CN102403175A - Method for depositing medium barrier layer on micro-nano electrode - Google Patents

Abstract

The invention discloses a method for depositing a medium barrier layer on a micro-nano electrode, which comprises the following steps: preparing a three-dimensional micro-discharge electrode on a substrate; and electrophoretically depositing carbon nanotubes on the surface of the microelectrode and simultaneously forming a magnesium oxide medium covering layer. The invention improves the inhibiting effect of the medium on the ionization current and prolongs the service life by improving the medium coverage of the surfaces of the carbon nano tube and the micro discharge electrode, and has simple preparation steps and low preparation cost.

Description

A method of depositing a dielectric barrier layer on a micro-nano electrode

technical field

The invention relates to a micro-discharge device in the technical field of microelectronics, in particular to a method for depositing a dielectric barrier layer on a micro-nano electrode.

Background technique

The gas ionization characteristics are closely related to the properties of the gas. Different gases have different critical discharge voltages and critical discharge currents, which can be used as the basis for distinguishing different gas components and concentrations. As a gas sensor, this type of sensor has the advantages of short response time, high sensitivity, and fast recovery. However, the geometric size of the ionization electrode prepared by the conventional method is relatively large, and the working voltage of thousands of volts is required, which greatly limits the application in the sensor. With the development of micro-nano technology, a micro-nano discharge electrode structure has emerged that combines one-dimensional nanomaterials such as carbon nanotubes with micron intermittent electrodes prepared by micro-processing technology, which can reduce the working voltage of gas discharge under atmospheric pressure to several Below ten volts, the feasibility and practicability of gas qualitative and quantitative detection by using gas discharge characteristics are greatly improved.

However, such devices still have the problem that the discharge current changes too fast and the degree of ionization is difficult to control, thereby reducing the service life and working reliability of the device. Therefore, how to limit the degree of ionization while reducing the ionization threshold voltage has become a major problem that must be solved in the application of such devices.

The dielectric barrier discharge (DBD) structure adds an insulating medium to the surface and space of the discharge electrode, so that the generated ionized charge accumulates on the surface of the medium, generating a built-in electric field opposite to the direction of the applied electric field, so that the total electric field strength between the electrode gaps drop and stop discharging. When the reverse applied field strength is applied, a new discharge cycle begins. Therefore, the self-limiting effect of the DBD structure can effectively suppress the free growth of the ionization current, thereby obtaining a more stable ionization state and increasing the service life of the device.

Wu Jiahao and others proposed a carbon nanotube dielectric barrier gas sensor based on micromechanical technology (“A MEMS-based ionization gas sensor using carbon nanotubes and dielectric barrier”, Proceedings of the ^3rd IEEE Int.Conf.on Nano/ MicroEngineered and Molecular Systems, pages 824-827), the composition of the sensor is to set one or more pairs of parallel three-dimensional microelectrodes with a pitch of micron scale on an insulating substrate such as glass, and use the opposite side walls between the electrodes as the discharge area, and Carbon nanotubes were deposited on the electrode surface by electrophoresis to further reduce the ionization threshold voltage. In order to suppress damage to the device caused by excessive ionization current, a dielectric layer is covered on the surface of the microelectrode deposited with carbon nanotubes to form a carbon nanotube dielectric barrier discharge structure. The research results show that this technology can effectively limit the free growth of the discharge current and improve the working life of the device. However, in the preparation of the device, the dielectric layer is deposited by sputtering, which requires special thin film deposition equipment, and the preparation cost is relatively high. Moreover, the general sputtering deposition method has poor coverage of three-dimensional microstructures, which affects the integrity of the dielectric coverage on the sidewall electrodes.

Contents of the invention

Aiming at the deficiencies and defects of the prior art, the present invention provides a method for depositing a dielectric barrier layer on a micro-nano electrode, using an electrophoresis method to form a dielectric layer while depositing carbon nanotubes on the electrode, thereby effectively improving the dielectric barrier layer. The covering effect improves the performance and working stability of the device, simplifies the operation steps and reduces the preparation cost.

