Field-effect Transistor Gas Sensor Research Articles

Theoretical approaches toward designing sensitive materials for carbon nanotube-based field-effect transistor gas sensors

Screening sensitive materials is one of the keys to designing high-performance carbon nanotube-based field-effect transistor gas sensors. Here, we proposed a reliable way (e.g., H2S) to design sensitive materials with high efficiency based on theory and experiment. Our results demonstrated that the interaction between H2S and the sensitive materials must satisfy both energy level and parity match, and the maximum overlap of the orbital wave function. Especially, the gas ΔQ exhibits a strong linear scaling with the metal φ (ΔQ∝φ). Meanwhile, Δφ will result in changes in the threshold voltage of the sensor (ΔVth∝Δφ) in experiments, which would lead to different response intensities. Therefore, the greater the ΔQ, the more changes in the threshold voltage, and corresponding higher response intensity. Expectedly, our experimental results show that the response intensity at equivalent concentrations is in high agreement with the theory (Pt > Pd > Ag), and the limit of H2S detection is low to 20 ppb.

Discriminative Analysis of NOx Gases by Two-Dimensional Violet Phosphorus Field-Effect Transistors.

Two-dimensional violet phosphorus (VP) has emerged as a new sensing material in various sensing applications due to its unique electrical properties and high stability among allotropes of phosphorus. Currently, the research of the VP-based analysis method is at the early stage. In this work, a VP nanosheet-based field-effect transistor (FET) sensor is reported for the detection of NO2 and N2O gases with extraordinary sensing performance. This sensor can achieve excellent sensitivity of up to ∼50% current change/ppm and a low detection limit of 5.9 ppb and enables the NO2 analysis in various mixed gases. Moreover, this sensor can effectively distinguish between NO2 and N2O gases, which is a big challenge for current FET or chemiresistor gas sensors. The different sensing behaviors of the VP sensor to NO2 and N2O gases have been investigated, and the mechanism study shows that the adsorption energy, bond length of the gas molecule on the VP surface, and the decomposition of N2O led to the differential responses. This work is one of the pioneer studies of VP gas sensors and presents a new sensing method for the discriminative analysis of NO2 and N2O for greenhouse gas emission monitoring and air quality control.

Gate-Tunable Graphene/ZnO-Based Dual- Channel Field-Effect Transistor Gas Sensor for Simultaneous Detection of CO2 and NO2 Gases

Gate-Tunable Graphene/ZnO-Based Dual- Channel Field-Effect Transistor Gas Sensor for Simultaneous Detection of CO₂ and NO₂ Gases

Quantum Dots-Sensitized High Electron Mobility Transistor (HEMT) for Sensitive NO2 Detection

Colloidal quantum dots (CQDs) are gaining increasing attention for gas sensing applications due to their large surface area and abundant active sites. However, traditional resistor-type gas sensors using CQDs to realize molecule recognition and signal transduction at the same time are associated with the trade-off between sensitivity and conductivity. This limitation has restricted their range of practical applications. In this study, we propose and demonstrate a monolithically integrated field-effect transistor (FET) gas sensor. This novel FET-type gas sensor utilizes the capacitance coupling effect of the CQD sensing film based on a floating gate, and the quantum capacitance plays a role in the capacitance response of the CQD sensing film. By effectively separating the gate sensing film from the two-dimensional electron gas (2DEG) conduction channel, the lead sulfide (PbS) CQD gate-sensitized FET gas sensor offers high sensitivity, a high signal-to-noise ratio, and a wide range, with a real-time response of sub-ppb NO2. This work highlights the potential of quantum dot-sensitized FET gas sensors as a practical solution for integrated gas sensor chip applications using CQDs.

Field Effect Transistor Gas Sensors Based on Mechanically Exfoliated Van der Waals Materials

The high surface-to-volume ratio and flatness of mechanically exfoliated van der Waals (vdW) layered materials make them an ideal platform to investigate the Langmuir absorption model. In this work, we fabricated field effect transistor gas sensors, based on a variety of mechanically exfoliated vdW materials, and investigated their electrical field-dependent gas sensing properties. The good agreement between the experimentally extracted intrinsic parameters, such as equilibrium constant and adsorption energy, and theoretically predicted values suggests validity of the Langmuir absorption model for vdW materials. Moreover, we show that the device sensing behavior depends crucially on the availability of carriers, and giant sensitivities and strong selectivity can be achieved at the sensitivity singularity. Finally, we demonstrate that such features provide a fingerprint for different gases to quickly detect and differentiate between low concentrations of mixed hazardous gases using sensor arrays.

