FET Gas Sensor Device

Abstract

A field effect transistor (FET) gas sensor device (100) arranged to sense a gas, and a method of sensing a gas by the 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 form an FET channel-gate junction (150), and the applied gate potential is arranged to control the current flowing through the semiconductor channel by this FET channel-gate junction. The FET gas sensor device further comprises a space (200) arranged between the gate and the semiconductor channel and configured to receive the gas, whereby the received gas is arranged to affect the electrical characteristics of the FET channel-gate junction, wherein the FET gas sensor device is arranged to sense the gas based on the electrical characteristics affected by the FET channel-gate junction.

Description

Technical Field

[0001] The present invention relates to a field effect transistor (FET) gas sensor device.

Background Art

[0002] A field effect transistor (FET) can be used, inter alia, to determine gas components in a gas mixture. For example, the gate electrode of an FET can react to a gas component, thereby causing a change in the control voltage applied to the gate electrode. The occurrence of a change in the flow of current occurring between the source electrode and the drain electrode can be detected and associated with the concentration of the gas component.

[0003] This type of FET sensor can be used to detect atoms, molecules, and ions in a gas. Such sensors for gas analysis were first presented by Lundstrom (I. Lundstrom, S. Shivaraman, C. Svensson and L. Lundkvist, A hydrogen-sensitive MOS field effect transistor, Appl. Phys. Lett. 26, 55 (1975)). In this study, a metal oxide semiconductor FET (MOSFET) was used to detect hydrogen.

[0004] However, it should be noted that a general problem associated with using an FET for gas sensing is that the general architecture or structure of the FET can lead to limitations in the sensitivity to sense a gas.

[0005] Therefore, an object of the present invention is to provide an FET type sensor that can provide improved sensitivity, response time, accuracy, and / or specificity related to gas sensing.

Summary of the Invention

[0006] In order to improve the sensitivity, response time, accuracy, and / or specificity of conventional FET-type gas sensors, it is notable to provide alternatives to these gas sensors.

[0007] This and other objects are achieved by providing a FET gas sensor device and method having the features in the independent claims. Preferred embodiments are defined in the dependent claims.

[0008] Thus, according to a first aspect of the present invention, there is provided a field effect transistor (FET) gas sensor device arranged to sense a gas. The FET gas sensor device comprises at least one gate, a source, a drain, and a semiconductor channel disposed between the source and the drain. The semiconductor channel and the at least one gate form a FET channel-gate junction, and by this FET channel-gate junction, the applied gate potential is arranged to control the current flowing through the semiconductor channel. The FET gas sensor further comprises at least one space disposed between the at least one gate and the semiconductor channel. The at least one space is configured to receive a gas, whereby the gas received in the at least one space is arranged to affect at least one electrical property of the FET channel-gate junction, wherein the FET gas sensor device is arranged to sense the gas based on at least one electrical property affected by the FET channel-gate junction.

[0009] According to a second aspect of the present invention, there is provided a method of sensing a gas by a field effect transistor (FET) gas sensor device. The FET gas sensor device comprises at least one gate, a source, a drain, and a semiconductor channel disposed between the source and the drain, wherein the semiconductor channel and the at least one gate form an FET channel-gate junction, and by this FET channel-gate junction, the gate potential is arranged to control the current flowing through the semiconductor channel. The FET gas sensor further comprises at least one space disposed between the at least one gate and the semiconductor channel. The method comprises biasing the source and the drain at a first voltage to generate a current flowing through the semiconductor channel. The method further comprises biasing the gate at a second voltage and controlling the current flowing through the semiconductor channel by an FET channel-gate junction formed by the semiconductor and the at least one gate. The method further comprises receiving a gas in the at least one space, whereby the gas received in the at least one space is arranged to affect at least one electrical property of the FET channel-gate junction. The method further comprises sensing the gas based on at least one electrical property affected by the FET channel-gate junction.

[0010] Thus, the present invention is based on the concept and idea of providing an FET gas sensor device having one or more such spaces between the gate and the semiconductor channel such that the gas receiving space is directly coupled to the FET channel-gate junction. By the arrangement of the gas receiving space between the gate and the semiconductor channel, the gas to be sensed can be received or injected between the gate and the semiconductor channel during sensing. The presence of the gas between the gate and the semiconductor channel in the space as provided enhances the ability of the semiconductor channel of the FET gas sensor device to respond to the gas. In other words, the gas received in the space interacts with and / or couples to the FET channel-gate junction. As a result, the FET gas sensor device improves the sensitivity, response time, accuracy, and / or specificity of gas sensing.

[0011] The present invention is advantageous in that the arrangement of the gate and the semiconductor channel in the same (common) plane (e.g., on the same side (surface) of the substrate) leads to an effective response of the FET gas sensor device to the gas received in the space between the gate and the semiconductor channel. Since the space is directly coupled to the FET channel-gate junction, the present invention is more efficient in gas sensing ability compared to prior art FET sensors, in particular, prior art back-gate type FET sensors where the gate and the semiconductor are arranged in different planes (e.g., on both sides (surfaces) of the substrate). These types of FET sensors have been observed to have a relatively weak capacitive coupling with the semiconductor channel. In clear contrast, the arrangement of the FET gas sensor device of the present invention achieves a strong coupling with the FET channel-gate junction. The architecture or structure of the FET gas sensor device of the present invention enables direct coupling and / or transmission with the semiconductor channel, thereby greatly enhancing the gas sensitivity of the FET gas sensor device.

[0012] The present invention is further advantageous in that the structure and / or arrangement of the FET gas sensor device has high mutual conductance, miniaturization, and / or low energy consumption.

