Self-reference optical temperature sensor and preparation method thereof

Abstract

The invention provides a self-reference optical temperature sensor and a preparation method thereof. The sensor comprises a wafer substrate; the temperature sensitive film is formed on the wafer substrate, and coupling gratings are arranged at the two ends of the temperature sensitive film; an optical waveguide is arranged between the coupling gratings and comprises a temperature-sensitive sensing cavity and a temperature-insensitive reference cavity which are respectively arranged on two sides; the waveguide width of the temperature-insensitive reference cavity is smaller than that of the temperature-sensitive sensing cavity; and the negative thermo-optical coefficient material film covers the temperature-insensitive reference cavity and is used for compensating the positive thermo-optical coefficient of the temperature-sensitive film, so that the temperature-insensitive reference cavity is insensitive to the temperature. According to the invention, the temperature insensitivity of the resonant cavity is realized based on the compensation of the negative thermo-optical coefficient material as the reference of the temperature-sensitive resonant cavity, the resonant wavelength difference between the sensing cavity and the reference cavity is used as the sensing basis, the output wavelength drift noise of the laser is inhibited, and the stability of the optical resonant temperature sensor is effectively improved; the device preparation method is simple and convenient.

Description

Technical Field

[0001] The present invention relates to the technical field of optical temperature sensors, and in particular to a self-reference optical temperature sensor and a preparation method thereof. Background Art

[0002] With the continuous advancement of science and technology, the requirements for precision temperature monitoring in high-tech fields such as artificial intelligence and aerospace are becoming increasingly higher. Optical temperature sensors have been widely used due to their great advantages in high quality factor and anti-electromagnetic interference compared to traditional resistive temperature sensors. Optical resonant temperature sensors have been widely developed due to their high sensitivity, small mode volume, and CMOS process compatibility. As a key indicator parameter of the sensor, the stability of optical resonant temperature sensors has been widely studied and characterized.

[0003] Through the search of existing technologies, we found that:

[0004] Rui Luo et al. from the Institute of Optics at the University of Rochester wrote an article titled “Self-referenced temperature sensing with a lithium niobate microdisk resonator” in Optics Letters, 2017, 7. They used the birefringence effect of lithium niobate crystals, that is, the difference in refractive index and thermo-optic coefficient of lithium niobate in transverse magnetic (TM) mode and transverse electric (TE) mode, and used the difference in resonant wavelengths in the two modes as a sensor to demonstrate a microdisk resonant temperature sensor that can self-reference sensing, achieving a measurement uncertainty as low as 0.8mK. However, its sensitivity dropped to 6.7pm / K, greatly reducing the sensing sensitivity. And because the sensing needs to use the difference in resonant wavelengths in the two modes, two sets of test equipment are required, which increases the complexity and cost of the test.

[0005] Qiancheng Zhao et al. from the University of California, USA, wrote an article titled "Integrated reference cavity with dual-mode optical thermometry for frequency correction" in Optica, 2021, 8. They used the difference in refractive index of silicon nitride microrings in transverse magnetic (TM) mode and transverse electric (TE) mode, and used a dual-channel frequency locking circuit to lock the resonance peaks in different modes, achieving a high stability of 0.31kHz / s. However, its sensitivity is as low as 188MHz / K, and the use of a dual-channel frequency locking circuit for testing increases the complexity of the test system.

[0006] Sergey Dedyulin and others from the Canadian National Metrology Committee wrote an article titled "Practical ring-resonator thermometer with an uncertainty of 10mK" in Measurement, 2023, 221, which characterized the temperature stability of silicon-based microring resonant temperature sensors better than 10mK, and proposed for the first time all sources of uncertainty of packaged microring resonant thermometers. At the same time, through 11 months of testing, its long-term stability was characterized. However, since the noise sources in the test process include the temperature fluctuation noise of the temperature measurement environment and the laser output wavelength drift noise, which are characterized by related equipment and then manually removed during data processing, they cannot be applied in practical applications.

