g_MeOH h⁻¹ g_cat⁻¹ for CO₂ hydrogenation to methanol at 573 K and 5 MPa. The ZrO₂ stabilizes the structure of In₂O₃, increases oxygen vacancies, and enhances CO₂ adsorption, causing the improved activity. Full article

NO₂-sensing properties of semiconductor gas sensors using porous In₂O₃ powders loaded with and without 0.5 wt% Au (Au/In₂O₃ and In₂O₃ sensors, respectively) were examined in wet air (70% relative humidity at 25 °C). In addition, the effects of Au loading on the increased NO₂ response were discussed on the basis of NO₂ adsorption/desorption properties on the oxide surface. The NO₂ response of the Au/In₂O₃ sensor monotonically increased with a decrease in the operating temperature, and the Au/In₂O₃ sensor showed higher NO₂ responses than those of the In₂O₃ sensor at a temperature of 100 °C or lower. In addition, the response time of the Au/In₂O₃ sensor was much shorter than that of the In₂O₃ sensor at 30 °C. The analysis based on the Freundlich adsorption mechanism suggested that the Au loading increased the adsorption strength of NO₂ on the In₂O₃ surface. Moreover, the Au loading was also quite effective in decreasing the baseline resistance of the In₂O₃ sensor in wet air (i.e., increasing the number of free electrons in the In₂O₃), which resulted in an increase in the number of negatively charged NO₂ species on the In₂O₃ surface. The Au/In₂O₃ sensor showed high response to the low concentration of NO₂ (ratio of resistance in target gas to that in air: ca. 133 to 0.1 ppm) and excellent NO₂ selectivity against CO and ethanol, especially at 100 °C. Full article

We demonstrate high-power GaN-based vertical light-emitting diodes (LEDs) (VLEDs) on a 4-inch silicon substrate and flip-chip LEDs on a sapphire substrate. The GaN-based VLEDs were transferred onto the silicon substrate by using the Au–In eutectic bonding technique in combination with the laser lift-off (LLO) process. The silicon substrate with high thermal conductivity can provide a satisfactory path for heat dissipation of VLEDs. The nitrogen polar n-GaN surface was textured by KOH solution, which not only improved light extract efficiency (LEE) but also broke down Fabry–Pérot interference in VLEDs. As a result, a near Lambertian emission pattern was obtained in a VLED. To improve current spreading, the ring-shaped n-electrode was uniformly distributed over the entire VLED. Our combined numerical and experimental results revealed that the VLED exhibited superior heat dissipation and current spreading performance over a flip-chip LED (FCLED). As a result, under 350 mA injection current, the forward voltage of the VLED was 0.36 V lower than that of the FCLED, while the light output power (LOP) of the VLED was 3.7% higher than that of the FCLED. The LOP of the FCLED saturated at 1280 mA, but the light output saturation did not appear in the VLED. Full article

The reach and impact of the Internet of Things will depend on the availability of low-cost, smart sensors—“low cost” for ubiquitous presence, and “smart” for connectivity and autonomy. By using wafer-level processes not only for the smart sensor fabrication and integration, but also for packaging, we can further greatly reduce the cost of sensor components and systems as well as further decrease their size and weight. This paper reviews the state-of-the-art in the wafer-level vacuum packaging technology of smart sensors. We describe the processes needed to create the wafer-scale vacuum microchambers, focusing on approaches that involve metal seals and that are compatible with the thermal budget of complementary metal-oxide semiconductor (CMOS) integrated circuits. We review choices of seal materials and structures that are available to a device designer, and present techniques used for the fabrication of metal seals on device and window wafers. We also analyze the deposition and activation of thin film getters needed to maintain vacuum in the ultra-small chambers, and the wafer-to-wafer bonding processes that form the hermetic seal. We discuss inherent trade-offs and challenges of each seal material set and the corresponding bonding processes. Finally, we identify areas for further research that could help broaden implementations of the wafer-level vacuum packaging technology. Full article