[0013] An electric field effect transistor (FET) gas sensor device arranged to sense gas is provided. Here, "gas" means substantially any gas, particularly hydrogen gas (H2). The FET gas sensor device comprises at least one gate, a source, a drain, and a semiconductor channel disposed between the source and the drain. The electrical potential of the gate communicates with the channel of the semiconductor material, and the voltage bias applied between the source and the drain biases the current to flow between the source and the drain. These FET components and their operation are known to those skilled in the art, and thus it will be understood that any further description thereof is omitted. The semiconductor channel and at least one gate form an FET channel-gate junction, and this FET channel-gate junction is arranged such that the applied gate potential controls the current flowing through the semiconductor channel. Therefore, since the electric field in the semiconductor channel changes by biasing the gate with a voltage, the term "FET channel-gate junction" can be described as representing the correlation between the current flowing through the channel and the gate potential (voltage) that forms the FET channel-gate junction. The FET gas sensor device further comprises at least one space disposed between at least one gate and the semiconductor channel. Here, the term "space" means a three-dimensional (3D) (air) gap, space, margin, region, void, etc. disposed or provided between the gate and the semiconductor channel. In other words, since the gate and the semiconductor are physically separated within the FET gas sensor device, the space is provided between the gate and the semiconductor channel.

[0014] At least one space of the FET gas sensor device is configured to receive gas. Thus, the FET gas sensor device allows gas to enter the space between the gate and the semiconductor channel. The gas received within at least one space is arranged to affect at least one electrical property of the FET channel-gate junction. Thus, in the case where gas is received (enters) into the space between the gate and the semiconductor channel of the FET gas sensor device, the electrical properties of the FET channel-gate junction can be affected or acted upon by the presence of the gas in the space. The FET gas sensor device is arranged to sense gas based on at least one electrical property affected by the FET channel-gate junction. Thus, the FET gas sensor device is arranged or configured to sense or detect gas based on (as a function of) the electrical properties of the FET channel-gate junction, where the gas affects or acts upon the electrical properties of the FET channel-gate junction.

[0015] According to one embodiment of the present invention, at least one gate, a semiconductor channel, at least one space, and at least one of a source and a drain may be arranged in the same plane. Therefore, the gate, the semiconductor channel, the space, and the source and / or drain of the FET gas sensor device are arranged in the same (common) plane. The arrangement of the FET gas sensor device components in the same common plane leads to a particularly effective response of the FET gas sensor device to the gas received in the space between the gate and the semiconductor channel. This architecture or structure of the FET gas sensor device of the present invention enables direct coupling and / or transmission with the semiconductor channel, thereby greatly enhancing the gas sensitivity of the FET gas sensor device. Therefore, the source, the drain, and the channel are arranged in the same planar configuration. Also, at least one gate, at least one air gap, and the channel are arranged in the same planar configuration. Preferably, at least one gate, the space, the channel, and at least one of the source or the drain are arranged in the same planar configuration. Preferably, at least one gate, the space, the channel, the source, and the gate are arranged in the same planar configuration. Therefore, at least one gate, the space, the channel, the source, and the gate are arranged in a common plane. Preferably, two gates, two spaces, the channel, the source, and the gate are arranged in the same planar configuration. Therefore, two gates, two spaces, the channel, the source, and the gate are arranged in a common plane.

[0016] According to one embodiment of the present invention, the FET gas sensor device further comprises a substrate, wherein at least one gate, a semiconductor channel, at least one space, and at least one of the source and the drain are arranged in a common plane parallel to the surface of the substrate. The arrangement of the FET gas sensor device components in the same common plane parallel to the surface of the substrate enables very efficient manufacturing of the device and requires fewer manufacturing steps. Such an arrangement also provides the possibility of defining the size of the space in the processing of the FET gas sensor device, wherein the size of the space is 500 nm or less, which is particularly suitable for gas sensing purposes.

[0017] According to one embodiment of the present invention, the FET gas sensor device may further comprise at least one layer provided on at least a part of the semiconductor channel, wherein the at least one layer comprises a first layer arranged to interact with a gas received in the at least one space. The term "layer" herein means a (relatively thin) layer, coating, cover, film, etc. Thus, the FET gas sensor may comprise one or more layers, coatings, covers, films, etc. provided on at least a part of the semiconductor channel. This embodiment is advantageous in that the layer can improve one or more gas sensing characteristics of the FET gas sensor device.

[0018] At least one layer may comprise a first layer arranged to interact with a gas received within at least one space. In other words, the first layer (which may also be referred to as a sensing layer) is configured or arranged to interact with a gas received within the space. The first (sensing) layer here contacts a gas received within at least one space between the gate and the semiconductor channel. The gas received within the space may interact with the first layer, and the gas may thereby affect at least one electrical property of the FET channel-gate junction. In other words, the interaction between the first layer and the gas couples to the FET channel-gate junction, thereby modulating the potential (voltage) emitted from the gate and sensed by the semiconductor channel. The gas received or injected into the space may interact with the first layer and change the electrical properties of the FET channel-gate junction. As a result, the FET gas sensor device is arranged to sense the gas based on the electrical properties affected by the FET channel-gate junction, and thereby this effect is enhanced by the first layer. According to one example, the first layer may be configured to perform an enhanced interaction with one or more target compounds in the gas (compared to other constituents of the gas). It should be noted that the differentiated interaction of the first layer with various specific target compounds may enable a more specific sensing or detection of the target compounds.