Two-dimensional MoSi2As4-based field-effect transistors integrating switching and gas-sensing functions.

Multifunctional nanoscale devices integrating multiple functions are of great importance for meeting the requirements of next-generation electronics. Herein, using first-principles calculations, we propose multifunctional devices based on the two-dimensional monolayer MoSi2As4, where a single-gate field-effect transistor (FET) and FET-type gas sensor are integrated. After introducing the optimizing strategies, such as underlap structures and dielectrics with a high dielectric constant (κ), we designed a 5 nm gate-length MoSi2As4 FET, whose performance fulfilled the key criteria of the International Technology Roadmap for Semiconductors (ITRS) for high-performance semiconductors. Under the joint adjustment of the underlap structure and high-κ dielectric material, the on/off ratio of the 5 nm gate-length FET reached up to 1.38 × 104. In addition, driven by the high-performance FET, the MoSi2As4-based FET-type gas sensor showed a sensitivity of 38% for NH3 and 46% for NO2. Moreover, the weak interaction between NH3 (NO2) and MoSi2As4 favored the recycling of the sensor. Furthermore, the sensitivity of the sensor could be effectively improved by the gate voltage, and was increased up to 67% (74%) for NH3 (NO2). Our work provides theoretical guidance for the fabrication of multifunctional devices combining a high-performance FET and sensitive gas sensor.

InP3 Monolayer as a Promising 2D Sensing Material in SF6 Insulation Devices.

In this letter, we perform a first-principles study on the adsorption performance of the InP3 monolayer upon three SF6 decomposed species, including SO2, SOF2, and SO2F2, to investigate its potential as a resistance-type, optical or field-effect transistor gas sensor. Results indicate that the InP3 monolayer exhibits strong chemisorption upon SO2 but weak physisorption upon SO2F2. The most admirable adsorption behavior is upon SOF2, which provides a favorable sensing response (−19.4%) and recovery property (10.4 s) at room temperature as a resistance-type gas sensor. A high response of 180.7% upon SO2 and a poor one of −1.9% upon SO2F2 are also identified, which reveals the feasibility of the InP3 monolayer as a resistance-type sensor for SO2 detection with recycle use via a heating technique to clean the surface. Moreover, the InP3 monolayer is a promising optical sensor for SO2 detection due to the obvious changes in adsorption peaks within the range of ultraviolet and is a desirable field-effect transistor sensor for selective and sensitive detection of SO2 and SOF2 given the evident changes of QT and Eg under the applied electric field.

Large modulation of mobile carriers within MoS2 by decoration of molecular dopants to enhance its gas sensing

Large area functional MoS2 thin films are emerging in many opto-electric applications. In this sense, control of charge transfer via molecular decoration to build up a better gas sensing application is a key issue. We have systematically investigated a feasible fabrication process to realize an optimal molecule decoration with tetrafluorotetracyanoquinodimethane (F4TCNQ) on the surface of MoS2. The field effect transistor gas sensors have been improved remarkably to response on NH3 under all range of analyte concentration by two or three orders of magnitude after molecular decoration. All this improvement can be attributed to charge transfer within a three-body system including NH3, F4TCNQ and MoS2. This research may provide insight guidance to develop large scale high-performance gas-sensors and stimulate an interest to future investigate charge transfer mechanism within molecule decorated two-dimensional materials.