The present invention is achieved through the following technical solutions. The present invention adopts an electrophoretic deposition method, adding excessive magnesium nitrate in the electrophoretic solution of carbon nanotubes, and through the precipitation in the process of electrophoretic deposition of carbon nanotubes, and subsequent heat treatment, on the surface of the microelectrode form a dielectric film.

A method for forming a dielectric barrier layer on a micro-nano electrode according to the present invention comprises the following steps:

Step 1. Prepare three-dimensional micro-discharge electrodes on the substrate;

The substrate is glass, or high-resistance silicon, or ceramics, or a substrate with insulating materials deposited on the surface.

The electroplating seed layer of the microdischarge electrode was prepared by common photolithography, thin film deposition, and photoresist stripping methods.

The method of mask electroplating is used to electroplate three-dimensional micro-discharge electrodes on the seed layer, and the electroplating materials are nickel, gold, copper and other metals.

Step 2. Deposition of 1D nanomaterials and dielectric layers

An electrophoresis method is used to deposit one-dimensional nanomaterials and a dielectric layer on the above-mentioned three-dimensional micro-discharge electrodes. The electrophoretic solution is added with an excess charge auxiliary salt magnesium nitrate, and the medium layer is magnesium oxide.

Step 3. Dielectric layer heat treatment

The above sample deposited with carbon nanotubes and medium was subjected to vacuum heat treatment to obtain a stable MgO medium layer.

The micro-discharge electrode is a cathode-anode electrode pair composed of one or more parallel micro-electrodes, and is made of a material with good electrical conductivity.

The size of the three-dimensional micro-discharge electrode pair is 20um in width, 2000um in length, 10-20um in spacing, and 5-15um in height.

The one-dimensional nanomaterial is one of carbon nanotubes, silicon carbide nanowires, silicon nanowires, and zinc oxide nanowires.

The parameters of the electrophoresis method are: the weight percentage concentration of carbon nanotubes in the electrophoresis solution is: 0.1%, the solvent is acetone, the charging auxiliary salt is magnesium nitrate, the concentration is 1-10×10 ^-4 mol/L, the electrode cathode For the sample, the anode is a stainless steel sheet. During electrophoretic deposition, an electric field strength of 5-15 V/cm is applied for 2-4 minutes.

The heat treatment of the dielectric layer is: heat treatment under vacuum, parameter: 300-500° C., 1 hour.

The beneficial effects of the present invention are:

1. The coverage of the dielectric layer on the side wall of the electrode and the surface of the one-dimensional nanomaterial is improved, and the limiting effect of the device on the ionization current is improved.

2. The dielectric layer is formed while the carbon nanotubes are deposited by electrophoresis, which is beneficial to simplify the process and reduce the cost.

3. Magnesium oxide has good resistance to ion bombardment, which can further improve the working life of the device.

Detailed ways

The embodiments of the present invention are described in detail below: this embodiment is implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are provided, but the protection scope of the present invention is not limited to the following embodiments.

Example 1

This embodiment is implemented under the following implementation conditions and technical requirements:

1. Preparation of three-dimensional metal micro-discharge electrodes;

Using insulating glass as the substrate, the photolithography process is used to form the photoresist pattern of the micro-discharge electrode on the surface of the substrate, and then the metal seed layer is deposited on it by sputtering, and the photoresist is removed by the stripping process to obtain the electrode pattern of the seed layer . The selected seed layer material is Cu/Ti, the thickness of Cu is 0.12um, and the thickness of Ti is 0.03um. On the above-mentioned sample with the electrode pattern of the seed layer, a photoresist mask electroplating pattern was formed by using a photolithography process, and the height of the photoresist was 10 um. Put the above sample into the Watts nickel electroplating solution, use it as the cathode, and the nickel plate as the anode, apply the electroplating current density of 0.2A/dm ² for 30 minutes, and obtain an electrode width of 20um, a length of 2000um, and an electrode spacing of 10um, nickel discharge electrode with a height of 5um.