[0007] The patent application number is CN111649840A, which discloses an optical resonator low-temperature temperature sensor and its preparation and packaging method. The device includes a wafer substrate and a temperature-sensitive film. The temperature-sensitive film is provided with an input grating coupler, an output grating coupler and an optical signal transmission component. The optical signal transmission component includes an optical waveguide and an optical resonant cavity. A protective layer is provided above the temperature-sensitive film. It optimizes the packaging structure to achieve deep low-temperature application of the optical resonant temperature sensor, broadening the application temperature range. However, it adopts a single-ring resonant cavity structure, and its stability is easily affected by system noise, and it does not characterize the stability of the sensor.

[0008] The patent application number CN108414448A discloses an optical sensor based on a dual-resonance cavity cascade, including a broadband light source and two resonant cavities; one resonant cavity is a reference resonant cavity; the other resonant cavity is a sensing resonant cavity; the two resonant cavities are coupled to each other through a common straight waveguide. The sensor is dedicated to monitoring the substance content in the liquid to be tested, and is not used in the field of temperature sensing and monitoring. In particular, by contacting both resonant cavities with the liquid to be tested, the temperature sensitivity and dispersion characteristics of the two resonant cavities are the same, thereby eliminating the influence of temperature noise.

[0009] In summary, optical resonant temperature sensors utilize the dependence of the resonant wavelength on temperature and have the advantages of high sensitivity, small size, and resistance to electromagnetic interference. However, due to the complexity of the test equipment, such as the drift of the laser output wavelength, power fluctuations, and fluctuations in the test environment, the sensor test is greatly uncertain, which seriously affects the stability of the sensor. The optical resonant temperature sensor that uses the crystal birefringence effect for self-reference achieves high stability, but the sensitivity is greatly reduced. Therefore, it is urgent to propose an optical resonant temperature sensor with high sensitivity, simple test equipment, and self-reference. Summary of the invention

[0010] In view of the defects in the prior art, an object of the present invention is to provide a self-referencing optical temperature sensor and a preparation method thereof.

[0011] According to one aspect of the present invention, there is provided a self-reference optical temperature sensor, comprising:

[0012] Wafer substrate;

[0013] A temperature sensitive film is formed on the wafer substrate, wherein coupling gratings are provided at both ends of the temperature sensitive film, and the coupling gratings are used to realize optical signal transmission; an optical waveguide is provided between the coupling gratings, and the optical waveguide includes a temperature sensitive sensing cavity and a temperature insensitive reference cavity respectively provided on both sides; the waveguide width of the temperature insensitive reference cavity is smaller than the waveguide width of the temperature sensitive sensing cavity;

[0014] A negative thermo-optic coefficient material film is covered on the temperature-insensitive reference cavity. The negative thermo-optic coefficient material film is used to compensate for the positive thermo-optic coefficient of the temperature-sensitive film, thereby achieving the insensitivity of the temperature-insensitive reference cavity to temperature.

[0015] Optionally, the structures of the temperature sensitive sensing cavity and the temperature insensitive reference cavity are any one of a microring structure, a microdisk structure and a nanobeam structure cavity; the coupling grating includes an input coupling grating and an output coupling grating, the optical waveguide includes a first straight waveguide connected to the input coupling grating and a second straight waveguide connected to the output coupling grating, the width of the first straight waveguide is the same as the waveguide width of the temperature sensitive sensing cavity, the width of the second straight waveguide is the same as the waveguide width of the temperature insensitive reference cavity, the temperature sensitive sensing cavity is coupled to the first straight waveguide, and the temperature insensitive reference cavity is coupled to the second straight waveguide.

[0016] Optionally, the waveguide width of the temperature sensitive sensing cavity is 450-500 nm, and the coupling gap between the temperature sensitive sensing cavity and the first straight waveguide is 120-150 nm.

[0017] Optionally, the waveguide width of the temperature-insensitive reference cavity is 320-400 nm, and the coupling gap between the temperature-insensitive reference cavity and the second straight waveguide is 150-330 nm.

