Optical Fiber Humidity Sensor and Forming Method

Abstract

The present invention provides an optical fiber humidity sensor and a forming method thereof, comprising: a humidity-sensitive thin film for absorbing moisture; a first support structure, with the humidity-sensitive thin film located on the first surface of the first support structure; a strain beam connected to the first support structure, capable of deforming when the strain beam is stressed; a first high-reflection film located on the second surface of the first support structure; and a second high-reflection film opposite to the first high-reflection film and aligned with the first high-reflection film, an FP cavity being formed between the first high-reflection film and the second high-reflection film, and the distance between the first high-reflection film and the second high-reflection film being the cavity length of the FP cavity. In the present invention, after the humidity-sensitive thin film absorbs moisture, the internal stress changes, resulting in the deformation of the first support structure, thereby changing the cavity length of the FP cavity, causing the wavelength of the interference light output by the FP cavity to change. By reading the wavelength of the interference light output by the FP cavity, the environmental humidity can be accurately known. The present invention can be used in any harsh environment and improves the measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and in particular to an optical fiber humidity sensor and a forming method thereof. Background Art

[0002] Environmental humidity and environmental temperature are two important factors affecting human comfort; at the same time, humidity is also an important factor affecting the reliable operation of some devices, such as high-impedance circuits, electrostatic-sensitive devices, high-voltage devices, etc.; for many materials and manufactured products, humidity is also an important factor affecting their storage and use. The detection of humidity usually adopts physical effects related to the concentration of water molecules. With the continuous improvement of the requirements for humidity measurement, the existing suction-type hygrometers can no longer meet the requirements of practical applications.

[0003] In recent years, with the development of MEMS technology, humidity sensors based on MEMS micro-nano processing technology have been widely studied and used in large quantities. The most common MEMS humidity sensors are capacitance detection type and resistance detection type. Capacitive MEMS humidity sensors usually use a humidity-sensitive material (polymer or oxide dielectric) as the dielectric layer between the upper and lower two capacitor plates, and at the same time, the upper capacitor plate is made in a porous form to allow external water molecules to fully contact and be absorbed by the humidity-sensitive dielectric layer. When the intermediate dielectric layer absorbs moisture, the dielectric constant will change, thereby causing a change in the capacitance. By converting the change amount of this capacitance into changes in voltage, frequency or digital, the information of the external humidity is finally obtained. Resistance-type humidity sensors usually utilize the phenomenon that the resistivity of some non-metallic conductors is greatly affected by environmental humidity, and deposit the humidity-sensing material on the top of the interdigital electrodes to provide a large contact area. When the upper layer material absorbs water molecules, the resistivity between the electrodes changes, and then the humidity information is obtained by circuit measurement.

[0004] However, in some occasions with electromagnetic interference, power supply difficulties or where electrical sensors cannot be used, the use of existing capacitive MEMS humidity sensors will be restricted. Therefore, a humidity sensor is needed to enable the humidity sensor to be used in harsh environments and at the same time have the characteristics of high measurement accuracy. Summary of the Invention

[0005] The purpose of the present invention is to provide an optical fiber humidity sensor and a forming method thereof, which can be used in harsh environments and can improve the measurement accuracy.

[0006] To achieve the above purpose, the present invention provides an optical fiber humidity sensor, comprising:

[0007] A humidity-sensitive thin film for absorbing moisture in the atmosphere;

[0008] The first support structure includes opposite first and second surfaces, and the humidity-sensitive thin film is located on the first surface of the first support structure;

[0009] The strain beam is connected to the first support structure, and the strain beam can deform when a force is applied;

[0010] The first high-reflection film is located on the second surface of the first support structure;

[0011] The second high-reflection film is opposite to and aligned with the first high-reflection film. An FP cavity is formed between the first high-reflection film and the second high-reflection film, and the distance between the first high-reflection film and the second high-reflection film is the cavity length of the FP cavity; and

[0012] The second support structure includes opposite first and second surfaces, and the second high-reflection film is located on the first surface of the second support structure.

