SELECTIVE GAS SENSOR

Abstract

A selective gas sensor has a light source, a sensor chip and a light detector. The sensor chip has an optical input and an optical output. The light source is optically connected with the optical input of the sensor chip. The optical output of the sensor chip is optically connected with the optical input of the light detector with ability to guide a light from the light source output to the optical input of the light detector The sensor chip includes a substrate, an asymmetric Mach-Zehnder interferometer, including multiple asymmetrical Mach-Zehnder interferometer structures optically connected in parallel, each having different pores size of the polymer cladding and has multiple outputs that correspond to each of the Mach-Zehnder interferometer structures outputs The pore sizes of each polymer cladding differ by 0.02 nm to 0.1 nm. A method for manufacturing the proposed selective gas sensor is also disclosed.

Claims

1. A selective gas sensor, comprising a light source, a sensor chip and a light detector; the sensor chip having an optical input and an optical output, where the light source is optically connected with the optical input of the sensor chip; the optical output of the sensor chip is optically connected with the optical input of the light detector with ability to guide a light from the light source output, through the sensor chip, to the optical input of the light detector; wherein the sensor chip comprises a substrate, an asymmetric Mach-Zehnder interferometer, having an input and an output; and a cladding, wherein the asymmetric Mach-Zehnder interferometer includes multiple asymmetrical Mach-Zehnder interferometer structures optically connected in parallel, each having different pores size of the polymer cladding that covers both the reference arm and the measurement arm of each respective Mach-Zehnder interferometer, and has multiple outputs that correspond to each of the Mach-Zehnder interferometer structures outputs; wherein the pore sizes of each polymer cladding differ by 0.02 nm to 0.1 nm.

2. The selective gas sensor according to claim 1, wherein the substrate comprises a glass, a quartz, or a polymer film.

3. The sensor according to claim 1, wherein the light source, the sensor chip, and the light detector are optically connected with an optical fiber.

4. The sensor according to claim 1, wherein the polymer cladding one has pores size from 0.23 nm to 0.35 nm; the polymer cladding two has pores size from 0.18 nm to 0.25 nm; the polymer cladding three has pores size from 0.13 nm to 0.2 nm; and the polymer cladding four has pores size from 0.08 nm to 0.15 nm.

5. A method for manufacturing of the sensor chip for the selective gas sensor according to claim 1, comprising the following steps: (i) providing at least one substrate, comprising of a glass, a quartz, or a polymer film, (ii) depositing on the substrate at least one photoresist layer of epoxy-based negative photoresist, (iii) creation at least two optically connected in parallel Mach-Zehnder interferometer structures in the polymer layer, (iv) deposition of polymer claddings on each Mach-Zehnder interferometer structure, (v) thermal treatment of the polymer claddings selecting thermal treatment time and temperature to create the desired pores size of each polymer claddings to obtain different pores size of the polymer claddings on respective Mach-Zehnder interferometer structures.

6. The method according to claim 5, wherein depositing on the substrate of at least one photoresist layer of epoxy-based negative photoresist is made by spin-coating.

7. The method according to claim 5, wherein creation of the Mach-Zehnder interferometer structures in the polymer layer is made by optical lithography.

8. The method according to claim 5, wherein deposition of the polymer claddings on the Mach-Zehnder interferometer structures is made by spray-coating.

9. The method according to claim 5, wherein at the step (iii) at least four optically connected in parallel Mach-Zehnder interferometer structures are created in the polymer layer.

10. The method according to claim 5, wherein thermal treatment of the polymer claddings at the step (v) is made by keeping first polymer cladding at the temperature from 60 to 75 C. for 60-300 seconds; second polymer cladding at the temperature from 75 to 90 C. for 60-300 seconds; third polymer cladding at the temperature from 90 to 105 C. for 60-300 seconds; and fourth polymer cladding at the temperature from 105 to 120 C. for 60-300 seconds.

11. (canceled)

12. The sensor according to claim 2, wherein the light source, the sensor chip, and the light detector are optically connected with an optical fiber.

