Abstract
A field effect transistor, FET, gas sensor device (100) arranged to sense gas, and a method of sensing gas by a FET gas sensor device, are provided. The FET gas sensor device comprises at least one gate (110a, 110b), a source (120), a drain (130), and a semiconductor channel (140). The semiconductor channel and the gate(s) form a FET channel-gate coupling (150) by which an applied gate potential is arranged to control a current flowing through the semiconductor channel. The FET gas sensor device further comprises space(s) (200) arranged between the gate(s) and the semiconductor channel and configured to receive gas, whereby received gas is arranged to influence electrical property(ies) of the FET channel-gate coupling, and wherein the FET gas sensor device is arranged to sense gas based on the influenced electrical property(ies) of the FET channel-gate coupling.
Claims
1. A field effect transistor, FET, gas sensor device arranged to sense gas, comprising at least one gate, a source, a drain, a semiconductor channel arranged between the source and the drain, wherein the semiconductor channel and the at least one gate form a FET channel-gate coupling by which an applied gate potential is arranged to control a current flowing through the semiconductor channel, at least one space arranged between the at least one gate and the semiconductor channel, a substrate, wherein the at least one gate, the semiconductor channel, the at least one space, and at least one of the source and the drain, are arranged in a same plane parallel to a surface of the substrate, wherein the at least one space is configured to receive gas, and at least one layer provided on at least a portion of the semiconductor channel, wherein the at least one layer comprises a first layer comprising metal nanoparticles, wherein the first layer is arranged to interact with gas received in the at least one space, and a third layer, wherein the third layer is dielectric and is arranged to passivate a surface of the semiconductor channel, wherein the third layer is provided on at least a portion of the semiconductor channel, and the first layer is arranged on at least a portion of the third layer, wherein the at least one layer comprises a portion provided on a surface of the semiconductor channel facing a gate of the at least one gate, whereby gas, received in the at least one space, is arranged to influence at least one electrical property of the FET channel-gate coupling, and wherein the FET gas sensor device is arranged to sense gas based on the influenced at least one electrical property of the FET channel-gate coupling.
2. The FET gas sensor device according to claim 1, wherein the first layer is separated from a main conducting channel, generated in a side surface of the semiconductor channel, by the third layer.
3. The FET gas sensor device according to claim 1, wherein the first layer comprises nanoparticles of at least one metal selected from the group consisting of platinum, Pt, palladium, Pd, gold, Au, and nickel, Ni.
4. The FET gas sensor device according to claim 1, wherein the at least one layer comprises a second layer arranged on at least a portion of the first layer, wherein the second layer comprises at least one polymer and is arranged to protect the first layer from humidity.
5. The FET gas sensor device according to claim 1, wherein the third layer has a thickness in the range of 0.5 nm-10 nm.
6. The FET gas sensor device according to claim 5, wherein the third layer has a thickness in the range of 0.5 nm-5 nm.
7. The FET gas sensor device according to claim 1, wherein the semiconductor channel elongates along an axis, A, and wherein the FET gas sensor device comprises two gates arranged on opposite sides of the semiconductor channel, perpendicular to the axis, A.
8. The FET gas sensor device according to claim 1, wherein at least a portion of the semiconductor channel comprises a nanowire.
9. The FET gas sensor device according to claim 1, wherein at least one of the at least one gate, the source, the drain, and the semiconductor channel are arranged on a surface of the substrate.
10. The FET gas sensor device according to claim 9, wherein the semiconductor channel is arranged above the surface of the substrate.
11. The FET gas sensor device according to claim 1, further comprising a measuring unit configured to measure the influenced at least one electrical property of the FET channel-gate coupling, and sense gas based on the measured influenced at least one electrical property of the FET channel-gate coupling.
12. The FET gas sensor device according to claim 11, wherein the measuring unit is further configured to determine a concentration of molecular hydrogen, H.sub.2, in the gas based on the influenced at least one electrical property of the FET channel-gate coupling.
13. The FET gas sensor device according to claim 1, wherein the source, the drain, and the semiconductor channel are formed from a same layer of semiconductor material.