[0013] Optionally, in the optical fiber humidity sensor, a frame is further included for supporting the strain beam. The frame is located between the strain beam and the second support structure, and one end of the frame is connected to the strain beam and the other end is connected to the second support structure.

[0014] Optionally, in the optical fiber humidity sensor, the surface of the strain beam and the surface of the first support structure are in the same plane.

[0015] Optionally, in the optical fiber humidity sensor, the strain beam is in a bent strip shape, with one end connected to the support structure and the other end connected to the frame.

[0016] Optionally, in the optical fiber humidity sensor, the cross-section of the first support beam structure is square, and at least one strain beam is connected to each side.

[0017] Optionally, in the optical fiber humidity sensor, an antireflection film located on the second surface of the second support structure and a third support structure are further included. The third support structure has a second through hole, the radial direction of the second through hole is perpendicular to the second surface of the second support structure, and the antireflection film is located on the second surface of the second support structure exposed by the second through hole.

[0018] Optionally, in the optical fiber humidity sensor, the first high-reflection film includes a composite dielectric film or a metal film.

[0019] Optionally, in the optical fiber humidity sensor, both the second high-reflection film and the antireflection film include composite dielectric films.

[0020] Optionally, in the fiber optic humidity sensor, it further includes a fiber optic structure for receiving the light output from the FP cavity. The fiber optic structure is located within the second through hole and is aligned with the anti-reflection film.

[0021] Correspondingly, the present invention also provides a method for forming a fiber optic humidity sensor, including:

[0022] Providing an SOI wafer, the SOI wafer includes a bottom layer of silicon and an intermediate oxide layer and a top layer of silicon stacked in sequence on the bottom layer of silicon. Partially etching the top layer of silicon and the intermediate oxide layer to form a first through hole located between the patterned top layer of silicon and the patterned intermediate oxide layer. The surface of the bottom layer of silicon is exposed by the first through hole, and the patterned top layer of silicon and the patterned intermediate oxide layer serve as a frame;

[0023] Forming a first high-reflection film on the surface of the bottom layer of silicon exposed by the first through hole;

[0024] Providing a glass sheet and forming a second high-reflection film on one surface of the glass sheet;

[0025] Aligning the first high-reflection film with the second high-reflection film and bonding the patterned top layer of silicon to the glass sheet. The glass sheet serves as a second support structure;

[0026] Etching the bottom layer of silicon to form a first support structure and a strain beam; and

[0027] Forming a humidity-sensitive thin film on the surface of the first support structure.

[0028] Optionally, in the method for forming a fiber optic humidity sensor, after bonding the patterned top layer of silicon to the glass sheet, it further includes:

[0029] Removing a part of the thickness of the bottom layer of silicon.

[0030] Optionally, in the method for forming a fiber optic humidity sensor, after forming a humidity-sensitive thin film on the surface of the first support structure, it further includes:

[0031] Forming an anti-reflection film on the second surface of the second support structure.

[0032] In the fiber optic humidity sensor and the forming method provided by the present invention, after the humidity-sensitive thin film absorbs moisture, the internal stress changes, causing the first support structure to deform, which in turn causes the strain beam to deform, thereby changing the cavity length of the FP cavity. The change amount of the cavity length is proportional to the environmental humidity, and finally causes the wavelength of the interference light output by the FP cavity to change. By reading the wavelength of the interference light output by the FP cavity, the environmental humidity can be accurately known. The fiber optic humidity sensor of the present invention can be used in any harsh environment and improves the measurement accuracy. Brief Description of the Drawings

[0033] Figure 1 is a schematic structural diagram of the fiber optic humidity sensor according to an embodiment of the present invention;

[0034] Figure 2 is a top view of the fiber optic humidity sensor according to an embodiment of the present invention;

[0035] Figure 3 is a flowchart of the method for forming the fiber optic humidity sensor according to an embodiment of the present invention;

