GB2597267A

GB2597267A - Thin film transistor gas sensor system

Info

Publication number: GB2597267A
Application number: GB2011065.6A
Authority: GB
Inventors: Cachelin Pascal; Per Gustav Tobjork Daniel
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2020-07-17
Filing date: 2020-07-17
Publication date: 2022-01-26
Also published as: GB202011065D0

Abstract

A gas sensor system comprising a first top-gate thin film transistor (TFT) gas sensor (100, fig 1) configured to detect a first target gas and comprising a first dielectric layer 109; a second top-gate TFT gas sensor (200, fig 1) configured to detect a second target gas and comprising a second dielectric layer 109, wherein the first dielectric layer and second dielectric layer differ in at least one of thickness and composition. The first and second dielectric layers may each comprise a polymer. These polymers may be different. The first layer may comprise a first material and the second layer may comprise a second material, these two being different. The first material may have greater polarity and polarity Hansen solubility parameter than the second material. The first material may be protic and may be substituted with a hydroxyl or amino group. The second material may be aprotic. The first target gas may be ethylene. The second target gas may be 1-methylcyclopropene (1-MCP). A method of detecting the presence or concentration of the target gases using the system is disclosed.

Description

Thin Film Transistor Gas Sensor System BACKGROUND

Embodiments of the present disclosure relate to thin film transistor gas sensors systems.

Thin film transistors (TFTs) have been previously used as gas sensors. For example, such use of thin film transistors as gas sensors is described in Feng et al, "Unencapsulated Air-stable Organic Field Effect Transistor by All Solution Processes for Low Power Vapor Sensing" Scientific Reports 6:20671 DOI: 10.1038/srep20671 and Besar et al, "Printable ammonia sensor based on organic field effect transistor", Organic Electronics, Volume 15, Issue 11, November 2014, Pages 3221-3230. In thin film transistor gas sensors, a semiconducting layer is in electrical contact with source and drain electrodes and a gate dielectric is disposed between the semiconducting layer and a gate electrode. Interaction of a target gas with the TFT gas sensor may alter the drain current of the TFT gas sensor.

Zhang et al. "Organic Field-Effect Transistors-Based Gas Sensors" Chem. Soc. Rev.. 2015. 44,2087-2107 discloses gas discrimination systems having sensory arrays of organic field effect transistors.

WO 2020/021251 discloses a top gate thin film transistor gas sensor in which die target gas may pass through the top gate and interact with a semiconducting layer of the gas sensor.

SUMMARY

In some embodiments, the present disclosure provides a gas sensor system comprising a first top gate TFT gas sensor and a second top gate TFT gas sensor having respective first and second dielectric layers. The first top gate TFT gas sensor is configured to detect a first target gas. The second top gate TFT gas sensor is configured to detect a second target gas. The first dielectric layer and second dielectric layer differ in at least one of thickness and composition.

Optionally, the first top gate TFT gas sensor and the second top gate TFT gas sensor differ only in the respective first and second dielectric layers.

Optionally, the first dielectric layer and second dielectric layer each comprise a polymer.

Optionally, the first dielectric layer comprises a first material and the second dielectric layer comprises a second material which is different from the first material.

Optionally, the first material and second material are different polymers.

Optionally, the first material has a greater polarity than the second material.

Optionally, the first material has a greater polarity Hansen solubility parameter (SP) than the second material.

Optionally, the firs( material is a protic material. Optionally the firs( material is substituted with a hydroxyl or amino group, e.g. a polymer having a repeat unit substituted with a 10 hydroxyl or amino group pendant from the polymer backbone.

Optionally, the second material is aprotic.

Optionally, the second dielectric layer does not comprise a protic material. Optionally, the second material is a perfluorinated material.

Optionally, the first dielectric layer does not comprise an aprotic material.

Optionally, the first target gas is ethylene.

Optionally, the second target gas is 1-methylcyclopropene.

Optionally, the semiconducting layer comprises an organic semiconductor.

In some embodiments, the present disclosure provides a method of detecting the presence or concentration of at least one of a first target gas and a second target gas in an environment 20 comprising: exposing a gas sensor system as described herein to the environment; measuring responses of the first and second top gate TFT gas sensors; and determining from the response the presence or concentration of at least one of the first gas and second target gas

DESCRIPTION OF THE DRAWINGS

The disclosed technology and accompanying figures describe some implementations of the disclosed technology.

