Convection enhanced Pirani vacuum gauge

Abstract

The invention discloses a convection enhanced Pirani vacuum gauge, which comprises a shell, a left accommodating cavity and a right accommodating cavity are arranged in the shell, the left accommodating cavity is provided with an air inlet, the right accommodating cavity is provided with an air outlet, and the left accommodating cavity and the right accommodating cavity are communicated through a channel; a convection enhancing device is arranged in the left containing cavity, and a sensing unit is arranged in the right containing cavity. The Pirani vacuum gauge is based on the MEMS technology, the vibration of the convection enhancement device is used for generating airflow, natural convection heat exchange is converted into forced convection heat exchange, on one hand, the technology integration degree can be improved, power consumption can be reduced, on the other hand, the convection heat exchange efficiency can be greatly improved, the sensitivity can be improved, the packaging size can be more compact, and the packaging cost can be reduced. The temperature drift compensation can be realized by arranging the symmetrically arranged compensation elements, and the error caused by the introduction of the convection enhancement device is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of vacuum measurement, and particularly relates to a convection-enhanced Pirani vacuum gauge. Background Art

[0002] Vacuum degree measurement, as a key technology in modern precision manufacturing and scientific research, plays a crucial role in fields such as semiconductors, aerospace, biomedicine, new energy, and industrial manufacturing. Especially in the semiconductor manufacturing field, its accuracy directly affects the yield and performance of key processes such as thin film deposition, ion implantation, and nanoscale etching.

[0003] A Pirani vacuum gauge is a vacuum gauge made based on the gas kinetic effect and using the inverse relationship between vacuum degree and gas heat dissipation. As the core device for heat conduction type vacuum measurement, it is widely used in the field of medium and low vacuum degree detection. Its structure mainly includes a mechanical support component, a sensing unit, and a signal processing circuit. The mechanical support structure generally includes a ceramic bracket for ensuring the axial tension of the filament, a double-layer shielding housing for maintaining a constant temperature environment, and a vacuum flange interface for realizing gas path connection; the signal processing circuit integrates modules such as a Wheatstone bridge; the sensing unit is a filament placed in a metal or glass sealed cavity, usually made of metal wires such as platinum. The signal processing circuit provides a certain amount of power to raise the temperature of the metal wire. The level of vacuum degree affects heat dissipation and thus affects the temperature of the metal wire when reaching equilibrium. The temperature change of the metal wire can be converted into a resistance change and read out through the circuit, thereby measuring the vacuum degree.

[0004] Power consumption, accuracy, sensitivity, and response time are important performance indicators of the Pirani vacuum gauge. In traditional designs, there are problems of temperature drift and cross-interference, which seriously affect the accuracy and sensitivity. Therefore, many Pirani vacuum gauges add a compensation unit in the sensing unit part to achieve compensation for environmental temperature drift, and also effectively suppress the measurement errors caused by radiative heat transfer and solid heat conduction during single metal wire sensing. The filament usually uses metal materials and has a large volume, high power consumption, and a large heat capacity, with a significant lag effect on temperature change. When the gas pressure changes, the filament needs a long time to reach a new equilibrium state through natural convection heat exchange. This heat relaxation process directly restricts the response speed. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a convection-enhanced Pirani vacuum gauge to achieve the purposes of enhancing convection, improving sensitivity, reducing power consumption, and realizing miniaturization.

[0006] To achieve the above purposes, the technical solution of the present invention is as follows:

[0007] A convection-enhanced Pirani vacuum gauge, comprising a housing, wherein a left accommodation cavity and a right accommodation cavity are provided inside the housing, an air inlet is opened on the left accommodation cavity, an air outlet is opened on the right accommodation cavity, and the left accommodation cavity and the right accommodation cavity are communicated through a channel; a convection enhancement device is arranged in the left accommodation cavity, and a sensing unit is arranged in the right accommodation cavity.

[0008] In the above solution, one end of the convection enhancement device is fixed to the left inner wall of the housing, and the other end is suspended. The convection enhancement device and the channel are on the same horizontal plane. The air inlet is arranged below the convection enhancement device, the air outlet and the channel are on the same horizontal plane, and the sensing unit is located below the channel and the air outlet.