2. Electrophoretic deposition of carbon nanotubes and dielectric layers;

On the Ni electrode obtained in step 1, carbon nanotubes were deposited by electrophoresis. The parameters of the electrophoretic deposition are: the concentration of carbon nanotubes in the electrophoretic solution is 0.1% by weight, the solvent is acetone, the concentration of magnesium nitrate is 1×10 ^-4 mol/L, the cathode is the deposition sample, and the anode is a stainless steel sheet. During electrophoretic deposition, an electric field strength of 15 V/cm was applied for 2 minutes.

3. Heat treatment of the dielectric layer;

Put the sample after 2 steps into a vacuum annealing furnace for thermal decomposition treatment, the annealing temperature is 300°C, and the time is 1 hour.

The distance between the micro-discharge electrodes prepared in this example is 10 microns, and the electrode surface is covered with uniform carbon nanotubes. The surface of the carbon nanotubes is covered by magnesium oxide grains, but the morphology of the carbon nanotubes is still maintained. The ionization performance of the device was tested, the ionization threshold voltage was lower than 10V, and the peak value of the ionization current was less than 10uA, indicating that the device not only ionized at a lower voltage, but also that the dielectric layer had a good inhibition on the growth of the ionization current effect.

Example 2

This embodiment is implemented under the following conditions of implementation and technical requirements:

1. Preparation of three-dimensional metal micro-discharge electrodes;

Using insulating high-resistance glass as the substrate, firstly use the photolithography process to form the photoresist pattern of the discharge electrode on the surface of the substrate, then sputter and deposit the metal seed layer on it, remove the photoresist by stripping process, and obtain the seed layer electrode structure. The selected seed layer material is Cu/Ti, the thickness of Cu is 0.12um, and the thickness of Ti is 0.03um. Then, on the sample prepared with the seed layer, a photoresist mask electroplating pattern was formed by using a photolithography process, and the height of the photoresist was 15um. Put the above sample into the Watts nickel electroplating solution, use it as the cathode, and the nickel plate as the anode, apply the electroplating current density of 0.2A/dm ² for 60 minutes, and obtain an electrode width of 20um, a length of 2000um, and an electrode spacing of 15um, nickel discharge electrode with a height of 10um.

2. Electrophoretic deposition of carbon nanotubes and dielectric layers;

On the Ni electrode obtained in step 1, carbon nanotubes are deposited by electrophoresis. The parameters of the electrophoretic deposition are as follows: the weight percent concentration of carbon nanotubes in the electrophoretic solution is 0.1%, the solvent is acetone, the concentration of magnesium nitrate is 5×10 ^-4 mol/L, the cathode is the deposited sample, and the anode is a stainless steel sheet. During electrophoretic deposition, an electric field strength of 10 V/cm was applied for 3 minutes.

3. Heat treatment of the dielectric layer;

Put the sample after step 2 into a vacuum annealing furnace for thermal decomposition treatment at an annealing temperature of 400°C for 1 hour.

The distance between the electrodes of the micro-discharge electrode prepared in this example is 15 microns, and the surface of the electrode is covered with uniform carbon nanotubes. The surface of the carbon nanotubes is covered by magnesium oxide grains, but the morphology of the carbon nanotubes is still maintained. The ionization performance of the device was tested, the ionization threshold voltage was lower than 10V, and the peak value of the ionization current was less than 10uA, indicating that the device not only ionized at a lower voltage, but also that the dielectric layer had a good inhibition on the growth of the ionization current effect.

Example 3

This embodiment is implemented under the following conditions of implementation and technical requirements:

1. Preparation of three-dimensional metal micro-discharge electrodes;

Using a silicon wafer with a silicon oxide layer deposited on its surface as a substrate, first use a photolithography process to form a photoresist pattern of the discharge electrode on the substrate surface, then sputter and deposit a metal seed layer on it, and remove the photoresist by a lift-off process , to obtain the seed layer electrode structure. The selected seed layer material is Cu/Ti, the thickness of Cu is 0.12um, and the thickness of Ti is 0.03um. Then, on the sample deposited with the seed layer, a photoresist mask electroplating pattern was formed by using a photolithography process, and the height of the photoresist was 20um. Put the above sample into the Watts nickel electroplating solution, use it as the cathode, and the nickel plate as the anode, apply the electroplating current density of 0.2A/dm ² for 90 minutes, and obtain an electrode width of 20um, a length of 2000um, and an electrode spacing of 20um, nickel discharge electrode with a height of 15um.

