阅读说明：本技术 一种片上光学丙酮气体传感器及其制备工艺和应用 (On-chip optical acetone gas sensor and preparation process and application thereof ) 是由 王志明 牛浩芸 余鹏 于 2021-08-27 设计创作，主要内容包括：一种片上光学丙酮气体传感器及其制备工艺和应用。本发明公开了一种片上光学丙酮气体传感器,包括依次层叠的衬底层、波导下包层、波导芯层、波导上包层、气敏薄膜；所述气敏薄膜包括聚乙烯亚胺和氨基化石墨烯的分层薄膜。本发明的片上光学丙酮气体传感器能利用聚乙烯亚胺和氨基化石墨烯做为气敏薄膜覆盖到传感器结构上,可以实现对丙酮气体的低检测极限,高灵敏度传感,而且实验证明该薄膜具有良好的重复性和稳定性。该传感器利用马赫曾德尔干涉仪对微小折射率变化敏感的性质,可以大大提高传感器的灵敏度和检测极限。(An on-chip optical acetone gas sensor and a preparation process and application thereof. The invention discloses an on-chip optical acetone gas sensor, which comprises a substrate layer, a waveguide lower cladding, a waveguide core layer, a waveguide upper cladding and a gas-sensitive film which are sequentially stacked; the gas-sensitive film comprises a layered film of polyethyleneimine and aminated graphene. The on-chip optical acetone gas sensor can cover the sensor structure by using the polyethyleneimine and the aminated graphene as gas-sensitive films, can realize low detection limit and high sensitivity sensing of acetone gas, and experiments prove that the film has good repeatability and stability. The sensor utilizes the property that the Mach-Zehnder interferometer is sensitive to tiny refractive index change, and can greatly improve the sensitivity and the detection limit of the sensor.)

1. An on-chip optical acetone gas sensor, comprising: the gas-sensitive film comprises a substrate layer, a waveguide lower cladding, a waveguide core layer, a waveguide upper cladding and a gas-sensitive film which are sequentially stacked; the gas-sensitive film comprises a layered film of polyethyleneimine and aminated graphene.

2. The on-chip optical acetone gas sensor according to claim 1, wherein: the substrate layer is made of silicon.

3. The on-chip optical acetone gas sensor according to claim 1, wherein: the waveguide lower cladding is made of silicon dioxide.

4. The on-chip optical acetone gas sensor according to claim 1, wherein: the waveguide core layer is made of silicon nitride.

5. The on-chip optical acetone gas sensor according to claim 1, wherein: the waveguide upper cladding is made of silicon dioxide.

6. A process for preparing an on-chip optical acetone gas sensor according to claim 1, wherein: the method comprises the following steps:

s1 providing a silicon substrate layer;

s2, depositing silicon dioxide on the substrate layer to form a waveguide lower cladding layer;

s3 depositing silicon nitride on the lower waveguide cladding to form a waveguide core layer;

s4, etching a Mach-Zehnder interferometer structure on the waveguide core layer;

s5, continuing to deposit silicon dioxide on the waveguide core layer to form a waveguide upper cladding layer;

s6, etching a sensing area on the upper cladding layer of the waveguide;

s7 layering the surface of the upper cladding layer of the waveguide to manufacture a layered film of polyethyleneimine and aminated graphene.

7. The process for preparing an on-chip optical acetone gas sensor according to claim 6, wherein: the preparation method of the layered film comprises the following steps:

s71, pouring the polyethyleneimine solution into a beaker, then measuring deionized water, pouring the deionized water into the beaker, and diluting the polyethyleneimine solution to obtain a polyethyleneimine solution with the mass fraction of 1%; obtaining uniformly dispersed polyethyleneimine solution after ultrasonic treatment;

s72, directly pouring a certain amount of aminated graphene aqueous dispersion into a beaker, putting the beaker into an ultrasonic cleaning machine, and carrying out ultrasonic treatment on the solution to obtain an evenly dispersed aminated graphene aqueous dispersion;

s73, spraying the prepared polyethyleneimine solution onto the surface of the structure, placing the structure into a culture dish after the spraying is finished, sealing, and then placing into an oven for drying;

s74, a certain amount of aminated graphene water dispersion liquid is dripped on the polyethyleneimine film by using a liquid transfer gun to form a layered film; and (3) placing the acetone sensor covered with the layered film into a culture dish, sealing, and then placing into an oven for drying to obtain a sensor finished product.