[0009] In the above solution, the convection enhancement device is a micro piezoelectric fan, and the micro piezoelectric fan comprises a support structure, a piezoelectric vibration unit and a mechanical amplification structure. The piezoelectric vibration unit is fixed on the inner wall of the housing through the support structure, and the mechanical amplification structure is fixed at the end of the piezoelectric vibration unit.

[0010] In a further technical solution, the support structure is made of composite material, engineering plastic or metal alloy, the piezoelectric vibration unit is made of piezoelectric ceramic material PZT, and the mechanical amplification structure is an elastic diaphragm, including PET material or aluminum alloy.

[0011] In the above solution, the sensing unit comprises a substrate, a dielectric thin film is deposited on the substrate, a heating element is arranged on the dielectric thin film, compensation elements are symmetrically arranged on both sides of the heating element, and a cavity is opened on the back of the substrate.

[0012] In a further technical solution, the substrate is a silicon substrate, and the substrate and the housing are fixed by bonding with an adhesive or by a bonding method.

[0013] In a further technical solution, the heating element and the compensation element are silicon wires or metal wires, and are patterned by MEMS process.

[0014] In a further technical solution, the dielectric thin film is made of silicon dioxide, silicon nitride by a deposition process, or combined into a silicon dioxide / silicon nitride laminated structure.

[0015] In the above solution, the housing is made of stainless steel, kovar alloy or ceramic material, and the inner wall of the housing has a nano coating.

[0016] In the above solution, a control circuit board connected to the convection enhancement device and the sensing unit is arranged inside the housing.

[0017] Through the above technical solution, a convection-enhanced Pirani vacuum gauge provided by the present invention has the following beneficial effects:

[0018] 1. The present invention has successfully achieved miniaturization by combining MEMS process technology, greatly reducing the volume of the Pirani vacuum gauge.

[0019] 2. By setting up a convection enhancement device, the present invention increases the convection velocity of gas molecules, converts natural convection heat transfer into forced convection heat transfer, makes the heat exchange process more sufficient and rapid, and solves the problems of slow response and low accuracy of traditional Pirani vacuum gauges in low-vacuum and high-vacuum environments.

[0020] 3. The present invention reasonably sets the positions of the air inlet, air outlet and channels. By optimizing the gas flow path and increasing the indirect contact area between the gas and the heating element, the heat conduction efficiency is significantly improved, the thermal inertia is reduced, and thus the response speed of temperature change and vacuum degree is accelerated.

[0021] 4. By setting compensation elements placed symmetrically, the present invention can achieve temperature drift compensation and reduce the error caused by the introduction of the convection enhancement device.

[0022] In summary, the vacuum gauge of the present invention can provide fast and stable measurement results in different vacuum environments, has higher measurement accuracy and a wider application range; especially in special environments such as low temperature and high vacuum, it can still maintain excellent performance and meet the vacuum measurement requirements in high-precision scientific experiments and industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art.

[0024] Figure 1 Schematic diagram of a convection-enhanced Pirani vacuum gauge disclosed in an embodiment of the present invention.

[0025] Figure 2 Schematic diagram of the gas flow path inside the Pirani vacuum gauge provided by the present invention.

[0026] Figure 3 Schematic diagram of the convection enhancement device, (a) is the groove structure, and (b) is the support plate structure.

[0027] In the figure, 1. Outer shell; 2. Convection enhancement device; 3. Sensing unit; 4. Air inlet; 5. Left accommodation cavity; 6. Channel; 7. Right accommodation cavity; 8. Air outlet; 21. Support structure; 22. Piezoelectric vibration unit; 23. Mechanical amplification structure; 31. Compensation element; 32. Heating element; 33. Dielectric film; 34. Substrate; 35. Cavity. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention.

[0029] The present invention provides a convection-enhanced Pirani vacuum gauge, as Figure 1 and Figure 2 shown, which includes a housing 1. A left accommodation cavity 5 and a right accommodation cavity 7 are arranged inside the housing 1. An air inlet 4 is opened on the left accommodation cavity 5, and an air outlet 8 is opened on the right accommodation cavity 7. The left accommodation cavity 5 and the right accommodation cavity 7 are communicated through a channel 6; a convection enhancement device 2 is arranged in the left accommodation cavity 5, and a sensing unit 3 is arranged in the right accommodation cavity 7.

