Method for manufacturing a filament for use in a Pirani vacuum gauge and a Pirani vacuum gauge having such a filament
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- INFICON AG
- Filing Date
- 2025-11-18
- Publication Date
- 2026-05-29
Smart Images
Figure 2026089041000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for manufacturing a filament for use in a Pirani vacuum gauge and to a Pirani vacuum gauge having such a filament. The present invention particularly relates to a method for providing a thin protective coating / layer / membrane on the filament.
Background Art
[0002] Background of the Invention Gas pressure measuring devices for use in vacuum systems are often based on the principle of heat conduction / thermal conductivity, i.e., the Pirani principle, and are therefore generally called Pirani vacuum gauges or heat transfer gauges. A Pirani vacuum gauge consists of a metal sensor wire or filament (usually tungsten, gold-plated tungsten, nickel or platinum - a first Pirani vacuum gauge used tantalum as the filament material) suspended in a tube connected to the system in which the vacuum is measured. When the sensor wire is heated, it loses heat to the surroundings by two main mechanisms, namely, thermal radiation and heat conduction. Thermal radiation is independent of gas pressure, but heat conduction is governed by gas pressure. At lower pressures, there are fewer molecules that collide with the hot filament and remove heat from it. As a result, the heat loss is slower in vacuum than under normal atmospheric conditions. Therefore, measuring the heat loss is an indirect indicator of gas pressure. The electrical resistance of the wire changes with its temperature and thus indicates the temperature of the wire. It is preferable to use a sensor wire having a high temperature coefficient of resistance because in that case, a change in temperature or heat transfer from the wire can be better detected by a more significant change in resistance for which the pressure is sought. In many systems, the wire is maintained at a constant resistance by controlling the current passing through the wire. The resistance can be set using a bridge circuit such as a Wheatstone bridge. In that case, the current required to keep the resistance constant is a measure of the vacuum / pressure.
[0003] The heating element / Pirani element / wire can be used in conjunction with a sensor element located in close proximity to the heating element. The heating element is suspended, for example, inside a tube (in a vacuum), and the sensor element is mounted, for example, on the wall of the tube (closed to a vacuum like a "lamp"). Both preferably contain filaments having the same properties. The sensor element is used to measure temperature, which is then used for temperature compensation.
[0004] The use of such sensor wires in invasive gases or vapors can lead to changes in the wire's properties. Often, the wire itself is attacked / corroded, making it thinner and altering its resistance. This alters the properties of the Pirani vacuum gauge, resulting in inaccurate pressure readings. When used in vapor, substances can deposit on the wire, or the wire can be etched and thus degraded. In conductive deposits, the wire's resistance can change. The temperature coefficient, in this case, depends on the wire and the deposits. At the same time, heat transfer to the ambient gas will change. Both can again alter and alter the properties, again leading to erroneous readings of the gas pressure.
[0005] The surface of the wire / filament needs to be protected from oxidation and other corrosive processes. This is especially true for tungsten filaments. This protection ensures stable performance over long periods of time and therefore extends the lifespan / service life of the filament. One way to achieve this is with gold-plated tungsten filament.
[0006] Traditionally, tungsten filaments are annealed in an oxygen-containing environment, such as air, to form a thin oxide layer on their surface to stabilize it and prevent further changes in the future. Such annealing processes can be carried out in various types of ovens, such as muffle ovens. Oxide formation depends on the temperature and duration of the annealing process, which can be controlled manually or automatically. Recent ovens have good environmental control, equipped with precision thermometers and the possibility of cleaning the oven with inert gas. Despite these improvements, it remains difficult to precisely control the oxidation rate, thickness, and composition of the formed oxide film.
[0007] Apart from avoiding oxidation, gold coating / plating offers further advantages, such as providing a bright surface. On the one hand, a bright surface emits low thermal radiation, which dominates power loss in high vacuum and improves the performance of Pirani vacuum gauges. On the other hand, due to gold's high conductivity, tungsten filaments have lower resistance when coated / plated with gold. The thicker the gold layer, the lower the electrical resistance. As a result, replacing a damaged sensor with a new one and further adjustment of its electronic components can be difficult. In contrast, the electrical resistance of a protected tungsten filament remains unchanged and does not depend on the thickness of the insulating protective material, such as glass, ceramic, paint, or plastic (as provided in WO2009059654A1 "Heat conducting gas pressure measurement arrangement"). Various manufacturing techniques have been proposed to produce such filaments, including melting into glass or immersion in paint, and casting or sintering techniques into thermoplastic materials. Ideally, the filament should be coated immediately after manufacture to protect it from oxidation. However, the protective layer needs to be partially removed where it is necessary to form good electrical and thermal contacts with other components of the Pirani vacuum gauge. As a result, this adds more steps to the manufacturing / production process and increases production costs.