Quantum Dots-Sensitized High Electron Mobility Transistor (HEMT) for Room-Temperature Gas Detection

Introduction Nowadays there is an increasing demand for low power and low-cost gas sensors for a wide range of applications. With the advantages of miniaturization, low power consumption and good compatibility with the standard CMOS circuit, gas sensing field effect transistors (FETs) are the most attractive approaches.Since the first Pd gate field effect transistor gas sensor came into our insight [1], researchers have done a lot of work to materialize the device potential, starting with the choice of the sensing materials and sensor structure [2]. Due to the proximity of two-dimensional electron gas (2DEG) to the sensing surface and high sheet carrier concentration in the order of 1012~1013 cm−2, high electron mobility transistors (HEMTs) are extremely sensitive to the surface charge and variation in the environmental conditions, thereby enabling the sensing of the gases at low concentrations.In this paper, we demonstrate ppm level NO2 detection using AlGaAs/GaAs HEMT-based gas sensor with controlling gate and a PbS quantum dots sensitization layer. Experiment The HEMT structures in this paper were grown by molecular beam epitaxy (MBE) on GaAs substrate [3]. It was composed of an undoped 300 nm thick GaAs buffer layer, 15 nm thick In0.2Ga0.8As channel layer, 4 nm thick Al0.3Ga0.7As spacer layer, Si δ-doping layer, 25 nm thick Al0.3Ga0.7As barrier layer, and 30 nm thick GaAs cap layer. The sheet electron concentration of the HEMT was 2.3 × 1012 cm−2 with a mobility of 5.0 × 103 cm2V−1s−1 at 300 K.The sensing materials, PbS CQDs, were prepared by wet chemical synthesis technique according to previously paper [4], and the PbS quantum dots sensitization layer was formed as a sensing receptor on the exposed Au gate electrode using an electrohydrodynamic jet printer (HWK Co. Ltd., China).The CQDs capped with abundant oleic acid and oleylamine have stable dispersibility, a certain viscosity in the solvent and excellent solution processability, which makes it readily capable of being integrated with the electrohydrodynamic jet printing process at room temperature. The principle is to apply a high voltage power supply between the conductive nozzle (first electrode) and the conductive substrate (second electrode) and use a strong electric field force between nozzle and the substrate to pull the liquid out of the nozzle to form a droplet.Gas sensing characteristics were measured in a vacuum chamber probe station. The gas mixed in the mixing chamber flowed through the inlet of the chamber and out through the outlet. The flow rates of the gases were controlled by mass flow controllers (MFCs). Gas pressure and humidity in the probe station chamber remained constant for stable gas measurement. A series of electrical measurements of the fabricated sensors were carried out using the probe station and a semiconductor parameter analyzer (B1500A, Agilent Technologies). And the sensor response was defined as R=|Ig-I0|/I0, the I0 and Ig is the source to drain current in air and target gas atmosphere, respectively. Results and Conclusions The HEMT-type sensor showed high responsibility and excellent repeatability towards ppm level NO2. In this paper, extremely low concentration of the NO2 (0~25 ppm) was introduced, which shows a high response of 36.1% towards 25 ppm NO2 at room temperature, much higher than reported results [5-7], which even operated at a high temperature over 300 oC.In summary, through gate sensitization, the HEMT shows high sensitivity for ppm level NO2 detection at room temperature, the sensing performance can be both attributed to the receptor function of PbS quantum dots and the transducer function of HEMT. And the results of this paper will pave our future way for multiple target gas detection with in one chip.

The Functionalization of Low Dimensional Materials for a Multi-Functional Gas Sensor Platform

Presently, most space missions rely on large, heavy, and high-power instrumentation such as mass spectrometers for chemical analysis on planetary bodies. The weight of these payloads is prohibitive to mission cost, and ultimately hinders scientific advancement. This hindrance has driven us to develop a multi-functional gas sensor platform based on the additive manufacturing of low-dimensional materials. The discovery of low-dimensional materials such as graphene and carbon nanotubes (CNTs) has instigated a push to apply these materials in device design. The unique electrical and physical properties of these materials coupled to their high surface area to volume ratio make them outstanding candidates as extremely sensitive gas sensing elements for both chemiresistive and field effect transistor (FET) based devices. The detection of gases using low-dimensional materials as sensing elements relies on change in the resistance of the sensing element associated with electron donation or extraction by the gas to be detected. For most low-dimensional materials, this mechanism is not especially selective. This lack of selectivity necessitates the functionalization of said materials with catalytically appropriate functional units to promote device selectivity while maintaining the high sensitivity of the low-dimensional materials. We will present our efforts on the functionalization of chemiresistive and FET gas sensors using CNTs, graphene and transition metal dichalcogenides with both physical vapor deposition and solution phase approaches. This functionalization will ultimately allow for the fabrication of an array of gas sensors with each sensor demonstrating varied selectivity for the gases of interest. Our functional group choice, process optimization and ultimately sensor performance will be demonstrated.

