CN116256399A

CN116256399A - Carbon tube gas sensor based on fractal electrode

Info

Publication number: CN116256399A
Application number: CN202310048934.1A
Authority: CN
Inventors: 丁鹏飞; 刘欢; 贺庆国; 程建功
Original assignee: Shanghai Institute of Microsystem and Information Technology of CAS
Current assignee: Shanghai Institute of Microsystem and Information Technology of CAS
Priority date: 2023-02-01
Filing date: 2023-02-01
Publication date: 2023-06-13

Abstract

The invention relates to a carbon tube gas sensor based on a fractal electrode, which comprises: fractal electrodes (1, 2), wherein the fractal electrodes (1, 2) are deposited on two sides of a monocrystalline silicon piece (5); the carbon nano-tubes (6) are oriented orderly, and the carbon nano-tubes (6) are deposited between two fractal electrodes (1, 2) of a monocrystalline silicon wafer (5); and the sensitive material (7) is mutually compounded with the carbon nano tube (6) and is used as a sensitive layer for detecting gas. The invention provides a three-dimensional fractal electrode, a carbon tube can be induced under a strong electric field at a fractal angle so as to grow in an oriented order, and the obtained sensor has high mobility and high sensitivity.

Description

Carbon tube gas sensor based on fractal electrode

Technical Field

The invention belongs to the field of sensors, and particularly relates to a carbon tube gas sensor based on a fractal electrode.

Background

In recent years, a gas sensor based on carbon tubes has the characteristics of room temperature operation, low power consumption, high sensitivity and the like, and becomes a research hot spot of the gas sensor. However, most of carbon tube-based gas sensors are based on interdigital electrodes, and carbon tubes and organic sensitive materials are coated between the interdigital electrodes to form the sensor together. The carbon tubes are large in size and poor in solubility, so that the carbon tubes coated between the electrodes are in a randomly distributed and disordered structure, resulting in low mobility and poor repeatability of the device. The carbon nanotube devices distributed based on the random network often have low-frequency noise, which finally results in low signal-to-noise ratio and insufficient reliability of device detection results. These can be attributed to the uneven distribution of the carbon nanotubes, which causes carrier scattering, and thus causes signal fluctuation, sensitivity reduction, etc., which lowers the detection limit. Thus, it is necessary to prepare carbon tubes in an oriented arrangement on the electrodes.

CN 106290488B describes an amino-based functionalized carbon tube formaldehyde gas sensor prepared based on interdigitated electrodes.

CN206886666U describes a carbon nanotube electric field orientation instrument device, including studying the influence of electric field intensity and electric field type on orientation effect.

CN105551968B describes a field effect transistor with directional/disordered composite single-layer carbon nanotubes as channels and a manufacturing method thereof, which comprises researching the influence of factors such as density of carbon tube solution and the like on the electrical properties of the film.

A fractal structure for locally enhancing the electric field strength is described in Liyuan Pei et al Journal of Materials Chemistry A (2021), p.17400-17414 entitled "Nanosupercapacitors with fractal structures: searching designs to push the limit", but does not relate to a gas sensor but to a nano-capacitor (NSC).

However, the above-described technique has a disadvantage in that the carbon tubes are arranged randomly, and the sensitivity of the sensor is poor.

Disclosure of Invention

The invention aims to solve the technical problem of providing a carbon tube gas sensor based on a fractal electrode, wherein the carbon tube gas sensor provides a three-dimensional fractal electrode, and a carbon tube can be induced to grow in an oriented order under a strong electric field of a fractal angle, so that the obtained sensor has high mobility and high sensitivity.

The invention provides a carbon tube gas sensor based on a fractal electrode, which comprises: fractal electrodes deposited on two sides of the monocrystalline silicon piece; the carbon nano tube is deposited between two fractal electrodes of the monocrystalline silicon piece; the sensing material and the carbon nano tube are mutually compounded and serve as a sensing layer for detecting gas.