[0036] Figure 4 is a schematic structural diagram of the fiber optic humidity sensor after etching the top silicon layer according to an embodiment of the present invention;

[0037] Figure 5 is a schematic structural diagram of the fiber optic humidity sensor after etching the intermediate oxide layer according to an embodiment of the present invention;

[0038] Figure 6 is a schematic structural diagram of the fiber optic humidity sensor after forming the first high - reflection film according to an embodiment of the present invention;

[0039] Figure 7 is a schematic structural diagram of the fiber optic humidity sensor after forming the second high - reflection film according to an embodiment of the present invention;

[0040] Figure 8 is a schematic structural diagram of the fiber optic humidity sensor after bonding the top silicon layer and the glass sheet according to an embodiment of the present invention;

[0041] Figure 9 is a schematic structural diagram of the fiber optic humidity sensor after thinning the bottom silicon layer according to an embodiment of the present invention;

[0042] Figure 10 is a schematic structural diagram of the fiber optic humidity sensor after forming the anti - reflection film according to an embodiment of the present invention;

[0043] Figure 11 is a schematic structural diagram of the fiber optic humidity sensor after forming the first support structure according to an embodiment of the present invention;

[0044] Figure 12 is a schematic structural diagram of the fiber optic humidity sensor after forming the humidity - sensitive thin film according to an embodiment of the present invention;

[0045] Figure 13 is a schematic structural diagram of the fiber optic humidity sensor after forming the third support structure according to an embodiment of the present invention;

[0046] In the figure: 110 - humidity-sensitive film, 120 - first support structure, 130 - strain beam, 140 - first high-reflection film, 150 - second high-reflection film, 160 - second support structure, 161 - glass sheet, 170 - frame, 171 - bottom silicon, 172 - intermediate oxide layer, 173 - top silicon, 174 - patterned top silicon, 175 - patterned intermediate oxide layer, 180 - antireflection film, 190 - third support structure. Detailed implementation manners

[0047] The following will describe in more detail the detailed implementation manners of the present invention in conjunction with the schematic diagrams. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the drawings are all in a very simplified form and use non-precise scales, only for the purpose of facilitating and clearly assisting in explaining the objectives of the embodiments of the present invention.

[0048] In the following text, terms such as "first" and "second" are used to distinguish between similar elements and are not necessarily used to describe a specific order or time sequence. It is understood that, under appropriate circumstances, these terms used in this way can be replaced. Similarly, if the method described herein includes a series of steps, and the order of these steps presented herein is not necessarily the only order in which these steps can be executed, and some of the described steps can be omitted and / or some other steps not described herein can be added to the method.

[0049] Please refer to Figure 1 and Figure 2 , the present invention provides an optical fiber humidity sensor, comprising:

[0050] A humidity-sensitive film 110 for absorbing moisture in the atmosphere;

[0051] A first support structure 120 including an opposite first surface and a second surface, and the humidity-sensitive film 110 is located on the first surface of the first support structure 120;

[0052] A strain beam 130 connected to the first support structure 120, and the strain beam 130 can generate deformation when stressed;

[0053] A first high-reflection film 140 located on the second surface of the first support structure 120;

[0054] A second high-reflection film 150 opposite to and aligned with the first high-reflection film 140, an FP cavity is formed between the first high-reflection film 140 and the second high-reflection film 150, and the distance between the first high-reflection film 140 and the second high-reflection film 150 is the cavity length of the FP cavity; and

[0055] A second support structure 160 including an opposite first surface and a second surface, and the second high-reflection film 150 is located on the first surface of the second support structure 160.

[0056] Among them, there is a certain distance between the first high - reflection film 140 and the second high - reflection film 150, and the axes of the first high - reflection film 140 and the second high - reflection film 150 coincide.

[0057] Furthermore, the fiber optic humidity sensor further includes a frame 170 for supporting the strain beam 130. The frame 170 is located between the strain beam 130 and the second support structure 160. One end of the frame 170 is connected to the strain beam 130, and the other end of the frame 170 is connected to the second support structure 160.