14. The FET gas sensor device according to claim 1, wherein the at least one space is 500 nm.
15. The FET gas sensor device according to claim 14, wherein the at least one space is 5-100 nm.
16. A method of sensing gas by a field effect transistor, FET, gas sensor device comprising at least one gate, a source, a drain, a semiconductor channel arranged between the source and the drain, wherein the semiconductor channel and the at least one gate form a FET channel-gate coupling by which a gate potential is arranged to control a current through the semiconductor channel, at least one space arranged between the at least one gate and the semiconductor channel, and a substrate, wherein the at least one gate, the semiconductor channel, the at least one space, and at least one of the source and the drain, are arranged in a same plane parallel to a surface of the substrate, wherein the FET gas sensor device further comprises at least one layer provided on at least a portion of the semiconductor channel, wherein the at least one layer comprises a first layer comprising metal nanoparticles, wherein the first layer is arranged to interact with gas received in the at least one space, and a third layer, wherein the third layer is dielectric and is arranged to passivate a surface of the semiconductor channel, wherein the third layer is provided on at least a portion of the semiconductor channel, and the first layer is arranged on at least a portion of the third layer, wherein the at least one layer comprises a portion provided on a surface of the semiconductor channel facing a gate of the at least one gate, the method comprising biasing the source and the drain with a first voltage for generating a current flowing through the semiconductor channel, biasing the gate with a second voltage and controlling the current flowing through the semiconductor channel via a FET channel-gate coupling formed by the semiconductor and the at least one gate, receiving gas in the at least one space, whereby gas, received in the at least one space, is arranged to influence at least one electrical property of the FET channel-gate coupling, sensing gas based on the influenced at least one electrical property of the FET channel-gate coupling.
17. The method according to claim 16, further comprising measuring the influenced at least one electrical property of the FET channel-gate coupling, and sensing gas based on the measured influenced at least one electrical property of the FET channel-gate coupling.
18. The method according to claim 16, further comprising providing the first layer on at least a portion of the semiconductor channel, wherein the first layer comprises nanoparticles of at least one metal selected from the group consisting of platinum, Pt, palladium, Pd, gold, Au, and nickel, Ni, measuring the current through the semiconductor channel, and determining a concentration of molecular hydrogen, H.sub.2, in the gas based on the measured current.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.
[0041] FIG. 1 schematically shows a FET gas sensor 10 according to an example of the prior art.
[0042] FIG. 2a schematically shows a FET gas sensor device according to an exemplifying embodiment of the present invention.
[0043] FIGS. 2b-d schematically show cross sections of a FET gas sensor device according to exemplifying embodiments of the present invention.
[0044] FIG. 3a schematically shows a FET gas sensor device according to an exemplifying embodiment of the present invention.
[0045] FIG. 3b schematically show cross sections of a FET gas sensor device according to exemplifying embodiments of the present invention.
[0046] FIG. 4a schematically shows a FET gas sensor device according to an exemplifying embodiment of the present invention.
[0047] FIG. 4b schematically show cross sections of a FET gas sensor device according to exemplifying embodiments of the present invention.
[0048] FIG. 5a schematically shows a FET gas sensor device according to an exemplifying embodiment of the present invention.
[0049] FIG. 5b schematically show cross sections of a FET gas sensor device according to exemplifying embodiments of the present invention.
[0050] FIG. 6 schematically shows a flow chart of a method according to an exemplifying embodiment of the present invention.
[0051] FIGS. 7a and 7b schematically show the performance of a FET gas sensor device according to exemplifying embodiments of the present invention.
DETAILED DESCRIPTION
[0052] FIG. 1 schematically shows a FET gas sensor 10 according to an example of the prior art. Gas sensing is very important for security and environmental monitoring. Hydrogen sensing is taken as an example, but other gases could be sensed as well. Hydrogen gas is highlighted as a clean fuel because only water is produced in hydrogen combustion.
[0053] Meanwhile, hydrogen gas is a flammable gas with a low explosion limit of 4% by volume in air. Hence, even a relatively low-level leakage of hydrogen gas may be a serious concern for its secure production and utilization. Thereby, a sensitive and rapid sensor for gas (hydrogen) leakage detection is of high demand, and in particular for the safety needs in the development of hydrogen energy.
[0054] FETs have been explored as a device platform for hydrogen gas sensing due to their high transconductance, miniaturization, and low-energy consumption. The prior art FET gas sensor 10 as exemplified in FIG. 1 comprises a source 120, a drain 130, and a semiconductor channel 140 arranged between the source 120 and the drain 130. The source 120, the drain 130 and the semiconductor channel 140 are arranged on an insulating substrate 145. In turn, the insulating substrate 145 is arranged on a gate 110. However, a problem with FET gas sensors 10 of this kind is the low (limited) gas sensitivity and/or detection limit. Hence, it is of interest to provide alternatives to the FET-type gas sensors of the prior art in order to improve the sensitivity, response time, accuracy, and/or specificity of these gas sensors.
