CMOS Monolithic Electrochemical Gas Sensor Microsystem Using Room Temperature Ionic Liquid (original) (raw)
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Sensors and Actuators B: Chemical, 2017
The growing impact of airborne pollutants and explosive gases on human health and occupational safety has escalated the demand of sensors to monitor hazardous gases. This paper presents a new miniaturized planar electrochemical gas sensor for rapid measurement of multiple gaseous hazards. The gas sensor features a porous polytetrafluoroethylene substrate that enables fast gas diffusion and room temperature ionic liquid as the electrolyte. Metal sputtering was utilized for platinum electrodes fabrication to enhance adhesion between the electrodes and the substrate. Together with carefully selected electrochemical methods, the miniaturized gas sensor is capable of measuring multiple gases including oxygen, methane, ozone and sulfur dioxide that are important to human health and safety. Compared to its manually-assembled Clark-cell predecessor, this sensor provides better sensitivity, linearity and repeatability, as validated for oxygen monitoring. With solid performance, fast response and miniaturized size, this sensor is promising for deployment in wearable devices for real-time point-of-exposure gas pollutant monitoring.
This paper presents an electrochemical gas sensor array system for health and safety monitoring. The system incorporates a custom room temperature ionic-liquid gas sensor array, a custom multi-mode electrochemical sensor readout board, and a commercial low power microcontroller board. Sensors for multiple gas targets were implemented in a miniaturized 22 array where each sensor consumes less than 3.2μW and occupies a sensing areavolumeof350mm3. A novel resource-sharing circuit architecture tailored to the gas sensor array was utilized to significantly decrease power, cost and size. The system supports multiple electrochemical measurement modes to provide orthogonal data to in-module sensor array algorithms for better prediction accuracy. The system achieves a resolution as high as 0.01vol% in amperometry mode and 0.06vol% in AC impedance mode for oxygen as an example target gas.
Toward Membrane-Free Amperometric Gas Sensors: A Microelectrode Array Approach
Room temperature ionic liquids (RTILs) have been applied to a microelectrode array and been demonstrated to form effective, membrane-free amperometric gas sensors. Determining the RTIL [P6,6,6,14][FAP] as the most appropriate choice for extended use, the amperometric quantification of oxygen has been demonstrated. The response of the sensor was quantified by both cyclic voltammetry and chronoamperometry. A range of O2 contents (2−13% v/v) and RTIL layer thicknesses (from ca. 6 to 125 μm) have been investigated. The combination of microelectrode array and RTIL, as well as the absence of membrane and volatile solvent, results in an elegant, easy to calibrate gas sensor with potential utility in standard and nonstandard conditions. http://pubs.acs.org/doi/abs/10.1021/ac1006359
Sensors and actuators. B, Chemical, 2017
Intense study on gas sensors has been conducted to implement fast gas sensing with high sensitivity, reliability and long lifetime. This paper presents a rapid amperometric method for gas sensing based on a room temperature ionic liquid electrochemical gas sensor. To implement a miniaturized sensor with a fast response time, a three electrode system with gold interdigitated electrodes was fabricated by photolithography on a porous polytetrafluoroethylene substrate that greatly enhances gas diffusion. Furthermore, based on the reversible reaction of oxygen, a new transient double potential amperometry (DPA) was explored for electrochemical analysis to decrease the measurement time and reverse reaction by-products that could cause current drift. Parameters in transient DPA including oxidation potential, oxidation period, reduction period and sample point were investigated to study their influence on the performance of the sensor. Oxygen measurement could be accomplished in 4 s, and th...