[0058] Preferably, the surface of the strain beam 130 and the surface of the first support structure 120 are in the same plane. The thickness of the strain beam 130 is the same as the thickness of the first support structure 120. The strain beam 130 is in a bent strip shape. The strain beam 130 is in a bent strip shape, with one end connected to the first support structure 120 and the other end connected to the frame 170. Please refer to Figure 2 , the strain beam 130 is made into a strip shape, and then the strip is bent to form a shape similar to an S - shape. The strip is narrow in width, so that the strain beam 130 occupies a small area and is more sensitive. There are multiple strain beams 130, and at least one strain beam 130 is connected to each side of the first support structure 120. The cross - section of the first support structure 120 is square, and at least one strain beam 130 is connected to each side. The frame 170 encloses the first support structure 120 and the strain beam 130 in the middle. The cross - section of the frame 170 is annular, and one end of the strain beam 130 is connected to the first support structure 120, and the other end is connected to the inner side of the ring of the frame 170.

[0059] Furthermore, the fiber optic humidity sensor further includes: an anti - reflection film 180 and a third support structure 190 located on the second surface of the second support structure 160. The third support structure 190 has a second through - hole, and the radial direction of the second through - hole is perpendicular to the second surface of the second support structure 160. The anti - reflection film 180 is located on the second surface of the second support structure 160 exposed by the second through - hole. The axis of the anti - reflection film 180 coincides with the axis of the second high - reflection film 150.

[0060] Preferably, the first high - reflection film 140 includes a composite dielectric film or a metal film. The material of the metal film includes gold or aluminum. The composite dielectric film includes one of multi - layer alternately arranged silicon oxide and tantalum oxide, multi - layer alternately arranged silicon oxide and titanium oxide, and multi - layer alternately arranged silicon oxide and nitrogen oxide; the second high - reflection film 150 includes a composite dielectric film, and the composite dielectric film includes one of multi - layer alternately arranged silicon oxide and tantalum oxide, multi - layer alternately arranged silicon oxide and titanium oxide, and multi - layer alternately arranged silicon oxide and nitrogen oxide. The anti - reflection film 180 includes a composite dielectric film, and the composite dielectric film includes one of multi - layer alternately arranged silicon oxide and tantalum oxide, multi - layer alternately arranged silicon oxide and titanium oxide, and multi - layer alternately arranged silicon oxide and nitrogen oxide.

[0061] Further, the fiber optic humidity sensor further includes a fiber optic structure (not shown in the figure) for receiving the light output by the antireflection film 180. The fiber optic structure is located in the second through hole and is aligned with the antireflection film 180. The third support structure 190 not only supports the second support structure 160, but also can support the light ray structure. After the humidity-sensitive film absorbs moisture, its mass changes, causing the strain beam 130 to deform, thereby changing the cavity length of the FP cavity. The change amount of the cavity length is proportional to the ambient humidity, and finally causes the wavelength of the interference light output by the FP cavity to change. The interference light output by the FP cavity passes through the antireflection film 180 and reaches the fiber optic structure. By reading the wavelength of the interference light output by the FP cavity, the fiber optic structure can accurately know the ambient humidity.

[0062] Please refer to Figure 3 , the present invention provides a method for forming a fiber optic humidity sensor, including:

[0063] S11: Provide an SOI wafer, partially etch the top layer silicon and the intermediate oxide layer to form a first through hole between the patterned top layer silicon and the patterned intermediate oxide layer. The surface of the bottom layer silicon is exposed by the first through hole, and the patterned top layer silicon and the patterned intermediate oxide layer serve as a framework;

[0064] S12: Form a first high-reflection film on the surface of the bottom layer silicon exposed by the first through hole;

[0065] S13: Provide a glass sheet and form a second high-reflection film on one surface of the glass sheet;

[0066] S14: Align the first high-reflection film with the second high-reflection film, and bond the patterned top layer silicon to the glass sheet. The glass sheet serves as the second support structure;

[0067] S15: Etch the bottom layer silicon to form a first support structure and a strain beam; and

[0068] S16: Form a humidity-sensitive film on the surface of the first support structure.