The fractal electrode consists of a plurality of fractal structures with a plurality of right-angle structures, and a fractal structure curve is formed by repeatedly iterating for more than 2-20 times based on sierpinski square fractal fractal functions. The preferred number of iterations is 2-6. The essential purpose is to improve the beam collecting capacity of electrons in an effective area through the fractal angle of the fractal structure, so that a high field intensity area is formed.

The spacing of the fractal electrodes is equal to the width of the fractal electrodes, and the numerical range is from submicron level to tens of microns.

And a bonding layer is arranged between the fractal electrode and the monocrystalline silicon piece. .

And (3) under the induction action of an electric field, the carbon nanotube dispersion liquid sequentially grows and orderly arranges along the field intensity direction of the fractal structure, and after the solution is volatilized, the oriented ordered carbon nanotubes are obtained. Under the action of an electric field, the carbon nanotubes are more concentrated at the fractal angle of the fractal structure and are induced to be polarized in a high field intensity region, and the polarization direction is distributed along the field intensity of the electric field, so that the directional arrangement of the carbon nanotubes is finally realized.

The solvent of the carbon nano tube dispersion liquid is at least one of N, N-dimethylformamide, chlorobenzene and toluene; the concentration of the carbon nanotube dispersion liquid ranges from 0.01mg/1mL to 0.1mg/1mL.

The concentration of the sensitive material ranges from 0.1mg/mL to 1mg/mL. The preferred concentration is 0.5mg/mL.

The sensitive material is 2- (2, 6-bis ((E) -5-bromo-2-hydroxystyryl) -4H-pyran-4-ylidene) malononitrile. Due to the interaction force of the sensitive material and the carbon nanotubes, small molecules of the sensitive material are combined with the oriented carbon nanotubes through non-covalent bonds through interactions such as van der Waals force, electrostatic interaction, hydrogen bond and the like.

Because the fractal angle of the fractal electrode is easier to collect electrons, and the carbon nanotubes are aligned and concentrated in the fractal angle, the change of the current carrier of the detection target gas can be better reflected to the current flowing through the carbon nanotubes. This process greatly reduces the scattering of carriers, and thus can improve the detection sensitivity for gas as compared to existing gas sensors.

The gas-sensitive thin film sensor is obtained by compounding the carbon nano tube and the sensitive material, and is realized by changing the sensitive material compounded with the carbon nano tube aiming at different target gas detection. The concentration detection of the target gas can be realized through the magnitude of the resistance change rate according to the resistance change of the sensor caused by the action of the sensor and the analyte gas.

Advantageous effects

According to the invention, through the related fractal design of the electrode structure and the coordination of the electric field, the carbon nano tubes are induced to be arranged directionally, so that the carbon-based gas sensing device with the oriented arrangement is formed. Compared with the existing gas sensor, the sensor provided by the invention can greatly improve the detection sensitivity.

Drawings

FIG. 1 is a top view of a carbon tube gas sensor of the present invention.

FIG. 2 is a fractal angle cross-sectional view of a carbon tube gas sensor of the present invention, wherein a composite sensitive layer comprising carbon nanotubes and a sensitive material is disposed between channels.

FIG. 3 is a graph showing the continuous measurement of ice poisoning simulants at different concentrations between 3ppm and 8ppt for a carbon tube gas sensor according to the present invention.

FIG. 4 is a graph showing a continuous measured curve of a carbon tube gas sensor of the present invention at a concentration of 40ppt for an icetoxin mimetic.

Fig. 5 is a molecular structure diagram of a sensitive material.

Detailed Description

The invention will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention. Further, it is understood that various changes and modifications may be made by those skilled in the art after reading the teachings of the present invention, and such equivalents are intended to fall within the scope of the claims appended hereto.

Example 1

The present embodiment provides a gas sensor on a silicon or silicon dioxide substrate. Integrating the gas sensor on the substrate in this way makes it possible to mass-produce the sensor at relatively low cost. In principle, standard semiconductor processes such as deposition, lithography and etching techniques can be used to fabricate the sensor.

