A ruthenium oxide thick film resistance temperature sensor and a method of making the same

Abstract

The application belongs to the technical field of temperature sensors, and provides a ruthenium oxide thick film resistance temperature sensor and a preparation method thereof, which comprises a sensor chip, an adapter and a wire, the resistance surface of the sensor chip is bonded on the adapter through epoxy resin; the adapter comprises a mounting seat and a shell, the shell is sleeved outside the mounting seat, and a heat sink space is formed between the shell and the mounting seat; the sensor chip and the wire are both arranged in the heat sink space, the sensor chip is connected with the mounting seat, and the wire is wound on the sensor chip and the mounting seat; one end of the wire is connected with the sensor chip, and the other end of the wire extends out of the shell; the sensor chip comprises an insulating substrate, an electrode arranged on the insulating substrate, and a ruthenium oxide-based thick film sensitive layer covering the electrode and connected with the insulating substrate.

Description

Technical Field

[0001] This invention belongs to the field of temperature sensor technology, specifically relating to a ruthenium oxide thick-film resistive temperature sensor and its preparation method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Temperature measurement is a key technology in fields such as low-temperature physics experiments, quantum computing, and space exploration. Achieving high-sensitivity and high-stability temperature measurement in the ultra-low temperature range of 10 mK to 45 K is of great significance. Existing low-temperature sensors typically include rhodium-iron resistance thermometers, germanium resistance thermometers, and oxide resistance thermometers. Among them, oxide resistance thermometers have received increasing attention in recent years due to their simple structure, high reliability, and the ability to be mass-produced using thick-film processes.

[0004] In metal oxide material systems, ruthenium oxide (RuO2) is widely used in the fabrication of low-temperature resistance thermometers due to its metal-like conductivity, excellent chemical stability, and sensitive temperature response at low temperatures. Thick-film resistors based on the RuO2-glass composite system can form a stable conductive network structure at low temperatures and exhibit significant resistance-temperature response characteristics, thus making them suitable for low-temperature temperature measurement.

[0005] The resistance-temperature characteristics of existing RuO2 thick-film temperature sensors are significantly affected by factors such as RuO2 particle size, glass phase ratio, and sintering process parameters. Different devices often exhibit some degree of variation, thus requiring individual calibration. In extremely low-temperature environments, temperature sensors may also be affected by parasitic heating and insufficient thermal coupling, impacting measurement stability and accuracy.

[0006] Designing a temperature sensor with high sensitivity, good repeatability, and excellent long-term stability in the ultra-low temperature range of 10 mK to 45 K, making it suitable for temperature measurement in dilution cooling environments, is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the aforementioned issues, this invention proposes a ruthenium oxide thick-film resistance temperature sensor and its fabrication method. Through the selection of specific material systems, device structure design, and optimization of the fabrication process, the temperature sensor achieves high sensitivity and high stability temperature measurement within an extremely low temperature range.

[0008] According to some embodiments, the first aspect of the present invention provides a ruthenium oxide thick-film resistance temperature sensor, employing the following technical solution: A ruthenium oxide thick-film resistance temperature sensor includes a sensor chip, an adapter, and wires. The resistive surface of the sensor chip is bonded to the adapter with epoxy resin. The adapter includes a mounting base and a housing. The housing is fitted over the mounting base, and a heat sink space is formed between the housing and the mounting base. The sensor chip and the wires are both disposed within the heat sink space. The sensor chip is connected to the mounting base, and the wires are wound around the sensor chip and the mounting base. One end of the wire is connected to the sensor chip, and the other end extends from the housing. The sensor chip includes an insulating substrate, electrodes disposed on the insulating substrate, and a ruthenium oxide-based thick film sensitive layer covering the electrodes and connected to the insulating substrate. The ruthenium oxide-based thick film sensitive layer employs a composite system of ruthenium oxide particles and a glass powder matrix. The resistance-temperature characteristics of the temperature sensor are optimized by adjusting the ratio of ruthenium oxide particles to the glass powder matrix. The ruthenium oxide particles are dispersed in the glass matrix to form a continuous conductive grid, which constitutes the ruthenium oxide-based thick film sensitive layer. The sensor chip's packaging structure employs a double-layer heterogeneous interface connection.