Monolithic CMOS multi-transducer gas sensor microsystem for organic and inorganic analytes
Sensors and Actuators B: Chemical, 2007
A monolithically integrated multi-transducer microsystem to detect organic and inorganic gases is presented. The system comprises two polymerbased sensor arrays based on capacitive and gravimetric transducers, a metal-oxide-based sensor array, the respective driving and signal processing electronics and a digital communication interface (see the first figure). The chip has been fabricated in industrial 0.8-m, complementary-metaloxide-semiconductor (CMOS) technology with subsequent post-CMOS micromachining. The simultaneous detection of organic and inorganic target analytes with the single chip multi-transducer system has been demonstrated. The system is very flexible and can provide different information of interest: the capacitive sensors can, e.g., act as humidity sensors to deal with the cross-sensitivity of the metal-oxide-based sensors to water, or the capacitive sensors can be coated with differently thick polymer layers to detect organic volatiles even in a background of water. The multi-transducer approach provides a wealth of information that can be used to improve the system discrimination capability and performance in gas detection. (A. Hierlemann). relying on a platform technology was identified as the most promising attempt to achieve major progress . Once the platform technology has been chosen, the components of the toolbox such as transducers, sensor modules, and circuit modules can be developed, some of which afterwards can be assembled into a customized system that meets the respective applications needs. A multitude of development activities are necessary to obtain all the modules needed for such a CMOS "toolbox": (a) the design and miniaturization of transducers and directly related electronic components (potentiostats, heaters, amplifiers, etc.), (b) the development of digital-to-analog and analog-to-digital conversion units, interface and communication units, (c) the development of additional and auxiliary functions, which are pivotal for the system performance (e.g., temperature control, temperature sensors, humidity sensors), and (d) the development of dedicated microsystem packaging solutions, which are suitable for chemical or gas analysis . It is important to note that the package has to be thought of already in the initial conception phase of a microsystem, since the design and architecture of a microsystem heavily depend on the envisaged packaging concept, as will become evident later in this paper (see system description and layout).
CMOS Single Chip Gas Detection Systems — Part I
Sensors Update, 2002
The current trend to control indoor air-quality and to monitor environmental pollution has created a strong demand for miniaturized and inexpensive gas sensors for volatile organic compounds (VOCs). Gas sensor arrays based on industrial CMOS-processes combined with post-CMOS micromachining (CMOS MEMS) are a promising approach to low-cost sensor devices. In this article, the state of research of CMOS-based gas sensor systems is reviewed, and a platform technology is described, which provides the possibility of monolithically integrating several different transducers on a single chip. A design environment, batch-fabrication processes, and fast testing procedures were developed to realize an example single-chip gas detection system. The chip includes the transducers, their biasing circuitry, reference elements, a digital interface, and a temperature sensor. The three polymer-based transducers and their interface electronics will be detailed in the second part of this article [1].
A robust, miniaturised electrochemical gas sensor for oxygen (O 2) has been constructed using a commercially available Pt microarray thin-film electrode (MATFE) with a gellified electrolyte containing the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 2 mim] [NTf 2 ]) and poly(methyl methacrylate) (PMMA) in a 50 : 50 mass ratio. Diffusion coefficients and solubilities for oxygen in mixtures of PMMA/RTIL at different PMMA doping concentrations (0–50% mass) were derived from potential step chronoamperometry (PSCA) on a Pt microdisk electrode. The MATFE was then used with both the neat RTIL and 50% (by mass) PMMA/RTIL gel, to study the analytical behavior over a wide concentration range (0.1 to 100 vol% O 2). Cyclic voltammetry (CV) and long-term chronoampero-metry (LTCA) techniques were employed and it was determined that the gentler CV technique is better at higher O 2 concentrations (above 60 vol%), but LTCA is more reliable and accurate at lower concentrations (especially below 0.5% O 2). In particular, there was much less potential shifting (from the unstable Pt quasi-reference electrode) evident in the 50% PMMA/RTIL gel than in the neat RTIL, making this a much more suitable electrolyte for long-term continuous oxygen monitoring. The mass production and low-cost of the electrode array, along with the minimal amounts of RTIL/PMMA required, make this a viable sensing device for oxygen detection on a bulk scale in a wide range of environmental conditions.
