Miniature sensitive structure of photoionization gas sensor

Abstract

A miniature sensitive structure of a photoionization gas sensor belongs to the technical field of sensor manufacturing. The problems that a sensitive structure of a photoionization gas sensor is large in size and high in power consumption are solved. An ultraviolet light source cavity is a rectangular cavity with an opening in the upper side, the rectangular cavity is filled with working gas, the upper end opening is embedded in the bottom face of a micro ionization chamber, and a transparent baffle is further arranged between the upper end opening and the bottom face of the micro ionization chamber; exciting electrodes are attached to two opposite side walls of the ultraviolet light source cavity; the bottom surface and the top surface of the micro ionization chamber are electrode plates distributed with through holes; the micro ionization chamber is filled with gas to be detected; the gas to be detected is decomposed under the ionization of ultraviolet light to generate micro current, and the micro current is transmitted out through the electrode plate. The invention is suitable for serving as a sensitive structure of the sensor.

Description

Technical Field

[0001] The invention belongs to the technical field of sensor manufacturing. Background Art

[0002] Photoionization Detector (PID) is a type of sensor that has emerged rapidly and developed vigorously in the past 20 years. It has the advantages of high sensitivity, high precision, fast response, and continuous testing. It can be widely used in the detection of aromatic hydrocarbons, ketones, aldehydes, unsaturated hydrocarbons, etc. The sensor can not only be used in gas detectors, but also as a detection unit of security network monitoring systems. At the same time, it can be embedded in gas chromatographs to directly measure trace hydrocarbon compounds in the atmosphere.

[0003] PID is made based on the principle of photoionization effect of organic gas. Ultraviolet light is generated by using ultraviolet lamp with specific ionization energy to bombard gas molecules in the ionization chamber, ionizing and breaking the organic gas contained in the gas into positively charged ions and negatively charged electrons. Under the action of the electric field, ions and electrons move toward the plate, thus forming a weak ion current that can be detected. By measuring the magnitude of the current through the amplification circuit and test equipment, the concentration of organic gas can be detected.

[0004] Although PID has made great progress in recent years, the current PID has disadvantages such as large size, high power consumption, and high manufacturing cost, and lacks a miniaturized, low-power photoionization gas sensor. Summary of the invention

[0005] The present invention aims to solve the problem of large volume and high power consumption of the sensitive structure of a photoionization gas sensor, and now provides a micro-sensitive structure of a photoionization gas sensor.

[0006] The micro sensitive structure of a photoionization gas sensor described in the present invention comprises a micro ionization chamber, an ultraviolet light source cavity and an excitation electrode;

[0007] The ultraviolet light source cavity is a rectangular cavity with an upper opening, the rectangular cavity is filled with working gas, the upper port of the rectangular cavity is embedded in the bottom surface of the micro ionization chamber, and a transparent baffle is also arranged between the upper port of the rectangular cavity and the bottom surface of the micro ionization chamber;

[0008] Excitation electrodes are attached to the opposite side walls of the ultraviolet light source cavity;

[0009] The bottom and top surfaces of the micro ionization chamber are both electrode plates covered with through holes;

[0010] The exciting electrode is powered on to excite the working gas to emit ultraviolet light, and the ultraviolet light enters the micro-ionization chamber through the transparent baffle and the hole on the bottom surface of the micro-ionization chamber;

[0011] The micro ionization chamber is used to fill the gas to be tested; the gas to be tested decomposes under ultraviolet photoionization to generate micro current, and the micro current is transmitted through the electrode plate.

[0012] Furthermore, in the present invention, the bottom surface of the micro ionization chamber is a collecting electrode, and the top surface is a bias electrode.

[0013] Furthermore, in the present invention, the side wall of the micro ionization chamber is provided with air inlet and outlet holes.

[0014] Furthermore, in the present invention, the transparent baffle is a magnesium fluoride glass plate.

[0015] Furthermore, in the present invention, the thickness of the magnesium fluoride glass plate is 250um to 350um.

[0016] Furthermore, in the present invention, the exciting electrode is rectangular and made of gold.

[0017] Furthermore, in the present invention, an insulating layer is plated on the surface of the exciting electrode.

[0018] Furthermore, in the present invention, the size of the micro ionization chamber and the ultraviolet light source cavity are the same.

[0019] Furthermore, in the present invention, the working gas is Ar gas or He gas.

