CN209117761U - A kind of test device for extracting conductive film surface conductivity based on electromagnetic field near field - Google Patents

Abstract

The utility model relates to a test technology for the surface conductivity of a thin film, and aims to provide a test device for extracting the surface conductivity of a conductive thin film based on a near field of an electromagnetic field. The electromagnetic emission source is set on one side of the conductive film, and the direction of emitting electromagnetic waves is oriented and perpendicular to the conductive film; the magnetic field near-field probe and the electric field near-field probe are respectively placed on the upper and lower sides of the horizontal conductive film, and the two probes are kept with the conductive film. The same distance, the connection between the two is perpendicular to the conductive film. The utility model has no strict requirements on the shape and size of the conductive film, and can solve the problems of high requirements on the shape processing precision and large error of the conductive film when performing high-frequency testing in coaxial and waveguide. At the same time, the utility model can measure the surface conductivity of the conductive film at any position, at any frequency, and at any time, and obtain the distribution of the surface conductivity of the film with position, frequency and time, which is beneficial to improve the reliability and stability of the film application.

Description

A test device for extracting the surface conductivity of conductive films based on the near-field electromagnetic field

technical field

The utility model relates to a film surface conductivity test technology, in particular to a test device for extracting the surface conductivity of a conductive film based on an electromagnetic field near field. Rate.

Background technique

Conductive films are widely used in the flexible electronics industry and are in urgent demand. At present, the most commonly used conductive films in the industry are indium tin oxide (ITO) films, fluorine-doped tin oxide (FTO) films, and two-dimensional material films such as graphene. One of the key influencing factors for products such as solar cells. Mass production of high-quality electronic films requires not only precise process control during production, but also efficient quantitative testing of different products and batches. The current test methods include testing in coaxial, waveguide and other cavities, which require high precision in the shape processing of the conductive film and have a great impact on the test results of the processing error.

In the frontier research field of electromagnetic fields and electromagnetic waves, there are a lot of theoretical studies on new two-dimensional conductive films, including graphene, molybdenum disulfide, hexagonal boron nitride, etc. They are theoretically widely used in new waveguides, new antennas , the design of passive components such as new filters. At present, the production quality of these new thin films is unstable and the production scale is small, so their electrical conductivity needs to be strictly controlled and measured in production and design.

Utility model content

The technical problem to be solved by the utility model is to overcome the deficiencies in the prior art and provide a test device for extracting the surface conductivity of the conductive film based on the near field of the electromagnetic field.

In order to solve the technical problem, the solution of the present utility model is:

A test device for extracting the surface conductivity of a conductive film based on an electromagnetic field near field is provided. An electromagnetic emission source is arranged on one side of the conductive film, and the direction of the electromagnetic wave emitted is oriented and perpendicular to the conductive film; the distance between the electromagnetic emission source and the conductive film is greater than 2λ, λ is the wavelength of the emitted electromagnetic wave; the magnetic field near-field probe and the electric field near-field probe are respectively placed on the upper and lower sides of the horizontal conductive film.

As an improvement, the magnetic field near-field probe and/or the electric field near-field probe are replaced by a probe that has both magnetic field near-field detection and electric field near-field detection functions.

As an improvement, the connection line between the two probes intersects the conductive film, the emission direction of the electromagnetic emission source intersects the conductive film, and the distance between the two intersection points is not greater than D _MAX /2, where D _MAX is the emission direction of the emission source. maximum diameter.

As an improvement, the electromagnetic emission source is a horn antenna.

As an improvement, the distance between the two probes and the conductive film is smaller than the distance between the electromagnetic emission source and the conductive film.

As an improvement, the two probes are respectively connected to the industrial computer through signal lines, and the electromagnetic emission source is connected to the controller through signal lines.