[0055] FIG. 2a schematically shows a FET gas sensor device 100 according to an exemplifying embodiment of the present invention. The FET gas sensor device 100, which in FIG. 1 may represent a side-gate FET gas sensor device, is arranged to sense gas, e.g. hydrogen gas, H.sub.2. The FET gas sensor device 100 comprises at least one gate 110a. In FIG. 1a, only a single gate 110a is shown, but the FET gas sensor device 100 may alternatively comprise two or more gates. The FET gas sensor device 100 further comprises a source 120, a drain 130, and a semiconductor channel 140 arranged between the source 120 and the drain 130. The semiconductor channel 140 elongates along an axis, A, and as the source 120 and the drain 130 are arranged on either ends of the semiconductor channel 140, the source 120, the drain 130 and the semiconductor channel 140 form an array of components elongating along the axis, A.
[0056] According to this example of the FET gas sensor device 100, the gate 110a, the source 120, the drain 130 and the semiconductor channel 140 are arranged on an insulating substrate 145. The gate 110a, the source 120, the drain 130 and the semiconductor channel 140 are hereby arranged in a common plane. The semiconductor channel 140 and the gate 110a form a (schematically indicated) FET channel-gate coupling 150 by which a potential applied to the gate 110a is arranged to control a current flowing through the semiconductor channel 140. The FET channel-gate coupling 150 hereby represents a correlation between the current through the semiconductor channel 140 and the gate 110a potential (voltage), forming the FET channel-gate coupling 150.
[0057] The gate 110a is physically separated from the semiconductor channel 140 in a direction, B, perpendicular to the axis, A. The FET gas sensor device 100 hereby comprises at least one space 200, indicated by dashed lines, arranged between the gate 110a and the semiconductor channel 140. The space(s) 200 hereby constitute(s) a three-dimensional (3D) space, room, area, void, or the like, which is arranged or provided between the gate 110a and the semiconductor channel 140. Hence, the gate 110a is spaced apart from the semiconductor channel 140, forming a gap between the gate 110a and the semiconductor channel 140, whereby the gap is not occupied by solid material. The gap forms the gas-receiving space(s) 200 for receiving gas to be sensed. The space(s) 200 may be open to the environment to allow gas communication with the environment. Thus, gas present in the gas-receiving space(s) 200 can be replaced with new gas from the environment.
[0058] The width, w, of the space(s) 200 may be defined by the arrangement of the gate 110a from the semiconductor channel 140, i.e. the distance between the gate 110a and the semiconductor channel 140 parallel to the direction, B. The length, l, of the space(s) 200 may be defined by the length of the gate 110a and/or the semiconductor channel 140 parallel to the axis, A. The height, h, of the space(s) 200 may be defined by the height of the gate 110a and/or semiconductor channel 140 perpendicular to the axis, A, and perpendicular to the direction, B. According to the example of the FET gas sensor device 100 of FIG. 1, the space 200 provided between the gate 110a and the semiconductor channel 140, has a parallelepiped shape as indicated by the dashed lines.
[0059] The space 200 is configured to receive gas in that the FET gas sensor device 100 allows for gas to enter the space 200 between the gate 110a and the semiconductor channel 140. Gas which is received in the space 200 is arranged to influence at least one electrical property of the FET channel-gate coupling 150. The FET gas sensor device 100 is arranged to sense gas based on the influenced at least one electrical property of the FET channel-gate coupling 150. Hence, the FET gas sensor device 100 is arranged or configured to sense or detect (the) gas based on (as a function of) the electrical property(ies) of the FET channel-gate coupling 150, wherein the gas influences of affects the electrical property(ies) of the FET channel-gate coupling 150.
[0060] FIG. 2b schematically shows a cross section of a FET gas sensor device 100, along the axis, A, according to an exemplifying embodiment of the present invention. The FET gas sensor device 100 as exemplified in FIG. 2b corresponds to the FET gas sensor device 100 as exemplified in FIG. 2a, and it is referred to FIG. 2a and the associated text for an increased understanding of the features and/or functioning of the FET gas sensor device 100. In FIG. 2b, the semiconductor channel 140 and the gate 110a, which are arranged on the insulating substrate 145, are arranged at distance from each other along the direction, B, perpendicular to the axis, A. The gate 110a and the semiconductor channel 140 thereby form a space 200 between the gate 110a and the semiconductor channel 140. The distance between the semiconductor channel 140 and the gate 110a defines the width, w, of the space(s) 200, and the height, h, of the space(s) 200 is defined by the height of the semiconductor channel 140 and/or the gate 110a. The space 200 is configured to receive gas, whereby gas, received in the space 200, is arranged to influence electrical property(ies) of the FET channel-gate coupling 150. The FET gas sensor device 100 is arranged to sense gas based on the influenced electrical property(ies) of the FET channel-gate coupling 150.
