A gas sensor device based on a nano-scale thickness micro-resonator

Abstract

The present invention discloses a gas sensor device based on a microresonator with a nanoscale thickness, comprising a microresonator and a bus waveguide. Among them, the thickness h of the microresonator is less than one hundred nanometers, forming a huge evanescent field energy, which interacts violently with the gas in the surrounding environment. The bus waveguide is located on one side of the microresonator device with a nanoscale thickness to realize the coupled measurement of the optical field in the microresonator. The proposed waveguide structure not only greatly enhances the interaction between the optical field and the ambient gas, improves the performance of the gas sensor device, but also significantly reduces the effective refractive index of the device, improves the processing tolerance of the device, and lays a foundation for realizing high-sensitivity and high-reliability on-chip gas sensors and on-chip multi-parameter sensors.

Description

Technical Field

[0001] The present invention belongs to the field of optical gas sensors, and particularly relates to a gas sensor device based on a nanoscale-thickness micro-resonator. Background Art

[0002] Gas sensors have a wide range of application fields, covering many people's livelihood and national key fields such as industry, agriculture, environment, transportation, national defense, medical treatment, aerospace, etc. With the development of mobile and wearable devices, traditional gas sensors are gradually difficult to meet people's requirements for the portability and integrability of gas sensors. In recent years, scientific researchers have conducted a large number of research and explorations on miniaturized gas sensors. Among them, on-chip optical gas sensors have attracted more and more extensive attention due to their advantages of high integration, good stability, anti-electromagnetic interference, long lifespan, and non-contact measurement. Compared with other material systems, silicon-based photon devices have gradually developed into a popular direction of on-chip optical gas sensors due to their advantages of high system integration, good physical and chemical stability, and the compatibility of processing technology with CMOS technology in the microelectronics industry. Generally speaking, the working principle of an on-chip optical gas sensor is that the evanescent field of a waveguide device interacts with the gas to be measured, modulating the optical signal in the waveguide, thereby realizing gas sensing. As a widely used silicon-based waveguide device, a micro-resonator has the advantages of simple structure, low loss, easy on-chip integration and processing, etc., and is widely used in the sensing field. Its sensing sensitivity and detection limit mainly depend on the interaction intensity between the gas and the evanescent field of the waveguide. Therefore, increasing the proportion of the evanescent field of the waveguide is crucial for improving the performance of on-chip gas sensors.

[0003] In terms of papers, researchers have reported various waveguide structures to increase the proportion of evanescent fields, such as slot waveguides, suspended waveguides, photonic crystal waveguides, etc. For example, in 2008, the research group led by Professor M. Lipson at Cornell University in the United States reported a silicon-based waveguide integrated device for gas sensing (Optics Express 16, 4296 - 4301, 2008). Using a slot-type silicon micro-ring resonator, the proportion of the waveguide evanescent field was 23%. The acetylene gas was sensed by comparing the change in the resonant wavelength before and after the change in the gas environment. In 2014, the research group led by Professor Jin Chongjun at Sun Yat-sen University proposed a slot-type photonic crystal microcavity for on-chip gas sensing (IEEE Photonics Journal 6, 6802509, 2014), and the proportion of the waveguide evanescent field was 61.7%. In 2015, the research group led by Professor G. Z. Mashanovich at the University of Southampton in the UK designed a slot-type silicon waveguide (IEEE Photonics Technology Letters, 27, 1197 - 1199, 2015), achieving a waveguide evanescent field proportion of more than 58%. In 2020, the research group led by Professor K. Gylfason at the Royal Institute of Technology in Sweden used a silicon-based suspended waveguide device with an evanescent field proportion of 65.4% to achieve absorption sensing of CO2 gas (Optics Letters, 45, 109 - 112, 2020).

[0004] In terms of patents, researchers have applied for a number of patents based on new waveguide structures to improve gas sensing performance. For example, in 2013, Zhao Yong et al. from Northeastern University invented a method for measuring multi-component gas concentration based on a photonic crystal slot waveguide, achieving high-sensitivity measurement of multi-component gas concentration (Chinese invention patent: 201310010637.4); in 2022, Chen Weiwei et al. from Ningbo University invented a mid-infrared gas sensor based on a tapered sub-micron grating - slot waveguide, which has the advantages of high sensitivity, low detection threshold, and fast response time (Chinese invention patent: 202210621443.7); in 2022, Liu Li et al. from China University of Geosciences invented a refractive index sensor based on a suspended side sub-wavelength grating waveguide micro-ring, which expanded the detection range and achieved simultaneous measurement of multiple mixtures (Chinese invention patent: 202210998461.7).

