Editorial

2 pages, 158 KiB

Open AccessEditorial

Editorial for the Special Issue on Nanostructure Based Sensors for Gas Sensing: from Devices to Systems

by Nicola Donato and Sabrina Grassini

Micromachines 2019, 10(9), 591; https://doi.org/10.3390/mi10090591 - 09 Sep 2019

Viewed by 1503

The development of solid state gas sensors based on microtransducers and nanostructured
sensing materials is the key point in the design of new portable measurement systems with sensing and identification performances comparable with those of most sophisticated analytical techniques. In such a context, [...] Read more.

The development of solid state gas sensors based on microtransducers and nanostructured
sensing materials is the key point in the design of new portable measurement systems with sensing and identification performances comparable with those of most sophisticated analytical techniques. In such a context, a lot of effort must be spent of course in the development of the sensing material, but also in the choice of the transducer mechanism and structure, in the electrical characterization of the sensor prototypes, as well as in the design of suitable measurement setups. [...] Full article

(This article belongs to the Special Issue Nanostructure Based Sensors for Gas Sensing: from Devices to Systems)

Research

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11 pages, 4812 KiB

Open AccessArticle

Effects of UV Irradiation on the Sensing Properties of In₂O₃ for CO Detection at Low Temperature

by Lucio Bonaccorsi, Angela Malara, Andrea Donato, Nicola Donato, Salvatore Gianluca Leonardi and Giovanni Neri

Micromachines 2019, 10(5), 338; https://doi.org/10.3390/mi10050338 - 22 May 2019

Cited by 9 | Viewed by 2480

Abstract

In this study, UV irradiation was used to improve the response of indium oxide (In₂O₃) used as a CO sensing material for a resistive sensor operating in a low temperature range, from 25 °C to 150 °C. Different experimental [...] Read more.

In this study, UV irradiation was used to improve the response of indium oxide (In₂O₃) used as a CO sensing material for a resistive sensor operating in a low temperature range, from 25 °C to 150 °C. Different experimental conditions have been compared, varying UV irradiation mode and sensor operating temperature. Results demonstrated that operating the sensor under continuous UV radiation did not improve the response to target gas. The most advantageous condition was obtained when the UV LED irradiated the sensor in regeneration and was turned off during CO detection. In this operating mode, the semiconductor layer showed an apparent “p-type” behavior due to the UV irradiation. Overall, the effect was an improvement of the indium oxide response at 100 °C toward low CO concentrations (from 1 to 10 ppm) that showed higher results than in the dark, which is promising to extend the detection of CO with an In₂O₃-based sensor in the sub-ppm range. Full article

(This article belongs to the Special Issue Nanostructure Based Sensors for Gas Sensing: from Devices to Systems)

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7 pages, 2550 KiB

Open AccessArticle

A Miniaturized Amperometric Hydrogen Sulfide Sensor Applicable for Bad Breath Monitoring

by Hithesh K. Gatty, Göran Stemme and Niclas Roxhed

Micromachines 2018, 9(12), 612; https://doi.org/10.3390/mi9120612 - 22 Nov 2018

Cited by 10 | Viewed by 4037

Abstract

Bad breath or halitosis affects a majority of the population from time to time, causing personal discomfort and social embarrassment. Here, we report on a miniaturized, microelectromechanical systems (MEMS)-based, amperometric hydrogen sulfide (H₂S) sensor that potentially allows bad breath quantification through [...] Read more.

Bad breath or halitosis affects a majority of the population from time to time, causing personal discomfort and social embarrassment. Here, we report on a miniaturized, microelectromechanical systems (MEMS)-based, amperometric hydrogen sulfide (H₂S) sensor that potentially allows bad breath quantification through a small handheld device. The sensor is designed to detect H₂S gas in the order of parts-per-billion (ppb) and has a measured sensitivity of 0.65 nA/ppb with a response time of 21 s. The sensor was found to be selective to NO and NH₃ gases, which are normally present in the oral breath of adults. The ppb-level detection capability of the integrated sensor, combined with its relatively fast response and high sensitivity to H₂S, makes the sensor potentially applicable for oral breath monitoring. Full article

(This article belongs to the Special Issue Nanostructure Based Sensors for Gas Sensing: from Devices to Systems)

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12 pages, 10609 KiB

Open AccessArticle

A Set of Platforms with Combinatorial and High-Throughput Technique for Gas Sensing, from Material to Device and to System

by Zhenghao Mao, Jianchao Wang, Youjin Gong, Heng Yang and Shunping Zhang

Micromachines 2018, 9(11), 606; https://doi.org/10.3390/mi9110606 - 19 Nov 2018

Cited by 10 | Viewed by 2854

Abstract

In a new E-nose development, the sensor array needs to be optimized to have enough sensitivity and selectivity for gas/odor classification in the application. The development process includes the preparation of gas sensitive materials, gas sensor fabrication, array optimization, sensor array package and [...] Read more.