[0009] As a further technical limitation, the mounting base adopts a fixed column, and end flanges are respectively provided at both ends of the fixed column, forming a heat sink space between the outer shell, the fixed column and the two end flanges; the fixed column is provided with a chip mounting area for placing the sensor chip.

[0010] As a further technical limitation, the electrode is connected to the aviation pin via a wire, and the wire is wound around the surface of the adapter to form an integrated heat sink; the wire and the electrode are connected by electronic spot welding technology to form an alloy solder joint at the connection point; the wire is fixed with varnish, and the thickness of the varnish coating on the surface of the adapter is less than 0.05 mm.

[0011] It should be noted that the conductor can be enameled copper wire.

[0012] As a further technical limitation, the electronic spot welding technology adopts a dual-pulse mode including a first pulse and a second pulse. The current of the first pulse is 1000~1200 A and the pulse width is 3 ms; the current of the second pulse is 800~1000 A and the pulse width is 5 ms; the pressure of the electrode is 2 N; and the diameter of the alloy weld spot is 150 μm.

[0013] As a further technical limitation, the electrode is a patch resistor electrode made of palladium-silver paste. By optimizing the composition and sintering process of the palladium-silver paste, ohmic contact characteristics with the ruthenium oxide-based thick film sensitive layer are obtained. The design of the electrode takes into account both minimizing contact resistance and uniformizing electric field distribution. The electrode width on the resistive side is 1.5mm to 2mm, and the electrode width on the back side is greater than 2mm.

[0014] As a further technical limitation, the composite system of ruthenium oxide particles and glass powder matrix adopts 10% to 40% ruthenium oxide particles and 45% to 70% glass powder matrix.

[0015] As a further technical limitation, the dual-layer heterogeneous interface used in the packaging structure includes an epoxy resin bonding structure between the sensor chip and the adapter, and an indium foil connection structure between the adapter and the external low-temperature cold plate.

[0016] Furthermore, the adapter is a gold-plated metal adapter made of oxygen-free copper; the thickness of the indium foil is set to 0.05mm~0.2mm to fill the microscopic interface gap between the gold-plated metal adapter and the low-temperature cold plate.

[0017] According to some embodiments, a second aspect of the present invention provides a method for fabricating a ruthenium oxide thick-film resistance temperature sensor, used to fabricate the ruthenium oxide thick-film resistance temperature sensor provided in the first aspect, employing the following technical solution: A method for fabricating a ruthenium oxide thick-film resistance temperature sensor includes fabricating a sensor chip and sequentially packaging and assembling the fabricated sensor chip; wherein, The fabrication process of the sensor chip includes: Ruthenium oxide particles were mixed with a glass powder matrix to prepare a ruthenium oxide-based thick film sensitive layer slurry; The prepared ruthenium oxide-based thick film sensitive layer paste was coated onto an insulating substrate using a screen printing process. Electrodes were fabricated on both sides of a ruthenium oxide-based thick film sensitive layer on an insulating substrate using palladium-silver paste; A segmented sintering process was performed on an insulating substrate with electrodes and a ruthenium oxide-based thick film sensitive layer to obtain a ruthenium oxide thick film conductive network structure. The obtained ruthenium oxide thick film conductive network structure was subjected to liquid nitrogen thermal shock treatment to release internal stress, resulting in a ruthenium oxide thick film resistance temperature sensor chip. In the process of packaging the prepared sensor chip, the surfaces of the sensor chip and the adapter are cleaned, and the resistive side of the sensor chip is attached to the surface of the adapter. The wires are soldered to the electrode surface of the sensor chip using an electronic spot welding machine. The wires are wrapped around the surface of the adapter and then fixed with varnish. The other end of the wires is soldered to the aviation pin using tin-lead soldering to complete the packaging of the sensor chip. After the prepared sensor chip is packaged, the sensor needs to be assembled. The specific process is as follows: the sensor chip is fixed on the mounting base to form a sensor chip assembly; wires are wound around the outside of the formed sensor chip assembly; and a housing is placed over the sensor chip assembly and wires; one end of the wire is connected to the sensor chip, and the other end extends out of the housing.