[0005] However, at present, the thickness of the top silicon layer of most silicon-based devices is several hundred nanometers, most of the light is confined in the waveguide, and the proportion of the waveguide evanescent field is relatively low, resulting in weak interaction between light and gas, which limits the performance of gas sensors. Summary of the Invention

[0006] The object of the present invention is to overcome the deficiencies of the existing technologies and propose a gas sensor device based on a nano-scale thickness micro-resonator.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] A gas sensor device based on a nano-scale thickness micro-resonator includes a substrate, a micro-resonator, and a bus waveguide. The substrate consists of a top silicon layer and a bottom silicon layer, and an insulating layer is provided between the top silicon layer and the bottom silicon layer; the micro-resonator and the bus waveguide are disposed on the top silicon layer. The thickness of the micro-resonator is less than one hundred nanometers, less than 1 / 6 of the working wavelength size, so as to form an evanescent field energy with an energy proportion exceeding 50%, and interact with the gas in the surrounding environment; the bus waveguide is located on one side of the micro-resonator device to realize the coupled measurement of the optical field in the micro-resonator; sub-wavelength grating cladding structures are provided on both sides of the micro-resonator and the bus waveguide. By passing an etching solution through the sub-wavelength grating cladding structures, the insulating layer below the micro-resonator and the bus waveguide is etched to obtain a cavity, so that the micro-resonator and the bus waveguide form a suspended structure.

[0009] Further, the insulating layer is composed of silicon dioxide, aluminum oxide, or silicon nitride.

[0010] Further, the etching solution uses a hydrofluoric acid solution.

[0011] Further, the bus waveguide is one of a waveguide with a sub-wavelength grating cladding, a strip waveguide supported by a side bracket, or a ridge waveguide.

[0012] Further, the micro-resonator is one or several of a micro-ring resonator, a micro-disk resonator, a photonic crystal resonator, and a Fabry-Perot cavity.

[0013] Further, the materials of the micro-resonator and the bus waveguide are composed of crystalline materials such as silicon, germanium, gallium arsenide, indium phosphide, lithium niobate, and aluminum gallium arsenide, or amorphous materials such as silicon dioxide, silicon nitride, and sulfides.

[0014] Further, the gas sensor device can operate in the visible light, near-infrared, and mid-infrared bands.

[0015] Further, the gas sensor device can achieve gas detection based on the resonance peak shift caused by the refractive index change, or based on the extinction ratio change of the resonance peak caused by the optical absorption loss; the gas sensor device can perform gas detection based on one resonance peak, and can also perform gas detection and multi-parameter decoupling based on several resonance peaks.

[0016] Compared with the existing technologies, the beneficial effects brought by the technical solution of the present invention are:

[0017] 1. The sub - wavelength structures distributed on both sides of the micro - resonator and the bus waveguide enable hydrofluoric acid to enter the middle insulating layer for etching. At the same time, the sub - wavelength structures can provide mechanical support for the micro - ring waveguide and the bus waveguide. The waveguide with a nanoscale thickness proposed in this invention has an evanescent - field proportion of more than 80%, greatly enhancing the interaction between the optical field and the gas and improving the sensing performance of the device.

[0018] 2. The waveguide device of the nanoscale - thickness micro - resonator proposed in this invention significantly reduces the effective refractive index of the device and improves the processing tolerance of the device. <(

[0019] 3. The gas sensor device based on the nanoscale - thickness micro - resonator proposed in this invention has the advantages of high integration, good stability, anti - electromagnetic interference, long life, etc. It can be further integrated with optoelectronic devices and electronic devices integrated on the same chip to achieve monolithic integration of the sensing system. [[ID=!0]]

[0020] 4. The manufacturing process of the gas sensor device based on the nanoscale - thickness micro - resonator proposed in this invention is compatible with the CMOS process, and it is expected to achieve mass production of high - quality and low - cost devices.