[0018] Optionally, the optical waveguide further includes a tapered waveguide, which is used to connect the first straight waveguide and the second straight waveguide, and the widths of both ends of the tapered waveguide are respectively the same as the widths of the temperature sensitive sensing cavity and the temperature insensitive reference cavity.

[0019] Optionally, the negative thermo-optic coefficient material film is made of a crystalline material or a polymer material.

[0020] Optionally, the crystal material is titanium dioxide or tantalum pentoxide; and the polymer material is PMMA or SU8 glue.

[0021] Optionally, the negative thermo-optic coefficient material film has a thickness of 300-800 nm.

[0022] According to another aspect of the present invention, there is provided a method for preparing the above-mentioned self-reference optical temperature sensor, the method comprising:

[0023] After spin coating photoresist on the wafer substrate, electron beam direct writing lithography is used, and patterned photoresist is formed after development. Then, plasma deep silicon etching is used to shallowly etch the area without photoresist protection to realize the preparation of coupled grating.

[0024] The wafer substrate is spin-coated with photoresist again, and patterned photoresist is formed by electron beam direct writing lithography and development. Then, plasma deep silicon etching is used to fully etch the area without photoresist protection to realize the preparation of optical waveguide.

[0025] Continue to spin-coat the photoresist, use electron beam direct writing to form a sacrificial layer, and perform sputtering deposition of negative thermo-optical coefficient materials after development;

[0026] The photoresist used for the sacrificial layer is removed to obtain a self-reference optical temperature sensor.

[0027] Optionally, if the material of the negative thermo-optical coefficient material film is a polymer material, silicon dioxide is deposited as a mask layer after the development operation, and then the polymer material is coated by spin coating.

[0028] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0029] 1. The self-reference optical temperature sensor provided by the present invention realizes the insensitivity of the resonant cavity to temperature by covering a material modified with a negative thermo-optic coefficient above a temperature-insensitive reference cavity, which serves as a reference for the temperature-sensitive resonant cavity, thereby achieving a reference effect.

[0030] 2. The self-referencing optical temperature sensor provided by the present invention uses a temperature-insensitive resonant cavity covered with a negative thermo-optical coefficient material as a reference, and uses the difference in resonant wavelength between the sensing resonant cavity structure and the reference resonant cavity structure as a sensing peak, thereby reducing the influence of laser power fluctuations and output wavelength drift, and improving the stability of the sensor.

[0031] 3. The preparation method of the self-reference optical temperature sensor provided by the present invention is compatible with the traditional complementary metal oxide semiconductor (CMOS) process, has a mature process, does not require complicated preparation steps, has a simple and convenient process, can be mass-produced, and is conducive to integration with other sensors and other devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0033] Figure 1 A schematic diagram of the structure of a self-referencing optical temperature sensor according to an embodiment of the present invention;

[0034] Figure 1 Middle: 1 is a temperature-sensitive sensing cavity, 2 is a temperature-insensitive reference cavity, 3 is a tapered waveguide, 4a is an input coupling grating, and 4b is an output coupling grating;

[0035] Figure 2 A schematic diagram of the structure of a temperature-insensitive reference cavity portion of a self-referencing optical temperature sensor according to an embodiment of the present invention;

[0036] Figure 2 Middle: 5 is a negative thermo-optic coefficient material film, 2 is a temperature-insensitive reference cavity, and 7 is a silicon oxide layer;

[0037] Figure 3 is a transmission spectrum test curve of a self-reference optical temperature sensor in one embodiment of the present invention;

[0038] Figure 4 FIG. 1 is a schematic diagram of a method for preparing a self-referencing optical temperature sensor according to an embodiment of the present invention. Figure 1 ;

[0039] Figure 4 Middle: 5 is a negative thermo-optic coefficient material film, 8 is a top silicon layer, and 9 is a photoresist;

[0040] Figure 5 FIG. 1 is a schematic diagram of a method for preparing a self-referencing optical temperature sensor according to an embodiment of the present invention. Figure 2 ;

[0041] Figure 5 In the middle: 5 is a negative thermo-optic coefficient material film, 7' is silicon dioxide, and 9 is a photoresist. DETAILED DESCRIPTION

[0042] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0043] It should be noted that the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. Moreover, the terms "first", "second", etc. are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate so that the embodiments of the present invention described herein can be implemented in an order other than that illustrated or described herein.