[0018] As a further technical limitation, the segmented sintering process involves holding at 200-400°C to remove organic components; pre-sintering at 400-700°C to form a preliminary framework; and final sintering at 700-900°C for 10-30 minutes to form a dense ruthenium oxide thick film conductive network structure.

[0019] As a further technical limitation, the liquid nitrogen thermal shock treatment is carried out using automated equipment, which includes a linear stepper motor and a liquid nitrogen Dewar to control the thermal shock process; wherein the number of thermal cycles is 10-20 or 200, and the immersion time in liquid nitrogen each time is 60-120 seconds.

[0020] As a further technical limitation, the mass ratio of ruthenium oxide particles to glass powder matrix is ​​(10%–40%):(45%–70%); the prepared ruthenium oxide-based thick film sensitive layer slurry also includes at least one oxide modifier selected from manganese oxide, titanium oxide, and copper oxide.

[0021] As a further technical limitation, an adhesive material is used to fix the sensor chip onto the mounting base to obtain an adhesive assembly; the obtained adhesive assembly is subjected to thermal shock treatment to obtain a sensor chip assembly.

[0022] Furthermore, the thermal shock treatment performed on the obtained adhesive component includes multiple consecutive thermal shocks, each thermal shock including a low temperature holding stage and a room temperature recovery stage; in the low temperature holding stage, the adhesive component is placed in a cooling medium to cool for a first set time; in the room temperature recovery stage, the adhesive component after the low temperature holding stage is restored to room temperature and held for a second set time.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention constructs a ruthenium oxide-glass powder composite thick film material system, enabling the temperature sensor to possess highly stable resistance-temperature response characteristics in the ultra-low temperature range of 10 mK to 45K. By optimizing the size of the resistive electrode and printing larger electrodes on the back side of the substrate to connect the wires, the resistive surface is not affected by the wire size and can achieve a high fit with the adapter, reducing the interface thermal resistance. The composite connection structure of gold-plated metal adapter and indium foil bonding successfully solves the adapter heat conduction problem in ultra-low temperature systems. In the fabrication process of the temperature sensor, a rapid annealing furnace segmented sintering process is used, supplemented by the synergistic effect of liquid nitrogen thermal shock post-treatment and low-stress packaging structure.

[0024] This invention bonds the resistive surface of the sensor chip to the surface of the adapter through an ultra-thin epoxy resin layer to reduce interfacial thermal resistance. The solder joints are micro-alloyed solder joints formed by electronic spot welding technology between the wires and the palladium-silver electrodes to improve connection reliability. The wires are wound around the surface of the copper adapter and fixed with varnish to form an integrated heat sink to suppress parasitic heat leakage. During the packaging process, the precise coating and curing of epoxy resin, electronic spot welding parameters, and heat sink fabrication effectively solve the problems of large thermal hysteresis, easy solder joint failure, and severe heat leakage of wires in traditional packaging, significantly improving the temperature measurement accuracy, response speed, and long-term stability of the ultra-low temperature sensor.

[0025] This invention provides a heat sink space between the adapter mounting base and the housing. The sensor chip and wires are both placed in this heat sink space to form a heat sink structure. Before the wires pass through the housing, they are wound several times in the heat sink space to ensure full thermal contact between the wires and the adapter. The heat conducted along the wires is first transferred to the adapter and then transferred to the measured environment through the adapter. This reduces the impact of wire heat transfer on measurement accuracy, significantly improves thermal response performance, and the overall structure is compact, making it suitable for space-constrained applications. Attached Figure Description

[0026] The accompanying drawings, which form part of this embodiment, are used to provide a further understanding of this embodiment. The illustrative embodiments and their descriptions are used to explain this embodiment and do not constitute an improper limitation of this embodiment.