In a new E-nose development, the sensor array needs to be optimized to have enough sensitivity and selectivity for gas/odor classification in the application. The development process includes the preparation of gas sensitive materials, gas sensor fabrication, array optimization, sensor array package and E-nose system integration, which would take a long time to complete. A set of platforms including a gas sensing film parallel synthesis platform, high-throughput gas sensing unmanned testing platform and a handheld wireless E-nose system were presented in this paper to improve the efficiency of a new E-nose development. Inkjet printing was used to parallel synthesize sensor libraries (400 sensors can be prepared each time). For gas sensor selection and array optimization, a high-throughput unmanned testing platform was designed and fabricated for gas sensing measurements of more than 1000 materials synchronously. The structures of a handheld wireless E-nose system with low power were presented in detail. Using the proposed hardware platforms, a new E-nose development might only take one week. Full article

(This article belongs to the Special Issue Nanostructure Based Sensors for Gas Sensing: from Devices to Systems)

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17 pages, 6372 KiB

Open AccessArticle

Fabrication and Packaging of CMUT Using Low Temperature Co-Fired Ceramic

by Fikret Yildiz, Tadao Matsunaga and Yoichi Haga

Micromachines 2018, 9(11), 553; https://doi.org/10.3390/mi9110553 - 27 Oct 2018

Cited by 16 | Viewed by 3979

Abstract

This paper presents fabrication and packaging of a capacitive micromachined ultrasonic transducer (CMUT) using anodically bondable low temperature co-fired ceramic (LTCC). Anodic bonding of LTCC with Au vias-silicon on insulator (SOI) has been used to fabricate CMUTs with different membrane radii, 24 µm, [...] Read more.

This paper presents fabrication and packaging of a capacitive micromachined ultrasonic transducer (CMUT) using anodically bondable low temperature co-fired ceramic (LTCC). Anodic bonding of LTCC with Au vias-silicon on insulator (SOI) has been used to fabricate CMUTs with different membrane radii, 24 µm, 25 µm, 36 µm, 40 µm and 60 µm. Bottom electrodes were directly patterned on remained vias after wet etching of LTCC vias. CMUT cavities and Au bumps were micromachined on the Si part of the SOI wafer. This high conductive Si was also used as top electrode. Electrical connections between the top and bottom of the CMUT were achieved by Au-Au bonding of wet etched LTCC vias and bumps during anodic bonding. Three key parameters, infrared images, complex admittance plots, and static membrane displacement, were used to evaluate bonding success. CMUTs with a membrane thickness of 2.6 µm were fabricated for experimental analyses. A novel CMUT-IC packaging process has been described following the fabrication process. This process enables indirect packaging of the CMUT and integrated circuit (IC) using a lateral side via of LTCC. Lateral side vias were obtained by micromachining of fabricated CMUTs and used to drive CMUTs elements. Connection electrodes are patterned on LTCC side via and a catheter was assembled at the backside of the CMUT. The IC was mounted on the bonding pad on the catheter by a flip-chip bonding process. Bonding performance was evaluated by measurement of bond resistance between pads on the IC and catheter. This study demonstrates that the LTCC and LTCC side vias scheme can be a potential approach for high density CMUT array fabrication and indirect integration of CMUT-IC for miniature size packaging, which eliminates problems related with direct integration. Full article

(This article belongs to the Special Issue Nanostructure Based Sensors for Gas Sensing: from Devices to Systems)

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7 pages, 1418 KiB

Open AccessArticle

A Mini-System Integrated with Metal-Oxide-Semiconductor Sensor and Micro-Packed Gas Chromatographic Column

by Jianhai Sun, Zhaoxin Geng, Ning Xue, Chunxiu Liu and Tianjun Ma

Micromachines 2018, 9(8), 408; https://doi.org/10.3390/mi9080408 - 17 Aug 2018

Cited by 21 | Viewed by 4264

Abstract

In this work, a mini monitoring system integrated with a microfabricated metal oxide array sensor and a micro packed gas chromatographic (GC) column was developed for monitoring environmental gases. The microfabricated packed GC column with a 1.6 m length was used to separate [...] Read more.

In this work, a mini monitoring system integrated with a microfabricated metal oxide array sensor and a micro packed gas chromatographic (GC) column was developed for monitoring environmental gases. The microfabricated packed GC column with a 1.6 m length was used to separate the environmental gas, and the metal oxide semiconductor (MOS) array sensor, fabricated with nano-sized SnO-SnO₂ sensitive materials, was able to effectively detect each component separated by GC column. The results demonstrate that the monitoring system can detect environmental gas with high precision. Full article

(This article belongs to the Special Issue Nanostructure Based Sensors for Gas Sensing: from Devices to Systems)

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13 pages, 4114 KiB

Open AccessArticle

The Fabrication of Au@C Core/Shell Nanoparticles by Laser Ablation in Solutions and Their Enhancements to a Gas Sensor

by Xiaoxia Xu, Lei Gao and Guotao Duan

Micromachines 2018, 9(6), 278; https://doi.org/10.3390/mi9060278 - 01 Jun 2018

Cited by 12 | Viewed by 3285

Abstract

A convenient and flexible route is presented to fabricate gold noble metal nanoparticles wrapped with a controllable ultrathin carbon layer (Au@C) in one step based on laser ablation of the noble metal targets in toluene-ethanol mixed solutions. The obtained metal nanoparticles were <20 [...] Read more.

