Sensor device and method for detecting components in gas

Abstract

The present invention relates to a sensor device and a method for detecting a component in a gas, the sensor device comprising a planar substrate (3) defining a substrate plane (4) and a waveguide (2) for guiding an electromagnetic wave. The waveguide (2) extends in a length direction in a waveguide plane (4') parallel to the substrate plane (4) and has a width (W, w) and a height (h), wherein the ratio of the width (W, w) to the height (h) is greater than 5. The height (h) of the waveguide (2) is smaller than the wavelength of the electromagnetic wave. The waveguide (2) is supported on the substrate (3) by a support structure (5) extending from the substrate (3) to the waveguide (2) along the length direction of the waveguide (2), the support structure (5) having a width (Ws) smaller than the width (W, w) of the waveguide (2). The present invention also relates to a method for detecting a component in a gas and a method for manufacturing a sensor device (1).

Description

[0001] This application is a divisional application of an application filed on June 27, 2016, with application number 201680037187.X, and invention name “Sensor device and method for detecting components in gas”. Technical Field

[0002] The invention relates to a sensor device comprising a waveguide for guiding electromagnetic waves and to a method of detecting a component in a fluid such as a gas. background

[0003] Optical sensing using the absorption bands of various gases in the visible or infrared (IR) wavelength range is an established method. Absorption can be measured in a cavity with a reflector to achieve an effective interaction length that is longer than the physical size of the cavity. This method is limited by light losses in the reflector. For IR, the source is often a broadband incandescent lamp. To obtain spectral resolution, spectral analysis is then required. The detector can be a thermal or semiconductor based photon detector.

[0004] In order to make sensitive devices with long optical path lengths, high quality mirrors must be used, or the physical path and therefore the device size must be long. For many applications, low gas flow rates and large volumes of the gas chamber limit the response speed of the sensor.

[0005] US 2014 / 0264030 A1 describes a method and apparatus for mid-infrared sensing.

[0006] WO 2008 / 125797 A1 describes a waveguide device using evanescent wave coupling between a waveguide and a groove. SUMMARY OF THE INVENTION

[0007] The object of the present invention is to alleviate the disadvantages of the prior art. In particular, it is an object to provide a sensor device which can be small while maintaining sufficient sensitivity to detect components in a gas.

[0008] Therefore, the present invention relates to a sensor device comprising:

[0009] a planar basis defining a basis plane,

[0010] A waveguide for guiding electromagnetic waves, the waveguide extending in a length direction in a waveguide plane parallel to a substrate plane, the waveguide having a width in the waveguide plane in a direction perpendicular to the length direction and a height out of the waveguide plane in a direction perpendicular to the length direction, wherein a ratio of width to height is greater than 5,

[0011] where the height of the waveguide is smaller than the wavelength of the electromagnetic wave, and

[0012] wherein the waveguide is supported on a substrate at a support point of the waveguide by a support structure extending from the substrate to the waveguide along the length direction of the waveguide, the support structure having a width that is smaller than the width of the waveguide, and wherein the width of the waveguide varies along the length direction of the waveguide, and wherein the width of the support structure varies accordingly along the length direction of the waveguide.

[0013] Thus, a simple way of changing the size of the support structure is provided, which also enables the width of the support structure to be reduced to the extent that the support structure is removed. Thus, the support can be customized along the length of the waveguide. The gradual change in the width of the support structure also has the advantage of reducing reflections of electromagnetic waves propagating in the waveguide.

[0014] A sensor device is thereby provided which can be miniaturized while maintaining good sensitivity to detect components in a gas. The characteristics of the waveguide provide for guiding electromagnetic waves with an evanescent field outside the core of the waveguide. Due to the dimensional characteristics of the waveguide and the support, the device can be manufactured with planar microfabrication techniques with reduced optical losses. Optical losses can be reduced because the planarity of the upper surface of the waveguide can be well controlled, while losses on the lateral surfaces can be reduced due to the high width to height ratio.

[0015] The ratio of width to height may be greater than 10 or greater than 20. The width of the support structure at the support point of the waveguide may be less than half the width of the waveguide, less than 1 / 4 the width of the waveguide, or less than 1 / 10 the width of the waveguide. Preferably, the width of the support structure at the support point of the waveguide is small to reduce light loss through the support structure. The support structure may have a shape with a cross-sectional width that decreases from the support to the waveguide to make the support structure more mechanically rigid.

[0016] The waveguide may be supported along at least a first portion of the length direction, wherein the width of the waveguide and hence the support structure is reduced such that the waveguide is freely suspended along at least a second portion of the length direction.

[0017] Thus, a larger portion of the waveguide may be affected by the surrounding gas and any light losses through the support may be reduced.