[0027] Figure 1 This is a schematic diagram of the resistive electrode structure of the ruthenium oxide thick film temperature sensor in Embodiment 1 of the present invention; wherein, Figure 1 (a) in the diagram is a top view of the structure. Figure 1 (b) in the diagram is a front view of the structure. Figure 1 (c) in the diagram is a schematic diagram of the overall structure; Figure 2 This is a schematic diagram of the micro-conductive network structure of the sensitive resistor layer in Embodiment 1 of the present invention; Figure 3This is a schematic diagram of a ruthenium oxide thick film temperature sensor according to Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the assembly structure of the ruthenium oxide thick film temperature sensor with housing in Embodiment 1 of the present invention; Figure 5 This is an overall schematic diagram of the ruthenium oxide thick film temperature sensor in Embodiment 1 of the present invention; Figure 6 This is a schematic diagram of the mounting base in Embodiment 1 of the present invention; Figure 7 This is an exploded structural diagram of the assembly mold in Embodiment 1 of the present invention; Figure 8 This is a schematic diagram of the internal structure of a ruthenium oxide thick film temperature sensor according to Embodiment 1 of the present invention; Figure 9 This is a schematic diagram comparing the temperature rise and fall (RT) curves of a traditional packaged sensor in the 3.2 K-45 K temperature range. Figure 10 This is a schematic diagram comparing the temperature rise and fall (RT) curves of the ruthenium oxide thick film temperature sensor in Embodiment 2 of the present invention in the temperature range of 3.2 K-45 K; Figure 11 This is a schematic diagram of the RT curve of the ruthenium oxide thick film temperature sensor in the second embodiment of the present invention in a wide temperature range of 10 mK-45 K; Figure 12 This is a graph showing the temperature rise and fall (RT) curves of the blood vessel experiment in Embodiment 2 of the present invention. Figure 13 This is a temperature control curve diagram of the blood vessel experiment in Embodiment 2 of the present invention; The components are as follows: 1. Ruthenium oxide sensitive resistor layer; 2. Electrode; 3. Ceramic substrate; 4. Ruthenium oxide particles; 5. Adapter; 6. Sensor chip; 7. Wire; 8. Solder joint; 9. Epoxy resin; 10. Varnish; 11. Aviation pin; 12. Housing; 13. Mounting base; 14. Base; 15. Cover plate; 16. Fixing post; 17. Chip mounting area; 18. End flange. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] In this invention, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any component or element in this invention. They should not be construed as limiting the invention.

[0032] In this invention, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0033] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0034] Example 1 Embodiment 1 of the present invention introduces a ruthenium oxide thick film resistance temperature sensor.

[0035] To achieve accurate measurement of mK-level low temperatures and minimize sensor size, this embodiment proposes a ruthenium oxide thick-film resistance temperature sensor to address issues such as large adapter size, poor thermal response, and unstable assembly process in existing technologies.

[0036] Below, this embodiment combines Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 and Figure 8 This section provides a detailed description of the ruthenium oxide thick-film resistance temperature sensor proposed in this embodiment.

[0037] A ruthenium oxide thick-film resistance temperature sensor includes a sensor chip 6, an adapter 5, and a wire 7. The resistive surface of the sensor chip 6 is bonded to the adapter 5 with epoxy resin 9. The adapter 5 includes a mounting base 13 and a housing 12. The housing 12 is fitted outside the mounting base 13, and a heat sink space is formed between the housing 12 and the mounting base 13. The sensor chip 6 and the wire 7 are both disposed in the heat sink space, and the sensor chip 6 is connected to the mounting base 13. The wire 7 is wound around the sensor chip 6 and the mounting base 13. One end of the wire 7 is connected to the sensor chip 6, and the other end extends out of the housing 12.