8. The process for preparing an on-chip optical acetone gas sensor according to claim 6, wherein: in the step S4, a mach-zehnder interferometer structure is etched on the silicon nitride by ultraviolet lithography and Reactive Ion Etching (RIE).

9. The process for preparing an on-chip optical acetone gas sensor according to claim 6, wherein: in step S6, a sensing area is etched on the sensing arm by ultraviolet lithography and Reactive Ion Etching (RIE).

10. Use of an on-chip optical acetone gas sensor according to claim 1 wherein: the on-chip optical acetone gas sensor is applied to acetone detection.

Technical Field

The invention relates to the field of optical sensors, in particular to an on-chip optical acetone gas sensor and a preparation process and application thereof.

Background

In the last years, the integrated optical sensor has attracted more and more students' attention due to the advantages of electromagnetic interference resistance, short response time, and suitability for extreme environments. The principles of these sensors are mostly based on changes in light absorption or reflectance, changes in luminescence intensity, Surface Plasmon Resonance (SPR) or evanescent wave analysis. Of these, Mach-Zehnder interferometer (MZI) waveguides based on evanescent wave sensing are very attractive because they are very sensitive to small refractive index changes and have been successfully used in many fields such as pressure sensing, detection of gases, volatile organic compounds, detection of DNA/RNA, proteins and other biomolecules. For the detection of a single gas, the realization of high sensitivity, selectivity, repeatability and stability is the greatest challenge to the performance of the sensor. At present, the application of the integrated optical sensor in China is less.

In recent years, diabetes gradually becomes younger, and the concentration of acetone gas exhaled by a human body is particularly important in medical detection as the most reliable and valuable marker for diabetes detection. The detection of the acetone gas with low concentration is realized, which is beneficial to the early discovery and early treatment of diabetes. The traditional detection method needs to collect blood and urine, has long detection time and high cost and brings harm to patients. Even though gas chromatographs, mass spectrometers or near-and mid-infrared laser spectrometers have traditionally been used, they perform very well in terms of sensitivity, specificity (without interference), but are bulky and expensive and limited to high-end laboratories. On the other hand, there are low-cost devices, thin film transistors, metal oxide or electrochemical gas sensors, but these sensors have limited sensitivity, poor stability, harsh conditions of use (e.g., sensitivity can be maintained at high temperatures), and cross-responsiveness to other gases.

Disclosure of Invention

The invention provides an on-chip optical acetone gas sensor with higher sensitivity, smaller volume and stronger anti-interference capability, a preparation process and application thereof, aiming at solving the defects of limited sensitivity, poor stability, harsh use conditions and the like of the traditional electrochemical acetone gas sensor in the prior art.

The invention provides an on-chip optical acetone gas sensor, which comprises a substrate layer, a waveguide lower cladding, a waveguide core layer, a waveguide upper cladding and a gas-sensitive film which are sequentially stacked; the gas-sensitive film comprises a layered film of polyethyleneimine and aminated graphene.

The invention also provides the following optimization scheme:

preferably, the substrate layer is made of silicon. Preferably, the substrate layer material is a standard 4 inch high purity silicon wafer.

Preferably, the waveguide lower cladding is made of silica. The waveguide lower cladding material is preferably silica having a thickness of 2 μm.

Preferably, the waveguide core layer is made of a silicon nitride material. The waveguide core material is preferably silicon nitride with a thickness of 250 nm.

Preferably, the waveguide upper cladding is made of silica. The waveguide upper cladding material is preferably silica with a thickness of 1 μm.

The invention also provides a preparation process of the on-chip optical acetone gas sensor, which comprises the following steps:

s1 providing a silicon substrate layer;

s2, depositing silicon dioxide on the substrate layer to form a waveguide lower cladding layer;

s3 depositing silicon nitride on the lower waveguide cladding to form a waveguide core layer;

s4, etching a Mach-Zehnder interferometer structure on the waveguide core layer;

s5, continuing to deposit silicon dioxide on the waveguide core layer to form a waveguide upper cladding layer;

s6, etching a sensing area on the upper cladding layer of the waveguide;

s7 layering the surface of the upper cladding layer of the waveguide to manufacture a layered film of polyethyleneimine and aminated graphene.