13. The sensor according to claim 2, wherein the polymer cladding one has pores size from 0.23 nm to 0.35 nm; the polymer cladding two has pores size from 0.18 nm to 0.25 nm; the polymer cladding three has pores size from 0.13 nm to 0.2 nm; and the polymer cladding four has pores size from 0.08 nm to 0.15 nm.

14. The sensor according to claim 3, wherein the polymer cladding one has pores size from 0.23 nm to 0.35 nm; the polymer cladding two has pores size from 0.18 nm to 0.25 nm; the polymer cladding three has pores size from 0.13 nm to 0.2 nm; and the polymer cladding four has pores size from 0.08 nm to 0.15 nm.

Description

SHORT DESCRIPTION OF DRAWINGS

[0018] FIG. 1 shows principal scheme of the device;

[0019] FIG. 2 shows the structural scheme of one embodiment of the sensor chip;

[0020] FIG. 3 schematically shows gas interaction with cladding layer and induced refractive index changes due to filling of pores of the cladding layer;

[0021] FIG. 4 shows the manufacturing workflow;

[0022] FIG. 5 shows the scheme of a test device;

[0023] FIG. 6 shows an example of an experimental measurement of the proposed sensor signal, when exposed to 50 ppm ammonia in nitrogen;

[0024] FIG. 7 shows the structural scheme of another embodiment of the sensor chip;

[0025] FIG. 8shows an example of an experimental measurement of the proposed sensor signal, when exposed to Isopropanol vapours.

[0026] The proposed selective gas sensor (FIG. 1), comprises a light source (1), a sensor chip (2) and a light detector (3). The sensor chip (2) is designed to have an optical input (20) and an optical output (21), where the lightsource (1) is optically connected with the optical input (20) of the sensor chip (2). The optical output (21) of the sensor chip (2) is optically connected with the optical input of the light detector (3) with ability to guide a light from the light source (1) output, through the sensor chip (2), to the optical input of the light detector (3).

[0027] The sensor chip (2) comprises a substrate (22), an asymmetric Mach-Zehnder interferometer (23), having an input (24) and an output (25); and a cladding (30).

[0028] According to the invention, the substrate (22) can be a glass, or a quartz, or a polymer film.

[0029] The asymmetric Mach-Zehnder interferometer (23) comprises multiple asymmetrical Mach-Zehnder interferometer structures (23, 23, 23, 23) optically connected in parallel (FIG. 2), each having different pores size of the polymer cladding (31, 32, 33, 34) that covers both the reference arm and the measurement arm of each respective Mach-Zehnder interferometer and has multiple outputs that correspond to each of the Mach-Zehnder interferometer structures (23, 23, 23, 23) outputs. The pore sizes of each polymer cladding (31, 32, 33, 34) differ by 0.02 nm to 0.1 nm.

[0030] The cladding material may be a organic polymer, for instance, poly(methyl methacrylate), or polysulfon.

[0031] According to the preferred embodiment, the light source (1), the sensor chip (2), and the light detector (3) are optically connected with an optical fiber (40).

[0032] According to another embodiment, the sensor comprises at least four optically connected in parallel Mach-Zehnder interferometer structures (23, 23, 23, 23)FIG. 2, which are created in the polymer layer and having different claddings (31, 32, 33, 34). In this embodiment, the polymer cladding one (31) has pores size from 0.23 nm to 0.35 nm; the polymer cladding two (32) has pores size from 0.18 nm to 0.25 nm; the polymer cladding three (33) has pores size from 0.13 nm to 0.2 nm; the polymer cladding four (34) has pores size from 0.08 nm to 0.15 nm.

[0033] Due to external gas filling pores of cladding material, refractive index of cladding (30) changes (FIG. 3). As part of mode is dilated in to cladding (30), refractive index changes in this layer also influence the mode transmittance through device through change its phase. As the device is made asymmetric, there will be a phase difference between both interferometer arms, leading to changes in output intensity. By detecting these changes, external gas presence can be detected. For this purpose, the device needs to have single-mode waveguides at the working wavelength. This can be achieved through waveguide dimension tuning. Asymmetry alterations will allow to measure wide range of Ammonia concentrations (lower asymmetry for low concentration, higher asymmetry for larger concentrations). Different claddings (30) allow to selectively measure concentrations of other gases that could be present in the environment.