Using the device of the utility model to realize the method of extracting the surface conductivity of the conductive film based on the near field of the electromagnetic field, the conductive film is irradiated by the electromagnetic wave emitted by the electromagnetic emission source to generate an induced current on the surface, and the magnetic field near field probe and the electric field near field are used to irradiate the conductive film. The probe measures the amplitude and phase of the horizontal magnetic field and the horizontal electric field formed by the induced current on both sides of the conductive film; finally, the surface conductivity of the conductive film is calculated by using the measurement data;

Specifically, the method includes:

(1) Using the electromagnetic emission source to emit electromagnetic waves to the conductive film at a distance of 2λ, to ensure that the electromagnetic waves are equivalent to plane waves when irradiated to the conductive film;

(2) Use the probe to measure the amplitude and phase of the horizontal magnetic field and the amplitude and phase of the horizontal electric field at equal distances on both sides of the film respectively; through the transmission line theory and boundary conditions, use the amplitude and phase of the horizontal magnetic field to calculate the surface current of the film. The surface electric field is obtained by calculating the amplitude and phase of the horizontal electric field; then the surface conductivity at the intersection of the line between the two probes and the conductive film is obtained through the surface electric field and the surface current;

(3) Simultaneously changing the positions of the two probes, and repeating the operations of steps (1) and (2), thereby obtaining the surface conductivity at different positions of the conductive film.

Before starting the test, both probes are calibrated with a vector network analyzer and standards so that the corresponding data for electric and magnetic fields can be accurately measured.

The calculation of the surface current and surface electric field of the thin film through transmission line theory and boundary conditions specifically refers to:

The two probes are placed above and below the conductive film, respectively, and their distances from the film are respectively d ₁ and d ₂ ; the horizontal electric field and magnetic field measured by the two probes are respectively recorded as (E ^I , H ^I ) and (E ^II , H ^II );

In the direction perpendicular to the conductive film, the conductive film is equivalent to a resistor whose resistance value is Re _eq =1/σ, Re _eq is the surface conductivity of the conductive film to be tested, and σ is the surface conductivity of the conductive film to be tested; On both sides of the conductive film, the vertical space between the probe and the conductive film is equivalent to two air transmission lines, whose propagation constant and characteristic impedance are respectively k _z0 =ω/c, Z _c0 =(μ ₀ /ε ₀ ) ^0.5 ; In the formula, ω=2πf is the angular frequency, f is the frequency of the emitted electromagnetic wave, c is the speed of light in vacuum, μ ₀ is the vacuum magnetic permeability, and ε ₀ is the vacuum permittivity.

According to the definition of ABCD matrix:

In the above formula, since the parallel components of the electric field are equal everywhere, there is E ^I =E ^II ; among them, E ^II , H ^I , H ^II are the measured values of the probe, Z _c0 , k _z0 , d ₁ , d ₂ are known quantities; j is the imaginary unit symbol.

Through the inverse operation of the above matrix, the surface conductivity σ of the film is obtained.

In the present invention, when the distance between the probe and the conductive film is less than λ/20, the matrix is further simplified as

which is

According to formula (3), the surface conductivity σ of the film is obtained.

Description of the realization principle of the utility model:

The conductive film material is placed in free space, and the excitation source emits a plane wave from above the film. When the plane wave is irradiated to the surface of the film material, a horizontal electric field of a certain intensity will be formed above and below the film due to the reflection and transmission of the electric field on the surface of the film; its horizontal electric field The surface current of the film material will be excited, and the magnitude and phase of the surface current depend on the surface conductivity of the material; the surface current will lead to the sudden change of the magnetic field on the upper and lower surfaces of the film; For the thin film, its corresponding surface horizontal electric field and horizontal magnetic field information are different. By testing the electric field and magnetic field, the surface conductivity of the thin film can be deduced.