[0008] There is a need for filaments with improved properties, particularly those with longer lifespan and improved corrosion resistance. Furthermore, there is a need for improved or alternative methods for manufacturing such filaments. [Overview of the Initiative] [Problems that the invention aims to solve]
[0009] An object of the present invention is to provide a filament, particularly a filament for use in Pirani vacuum gauges, that has stable performance over long periods of time, i.e., achieves long-lasting reproducibility. A further object of the present invention is to provide a filament with improved corrosion resistance that can be used in invasive environments. In particular, an object of the present invention is to provide a method for manufacturing such a filament, especially in an economical manner. [Means for solving the problem]
[0010] The latter objective is achieved by the method for manufacturing a filament as defined in claim 1 and further detailed in dependent claims 2 to 11.
[0011] The former objective is achieved by the filament described in claim 12, i.e., the filament manufactured according to the method proposed by the present invention.
[0012] A Pirani vacuum gauge with superior properties is achieved by using the filament according to the present invention, as shown in claims 13 and 14.
[0013] The method for manufacturing a filament according to the present invention, for use in a Pirani vacuum gauge, -The method includes the step of dispersing a plurality of filaments, for example made of tungsten / wolfram (or platinum or nickel), in a processing ( / vacuum / deposition) chamber onto at least one support such that the plurality of filaments are freely positioned on the support such as a Petri disc / Petri dish, the at least one support may be heated, and the method further includes - The process includes the step of applying a thin protective film / coating onto a filament by a gas-phase thin-film deposition process, particularly by an atomic layer deposition (ALD) or chemical vapor deposition (CVD) process.
[0014] Filaments can be of any shape and form, and in particular, they can be linear, coiled / helical, or double-coiled.
[0015] In addition to conventional coating techniques, dielectric materials can be precisely deposited from the gas phase in a controlled manner using thin-film deposition processes, such as atomic layer deposition (in short ALD) or chemical vapor deposition (in short CVD). The essential difference between ALD and CVD is that layer growth in ALD occurs periodically by self-saturated surface reactions. This essentially generates one atomic layer after another, and the layer is built up gradually. This characteristic is achieved by the process conditions, particularly the appropriate selection of reactants. The advantage of these thin-film deposition processes is their ability to precisely control the coating thickness in the nanometer range, allowing, for example, coating a very thin oxide layer immediately after filament formation. Due to the extremely thin thickness, the layer can be locally penetrated / broken by mechanical force or chemical processes at the contact points to form good electrical / thermal contacts. Furthermore, thin coatings can reduce emissivity and thus improve the performance of Pirani vacuum gauges. In the case of Pirani vacuum gauges, at high vacuum, the main heat loss is due to thermal radiation, which is governed by the emissivity of the filament surface.
[0016] Coating bare filaments offers a significant cost advantage compared to coating assembled sensors. The filament dimensions are much smaller than assembled sensors, making it possible to coat thousands of filaments simultaneously per batch.
[0017] In this embodiment of the method, the following steps are performed before applying a thin protective film: - The step of applying ozone plasma to the filament, particularly at a temperature in the range of 80°C to 200°C, preferably 100°C, and especially for a duration in the range of 5 to 10 minutes.
[0018] In a further embodiment of this method, the step of applying a thin protective film includes: a) The step of introducing a first precursor, such as trimethylaluminum TMA, into a processing chamber in a pulsed manner having a pulse time / duration in the range of 0.1 to 0.5 seconds, more specifically 0.2 seconds; b) A step of purging the processing chamber with a further purging gas, in particular an inert gas such as N2, for a duration in the range of 2 to 5 seconds, in particular a flow rate in the range of 100 to 200 sccm, preferably a flow rate of 150 sccm, c) The step of introducing a second precursor, such as H2O, into the processing chamber in a pulsed manner, particularly in the range of 0.1 to 0.5 seconds, more specifically, a pulse time / duration of 0.2 seconds, d) The process includes purging the processing chamber with a purge gas, particularly an inert gas such as N2, for a longer duration than in step b), particularly in the range of 4 to 6 seconds, and at a higher flow rate than in step b), particularly in the range of 150 to 300 sccm, preferably 200 sccm. Steps a) to d) form a single cycle of the atomic layer deposition (ALD) process, which is repeated several times, for example, in the range of 30 to 100 times. Steps a) to d) are all carried out at the same temperature in the range of 80°C to 200°C, preferably 100°C.