Figure 1 illustrates gas sensor system containing a first top gate TFT gas sensor and a second top gate TFT gas sensor; Figure 2 illustrates a top gate, bottom contact OTFT gas sensor according to some embodiments; Figure 3 illustrates a top gate, top contact OTFT gas sensor according to some embodiments; Figure 4 is a graph of drain current vs. time upon exposure to ethylene of a top gate OTFT gas sensor containing a Teflon AF2400 dielectric layer; and Figure 5 is a graph of drain current vs. time upon exposure to 1-MCP of a top gate OTFT gas sensor containing a polyvinylphenol dielectric layer.

The drawings are not drawn to scale and have various viewpoints and perspectives. The drawings are some implementations and examples. Additionally, some components and/or operations may be separated into different blocks or combined into a single block for the purposes of discussion of some of the embodiments of the disclosed technology. Moreover, while the technology is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the technology to the particular implementations described. On the contrary, the technology is intended to cover all modifications, equivalents, and alternatives falling within the scope of the technology as defined by the appended claims.

DETAILED DESCRIPTION

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." As used herein, the terms "connected," "coupled," or any variant thereof means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, electromagnetic, or a combination thereof Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

As used herein, by a material "over" a layer is meant that the material is in direct contact with the layer or is spaced apart therefrom by one or more intervening layers.

As used herein, by a material "on" a layer is meant that the material is in direct contact with that layer.

A layer -between" two other layers as described herein may be in direct contact with each of the two layers it is between or may be spaced apart from one or both of the two other layers by one or more intervening layers.

The teachings of the technology provided herein can be applied to other systems, not necessarily the system described below. The elements and acts of the various examples described below can be combined to provide further implementations of the technology. Some alternative implementations of the technology may include not only additional elements to those implementations noted below, but also may include fewer elements.

These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. Details of the system may vary considerably in its specific implementation, while still being encompassed by the technology disclosed herein. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

To reduce the number of claims, certain aspects of the technology are presented below in certain claim forms, but the applicant contemplates the various aspects of the technology in any number of claim forms. For example, while some aspect of the technology may be recited as a computer-readable medium claim, other aspects may likewise be embodied as a computer-readable medium claim, or in other forms, such as being embodied in a meansplus-function claim.

In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

The techniques introduced here can be embodied as special-purpose hardware (e.g., circuitry), as programmable circuitry appropriately programmed with software and/or firmware, or as a combination of special-purpose and programmable circuitry. Hence, embodiments may include a machine-readable medium having stored thereon instructions which may be used to program a computer (or other electronic devices) to perform a process. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, compact disc read-only memories (CD-ROMs), magneto-optical disks, ROMs, random access memories (RAMs), erasable programmable read-only memories (EPROMs), electrically erasable programmable read-only memories (EEPROMs), magnetic or optical cards, flash memory, or other type of media / machine-readable medium suitable for storing electronic instructions. The machine-readable medium includes non-transitory medium, where non-transitory excludes propagation signals. For example, a processor can be connected to a non-transitory computer-readable medium that stores instructions for executing instructions by the processor.

The present inventors have found that sensitivity of a top gate TFT gas sensor to a gas may be increased or decreased by selecting the thickness and / or composition of the gate electrode. The present inventors have further found that sensitivity of a top gate TFT sensor to a target gas may be tuned by selecting a polarity of the dielectric according to a polarity of the target gas.

The present inventors have further found that a top gate TFT gas sensor having a dielectric layer containing a relatively non-polar material may be more sensitive to a relatively polar gas as compared to a relatively non-polar gas. Conversely, the present inventors have found that a top gate TFT sensor having a dielectric layer containing a relatively polar material may be more sensitive to a relatively polar gas as compared to a relatively non-polar gas. Use of a gas sensor system containing a top gate TFT with a relatively non-polar dielecnic material and a top gate TFT with a relatively polar dielectric material may enable differentiation between a polar and non-polar gas in an environment.

By "sensitivity" of a TFT gas sensor to a gas as used herein is meant a maximum percentage change in drain current upon exposure of the TFT gas sensor to a given concentration of the gas.

Figure 1 illustrates a gas sensor system according to some embodiments of the present disclosure.

The gas sensor system contains a first top gate TFT gas sensor 100 and a second top gate TFT gas sensor 200 wherein the first and second top gate TFT gas sensors have different dielectric layers, e.g. dielectric layers differing in at least one of thickness and composition.