[0019] According to one embodiment of the present invention, at least one layer comprises a portion provided on the surface of the semiconductor channel facing the gate. By disposing the first layer on the surface of the channel facing the gate, the coupling between the gate, the sensing layer, and the semiconductor channel can be improved, which may provide an improvement in sensitivity. In one embodiment, the side surface of the semiconductor channel faces the gate, and the first layer is disposed on this side surface. Thus, the first layer is disposed between the gate / space and the semiconductor channel, enabling a direct coupling.

[0020] According to one embodiment of the present invention, at least one layer includes a first portion provided on the surface of a channel facing one gate and a second portion provided on the surface of a channel facing a second gate. According to one example, the first layer includes a portion provided on the surface of a channel that is in the same plane as the gate, the space, the channel, the source, and the drain.

[0021] According to one embodiment of the present invention, the first layer may include at least one metal. Thus, the first layer may include or even consist of one or more metals. This embodiment is advantageous in that a metal first layer can further enhance the gas sensitivity of the FET gas sensor device.

[0022] According to one embodiment of the present invention, the first layer includes one of at least one metal film, metal nanoparticles (NPs), and at least one metal nanoparticle selected from the group consisting of platinum (Pt), palladium (Pd), gold (Au), and nickel (Ni). Thus, the first layer may include or even consist of one or more (relatively thin) metal films, or the first layer may include metal nanoparticles of platinum (Pt), palladium (Pd), gold (Au), and / or nickel (Ni). "Nanoparticles" means particles having a small size of less than about 100 nm, preferably less than 20 nm. This embodiment is advantageous in that the metal film or nanoparticles of the first layer are particularly suitable for the gas sensing property of the FET gas sensor device. The nanoparticles may be designed to have a desired size that enables enhanced interaction with specific gas substances. This embodiment is particularly advantageous in that the mentioned metal nanoparticles act as a catalyst for molecular hydrogen (H2) so as to react and penetrate the first layer towards the interface between the sensing layer and the semiconductor channel. The nanoparticles may include alloy or oxide nanoparticles.

[0023] According to one embodiment of the present invention, at least one layer may comprise a second layer disposed on at least a part of the first layer, wherein the second layer comprises at least one polymer and is disposed to protect the first layer from moisture. Thus, the FET gas sensor may comprise, or consist of, a second layer comprising one or more polymers, wherein this second layer is disposed at least partially on the first layer to protect the first layer from moisture.

[0024] According to one embodiment of the present invention, at least one layer may comprise a third layer, the third layer being a dielectric and disposed to passivate the surface of the semiconductor channel. Thus, the FET gas sensor may comprise a third dielectric layer configured or disposed to passivate the surface of the semiconductor channel. The term "passivation" here means protection, shielding, etc. The third layer, which may also be referred to as a barrier layer, may be configured to protect the semiconductor channel from degradation by gas. According to one example, the third (barrier) layer may comprise, or even consist of, an oxide. According to one example, the third layer may comprise at least one of an oxide (silicon dioxide, SiO2, hafnium oxide, HfO x , aluminum oxide, AlO X ) and a nitride. The third layer may be, for example, an electrical insulator.

[0025] According to one embodiment of the present invention, the third layer may be provided on at least a part of the semiconductor channel, and the first layer may be disposed on at least a part of the third layer. Thus, the third (barrier) layer is disposed on the semiconductor channel, and the first (sensing) layer is disposed on the third (barrier) layer. According to one example, the third layer may comprise the first layer.

[0026] According to an embodiment of the present invention, the third layer may have a thickness in the range of 0.5 nm to 10 nm. Thus, the third layer may be relatively thin. By having a space or distance of less than 500 nm, for example, between the gate and the semiconductor channel, a main conduction channel can be surely generated within the side surface of the semiconductor channel or nanowire separated only by the first layer to the third layer. The relatively thin third layer according to this embodiment may enable tunneling of electrons through the third layer. In one example, electrons can tunnel between the first layer (metal NPs embedded therein) and the semiconductor channel, and thus balance them. Therefore, NPs having a potential energy below the Fermi level are filled with electrons. When exposed to H2 gas, Pd NPs can react with H2 even at room temperature. This gas reaction forms a new phase within the NPs, generates an interfacial dipole between the NPs and SiO2, thereby raising the potential energy of the NPs. As a result, some filled NP states are lifted above the Fermi level, and electrons in these states are detrapped to generate a current signal and returned to the semiconductor channel. The electron trap / detrapping process generates, for example, a direct communication between the Pd NP-H2 reaction and the main conduction channel, thus enabling a very efficient signal transmission.

[0027] According to an embodiment of the present invention, the third layer may have a thickness in the range of 0.5 nm to 5 nm. Since the (very) thin third layer leads to a more efficient signal transmission, this embodiment is particularly advantageous with respect to the tunneling effect as described above.

[0028] According to one embodiment of the present invention, the semiconductor channel may be elongated along an axis (A), where the FET gas sensor device comprises two gates arranged on both sides of the semiconductor channel perpendicular to the axis (A). This embodiment is advantageous in that providing two gates can enhance the FET channel - gate coupling, which can lead to a higher sensitivity to the gas received and / or present in the space between the gate and the semiconductor channel. Therefore, according to this embodiment, the FET gas sensor device is provided with a dual - side - gate architecture that can further enhance the gas sensitivity as compared to a single - side - gate architecture with a single gate. According to one embodiment of the present invention, the two gates, source, drain, channel, and space are arranged parallel to and on the surface of a substrate in a common plane.