2. Electrophoretic deposition of carbon nanotubes and dielectric layers;

On the Ni electrode obtained in step 1, carbon nanotubes are deposited by electrophoresis. The parameters of the electrophoretic deposition are: the concentration of carbon nanotubes in the electrophoretic solution is 0.1% by weight, the solvent is acetone, the concentration of magnesium nitrate is 10×10 ^-4 mol/L, the cathode is the deposition sample, and the anode is a stainless steel sheet. During electrophoretic deposition, an electric field strength of 5 V/cm was applied for 4 minutes.

3. Heat treatment of the dielectric layer;

Put the sample after step 2 into a vacuum annealing furnace for thermal decomposition treatment. The annealing temperature is 500°C, and the time is 1 hour.

The distance between the electrodes of the micro-discharge electrode prepared in this example is 20 microns, and the surface of the electrode is covered with uniform carbon nanotubes. The surface of the carbon nanotubes is covered by magnesium oxide grains, but still presents the morphology of carbon nanotubes. The ionization performance of the device was tested, the ionization threshold voltage was lower than 10V, and the peak value of the ionization current was less than 10uA, indicating that the device not only ionized at a lower voltage, but also that the dielectric layer had a good inhibition on the growth of the ionization current effect.

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as limiting the present invention. Various modifications and alterations to the present invention will become apparent to those skilled in the art upon reading the above disclosure. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (9)

1. the method on a deposition medium barrier layer on the micro-nano electrode comprises the steps:

Step 1, the three-dimensional micro discharge electrode of preparation on substrate;

Step 2 adopts electrophoresis method, and the deposition monodimension nanometer material also forms dielectric layer simultaneously on above-mentioned three-dimensional micro discharge electrode, adds excessive charged auxiliary salt magnesium nitrate in the electrophoresis liquid, and dielectric layer is a magnesia;

Step 3, dielectric layer heat treatment.

2. according to claim 1 on the micro-nano electrode method on deposition medium barrier layer, it is characterized in that said step 1 is specially: adopt the method for photoetching, thin film deposition, photoresist lift off, the plating seed layer of preparation micro discharge electrode pattern on substrate; Adopt the method for mask plating, on above-mentioned Seed Layer, electroplate three-dimensional micro discharge electrode.

3. according to claim 1 and 2 on the micro-nano electrode method on deposition medium barrier layer, it is characterized in that said substrate is a glass, or High Resistivity Si, or pottery or surface deposition have the substrate of insulating material.

4. according to claim 1 and 2 on the micro-nano electrode method on deposition medium barrier layer, it is characterized in that, said micro discharge electrode, right for the anodic-cathodic that one or more pairs of parallel microelectrodes are formed, make by electric conducting material.

5. according to claim 4 on the micro-nano electrode method on deposition medium barrier layer, it is characterized in that said three-dimensional micro discharge electrode pair is of a size of width 20um, length 2000um, spacing 10-20um, height 5-15um.

6. according to claim 1 on the micro-nano electrode method on deposition medium barrier layer, it is characterized in that said one-dimensional material is a kind of in CNT, silicon carbide nanometer line, silicon nanowires, the zinc oxide nanowire.

7. according to claim 6 on the micro-nano electrode method on deposition medium barrier layer, it is characterized in that said one-dimensional material is a CNT.

8. according to claim 1 on the micro-nano electrode method on deposition medium barrier layer; It is characterized in that the parameter of said electrophoresis method is: the CNT weight percent concentration in the electrophoresis solution is 0.1%, and solvent is an acetone; Charged auxiliary salt is a magnesium nitrate, and concentration is 1-10 * 10 ^-4Mol/L, electrode cathode are sample, and anode is a stainless sheet steel; Apply electric field strength 5-15V/cm during electrophoretic deposition, the time is 2-4 minute.

9. according to claim 1 on the micro-nano electrode method on deposition medium barrier layer, it is characterized in that said dielectric layer heat treatment is: heat treatment under the vacuum condition, parameter: 300-500 ℃, 1 hour.