Figure 1 illustrates a gas sensor system containing two top gate TFT gas sensors which differ in at least one of thickness and composition of their respective dielectric layers. In other embodiments, the gas sensor system may comprise one or more further top gate TFT gas sensors wherein each of the top gate TFT gas sensors differ in at least one of dielectric layer thickness and composition.

For simplicity, Figure 1 illustrates gas sensor system containing only one first TFT gas sensor and only one second TFT gas sensor. It will be understood that a gas sensor system as described herein may comprise a plurality of one or more of the first, second and any further top gate TFT gas sensors as described herein.

The gas senor system as described herein may be an electronic nose or e-nose system configured to detect a plurality of different gases, for example 2 or more, 5 or more or 10 or more different gases Optionally, the difference in dielectric layers is the only difference between the first and second top gate TFT gas sensors.

The dielectric layers of the first and second top gate TFT gas sensors may each have a thickness in the range of about 100-2000 nm. In some embodiments, the dielectric layers of the first and second top gate TFTs have different thicknesses, optionally at thickness of at least 100 nm. The material or materials of the dielectric layer of these embodiments may be the same or different.

In some embodiments, the dielectric layer of the first top gate TFT gas sensor contains a first dielectric material and the dielectric layer of the second top gate TFT gas sensor contains a second dielectric material which is different from the first dielectric material. Preferably, the second dielectric layer is free from the first material and the first dielectric layer is free from the second dielectric material.

Optionally, the first dielectric material has a greater polarity than the second dielectric material.

Optionally, the first dielectric material has a polarity (SP) Hansen solubility parameter which is at least 1, 3 or 5 MPal/2 greater than that of the second dielectric material.

Optionally, each of the polarity (813) hydrogen bonding OW and dispersion (3D) parameters of the first dielectric material are at least 1 MPalf2 or at least 3 or 5 greater than that of the second dielectric material.

Optionally, the first and second dielectric materials are both polymers.

Optionally the first dielectric material, e.g. a first dielectric polymer, comprises a protic substituent, e.g. and the second dielectric material, e.g. a second dielectric polymer, is nonprotic. The first dielectric polymer may be substituted with a protic group pendant from the polymer backbone.

In some embodiments, the first dielectric polymer comprises a hydroxyl group or a primary (-NW) or secondary amine substituent group pendant from the polymer backbone.

In some embodiments, the second dielectric material is a perfluorinated polymer comprising carbon-fluorine bonds and the second dielectric material does not contain a perfluorinated polymer.

Polar polymers include, without limitation, poly(vinyl phenol) (PHS), poly vmylalcohol (PVA), polyvinylpyrrolidine (PVP), and poly(vinyl halides) like PVC.

Non-polar polymers include, without limitation, poly(vinyl cinnamate) P(VCn), polystyrene (PS). polyethylene (PE) and hydrocarbon functionalised PE derivatives like polypropylene(PP), poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP), P(VDF-TrFE-CTFE), Polyethylene terephthalate (PET). Benzocyclobutane-based polymers. and perfluorinated polymers such as PTFE or copolymers comprising tetrafluoroethylene repeat units and a co-repeat unit, for example Teflon AF2400.

The polymer may be crosslinkable.

In use, the gas sensor system may he exposed to an environment containing two or more target gases. In a preferred embodiment, the first top gate TFT gas sensor contains a dielectric material which is more polar than a dielectric material of the second top gate TFT gas sensor and the target gases include a first target gas which is more polar than the second target gas.

Optionally, the first target gas has a dipole moment of greater than 0.5 Debyes, optionally greater than 0.6 or 0.8 Debyes. Optionally, the first target gas is a hydrocarbon which does not have a mirror plane bisecting a carbon-carbon bond of the hydrocarbon. In a preferred embodiment, the first target gas is 1-methylcyclopropene (1-MCP).

Optionally, the second target gas has a dipole moment of less than or equal to 0.4 Debyes, optionally less than or equal to 0.2 Debyes. Optionally, the second target gas is a hydrocarbon which has a mirror plane bisecting a carbon-carbon bond of the hydrocarbon. In a preferred embodiment, the second large( gas is ethylene.

Figure 1 illustrates a gas sensor system containing one firs( top gate TFT gas sensor 100 and one second top gate TFT gas sensor 200. In other embodiments, the gas sensor system may comprise a plurality of first top gate TFT gas sensors and / or a plurality of second top gate TFT gas sensors. In some embodiments, in use responses of only the firs( and second top gate TFT gas sensors exposed to an environment are measured. In some embodiments, in use responses of one or more further TFT gas sensors exposed to the environment are measured.