[0044] Various structural schematic diagrams according to embodiments of the present application are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may further design regions / layers with different shapes, sizes, and relative positions according to actual needs, which all belong to the scope of protection of the present invention.

[0045] Reference Figure 1 and Figure 2 A self-reference optical temperature sensor provided by an embodiment of the present invention comprises a wafer substrate, a temperature-sensitive film and a negative thermo-optic coefficient material film 5, wherein the wafer substrate provides a stable support for the sensor, the wafer substrate comprises a silicon substrate and a silicon oxide layer 7 located above the silicon substrate, the temperature-sensitive film is formed on the wafer substrate, coupling gratings are arranged at both ends of the temperature-sensitive film, and the coupling gratings are used to realize optical signal transmission; an optical waveguide is arranged between the coupling gratings, and the optical waveguide comprises a temperature-sensitive sensing cavity 1 (i.e., a sensing resonant cavity) and a temperature-insensitive reference cavity 2 (i.e., a reference resonant cavity) respectively arranged on both sides; the negative thermo-optic coefficient material film 5 covers the temperature Above the insensitive reference cavity 2, since waveguides of different widths have different binding abilities for optical signals, the temperature-insensitive reference cavity 2 requires part of the optical energy to leak into the negative thermo-optic coefficient material film 5 to achieve temperature insensitivity; while for the temperature-sensitive sensing cavity 1, the optical energy must be completely confined inside the optical waveguide. In order to allow part of the optical field to leak into the negative thermo-optic coefficient material film 5 and achieve its compensation effect, the waveguide width of the temperature-insensitive reference cavity 2 is smaller than the waveguide width of the temperature-sensitive sensing cavity 1; the negative thermo-optic coefficient material film 5 is used to compensate for the positive thermo-optic coefficient of the temperature-sensitive film to achieve the insensitivity of the temperature-insensitive reference cavity 2 to temperature.

[0046] Exemplarily, the material of the temperature sensitive film is silicon, and a negative thermo-optic coefficient material is coated on the top of the silicon-based resonant cavity. The negative thermo-optic coefficient of the material is used to compensate for the positive thermo-optic coefficient of silicon, thereby making the silicon-based resonant cavity insensitive to temperature and achieving a reference effect.

[0047] In some embodiments, by adopting different preparation processes, the structures of the temperature-sensitive sensing cavity 1 and the temperature-insensitive reference cavity 2 are any one of a micro-ring structure, a micro-disk structure, and a nano-beam structure cavity.

[0048] In the embodiment of the present invention, the coupling grating includes an input coupling grating 4a and an output coupling grating 4b, the optical waveguide also includes a first straight waveguide connected to the input coupling grating 4a and a second straight waveguide connected to the output coupling grating 4b, the temperature sensitive sensing cavity 1 is coupled to the first straight waveguide, and the temperature insensitive reference cavity 2 is coupled to the second straight waveguide. The widths of the first straight waveguide and the second straight waveguide are different, and are respectively the same as the waveguide widths of the corresponding resonant cavity structures, so as to achieve critical coupling between the two and achieve effective coupling of optical signals.

[0049] For the temperature-sensitive sensing cavity, the light field must be completely confined inside the waveguide. In some embodiments, the waveguide width of the temperature-sensitive sensing cavity 1 is 450-500 nm, and the coupling gap between the temperature-sensitive sensing cavity 1 and the first straight waveguide is 120-150 nm.

[0050] For the temperature-insensitive reference cavity, in order to achieve the compensation effect of the negative thermo-optic coefficient material, the light field in the straight waveguide needs to partially leak out to the outside into the covering layer. In some embodiments, the waveguide width of the temperature-insensitive reference cavity 2 is 320 to 400 nm, and the coupling gap between the temperature-insensitive reference cavity 2 and the second straight waveguide is 150 to 330 nm.