A convenient and flexible route is presented to fabricate gold noble metal nanoparticles wrapped with a controllable ultrathin carbon layer (Au@C) in one step based on laser ablation of the noble metal targets in toluene-ethanol mixed solutions. The obtained metal nanoparticles were <20 nm in size after ablation, and the thickness of the wrapped ultrathin carbon layer was 2 nm in a typical reaction. The size of the inner noble metal nanoparticles could be controlled by adjusting the power of laser ablation, and the thickness of the ultrathin carbon layer can be controlled from 0.6 to 2 nm by laser ablation in different components of organic solution. Then the resultant Au@C core/shell nanoparticles were modified on the surface of In₂O₃ films through a sol-gel technique, and the hydrogen sulfide (H₂S) gas-sensing characteristics of the products were examined. Compared to pure and Au-modified In₂O₃, the Au@C-modified In₂O₃ materials exhibited a revertible and reproducible performance with good sensitivity and very low response times (few seconds) for H₂S gas with a concentrations of 1 to 5 ppm at room temperature. Evidence proved that the ultrathin carbon layer played an important role in the improved H₂S sensor performance. Other noble metals wrapped by the homogeneous carbon shell, such as Ag@C, could also be prepared with this method. Full article

(This article belongs to the Special Issue Nanostructure Based Sensors for Gas Sensing: from Devices to Systems)

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Graphical abstract

7 pages, 3380 KiB

Open AccessArticle

Electrospray Deposition of ZnO Thin Films and Its Application to Gas Sensors

by Wenwang Li, Jinghua Lin, Xiang Wang, Jiaxin Jiang, Shumin Guo and Gaofeng Zheng

Micromachines 2018, 9(2), 66; https://doi.org/10.3390/mi9020066 - 02 Feb 2018

Cited by 19 | Viewed by 5843

Abstract

Electrospray is a simple and cost-effective method to fabricate micro-structured thin films. This work investigates the electrospray process of ZnO patterns. The effects of experimental parameters on jet characteristics and electrosprayed patterns are studied. The length of stable jets increases with increasing applied [...] Read more.

Electrospray is a simple and cost-effective method to fabricate micro-structured thin films. This work investigates the electrospray process of ZnO patterns. The effects of experimental parameters on jet characteristics and electrosprayed patterns are studied. The length of stable jets increases with increasing applied voltage and flow rate, and decreases with increasing nozzle-to-substrate distance, while electrospray angles exhibit an opposite trend with respect to the stable jet lengths. The diameter of electrosprayed particles decreases with increasing applied voltage, and increases with flow rate. Furthermore, an alcohol gas sensor is presented. The ZnAc is calcined into ZnO, which reveals good repeatability and stability of response in target gas. The sensing response, defined as the resistance ratio of R₀/R_g, where R₀ and R_g are resistance of ZnO in air and alcohol gas, increases with the concentration of alcohol vapors and electrospray deposition time. Full article

(This article belongs to the Special Issue Nanostructure Based Sensors for Gas Sensing: from Devices to Systems)

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Review

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26 pages, 2166 KiB

Open AccessReview

Recent Progress in Gas Sensor Based on Nanomaterials

by Danyang Lun and Ke Xu

Micromachines 2022, 13(6), 919; https://doi.org/10.3390/mi13060919 - 10 Jun 2022

Cited by 14 | Viewed by 2696

Abstract

Nanomaterials-based gas sensors have great potential for substance detection. This paper first outlines the research of gas sensors composed of various dimensional nanomaterials. Secondly, nanomaterials may become the development direction of a new generation of gas sensors due to their high sensing efficiency, [...] Read more.

Nanomaterials-based gas sensors have great potential for substance detection. This paper first outlines the research of gas sensors composed of various dimensional nanomaterials. Secondly, nanomaterials may become the development direction of a new generation of gas sensors due to their high sensing efficiency, good detection capability and high sensitivity. Through their excellent characteristics, gas sensors also show high responsiveness and sensing ability, which also plays an increasingly important role in the field of electronic skin. We also reviewed the physical sensors formed from nanomaterials in terms of the methods used, the characteristics of each type of sensor, and the advantages and contributions of each study. According to the different kinds of signals they sense, we especially reviewed research on gas sensors composed of different nanomaterials. We also reviewed the different mechanisms, research processes, and advantages of the different ways of constituting gas sensors after sensing signals. According to the techniques used in each study, we reviewed the differences and advantages between traditional and modern methods in detail. We compared and analyzed the main characteristics of gas sensors with various dimensions of nanomaterials. Finally, we summarized and proposed the development direction of gas sensors based on various dimensions of nanomaterials. Full article

(This article belongs to the Special Issue Nanostructure Based Sensors for Gas Sensing: from Devices to Systems)

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