The gas sensor system may comprise one or more control TFT gas sensors to provide a baseline for measurements of the first and second top gate TFT gas sensors to take into account variables such as one or more of humidity, temperature, pressure, variation of sensor parameter measurements over time (such as variation of TFT sensor drain current over time), and gases other than a target gas or target gases in the atmosphere. One or more control TFT gas sensors may be isolated from the atmosphere, for example by encapsulation of the or each TFT control sensor, to provide a baseline measurement other than gases in the atmosphere.

The response of the TFT gas sensor to an environment may be a change which is directly proportional to a concentration of a target gas in the environment. The TFT gas sensor response to a target gas may be calibrated by measuring response of the TFT gas sensor to one or more known concentrations of the target in an environment.

The response may be a change in drain current.

A measurement module 300 configured to measure the response of the top gate TFT gas sensors of the top gate TFT gas sensor system may be in wired or wireless communication with processor (now shown) configured to determine a presence, a concentration, and / or a change in concentration, of target gases in the environment.

Each of the top gate TFT gas sensors of the gas sensor system may be supported on a common substrate and / or contained in a common housing.

In use, each top gate TFT gas sensor of the gas sensor system may be connected to a common power source, or two or more of the TFT gas sensors may be powered by different power sources.

In use, power to all of the TFT gas sensors of the gas sensor system may be controlled by a single switch or power to two or more of the TFT gas sensors may be controlled by different switches.

Figure 2 is a schematic illustration of a top gate TFT gas sensor according to some embodiments which may be a first or second top gate TFT gas sensor as descrthed herein. The top gate TFT gas sensor comprises source and drain electrodes 103, 105 respectively disposed over a substrate 101; a semiconductor layer 107 in electrical contact with the source and drain electrodes; and a dielectric layer 109 between gate electrode 111 and the semiconductor layer.

The top gate TFT of Figure 2 is a bottom contact, top gate TFT in which the semiconducting layer is disposed between the source and drain electrodes and the dielectric layer.

Figure 3 is a schematic illustration of a top gate, top contact TFT gas sensor according to some embodiments. The top gate TFT gas sensor is as described with reference to Figure 2 except that the semiconducting layer 107 is disposed between the substrate 101 and the source and drain electrodes 103, 105.

In some embodiments, the dielectric layer of a top-gate TFT gas sensor as described herein, e.g. as described with reference to Figure 2 or 3, is a gas-permeable material, preferably an organic material, e.g. a polymer.

In some embodiments, the top gate electrode of a top gate TFT gas sensor as described herein, e.g. as described with reference to Figure 2 or 3, is patterned, e.g., comprises fingers, comb like structures and/or the like, to provide channels, apertures or the like that allow passage of gas through the top gate electrode, for example as described in WO 2020/021251, the contents of which are incorporated herein by reference.

Figures 2 and 3 illustrate top-gate TFTs with a single dielectric layer. In other embodiments, a top gate TFT gas sensor as described herein may comprise one or more further dielectric layers disposed between the organic semiconducting layer and the gate electrode.

Dielectric layer deposition The dielectric material may be deposited by thermal evaporation, vacuum processing or lamination techniques as are known in the art. The dielectric material may be deposited from solution using, for example, spin coating or ink jet printing techniques and other solution deposition techniques discussed above with respect to die semiconductor layer. In the case of a top-gate OTFT gas sensor, the organic semiconductor layer should not he dissolved if the dielectric is deposited from solution.

Techniques to avoid such dissolution include: use of orthogonal solvents for example use of a solvent for deposition of the organic semiconducting layer that does not dissolve the dielectric layer in the case of a bottom gate device or vice versa in the case of a top gate device; cross linking of the dielectric layer before deposition of the organic semiconductor layer in the case of a bottom gate device; or deposition from solution of a blend of the dielectric material and the organic semiconductor followed by vertical phase separation as disclosed in, for example, L. Qin, et al., Adv. Mater. 2008, 20, 1141.

The thickness of the dielectric layer is preferably less than 2 micrometres, more preferably less than 500 nm.

Semiconducting layer The semiconducting layer of each top gate TFT gas sensor as described herein may comprise or consist of an organic or inorganic semiconductor. Preferably, the semiconducting layer comprises or consists of at least one organic semiconductor.