Preferably, the preparation method of the layered film comprises the following steps:

s71, pouring the polyethyleneimine solution into a beaker, then measuring deionized water, pouring the deionized water into the beaker, and diluting the polyethyleneimine solution to obtain a polyethyleneimine solution with the mass fraction of 1%; obtaining uniformly dispersed polyethyleneimine solution after ultrasonic treatment;

s72, directly pouring a certain amount of aminated graphene aqueous dispersion into a beaker, putting the beaker into an ultrasonic cleaning machine, and carrying out ultrasonic treatment on the solution for 30min to obtain an evenly dispersed aminated graphene aqueous dispersion;

s73, spraying the prepared polyethyleneimine solution onto the surface of the structure, placing the structure into a culture dish after the spraying is finished, sealing, and then placing into an oven for drying;

s74, a certain amount of aminated graphene water dispersion liquid is dripped on the polyethyleneimine film by using a liquid transfer gun to form a layered film; and (3) placing the acetone sensor covered with the layered film into a culture dish, sealing, and then placing into an oven for drying to obtain a finished product.

Preferably, in step S4, the mach-zehnder interferometer structure is etched on the silicon nitride by ultraviolet lithography, Reactive Ion Etching (RIE).

Preferably, in step S6, the sensing region is etched on the sensing arm by ultraviolet lithography and Reactive Ion Etching (RIE).

Preferably, the on-chip optical acetone gas sensor is applied to acetone detection.

The on-chip optical acetone gas sensor can cover the sensor structure by using the polyethyleneimine and the aminated graphene as gas-sensitive films, can realize low detection limit and high sensitivity sensing of acetone gas, and experiments prove that the film has good repeatability and stability.

Drawings

FIG. 1 is a diagram showing the structure of an acetone gas sensor on a chip according to the present invention.

Fig. 2 is a scanning electron microscope image of the polyethyleneimine monolayer film and the polyethyleneimine and aminated graphene layered film according to the present invention.

FIG. 3 is a flow chart of the preparation of the on-chip acetone gas sensor of the present invention.

FIG. 4 is a graph showing the relationship between the concentration of acetone gas and the optical power measured by the on-chip acetone gas sensor of the present invention.

Detailed Description

In order that those skilled in the art will better understand the technical solutions of the present invention, the present invention will be further described in detail with reference to the following embodiments.

The invention provides an on-chip optical acetone gas sensor, which comprises a substrate layer, a waveguide lower cladding, a waveguide core layer, a waveguide upper cladding and a gas-sensitive film which are sequentially stacked; the gas-sensitive film comprises a layered film of polyethyleneimine and aminated graphene.

The substrate layer material was a standard 4 inch high purity silicon wafer.

The waveguide lower cladding material is preferably silica having a thickness of 2 μm. The waveguide lower cladding layer is the buffer layer.

The waveguide core material is preferably silicon nitride with a thickness of 250 nm.

The waveguide upper cladding material is preferably silica with a thickness of 1 μm.

The invention also provides a preparation process of the on-chip optical acetone gas sensor, which comprises the following steps:

s1 providing a silicon substrate layer;

s2, depositing silicon dioxide on the substrate layer to form a waveguide lower cladding layer;

s3 depositing silicon nitride on the lower waveguide cladding to form a waveguide core layer;

s4, etching a Mach-Zehnder interferometer structure on the waveguide core layer;

s5, continuing to deposit silicon dioxide on the waveguide core layer to form a waveguide upper cladding layer;

s6, etching a sensing area on the upper cladding layer of the waveguide;

s7 layering the surface of the upper cladding layer of the waveguide to manufacture a layered film of polyethyleneimine and aminated graphene.