[0018] A useful method for manufacturing the waveguide and the support structure is to use etching. The repeatability when etching is used is limited. Therefore, there is a limit on the minimum possible size of the support structure in the etching direction. As a method of reducing the contact area between the support structure and the waveguide, the sensor device can be arranged with multiple sections of the waveguide freely suspended along the length direction, so that multiple support columns are formed, where the distance from the center of the support column to the center of the adjacent support column varies along the length direction. By varying the center-to-center distance, unwanted constructive or destructive interference between the propagating wave and the wave reflected at the support can be avoided. The center-to-center distance of the supports can be randomized.

[0019] The apparatus may comprise means for applying a force to the freely hanging portion of the waveguide so as to deflect the waveguide.

[0020] Thus, an electromagnetic wave propagating through the waveguide can be modulated by deflection of the waveguide. The force can be provided by applying an electrical potential between the substrate and the waveguide at least at the freely suspended second portion of the waveguide so as to deflect the waveguide relative to the substrate. Alternatively, the force can be applied by thermal actuation, piezoelectric actuation, etc.

[0021] The waveguide may comprise at least one gap along the length direction of the waveguide, the at least one gap being smaller than the wavelength of the electromagnetic wave, preferably smaller than 1 / 5 or 1 / 10 of the wavelength of the electromagnetic wave.

[0022] Thus, the waveguide may be provided with a thermal barrier and / or an electrical barrier which still allows electromagnetic radiation to be transmitted with low losses. This may be used to prevent the propagation of thermal or electrical interference from one part of the waveguide to another part of the waveguide.

[0023] The apparatus may include a radiant heat source positioned to couple an electromagnetic wave from the radiant heat source into the waveguide, the radiant heat source having an extension less than 1 / 5 of a wavelength of the electromagnetic wave.

[0024] This small radiative heat source has the advantage of being able to be located within the evanescent field of the waveguide, creating a strong overlap between the near field of the emitter and the waveguide mode. Due to the small extension relative to the wavelength, it also acts as a partially polarized radiation source. This can be used to excite a preferred propagation mode in the waveguide.

[0025] In the cross section of the waveguide, the radiant heat source may be positioned within one wavelength of the electromagnetic wave from the waveguide so as to excite a preferred propagation mode in the waveguide, preferably within 1 / 5 of the wavelength of the electromagnetic wave.

[0026] The radiant heat source may be adjacent to the waveguide or wherein the radiant heat source is spaced apart from the waveguide.

[0027] The advantage of having the radiant heat source adjacent to the waveguide is that the waveguide will act to conduct the heat from the radiant source. Therefore, the excitation frequency of the excitation heat source can be high. On the other hand, spacing the radiant heat source from the waveguide can reduce the thermal mass and thus improve energy efficiency.

[0028] The sensor device may comprise a detection element positioned to couple the electromagnetic wave from the waveguide to the detection element.The detection element may be a thermal or semiconductor based photon detector.

[0029] Thus, electromagnetic waves propagating through the waveguide may be coupled from the waveguide to a detection element to detect any absorption by gas components surrounding the waveguide.

[0030] In a cross section of the waveguide, the detection element may be positioned within one wavelength of the electromagnetic wave from the waveguide in order to detect a preferred propagation mode in the waveguide, preferably within 1 / 10 of the wavelength of the electromagnetic wave.

[0031] The coupling between the preferred propagation mode in the waveguide and the detection element can thus be improved.

[0032] The detection element may abut the waveguide, thereby increasing the frequency range of detection.Alternatively, the detection element may be spaced apart from the waveguide, thereby reducing the thermal mass of the element.

[0033] The waveguide may comprise a periodic structure, preferably a structure which is periodic in the length direction of the waveguide.

[0034] Thus, the structure can act as a grating to guide a propagating electromagnetic wave in a desired direction. For example, the grating can be used to guide the electromagnetic wave in the direction of the waveguide when coupling electromagnetic energy from an excitation heat source into the waveguide. The grating can be used to guide the electromagnetic wave out of the waveguide, for example, when coupling electromagnetic energy from the waveguide to a detection element.

[0035] The periodic structure may include diffractive elements such as grooves or openings in the waveguide, variations in waveguide dimensions, material variations in the waveguide, or structures deposited onto the waveguide.

[0036] The periodic structure can act as a wavelength filter by directing light of a specific wavelength back or out of the waveguide while selectively allowing the transmission of other wavelengths.

[0037] The radiant heat source and / or the detection element may be included in the periodic structure. The detection element may have an extension less than 1 / 5 of the wavelength of the electromagnetic wave. The detection element may thus be incorporated in the periodic structure.