[0038] In this embodiment, the outer shell 12 is connected to the adapter 5 by threads to reduce the impact of heat radiation on the performance of the bare die; both the adapter 5 and the outer shell 12 are made of high-purity oxygen-free copper (TUO) and the surface is gold-plated, with the gold plating thickness preferably being 2~10 μm.

[0039] It should be noted that oxygen-free copper retains high thermal conductivity even at ultra-low temperatures, ensuring a high degree of temperature consistency between the bare die and the measured location. The main function of the gold plating layer is to prevent copper oxidation in air and ensure good thermal conductivity and surface uniformity at ultra-low temperatures. Furthermore, the gold plating layer has high reflectivity, effectively reducing the heating effect of thermal radiation on the sensor.

[0040] In this embodiment, the bottom surface of the adapter 5 is designed as a smooth plane with a through hole in the middle, which is used to tightly install it onto the cold plate to be tested by bolts, thereby fixing the ultra-low temperature sensor.

[0041] In this embodiment, the sensor chip 6 is a ruthenium oxide-based thick-film resistor die, the electrode 2 is a palladium-silver electrode, and the substrate is 96%–99% alumina ceramic. Both the ruthenium oxide resistor and the palladium-silver electrode are fabricated by screen printing followed by high-temperature sintering. The ruthenium oxide resistor paste contains ruthenium-based oxide nanoparticles, borosilicate glass powder, and an organic carrier containing various organic solvents. The palladium-silver electrode is formed by sintering the palladium-silver paste.

[0042] In this embodiment, the resistive side (i.e. the side with the resistive pattern) of the sensor chip 6 is bonded to the adapter 5 with epoxy resin 9 to avoid the influence of thermal resistance of the alumina substrate; the palladium-silver electrode has a structure that surrounds the ruthenium oxide substrate, extending from the front to the side and back, which facilitates soldering.

[0043] Epoxy resin 9 is key to performance optimization, and a low-thermal-stress, low-temperature-curing epoxy resin is selected. Through precise processing, its final thickness is controlled within the range of 5~15 μm, thereby minimizing interfacial thermal resistance while ensuring bond strength.

[0044] It should be noted that the thickness is controlled within the range of 5~15 μm in this embodiment based on the following considerations: if it is too thick, it will increase the thermal resistance of the epoxy resin itself, increase thermal hysteresis, and easily lead to uneven epoxy resin layer, increasing the risk of deformation; if it is too thin, the insulation of the epoxy resin layer will be reduced, and it may even lead to short circuit, affecting the normal testing of the sensor.

[0045] In this embodiment, the process of precision coating and curing of epoxy resin includes: accurately weighing the epoxy resin main agent and catalyst at a mass ratio of 100:3.5; placing the mixed epoxy resin in a vacuum degassing mixer and stirring at a speed of 800~1200 r / min and a vacuum degree of 100 Pa for 5~10 min until no visible bubbles are visible in the mixture; using a precision dispensing needle or scraper, taking a small amount of the degassed epoxy resin and uniformly coating a thin layer on the resistive surface of the sensor chip 6; subsequently, applying a constant force with a fixing clamp and placing the sensor chip 6 in the predetermined position of the adapter 5. The entire assembly is placed in a vacuum drying oven and cured at 65°C for 2 hours; after curing, the thickness of the epoxy resin 9 is measured to be 5~15 μm using a white light interferometer; this precision process ensures the ultra-thin and uniform adhesive layer.

[0046] In this embodiment, one end of the wire 7 is connected to the electrode of the sensor chip 6, and the other end is connected to the aviation pin 11, facilitating quick insertion and removal testing. The conductor diameter of the wire 7 is 0.1-0.3 mm, and it is coated with polyimide insulating varnish.