[0020] The micro-ionization chamber and the micro-ultraviolet light source, the window glass of the ultraviolet light source cavity and the ionization chamber cavity are of the same size, and the photon energy is 10.6eV. Since the photon energy of the ultraviolet light source is greater than the ionization energy of general organic gases and less than the ionization energy of gases such as oxygen and nitrogen, the micro-photoionization gas sensor based on the micro-ionization chamber and the micro-ultraviolet light source proposed by the invention can measure the concentration of organic gases in the atmosphere, thereby realizing the miniaturization of the photoionization gas sensor, and further reducing the power consumption of the photoionization gas sensor. In addition, the detection gas of the micro-ionization chamber and the micro-ultraviolet light source proposed by the present invention enters the micro-ionization chamber from the air inlet and outlet holes and is ionized by the vacuum ultraviolet light source emitted by the micro-ultraviolet light source. The detection gas in the inner cavity of the micro-ionization chamber is within the effective range of the micro-ultraviolet light source. The entire inner cavity of the ionization chamber is used as an effective ionization area, which effectively utilizes the micro-ultraviolet light source and improves the ionization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the micro-sensitive structure of the photoionization gas sensor of the present invention. DETAILED DESCRIPTION

[0022] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0023] Specific implementation method 1: refer to Figure 1 Specifically describing this embodiment, a micro-sensitive structure of a photoionization gas sensor described in this embodiment includes a micro-ionization chamber 3, an ultraviolet light source cavity 5 and an excitation electrode 4;

[0024] The ultraviolet light source cavity 5 is a rectangular cavity with an upper opening, the rectangular cavity is filled with working gas, the upper port of the rectangular cavity is embedded in the bottom surface of the micro ionization chamber 3, and a transparent baffle 6 is also provided between the upper port of the rectangular cavity and the bottom surface of the micro ionization chamber 3;

[0025] Excitation electrodes 4 are attached to the opposite side walls of the ultraviolet light source cavity 5;

[0026] The bottom surface 2 and the top surface 1 of the micro ionization chamber 3 are both electrode plates covered with through holes;

[0027] The excitation electrode 4 is powered on to excite the working gas to emit ultraviolet light, and the ultraviolet light enters the micro ionization chamber 3 through the transparent baffle 6 and the hole on the bottom surface of the micro ionization chamber 3;

[0028] The micro ionization chamber 3 is used to fill the gas to be tested; the gas to be tested decomposes under ultraviolet photoionization to generate micro current, and the micro current is transmitted through the electrode plate.

[0029] In this embodiment, the gas to be tested enters the ionization chamber cavity through the air inlet hole, and an ionization reaction occurs under the irradiation of vacuum ultraviolet light. The ions and electrons generated by the ionization reaction move in a directional manner in the electric field formed by the bias electrode to form an ionization current, which is collected by the collecting electrode and fed back to the subsequent detection circuit through the lead-out end of the collecting electrode. The size range of the microstructure in this embodiment is 3mm-10mm in length, 2mm-8mm in width, and 2mm-8mm in height.

[0030] The micro ionization chamber and micro ultraviolet light source proposed in the present invention are used to manufacture micro photoionization gas sensors, which have a very wide range of applications, including detection of organic gas concentration, safety and health detection of enterprises that use, produce, store and transport various organic compounds, emergency accidents in environmental protection, industrial hygiene consultation, public security inspection and other fields.

[0031] Furthermore, in the present invention, the bottom surface 2 of the micro ionization chamber 3 is a collecting electrode, and the top surface 1 is a bias electrode.

[0032] In this embodiment, the bias electrode and the collecting electrode are made of stainless steel, and the coating is made of stainless steel with a thickness of less than 0.5 mm. The micro ionization chamber adopts an integrated packaging structure and is connected to the outside world through an air inlet hole, so that the micro ionization chamber has good gas flow and consistency.

[0033] Furthermore, in the present invention, the side wall of the micro ionization chamber 3 is provided with air inlet and outlet holes.

[0034] Furthermore, in the present invention, the transparent baffle 6 is a magnesium fluoride glass plate.

[0035] In this embodiment, magnesium fluoride glass is anisotropic material, and the axis with a smaller linear expansion coefficient is selected. In order to ensure the packaging process, magnesium fluoride glass needs to be directional cut, and the magnesium fluoride glass is cut into lenses with a thickness of 250 to 350 um to obtain a lens material with a uniform and constant linear expansion coefficient.

[0036] Furthermore, in the present invention, the thickness of the magnesium fluoride glass plate is 250um to 350um.

[0037] Furthermore, in the present invention, the exciting electrode 4 is rectangular and made of gold.

[0038] Furthermore, in the present invention, the surface of the exciting electrode 4 is plated with an insulating layer.

[0039] Furthermore, in the present invention, the micro ionization chamber 3 and the ultraviolet light source cavity 5 have the same size.

[0040] Furthermore, in the present invention, the working gas is Ar gas or He gas.