[0061] The FET gas sensor device 100 as exemplified in FIG. 2b comprises a first layer (sensing layer) 300 provided on at least a portion of the semiconductor channel 140. The first layer 300, also denoted sensing layer, is arranged to interact with gas received in the space 200. The first layer 300, which may comprise at least one metal, may further comprise or consist of a film of metal(s), or comprise nanoparticles of metal(s) selected from the group consisting of platinum, Pt, palladium, Pd, gold, Au, and nickel, Ni. One or more electrical properties of the FET channel-gate coupling 150 (e.g. the semiconductor channel 140 conductance) is modulated with the gate 110a, and the first layer 300 is directly coupled to the semiconductor channel 140. The FET channel-gate coupling 150 is enhanced due to the first layer 300 being located between the semiconductor channel 140 and the gate 110a. According to one example, the presence of the gas in the gas-receiving space(s) 200 may influence the surface charge density of the first layer 300 and may influence the conduction properties of the semiconductor channel 140. According to the example of FIG. 2b, at least a portion of the first layer 300 is arranged in between the gate 110a and the semiconductor channel 140. One interaction mechanism may involve adsorption or absorption of a compound on or in the first layer 300 and change the charge distribution in layers on the semiconductor channel 140. The changes in charge distribution may be transduced to a potential signal seen by the semiconductor channel 140. According to an example, the first layer 300 may be disposed as a lining configured to at least partially enclose the space(s) 200. According to an example, at least a portion of the layer 300 is provided on a side surface of the channel. According to an example, at least a portion of the layer 300 is provided on a surface of the channel facing the space and the gate. According to another example, the first layer 300 is disposed so that it is in gas communication with gas present in the gas-receiving space 200. The minimum distance between the surface of the first layer 300 and the surface of the gate 110a is equal to or less than 500 nm. In the example of FIG. 2b, this distance is 5-100 nm, as this dimension is particularly suitable for gas-sensing purposes.
[0062] FIG. 2c schematically shows a cross section of a FET gas sensor device 100 according to an exemplifying embodiment of the present invention. The FET gas sensor device 100 as exemplified in FIG. 2c corresponds to the FET gas sensor device 100 as exemplified in FIG. 2b, and it is referred to FIG. 2b and the associated text for an increased understanding of the features and/or functioning of the FET gas sensor device 100. Compared to the FET gas sensor device 100 shown in FIG. 2b, the FET gas sensor device 100 shown in FIG. 2c further comprises a second layer 310 arranged on at least a portion of the first layer 300. Hence, the first layer 300 is provided on at least a portion of the semiconductor channel 140, and the second layer 310 is arranged on at least a portion of the first layer 300. The second layer 310 comprises at least one polymer and is arranged to protect the first layer 300 from humidity.
[0063] FIG. 2d schematically shows a cross section of a FET gas sensor device 100 according to an exemplifying embodiment of the present invention. Compared to the FET gas sensor device 100 shown in FIG. 2b, the FET gas sensor device 100 shown in FIG. 2d further comprises a third layer 320 provided on at least a portion of the semiconductor channel 140. The third layer 320, also denoted barrier layer or passivation layer, of the FET gas sensor device 100, is dielectric and is arranged to passivate a surface of the semiconductor channel 140. The third layer 320 is provided on at least a portion of the semiconductor channel 140, and the first layer 300 is arranged on at least a portion of the third layer 320. According to one example, gas molecules in the space(s) 200 may form a dipole layer at the interface between the first layer 300 and the third layer 320 and may influence the electric conduction properties of the semiconductor channel 140. According to yet another example, gas introduced in the space(s) 200 may interact with the traps at the interface between the third (dielectric) layer 320 and the semiconductor channel 140 and may influence the electrical property(ies) of the FET channel-gate coupling 150.
[0064] FIG. 2e schematically shows a cross section of a FET gas sensor device 100 according to an exemplifying embodiment of the present invention. The FET gas sensor device 100 comprises, on the semiconductor channel 140, the first layer 300 according to FIG. 2b and the associated text, the second layer 310 according to FIG. 2c and the associated text, and the third layer 320 according to FIG. 2d and the associated text.