[0051] In some embodiments, the optical waveguide also includes a tapered waveguide 3. The tapered waveguide 3 with a gradually varying width is used to connect a first straight waveguide and a second straight waveguide of different widths. The widths at both ends of the tapered waveguide 3 are respectively the same as the waveguide widths of the temperature sensitive sensing cavity 1 and the temperature insensitive reference cavity 2, so as to achieve effective transmission of optical signals between waveguides of different widths and reduce device losses.

[0052] In the embodiment of the present invention, the temperature-insensitive reference cavity 2 is covered with a negative thermo-optic coefficient material to compensate for the positive thermo-optic coefficient of a temperature-sensitive film such as silicon material, silicon nitride, silicon oxide, etc., so as to achieve the insensitivity of the silicon-based resonant cavity to temperature, thereby being used as a reference for the temperature-sensitive sensing cavity 1, reducing the effects of laser power fluctuations, output wavelength drift, etc., and improving the stability of the sensor. Further, in order to achieve the temperature insensitivity of the reference resonant cavity, when the negative thermo-optic coefficient material film 5 is over-compensated, that is, for the negative thermo-optic coefficient material film 5 of the same thickness, the reference resonant cavity waveguide width is too narrow, so that the proportion of light energy leaked to the cladding is too large, the negative thermo-optic coefficient material plays a dominant role, and the temperature sensitivity becomes negative, then the resonant wavelength of the reference resonant cavity structure will blue-shift with the increase of temperature. When the difference between the two resonant wavelengths is used as the sensing basis, the sensitivity of the sensor can be greatly improved.

[0053] In some embodiments, the negative thermo-optic coefficient material film 5 is made of a crystalline material or a polymer material.

[0054] For example, the crystal material is titanium dioxide or tantalum pentoxide, etc.; the polymer material is PMMA or SU8 glue, etc. Since the crystal material has a high refractive index, the waveguide width of the temperature-insensitive reference cavity 2 does not need to be too narrow to achieve the compensation effect. If the negative thermo-optic coefficient material is a polymer material such as SU8 glue, the waveguide width of the temperature-insensitive reference cavity 2 needs to be narrow enough so that enough light field leaks to the top cover layer to achieve insensitivity to temperature.

[0055] The negative thermo-optic coefficient material is covered on the top of the temperature-insensitive reference cavity 2. The thickness of the negative thermo-optic coefficient material film 5 covered on the top is selected according to the waveguide width of the temperature-insensitive reference cavity 2. The narrower the waveguide width of the temperature-insensitive reference cavity 2, the lower the thickness of the negative thermo-optic coefficient material film 5 is required to achieve the insensitivity to temperature. In some embodiments, the thickness of the negative thermo-optic coefficient material film 5 is 300 to 800 nm.

[0056] The device in the above embodiment of the present invention comprises an optical resonant cavity waveguide with different widths prepared on a substrate and coupling gratings at both ends for optical signal transmission, wherein the two optical resonant cavities include a temperature-sensitive sensing cavity 1 and a temperature-insensitive reference cavity 2, wherein the temperature-insensitive reference cavity 2 is covered with a negative thermo-optical coefficient material. The optical signal enters the straight waveguide from the input coupling grating 4a. Since the straight waveguide has a strong limiting effect on the light field, the optical signal will first be transmitted along the first straight waveguide. At the coupling point with the temperature-sensitive sensing cavity waveguide, the optical signal of a specific wavelength will be coupled into the temperature-sensitive sensing cavity waveguide in the form of an evanescent wave, and after the cavity waveguide circulation, it will be coupled back to the first straight waveguide in the form of an evanescent wave, thereby realizing the resonance enhancement of the optical signal of a specific wavelength. The optical signal is transmitted along the tapered waveguide 3 into the second straight waveguide with a narrower width. At the coupling point with the temperature-insensitive reference cavity waveguide, the optical signal of a specific wavelength will be coupled into the reference resonant cavity in the form of an evanescent wave. After circulating in the cavity waveguide, it will be coupled back to the second straight waveguide in the form of an evanescent wave. Finally, the optical signal is output by the output coupling grating 4b. The sensor uses a dual resonant cavity structure to form a self-reference. The optical signal will first enter the temperature-sensitive sensing cavity 1 to generate a resonant peak signal. The tapered waveguide 3 is used to connect two straight waveguides with different widths between the two resonant cavities to achieve effective transmission of the optical signal. Then it enters the temperature-insensitive reference cavity 2 to generate a resonant peak signal. Due to the narrow width of the temperature-insensitive reference cavity waveguide, part of the optical field leaks into the negative thermo-optic coefficient material cladding to achieve a compensation effect. The two rings have different effective refractive indices, and the two resonant peak signals generated are different. Finally, the optical signal in the straight waveguide will be output at the output coupling grating 4b.