[0041] In this embodiment, the ultraviolet light source cavity 5 is made by micromachining technology, the size of the window glass 6 is the same as that of the ionization chamber cavity 3, and the photon energy is 10.6eV. Since the photon energy of the ultraviolet light source is greater than the ionization energy of general organic gases and less than the ionization energy of gases such as oxygen and nitrogen, the PID made based on the micro ionization chamber and the micro ultraviolet light source can measure the concentration of organic gases in the atmosphere, thereby realizing the miniaturization of the photoionization gas sensor.

[0042] In this embodiment, the ultraviolet light source cavity 5 and the ionization chamber cavity 3 are manufactured by micromachining technology. First, silicon oxide and silicon nitride masks are manufactured on magnesium fluoride glass and single silicon wafers by oxidation process and LPCVD process, and then the design pattern is transferred to magnesium fluoride glass and single silicon wafer by photolithography process, and silicon oxide, silicon nitride, single silicon and magnesium fluoride glass are removed by dry etching process, and magnesium fluoride glass and single silicon wafer are etched to the required depth, thereby completing the manufacture of ultraviolet light source cavity 5 and ionization chamber cavity 3.

[0043] In this embodiment, the sealing of magnesium fluoride glass and ultraviolet light source cavity 5 adopts low-temperature glass solder welding method. Low-temperature glass solder is formed by doping with multi-component inorganic substances, mainly including: zinc oxide, silicon dioxide, lead oxide, yttrium trioxide, etc. The linear expansion coefficient of low-temperature glass solder is adjusted by adjusting the magnesium oxide doping content to match the linear expansion coefficient of the window material. Solder is applied on the top of the micro ultraviolet light source cavity 5, and the magnesium fluoride glass window and the ionization chamber cavity 3 are aligned and a force of 10N is applied thereon to close the magnesium fluoride glass window and the ionization chamber cavity 3. The vacuum degree is raised to 10-5Tor by a vacuum high-temperature furnace, and then a mixed gas of 1 to 10Tor is filled in, and the temperature is raised to 440°C at a rate of about 1.5°C / min, maintained for 2 hours, and the furnace temperature is lowered at the same rate to complete the sealing of the ultraviolet light source cavity 5 and the ionization chamber cavity 3. The excitation electrode 4 and the ultraviolet light source cavity 5 are welded together by insulating solder to avoid leakage accidents during the excitation process. The micro ionization chamber and micro ultraviolet light source proposed in the present invention are used to manufacture a micro photoionization gas sensor, which can detect the concentration of organic gases in various fields.

[0044] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A micro-sensitive structure of a photoionization gas sensor, characterized in that: It comprises a micro ionization chamber (3), an ultraviolet light source cavity (5) and an excitation electrode (4); The ultraviolet light source cavity (5) is a rectangular cavity with an upper opening, the rectangular cavity is filled with working gas, the upper port of the rectangular cavity is embedded in the bottom surface of the micro ionization chamber (3), and a transparent baffle (6) is also provided between the upper port of the rectangular cavity and the bottom surface of the micro ionization chamber (3); Excitation electrodes (4) are attached to two opposite walls of the ultraviolet light source cavity (5); The bottom surface (2) and the top surface (1) of the micro ionization chamber (3) are both electrode plates covered with through holes; The exciting electrode (4) is powered on to excite the working gas to emit ultraviolet light, and the ultraviolet light enters the micro ionization chamber (3) through the transparent baffle (6) and the hole on the bottom surface of the micro ionization chamber (3); The micro ionization chamber (3) is used to fill the gas to be tested; the gas to be tested decomposes under ultraviolet photoionization to generate micro current, and the micro current is transmitted through the electrode plate.

2. The micro-sensitive structure of the photoionization gas sensor according to claim 1, characterized in that: The bottom surface (2) of the micro ionization chamber (3) is a collecting electrode, and the top surface (1) is a bias electrode.

3. The micro-sensitive structure of the photoionization gas sensor according to claim 1 or 2, characterized in that: The side wall of the micro ionization chamber (3) is provided with air inlet and outlet holes.

4. The micro-sensitive structure of the photoionization gas sensor according to claim 3, characterized in that: The transparent baffle (6) is a magnesium fluoride glass plate.

5. The micro-sensitive structure of the photoionization gas sensor according to claim 4, characterized in that: The thickness of the magnesium fluoride glass plate is 250um to 350um.

6. The micro-sensitive structure of the photoionization gas sensor according to claim 1 or 2, characterized in that: The exciting electrode (4) is rectangular and made of gold.

7. The micro-sensitive structure of the photoionization gas sensor according to claim 6, characterized in that: The surface of the exciting electrode (4) is plated with an insulating layer.

8. The micro-sensitive structure of the photoionization gas sensor according to claim 1, characterized in that: The micro ionization chamber (3) and the ultraviolet light source cavity (5) have the same size.

9. The micro-sensitive structure of the photoionization gas sensor according to claim 1, characterized in that: The working gas is Ar gas or He gas.

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