[0038] This can be used to increase the electromagnetic coupling between the radiant heat source and / or the detection element and the waveguide.

[0039] The waveguide may be single crystal silicon with a high refractive index and low optical losses in the wavelength range of 0.4-10 μm or even less optical losses at 1.2-7 μm. Alternatively, the waveguide may comprise other materials such as germanium, silicon germanium, silicon nitride, sapphire and diamond.

[0040] The waveguide may be made of a material of a first component, and the support may be made of a material of a second component. At the wavelength of the electromagnetic wave, the refractive index in the first material may be higher than the refractive index in the second material. The material of the first component may be, for example, single crystal silicon, and the material of the second component may be silicon dioxide.

[0041] The material of the first component may be selected independently of the material of the second component.

[0042] As mentioned above, the material of the first component may be selected from germanium, silicon germanium, silicon nitride, sapphire and diamond.

[0043] Therefore, light loss between the waveguide and the support can be reduced.

[0044] The substrate, support and waveguide can be formed by an SOI wafer including a silicon substrate, a silicon dioxide layer and a silicon device layer, wherein the silicon substrate of the SOI wafer forms the substrate of the device, the silicon dioxide layer of the SOI wafer forms the support of the device, and the silicon device layer of the SOI wafer forms the waveguide of the device.

[0045] The waveguide and the support may form a T-shaped cross-sectional structure.

[0046] Therefore, the waveguide can be supported while reducing light loss between the waveguide and the support.

[0047] The wavelength of the electromagnetic wave may be in the range of 0.4-10 μm, preferably in the range of 1.2-7 μm. More preferably, the wavelength of the electromagnetic wave is in the range of 3-7 μm. In the wavelength range of 3-7 μm, it is important to minimize the influence of the support.

[0048] Thus, electromagnetic waves may be used to detect one or more components in the material surrounding the waveguide.The material surrounding the waveguide may be, for example, a gas or a liquid.

[0049] The invention also relates to a gas sensor device comprising a sensor device as disclosed herein for detecting at least one component in a gas in contact with a waveguide. The at least one component in the gas comprises carbon monoxide, carbon dioxide, nitrous oxide, water vapor, hydrocarbons, ammonia, chlorofluorocarbons and / or CFS:s. The sensor device may optionally be a liquid sensor device comprising a sensor device as disclosed herein for detecting at least one component in a liquid in contact with a waveguide.

[0050] The present invention also relates to a method for detecting components in a gas, comprising:

[0051] Providing a sensor device as described above in this application,

[0052] providing a gas in contact with the waveguide,

[0053] Transmitting an electromagnetic wave into the first section of the waveguide,

[0054] allowing the electromagnetic wave to interact with the gas in the region of the evanescent wave of the electromagnetic wave surrounding the waveguide,

[0055] detecting the electromagnetic wave at the second portion of the waveguide, and

[0056] The components in the gas are detected based on the detected electromagnetic waves.

[0057] Thus, components in the gas can be detected even at low gas volumes and / or low gas flows.

[0058] Optionally, the invention relates to a corresponding method of detecting a component in a liquid in contact with a waveguide.

[0059] The sensor device may include a radiative heat source positioned so as to couple an electromagnetic wave from the source into a waveguide, the source having an extension less than 1 / 5 of the wavelength of the electromagnetic wave, wherein the electromagnetic wave is provided by exciting the radiative heat source with an alternating current, wherein the alternating current has a frequency above a thermal cutoff frequency of a thermal conduction and / or convection path from the source to the detector, thereby preventing propagation of the heat wave from the source to the detector while allowing propagation of the electromagnetic radiation. The heat may be conducted and / or convected not only through the waveguide but also through the substrate and even air.

[0060] The invention also relates to a method of manufacturing a sensor device as disclosed herein, comprising:

[0061] Provide chips,

[0062] Fabricating waveguides in wafers, and

[0063] The support structure is fabricated in the wafer.

[0064] By using a planar wafer of material, the sensor devices can be miniaturized and manufactured in batches in the wafer. Thus, by manufacturing a wafer with several devices at the same time, the manufacturing costs can be reduced.

[0065] The method may include:

[0066] providing a wafer including a base layer, an intermediate layer and a device layer,

[0067] Fabricating waveguides in the device layer, and

[0068] Manufacturing the support structure in the middle layer,

[0069] Wherein the base layer forms the base of the device.

[0070] Thus, the different layers provide for simple manufacturing of the different components of the device (i.e., waveguide, support structure and substrate). The different layers may be optimized for the purpose of manufacturing and / or operating the sensor device, for example materials for the device layers may be selected to have suitable optical properties, materials in the intermediate layers may be selected to have optical properties that reduce light losses through the support. Materials in the device layers and intermediate layers may be selected to have material properties with suitable manufacturing selectivity, for example suitable etching selectivity if the device is manufactured by wet or dry etching.