[0057] The sensor of the above embodiment of the present invention is based on an optical resonant cavity as a basic unit, and is insensitive to temperature by covering a negative thermo-optic coefficient material on the top of a resonant cavity as a reference cavity. Figure 3 The transmission spectrum test curve of the self-reference optical temperature sensor is shown. The wider resonance peak is generated by the temperature-insensitive reference cavity 2, and the narrower resonance peak is generated by the temperature-sensitive sensing cavity 1. The difference between the resonance peaks of the two resonant cavities is used as the sensing peak to reduce the influence of laser power fluctuation and output wavelength drift, thereby improving the stability of the sensor.

[0058] Based on the same concept, another embodiment of the present invention provides a method for preparing the above-mentioned self-reference optical temperature sensor, comprising the following steps:

[0059] S1. First, a grating coupler for optical signal coupling is prepared on a wafer substrate: after spin coating photoresist on the wafer substrate, electron beam direct writing lithography is used, and patterned photoresist is formed after development, and then plasma deep silicon etching is used to shallowly etch the area without photoresist protection to realize the preparation of coupling grating;

[0060] S2. Prepare optical waveguides on wafer substrates: spin-coat photoresist on the wafer substrates again, use electron beam direct writing lithography, develop to form patterned photoresist, and then use plasma deep silicon etching to fully etch the areas without photoresist protection, so as to prepare optical waveguides including straight waveguides, tapered waveguides and resonant cavities; the width of each waveguide is set during the layout design, and the etching depth of each waveguide is the same;

[0061] S3, continue to spin-coat the photoresist, use electron beam direct writing to form a sacrificial layer, and perform sputtering deposition of a negative thermo-optical coefficient material after development;

[0062] Optionally, the top coating of the negative thermo-optical coefficient material may be performed by magnetron sputtering, atomic layer deposition, low pressure chemical vapor deposition, spin coating, etc.

[0063] S4. Use acetone, isopropyl alcohol, and deionized water to remove the photoresist used for the sacrificial layer, complete the preparation of the entire device, and obtain a self-reference optical temperature sensor.

[0064] If the material of the negative thermo-optic coefficient material film is a polymer material such as PMMA, SU8, etc., which can only be completed by a spin coating process, and selective coating cannot be performed, the above method also includes: depositing silicon dioxide as a mask layer after the development operation to protect the non-reference ring area from the influence of the polymer material, and then coating the polymer material by spin coating. During the spin coating process, the polymer material such as PMMA, SU8, etc. is only spin-coated on the surface of the reference ring area, and other areas will not be affected due to the protection of silicon oxide.

[0065] Specifically, the process includes:

[0066] Step 1, after the waveguide etching is completed, the residual photoresist on the substrate surface is removed by ultrasonic cleaning with acetone, isopropanol, and deionized water, and then the photoresist is spin-coated on the substrate surface. After electron beam exposure and development operations, the photoresist in the non-reference ring area is removed;

[0067] Step 2, depositing a layer of silicon dioxide on the surface of the substrate by low-pressure vapor deposition;

[0068] Step 3, use acetone, isopropanol, and deionized water to ultrasonically clean and remove the photoresist on the surface of the substrate, and spin-coat SU8 glue, a negative thermo-optical coefficient material, to complete the preparation of the entire device.