As shown in fig. 3, the preparation method of the layered film is as follows:

s71, pouring the polyethyleneimine solution into a beaker, then measuring deionized water, pouring the deionized water into the beaker, and diluting the polyethyleneimine solution to obtain a polyethyleneimine solution with the mass fraction of 1%; obtaining uniformly dispersed polyethyleneimine solution after ultrasonic treatment;

s72, directly pouring a certain amount of aminated graphene aqueous dispersion into a beaker, putting the beaker into an ultrasonic cleaning machine, and carrying out ultrasonic treatment on the solution for 30min to obtain an evenly dispersed aminated graphene aqueous dispersion;

s73, spraying the prepared polyethyleneimine solution onto the surface of the structure, placing the structure into a culture dish after the spraying is finished, sealing, and then placing into an oven for drying;

s74, a certain amount of aminated graphene water dispersion liquid is dripped on the polyethyleneimine film by using a liquid transfer gun to form a layered film; and (3) placing the acetone sensor covered with the layered film into a culture dish, sealing, and then placing into an oven for drying to obtain a finished product.

Preferably, in step S4, the mach-zehnder interferometer structure is etched on the silicon nitride by ultraviolet lithography, Reactive Ion Etching (RIE).

Preferably, in step S6, the sensing region is etched on the sensing arm by ultraviolet lithography and Reactive Ion Etching (RIE).

The preparation process of the on-chip acetone gas sensor comprises the following specific processes:

providing a substrate layer, wherein the substrate layer is made of a high-purity silicon wafer; and growing a layer of silicon dioxide on the substrate layer to serve as a buffer layer, wherein the silicon dioxide is grown by a thermal oxidation growth method or a Plasma Enhanced Chemical Vapor Deposition (PECVD) method. And secondly, using a layer of silicon nitride as a waveguide core layer by Low Pressure Chemical Vapor Deposition (LPCVD) or Plasma Enhanced Chemical Vapor Deposition (PECVD). The mach-zehnder interferometer structure is then etched on the silicon nitride through the processes of ultraviolet lithography and Reactive Ion Etching (RIE) in sequence. Then, a layer of silicon dioxide is deposited on the silicon nitride through a Plasma Enhanced Chemical Vapor Deposition (PECVD) method to be used as a waveguide cladding, the position of the sensing arm is found on the cladding, and a sensing area is etched on the sensing arm through a method of ultraviolet lithography and reactive ion etching. And finally, air-spraying a polyethyleneimine solution on the surface of the structure, dripping the aminated graphene aqueous dispersion after the drying box is kept still for 24 hours, and keeping the drying box still for 24 hours for testing.

The invention applies the high polymer material film with good gas-sensitive characteristic to the integrated optical sensor, and uses the film material to replace the waveguide cladding structure, thus realizing that the acetone gas can keep high sensitivity under extremely low concentration, and can be repeatedly and stably sensed. The application provides a waveguide based on an on-chip Mach-Zehnder interferometer structure, as shown in figure 1, the waveguide has a high-sensitivity surface by optimally designing the thickness of a waveguide core layer, the rib width of the waveguide, the etching thickness of the waveguide and the area size of a sensing area. And covering a layered film of polyethyleneimine and aminated graphene on a sensing arm of the interferometer structure waveguide. The film is made of branched polyethyleneimine. The nucleophilic addition reversible reaction occurs between various amino functional groups such as primary amine, secondary amine and the like in the branched polyethyleneimine and carbonyl in acetone, the adsorption capacity of the reaction is far greater than that of physical adsorption, and the sensitivity to acetone is improved. Similarly, aminated graphene also contains amino functional groups, and nucleophilic addition reversible reaction can also occur, the reaction is rightward in the response process of the sensor, the reaction is leftward in the response recovery process, and the process from response to recovery can be proved by first red shift and then blue shift of an absorption peak in a spectrum. The two cover in proper order and form the layering film on sensor surface, and amination graphite alkene film has great specific surface area for the layering film has more folds in comparison with single-layer polyethyleneimine film surface, has increased the adsorption area, provides more absorption hole sites, makes the absorption and desorption of acetone gas go on more fast. The characteristics prove that the sensor not only has good selectivity to acetone gas, but also has repeatability. In fig. 2, (a) is a polyethyleneimine film, and (b) is a layered film of polyethyleneimine and aminated graphene. The gas-sensitive characteristics of the layered film can be maximized by combining the high-sensitivity surface of the mach-zehnder interferometer structure. In the test, a helium-neon laser is selected to couple light with the wavelength of 632.8nm into the input end of a waveguide structure, when the light passes through a sensing arm, the layered film absorbs acetone gas molecules, and at the moment, the effective refractive index of the sensing arm waveguide is changed, so that the light intensity of the output end is changed, and the output end of the waveguide is connected with an optical power meter to measure the change of the light intensity, so that the corresponding relationship of the change of the concentration of the acetone gas is obtained. The entire testing process does not require expensive equipment and can be performed at room temperature.