[0047] In this embodiment, solder joint 8 is an alloy solder joint formed by partially melting the wire 7 and the palladium-silver electrode using an electronic spot welding machine. This solder joint replaces the traditional manual indium solder joint, which is prone to falling off, and has the advantages of high strength, low contact resistance, and good consistency. The specific process is as follows: using an electronic spot welding machine equipped with a micro-alignment system, the insulating varnish of about 2 mm at the end of the wire 7 is first removed with a blade, and the exposed copper wire end is aligned with the palladium-silver electrode of the sensor chip 6. The spot welding parameters are set as follows: the first pulse current is 1000~1200 A with a pulse width of 3 ms; the second pulse current is 800~1000 A with a pulse width of 5 ms; the electrode pressure is 2 N; after triggering the welding, a silver-copper alloy solder joint 8 with a diameter of about 150 μm is formed. These process parameters can ensure sufficient fusion without damaging the fragile alumina substrate.

[0048] In this embodiment, after the solder joint 8 is fabricated, the wire 7 is tightly wound 5 to 10 turns around the cylindrical side of the adapter 5. Subsequently, a layer of GE Varnish varnish 10 is applied and cured to firmly fix the wire to the surface of the adapter 5, forming an efficient wound heat sink; this structure utilizes the high thermal conductivity of copper to provide an excellent thermal anchor point for the wire.

[0049] In this embodiment, the diameter of the aviation pin 11 is 0.4~0.8 mm, the surface is gold-plated, and it is connected to the other end of the wire 7 by soldering and fixed to the insulator of the housing 12 to realize the external electrical connection of the device.

[0050] The design of the aviation pin 11 enables rapid connection and testing of sensors, while avoiding the inefficiency and unreliability problems caused by direct soldering of wires to wires.

[0051] It should be noted that the sensor chip 6 in this embodiment uses a ruthenium oxide resistor die, which serves as a temperature sensing element and has an electrode structure for electrical connection; the adapter 5 includes a mounting base 13 and a housing 12, which are made of a high thermal conductivity metal material to support and protect the ruthenium oxide resistor die; the resistor die is bonded to the mounting base 13, and an adhesive layer is disposed between the ruthenium oxide resistor die and the mounting base 13 to achieve a fixed connection and heat conduction between the two; the wire 7 is electrically connected to the electrodes of the ruthenium oxide resistor die for signal output.

[0052] In this embodiment, a heat sink space is provided between the mounting base 13 of the adapter 5 and the housing 12. The sensor chip 6 and the wire 7 are both placed in the heat sink space to form a heat sink structure. Before the wire 7 passes out of the housing 12, it is first wound several times in the heat sink space to make full thermal contact between the wire 7 and the adapter 5. The heat conducted along the wire 7 is first transferred to the adapter 5, and then transferred to the measured environment through the adapter 5. This reduces the impact of wire heat transfer on measurement accuracy, significantly improves thermal response performance, and the overall structure is compact, making it suitable for space-constrained application scenarios.

[0053] The sensor chip 6 is the core temperature sensing element of the sensor proposed in this embodiment. Its structure and size directly affect the sensitivity and response speed of the sensor. The size of the sensor chip 6 is axb, where a is the length, which is 3~10mm and b is the width, which is 5~15mm. The determination of this size range takes into account the following factors: (1) If the size is too small, the resistance value will be too low, which will affect the measurement sensitivity; (2) If the size is too large, the heat capacity will be increased, the thermal response speed will be reduced, and the overall volume of the sensor will be increased; (3) It is compatible with the adapter installation area.

[0054] The specific dimensions of sensor chip 6 can be determined according to actual application requirements. The most preferred dimensions are a length of 5mm and a width of 7mm. This size achieves a good balance between sensitivity and response speed, while also facilitating assembly.