[0029] According to one embodiment of the present invention, at least a part of the semiconductor channel may comprise a nanowire. The term "nanowire" here means that the semiconductor channel is preferably in the form of a thin wire with a diameter less than 100 nm in cross - section. This embodiment is advantageous in that a nanowire having a relatively small cross - section (i.e., a relatively small cross - sectional area of the semiconductor channel) can improve the coupling between the semiconductor channel and, when provided, a first layer. In the case where a first layer is provided, at least a part of the first layer may be disposed on the nanowire by way of example. Further, the semiconductor channel may be a 1D nanowire (channel), where the 1D nanowire has a particularly strong electrical coupling with the first layer.

[0030] According to one embodiment of the present invention, the FET gas sensor device may further comprise a substrate, where at least one of the at least one gate, source, drain, and semiconductor channel is disposed on the surface of the substrate. Thus, the gate, source, drain, and / or semiconductor channel are disposed on the same surface (i.e., the same side) of the substrate. The term substrate here means a substrate for the mechanical and / or electrical support of the components disposed thereon. The substrate may be insulating.

[0031] According to an embodiment of the present invention, the semiconductor channel may be disposed above the surface of the substrate. Thus, the semiconductor channel may be suspended, and this arrangement may be referred to as a "floating (semiconductor) channel". This embodiment is advantageous in that the FET gas sensor device achieves further improved thermal management. For example, in the case of providing an insulating substrate, the heat dissipation from the semiconductor channel (for example, in the form of a (1D) nanowire) to the insulating substrate is significantly reduced. Thereby, the heat from the Joule effect of the current in the semiconductor channel is accumulated in the semiconductor channel, and the semiconductor channel (and the first layer if provided) is heated. This increase in temperature can accelerate the reaction of the FET gas sensor device, and thus can improve the sensitivity and / or response time of the FET gas sensor device.

[0032] According to an embodiment of the present invention, the FET gas sensor device may further include a measurement unit configured to measure at least one electrical property affected by the FET channel-gate coupling and sense a gas based on the at least one measured electrical property affected by the FET channel-gate coupling. Here, the "measurement unit" means any unit, device, arrangement, component, etc. arranged or configured to measure an electrical property affected by the FET channel-gate coupling. This embodiment is advantageous in that the measurement unit can efficiently and accurately measure the electrical property affected by the FET channel-gate coupling. As a result, the FET gas sensor device can sense and / or detect the gas more efficiently and accurately.

[0033] According to an embodiment of the present invention, the measurement unit may be further configured to determine the concentration of molecular hydrogen (H2) in the gas based on at least one electrical property affected by the FET channel-gate coupling. This embodiment is advantageous in that the FET gas sensor device can sense and / or detect molecular hydrogen (H2).

[0034] According to one embodiment of the present invention, the source, the drain, and the semiconductor channel may be formed from the same layer of semiconductor material. Thus, the source, the drain, and the (structure of the) semiconductor channel of the FET gas sensor device are formed from the same (common) layer of semiconductor material. By forming the source, the drain, and the channel by patterning from a thin film of the same layer of material, very efficient manufacture of the device may be made possible. The formation of these FET gas sensor device components from the same semiconductor material may be carried out, for example, by lithographic patterning followed by dry etching.

[0035] According to one embodiment of the present invention, at least one space is 500 nm or less. Thus, the space arranged between at least one gate of the FET gas sensor device and the semiconductor channel is smaller than or equal to 500 nm.

[0036] According to one embodiment of the present invention, the FET gas sensor device is configured to passively or actively induce a gas flow through at least one space of the FET gas sensor device. The FET gas sensor device may include any unit, device, etc. for driving the gas flow into and through the gas receiving space. This passive or active gas flow induction may further improve the sensitivity and / or response time sensed by the FET gas sensor device.

[0037] According to one embodiment of the second aspect of the present invention, the method may further comprise measuring at least one electrical property affected by the FET channel-gate coupling and sensing a gas based on the measured at least one electrical property affected by the FET channel-gate coupling.

[0038] According to an embodiment of the second aspect of the present invention, the method may further comprise providing a layer on at least a part of the semiconductor channel, wherein the layer comprises one of at least one metal film, metal nanoparticles, and at least one metal nanoparticle selected from the group consisting of platinum (Pt), palladium (Pd), gold (Au), and nickel (Ni). The method may further comprise measuring a current passing through the semiconductor channel and determining a concentration of molecular hydrogen (H2) in the gas based on the measured current.

[0039] Further objects, features, and advantages of the present invention will become apparent by considering the following detailed disclosure, drawings, and appended claims. Those skilled in the art will recognize that different features of the present invention may be combined to create embodiments other than those described below.

[0040] Next, this and other aspects of the present invention will be described in more detail with reference to the accompanying drawings showing embodiments of the present invention.

Brief Description of the Drawings

[0041]

Figure 1

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DETAILED DESCRIPTION OF THE INVENTION

[0042] FIG. 1 schematically shows a FET gas sensor 10 according to an example of the prior art. Gas sensing is very important for safety and environmental monitoring. Hydrogen sensing is taken as an example, but other gases may be sensed as well. Hydrogen gas is emphasized as a clean fuel because only water is produced in hydrogen combustion. On the other hand, hydrogen gas is a flammable gas with a lower explosive limit of 4% by volume in air. Therefore, even a relatively low level of leakage of hydrogen gas can be a serious concern in its safe production and use. Thereby, a highly sensitive and rapid sensor for gas (hydrogen) leakage detection is strongly demanded, especially for safety needs in the development of hydrogen energy.