[0069] Further, after bonding the patterned top layer silicon to the glass sheet, the method for forming the fiber optic humidity sensor further includes:

[0070] Remove a part of the thickness of the bottom layer silicon.

[0071] Further, after forming the humidity-sensitive film on the surface of the first support structure, the method for forming the fiber optic humidity sensor further includes:

[0072] Form an antireflection film on the second surface of the second support structure.

[0073] Further, after forming the antireflection film, the method for forming the fiber optic humidity sensor further includes:

[0074] A third support structure is formed on the second surface of the second support structure. The third support structure has a second through hole, and an antireflection film is exposed in the second through hole.

[0075] Further, after forming the antireflection film, the method for forming the fiber optic humidity sensor further includes:

[0076] A fiber optic structure is formed in the second through hole, and the fiber optic structure is aligned with the antireflection film.

[0077] For the specific forming method, please refer to Figure 4 and Figure 5 , first, provide an SOI wafer. The SOI wafer includes a bottom layer of silicon 171, an intermediate oxide layer 172, and a top layer of silicon 173 that are sequentially stacked on the bottom layer of silicon 171. After lithography processing on the top layer of silicon 173, etching is performed using the Deep RIE process to form a square hole in the axial direction of the patterned top layer of silicon 174. The square hole exposes the surface of the intermediate oxide layer 172. Then, the exposed intermediate oxide layer 172 in the square hole is removed by wet etching or dry etching to form a square hole in the patterned intermediate oxide layer 175, and the square hole exposes the surface of the bottom layer of silicon 171. The square hole in the patterned top layer of silicon 174 and the square hole in the patterned intermediate oxide layer 175 form a first through hole.

[0078] Next, please refer to Figure 6 , deposit a high - reflection film on the surface of the bottom layer of silicon 111 exposed by the first through hole. The reflectivity of the high - reflection film is higher than 95%. Perform patterning on the high - reflection film to form a first high - reflection film 140.

[0079] Please refer to Figure 7 , provide a glass sheet 161, deposit a high - reflection film on the surface of the glass sheet 161. The reflectivity of the high - reflection film is higher than 95%. Perform patterning on the high - reflection film to form a second high - reflection film 150.

[0080] Please refer to Figure 8 , align the first high - reflection film 140 with the second high - reflection film 150, bond the patterned top layer of silicon 174 and the glass sheet 161. The glass sheet 161 serves as the second support structure 160. The second support structure 160 is divided into an opposite first surface and a second surface, and the second high - reflection film 150 is located on the second surface of the second support structure 160.

[0081] Please refer to Figure 9 and Figure 10 , perform thinning processing on the bottom layer of silicon 171 to remove a part of the thickness of the bottom layer of silicon 171, and form an antireflection film 180 on the second surface of the second support structure 160.

[0082] Please refer to Figure 11 and Figure 2, the underlying silicon 171 is etched and thinned to form the first support structure 120 and the strain beam 130.

[0083] Please refer to Figure 12 and Figure 13 , a humidity-sensitive film 110 is formed on the surface of the first support structure 120, a third support structure 190 is formed on the second surface of the second support structure 160, the third support structure 190 has a second through hole, and the antireflection film 180 is exposed in the second through hole. Finally, a light structure is formed in the first through hole, and the light structure is aligned with the antireflection film 180.

[0084] In summary, in the fiber optic humidity sensor and the forming method provided by the embodiments of the present invention, after the humidity-sensitive film absorbs moisture, the internal stress changes, causing the first support structure to deform, thereby causing the strain beam to deform, thus changing the cavity length of the FP cavity. The change amount of the cavity length is proportional to the environmental humidity, and finally the wavelength of the interference light output by the FP cavity changes. By reading the wavelength of the interference light output by the FP cavity, the environmental humidity can be accurately known. The fiber optic humidity sensor of the present invention can be used in any harsh environment and improves the measurement accuracy.

