Field Programmable Gate Array based Readout for Surface Acoustic Wave Portable Gas Detector

Surface acoustic wave (SAW) is one of the most promising technology in the field of gas sensing at low concentrations. Field deployable portable SAW detectors are, however, prone to noise, there by limiting the detection at low concentrations. To meet the current requirements of gas detection at low concentrations, the readout methodology needs to be based on minimal hardware and better noise management. In this paper we describe a readout scheme for portable SAW gas detectors incorporating a field programmable gate array (FPGA). The developed readout system includes a modified reciprocal frequency counter for differential SAW sensor, median noise filtering and moving averages smoothing for noise management, peak detection and interfacing with external display, all implemented in FPGA. The developed readout was tested against VOCs using a lab developed vapour generator and the results have been presented in the paper. The readout system is compact, low power consuming and expandable through software thus ideal for portable handheld applications

Bulk and Surface Acoustic Wave Sensor Arrays for Multi-Analyte Detection: A Review

Bulk acoustic wave (BAW) and surface acoustic wave (SAW) sensor devices have successfully been used in a wide variety of gas sensing, liquid sensing, and biosensing applications. Devices include BAW sensors using thickness shear modes and SAW sensors using Rayleigh waves or horizontally polarized shear waves (HPSWs). Analyte specificity and selectivity of the sensors are determined by the sensor coatings. If a group of analytes is to be detected or if only selective coatings (i.e., coatings responding to more than one analyte) are available, the use of multi-sensor arrays is advantageous, as the evaluation of the resulting signal patterns allows qualitative and quantitative characterization of the sample. Virtual sensor arrays utilize only one sensor but combine itwith enhanced signal evaluation methods or preceding sample separation, which results in similar results as obtained with multi-sensor arrays. Both array types have shown to be promising with regard to system integration and low costs. This review discusses principles and design considerations for acoustic multi-sensor and virtual sensor arrays and outlines the use of these arrays in multi-analyte detection applications, focusing mainly on developments of the past decade

Nanostructured Gas Sensors for Health Care: An Overview

Nanostructured platforms have been utilized for fabrication of small, sensitive and reliable gas sensing devices owing to high functionality, enhanced charge transport and electro-catalytic property. As a result of globalization, rapid, sensitive and selective detection of gases in environment is essential for health care and security. Nonmaterial such as metal, metal oxides, organic polymers, and organic-inorganic hybrid nanocomposites exhibit interesting optical, electrical, magnetic and molecular properties, and hence are found potential gas sensing materials. Morphological, electrical, and optical properties of such nanostructures can be tailored via controlling the precursor concentration and synthesis conditions resulting to achieve desired sensing. This review presents applications of nano-enabling gas sensors to detect gases for environment monitoring. The recent update, challenges, and future vision for commercial applications of such sensor are also described here

CMOS compatible solidly mounted resonator for air quality monitoring

Air pollution has become a growing concern around the world. Human exposure to hazardous air pollutants is associated with a range of health problems and increased mortality. An estimated 40,000 early deaths per year are caused by the exposure to air pollutants in the UK alone, which cost over £20 billion annually to individuals and health services1. In this work, novel solidly mounted resonator (SMR) devices were developed for integration in a low-cost, portable air quality monitor for the real-time monitoring of particulate matter and volatile organic compounds (VOCs). Finite element models of the SMRs were developed to aid their design and simulate the response of the sensors to particles and exposure to VOCs. For particle sensing, a SMR based unit was developed, working in a dual mode configuration. The unit was characterised inside an environmental chamber, together with commercial reference instruments, to particles of known size and composition. A detection limit of 20 μg/m3 was found (below the safe exposure limit). To target fine particles (<2.5 μm), a virtual impactor was incorporated into the system. For VOC detection, the SMR devices were functionalised with polymer coatings to detect acetone and toluene vapours (most common VOCs in air). A polymer drop-coating system was developed to complete this aim (polymer film thicknesses <100nm). An automated VOC test station was developed to characterise the SMR based sensors to low ppm concentrations of the target vapours (<200 ppm). The SMR devices demonstrated a limit of detection of 5 ppm to toluene and 50 ppm of acetone (well below the safe exposure limits). A novel CMOS based SMR device, suitable for volume production and monolithic integration, was designed with an integrated microheater and CMOS acoustic mirror. The heater was included to vary the temperature of the sensing area (to enhance the sensitivity of the SMR to a particular VOC through temperature modulation or to clear particles off the surface). The fabricated device (1.9 GHz) exhibited good performance

EUROSENSORS XVII : book of abstracts

Fundação Calouste Gulbenkien (FCG).Fundação para a Ciência e a Tecnologia (FCT)

Front-end circuits for chemical and molecular sensing

This research demonstrates two building blocks for CMOS integrated sensor IC for molecular or chemical sensing. One of them for molecular sensing is the capacitance sensing circuit to detect the change of the dielectric constant of novel nanowell devices. The size of nanowell (10nm-100nm) enables high fidelity detection and analysis through Broadband Dielectric Spectroscopy (BDS) of the parallel-plate capacitor formed by the nanowell and the targeted molecules. The signal tranduction is done by a novel, continuous-time detection circuit using a low-noise lock-in architecture which generates the current output containing the information about the admittance of the sensor as a function of the frequency for BDS. This current signal is processed in the current domain by a low power current-mode A/D converter. The current signal transducer has a quasilinear capacitance resolution of 164pA/aF (at 1Ghz) and power consumption of only 30uW in 0.18um TSMC CMOS technology. Another building block is a low noise front end for feature extraction for gas and nanoparticle detection using Van der Waals sensors. The output of such a sensor consists of particle specific information in the low frequency range from 0 to 100 KHz in the form of stochastic fluctuations. Such detection schemes are termed as fluctuation enhanced sensing, which exploit the statistics of the noise in the low frequency spectrum. The front end consists of a low pass filter bank to process the amplified signal from a low-noise transimpedance amplifier. It handles the noise-like information signal from the sensor with filters having increasing cut-off frequencies. It is designed to operate at temperature as high as 200C with low leakage currents to maximize the stochastic fluctuation noise generation. The front-end system was fabricated with TSMC 0.18um technology and tested. The gain of the front-end circuit is at least 87dB and its power consumption with one transimpedance amplifier and 10 filters is just 1.1mW. Moreover, the worst-case maximum input current signal is 0.2uApp while satisfying 5% THD and the equivalent input current noise level is under 7nA. The front-end circuit demonstrates the considerably high dynamic range with the low noise input range suitable for applications for sensing using fluctuation enhanced techniques