[0043] FETs have been utilized 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 illustrated in FIG. 1 includes a source 120, a drain 130, and a semiconductor channel 140 disposed between the source 120 and the drain 130. The source 120, the drain 130, and the semiconductor channel 140 are disposed on an insulating substrate 145. Further, the insulating substrate 145 is disposed on a gate 110. However, a problem with this type of FET gas sensor 10 is its low (limited) gas sensitivity and / or detection limit. Therefore, it is noteworthy to provide alternatives to these gas sensors in order to improve the sensitivity, response time, accuracy, and / or specificity of prior art FET-type gas sensors.

[0044] FIG. 2a schematically shows a FET gas sensor device 100 according to an exemplary embodiment of the present invention. The FET gas sensor device 100, which may represent a side-gate FET gas sensor device in FIG. 1, is arranged to sense a gas, such as hydrogen gas (H2). The FET gas sensor device 100 includes at least one gate 110a. Although only a single one 100a is shown in FIG. 1a, the FET gas sensor device 100 may alternatively include two or more gates. The FET gas sensor device 100 further includes a source 120, a drain 130, and a semiconductor channel 140 disposed between the source 120 and the drain 130. The semiconductor channel 140 is elongated along an axis (A), and since the source 120 and the drain 130 are disposed on both sides of the semiconductor channel 140, the source 120, the drain 130, and the semiconductor channel 140 form an array of elongated components along the axis (A).

[0045] 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 disposed on the insulating substrate 145. The gate 110a, the source 120, the drain 130, and the semiconductor channel 140 are, here, disposed in a common plane. The semiconductor channel 140 and the gate 110a form a FET channel-gate junction 150 (shown schematically), and by this FET channel-gate junction, the potential applied to the gate 110a is arranged to control the current flowing through the semiconductor channel 140. The FET channel-gate junction represents, here, the correlation between the current flowing through the semiconductor channel 140, which forms the FET channel-gate junction 150, and the potential (voltage) of the gate 110a.

[0046] 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, here, comprises at least one space 200, shown by a dotted line, disposed between the gate 110a and the semiconductor channel 140. The space 200 constitutes, here, a three-dimensional (3D) space, margin, region, void, etc., disposed or provided between the gate 110a and the semiconductor channel 140. Thus, the gate 110a is spaced apart from the semiconductor channel 140 to form a gap between the gate 110a and the semiconductor channel 140, whereby the gap is not occupied by a solid material. The gap forms a gas acceptance space 200 for accepting the gas to be sensed. The space 200 may be open to the environment to enable gas communication with the environment. Therefore, the gas present in the gas acceptance space 200 can be exchanged with fresh gas from the environment.

[0047] The width, w, of the space 200 can 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 1 of the space 200 can 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 200 can be defined by the height of the gate 110a and / or the 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 in FIG. 2a, the space 200 provided between the gate 110a and the semiconductor channel 140 has a rectangular parallelepiped shape indicated by the dotted line.

[0048] The space 200 is configured to receive gas in that the FET gas sensor device 100 enables gas to enter the space 200 between the gate 110a and the semiconductor channel 140. The gas received in the space 200 is arranged to affect at least one electrical property of the FET channel-gate junction 150. The FET gas sensor device 100 is arranged to sense gas based on at least one electrical property affected by the FET channel-gate junction 150. Thus, the FET gas sensor device 100 is arranged or configured to sense or detect gas (as a function thereof) based on the electrical properties of the FET channel-gate junction 150, where the gas affects or acts on the electrical properties of the FET channel-gate junction 150.

[0049] Figure 2b schematically shows a cross-section of the FET gas sensor device 100 along axis (A) according to an exemplary embodiment of the present invention. The FET gas sensor device 100 illustrated in Figure 2b corresponds to the FET gas sensor device 100 illustrated in Figure 2a, which is referred to Figure 2a and its related documentation for an improved understanding of the features and / or functions of the FET gas sensor device 100. In Figure 2b, the semiconductor channel 140 and the gate 110a disposed on the insulating substrate 145 are spaced apart from each other along a direction B perpendicular to the axis (A). Thereby, the gate 110a and the semiconductor channel 140 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 200, and the height, h, of the space 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 the gas received within the space 200 is arranged to affect the electrical characteristics of the FET channel-gate junction 150. The FET gas sensor device 100 is arranged to sense gas based on the electrical characteristics affected by the FET channel-gate junction 150.

[0050] The FET gas sensor device 100 illustrated in FIG. 2b includes a first layer (sensing layer) 300 provided over at least a portion of the semiconductor channel 140. The first layer 300, also referred to as the sensing layer, is arranged to interact with the gas received within the space 200. The first layer 300, which may comprise at least one metal, may further comprise, or consist of, a film of the metal, or may comprise nanoparticles of a metal selected from the group consisting of platinum (Pt), palladium (Pd), gold (Au), and nickel (Ni). One or more electrical properties (e.g., the conductivity of the semiconductor channel 140) of the FET channel-gate junction 150 are modulated by the gate 110a, and the first layer 300 is directly coupled to the semiconductor channel 140. The FET channel-gate junction 150 is enhanced by the first layer 300 positioned between the semiconductor channel 140 and the gate 110a. According to one example, the presence of the gas within the gas receiving space 200 may affect the surface charge density of the first layer 300 and may also affect the conduction characteristics of the semiconductor channel 140. According to the example of FIG. 2b, at least a portion of the first layer 300 is disposed between the gate 110a and the semiconductor channel 140. One interaction mechanism may involve the adsorption or absorption of a compound on or within the first layer 300, which may change the charge distribution within the layer on the semiconductor channel 140. The change in the charge distribution may be converted into a potential signal seen by the semiconductor channel 140. According to one example, the first layer 300 may be disposed as a lining configured to at least partially enclose the space 200. According to one example, at least a portion of the layer 300 is provided on the side surface of the channel. According to one example, at least a portion of the layer 300 is provided on the surface of the channel facing the space and the gate. According to another example, the first layer 300 is disposed to be in gas communication with the gas present within 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 between 5 and 100 nm because this dimension is particularly suitable for gas sensing purposes.