The electrochemical reduction of oxygen (O 2) has been studied on commercially-available integrated Pt thin-film electrodes (TFEs). Chemically reversible (but electrochemically quasi-reversible) cyclic voltammetry was observed in the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 2 mim][NTf 2 ]), showing superior behaviour of TFEs compared to screen-printed electrodes for oxygen sensing. As a step towards the preparation of robust gas sensors, the RTIL was mechanically stabilised on the TFE surface by the addition of poly(methyl methacrylate) (PMMA). At a PMMA concentration in the RTIL of ca. 50% mass, electrolyte flow was not evident. O 2 reduction peak currents were found to decrease systematically with increasing PMMA content, reflecting the higher viscosity of the electrolyte medium. Linear calibration graphs were obtained for 0–100% vol. oxygen at all PMMA–RTIL mixtures studied. The sensitivities decreased as [PMMA] increased, but the limits of detection were relatively unchanged. Mechanical stability of the sensors was tested in different orientations (flat, upside down, sideways) with both the neat RTIL and 50% mass electrolyte. Whilst the electrochemical responses were dramatically changed for the neat RTIL, the responses in the PMMA– RTIL mixture were independent of electrode orientation. Additionally, the oxygen response in the PMMA–RTIL mixture was less affected by atmospheric impurities and moisture, compared to the neat RTIL. This suggests that these low-cost miniaturised devices can successfully be used for oxygen sensing applications in field situations, especially where portability is essential.
Fast, Versatile, and Low-Cost Interface Circuit for Electrochemical and Resistive Gas Sensor
IEEE Sensors Journal, 2000
Chemical sensors for gas detection nowadays are widely used in several applications; basically, electrochemical sensors and semiconductor devices are used for this purpose. In both cases, the sensor value estimation is usually implemented as a current measurement and they are often referred as currentoutput sensors. In this paper, a versatile and low-cost interface circuit for such kind of sensors is presented. The proposed solution is characterized by a wide measurement range, yielding flexibility of use with sensors showing different baseline values. In addition, the fast readout time, on the order of tens of milliseconds, guarantees an accurate acquisition of the sensor data even in presence of fast transients, for example when using sensors operated in pulsed thermal regimes. The front-end works with a single-voltage power supply and furnishes a time-coded digital output signal, thus it is suitable to be directly interfaced to a microcontroller for the management of the measurement process, data elaboration, and presentation. Simplicity and compactness of the electronic interface make possible the integration in a single-chip solution, together with the digital electronics. Reproducibility of the circuit, for applications requiring the simultaneous acquisition of multiple sensors, is furthermore facilitated. The proposed approach has been validated with experimental tests conducted on a discrete component prototype. The system characterization has shown a maximum linearity error in the estimation of the sensor current or resistance of ∼5% over a measurement range of seven decades; the measurement time is <30 ms in all the considered input range. Fast thermal transients of different semiconductor sensors for gas sensing have been successfully acquired, demonstrating the validity of the proposed approach. Power dissipation (<25 mW at 3.3 V) and the front-end cost (∼10 $) make the presented solution suitable for the employment in low-cost and low-power gas detection systems.
CMOS Interfacing for Integrated Gas Sensors: A Review
IEEE Sensors Journal, 2000
Modern gas sensor technology is becoming an important part of our lives. It has been applied within the home (monitoring CO levels from boilers), the workplace (e.g., checking levels of toxic gases) to healthcare (monitoring gases in hospitals). However, historically the high price of gas sensors has limited market penetration to niche applications, such as safety in mines or petrochemical plants. The high price may be attributed to several different components: 1) cost of a predominantly manual manufacturing process; 2) need for interface circuitry in the form of discrete components on a PCB; and 3) fireproof packaging, making the cost of gas detection instruments typically many hundreds of dollars. Consequently, there has been a considerable effort over the past 20 years, towards the goal of low-cost ($1-$5) gas sensors, employing modern microelectronics technology to manufacture both the sensing element and the signal conditioning circuitry on a single silicon chip. In this paper, we review the emerging field of CMOS gas sensors and focus upon the integration of two main gas-sensing principles, namely, resistive and electrochemical and associated circuitry by CMOS technology. We believe that the combination of CMOS technology with more recent MEMS processing is now mature enough to deliver the exacting demands required to make low-power, low-cost smart gas sensors in high volume and this should result in a new generation of CMOS gas sensors. These new integrated, mass-produced gas sensors could open up mass markets and affect our everyday lives through application in cars, cell phones, watches, etc.