Field-Effect Sensors

This Special Issue focuses on fundamental and applied research on different types of field-effect chemical sensors and biosensors. The topics include device concepts for field-effect sensors, their modeling, and theory as well as fabrication strategies. Field-effect sensors for biomedical analysis, food control, environmental monitoring, and the recording of neuronal and cell-based signals are discussed, among other factors

Advancements in microfabricated gas sensors and microanalytical tools for the sensitive and selective detection of odors

In recent years, advancements in micromachining techniques and nanomaterials have enabled the fabrication of highly sensitive devices for the detection of odorous species. Recent efforts done in the miniaturization of gas sensors have contributed to obtain increasingly compact and portable devices. Besides, the implementation of new nanomaterials in the active layer of these devices is helping to optimize their performance and increase their sensitivity close to humans’ olfactory system. Nonetheless, a common concern of general-purpose gas sensors is their lack of selectivity towards multiple analytes. In recent years, advancements in microfabrication techniques and microfluidics have contributed to create new microanalytical tools, which represent a very good alternative to conventional analytical devices and sensor-array systems for the selective detection of odors. Hence, this paper presents a general overview of the recent advancements in microfabricated gas sensors and microanalytical devices for the sensitive and selective detection of volatile organic compounds (VOCs). The working principle of these devices, design requirements, implementation techniques, and the key parameters to optimize their performance are evaluated in this paper. The authors of this work intend to show the potential of combining both solutions in the creation of highly compact, low-cost, and easy-to-deploy platforms for odor monitoringPostprint (published version

Towards Integrated Fluorescence Sensing

This thesis is an account of ongoing efforts in the Integrated Biomorphic Information Systems Laboratory and the Laboratory for MicroTechnologies towards the implementation of integrated microfabricated biosensing platforms with on-chip fluorescence detection capability. The first chapter is a published, exhaustive, and critical review of state-of-the-art microfluorometers, and it offers a set of performance metrics for evaluating sensors of different architectures. The second chapter consists of material from two journal papers, currently in preparation, in which the development of a polymeric optical filter material for UV fluorescence spectroscopy is presented and its integration with a CMOS active pixel sensor (APS) discussed. The third chapter, which is also an archival publication, presents initial efforts towards achieving high-sensitivity CMOS photodetectors for photon counting-based fluorescence assays in integrated platforms

Alternative piezoresistor designs for maximizing cantilever sensitivity.

Over the last 15 years, researchers have explored the use of piezoresistive microcantilevers/resonators as gas sensors because of their relative ease in fabrication, low production cost, and their ability to detect changes in mass or surface stress with fairly good sensitivity. However, existing microcantilever designs rely on irreversible chemical reactions for detection and researchers have been unable to optimize symmetric geometries for increased sensitivity. Previous work by our group showed the capability of T-shaped piezoresistive cantilevers to detect gas composition using a nonreaction-based method – viscous damping. However, this geometry yielded only small changes in resistance. Recently, computational studies performed by our group indicated that optimizing the geometry of the base piezoresistor increases device sensitivity up to 700 times. Thus, the focus of this work is to improve the sensitivity of nonreaction-based piezoresistive microcantilevers by incorporating asymmetric piezoresistive sensing elements in a new array design. A three-mask fabrication process was performed using a 4 silicon-on-insulator wafer. Gold bond pads and leads were patterned using two optical lithography masks, gold sputtering, and acetone lift-off techniques. The cantilevers were patterned with electron-beam lithography and a dry etch masking layer was then deposited via electronbeam evaporation of iron. Subsequently, the silicon device layer was deep reactive ion etched (DRIE) to create the vertical sidewalls and the sacrificial silicon dioxide layer was removed with a buffered oxide etch, completely releasing the cantilever structures. Finally, the device was cleaned and dried with critical point drying to prevent stiction of the devices to the substrate. For the resonance experiments, the cantilevers were driven electrostatically by applying an AC bias, 10 Vpp, to the gate electrode. A DC bias of 10 V was placed across the piezoresistor in series with a 14 kÙ resistor. The drive frequency (0 – 80 kHz) was swept until the cantilever resonated at its natural frequency, which occurred when the output of the lock-in amplifier reached its maximum. These devices have been actuated to resonance under vacuum and their resonant frequencies and Qfactors measured. The first mode of resonance for the asymmetric cantilevers was found to range between 40 kHz and 63 kHz, depending on the piezoresistor geometry and length of the cantilever beam. The redesigned piezoresistive microcantilevers tested yielded static and dynamic sensitivities ranging from 1-6 Ù/Ìm and 2-17 Ù/Ìm displacement, respectively, which are 40 –730 times more sensitive than the best symmetric design previously reported by our group. Furthermore, the Q-factors ranged between 1700 and 4200, typical values for MEMS microcantilevers