[0071] The waveguide may be formed in the device layer by etching, and wherein the support structure is formed in the intermediate layer by under-etching the waveguide.

[0072] Therefore, the sensor device can be manufactured by relatively simple manufacturing techniques suitable for batch processing.By depositing a protection layer or the like, the waveguide can be protected from under-etching by the etch selectivity of the material.

[0073] The wafer may be an SOI wafer including a silicon substrate, a silicon dioxide layer and a silicon device layer, wherein the silicon substrate of the SOI wafer corresponds to the substrate layer, the silicon dioxide layer of the SOI wafer corresponds to the intermediate layer, and the silicon device layer of the SOI wafer corresponds to the device layer.

[0074] Therefore, the material of the wafer is suitable for batch manufacturing and operation of the sensor device as disclosed herein. The silicon device layer has suitable optical properties in the infrared region, the intermediate silicon dioxide layer has suitable optical properties to reduce light losses, and the material provides etch selectivity, such as by etching the silicon dioxide by buffered hydrofluoric acid (BHF), wherein the etch selectivity is very high.

[0075] The waveguide may be protected from etching, and wherein the support structure is etched after fabrication of the waveguide. The waveguide may be protected from etching by an etch stop material or by doping. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Various embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0077] Figure 1 A cross-sectional view of a waveguide supported by a substrate is shown.

[0078] Figure 2 A cross-sectional view of a waveguide freely suspended above a substrate is shown.

[0079] Figure 3 A top view showing a portion of a waveguide having supported and freely hanging portions is shown.

[0080] Figure 4 is a cross-sectional view of another waveguide supported by a substrate;

[0081] Figure 5 The radiant heat source and the detection element are shown.

[0082] Figure 6 A portion of a waveguide with a periodic structure and a radiation source is shown.

[0083] 7(a) and 7(b) show two examples of gas sensor devices including a waveguide, a radiant heat source, and at least one detection element.

[0084] Figure 8 A method of detecting components in a gas is shown.

[0085] Fig. 9 A method of manufacturing a sensor device is shown.

[0086] Detailed Description of Embodiments

[0087] The invention relates to a sensor device comprising a waveguide for guiding an electromagnetic wave having a wavelength λ. The wavelength of the electromagnetic wave is in the range of 0.4-10 μm, preferably in the range of 1.2-7 μm. Figure 1 1 shows a cross section of a portion of a waveguide 2 of a sensor device 1 according to one embodiment. The device comprises a substrate 3 forming a support for the sensor device. The substrate is in the form of a planar wafer of material and defines a substrate plane 4. The waveguide is parallel to the substrate plane 4, i.e. perpendicular to the substrate plane 4. Figure 1 The cross-sectional view of the waveguide plane 4' extends in the length direction.

[0088] The waveguide has a width W in the plane of the waveguide in a direction perpendicular to the length direction and a height h out of the plane of the waveguide in a direction perpendicular to the length direction. An important feature of the waveguide is that the ratio of width to height W / h is greater than 5. Due to these dimensional characteristics, the waveguide can be manufactured from a wafer of material (such as silicon) using planar manufacturing techniques. Therefore, the major surface of the waveguide (i.e., extending over the width of the waveguide) can be made very smooth. Due to the dimensional characteristics of the waveguide, the minor surfaces of the waveguide (i.e., extending over the height of the waveguide) have a smaller impact on the optical properties of the waveguide. Due to manufacturing problems, these minor surfaces are more irregular than the major surfaces.

[0089] The waveguide 2 is supported on the substrate 3 by a support structure 5 extending from the substrate to the waveguide along the length direction of the waveguide. The support structure 5 has a width Ws at the support point of the waveguide, which is smaller than the width W of the waveguide. Therefore, it is possible to reduce the light loss through the support structure 5. In the embodiment shown, the width of the support gradually increases towards the substrate, which provides a mechanically stronger structure.

[0090] The height h of the waveguide is smaller than the wavelength λ of the electromagnetic waves the waveguide is designed to guide. Thus, a waveguide is provided which can be used to guide electromagnetic waves, with a large fraction of the energy propagating as evanescent waves and with low levels of optical losses in the waveguide.