Organic field-effect transistor gas sensor based on GO/PMMA hybrid dielectric for the enhancement of sensitivity and selectivity to ammonia

Abstract Organic field-effect transistor (OFET) based ammonia gas sensors were fabricated by incorporating a simple solution processed hybrid dielectric, which consisting of poly(methyl methacrylate) (PMMA) and Graphene Oxide (GO) sheets. By carefully optimizing the proportion of GO sheets in the dielectric, a remarkable improvement of sensing performance was obtained when exposed to various NH3 concentrations. Compared with those with pure PMMA dielectric, the sensitivity of OFET sensors with hybrid dielectric had two orders of magnitude enhancement from 1.4% to 30%. The GO/PMMA hybrid dielectric based OFET also shows good selectivity for NH3 against H2S, SO2, and NO2. By analyzing the hybrid dielectric and the 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-pentacene) film through utilizing fourier transform infrared spectroscopy, X-ray diffraction and atomic force microscope, the enhanced sensing performance was attributed to the preferable interaction between functional groups on GO sheets and NH3 gas molecules. The improved sensing performance by the combination of GO and PMMA also suggests the possibility of proper dielectric functionality engineering for the further fabrication of OFET based gas sensors with high performance.

MEMS based highly sensitive dual FET gas sensor using graphene decorated Pd-Ag alloy nanoparticles for H2 detection

A low power, dual-gate field-effect transistor (FET) hydrogen gas sensor with graphene decorated Pd-Ag for hydrogen sensing applications was developed. The FET hydrogen sensor was integrated with a graphene-Pd-Ag-gate FET (GPA-FET) as hydrogen sensor coupled with Pt-gate FET as a reference sensor on a single sensor platform. The sensing gate electrode was modified with graphene by an e-spray technique followed by Pd-Ag DC/MF sputtering. Morphological and structural properties were studied by FESEM and Raman spectroscopy. FEM simulations were performed to confirm the uniform temperature control at the sensing gate electrode. The GPA-FET showed a high sensing response to hydrogen gas at the temperature of 25~254.5 °C. The as-proposed FET H2 sensor showed the fast response time and recovery time of 16 s, 14 s, respectively at the operating temperature of 245 °C. The variation in drain current was positively related with increased working temperature and hydrogen concentration. The proposed dual-gate FET gas sensor in this study has potential applications in various fields, such as electronic noses and automobiles, owing to its low-power consumption, easy integration, good thermal stability and enhanced hydrogen sensing properties.

Effect of varying gate distance on the threshold voltage shift in carbon nanotube field effect transistor gas sensors

Suspended individual carbon nanotubes show great promise in use as gas sensors, as they are not only highly sensitive and selective, but can be operated at a few μW of power consumption. This work reports on a novel architecture and process flow to reduce the voltage range needed for a full sensor characterization to the values given by modern technology. The developed fast and flexible fabrication run yields CNTFET devices with varying gate distances, improving gate coupling up to 25 times to previous own studies. Devices with long gate distances (dg=1.84μm) show a 3.2-times improved signal to noise ratio (voltage shift upon gas adsorption over signal variation) when compared to short gate distance devices (dg=0.24μm).

Selectivity of MoS2 gas sensors based on a time constant spectrum method

In this report, MoS2 field-effect transistor gas sensors were fabricated and demonstrated to selectively sense and distinguish different gas species. The sensing behaviors of three individual gas species including O2, water vapor, and ethanol were first characterized. The transient drain current responses after the gate voltage induced gas adsorption/desorption were then recorded and decomposed into multiple exponential terms with different time constants, which are indicators of specific gas species adsorbed on MoS2 surface. Using this time constant spectrum method, selective sensing among O2, water vapor and ethanol was demonstrated. It provides a simple and practical approach for MoS2 field-effect transistor gas sensors to selectively sense various gas species.