[0030] The housing 1 can be made of, but not limited to, metal materials such as stainless steel and kovar alloy, which can effectively shield electromagnetic interference, improve signal quality, and reduce measurement errors; it can also be made of ceramic materials with a thermal expansion coefficient relatively close to that of a silicon chip, such as alumina, etc.; it can also be designed with a specific structure of a silicon substrate and a silicon cover, and the channel 6, the air inlet 4, and the air outlet 8 are etched, and a packaging housing 1 is formed by bonding. Appropriate packaging materials can be selected according to different application characteristics. The inner wall of the housing 1 has a nano-coating to reduce the influence of surface effects on gas flow and improve measurement repeatability.

[0031] One end of the convection enhancement device 2 is fixed to the left inner wall of the housing 1, and the other end is suspended. The convection enhancement device 2 and the channel 6 are on the same horizontal plane. The air inlet 4 is arranged below the convection enhancement device 2. The air outlet 8 and the channel 6 are on the same horizontal plane, and the sensing unit 3 is located below the channel 6 and the air outlet 8. As Figure 2 shown, the gas entering from the air inlet 4 passes through the convection enhancement device 2 to increase the convection speed of gas molecules, then passes through the channel 6 and is discharged from the air outlet 8. During the gas flow process, the gas will pass through the sensing unit 3, and the sensing unit 3 measures the vacuum degree.

[0032] In this embodiment, the convection enhancement device 2 is a micro piezoelectric fan. The micro piezoelectric fan includes a support structure 21, a piezoelectric vibration unit 22, and a mechanical amplification structure 23. The piezoelectric vibration unit 22 is fixed to the inner wall of the housing through the support structure 21, and the mechanical amplification structure 23 is fixed to the end of the piezoelectric vibration unit 22.

[0033] Specifically, the support structure 21 is made of composite materials and engineering plastics to reduce the overall weight and optimize the vibration transfer efficiency, or it can also be made of metal alloy to balance the structural stability. The support structure 21 can adopt a groove structure as shown in (a) of Figure 3 . The piezoelectric vibration unit 22 is embedded in the groove of the support structure 21, and high-strength bonding is carried out between the two. The space occupied by the convection enhancement device 2 can be reduced, and it is also possible to make the mechanical amplification structure 23 reach a longer length under the premise of occupying the same space size. The support structure 21 can also be mechanically connected to the inner wall of the housing 1 with high strength, which greatly improves the system stability and makes the overall packaging volume more compact. It can also be adopted asFigure 3 The support plate structure shown in (b) in

[0034] The piezoelectric vibration unit 22 is a small-sized piezoelectric sheet, and usually a piezoelectric ceramic material PZT with a high piezoelectric constant and easy to process is selected. The piezoelectric vibration unit 22 is bonded to the support structure 21 with a glue having high-intensity bonding performance, such as UV curable glue, epoxy resin glue, etc.

[0035] The mechanical amplification structure 23 is an elastic diaphragm, which needs to meet the requirements of light weight, high rigidity, fatigue resistance, etc., to efficiently transmit the vibration of the piezoelectric vibration unit 22 and generate an air flow. A lightweight polymer material can be selected, such as a PET material with good flexibility; or a lightweight metal sheet with a lower hardness can be selected, such as aluminum alloy. The elastic diaphragm is also bonded to the piezoelectric vibration unit 22 with a glue having high-intensity bonding performance.

[0036] The sensing unit 3 includes a substrate 34, a dielectric thin film 33 is deposited on the substrate 34, a heating element 32 is arranged on the dielectric thin film 33, compensation elements 31 are symmetrically arranged on both sides of the heating element 32, and a cavity 35 is fabricated on the back of the substrate 34 through a reverse etching process.

[0037] The substrate 34 is a silicon substrate 34, and the substrate 34 is fixed to the housing 1 by bonding with an adhesive or by a bonding method.