[0091] The width of the waveguide can vary along the length of the waveguide. Figure 2 , where the waveguide is shown from above. Figure 1 The cross section shown in corresponds to plane A---A with the width W of the waveguide. By using microfabrication techniques for manufacturing equipment, such as wet etching or dry etching of materials, the width of the support varies accordingly along the length direction of the waveguide. Therefore, at another part of the waveguide, at B---B, the width of the waveguide is w, which is less than W. Then, the width Ws of the support structure 5 is reduced so that the waveguide is freely suspended. Multiple parts of the waveguide along the length direction are freely suspended, so that multiple support columns 21 are formed. Therefore, the support structure 5 includes multiple support columns 21. The distance d from the center of the support column to the center of the adjacent support column 21 (i.e., the center-to-center distance) varies along the length direction. By varying the center-to-center distance d, unwanted constructive or destructive interference between the propagating wave and the wave reflected at the support can be avoided. The center-to-center distance d between the support columns can be randomized.

[0092] exist Figure 3 In the figure, the corresponding Figure 2 The cross section of a portion of the waveguide 2 of the sensor device in section BB. The width of the waveguide 2 is w, and the height is h. When Figure 1 By comparison, the support structure 5 extending from the substrate 3 is reduced by reducing the width of the waveguide. Thus, a waveguide may be provided which is supported along at least a first portion of its length, and freely suspended along at least a second portion of its length.

[0093] In addition, Figure 3 A sensor device is shown in Figure 1, which may include means for applying a force to the freely suspended portion of the waveguide. This is shown as means for applying a voltage potential between the substrate and the freely suspended portion of the waveguide. This force may be used to deflect the waveguide, which may be used to modulate electromagnetic waves propagating through the waveguide.

[0094] like Figure 2 As further shown in FIG. 1 , the waveguide may include one or more gaps 7 along the length of the waveguide. The gap is smaller than the wavelength of the electromagnetic wave, preferably smaller than 1 / 5 of the wavelength of the electromagnetic wave. The gap may act as a barrier to heat or electricity while still providing propagation of electromagnetic waves.

[0095] like Figure 1As shown, the waveguide and the support form a T-shaped cross-sectional structure. According to one embodiment, the support structure 5 has a uniform width in the cross section of the waveguide, forming a Figure 4 T-shape shown.

[0096] exist Figure 5 , an example of a radiant heat source 10 integrated on a section of a waveguide 2. The radiant heat source comprises a wire source extending across the waveguide and connected to a pair of electrical connection pads 11 for connecting a current source. The wire has a length extending across the waveguide and a width less than 1 / 5 of the wavelength of the electromagnetic wave. The radiant heat source is positioned on the surface of the waveguide so that the electromagnetic wave from the source is coupled into the waveguide. Thus, the source is positioned within one wavelength of the electromagnetic wave from the waveguide in order to excite a preferred propagation mode in the waveguide.

[0097] In a similar manner, the sensor device comprises a detection element positioned to couple the electromagnetic wave from the waveguide to the detection element. Figure 5 Can be used to illustrate a radiant heat detection element, as the structure is similar to a radiant heat source. In a cross section of a waveguide, the detection element is positioned within one wavelength of the electromagnetic wave from the waveguide to detect a preferred propagation mode in the waveguide, preferably within 1 / 5 of the wavelength of the electromagnetic wave from the waveguide. The detection element is adjacent to the waveguide or spaced apart from the waveguide.

[0098] like Figure 6 As shown, the waveguide 2 may include a structure 8 that is periodic in the length direction of the waveguide, such as a plurality of diffractive elements in the form of cut-out openings 9 shown as having a period p. Optionally, the diffractive elements may include grooves or openings in the waveguide, changes in waveguide dimensions, changes in the material of the waveguide, or structures deposited on the waveguide. The periodic structure 8 may include a radiation source 10, and the periodic structure may be used as a grating with a period, which may be configured to guide electromagnetic energy in the length direction of the waveguide. Similarly, a detection element may be included in the periodic structure.

[0099] The material of the waveguide 2 may be single crystal silicon, which has good optical properties in the wavelength range of 0.4-10 μm, or even better optical properties at the wavelength range of 1.2-7 μm. It is envisaged that the waveguide is made of a material of a first component and the support structure 5 is made of a material of a second component. Preferably, at the wavelength of the electromagnetic wave, the refractive index in the first material is higher than the refractive index in the second material. Thus, the support structure 5 may be made, for example, of silicon dioxide, which will reduce the light loss from the waveguide to the support structure due to the difference in refractive index.

[0100] According to one example, the substrate 3, the support structure 5 and the waveguide 2 of the sensor device are formed by a silicon-on-insulator (SOI) wafer including a silicon substrate, a silicon dioxide layer and a silicon device layer. The silicon substrate of the SOI wafer forms the substrate of the device, the silicon dioxide layer of the SOI wafer forms the support structure 5 of the device, and the silicon device layer of the SOI wafer forms the waveguide of the device.