The steps when the device of the utility model is used for testing are as follows: first, the magnetic field near-field probe and the electric field near-field probe are calibrated by using a vector network analyzer and standard parts, so that the true values of the electric field and the magnetic field can be measured; The electromagnetic emission source (such as a horn antenna, etc.) emits electromagnetic waves beyond several wavelengths, so as to ensure that the electromagnetic waves can be equivalent to plane waves when irradiated to the film; further, at a certain position above and below the film and vertically away from the film, use magnetic field near-field probes to respectively The amplitude and phase of the horizontal magnetic field are measured, and the amplitude and phase of the horizontal electric field are measured by using an electric field near-field probe at the same position under the film. Finally, through the transmission line theory and boundary conditions, the surface current and surface electric field of the film can be deduced, and then the surface conductivity of the film can be solved.

The surface conductivity obtained from this test is the conductivity at a point on the film that is directly above/below the probe. By changing the test position of the probe, the surface conductivity of the film at different positions can be obtained.

At the same time, the surface conductivity obtained by this test is the conductivity at the emission frequency of the electromagnetic emission source. By changing the emission frequency of the electromagnetic emission source and testing the amplitude and phase of the horizontal magnetic field and the horizontal electric field at the corresponding frequency with a near-field probe, the surface conductivity of the film at different frequencies can be deduced.

Using the multi-component probe, the horizontal electric field and the horizontal magnetic field above and below the film can be measured at the same time, so as to obtain the surface conductivity of the film at a certain time, and the surface conductivity of the film at different times can be obtained by changing the test time.

Compared with the prior art, the beneficial effects of the present utility model are:

The utility model has no strict requirements on the shape and size of the conductive film, and can solve the problems that the shape processing precision of the conductive film is relatively high and the error is large when the high-frequency test is performed in the coaxial and waveguide. At the same time, the utility model can measure the surface conductivity of the conductive film at any position, at any frequency, and at any time, and can obtain the distribution of the surface conductivity of the film with position, frequency and time, which is beneficial to improve the reliability and stability of the film application. .

Description of drawings

FIG. 1 is a schematic structural diagram of a testing device in the present invention.

Fig. 2 is the electromagnetic principle diagram of the present utility model.

FIG. 3 is a schematic diagram of the probe of the embodiment at a distance of 1 mm from the conductive film to be tested.

FIG. 4 is a schematic diagram of the probe of the embodiment with a distance of 0.2 mm from the conductive film to be measured.

FIG. 5 is the surface conductivity obtained when the probe of the embodiment is 1 mm away from the conductive film to be measured.

FIG. 6 is the surface conductivity obtained when the probe of the embodiment is 0.2 mm away from the conductive film to be measured.

Reference signs in Figure 1: 1 Electromagnetic emission source; 2 Near-field probe above the film (used to test the amplitude and phase of the horizontal electric field and horizontal magnetic field above the film); 3 Conductive film; 4 Near-field probe below the film ( for testing the amplitude and phase of the horizontal electric and magnetic fields beneath the film).

Detailed ways

The present utility model will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

In the utility model, the test device for extracting the surface conductivity of the conductive film based on the electromagnetic field near-field is to set an electromagnetic emission source 1 on one side of the conductive film 3, and the direction of its emission of electromagnetic waves is oriented and perpendicular to the conductive film 3; The distance between the conductive films 3 is greater than 2λ, where λ is the wavelength of the emitted electromagnetic wave; the near-field probes 2 and the near-field probes 4 are placed on the upper and lower sides of the horizontal conductive film 3 respectively, and the two probes and the conductive film 3 keep the same distance (with the conductive film 3). The distance is not greater than the distance between the electromagnetic emission source and the conductive film), the connection line between the two is perpendicular to the conductive film 3 and intersects the conductive film 3, the emission direction of the electromagnetic emission source 1 intersects the conductive film 3, and the two intersection The distance between them is not greater than D _MAX /2, where D _MAX is the maximum aperture of the emission source.

The electromagnetic emission source 1 can choose a horn antenna, which is connected to its controller through a signal line. The two probes are respectively connected to the industrial computer through signal lines. The magnetic field near-field probe and/or the electric field near-field probe may be optionally replaced with a probe having both magnetic field near-field detection and electric field near-field detection functions.