[0038] The dielectric thin film 33 is made of a material with low thermal conductivity, high insulation and high stability. Usually, materials such as silicon dioxide and silicon nitride are made through a deposition process, or can be combined into a silicon dioxide / silicon nitride laminated structure to optimize the dielectric performance and mechanical stability. The material selection needs to consider the working environmental conditions of the application.

[0039] The heating element 32 and the compensation element 31 are silicon wires or metal wires, and are patterned through MEMS processes.

[0040] A control circuit board connected to the piezoelectric vibration unit 22 of the convection enhancement device 2 and the heating element 32 of the sensing unit 3 is arranged inside the housing 1, which is not shown in the figure. The control circuit board can be placed at the bottom of the left accommodation cavity 5, and the control circuit board is electrically connected to the piezoelectric vibration unit 22 and the heating element 32 through wire bonding and other methods.

[0041] When the piezoelectric vibration unit 22 vibrates at a certain frequency under circuit control, the left side remains stationary due to high-strength bonding with the support structure 21, and the vibration on the right side is amplified by the mechanical amplification structure 23, and this vibration causes the air flow in the cavity. The process of natural convection heat transfer occurs slowly, and it is easy to form local stagnant flow, resulting in insufficient heat transfer and a long time required to reach a steady state. After introducing the convection enhancement device 2, the design of the air inlet 4, the air outlet 8, the channel 6 and the cavity 35 structure can guide the air flow and form Figure 2The airflow path shown, thus prompting the high-temperature gas to be carried away more quickly, while enabling the low-temperature gas to quickly replenish the vicinity of the heating element 32, improving the heat exchange rate. The positions of the air inlet 4, the channel 6, and the air outlet 8 are designed such that a low-impedance gas flow path is formed within the device, significantly reducing the flow disturbance and path deviation of the gas during the process of entering the measurement area, avoiding the non-uniform heat transfer phenomenon caused by the bending of gas streamlines, the formation of vortices, or the local dead cavity effect, thereby effectively enhancing the steady-state response characteristics and measurement consistency of the system.

[0042] When the heating element 32 in the sensing unit 3 heats up under a certain power drive and generates stable heat. At this time, heat exchange occurs between the heating element 32 and the surrounding gas molecules. When the gas molecules collide with the heating element 32, part of the heat will be carried away, causing the temperature of the heating element 32 to drop. When the vacuum degree is low, the gas molecules in the cavity are dense, and the collisions between the gas molecules and the heating element 32 are frequent, resulting in an enhanced heat conduction ability through the gas molecules, thus reducing the temperature of the heating element 32. When the vacuum degree is high. The gas in the cavity is thin, the gas density is low, the heat conduction ability through the gas molecules is weakened, and the temperature of the heating element 32 will be relatively high. This phenomenon makes the heat transferred through the gas molecules directly related to the pressure, and the resistance value of the heating element 32 usually has a clear response characteristic to temperature changes, and shows a positive temperature coefficient or a negative temperature coefficient characteristic according to the selected material. The system can measure the change in the resistance value of the heating element 32 under steady state, calculate its temperature, and then calculate the thermal conductivity of the gas and its corresponding pressure value based on the temperature of the heating element 32 in the thermal equilibrium state, that is, realize the measurement of the vacuum degree.

[0043] To suppress the interference of environmental temperature fluctuations on the measurement results, a compensation element 31 is arranged around the heating element 32. When the environmental temperature changes, the resistance value of the heating element 32 will be affected. The compensation element 31 and the heating element 32 simultaneously sense the fluctuations of the environmental temperature change, so the difference between the two will not be affected by the environmental temperature and is only related to fluid heat transfer. Since the convection enhancement device 2 is introduced into the device, an Figure 2 airflow path shown is formed within the cavity 35, and the temperature distribution within the right accommodation cavity 7 will be affected. To reduce this part of the error, in the present invention, the compensation elements 31 are symmetrically distributed on both sides of the heating element 32. The two symmetrically arranged compensation elements 31 are at the same distance from the heating element 32, so the heat transferred through non-gas heat conduction is the same and the influence of the environmental temperature is the same. If in the natural convection state, the temperatures of the two should be the same. Therefore, after the convection enhancement device 2 is introduced, the temperature difference between the two symmetrically arranged compensation elements 31 can reflect the influence of the convection enhancement device 2 on the temperature distribution in the sensing unit 3.

