Shih-Wen Chiu

Towards a Chemiresistive Sensor-Integrated Electronic Nose: A Review

Electronic noses have potential applications in daily life, but are restricted by their bulky size and high price. This review focuses on the use of chemiresistive gas sensors, metal-oxide semiconductor gas sensors and conductive polymer gas sensors in an electronic nose for system integration to reduce size and cost. The review covers the system design considerations and the complementary metal-oxide-semiconductor integrated technology for a chemiresistive gas sensor electronic nose, including the integrated sensor array, its readout interface, and pattern recognition hardware. In addition, the state-of-the-art technology integrated in the electronic nose is also presented, such as the sensing front-end chip, electronic nose signal processing chip, and the electronic nose system-on-chip.

Development of a portable electronic nose system for the detection and classification of fruity odors.

In this study, we have developed a prototype of a portable electronic nose (E-Nose) comprising a sensor array of eight commercially available sensors, a data acquisition interface PCB, and a microprocessor. Verification software was developed to verify system functions. Experimental results indicate that the proposed system prototype is able to identify the fragrance of three fruits, namely lemon, banana, and litchi.

A Low-Power Electronic Nose Signal-Processing Chip for a Portable Artificial Olfaction System

The bulkiness of current electronic nose (E-Nose) systems severely limits their portability. This study designed and fabricated an E-Nose signal-processing chip by using TSMC 0.18-μ m 1P6M complementary metal-oxide semiconductor technology to overcome the need to connect the device to a personal computer, which has traditionally been a major stumbling block in reducing the size of E-Nose systems. The proposed chip is based on a conductive polymer sensor array chip composed of multiwalled carbon nanotubes. The signal-processing chip comprises an interface circuit, an analog-to-digital converter, a memory module, and a microprocessor embedded with a pattern-recognition algorithm. Experimental results have verified the functionality of the proposed system, in which the E-Nose signal-processing chip successfully classified three odors, carbon tetrachloride (CCl4), chloroform (CHCl3), and 2-Butanone (MEK), demonstrating its potential for portable applications. The power consumption of this signal-processing chip was maintained at a very low 2.81 mW using a 1.8-V power supply, making it highly suitable for integration as an electronic nose system-on-chip.The bulkiness of current electronic nose (E-Nose) systems severely limits their portability. This study designed and fabricated an E-Nose signal-processing chip by using TSMC 0.18-μ m 1P6M complementary metal-oxide semiconductor technology to overcome the need to connect the device to a personal computer, which has traditionally been a major stumbling block in reducing the size of E-Nose systems. The proposed chip is based on a conductive polymer sensor array chip composed of multiwalled carbon nanotubes. The signal-processing chip comprises an interface circuit, an analog-to-digital converter, a memory module, and a microprocessor embedded with a pattern-recognition algorithm. Experimental results have verified the functionality of the proposed system, in which the E-Nose signal-processing chip successfully classified three odors, carbon tetrachloride (CCl4), chloroform (CHCl3), and 2-Butanone (MEK), demonstrating its potential for portable applications. The power consumption of this signal-processing chip was maintained at a very low 2.81 mW using a 1.8-V power supply, making it highly suitable for integration as an electronic nose system-on-chip.

Optical detection of organic vapors using cholesteric liquid crystals

The two organic vapors are acetone and toluene, which are identified using the colorimetry of cholesteric liquid crystals. The helical structure of cholesteric liquid crystal is diffused by organic vapor molecules, and the reflection spectrum of the cholesteric liquid crystal is red-shifted. The reflection spectra of the cholesteric liquid crystal reveal that the rates of variation of reflected color with the absorption of acetone and toluene vapors are different markedly because of the diversity of molecular polarities in the different molecular polarities of acetone and toluene vapors. A higher molecular polarity of the vapor causes a greater shift in the reflected color of cholesteric liquid crystal.

Cholesteric liquid crystal-carbon nanotube hybrid architectures for gas detection

The ability of a hybrid material that is based on cholesteric liquid crystal and carbon nanotube to detect acetone vapor is investigated. We find that the phase transition in this cholesteric liquid crystal-carbon nanotube hybrid will enable carbon nanotube to form conducting networks under the higher vapor concentration. This cholesteric liquid crystal-carbon nanotube hybrid exhibits an obvious change in reflected color and electrical resistance in the early and later stages of gas diffusion, respectively. This hybrid architecture has potential application as a gas sensor with a high dynamic range.