[0051] Figure 2c schematically shows a cross-section of the FET gas sensor device 100 according to an exemplary embodiment of the present invention. The FET gas sensor device 100 illustrated in Figure 2c corresponds to the FET gas sensor device 100 illustrated in Figure 2b, which is referred to Figure 2b and its related documents for an improved understanding of the features and / or functions of the FET gas sensor device 100. Compared with the FET gas sensor device 100 shown in Figure 2b, the FET gas sensor device 100 shown in Figure 2c further comprises a second layer 310 disposed on at least a part of the first layer 300. Thus, the first layer 300 is provided on at least a part of the semiconductor channel 140, and the second layer 310 is disposed on at least a part of the first layer 300. The second layer 310 comprises at least one polymer and is arranged to protect the first layer 300 from moisture.

[0052] Figure 2d schematically shows a cross-section of the FET gas sensor device 100 according to an exemplary embodiment of the present invention. Compared with the FET gas sensor device 100 shown in Figure 2b, the FET gas sensor device 100 shown in Figure 2d further comprises a third layer 320 provided on at least a part of the semiconductor channel 140. The third layer 320, also shown as a barrier layer or a passivation layer of the FET gas sensor device 100, is a dielectric and is arranged to passivate the surface of the semiconductor channel 140. The third layer 320 is provided on at least a part of the semiconductor channel 140, and the first layer 300 is disposed on at least a part of the third layer 320. According to one example, gas molecules in the space 200 may form a dipole layer at the interface between the first layer 300 and the third layer 320, which may affect the electrical conduction characteristics of the semiconductor channel 140. According to yet another example, the gas introduced into the space 200 may interact with traps at the interface between the third (dielectric) layer 320 and the semiconductor channel 140, which may affect the electrical characteristics of the FET channel-gate junction 150.

[0053] Figure 2e schematically shows a cross-section of the FET gas sensor device 100 according to an exemplary embodiment of the present invention. The FET gas sensor device 100 includes, on the semiconductor channel 140, a first layer 300 according to FIG. 2b and related documents, a second layer 310 according to FIG. 2c and related documents, and a third layer 320 according to FIG. 2d and related documents.

[0054] Figure 3a schematically shows the FET gas sensor device 100 according to an exemplary embodiment of the present invention. The FET gas sensor device 100 illustrated in FIG. 3a corresponds to the FET gas sensor device 100 illustrated in FIG. 2a, which is referred to FIG. 2a and its related documents for an improved understanding of the features and / or functions of the FET gas sensor device 100. In FIG. 3a, at least a part of the semiconductor channel 140 includes nanowires. As illustrated in FIG. 3a, the semiconductor channel 140 (as a whole) constitutes a nanowire, and the nanowire may include, for example, silicon, Si. The width of the nanowire parallel to the direction B is smaller compared to the width of the semiconductor channel 140 shown in FIG. 2a. Here, at least one space 200 arranged or configured to receive gas is disposed between at least one gate 110a and the semiconductor channel 140 including nanowires.

[0055] Figure 3b schematically shows a cross-section of the FET gas sensor device according to an exemplary embodiment of the present invention. The FET gas sensor device 100 illustrated in FIG. 3b corresponds to the FET gas sensor device 100 illustrated in FIG. 3a, which is referred to FIG. 3a and its related documents for an improved understanding of the features and / or functions of the FET gas sensor device 100. The first layer 300 is provided on at least a part of the nanowire (semiconductor channel) 140. The first layer 300 includes metal nanoparticles schematically shown at points, where the metal is selected from the group consisting of platinum (Pt), palladium (Pd), gold (Au), and nickel (Ni).

[0056] The FET gas sensor device 100 further comprises a third (barrier) layer 320, where the third layer 320 may comprise an oxide. By having a space or distance of less than 500 nm between the gate and the channel, a main conduction channel can be ensured to be generated within the side surface of the channel or nanowire separated only by the third layer from the metal nanoparticles embedded in the first layer. In one example, the oxide of the third layer is SiO2 having a thickness of less than 10 nm. In one example, the oxide of the third layer is SiO2 having a thickness of less than 7 nm. In one example, the oxide of the third layer is SiO2 having a thickness of less than 5 nm. In one example, the oxide of the third layer is SiO2 having a thickness of less than 2 nm. In one example, the oxide of the third layer is SiO2 having a thickness greater than 0.5 nm. In one example, the oxide of the third layer is SiO2 having a thickness greater than 1 nm. By having a thin third layer, tunneling of electrons through the third layer can be enabled. In one example, electrons can tunnel between the metal nanoparticles embedded in the first layer and the semiconductor channel, and thus balance them. Thus, NPs having a potential energy below the Fermi level are filled with electrons. When exposed to H2 gas, Pd NPs can react with H2 even at room temperature. This gas reaction forms a new phase within the NPs, generates an interfacial dipole between the NPs and SiO2, thereby raising the potential energy of the NPs. As a result, some of the filled NP states are lifted above the Fermi level, and the electrons in these states are detrapped and returned to the semiconductor channel, thus generating a current signal. The electron trap / detrapping process creates a direct communication between the Pd NP-H2 reaction and the main conduction channel, thus enabling a very efficient signal transmission.

