Ying Chen

Efficient integration of metal oxide nanocrystals with microelectromechanical systems (MEMS) microheaters is essential for developing compact gas‐sensing platforms, yet conventional deposition and patterning approaches often suffer from limited pattern fidelity and poor compatibility with suspended microheater structures. Here, we demonstrate a photoresist‐free strategy for the direct patterning and integration of In ₂ O ₃ nanocrystals onto suspended MEMS microheater membranes. This process is compatible with fragile suspended MEMS structures and produces sensing patterns with a linewidth of 200 µm confined to the suspended heating region. This approach enables sensor arrays comprising individually addressable microheater‐based gas sensors and facilitates their integration into compact gas‐sensing systems. By operating the sensors at distinct temperatures, dual‐temperature sensing responses are obtained from the same sensing material. When combined with machine‐learning‐based analysis, these responses enable reliable gas classification with an accuracy of up to 100%. Together, these results establish a directly patterned MEMS microheater platform that combines spatially defined nanocrystal integration with dual‐temperature sensing and data‐driven gas classification.

Detection of formaldehyde is of great significance for environmental monitoring and public health. Although amino-modified MOF nanomaterials have been widely adopted to improve the gas-sensing properties for hazardous gases, the fundamental enhancement mechanism is still insufficiently clarified, especially for formaldehyde-sensing material. In this work, the adsorption enthalpies of formaldehyde on UiO-66 and UiO-66-NH₂ were quantitatively extracted via MEMS variable-temperature adsorption experiments, yielding values of −21.8 and −45.9 kJ/mol, respectively. The results demonstrate that amino-modified UiO-66-NH₂ enables reversible adsorption between physisorption and chemisorption, which is more favorable for gas-sensing applications. Furthermore, a formaldehyde sensor was fabricated based on a MEMS resonant microcantilever. Gas-sensing performance tests indicate that the UiO-66-NH₂-based sensor displays a remarkable response to 0.5–10 ppm formaldehyde with a detection limit of 17 ppb and high selectivity. The significantly improved sensing performance experimentally validates the reasonability of the proposed mechanism. This work provides a reliable strategy for revealing the sensitivity enhancement mechanism and developing high-performance MOF-based formaldehyde sensors.

In situ growth of Pd nanoparticles on wood as a catalyst for developing a highly sensitive MEMS thermopile H ₂ sensor.

In this brief, an MEMS hydrogen thermal conductivity sensor (TCS) with high stability and fast-response performance is innovatively proposed. TCS has been widely applied in many crucial fields for hydrogen (H ${}_{{2}}\text {)}$ detection such as new energy vehicles. However, the change in gas flow rate can interfere with the TCS, significantly affecting the performance of the sensors. By using an integrated microchannel-enhanced silicon cap, the disturbance caused by the gas flow rate can be effectively suppressed. Compared to the sensor chip without a cap, when the gas flow rate changes from 20 to 200 sccm, the response change is reduced by 92.2%. In addition, by integrating a micropillar fin array structure on the sensor, the response time ${T} _{{90}}$ of the sensor is shortened to 200 ms, with an improvement of 32%. The sensor exhibits good linear response characteristics to H2 with concentrations ranging from 10 to 10 000 ppm, and the lowest detection limit (LOD) can reach 10 ppm. The TCS sensing chip in this brief is fabricated on a (111) silicon wafer by MEMS technology, and it is packaged with the microchannel cap wafer using a wafer-level bonding process, successfully achieving the fabrication of the sensor on a 4-in wafer.

During the thermal analysis of hazardous materials, the thermal instruments available may face the risk of contamination within heating chambers or damage to the instruments themselves. Herein, this work introduces an innovative detection technology that combines thermogravimetric and differential thermal analysis with an integrated MEMS cantilever. Integrating polysilicon thermocouples and a heat-driven resistor into a single resonant cantilever achieves remarkable precision with a mass resolution of 5.5 picograms and a temperature resolution of 0.0082 °C. Validated through the thermal analysis of nylon 6, the cantilever excels in detecting nanogram-level samples, making it ideal for analyzing hazardous materials like ammonium perchlorate and TNT. Notably, it has successfully observed the evaporation of TNT in an air atmosphere. The integrated MEMS cantilever detection chip offers a groundbreaking micro-quantification solution for hazardous material analysis, significantly enhancing safety and opening new avenues for application.