[0019] ALD (Artificial Laser Deposition) is a thin-film deposition technique that enables atomic-level thickness control through self-limiting reactions. The process involves alternating pulses of precursor and reactant. In the first step, the precursor—often a metal-organic compound or halide—reacts with available surface sites until all reaction sites are saturated, halting further growth and forming a monolayer. This self-limiting behavior ensures precise control. After excess precursor and byproducts are purged, reactants such as H2O or NH3 are introduced. The reactants then interact only with the newly formed surface layer, again in a self-limiting manner, to produce the final film (e.g., metal oxide, metal nitride). Repeating this cycle enables the controlled deposition of ultrathin films with precise thickness and uniformity. The purity of the resulting films is ensured by high-quality precursors and a carefully controlled reaction environment, minimizing impurities and defects such as pinholes.
[0020] The use of ALD thin-film deposition to coat a protective layer on tungsten filaments extends the range of applications for tungsten filaments as pressure-sensing elements to more corrosive environments where previously only platinum and nickel filaments were usable.
[0021] In further embodiments of this method, the steps of applying ozone plasma and applying a thin protective film are all performed at essentially the same (low) temperature, particularly in the range of 80°C to 200°C, preferably 100°C.
[0022] In a further embodiment of this method, a layer of insulating material, particularly ceramic, more specifically one of Al2O3, SiO2, AlN, Y2O3, and SiC, or a metallic material, particularly indium tin oxide (ITO), is formed on the filament.
[0023] In addition to the insulating material, an indium tin oxide (ITO) layer can be deposited. This can be a less expensive alternative to gold. This solution also makes it easier to form a good electrical contact between the filament and the support part.
[0024] In a further embodiment of the method, the average growth rate of the layer is in the range of 0.06 nm to 0.1 nm per ALD cycle, preferably 0.08 nm.
[0025] In a further embodiment, the method further includes determining the thickness of the layer deposited on the filament by measuring the thickness of the layer deposited on a reference substrate, such as a Si substrate or a quartz substrate, which undergoes the same deposition process as the filament, especially using a quartz crystal microbalance (QCM).
[0026] In a further embodiment of the method, the final thickness of the layer deposited on the filament is in the range of 3 nm to 10 nm, especially 5 nm.
[0027] In a further embodiment, the method further disperses the filaments in the processing chamber, and after closing the processing chamber, uses a vacuum pump (together with a vacuum valve and a vacuum measurement cell) to evacuate the processing chamber to a pressure of less than 10 -1 mbar.
[0028] In further embodiments, the method further includes shaking, oscillating, or vibrating at least one carrier and the filament together with it, particularly during the ALD or CVD process, more specifically after a certain number of ALD cycles, and more specifically periodically during the ALD or CVD process. This is to ensure that areas / points of contact between the filament and the carrier that were not previously coated subsequently receive coating. In this way, coating over the entire filament is ensured. Otherwise, coating holes may remain on the filament, which would become attack points for etching gases, for example, and thus be detrimental to the filament and should be avoided.
[0029] Alternatively, in further embodiments of the present method, instead of shaking, oscillating, or vibrating at least one carrier to move around the filament, the filament can be directly agitated using a pulsating gas flow (e.g., increasing the gas flow intermittently to oscillate when turned on) such as a flow of a first precursor, a purge gas, and at least one of the second / further precursors. Filament movement can be achieved, in particular, by injecting, blowing, or "blowing" the (purge) gas, for example, at the start or end of purging the processing chamber, or intermittently during purging.
[0030] In a further aspect of the present invention, it is proposed that a filament for use in a Pirani vacuum gauge may be manufactured according to the method presented above, using any combination of the embodiments described.
[0031] According to another aspect of the present invention, a Pirani vacuum gauge having the above-described filament is proposed, wherein the filament functions as a heating element and / or a measuring / sensing element.
[0032] The present invention will be described illustratively below with reference to the attached drawings. [Brief explanation of the drawing]
[0033] [Figure 1] A schematic diagram of the apparatus for carrying out the thin-film coating method according to the present invention is shown. [Modes for carrying out the invention]
[0034] Detailed description of the invention The coating of a protective layer on multiple filaments 1 is made possible, according to the present invention, by a gas-phase ALD thin film deposition process as described below, for example, using a preferred example of deposition of a preferred Al2O3 protective layer.