[0057] Figure 4a schematically shows a FET gas sensor device 100 according to an exemplary 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 includes two gates 110a, 110b disposed on both sides of the semiconductor channel 140 perpendicular to the axis (A). Thus, each of the gates 110a, 110b is separated from the semiconductor channel 140 along a direction B perpendicular to the axis (A). Therefore, compared with the FET gas sensor device 100 according to FIGS. 2a-2e, FIG. 3a, and / or FIG. 3b, which discloses a (single) side-gate FET gas sensor device 100, the FET gas sensor device 100 of FIG. 4a represents a double side-gate FET gas sensor device 100. Here, two spaces 200 arranged or configured to receive gas are disposed between the two gates 110a, 110b and the semiconductor channel 140 on both sides of the semiconductor channel 140.

[0058] Figure 4b schematically shows a cross-section of a FET gas sensor device 100 according to an exemplary embodiment of the present invention. The FET gas sensor device 100 illustrated in FIG. 4b corresponds to the FET gas sensor device 100 illustrated in FIG. 4a, which is referred to FIG. 4a and its related documents for an improved understanding of the features and / or functions of the FET gas sensor device 100. A first layer 300 is provided on at least a part of the nanowire (semiconductor channel) 140. The first layer 300 comprises metal nanoparticles schematically indicated by dots, where the metal is 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, where the third layer 320 may comprise an oxide.

[0059] FIG. 5a schematically shows a FET gas sensor device 100 according to an exemplary embodiment of the present invention. The FET gas sensor device 100 illustrated in FIG. 5a corresponds to the FET gas sensor device 100 illustrated in FIG. 4a, which is referred to FIG. 4a and its related documents for an improved understanding of the features and / or functions of the FET gas sensor device 100. Compared with FIG. 4a, the semiconductor channel 140 (in the form of a nanowire) is disposed above the surface of the substrate 145. Thus, the semiconductor channel 140 is suspended by the source 120 and the drain 130.

[0060] FIG. 5b schematically shows a cross-section of the FET gas sensor device 100 according to an exemplary embodiment of the present invention, showing the suspended arrangement of the semiconductor channel 140 above the surface of the substrate 145.

[0061] FIG. 6 shows a flowchart of a method 500 for sensing a gas by an FET gas sensor device. The FET gas sensor device includes at least one gate, a source, a drain, and a semiconductor channel disposed between the source and the drain, wherein the semiconductor channel and the at least one gate form an FET channel-gate junction, and the gate potential is arranged to control the current flowing through the semiconductor channel by this FET channel-gate junction. The FET gas sensor further includes at least one space disposed between the at least one gate and the semiconductor channel. Method 500 includes step 510 of biasing the source and the drain with a first voltage to generate a current flowing through the semiconductor channel. The method further includes step 520 of biasing the gate with a second voltage and controlling the current flowing through the semiconductor channel by the FET channel-gate junction formed by the semiconductor and the at least one gate. The method further includes step 530 of receiving a gas into the at least one space, whereby the gas received in the at least one space is arranged to affect at least one electrical property of the FET channel-gate junction. The method further includes step 540 of sensing the gas based on the at least one electrical property affected by the FET channel-gate junction.

[0062] FIG. 7a schematically shows the performance of an FET gas sensor device 100 according to an exemplary embodiment of the invention having a (single) side-gate FET gas sensor device 100, for example according to FIGS. 2a, 2b, 3a, and / or 3b. In FIG. 7a, a voltage signal (AV as a function of time T(V)) is shown between a prior art FET sensor (shown in FIGS. 1a and 1b) and a FET gas sensor device 100 according to the present invention. An air flow was periodically passed through both the prior art FET sensor and the FET gas sensor device 100. At the location of the first arrow 700, molecular hydrogen (H2) having a concentration of 2000 pm was introduced. The voltage signal 710 of the prior art FET sensor hardly reacted, while the voltage signal 720 of the FET sensor device 100 according to the present invention showed a large response. At the location of the second arrow 730, air was introduced and the graph showed a recovery behavior. This procedure was cycled multiple times with a repeatable response, and the FET gas sensor device 100 of the present invention showed a large response to the gas, while the prior art FET sensor showed only a minimal response to the gas.

[0063] FIG. 7b schematically shows the performance of a FET gas sensor device 100 according to an exemplary embodiment of the present invention having a dual-side-gate FET gas sensor device 100, such as according to FIGS. 4a, 4b, 5a, and / or 5b, compared to a FET gas sensor device 100 according to an exemplary embodiment of the present invention having a single-side-gate FET gas sensor device 100, such as according to FIGS. 2a, 2b, 3a, and / or 3b. At the location of the first arrow 740, molecular hydrogen (H2) having a concentration of 2000 ppm was introduced. The voltage signal 750 of the dual-side-gate FET gas sensor device 100 shows a larger response compared to the voltage signal 760 of the single-side-gate FET gas sensor device 100. At the location of the second arrow 770, air was introduced and the graph showed a recovery behavior. This procedure was cycled multiple times with a repeatable response.

[0064] Those skilled in the art will recognize that the present invention is not limited in any way to the preferred embodiments described above. In contrast, many modifications and variations are possible within the scope of the appended claims. For example, one or more of the gates 110a, 110b, semiconductor channel 140, space 200, etc. may have a shape, dimension, and / or size different from those shown / described.