The carbon tube gas sensor includes:

fractal electrodes

1 and 2, wherein the

fractal electrodes

1 and 2 are deposited on two sides of a monocrystalline silicon piece 5; the carbon nano-tubes 6 are oriented orderly, and the carbon nano-tubes 6 are deposited between the two

fractal electrodes

1 and 2 of the monocrystalline silicon piece 5; the sensitive material 7, the sensitive material 7 and the carbon nano tube 6 are mutually compounded to be used as a sensitive layer for detecting gas.

As can be seen from fig. 2, the structure carried on the substrate 5 (silicon substrate) comprises

fractal electrodes

1 and 2. The design curve of the fractal structure is formed based on sierpinski square fractal fractal function iterated 4 times.

The fractal electrode structure is realized by a standard semiconductor technology. The method comprises the following specific steps: the method comprises the steps of firstly oxidizing and cleaning a monocrystalline silicon wafer, secondly carrying out photoresist coating photoetching development based on a positive photoresist process, thirdly drying the obtained silicon wafer, carrying out a metal sputtering process, and finally carrying out an acetone photoresist removing process. The pitch of the

fractal electrodes

1 and 2, i.e., the channel pitch, may be between submicron and several tens of microns, and the

fractal electrodes

1 and 2 may be kept equal in width to the channel pitch.

As an example, the specific parameters of the

fractal electrodes

1 and 2 are: the thickness of the silicon wafer is 300 micrometers; the

fractal electrodes

1 and 2 are made of Au, the width is 20 micrometers, the height is 0.2 micrometers, a bonding layer Cr 4 is attached between the fractal electrodes and silicon, and the thickness is 30nm.

The channel spacing of the fractal electrode structure is, for example, 20 microns, and the specific value may be determined by the desired size of the sensor cell.

According to the above-described design of the fractal electrode, the method for preparing the oriented carbon nanotube film 6 includes: firstly, dissolving carbon nano tubes in N, N-dimethylformamide solution to prepare carbon tube dispersion liquid. Secondly, dripping a micro liter of carbon tube dispersion liquid into the fractal electrode treated by the oxygen plasma body; then 4V alternating current is applied to pins at two ends, the frequency is 1KHz, and the solution is completely dried. After drying, 1. Mu.l of the corresponding carbon tube dispersion was added dropwise, at which time a 4V alternating current was applied to the pins at both ends, at a frequency of 100Hz, until the solution was completely dried.

In the preparation method, the N, N-dimethylformamide is used as an organic solvent for dispersing the carbon nano tubes, and compared with toluene, chlorobenzene and other solutions, the carbon nano tubes can be dispersed best, so that the electric field induced polarization carbon nano tubes are more effective.

In the above preparation method, the concentration of the carbon tube dispersion liquid is in the range of 0.01mg/mL to 0.1mg/mL, and the preferable concentration is 0.02mg/mL. The carbon tube film prepared under the condition has better electrical property.

In the preparation method, the size of the applied electric field is the optimal condition under the condition that the channel spacing is 20 micrometers, and under the condition, the effect of the electric field on inducing the polarized carbon tube is optimal, and the structure of the carbon tube is not broken down.

In the above preparation method, the frequency of the applied electric field and the type of the electric field are optimal conditions at a channel pitch of 20 μm, under which the aligned carbon tube film can be obtained in a shorter time.

The concentration of the sensitive material 7 ranges from 0.1mg/1mL to 1mg/1mL, with a preferred concentration of 0.5mg/mL.

The details of the preparation method of the oriented carbon tube film are based on the fractal electrode, and the change of the parameters of the preparation details of the film is related to the channel width and the fractal angle number of the fractal electrode.

In combination with the design of the fractal electrode, high field intensity is formed in the 90-degree angle area of the fractal angle, and the high field intensity areas are closely communicated with each other. When the carbon nano tube dispersion is dripped on the gas sensing chip, the carbon nano tube dispersion is induced by polarization in a high field intensity area, so that a perfect carbon tube conductive channel is formed.