Specific implementation examples:

The schematic diagram of the measuring device of the present invention is shown in FIG. 1 , using a horn antenna as the electromagnetic emission source 1 , and placing it at a certain position above the conductive film 3 . The two probes are placed above and below the conductive film 3 respectively, and the distances from the conductive film 3 are respectively d ₁ and d ₂ . The electric and magnetic fields measured by the two probes are recorded as (E ^I , H ^I ) and (E ^II , H ^II ), respectively.

In the direction perpendicular to the conductive film 3, the device can be equivalently represented by the transmission line model shown in FIG. 2 . The conductive film 3 is equivalent to a resistor, and its resistance value is _Req =1/σ, and σ is the surface conductivity of the film to be measured. On both sides of the conductive film 3, the vertical space between the probe and the conductive film 3 is equivalent to two air transmission lines, and its propagation constant and characteristic impedance are k _z0 =ω/c, Z _c0 =(μ ₀ /ε ₀ ) ^0.5 , according to the definition of ABCD matrix, we have

In the above formula, since the parallel components of the electric field are equal everywhere, there is E ^I =E ^II . E ^II , H ^I , and H ^II are the measured values of the probe, and Z _c0 , k _z0 , d ₁ , and d ₂ are known quantities. The surface conductivity σ of the conductive film 3 can be solved by inverting the above matrix. In particular, when the distance between the probe and the conductive film 3 is less than λ/20, the above formula can be simplified as

which is

Using the test method described above, two examples of data calculations using 3D full-wave simulations are shown below.

As shown in Figure 3, suppose there is a conductive film with a surface resistance of 50Ω/square and a surface conductivity of 0.02S. A horn antenna is used to transmit a 6GHz plane wave and irradiate the film vertically. The horizontal electric field and the horizontal magnetic field (E ^II , H ^I , H ^II ) were extracted from the upper and lower sides of the film, at a vertical distance of 1 mm from the film. By inverse operation of formula (1), the surface conductivity of the thin film is calculated at each position on the thin film, as shown in FIG. 5 . The surface conductivities shown in Figure 5 are the local conductivities at different locations on the film surface at a certain moment.

Similarly, in Figure 4, keeping other settings unchanged, the horizontal electric field and the horizontal magnetic field are extracted at a vertical distance of 0.2 mm on both sides of the film, and the surface conductivity of the film is solved by the same principle, as shown in Figure 6 Show.

It can be seen from FIG. 5 and FIG. 6 that the value of the obtained surface conductivity in most of the solution regions is around 0.02S, which shows that the method of the present invention has high precision.

Claims (6)

1. a test device based on electromagnetic field near-field extraction conductive film surface conductivity, is characterized in that, is to set electromagnetic emission source on one side of conductive film, the direction of its emission electromagnetic wave is towards and perpendicular to conductive film; The distance between the conductive films is greater than 2λ, where λ is the wavelength of the emitted electromagnetic wave; the magnetic field near-field probe and the electric field near-field probe are placed on the upper and lower sides of the horizontal conductive film, respectively. in conductive films. 2 . The test device according to claim 1 , wherein the magnetic field near-field probe and/or the electric field near-field probe are replaced by a probe having both magnetic field near-field detection and electric field near-field detection functions. 3 . 3. testing device according to claim 1 is characterized in that, the connection line between two probes intersects with the conductive film, the emission direction of the electromagnetic emission source intersects with the conductive film, and the distance between the two intersection points is not greater than D _MAX /2, D _MAX is the maximum aperture of the emission source. 4. The test device according to claim 1, wherein the electromagnetic emission source is a horn antenna. 5 . The testing device according to claim 1 , wherein the distance between the two probes and the conductive film is smaller than the distance between the electromagnetic emission source and the conductive film. 6 . 6. The test device according to any one of claims 1 to 5, wherein the two probes are respectively connected to an industrial computer through a signal line, and the electromagnetic emission source is connected to the controller through a signal line.