The on-chip optical acetone gas sensor is mainly applied to acetone detection.

The foregoing is a detailed description of the invention and the following is an example of the invention.

Example one

The preparation method of the on-chip acetone gas sensor described in this embodiment is as follows:

s1, providing a substrate layer, wherein the substrate layer is made of a silicon wafer which is divided into 1cm by 3cm by a standard 4-inch silicon wafer;

depositing silicon dioxide with the thickness of 2 mu m on the substrate layer by a Plasma Enhanced Chemical Vapor Deposition (PECVD) method at the temperature of 2300 ℃;

s3800 ℃, depositing silicon nitride with the thickness of 250nm on silicon dioxide by using a Low Pressure Chemical Vapor Deposition (LPCVD) method;

s4, etching a Mach-Zehnder interferometer structure on the silicon nitride through ultraviolet lithography and Reactive Ion Etching (RIE), wherein the rib width of the etched waveguide is 2 mu m, and the etching depth is 10 nm;

depositing silicon dioxide with the thickness of 1 mu m on the etched structure by a Plasma Enhanced Chemical Vapor Deposition (PECVD) method at the temperature of 5300 ℃;

s6, etching a sensing area with the length of 15000 mu m and the width of 50 mu m on the sensing arm by Reactive Ion Etching (RIE) through ultraviolet photoetching again, wherein the etching depth is 1 mu m;

s7, manufacturing a required layered film of polyethyleneimine and aminated graphene in a layered manner;

the specific preparation process of the layered film of the polyethyleneimine and the aminated graphene comprises the following steps:

s71, 1ml of polyethyleneimine solution with the mass fraction of 50% is taken and poured into a beaker, and then 49ml of deionized water is taken and poured into the beaker to dilute the polyethyleneimine solution, so that the polyethyleneimine solution with the mass fraction of 1% is obtained. And (4) performing ultrasonic treatment for 30min to finally obtain a uniformly dispersed polyethyleneimine solution.

S72, directly pouring a certain amount of 0.5mg/ml aminated graphene aqueous dispersion into a beaker, putting the beaker into an ultrasonic cleaning machine, setting the cleaning temperature of the ultrasonic cleaning machine to be 40 ℃, and carrying out ultrasonic treatment on the solution for 30min to obtain the uniformly dispersed aminated graphene aqueous dispersion.

S73, spraying the prepared polyethyleneimine solution onto the surface of the structure through a spray pen, placing the structure into a culture dish after the air spraying is finished, sealing, and then placing into an oven at 80 ℃ for drying for 24 hours.

S74, a certain amount of aqueous dispersion of aminated graphene is dripped on the polyethyleneimine film by using a pipette to form a layered film. And (3) placing the acetone sensor covered with the layered film into a culture dish, sealing, and then placing into an oven at 80 ℃ for drying for 24 hours to be tested.

The experimental setup for detecting acetone gas concentration consisted of a helium-neon laser (3mW, 632.8nm), two objective lenses and an optical power meter. The finished sensor is placed on a position adjustment stage and the laser beam is coupled perpendicularly to the polished end face of the sensor through a first microscope objective. A second objective lens is placed at the output of the sensor to focus the light onto the probe surface of the optical power meter. The optical power meter can sense the optical power change of nW level. The finished sensor can be directly exposed in acetone gas (the concentration change of the acetone gas can be controlled by a static gas distribution method), and the output intensity of the sensor is monitored by an optical power meter, and the indication change of the optical power meter reflects the change of the concentration of the acetone gas. As shown in FIG. 4, in the range of the acetone gas concentration from 0.5ppm to 10ppm, the change in the optical power meter was approximately 37. mu.W/ppm, and the sensitivity of the sensor was estimated to be 1.51X 10^-5RIU/ppm，2.7×10^-2rad/ppm。

The detection limit of the on-chip acetone gas sensor prepared by the method is 0.5ppm, the response time is about 5 seconds, and the response complete recovery time is 2 minutes.