[0035] As shown in Figure 1, the filament 1 is introduced into a processing chamber 2 surrounding a processing space 3. The chamber 2 includes a carrier 4. The walls of the chamber 2 and / or the carrier 4 can be heated by a heating mechanism. A temperature controller 8, including a temperature sensor, controls the temperature inside the chamber 2, particularly in the carrier 4. The filament 1 is placed on the carrier 4 so as to be freely positioned on the carrier 4. The carrier 4 may be (occasionally) shaken, oscillated, or vibrated so that the filament 1 is moved / agitated during the coating process, ensuring that any previously uncoated contact areas / points of the filament 1 with the carrier 4 subsequently receive coating. This enhances the uniformity of the coating and ensures that the coating covers the entire filament 1.
[0036] Chamber 2 is closed and sealed, then vacuumed by the vacuum pump 5. -1The system is evacuated to a final pressure of less than mbar. As in conventional systems, the pumping system, separate from the vacuum pump 5, includes a vacuum valve 6 and a vacuum measuring cell 7 for monitoring the vacuum state. During this time, the heating mechanism heats the entire chamber 2, including the carrier 4 with the filament 1. To coat with Al2O3, the filament 1 is heated to a temperature of 100°C, which is set with the assistance of a temperature controller 8. Then, ozone plasma is applied to the filament 1 at a temperature of 100°C for approximately 5-10 minutes. The purpose of this short purification step is to remove potential residues on the surface of the filament 1 and to improve the adhesion of the target oxide layer without the formation of any oxide layer. Once the plasma purification is complete, the deposition process continues in cycles. One coating / deposition cycle is defined by the following four process steps: 1) Introduction of a first precursor such as TMA with a pulse time of 0.1 to 0.5 seconds; 2) Purge chamber 2 with a purge gas such as N2 for 2-5 seconds; 3) Introduction of a second precursor such as H2O with a pulse time of 0.1 to 0.5 seconds; 4) Purge chamber 2 with purge gas (N2) for 4-6 seconds.
[0037] The vapor pressure in the processing space 3 is large enough to rapidly coat the surface of the filament 1, so both precursors are vaporized at ambient temperature from precursor sources 9 and 11. The precursors are introduced into the chamber 2 in a pulsed manner. For this purpose, pulse valves 12 and 13 are opened for a period of 0.1 to 0.5 seconds. A purge gas, such as nitrogen, is supplied from a purge gas source 10 via a purge gas valve 14. By varying the purge gas flow with a flow regulator 15 during the coating cycle, a process pressure of approximately 1 mbar is set to ensure sufficient flow of precursors on the filament and good purging between process steps. A vacuum measuring cell 7 is used to monitor and regulate the process pressure.
[0038] Steps 1-4 described above are all performed at essentially the same temperature as the previous purification step, so only an Al2O3 layer is formed on filament 1. By using low-temperature conditions, tungsten oxide is not formed, and only a thin Al2O3 film is created. The average growth rate is approximately 0.08 nm per cycle. To achieve a preferred thickness of 5 nm protective coating, an order of 60 ALD cycles is required.
[0039] The first and second / further precursors and purge gas are sequentially introduced into chamber 2 via valves 12, 13, and 14 that pulse under controlled conditions at predetermined intervals, and the purge gas is preferably introduced via a gas flow regulator 15. The process can be fully automated using a process controller, thereby allowing even long processes with numerous cycles to be performed very economically. In addition to the use of just two precursors, several other precursors can also be utilized as needed, and profiles with variations in different material compositions can also be achieved. The thickness of the layer deposited on filament 1 can be monitored, for example, by measuring the thickness of the layer deposited on a reference substrate (not shown), such as a Si substrate or quartz substrate, which undergoes the same deposition process as filament 1, using a quartz crystal microbalance (QCM, not shown). The achieved layer quality can be verified by placing the filament thus produced in a Pirani vacuum gauge. These Pirani vacuum gauges are then used for extended periods, during which the drift of their readings is monitored. Chemical etching tests can also be used to evaluate the quality of the protective layer.
[0040] Preferred first precursors include, for example, trimethylaluminum (TMA) for producing an Al2O3 coating, titanium chloride or titanium tert-butoxide for producing a TiO2 coating, and tantalum ethoxide for producing a Ta2O5 coating. The second precursor is an oxidizing agent, preferably water (H2O). As a purging gas, an inert gas such as a noble gas, for example, argon, or preferably nitrogen, is used.