[0021] 5. The gas sensor device based on the nanoscale - thickness micro - resonator proposed in this invention has the advantage of a wide range of applications. It can not only be used for gas sensing but also for multi - parameter sensing such as gas, temperature, and humidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1a and Figure 1b are the three - dimensional schematic diagram and cross - sectional view of the gas sensor based on the micro - ring resonator in Specific Embodiment 1 of this invention.

[0023] Figure 2 is the scanning electron microscope image of the micro - ring resonator in Embodiment 1.

[0024] Figure 3 is the gas - sensing result diagram of the TE0 mode in the micro - ring resonator in Embodiment 1.

[0025] Figure 4a and Figure 4b are the three - dimensional schematic diagram and cross - sectional view of the gas sensor device based on the micro - disk resonator in Specific Embodiment 2 of this invention.

[0026] Figure 5 is the scanning electron microscope image of the micro - disk resonator in Embodiment 2.

[0027] Figure 6 is the theoretical simulation diagram of gas sensing of the TE0 and TE1 modes in the micro - disk resonator in Embodiment 2.

[0028] Figure 7These are the transmission spectra of the TE0 and TE1 modes in the micro-disk resonant cavity fitted under different gas and temperature environments in Example 2. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] Example 1

[0031] like Figure 1a As shown, a gas sensor device based on a nanometer-thick microring resonator includes a microring resonator 2, a bus waveguide 3, a substrate, and a suspended subwavelength grating cladding structure 4. The substrate is composed of top and bottom silicon layers, with an insulating layer 1 composed of silicon dioxide disposed between the top and bottom silicon layers. The microring resonator 2 and bus waveguide 3 are fabricated on the top silicon layer. The microring resonator 2, bus waveguide 3, and suspended subwavelength grating cladding structure 4 are 70 nm thick, the central insulating layer is 3 μm thick, and the bottom silicon layer is 800 μm thick. The width of the ring waveguide and bus waveguide of the microring resonator are both 1.2 μm, and the ring waveguide radius is 60 μm. The coupling spacing between the ring waveguide of the microring resonator 2 and the bus waveguide 3 is 300 nm, ensuring close to the just-coupled condition of the microring resonator 2.

[0032] To form the suspended membrane structure, the silicon dioxide insulating layer 1 is etched with a 6.67% hydrofluoric acid solution for 110 minutes to form a cavity. A suspended subwavelength grating cladding structure 4, located on either side of the microring resonator 2 and bus waveguide, allows hydrofluoric acid to enter the central insulating layer for etching. The suspended subwavelength grating cladding structure 4 also provides mechanical support for the microring resonator 2 and bus waveguide. The nanometer-thick waveguide proposed in this invention has an evanescent field fraction of 83%, enhancing the interaction between the evanescent field in the waveguide and the ambient gas, improving the device's sensing performance. Figure 1b 2 is a cross-sectional view of the microring resonator 2. Figure 2 This is a scanning electron microscope image of microring resonator 2.

[0033] When light propagates in a waveguide, some of the light leaks out of the waveguide, forming an evanescent field. The gas to be measured interacts with the evanescent field of the microring resonator. When the external gas environment changes, the change in the gas refractive index will cause the effective refractive index of the microring resonator to change, thereby affecting the phase of the light field in the microring resonator and causing the resonance peak in the microring transmission spectrum to shift, thus achieving gas sensing. Based on the microring transmission formula, the transmission spectrum of the TE0 mode in the microring resonator of the above-mentioned nanometer-thick microring resonator in air and carbon dioxide gas environments was theoretically simulated. The theoretical results are as follows: Figure 3As shown. The results show that the Q value of the microring is ~7000, the extinction ratio is about 14 dB. When the gas environment where the microring resonator is located changes from air to carbon dioxide, the resonance peak of the microring resonator shifts by about 0.1 nm. By monitoring the shift of the resonance peak in the transmission spectrum of the microring resonator, on-chip optical gas sensing can be achieved.