[0101] In FIG. 7( a) and FIG. 7( b), two examples of gas sensor devices including a sensor device for detecting at least one component in a gas are shown. In FIG. 7( a), the gas sensor device is used to detect a component in a gas. The sensor device includes a waveguide 2 on a support structure 5 as disclosed above, which is formed as a double helix and thus provides a very long waveguide on a small area. As an alternative, the waveguide can have a zigzag shape or other spiral shape. The sensor device also includes a radiant heat source 10 at a first portion of the waveguide and a detection element 13 on a second portion of the waveguide. The radiation source is driven by a current source 12 to generate an electromagnetic wave of a specific frequency coupled into the waveguide. The electromagnetic wave propagates along the waveguide, with most of the energy propagating as an evanescent wave in the space around the waveguide. In this space and in the region of the evanescent wave along the waveguide, any component of the gas having an absorption peak corresponding to the wavelength of the electromagnetic wave will absorb energy from the propagating wave. The amount of energy in the electromagnetic wave at the selected frequency will be detected by the detection element and will be a measure of the amount and / or presence of the component of the gas.

[0102] In Figure 7(b), a similar gas sensor device for detecting three different components of gas (Gas 1, Gas 2 and Gas 3) is shown. The gas sensor device differs from the device shown in Figure 7(a) in that the radiant heat source is configured to emit electromagnetic waves of several wavelengths corresponding to absorption peaks of more than one component of the gas. The presence (and amount) of any one of the three components of the gas (Gas 1, Gas 2 and Gas 3) in the region of the evanescent wave of the electromagnetic wave along the waveguide will be detected as absorption of energy. Each component of the gas can be detected by a dedicated detection element 13, 13', 13". The detection element can be coupled to the waveguide by a wavelength selective device (such as a grating) to tap off selected wavelengths of the propagating electromagnetic wave.

[0103] After having the sensor device as disclosed, in Figure 8800. The method 800 includes the steps of providing a sensor as disclosed herein 801, providing a gas in contact with a waveguide 802, and transmitting an electromagnetic wave into a first portion of the waveguide 803. The electromagnetic wave propagates through the waveguide with most of the electromagnetic energy propagating along the waveguide as an evanescent wave. The evanescent wave interacts 804 with the gas in the region surrounding the waveguide, which absorbs energy at a specific frequency of the electromagnetic wave. Thereafter, the electromagnetic wave is detected 805 by a detection element at a second portion of the waveguide. From the specific absorption spectrum, the component in the gas can be detected 806.

[0104] The sensor device 1 includes Figure 5 A radiant heat source 10 is shown positioned to couple electromagnetic waves from the source into the waveguide. The source has an extension less than 1 / 5 of the wavelength of the electromagnetic wave. The electromagnetic wave is provided by exciting the radiant heat source with an alternating current having a frequency above the thermal cutoff frequency of the thermal conduction and / or convection path from the source to the detector, thereby preventing the propagation of the thermal wave from the source to the detector while allowing the propagation of the electromagnetic radiation.

[0105] Components in the gas may include, for example, carbon monoxide, carbon dioxide, nitrous oxide, water vapor, hydrocarbons, ammonia and / or chlorofluorocarbons.

[0106] exist Fig. 9 A method for manufacturing a sensor device (a) is disclosed in the figure. The method includes the step (b) of providing a wafer including a substrate layer, an intermediate layer and a device layer. The wafer can be a SOI wafer including a silicon substrate, a silicon dioxide layer and a silicon device layer. A waveguide is manufactured in the device layer by photolithography and dry etching using a photoresist as an etching mask, (c) and (d). A support structure 5 is manufactured in the intermediate layer by wet isotropic etching (i.e., under-etching of the waveguide) (e). Finally, the photoresist etching mask is removed (f). Depending on the width of the waveguide, the width of the support structure 5 can be controlled, as shown on the left and right sides of the figure, and the waveguide can be freely suspended at a portion along the waveguide. The substrate layer of the wafer forms the substrate of the device. The silicon substrate of the SOI wafer corresponds to the substrate layer, the silicon dioxide layer of the SOI wafer corresponds to the intermediate layer, and the silicon device layer of the SOI wafer corresponds to the device layer.

[0107] Alternatively, the waveguide and the support structure 5 may be manufactured by manufacturing the waveguide and protecting the waveguide from etching by depositing an etch stop material. Afterwards, the support structure 5 may be etched. As another alternative, the material used to form the waveguide in the wafer may be doped to provide etch selectivity for etching the waveguide and the surrounding material.