[0041] In summary, the proposed ALD coating process can achieve the following advantages: -Uniform distribution of the protective layer thickness; - High density of the layer material, and therefore high opacity; - Good quality of the interface between the filament and the coating, i.e., good adhesion; - Low process temperatures can be used, especially for Al2O3 protective coatings; - The resulting protective coating extends the lifespan of the filament by more than 10 times compared to uncoated filament. [Explanation of symbols]
[0042] 1 filament 2. Vacuum / Processing / Deposit Chamber 3 Processing space 4. Carrier 5. Vacuum pump 6. Vacuum valve 7. Vacuum measurement cell / device 8 Temperature controller 9. First precursor source 10. Purge gas source 11 Second / Further Precursor Sources 12 First precursor valve 13 Second / Further Precursor Valves 14. Purge gas valve 15. Purge gas flow regulator
Claims
1. A method for manufacturing a filament (1) for use in a Pirani vacuum gauge, - The method includes the step of dispersing, for example, a plurality of tungsten filaments (1) in a processing chamber (2) onto at least one carrier (4), such as a Petri disc, so that the filaments (1) are freely positioned on the carrier (4), the at least one carrier (4) may be heated, and the method further includes A method comprising the step of applying a thin protective film onto the filament (1) by a thin film deposition process from the gas phase, particularly by an atomic layer deposition (ALD) or chemical vapor deposition (CVD) process.
2. Before applying a thin protective film, The method according to claim 1, wherein the step of applying ozone plasma to the filament (1) is performed, particularly at a temperature in the range of 80°C to 200°C, preferably 100°C, and particularly for a duration in the range of 5 to 10 minutes.
3. The step of applying a thin protective film is, a) The step of introducing a first precursor, for example trimethylaluminum (TMA), into the processing chamber (2) in a pulsed manner having a pulse duration in the range of 0.1 to 0.5 seconds, more specifically 0.2 seconds; b) The processing chamber (2) is purged with a purging gas, particularly N ２ The process involves purging with an inert gas, particularly for a duration of 2 to 5 seconds, with a flow rate of 100 to 200 sccm, preferably 150 sccm. c) A second precursor, for example, H ２ The steps include introducing O into the processing chamber (2) in a pulsed form having a pulse duration of 0.1 to 0.5 seconds, more specifically 0.2 seconds, d) The processing chamber (2) is further purged with a gas, particularly N ２ The process includes a step of purging with an inert gas such as the following, for a longer duration than in step b), particularly in the range of 4 to 6 seconds, and at a higher flow rate than in step b), particularly in the range of 150 to 300 sccm, preferably 200 sccm. The method according to claim 1 or 2, wherein steps a) to d) form a single cycle of the atomic layer deposition (ALD) process, which is repeated several times, for example, in the range of 30 to 100 times.
4. The method according to any one of claims 1 to 3, wherein the steps of applying the ozone plasma and applying the thin protective film are all performed at essentially the same temperature, particularly in the range of 80°C to 200°C, preferably at 100°C.
5. A layer of insulating material, especially a ceramic layer, more specifically Al ２ O ３ SiO ２ AlN, Y ２ O ３ The method according to any one of claims 1 to 4, wherein a layer of one of the following, SiC, or a layer of a metallic material, particularly a layer of indium tin oxide (ITO), is formed on the filament.
6. The method according to any one of claims 3 to 5, wherein the average growth rate of the layer is in the range of 0.06 nm to 0.1 nm per ALD cycle, preferably 0.08 nm.
7. The method according to any one of claims 1 to 6, further comprising the step of determining the thickness of a layer deposited on the filament (1) by measuring the thickness of a layer deposited on a reference substrate such as a Si substrate or a quartz substrate that undergoes the same deposition process as the filament (1), particularly using a quartz crystal microbalance (QCM).
8. The method according to any one of claims 3 to 6, wherein the final thickness of the layer deposited on the filament is in the range of 3 nm to 10 nm, particularly 5 nm.
9. Disperse the filament (1) in the processing chamber (2), and after closing the processing chamber (2), further include the step of evacuating the processing chamber (2) to a pressure of less than 10 －１ mbar. The method according to any one of claims 3 to 7.
10. The method according to any one of claims 1 to 9, further comprising the step of shaking, oscillating or vibrating the at least one carrier (4) and together with the filament (1) particularly during the ALD or CVD process, more specifically after a certain number of ALD cycles, and even more specifically periodically during the ALD or CVD process.
11. The method according to any one of claims 1 to 9, further comprising the step of stirring the filament (1) by intermittently increasing the gas flow, for example, by pulsating the gas flow, such as intermittently increasing the gas flow, such as the flow of the first precursor, the purge gas, and the second precursor, and in particular by injecting or ejecting the gas intermittently, for example, at the start or end of purging the processing chamber, or during purging.
12. A filament (1) for use in a Pirani vacuum gauge, manufactured according to the method described in any one of claims 1 to 11.
13. A Pirani vacuum gauge having a filament (1) as described in claim 12, wherein the filament (1) acts as a heating element and / or measuring element.