[0034] Example 2

[0035] As Figure 4a As shown, a gas sensor device based on a microring resonator with a nanoscale thickness includes a microdisk resonator 20, a bus waveguide 30, a substrate, and a suspended subwavelength grating cladding structure 40. The substrate is composed of a top silicon layer and a bottom silicon layer. An insulating layer 10 with a cavity is provided between the top silicon layer and the bottom silicon layer. The insulating layer 10 is composed of silicon dioxide, and the cavity is filled with air. The microdisk resonator is fabricated on the SOI wafer of the top silicon layer. Among them, the thicknesses of the microdisk resonator 20, the bus waveguide 30, and the suspended subwavelength grating cladding structure 40 are 70 nm, the thickness of the middle insulating layer is 3 μm, and the thickness of the bottom silicon layer is 800 μm. The widths of the bus waveguides are all 1.2 μm, the radius of the disk-shaped waveguide in the microdisk resonator is 60 μm, and the coupling distance between the microdisk resonator 20 and the bus waveguide 30 is 210 nm to ensure that the microdisk resonator 20 is close to the critical coupling condition. In order to form a suspended thin film structure, a 6.67% hydrofluoric acid solution is used to etch the silicon dioxide insulating layer, and the etching time is 110 minutes. The subwavelength structures distributed on both sides of the bus waveguide 30 allow the hydrofluoric acid to enter the middle insulating layer 1 for etching, and at the same time, the suspended subwavelength grating cladding structure 40 can mechanically support the bus waveguide. Since the waveguide structure with a nanoscale thickness proposed in the present invention achieves an evanescent field occupancy ratio of 83%, it enhances the interaction between the evanescent field in the waveguide and the ambient gas, and improves the sensing performance. Figure 4b is a cross-sectional view of the microdisk resonator. Figure 5 is a scanning electron microscope image of the microdisk resonator.

[0036] Specifically, in this embodiment, the transmission spectra of the above microdisk resonator in air and carbon dioxide gas environments are theoretically simulated, and the theoretical results are as Figure 6 shown. The results show that the Q value of the microdisk is ~4000, the extinction ratio is about 16 dB. When the gas environment where the microdisk resonator is located changes from air to carbon dioxide, that is, when the environmental refractive index changes, the resonance peak of the microdisk resonator shifts by about 0.1 nm. By monitoring the shift of the resonance peak in the transmission spectrum of the microdisk resonator, on-chip optical gas sensing can be achieved.

[0037] In order to overcome the cross-sensitivity phenomenon in gas sensing measurements, in this embodiment, the transmission spectra of two modes, TE0 and TE1, in the microdisk resonator are utilized for dual-parameter sensing of gas refractive index and temperature. The specific method is as follows: The structure of the dual-mode microdisk resonator is the same as that of the above-mentioned microdisk resonator. Both the TE0 mode and the TE1 mode can be coupled into the microdisk resonator from the waveguide and resonate in the microdisk. Changes in the gas refractive index and changes in the ambient temperature can both cause shifts in the resonant wavelength of the microdisk resonator. If the TE0 mode and the TE1 mode have linear irrelevance to the changes in the gas refractive index and temperature, the shifts in the resonant wavelengths of the two modes can be represented by a linear equation, and by solving the linear equation, the changes in the gas refractive index and temperature can be obtained. The specific derivation process is as follows:

[0038] The degrees to which the nth-order resonant wavelengths of the TE0 mode and the TE1 mode of the microdisk resonator are affected by the gas refractive index and temperature can be expressed as

[0039]

[0040] where A and B are the change coefficients of the resonant wavelength with respect to temperature and refractive index in the TE0 mode, C and D are the change coefficients of the resonant wavelength with respect to temperature and refractive index in the TE1 mode, dT and dn are respectively the changes in temperature and gas refractive index. If AD≠BC, it indicates that there is a unique solution to Equation (1), and then based on the shift amount of the microdisk resonant wavelength, the changes in temperature and gas refractive index can be calculated:

[0041]

[0042] Based on the shifts in the resonant wavelengths in each mode and the change coefficients of the resonant wavelengths of the two modes with respect to temperature and refractive index, the changes in temperature and gas refractive index can be calculated respectively.