[0069] like Figure 4 As shown, in a specific embodiment, a self-reference optical temperature sensor using negative thermo-optical coefficient material titanium dioxide compensation is prepared as follows:

[0070] Reference Figure 4 As shown in Figure 1), the wafer substrate adopts a standard SOI wafer, wherein the top silicon layer 8 has a thickness of 220nm and the buried oxide layer is 5um;

[0071] Reference Figure 4 As shown in Figure 2), the surface of the wafer substrate is spin-coated with electron beam photoresist 9, and the photoresist is patterned after electron beam exposure and development operations;

[0072] Reference Figure 4 As shown in Figure 3), a substrate covered with a patterned photoresist is subjected to deep silicon etching to achieve pattern transfer and complete the etching of the coupled grating, with an etching depth of 65nm to 75nm; after the etching is completed, acetone, isopropanol, and deionized water are used for ultrasonic cleaning to remove the photoresist on the surface of the substrate;

[0073] Reference Figure 4 As shown in Figure 4), the surface of the wafer substrate is again spin-coated with electron beam photoresist 9, and the photoresist is patterned after electron beam exposure and development operations;

[0074] Reference Figure 4 As shown in Figure 5), the substrate covered with the patterned photoresist is subjected to deep silicon etching to achieve pattern transfer, complete the etching of the straight waveguide and the resonant cavity waveguide, and the etching depth is 220nm; after the etching is completed, acetone, isopropanol, and deionized water are used for ultrasonic cleaning to remove the photoresist on the surface of the substrate;

[0075] Reference Figure 4 As shown in Figure 6), the surface of the wafer substrate is again spin-coated with electron beam photoresist 9, and after electron beam exposure and development operations, the photoresist is patterned to serve as a sacrificial layer for the lift-off process;

[0076] Reference Figure 4As shown in Figure 7), a wafer substrate covered with a sacrificial photoresist layer is magnetron sputtered with titanium dioxide as a negative thermo-optical coefficient material film 5;

[0077] Reference Figure 4 As shown in Figure 8), the sacrificial photoresist layer on the surface of the substrate is removed by ultrasonic cleaning with acetone, isopropanol and deionized water to complete the preparation of the device.

[0078] like Figure 5 As shown, in a specific embodiment, a self-reference optical temperature sensor using SU8 polymer compensation with a negative thermo-optic coefficient material is prepared. During the preparation process, the preparation process of the coupling grating and the optical waveguide is the same as that of the above-mentioned use of titanium dioxide as a negative thermo-optic coefficient material, and the coating process needs to be different. The specific process is as follows:

[0079] Reference Figure 5 As shown in Figure 1), after the waveguide etching is completed, the residual photoresist on the substrate surface is removed by ultrasonic cleaning with acetone, isopropanol and deionized water, and then the photoresist 9 is spin-coated on the substrate surface, and the photoresist is patterned after electron beam exposure and development operations;

[0080] Reference Figure 5 As shown in Figure 2), a layer of silicon dioxide 7' is deposited on the surface of the substrate by low-pressure vapor deposition;

[0081] Reference Figure 5 As shown in Figure 3), after using acetone, isopropanol and deionized water to ultrasonically clean and remove the photoresist on the substrate surface, SU8 glue is spin-coated as a negative thermo-optical coefficient material film 5 to complete the preparation of the device.

[0082] The above embodiment of the present invention uses a silicon-based optical resonant cavity as the basic structure and adopts a dual-ring cascade structure, in which one resonant cavity is used as a temperature-sensitive sensing cavity and the other resonant cavity is used as a temperature-insensitive reference cavity, so as to realize self-reference of temperature sensing, reduce the influence of laser power fluctuation and output wavelength drift, and improve the stability of the sensor. A negative thermo-optic coefficient material is coated on the surface of the silicon micro-ring to compensate for the positive thermo-optic coefficient of silicon, so as to realize the insensitivity of the silicon-based resonant cavity to temperature. The preparation method in the above embodiment of the present invention does not need to adopt complicated process steps, is compatible with the traditional complementary metal oxide semiconductor (CMOS) process, has mature process, can be mass-produced, and is conducive to integration with other sensors and other devices.