[0085] The above is only the preferred embodiment of the present invention and does not impose any limitation on the present invention. Any person skilled in the art, without departing from the technical solution of the present invention, makes any form of equivalent replacement or modification and other changes to the technical solution and technical content disclosed by the present invention, all of which belong to the content of the technical solution of the present invention and still fall within the protection scope of the present invention.

Claims

1. An optical fiber humidity sensor, characterized in that, Comprising: A humidity-sensitive thin film for absorbing moisture in the atmosphere; A first support structure including opposite first and second surfaces, with the humidity-sensitive thin film located on the first surface of the first support structure; A strain beam connected to the first support structure, capable of deforming when the strain beam is stressed; A first high-reflection film located on the second surface of the first support structure; A second high-reflection film opposite to and aligned with the first high-reflection film, with an FP cavity formed between the first high-reflection film and the second high-reflection film, and the distance between the first high-reflection film and the second high-reflection film being the cavity length of the FP cavity; A second support structure including opposite first and second surfaces, with the second high-reflection film located on the first surface of the second support structure; A frame for supporting the strain beam, located between the strain beam and the second support structure, with one end of the frame connected to the strain beam and the other end connected to the second support structure; And The strain beam is in a bent strip shape, and the cross-sectional shape of the strain beam is S-shaped, with one end connected to the first support structure and the other end connected to the frame.

2. The optical fiber humidity sensor according to claim 1, wherein, The surface of the strain beam and the surface of the first support structure are in the same plane.

3. The optical fiber humidity sensor according to claim 1, characterized in that, The cross-section of the first support structure is square, and at least one strain beam is connected to each side.

4. The optical fiber humidity sensor according to claim 1, characterized in that, Further comprising: An antireflection film and a third support structure located on the second surface of the second support structure. The third support structure has a second through hole, the radial direction of the second through hole is perpendicular to the second surface of the second support structure, and the antireflection film is located on the second surface of the second support structure exposed by the second through hole.

5. The optical fiber humidity sensor according to claim 1, characterized in that, The first high-reflection film includes a composite dielectric film or a metal film.

6. The optical fiber humidity sensor according to claim 4, wherein, Both the second high-reflection film and the antireflection film include composite dielectric films.

7. The optical fiber humidity sensor according to claim 4, characterized in that, Further comprising an optical fiber structure for receiving the light output from the FP cavity, with the optical fiber structure located in the second through hole and the optical fiber structure aligned with the antireflection film.

8. A method for forming the optical fiber humidity sensor according to any one of claims 1 to 7, characterized in that, Comprising: Providing a SOI silicon wafer, which includes a bottom layer silicon and an intermediate oxide layer and a top layer silicon stacked on the bottom layer silicon in sequence. Partially etching the top layer silicon and the intermediate oxide layer to form a first through hole between the patterned top layer silicon and the patterned intermediate oxide layer, with the first through hole exposing the surface of the bottom layer silicon, and the patterned top layer silicon and the patterned intermediate oxide layer serving as the frame; Forming a first high-reflection film on the surface of the bottom layer silicon exposed by the first through hole; Providing a glass sheet and forming a second high-reflection film on one surface of the glass sheet; Aligning the first high-reflection film with the second high-reflection film and bonding the patterned top layer silicon to the glass sheet, with the glass sheet serving as the second support structure; Etching the bottom layer silicon to form the first support structure and the strain beam; and Forming a humidity-sensitive thin film on the surface of the first support structure.

9. The method for forming the optical fiber humidity sensor according to claim 8, characterized in that, After bonding the patterned top layer silicon to the glass sheet, further comprising: Removing a part of the thickness of the bottom layer silicon.

10. The method for forming the optical fiber humidity sensor according to claim 8, wherein, After forming a humidity-sensitive thin film on the surface of the first support structure, further comprising: Forming an antireflection film on the second surface of the second support structure.

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