Claims

1. A field-effect transistor (FET) gas sensor device (100) arranged to sense gas, wherein the FET gas sensor device (100) comprises: at least one gate (110a, 110b); a source (120); a drain (130); a semiconductor channel (140) disposed between the source and the drain, wherein the semiconductor channel and the at least one gate form an FET channel-gate junction (150), and the applied gate potential is arranged to control the current flowing through the semiconductor channel by means of the FET channel-gate junction; at least one space (200) disposed between the at least one gate and the semiconductor channel; and; the at least one space is configured to receive gas; the gas received in the at least one space is arranged to affect at least one electrical property of the FET channel-gate junction, and the FET gas sensor device is arranged to sense gas based on the at least one electrical property affected by the FET channel-gate junction. An FET gas sensor device.

2. The FET gas sensor device according to claim 1, 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 the same plane.

3. Further comprising a substrate (145), 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 the same plane parallel to the surface of the substrate. The FET gas sensor device according to claim 2.

4. Further comprising at least one layer (300, 310, 320) provided on at least a part of the semiconductor channel, the at least one layer comprising a first layer (300) arranged to interact with the gas received in the at least one space. The FET gas sensor device according to any one of claims 1 to 3.

5. The FET gas sensor device according to claim 4, wherein the at least one layer comprises a part provided on the surface of the semiconductor channel facing the gate.

6. The FET gas sensor device according to claim 4 or 5, wherein the first layer comprises at least one metal.

7. The first layer is at least one metal film, metal nanoparticles, and at least one metal nanoparticle selected from the group consisting of platinum (Pt), palladium (Pd), gold (Au), and nickel (Ni). The FET gas sensor device according to claim 6, comprising one of them.

8. The at least one layer comprises a second layer (310) disposed on at least a part of the first layer, the second layer comprises at least one polymer, and is disposed to protect the first layer from moisture. The FET gas sensor device according to any one of claims 4 to 7.

9. The at least one layer comprises a third layer (320), the third layer is a dielectric, and is disposed to passivate the surface of the semiconductor channel. The FET gas sensor device according to any one of claims 4 to 8.

10. The third layer is provided on at least a part of the semiconductor channel, and the first layer is disposed on at least a part of the third layer. The FET gas sensor device according to claim 9, which depends on any one of claims 4 to 8.

11. The third layer has a thickness in the range of 0.5 nm to 10 nm. The FET gas sensor device according to claim 10, which depends on any one of claims 4 to 9.

12. The third layer has a thickness in the range of 0.5 nm to 5 nm. The FET gas sensor device according to claim 11.

13. The semiconductor channel is elongated along an axis (A), and the FET gas sensor device comprises two gates (110a, 110b) disposed on both sides of the semiconductor channel perpendicular to the axis (A). The FET gas sensor device according to any one of claims 1 to 12.

14. At least a part of the semiconductor channel comprises a nanowire. The FET gas sensor device according to any one of claims 1 to 13.

15. Further comprising a substrate (145), and at least one of the at least one gate, the source, the drain, and the semiconductor channel is disposed on the surface of the substrate. The FET gas sensor device according to any one of claims 1 to 14.

16. The FET gas sensor device according to claim 15, wherein the semiconductor channel is disposed above the surface of the substrate.

17. Measuring the at least one electrical property affected by the FET channel-gate coupling, and The FET gas sensor device according to any one of claims 1 to 16, further comprising a measuring unit configured to sense a gas based on the at least one electrical property measured and affected by the FET channel-gate coupling.

18. The measurement unit is further configured to determine the concentration of molecular hydrogen (H 2 ) in the gas based on the at least one electrical property affected by the FET channel-gate coupling, the FET gas sensor device according to claim 17.

19. The FET gas sensor device according to any one of claims 1 to 18, wherein the source, the drain, and the semiconductor channel are formed from the same layer of semiconductor material.

20. The FET gas sensor device according to any one of claims 1 to 19, wherein the at least one space is 500 nm or less.

21. A method (500) of sensing a gas by means of a field effect transistor (FET) gas sensor device (100), wherein the FET gas sensor device (100) comprises at least one gate (110a, 110b), a source (120), a drain (130), a semiconductor channel (140) disposed between the source and the drain, wherein the semiconductor channel and the at least one gate form an FET channel-gate coupling (150), and the gate potential is arranged to control the current flowing through the semiconductor channel by means of the FET channel-gate coupling, and at least one space (200) disposed between the at least one gate and the semiconductor channel, the method comprising biasing the source and the drain with a first voltage to generate a current flowing through the semiconductor channel (510), biasing the gate with a second voltage to control the current flowing through the semiconductor channel by means of an FET channel-gate coupling formed by the semiconductor channel and the at least one gate (520), receiving a gas into the at least one space (530), wherein the gas received into the at least one space is arranged to affect at least one electrical property of the FET channel-gate coupling Detecting a gas based on the at least one electrical property affected by the FET channel-gate coupling (540) and A method comprising. **Claim 22** Measuring the at least one electrical property affected by the FET channel-gate coupling, and Detecting a gas based on the measured at least one electrical property affected by the FET channel-gate coupling The method according to claim 21, further comprising. **Claim 23** Providing a layer on at least a part of the semiconductor channel, where the layer is At least one metal film, Metal nanoparticles, At least one metal nanoparticle selected from the group consisting of platinum (Pt), palladium (Pd), gold (Au), and nickel (Ni) Comprising one of, Measuring the current passing through the semiconductor channel, and Determining the concentration of molecular hydrogen (H 2 ) in the gas based on the measured current The method according to claim 21 or 22, further comprising.

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