Performance of LTCC embedded SiC gas sensors

A novel approach to encapsulation/packaging of SiC field effect transistor gas sensors for high temperature applications, such as exhaust and fuel gas emissions monitoring, based on direct co-firing of sensor devices and Low-Temperature Co-fired Ceramics (LTCC) has been investigated. Structural (SEM, EDX, XPS), electrical (I/V, C/V) as well as gas sensing characterization of packaged devices has shown that the “one-step” packaging process forms a hermetic package with retained transducer functionality and gas sensing characteristics without the need for any separate die attachment, (wire) bonding, and/or sealing of the package. Long-term stability testing at elevated temperatures of packaged devices has also shown promising results.

New generation SiC based field effect transistor gas sensors

With the advances in SiC processing and high temperature packaging technology over the past few years as well as the accumulation of knowledge regarding the sensing characteristics of different gate metal/insulator material combinations for different gaseous substances SiC based field effect high temperature sensors are moving towards commercial maturity. The route towards commercialization has, however, also led to the necessity of making new considerations regarding the basic transducer design and operation. The focus of this paper is thus the investigation of some basic transducer related parameters’ influence on sensor device performance, e.g. sensitivity and long-term stability, and characteristics to exemplify the importance of taking design, processing and operation parameters into account when developing field effect sensor devices for commercial applications.Two different types of devices, enhancement and depletion type MISFET sensors, with different gate dimensions and two different gate metallisations, Pt and Ir, have been processed. I/V-characteristics have been obtained under exposure to various concentrations of H2, NH3, CO and O2 and different bias conditions and the influence of gate dimensions and bias conditions on the sensitivity and dynamic range investigated. The long-term stability has also been studied and compared between different devices and bias conditions for conceptually different gas compositions. The results show that the type of basic transducer device, its design and mode of operation has a large influence on sensor performance. Depletion type devices offer better possibilities for tuning of sensitivity and dynamic range as well as improved long-term stability properties, whereas enhancement type devices require much less control of the processing to ensure good repeatability and yield. Some results have also been verified for two possible applications of SiC based field effect sensors, ammonia slip monitoring for the control of SCR/SNCR and combustion control in domestic/district heating facilities.

A new reducing agent to prepare single-layer, high-quality reduced graphene oxide for device applications

We report on a novel, efficient, and one-step approach to prepare single-layer reduced graphene oxide (RGO) suspensions and films using hydroxylamine hydrochloride. The effective chemical reduction of GO was evidenced by a significant increase in the C/O ratio and five orders of magnitude decrease in the GO resistance. Field-effect transistor gas sensors were fabricated using as-produced RGO sheets and the resulting sensor exhibited a fast response and a high sensitivity to low-concentration target gases at room temperature.

Modeling of porous silicon junction field effect transistor gas sensors: Insight into NO2 interaction

In this paper a lumped parameter electrical model for porous silicon junction field effect transistor (PSJFET) gas sensors is presented and experimentally validated. The PSJFET is an integrated p-channel JFET device modified with a porous silicon layer, the latter acting as sensing element. The model is described by using an analytical closed-form expression, which quantitatively links the sensor current to the analyte concentration in the environment, and validated by using experimental data of PSJFETs exposed to both synthetic air and NO2 with concentration of 300 ppb. Best fitting of experimental data with the proposed model allows one to get quantitative information on the effect of NO2 adsorption/desorption at the PS surface on electrical PS parameters, such as its conductance and surface charge density.

Electrical characteristics of a polyaniline/silicon hybrid field-effect transistor gas sensor

The fabrication of an array of polyaniline/silicon hybrid field-effect transistors is reported. The DC electrical characteristics have been found to be similar to those of conventional enhancement-mode metal–oxide–semiconductor devices. Investigations into the capacitance-voltage characteristics, the temperature dependence of the threshold voltage and the isothermal operating point were undertaken for devices with and without the polymeric material deposited within gaps in the gate electrodes. A delay observed in the response of the drain current on application of a gate voltage is shown to be dependent on both temperature and the presence of certain gases. This effect can be used to detect reversibly nitrogen dioxide at a concentration of 8 parts per million.