The selective detection of propane gas molecules using semiconductor gas sensors has always been a challenge within research. In this study, we successfully synthesized a γ-Fe₂O₃ nanomaterial with a selective catalytic effect on propane and loaded it onto a ZnO sensing material to construct a double-layer microsensor, which showed good sensing response characteristics in the detection of the refrigerant R290 (which is mainly propane). In addition, we also prepared a series of iron oxides, including nanomaterials such as α-Fe₂O₃, Fe₃O₄, and FeO, as well as γ-Fe₂O₃ materials with different specific surface areas obtained at various processing temperatures, and we carried out gas sensing research on R290. The results show that the γ-Fe₂O₃ material has a better sensitivity to R290, and the γ-Fe₂O₃ material calcined at 200 °C shows the best performance. Our results can provide a theoretical basis for the design and optimization of semiconductor gas sensors for alkane detection.

In a chamber-based digital PCR (dPCR) chip fabricated with polydimethylsiloxane (PDMS), bubble generation in the chambers at high temperatures is a critical issue. Here, we found that the main reason for bubble formation in PDMS chips is the too-high saturated vapor pressure of water at an elevated temperature. The bubbles should be completely prevented by reducing the initial pressure of the system to under 13.6 kPa to eliminate the effects of increased-pressure water vapor. Then, a cavity was designed and fabricated above the PCR reaction layer, and Parylene C was used as a shell covering the chip. The cavity was used for the negative generator in sample loading, PDMS degassing, PCR solution degassing in the digitization process and water storage in the thermal reaction process. The analysis was confirmed and finally achieved a desirable bubble-free, fast-digitization, valve-free and no-tubing connection dPCR.

Transmission electron microscopy (TEM) is a highly effective method for scientific research, providing comprehensive analysis and characterization. However, traditional TEM is limited to observing static material structures at room temperature within a high-vacuum environment. To address this limitation, a microchip was developed for in situ TEM characterization, enabling the real-time study of material structure evolution and chemical process mechanisms. This microchip, based on microelectromechanical System (MEMS) technology, is capable of introducing multi-physics stimulation and can be used in conjunction with TEM to investigate the dynamic changes of matter in gas and high-temperature environments. The microchip design ensures a high-temperature uniformity in the sample observation area, and a system of tests was established to verify its performance. Results show that the temperature uniformity of 10 real-time observation windows with a total area of up to 1130 μm² exceeded 95%, and the spatial resolution reached the lattice level, even in a flowing atmosphere of 1 bar.

Acetylene detection plays an important role in fault diagnosis of power transformers. However, the available dissolved gas analysis (DGA) techniques have always relied on bulky instruments and are time-consuming. Herein, a high-performance acetylene sensor was fabricated on a microhotplate chip using In₂O₃ as the sensing material. To achieve high sensing response to acetylene, Pd–Ag core-shell nanoparticles were synthesized and used as catalysts. The transmission electron microscopy (TEM) image clearly shows that the Ag shell is deposited on one face of the cubic Pd nanoseeds. By loading the Pd–Ag bimetallic catalyst onto the surface of In₂O₃ sensing material, the acetylene sensor has been fabricated for acetylene detection. Due to the high catalytic performance of Pd–Ag bimetallic nanoparticles, the microhotplate sensor has a high response to acetylene gas, with a limit of detection (LOD) of 10 ppb. In addition to high sensitivity, the fabricated microhotplate sensor exhibits satisfactory selectivity, good repeatability, and fast response to acetylene. The high performance of the microhotplate sensor for acetylene gas indicates the application potential of trace acetylene detection in power transformer fault diagnosis.

ZnMn₂O₄ nanotube based CO₂ sensor and sensing mechanism study.