Claims

1. A sensor device, comprising: a substrate (3) defining a substrate plane (4) and a waveguide (2) for guiding electromagnetic waves, The waveguide (2) extends in a length direction in a waveguide plane (4') parallel to the substrate plane (4), The waveguide (2) has a width (W, w) in the waveguide plane (4') in a direction perpendicular to the length direction and a height (h) out of the waveguide plane (4') in a direction perpendicular to the length direction, The sensor device comprises a support structure (5) supporting the waveguide (2) on the substrate (3), wherein the height (h) of the waveguide (2) is smaller than the wavelength of the electromagnetic wave, wherein the waveguide (2) is supported on the substrate (3) by the supporting structure (5), wherein the waveguide (2) is made of a material of a first component, and the support structure (5) is made of a material of a second component, wherein the support structure (5) comprises a plurality of support columns (21), so that the waveguide (2) is freely suspended along a plurality of sections in the length direction, and the distance from the center of one support column (21) to the center of an adjacent support column (21) varies along the length direction, and wherein the ratio of the width (W, w) to the height (h) of the waveguide (2) is greater than 5; wherein the waveguide (2) is configured to transmit the electromagnetic wave to a first portion of the waveguide (2) along its length, and wherein the waveguide (2) is configured so that during detection of a component in the fluid by the sensor device, the electromagnetic wave interacts with the fluid in a region of evanescent waves of the electromagnetic wave around the waveguide (2).

2. The sensor device according to claim 1, wherein At least a portion of the support structure has a width (Ws) at a support point of the waveguide (2) that is smaller than a width (W, w) of the waveguide (2).

3. The sensor device according to claim 1, wherein: The width (W, w) of at least a portion of the waveguide (2) varies along the length direction of the waveguide (2).

4. The sensor device according to claim 2, wherein: The width (W, w) of at least a portion of the waveguide (2) varies along the length direction of the waveguide (2).

5. The sensor device according to any one of claims 1 to 4, wherein: The width (Ws) of the support structure (5) varies along at least a portion of the length direction of the waveguide (2) corresponding to the width of the waveguide (2).

6. The sensor device according to any one of claims 1 to 4, wherein: The cross-sectional shape of at least a portion of the waveguide (2) is rectangular.

7. The sensor device according to claim 5, wherein: The cross-sectional shape of at least a portion of the waveguide (2) is rectangular.

8. The sensor device according to claim 6, wherein: The substrate (3) is made of the material of the first component.

9. The sensor device according to claim 7, wherein: The substrate (3) is made of the material of the first component.

10. The sensor device according to claim 1, wherein A portion of the support structure (5) exists between adjacent support pillars (21) of the plurality of support pillars (21) so as to allow the waveguide (2) to be freely suspended along a plurality of portions in the length direction.

11. The sensor device according to any one of claims 1 to 4 and 7 to 10, wherein: The sensor device comprises a radiant heat source (10) positioned so that electromagnetic waves from the radiant heat source (10) are coupled into the waveguide (2), the width of the radiant heat source (10) being less than 1 / 5 of one wavelength of the electromagnetic waves.

12. The sensor device according to claim 5, wherein: The sensor device comprises a radiant heat source (10) positioned so that electromagnetic waves from the radiant heat source (10) are coupled into the waveguide (2), the width of the radiant heat source (10) being less than 1 / 5 of one wavelength of the electromagnetic waves.

13. The sensor device according to claim 6, wherein: The sensor device comprises a radiant heat source (10) positioned so that electromagnetic waves from the radiant heat source (10) are coupled into the waveguide (2), the width of the radiant heat source (10) being less than 1 / 5 of one wavelength of the electromagnetic waves.

14. The sensor device according to any one of claims 1-4, 7-10 and 12-13, wherein: The sensor device comprises a detection element (13, 13', 13") which is positioned such that electromagnetic waves from the waveguide (2) are coupled to the detection element.

15. The sensor device according to claim 5, wherein: The sensor device comprises a detection element (13, 13', 13") which is positioned such that electromagnetic waves from the waveguide (2) are coupled to the detection element.

16. The sensor device according to claim 6, wherein: The sensor device comprises a detection element (13, 13', 13") which is positioned such that electromagnetic waves from the waveguide (2) are coupled to the detection element.

17. The sensor device according to claim 11, wherein: The sensor device comprises a detection element (13, 13', 13") which is positioned such that electromagnetic waves from the waveguide (2) are coupled to the detection element.

18. The sensor device according to claim 17, wherein: The waveguide (2) comprises a periodic structure (8), and the periodic structure (8) comprises a diffractive element (9).

19. The sensor device according to claim 18, wherein: The sensor device comprises the radiation heat source (10) and the detection element (13, 13', 13"), the radiation heat source (10) being positioned so that the electromagnetic waves from the radiation heat source (10) are coupled into the waveguide (2), and the detection element (13, 13', 13") being positioned so that the electromagnetic waves from the waveguide are coupled to the detection element, and wherein the radiation heat source (10) and / or the detection element are included in the periodic structure (8).