Example two

The preparation method of the on-chip acetone gas sensor described in this embodiment is as follows:

s1, providing a substrate layer, wherein the substrate layer is made of a silicon wafer which is divided into 1cm by 2cm by a standard 4-inch silicon wafer;

depositing silicon dioxide with the thickness of 2 mu m on the substrate layer by a Plasma Enhanced Chemical Vapor Deposition (PECVD) method at the temperature of 2300 ℃;

s3800 ℃, depositing silicon nitride with the thickness of 150nm on silicon dioxide by using a Low Pressure Chemical Vapor Deposition (LPCVD) method;

s4, etching a Mach-Zehnder interferometer structure on the silicon nitride through ultraviolet lithography and Reactive Ion Etching (RIE), wherein the rib width of the etched waveguide is 4 mu m, and the etching depth is 15 nm;

depositing silicon dioxide with the thickness of 1 mu m on the etched structure by a Plasma Enhanced Chemical Vapor Deposition (PECVD) method at the temperature of 5300 ℃;

s6, etching a sensing area with the length of 9000 microns and the width of 50 microns on the sensing arm by Reactive Ion Etching (RIE) through ultraviolet photoetching again, wherein the etching depth is 1 micron;

s7, manufacturing a required layered film of polyethyleneimine and aminated graphene in a layered manner;

the specific preparation process of the layered film of the polyethyleneimine and the aminated graphene comprises the following steps:

s71, 1ml of polyethyleneimine solution with the mass fraction of 50% is taken and poured into a beaker, and then 49ml of deionized water is taken and poured into the beaker to dilute the polyethyleneimine solution, so that the polyethyleneimine solution with the mass fraction of 1% is obtained. And (4) performing ultrasonic treatment for 30min to finally obtain a uniformly dispersed polyethyleneimine solution.

S72, directly pouring a certain amount of 0.5mg/ml aminated graphene aqueous dispersion into a beaker, putting the beaker into an ultrasonic cleaning machine, setting the cleaning temperature of the ultrasonic cleaning machine to be 40 ℃, and carrying out ultrasonic treatment on the solution for 30min to obtain the uniformly dispersed aminated graphene aqueous dispersion.

S73, spraying the prepared polyethyleneimine solution onto the surface of the structure through a spray pen, placing the structure into a culture dish after the air spraying is finished, sealing, and then placing into an oven at 80 ℃ for drying for 24 hours.

S74, a certain amount of aqueous dispersion of aminated graphene is dripped on the polyethyleneimine film by using a pipette to form a layered film. And (3) placing the acetone sensor covered with the layered film into a culture dish, sealing, and then placing into an oven at 80 ℃ for drying for 24 hours to be tested.

The experimental setup for detecting acetone gas concentration consisted of a helium-neon laser (3mW, 632.8nm), two objective lenses and an optical power meter. The finished sensor is placed on a position adjustment stage and the laser beam is coupled perpendicularly to the polished end face of the sensor through a first microscope objective. A second objective lens is placed at the output of the sensor to focus the light onto the probe surface of the optical power meter. The optical power meter can sense the optical power change of nW level. The finished sensor can be directly exposed in acetone gas (the concentration change of the acetone gas can be controlled by a static gas distribution method), and the output intensity of the sensor is monitored by an optical power meter, and the indication change of the optical power meter reflects the change of the concentration of the acetone gas. In the interval of change of the acetone gas concentration from 8ppm to 50ppm, the change of the optical power meter is about 14.8 μ W/ppm, and the sensitivity of the sensor can be estimated to be 6.89 × 10^-6RIU/ppm，8.19×10^-3rad/ppm。

The detection limit of the on-chip acetone gas sensor prepared by the method is 8ppm, the response time is about 5 seconds, and the response complete recovery time is 2 minutes.

The above is only a preferred embodiment of the present invention, and it should be noted that the above preferred embodiment should not be considered as limiting the present invention, and the protection scope of the present invention should be subject to the scope defined by the claims. It will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the spirit and scope of the invention, and these modifications and adaptations should be considered within the scope of the invention.