[0083] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the essence of the present invention. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A self-referencing optical temperature sensor, characterized in that: include: Wafer substrate; A temperature sensitive film is formed on the wafer substrate, and coupling gratings are provided at both ends of the temperature sensitive film, and the coupling gratings are used to realize optical signal transmission; an optical waveguide is provided between the coupling gratings, and the optical waveguide includes a temperature sensitive sensing cavity and a temperature insensitive reference cavity respectively provided on both sides; The waveguide width of the temperature-insensitive reference cavity is smaller than the waveguide width of the temperature-sensitive sensing cavity; A negative thermo-optic coefficient material film is covered on the temperature-insensitive reference cavity. The negative thermo-optic coefficient material film is used to compensate for the positive thermo-optic coefficient of the temperature-sensitive film, thereby achieving the insensitivity of the temperature-insensitive reference cavity to temperature.

2. The self-referencing optical temperature sensor according to claim 1, characterized in that: The structure of the temperature sensitive sensing cavity and the temperature insensitive reference cavity is any one of a micro-ring structure, a micro-disk structure and a nano-beam structure cavity; The coupling grating includes an input coupling grating and an output coupling grating, the optical waveguide includes a first straight waveguide connected to the input coupling grating and a second straight waveguide connected to the output coupling grating, the width of the first straight waveguide is the same as the waveguide width of the temperature sensitive sensing cavity, the width of the second straight waveguide is the same as the waveguide width of the temperature insensitive reference cavity, the temperature sensitive sensing cavity is coupled to the first straight waveguide, and the temperature insensitive reference cavity is coupled to the second straight waveguide.

3. The self-referencing optical temperature sensor according to claim 2, characterized in that: The waveguide width of the temperature sensitive sensing cavity is 450-500 nm, and the coupling gap between the temperature sensitive sensing cavity and the first straight waveguide is 120-150 nm.

4. The self-referencing optical temperature sensor according to claim 2, characterized in that: The waveguide width of the temperature-insensitive reference cavity is 320-400 nm, and the coupling gap between the temperature-insensitive reference cavity and the second straight waveguide is 150-330 nm.

5. The self-referencing optical temperature sensor according to claim 2, characterized in that: The optical waveguide further comprises a tapered waveguide, which is used to connect the first straight waveguide and the second straight waveguide, and the widths of both ends of the tapered waveguide are respectively the same as the widths of the temperature sensitive sensing cavity and the temperature insensitive reference cavity.

6. The self-referencing optical temperature sensor according to claim 1, characterized in that: The negative thermo-optic coefficient material film is made of a crystal material or a polymer material.

7. The self-referencing optical temperature sensor according to claim 6, characterized in that: The crystal material is titanium dioxide or tantalum pentoxide; the polymer material is PMMA or SU8 glue.

8. The self-referencing optical temperature sensor according to claim 1, characterized in that: The thickness of the negative thermo-optic coefficient material film is 300-800 nm.

9. A method for preparing a self-referencing optical temperature sensor according to any one of claims 1 to 8, characterized in that: include: After spin coating photoresist on the wafer substrate, electron beam direct writing lithography is used, and patterned photoresist is formed after development. Then, plasma deep silicon etching is used to shallowly etch the area without photoresist protection to realize the preparation of coupled grating. The wafer substrate is spin-coated with photoresist again, and patterned photoresist is formed by electron beam direct writing lithography and development. Then, plasma deep silicon etching is used to fully etch the area without photoresist protection to realize the preparation of optical waveguide. Continue to spin-coat the photoresist, use electron beam direct writing to form a sacrificial layer, and perform sputtering deposition of negative thermo-optical coefficient materials after development; The photoresist used for the sacrificial layer is removed to obtain a self-reference optical temperature sensor.

10. The method for preparing the self-reference optical temperature sensor according to claim 9, characterized in that: If the material of the negative thermo-optical coefficient material film is a polymer material, silicon dioxide is deposited as a mask layer after the development operation, and then the polymer material is coated by spin coating.

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