20. The sensor device according to any one of claims 1-4, 7-10, 12-13 and 15-19, wherein At the wavelength of the electromagnetic wave, the refractive index in the material of the first component is higher than the refractive index in the material of the second component.

21. The sensor device according to claim 5, wherein: At the wavelength of the electromagnetic wave, the refractive index in the material of the first component is higher than the refractive index in the material of the second component.

22. The sensor device according to claim 6, wherein: At the wavelength of the electromagnetic wave, the refractive index in the material of the first component is higher than the refractive index in the material of the second component.

23. The sensor device of claim 11, wherein: At the wavelength of the electromagnetic wave, the refractive index in the material of the first component is higher than the refractive index in the material of the second component.

24. The sensor device of claim 14, wherein: At the wavelength of the electromagnetic wave, the refractive index in the material of the first component is higher than the refractive index in the material of the second component.

25. The sensor device according to any one of claims 1-4, 7-10, 12-13, 15-19 and 21-24, wherein The substrate (3), the support structure (5) and the waveguide (2) are formed by an SOI wafer comprising a silicon substrate, a silicon dioxide layer and a silicon device layer, wherein the silicon substrate of the SOI wafer forms the substrate (3) of the sensor device, the silicon dioxide layer of the SOI wafer forms the support structure (5) of the sensor device, and the silicon device layer of the SOI wafer forms the waveguide (2) of the sensor device.

26. The sensor device of claim 5, wherein: The substrate (3), the support structure (5) and the waveguide (2) are formed by an SOI wafer comprising a silicon substrate, a silicon dioxide layer and a silicon device layer, wherein the silicon substrate of the SOI wafer forms the substrate (3) of the sensor device, the silicon dioxide layer of the SOI wafer forms the support structure (5) of the sensor device, and the silicon device layer of the SOI wafer forms the waveguide (2) of the sensor device.

27. The sensor device of claim 6, wherein: The substrate (3), the support structure (5) and the waveguide (2) are formed by an SOI wafer comprising a silicon substrate, a silicon dioxide layer and a silicon device layer, wherein the silicon substrate of the SOI wafer forms the substrate (3) of the sensor device, the silicon dioxide layer of the SOI wafer forms the support structure (5) of the sensor device, and the silicon device layer of the SOI wafer forms the waveguide (2) of the sensor device.

28. The sensor device of claim 11, wherein: The substrate (3), the support structure (5) and the waveguide (2) are formed by an SOI wafer comprising a silicon substrate, a silicon dioxide layer and a silicon device layer, wherein the silicon substrate of the SOI wafer forms the substrate (3) of the sensor device, the silicon dioxide layer of the SOI wafer forms the support structure (5) of the sensor device, and the silicon device layer of the SOI wafer forms the waveguide (2) of the sensor device.

29. The sensor device of claim 14, wherein: The substrate (3), the support structure (5) and the waveguide (2) are formed by an SOI wafer comprising a silicon substrate, a silicon dioxide layer and a silicon device layer, wherein the silicon substrate of the SOI wafer forms the substrate (3) of the sensor device, the silicon dioxide layer of the SOI wafer forms the support structure (5) of the sensor device, and the silicon device layer of the SOI wafer forms the waveguide (2) of the sensor device.

30. The sensor device of claim 20, wherein: The substrate (3), the support structure (5) and the waveguide (2) are formed by an SOI wafer comprising a silicon substrate, a silicon dioxide layer and a silicon device layer, wherein the silicon substrate of the SOI wafer forms the substrate (3) of the sensor device, the silicon dioxide layer of the SOI wafer forms the support structure (5) of the sensor device, and the silicon device layer of the SOI wafer forms the waveguide (2) of the sensor device.

31. A gas sensor device comprising a sensor device according to any one of claims 1 to 30 for detecting at least one component in a fluid, wherein: The at least one component in the fluid includes carbon monoxide, carbon dioxide, nitrous oxide, water vapor, hydrocarbons, ammonia, chlorofluorocarbons and / or CFS:s.

32. A method for detecting a component in a fluid, comprising: providing (801) a sensor device according to any one of claims 1 to 30, providing (802) a fluid in contact with the waveguide (2), transmitting (803) an electromagnetic wave to a first portion of said waveguide (2), allowing the electromagnetic wave to interact (804) with a fluid in the region of the evanescent wave of the electromagnetic wave around the waveguide (2), The electromagnetic wave is detected (805) at a second portion of the waveguide (2), and components in the fluid are detected (806) based on the detected electromagnetic wave.

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