An Electronic-Nose Sensor Node Based on a Polymer-Coated Surface Acoustic Wave Array for Wireless Sensor Network Applications

This study developed an electronic-nose sensor node based on a polymer-coated surface acoustic wave (SAW) sensor array. The sensor node comprised an SAW sensor array, a frequency readout circuit, and an Octopus II wireless module. The sensor array was fabricated on a large K2 128° YX LiNbO3 sensing substrate. On the surface of this substrate, an interdigital transducer (IDT) was produced with a Cr/Au film as its metallic structure. A mixed-mode frequency readout application specific integrated circuit (ASIC) was fabricated using a TSMC 0.18 μm process. The ASIC output was connected to a wireless module to transmit sensor data to a base station for data storage and analysis. This sensor node is applicable for wireless sensor network (WSN) applications.

Growth mechanisms of plasma-assisted molecular beam epitaxy of green emission InGaN/GaN single quantum wells at high growth temperatures

The results of the growth of thin (∼3 nm) InGaN/GaN single quantum wells (SQWs) with emission wavelengths in the green region by plasma-assisted molecular beam epitaxy are present. An improved two-step growth method using a high growth temperature up to 650 °C is developed to increase the In content of the InGaN SQW to 30% while maintaining a strong luminescence intensity near a wavelength of 506 nm. The indium composition in InGaN/GaN SQW grown under group-III-rich condition increases with increasing growth temperature following the growth model of liquid phase epitaxy. Further increase in the growth temperature to 670 °C does not improve the photoluminescence property of the material due to rapid loss of indium from the surface and, under certain growth conditions, the onset of phase separation.

A Bio-Inspired Two-Layer Sensing Structure of Polypeptide and Multiple-Walled Carbon Nanotube to Sense Small Molecular Gases

In this paper, we propose a bio-inspired, two-layer, multiple-walled carbon nanotube (MWCNT)-polypeptide composite sensing device. The MWCNT serves as a responsive and conductive layer, and the nonselective polypeptide (40 mer) coating the top of the MWCNT acts as a filter into which small molecular gases pass. Instead of using selective peptides to sense specific odorants, we propose using nonselective, peptide-based sensors to monitor various types of volatile organic compounds. In this study, depending on gas interaction and molecular sizes, the randomly selected polypeptide enabled the recognition of certain polar volatile chemical vapors, such as amines, and the improved discernment of low-concentration gases. The results of our investigation demonstrated that the polypeptide-coated sensors can detect ammonia at a level of several hundred ppm and barely responded to triethylamine.

Towards a fully integrated electronic nose SoC

Electronic noses (e-nose) have been studied for several years and extensively applied; however, they are limited by their volume and high manufacturing cost. Portable devices have become popular in recent years; therefore, it is crucial to integrate e-noses in portable devices (e.g., mobile phones). This study used TSMC 90nm 1P9M CMOS MSG technology to develop a front-end system-on-chip (SoC) for an electronic nose. The SoC contained interdigitated electrodes, multi-channel sensor interface circuits, an analog to digital converter, and a digital continuous restricted Boltzmann machine (CRBM). Various conducting-polymer materials were titrated on the interdigitated electrodes to form an on-chip sensor array. This SoC was controlled through an external microcontroller to perform odor identification and analysis. The simulation results of the SoC and gas classification show that this chip is suitable for portable applications and further integration.

An electronic-nose sensor node based on polymer-coated surface acoustic wave array for environmental monitoring

We report an electronic-nose sensor node based on polymer-coated surface acoustic wave (SAW) sensor array for environmental monitoring applications. The sensor node consists of a SAW sensor array, its readout circuitry and a Wireless Sensor Network (WSN) platform. The 2 × 2 non-continuous gas SAW sensor array is coated with different polymer composite materials for different gas detection. The frequency signals from the SAW array are processed by the frequency readout circuitry to obtain frequency shift information. The sensor data is transmitted from sensor nodes by Octopus II WSN platform. Experimental results have shown good performance of gas detection and recognition. In order to achieve a high efficient environmental monitoring sensing network, the decision supporting system by implementing weighted voting system (WVS) has also been considered.