[0065] FIG. 3a schematically shows a FET gas sensor device 100 according to an exemplifying embodiment of the present invention. The FET gas sensor device 100 as exemplified in FIG. 3a corresponds to the FET gas sensor device 100 as exemplified in FIG. 2a, and it is referred to FIG. 2a and the associated text for an increased understanding of the features and/or functioning of the FET gas sensor device 100. In FIG. 3a, at least a portion of the semiconductor channel 140 comprises a nanowire. As exemplified in FIG. 3a, the (entire) semiconductor channel 140 constitutes a nanowire, and the nanowire may for example comprise silicone, Si. The width of the nanowire parallel to the direction, B, is smaller compared to the width of the semiconductor channel 140, as shown in FIG. 2a. Here, the at least one space 200, arranged or configured to receive gas, is arranged between the at least one gate 110a and the semiconductor channel 140 comprising the nanowire.
[0066] FIG. 3b schematically shows a cross section of a FET gas sensor device according to an exemplifying embodiment of the present invention. The FET gas sensor device 100 as exemplified in FIG. 3b corresponds to the FET gas sensor device 100 as exemplified in FIG. 3a, and it is referred to FIG. 3a and the associated text for an increased understanding of the features and/or functioning of the FET gas sensor device 100. A first layer 300 is provided on at least a portion of the nanowire (semiconductor channel) 140. The first layer 300 comprises nanoparticles of metal(s), as schematically indicated by the dots, wherein the metal(s) is (are) selected from the group consisting of platinum, Pt, palladium, Pd, gold, Au, and nickel, Ni.
[0067] The FET gas sensor device 100 further comprises a third (barrier) layer 320, wherein the third layer 320 may comprise an oxide. Having a space, or distance between gate and channel, less than 500 nm, may ensure that the main conducting channel is generated in the side surface of the channel or nanowire, which is separated from the metal nanoparticles embedded in the first layer only by the third layer. In an example the oxide of the third layer is SiO.sub.2 with thickness less than 10 nm. In an example the oxide of the third layer is SiO.sub.2 with thickness less than 7 nm. In an example the oxide of the third layer is SiO.sub.2 with thickness less than 5 nm. In an example the oxide of the third layer is SiO.sub.2 with thickness less than 2 nm. In an example the oxide of the third layer is SiO.sub.2 with thickness more than 0.5 nm. In an example the oxide of the third layer is SiO.sub.2 with a thickness more than 1 nm. Having a thin third layer may allow tunneling of electrons through the third layer. In an example, electrons can tunnel between the metal nanoparticles embedded in the first layer and the semiconductor channel, thus equilibrate them. The NPs with potential energy below the Fermi-level will therefore be filled with electrons. When exposed to H.sub.2 gas, Pd NPs can react with H.sub.2 even at room temperature. The gas reaction will form new phase(s) in the NPs and generate interface dipoles between the NPs and the SiO.sub.2, which will raise the potential energy of the NPs. As a result, some filled NPs states will be lifted above the Fermi-level, and electrons in these states will be detrapped back to the semiconductor channel, thus generating the current signal. The electron trapping/detrapping processes generate direct communication between the Pd NPs-H.sub.2 reaction and the main conducting channel, thus enabling a very efficient signal transduction. FIG. 4a schematically shows a FET gas sensor device 100 according to an exemplifying embodiment of the present invention. The semiconductor channel 140 is exemplified as a (silicon, Si) nanowire according to the example of the FET gas sensor device 100 of FIG. 3a. The FET gas sensor device 100 comprises two gates 110a, 110b arranged on opposite sides of the semiconductor channel 140, perpendicular to the axis, A. Hence, each of the gates 110a, 110b is separated from the semiconductor channel 140 along the direction, B, perpendicular to the axis, A. Thus, compared to the FET gas sensor device 100 according to FIGS. 2a-e, 3a and/or 3b, disclosing (single) side gate FET gas sensor device(s) 100, the FET gas sensor device 100 in FIG. 4a represents a double side gate FET gas sensor device(s) 100. Here, two spaces 200 arranged or configured to receive gas are arranged on either side of the semiconductor channel 140, between the two gates 110a, 110b and the semiconductor channel 140.