[0034] The method for manufacturing of the sensor chip (2) for the selective gas sensor is also claimed. The method comprising the following steps: (i) providing at least one substrate (22), comprising of a glass, a quartz, or a polymer film; (ii) depositing on the substrate (22) at least one photoresist layer of epoxy-based negative photoresist; (iii) creation at least two optically connected in parallel Mach-Zehnder interferometer structures (23) in the polymer layer; (iv) deposition of polymer claddings (30) on each Mach-Zehnder interferometer structure (23); (v) thermal treatment of the polymer claddings (30) selecting thermal treatment time and temperature to create the desired pores size of each polymer claddings (30) to obtain different pores size of the polymer claddings (31, 32, 33, 34) on respective Mach-Zehnder interferometer structures (23, 23, 23, 23)FIG. 4.

[0035] The epoxy-based negative photoresist can be any epoxy-based negative photoresist, having refractive index between 1.58-1.7 at 633 nm.

[0036] According to the invention, depositing on the substrate (22) of at least one photoresist layer of epoxy-based negative photoresist can be made by spin-coating; creation of the Mach-Zehnder interferometer structures (23) in the polymer layer can be made by optical lithography; deposition of the polymer claddings (30) on the Mach-Zehnder interferometer structures (23) can be made by spray-coating.

[0037] According to one embodiment of the method, at the step (iii) at least four optically connected in parallel Mach-Zehnder interferometer structures (23, 23, 23, 23) are created in the polymer layer.

[0038] In general, to get polymer cladding with desired properties, it is thermally treated at the temperature from 55 to 150 C. for 30-400 seconds. According to invention, the connected in parallel Mach-Zehnder interferometer structures (23, 23, 23, 23), created in the polymer layer, each having claddings with different properties.

[0039] In the particular embodiment with four in parallel connected Mach-Zehnder interferometer structures (23, 23, 23, 23) have pores size as follows: the polymer cladding one (31)from 0.23 nm to 0.35 nm; the polymer cladding two (32)from 0.18 nm to 0.25 nm; the polymer cladding three (33)from 0.13 nm to 0.2 nm; the polymer cladding four (34)from 0.08 nm to 0.15 nm. To achieve this the thermal treatment of the polymer claddings (30) at the step (v) of the above method, is made by keeping first polymer cladding (31) at the temperature from 60 to 75 C. for 60-300 seconds; second polymer cladding (32) at the temperature from 75 to 90 C. for 60-300 seconds; third polymer cladding (33) at the temperature from 90 to 105 C. for 60-300 seconds; fourth polymer cladding (34) at the temperature from 105 to 120 C. for 60-300 seconds.

EXAMPLES OF IMPLEMENTATION OF THE INVENTION

[0040] Example 1. According to one embodiment, the device comprises asymmetrical Mach-Zehnder Interferometers (23) based on SU-8 waveguides structures. The Mach-Zehnder Interferometer (23) part of the structure is coated with PMMA (FIG. 5). Firstly, a SU-8 layer of thickness 1.2 um is deposited on the substrate using the spin-coating technique. The device is then structured using a direct write lithography procedure with illumination wavelength of 365 nm. Waveguide input consists of a taper structure with the input of 10 m that converts to a 1 m wide waveguide over 5 mm length. The rest of the waveguide structure consists of a 1 m wide waveguide. The asymmetrical Mach-Zehnder Interferometer (23) has one arm with a length of 10 mm while the other arm has a length of 10.125 mm. These structures are coated with PMMA using the spray-coating method. To do this PMMA is firstly dissolved in anisole and then sprayed through a mask on top of the structures to produce a 2 m thick layer. To test device sensitivity, the light irradiation with a wavelength of 632.8 nm is coupled into the chip with the lens with a magnification of 20, and output light is collected also with lens with a magnification of 20. The sensor is periodically exposed to 50 ppm ammonia gas in nitrogen. Examples of experimental data are shown in FIG. 6.