After the sensitive material solution is dripped, the sensitive material molecules are tightly distributed around the carbon tubes due to non-covalent interaction between the carbon tube solution and the sensitive material molecules, so that a carbon-based sensitive film in directional arrangement is formed between the fractal electrodes.

When the fractal electrode sensing device is placed in a gas atmosphere for target detection, the change of carriers between the two fractal electrodes can be influenced due to the interaction between the carbon-based sensitive film and target gas, and the change value of the actual resistance is finally fed back.

To illustrate the superiority of the fractal sensing device prepared by the method, the detection of the ice poisoning is taken as an example.

The sensitive material 7 is synthesized based on 2, 6-dimethyl-gamma-pyrone, malononitrile and 5-bromosalicylaldehyde, and the structural formula is shown in figure 5. The specific synthesis steps are as follows: 2, 6-dimethyl-gamma-pyrone and malononitrile are proportionally dissolved in acetic anhydride solution and react for 4 hours at 120 ℃ to obtain 2- (2, 6-dimethyl-4H-pyran-4-subunit) malononitrile. 2- (2, 6-dimethyl-4H-pyran-4-ylidene) malononitrile was then reacted with 5-bromosalicylaldehyde according to 1:2 are dissolved in acetonitrile and piperidine solution, and react for 24 hours at 120 ℃ to obtain the final sensitive material.

In fig. 3, time is plotted on the abscissa, and the rate of change of resistance is plotted on the ordinate. It can be seen that the sensor of this embodiment can achieve a detection sensitivity of 8ppt, far exceeding that of an interdigital electrode based sensor.

In fig. 4, time is plotted on the abscissa, and the rate of change of resistance is plotted on the ordinate. It can be seen that the sensor of this embodiment also has high stability and reproducibility.

The foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and various modifications can be made to the above-described embodiment of the present invention. All simple, equivalent changes and modifications made in accordance with the claims and the specification of this application fall within the scope of the patent claims.

Claims

1. The utility model provides a carbon tube gas sensor based on fractal electrode which characterized in that: the carbon tube gas sensor includes: fractal electrodes (1, 2), wherein the fractal electrodes (1, 2) are deposited on two sides of a monocrystalline silicon piece (5); the carbon nano-tubes (6) are oriented orderly, and the carbon nano-tubes (6) are deposited between two fractal electrodes (1, 2) of a monocrystalline silicon wafer (5); and the sensitive material (7) is mutually compounded with the carbon nano tube (6) and is used as a sensitive layer for detecting gas.

2. The carbon tube gas sensor of claim 1, wherein: the fractal electrodes (1, 2) are composed of a plurality of fractal structures with a plurality of right-angle structures, and fractal structure curves are formed by repeating iteration for more than 2-20 times based on sierpinski square fractal fractal functions.

3. The carbon tube gas sensor of claim 1, wherein: the spacing of the fractal electrodes (1, 2) is equal to the width of the fractal electrodes, and the numerical range is from submicron level to tens of microns.

4. The carbon tube gas sensor of claim 1, wherein: an adhesive layer (4) is arranged between the fractal electrodes (1, 2) and the monocrystalline silicon piece (5).

5. The carbon tube gas sensor of claim 1, wherein: and (3) sequentially growing and orderly arranging the carbon nano tube dispersion liquid along the field intensity direction of the fractal structure under the induction action of an electric field between the fractal electrodes (1 and 2), and obtaining the carbon nano tubes (6) with orderly orientation after the solution is volatilized.

6. The carbon tube gas sensor of claim 5, wherein: the solvent of the carbon nano tube dispersion liquid is at least one of N, N-dimethylformamide, chlorobenzene and toluene; the concentration of the carbon nanotube dispersion liquid ranges from 0.01mg/1mL to 0.1mg/1mL.

7. The carbon tube gas sensor of claim 1, wherein: the concentration of the sensitive material (7) ranges from 0.1mg/mL to 1mg/mL.

8. The carbon tube gas sensor of claim 7, wherein: the sensitive material (7) is 2- (2, 6-bis ((E) -5-bromo-2-hydroxystyryl) -4H-pyran-4-ylidene) malononitrile.