Organic semiconductors may be selected from conjugated non-polymeric semiconductors; polymers comprising conjugated groups in a main chain or in a side group thereof; and carbon semiconductors such as graphene and carbon nanotubes.

An organic semiconductor layer of a top gate organic TFT (OTFT) gas sensor as described 25 herein may comprise or consist of a semiconducting polymer and / or a non-polymeric organic semiconductor. The organic semiconductor layer may comprise a blend of a non-polymeric organic semiconductor and a polymer.

Exemplary organic semiconductors are disclosed in WO 2016/001095, the contents of which are incorporated herein by reference.

The organic semiconductor may be crystalline or amorphous.

The organic semiconducting layer may be deposited by any suitable technique, including evaporation and deposition from a solution comprising or consisting of one or more organic semiconducting materials and at least one solvent. Exemplary solvents include benzenes with one or more alkyl substituents, preferably one or more C t_to alkyl substituents, such as toluene and xylene; tetralin; and chloroform. Solution deposition techniques include coating and printing methods, for example spin coating dip-coating, slot-die coating, ink jet printing, gravure printing, flexographic printing and screen printing.

Inorganic semiconductors include, without limitation, n-doped silicon; p-doped silicon; compound semiconductors, for example III-V semiconductors such as GaAs or InGaAs; doped or undoped metal oxides; doped or undoped metal sulfides; doped or undoped metal selenides; and doped or undoped metal tellurides; and transition metal halides or pseudohalides, for example a fluoride, chloride, bromide, iodide, astatide, thiocyanate, selenocyanate or tellurocyanate of a transition metal, e.g. copper (I), silver (I) or cobalt.

The first or second top gate TFT gas sensor may comprise two or more semiconducting layers.

Optionally, the, or each, semiconducting layer has a thickness in the range of about 10-200 20 nm.

Electrodes The source, drain and gate electrodes may be selected from a wide range of conducting materials for example a metal, metal alloy, conductive metal compound (e.g. indium tin oxide) or conductive polymer. The source and drain electrodes may consist of a single conductive layer or may comprise two or more conductive layers. The gate electrode may consist of a single conductive layer or may comprise two or more conductive layers The gate electrode of top gate TFTs as described herein is permeable to at least one gas in the environment.

In some embodiments, the gate electrode comprises or consists of a gas-permeable material, preferably a conductive polymer. Exemplary conductive polymers include poly(ethylene dioxythiophene) (PEDOT) doped with a polyanion, e.g. poly(styrene sulfonate) (PSS) and polyaniline.

In some embodiments, the gate electrode has a pattern defining channels, apertures or die like that allow passage of gas through the top gate electrode to the dielectric layer, for example as described in WO 2020/021251, the contents of which are incorporated herein by reference. Optionally, the channels or apertures have a width of less than 200 microns.

The length of the channel defined between the source and drain electrodes of (he source and drain and gate electrodes of a top gate OTFT gas sensor as described herein may he up to 500 microns, preferably less than 200 microns, more preferably less than 100 microns.

Applications The gas sensor system and method as described herein may be used in monitoring the presence and / or concentration of one or both of ethylene and 1-MCP in a location where harvested fruit or plants are stored, such as a warehouse or store, or concentration of 1-MCP during transportation of harvested fruit or plants.

In some embodiments, the first, second and optional further top gate TFT gas sensors having different dielectric layer thicknesses or compositions as described herein are the only gas sensors of the gas sensor system described herein.

In some embodiments, the gas sensor system comprises one or more other gas sensors known to the skilled person including, without limitation, semiconductor gas sensors; photoionisation detectors; electrochemical sensors and IR sensors, pellistors, optical particle monitors, quartz crystal microbalance sensors, surface acoustic wave sensors (SAWS), cavity ring-down spectroscopy (CRDS) sensors and biosensors. Semiconductor sensors may comprise an organic semiconductor, an inorganic semiconductor or a combination thereof The organic semiconductor may be polymeric or non-polymeric.

Exemplary semiconductor sensors other than the top-gate TFT sensors described herein include bottom gate TFTs; vertical or horizontal chemiresistor sensors; and metal oxide semiconductor sensors.

In some embodiments, the gas sensor system as described herein is configured to detect only one or both of ethylene and 1-methylcyclopropene. In some embodiments, the gas sensor system as described herein is configured to detect one or more further gases.