[0068] FIG. 4b schematically shows a cross section of a FET gas sensor device 100 according to an exemplifying embodiment of the present invention. The FET gas sensor device 100 as exemplified in FIG. 4b corresponds to the FET gas sensor device 100 as exemplified in FIG. 4a, and it is referred to FIG. 4a and the associated text for an increased understanding of the features and/or functioning of the FET gas sensor device 100. A first layer 300 is provided on at least a portion of the nanowire (semiconductor channel) 140. The first layer 300 comprises nanoparticles of metal(s), as schematically indicated by the dots, wherein the metal(s) is (are) selected from the group consisting of platinum, Pt, palladium, Pd, gold, Au, and nickel, Ni. The FET gas sensor device 100 further comprises a third (barrier) layer 320, wherein the third layer 320 may comprise an oxide.
[0069] FIG. 5a schematically shows a FET gas sensor device 100 according to an exemplifying embodiment of the present invention. The FET gas sensor device 100 as exemplified in FIG. 5a corresponds to the FET gas sensor device 100 as exemplified in FIG. 4a, and it is referred to FIG. 4a and the associated text for an increased understanding of the features and/or functioning of the FET gas sensor device 100. Compared to FIG. 4a, the semiconductor channel 140 (in the form of a nanowire) is arranged above the surface of the substrate 145. Hence, the semiconductor channel 140 is suspended by the source 120 and the drain 130.
[0070] FIG. 5b schematically shows a cross section of a FET gas sensor device 100 according to an exemplifying embodiment of the present invention, showing the suspended arrangement of the semiconductor channel 140 above the surface of the substrate 145. FIG. 6 shows a flow chart of a method 500 of sensing gas by a FET gas sensor device. The FET gas sensor device comprises at least one gate, a source, a drain, and a semiconductor channel arranged between the source and the drain, wherein the semiconductor channel and the at least one gate form a FET channel-gate coupling by which a gate potential is arranged to control a current through the semiconductor channel. The FET gas sensor further comprises at least one space arranged between the at least one gate and the semiconductor channel. The method 500 comprises the step of biasing 510 the source and the drain with a first voltage for generating a current flowing through the semiconductor channel. The method further comprises the step of biasing 520 the gate with a second voltage and controlling the current flowing through the semiconductor channel via a FET channel-gate coupling formed by the semiconductor and the at least one gate. The method further comprises the step of receiving 530 gas in the at least one space, whereby gas, received in the at least one space, is arranged to influence at least one electrical property of the FET channel-gate coupling. The method further comprises the step of sensing 540 gas based on the influenced at least one electrical property of the FET channel-gate coupling.
[0071] FIG. 7a schematically shows the performance of a FET gas sensor device 100 according to an exemplifying embodiment of the present invention having a (single) side-gate FET gas sensor device 100, e.g. according to FIGS. 2a, 2b, 3a and/or 3b. In FIG. 7a, a comparison in voltage signal (Vr.sub.T(V)) as a function of time(s) is shown between a FET sensor of the prior art (as shown in FIGS. 1a, 1b) and a FET gas sensor device 100 according to the present invention. Both the prior art FET sensor and the FET gas sensor device 100 were subjected to a regular air flow. At the location of the first arrow 700, molecular hydrogen, H.sub.2, with a concentration of 2000 ppm was introduced. The voltage signal 710 of the prior art FET sensor does barely not react, while the voltage signal 720 of the FET sensor device 100 according to the invention shows significant response. At the location of the second arrow 730, air is introduced, and the graph shows the recovery behavior. The procedure is cycled several times with repeatable responses, showing significant responses to the gas for the FET gas sensor device 100 of the present invention, whereas the prior art FET sensor shows (a) minimal response(s) to the gas.
[0072] FIG. 7b schematically shows the performance of a FET gas sensor device 100 according to an exemplifying embodiment of the present invention having a single side-gate FET gas sensor device 100, e.g. according to FIGS. 2a, 2b, 3a and/or 3b, compared to a FET gas sensor device 100 according to an exemplifying embodiment of the present invention having a double side-gate FET gas sensor device 100, e.g. according to FIGS. 4a, 4b, 5a and/or 5b. At the location of the first arrow 740, molecular hydrogen, H.sub.2, with a concentration of 2000 ppm was introduced. The voltage signal 750 of the double side-gate FET gas sensor device 100 shows a more significant response compared to voltage signal 760 the single side-gate FET gas sensor device 100. At the location of the second arrow 770, air is introduced, and the graph shows the recovery behavior. The procedure is cycled several times with repeatable responses.
[0073] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, one or more of the gate(s) 110a, 110b, the semiconductor channel 140, the space(s) 200, etc., may have different shapes, dimensions and/or sizes than those depicted/described.