[0043] According to the simulation results, the values of A, B, C, and D are 8.106×10 -5 , 0.561, 8.091×10 -5 and 0.527 respectively. Furthermore, it is obtained that AD≠BC. Therefore, there is a unique solution to Equation (1), and the changing refractive index and temperature can be solved. Figure 7Transmission spectra of TE0 and TE1 modes in the above microdisk resonator respectively obtained by fitting in a gas environment of air (refractive index: 1.000292) and carbon dioxide (refractive index: 1.000449) and different temperature environments (293K and 295K). The offsets of the resonance peaks of TE0 and TE1 modes obtained under these two environmental settings are 0.247 nm and 0.241 nm respectively. According to formula (2), the changes in environmental refractive index and temperature can be calculated respectively. The calculation results show that the change in gas refractive index is 0.000168, and the relative error of the calculation result is 12%; the calculated temperature change is 1.9K, and the relative error of the calculation result is 5%. Therefore, the decoupled calculation of the gas environment refractive index and temperature can be achieved by using this method.

[0044] Finally, the method of the above embodiments is only a preferred implementation scheme and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0045] The present invention is not limited to the embodiments described above. The description of the specific embodiments above aims to describe and illustrate the technical solutions of the present invention. The above specific embodiments are only illustrative and not restrictive. Without departing from the spirit of the present invention and the scope protected by the claims, those of ordinary skill in the art can also make many specific transformations in various forms under the inspiration of the present invention, and these all belong to the protection scope of the present invention.

Claims

1. A gas sensor device based on a nanometer-thick micro-resonant cavity, characterized in that: The device comprises a substrate, a micro-resonant cavity and a bus waveguide, wherein the substrate is composed of a top silicon layer and a bottom silicon layer, and an insulating layer is provided between the top silicon layer and the bottom silicon layer; the micro-resonant cavity and the bus waveguide are provided on the top silicon layer, and the thickness of the micro-resonant cavity is less than 100 nanometers, which is less than 1 / 6 of the working wavelength, so as to form an evanescent field energy with an energy proportion of more than 50%, which interacts with the gas in the surrounding environment; the bus waveguide is located on one side of the micro-resonant cavity device to realize the coupled measurement of the light field in the micro-resonant cavity; a sub-wavelength grating cladding structure is provided on both sides of the micro-resonant cavity and the bus waveguide, and an etching liquid is passed through the sub-wavelength grating cladding structure to etch the insulating layer below the micro-resonant cavity and the bus waveguide to obtain a cavity, so that the micro-resonant cavity and the bus waveguide form a suspended structure; the gas sensor device can operate in the visible light, near-infrared and mid-infrared bands.

2. A gas sensor device based on a nanometer-thick micro-resonant cavity according to claim 1, characterized in that: The insulating layer is made of silicon dioxide, aluminum oxide or silicon nitride.

3. A gas sensor device based on a nanometer-thick micro-resonant cavity according to claim 1, characterized in that: The etching solution is a hydrofluoric acid solution.

4. A gas sensor device based on a nanometer-thick micro-resonant cavity according to claim 1, characterized in that: The bus waveguide is one of a waveguide containing a sub-wavelength grating cladding, a strip waveguide supported by a side support, or a ridge waveguide.

5. The gas sensor device based on a nanometer-thick micro-resonant cavity according to claim 1, characterized in that: The micro-resonant cavity is one or more of a micro-ring resonant cavity, a micro-disk resonant cavity, a photonic crystal resonant cavity, and a Fabry-Perot cavity.

6. A gas sensor device based on a nanometer-thick micro-resonant cavity according to claim 1, characterized in that: The materials of the micro-resonant cavity and bus waveguide are composed of crystalline materials such as silicon, germanium, gallium arsenide, indium phosphide, lithium niobate, and aluminum gallium arsenide, or amorphous materials such as silicon dioxide, silicon nitride, and sulfide.

7. A gas sensor device based on a nanometer-thick micro-resonant cavity according to claim 1, characterized in that: The gas sensor device can realize gas detection based on the movement of the resonance peak caused by the change of the refractive index, or realize gas detection based on the change of the resonance peak extinction ratio caused by optical absorption loss; the gas sensor device can realize gas detection based on one resonance peak, and can also realize gas detection and multi-parameter decoupling based on several resonance peaks.

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