[0044] Through the above temperature difference calculation, the influence of the convection enhancement device 2 and the ambient temperature fluctuation on the measurement can be corrected. Therefore, the symmetrically arranged compensation elements 31 can effectively reduce phenomena such as temperature drift and current drift that may occur during the measurement process, correct the measurement error introduced by the convection enhancement device 2, and through the difference of the compensation signals, the system can maintain a high measurement accuracy.

[0045] As described above, a convection-enhanced Pirani vacuum gauge of the present invention has the characteristics of high process integration, low power consumption, high convection heat transfer efficiency, high precision, high stability, etc. The main reasons include: First, a convection enhancement device 2 is introduced into the Pirani vacuum gauge, which improves the heat transfer efficiency of the system and promotes the system to stabilize faster; Second, a symmetrically distributed compensation unit is designed in the sensing unit 3 to compensate for the influence of ambient temperature fluctuation, current drift, and the introduction of the convection enhancement device 2; Third, through the design of the internal cavity and the gas flow channel 6, the flow of the heat transfer air flow is guided, thereby promoting the occurrence of the heat transfer process, reducing the pressure loss, and improving the precision.

[0046] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A convection-enhanced Pirani vacuum gauge, characterized in that, It includes a housing, within which there are a left accommodation cavity and a right accommodation cavity. An air inlet is provided on the left accommodation cavity, and an air outlet is provided on the right accommodation cavity. The left accommodation cavity and the right accommodation cavity are connected through a channel. A convection enhancement device is arranged in the left accommodation cavity, and a sensing unit is arranged in the right accommodation cavity.

2. The convection-enhanced Pirani vacuum gauge according to claim 1, wherein One end of the convection enhancement device is fixed to the left inner wall of the housing, and the other end is suspended. The convection enhancement device and the channel are on the same horizontal plane. The air inlet is arranged below the convection enhancement device. The air outlet and the channel are on the same horizontal plane. The sensing unit is located below the channel and the air outlet.

3. The Pirani vacuum gauge with enhanced convection according to claim 1, characterized in that, The convection enhancement device is a micro piezoelectric fan, which includes a support structure, a piezoelectric vibration unit, and a mechanical amplification structure. The piezoelectric vibration unit is fixed on the inner wall of the housing through the support structure, and the mechanical amplification structure is fixed at the end of the piezoelectric vibration unit.

4. The convection-enhanced Pirani vacuum gauge according to claim 3, wherein, The support structure is made of composite material, engineering plastic, or metal alloy. The piezoelectric vibration unit uses piezoelectric ceramic material PZT. The mechanical amplification structure is an elastic diaphragm, including PET material or aluminum alloy.

5. The Pirani vacuum gauge with enhanced convection according to claim 1, characterized in that, The sensing unit includes a substrate, on which a dielectric thin film is deposited. A heating element is arranged on the dielectric thin film, and compensation elements are symmetrically arranged on both sides of the heating element. A cavity is formed on the back of the substrate.

6. The convection-enhanced Pirani vacuum gauge according to claim 5, wherein The substrate is a silicon substrate, and the substrate and the housing are bonded through an adhesive or fixed through a bonding method.

7. A convection-enhanced Pirani vacuum gauge according to claim 5, characterized in that, The heating element and the compensation elements are silicon wires or metal wires, and are patterned through MEMS technology.

8. A convection-enhanced Pirani vacuum gauge according to claim 5, characterized in that, The dielectric thin film is made of silicon dioxide, silicon nitride through a deposition process, or combined into a silicon dioxide / silicon nitride laminated structure.

9. The Pirani vacuum gauge with enhanced convection according to claim 1, characterized in that, The housing is made of stainless steel, kovar alloy, or ceramic material, and the inner wall of the housing has a nano - coating.

10. The Pirani vacuum gauge with enhanced convection according to claim 1, characterized in that, A control circuit board connected to the convection enhancement device and the sensing unit is arranged inside the housing.

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