Examples

Top gate OTFT Gas Sensor 1 Source and drain contacts were deposited onto a clean glass substrate by thermal evaporation of 3 nm Cr followed by 40nm Au through shadow masks with channel length of 1 25 p m and a channel width of 4 mm. Semiconducting Polymer 1, illustrated below, was deposited over the substrate by spin coating from a 1%w/v solution in 1,2,4-trimethylbenzene to a thickness of 40nm and dried at 100°C for 1 or 1 Omi n in air. To form the dielectric layer, the polymer dielectric Teflon 0 AF2400 was spin coated from a 2.5 %w/v solution in a 50:50 v/v blend of fluorinated solvents FC-43 and FC-770 (3M) to a 300nm thickness and dried at 80°C for 10min, after a 5 minute initial drying phase while spinning. The gate was formed by thermal evaporation of Cr (3 nm) followed by Al (200 nm) through a shadow mask to form a gate electrode having a comb structure with comb fingers of 125 microns width and gaps of 125 microns between fingers.

Semiconducting Polymer 1 Top gate OTFT Gas Sensor 2 Top gate OTFT Gas Sensor 2 was prepared as described for Top gate OTFT Gas Sensor 1 except that polyvinylphenol (10% in 2-heptanone) was used in place of Teflon AF2400.

N..S.N S S NN t

S S 50 0 F F

C12 H25 Ethylene sensitivity Gas Sensor 1 and Gas Sensor 2 were exposed to lc, gas with and without 500 parts per million (ppm) of ethylene. The responses of the sensors to the gas was determined by the percentage change in source-drain current (IDs) of the device under constant operating conditions (VD = -4V, Vc, = -4V).

With reference to Figure 4, Gas Sensor 1 showed little response upon introduction of ethylene between 22.15 hours and 22.9 hours whereas Gas Sensor 2 showed a much stronger response to exposure to ethylene between these time points.

1-MCP sensitivity Gas Sensor 1 and Gas Sensor 2 were exposed to air with and without 1 ppm of 1-MCP.

With reference to Figure 5, Gas Sensor 2 showed little response upon introduction of 1-MCP between 2.78 hours and 3.04 hours whereas Gas Sensor 1 showed a much stronger response to exposure to 1-MCP between these time points.

Claims

Claims 1. A gas sensor system comprising a first top-gate TFT gas sensor configured to detect a first target gas and comprising a first dielectric layer; a second top gate TFT gas sensor configured to detect a second target gas and comprising a second dielectric layer, wherein the first dielectric layer and second dielectric layer differ in at least one of thickness and composition.
2. The gas sensor system according to claim 1 wherein the first top gate TFT gas sensor and the second top gate TFT gas sensor differ only in the respective first and second dielectric layers.
3. The gas sensor system according to any one of the preceding claims wherein the first dielectric layer and second dielectric layer each comprise a polymer.
4. The gas sensor system according to any one of the preceding claims wherein the first dielectric layer comprises a first material and the second dielectric layer comprises a second material which is different from the first material.
5. The gas sensor system according to claim 4 wherein the first material and second material are different polymers.
6. The gas sensor system according to claim 4 or 5 wherein the first material has greater polarity than the second material.
7. The gas sensor system according to claim 6 wherein the first material has a greater polarity Hansen solubility parameter (5P) than the second material.
8. The gas sensor system according to claim 6 or 7 wherein the first material is a protic material.
9. The gas sensor system according to claim 8 wherein the first material is substituted with a hydroxyl or amino group.
10. The gas sensor system according to claim 8 or 9 wherein the second material is aprotic.
11. The gas sensor system according to claim 10 wherein the second dielectric layer does not comprise a protic material.
12. The gas sensor system according to any one of claims 6-11 wherein the second material is a perfluorinated material.
13. The gas sensor system according to any one of claims 8-12 wherein the first dielectric layer does not comprise an aprotic material.
14. The gas sensor system according to any one of the preceding claims wherein the first target gas is ethylene.
15. The gas sensor system according to any one of the preceding claims wherein the second target gas is 1-methylcyclopropene.
16. The gas sensor system according to any one of the preceding claims wherein the semiconducting layer comprises an organic semiconductor.
17. A method of detecting the presence or concentration of at least one of a first target gas and a second target gas in an environment comprising: exposing a gas sensor system according to any one of the preceding claims to the environment; measuring responses of the first and second top gate TFT gas sensors; and determining from the response the presence or concentration of at least one of the first gas and second target gas.