[0041] Example 2. According to another embodiment, the device comprises two asymmetrical Mach-Zehnder interferometers (23, 23) based on SU-8 waveguides structures (FIG. 7). Both of the Mach-Zehnder interferometer (23, 23) part of the structure is coated with PMMA. The device is then structured using a direct write lithography procedure with illumination wavelength of 365 nm. Waveguide input comprises a taper structure with the input of 10 m that converts to a 1 m wide waveguide over 5 mm length. The rest of the waveguide structure comprises a 1 m wide waveguide. Both asymmetrical Mach-Zehnder interferometers (23, 23) have one arm with a length of 10 mm while the other arm has a length of 18 mm. These structures are coated with PMMA using the spray-coating method. After cladding deposition on first Mach-Zehnder interferometer (23), the cladding (31) is baked at 120 C. for 5 min. After cladding deposition on the second Mach-Zehnder interferometer (23), the cladding (32) is baked at 60 C. for 5 min. Due to the time and temperature difference in the baking procedures of each cladding (31, 32), the pore size will be different. This will strongly influence sensitivity to larger molecules while having minimal impact to detection of smaller molecules. To test device sensitivity, the light irradiation with a wavelength of 632.8 nm is coupled into the chip with the lens with a magnification of 20, and output light is collected also with lens with a magnification of 20. The sensor was periodically exposed to Isopropanol (IPA) vapours. Comparison of both sensor sensitivity to IPA is shown in FIG. 8. When embodiment according to this exampled was exposed to ammonia gas, the sensors showed no sensitivity change. The tested sensitivity to water was the same for both sensors.

[0042] Main advantage of the device is its high sensitivity, fast response time, robustness and simple fabrication. Thus, the sensor according to the present invention can be effectively used for ammonia detection. This is especially important for such areas as animal farms and cooling systems that use ammonia.

SOURCES OF INFORMATION

[0043] 1. Liu, X. et al. Sensors 12, 9635-9665 (2012). [0044] 2. Bamiedakis, N. et al. J. Light. Technol. 31, 1628-1635 (2013). [0045] 3. WO 2021/152345 A1; [0046] 4. Ali, A. R. et al. Chemosensors 5, 19 (2017). [0047] 5. Foreman, M. R. et al. Adv. Opt. Photonics 7, 168 (2015). [0048] 6. Hugon, O. et al. Sensors Actuators B Chem. 51, 316-320 (1998). [0049] 7. Sturaro, M. et al. Proceedings 1, 319 (2017). [0050] 8. Qin, J. et al. J. Phys. Chem. C 121, 24740-24744 (2017). [0051] 9. St-Gelais, R. et al. Sensors Actuators B Chem. 182, 45-52 (2013). [0052] 10. Gouva, P. M. P. et al. 96343D (2015). [0053] 11. GazDetect. https://www.gazdetect.com/download/pdf-anglais-infos-dg/EN-CSC300-Web.pdf. [0054] 12. Aeroqual. https://www.aeroqual.com/voc-sensors-monitors. [0055] 13. Evikon. https://www.evikon.eu/en/evikon-mci-m-1/solvent-vapors-detector-transmitter-e2608-voc-p-199. [0056] 14. lon Science. https://www.jonscience.com/products/tiger-handheld-voc-detector/?oclid=CiwKCAiA91bwBRAAEiwAnWa4050XzBfxALOM0w6Ee0c022ia DoQoiKacIOtAgePfERK19eGRLIK-YxoCEKsQAvD BwE. [0057] 15. U.S. Pat. No. 5,262,842 A. [0058] 16. WO 2021/152345 A1. [0059] 17. Chalyan T. et al.: Asymmetric Mach-Zehnder Interferometer Based Biosensors for Aflatoxin M1 Detection. Biosensors, vol. 6, no. 1. Jun. 1, 2016, DOI: 10.3390/bios6010001.