[0055] The sensor chip 6 includes a ceramic substrate 3, on which a ruthenium oxide sensitive resistor layer 1 and an electrode 2 are disposed. The electrode 2 is electrically connected to the ruthenium oxide sensitive resistor layer 1. The electrode 2 is formed on the surface of the sensor chip 6 by processes such as screen printing. The ruthenium oxide sensitive resistor layer 1 is disposed on a first side of the sensor chip 6. One end of the electrode 2 is electrically connected to the ruthenium oxide resistive region, and the other end of the electrode 2 extends to a second side of the sensor chip 6. The first side and the second side are two opposing sides. The first side faces the mounting base 13 and is bonded to the mounting base 13. Electrical signal connection is achieved by setting the electrode 2 extending to the second side. This connection method can achieve better heat conduction, thereby reducing thermal resistance and improving thermal response speed.

[0056] In this embodiment, the electrode 2 is a palladium-silver electrode, and the size of the ruthenium oxide sensitive resistor layer 1 is 4mm×4mm; the size of the back electrode needs to match the ruthenium oxide resistor area, while also considering the contact area with the mounting base 13; therefore, the size of the back electrode is limited to 1.8mm×4mm.

[0057] The adapter 5 consists of two parts: a mounting base 13 and a housing 12. The design of the adapter 5 directly affects the size, thermal response performance and ease of installation of the sensor. The mounting base 13 includes a fixing post 16, with end flanges 18 at both ends of the fixing post 16. The housing 12 is fitted over the mounting base 13, and a heat sink space is formed between the housing 12, the fixing post 16 and the two end flanges 18. The end flange 18 has a larger end face size than the fixed post 16. Both end flanges 18 are coaxially arranged with the fixed post 16, and the end face size of one end flange 18 is smaller than that of the other. The end face size of the smaller end flange 18 matches the inner diameter of the housing 12, while the end face size of the larger end flange 18 matches the outer diameter of the housing 12. When the housing 12 is fitted onto the mounting base 13, the inner surface of the housing 12 contacts the outer surface of the end flange 18 with the smaller end face size. Furthermore, one end face of the outer shell 12 is flush with the first end face of the end flange 18 with the smaller end face size, and the other end face of the outer shell 12 is in contact with the second end face of the end flange 18 with the larger end face size; thus, the inner surface of the outer shell 12, the outer surface of the fixing column 16, and the opposing surfaces of the two end flanges 18 form a heat sink space, wherein the second end face of the end flange 18 with the smaller end face size and the second end face of the end flange 18 with the larger end face size are two close end faces, which can also be referred to as two opposing planes, and the other end face of the end flange 18 is the first end face.

[0058] The two opposite planes of the two end flanges 18 are parallel. By setting these two end flanges 18, the contact area when the wire is wound is increased, and the two sides of the wire can be fixed.

[0059] Preferably, the distance between the two planes of the fixing post 16 is 5.2mm, and the size of the chip mounting area 17 is 5.44mm×9mm, which is suitable for a preferred 5mm×7mm resistor die.

[0060] A chip mounting area 17 is provided on the fixing post 16; the sensor chip 6 is fixed at the chip mounting area 17, forming a sensor chip assembly with the mounting base 13; after one end of the wire 7 is electrically connected to the electrode 2 of the sensor chip 6, it is wound around the outer surface of the sensor chip assembly a set number of times and then extends out from the outer shell 12, wherein the wire wound around the outer surface of the sensor chip assembly is in the heat sink space.

[0061] In this embodiment, the outer shell 12 is a sleeve-shaped structure, which is sleeved on the outside of the mounting base 13, and the outer shell 12 and the mounting base 13 are connected in a detachable manner, such as threaded connection, bolt connection, snap-fit ​​connection, flange connection, etc.

[0062] In one or more embodiments, the housing 12 is threadedly connected to the mounting base 13. The housing 12 has an outer diameter of 10mm and an inner diameter of 9mm, and is provided with an M8 internal thread for threaded connection with the mounting base 13. Threaded connections have the advantages of simple structure, reliable connection, and ease of assembly and disassembly. It should be noted that the adapter 5 is also provided with a mounting hole, which is used to fix the sensor to the part under test. The mounting hole can be located at the bottom of the mounting base 13; the mounting hole can be a through hole or a threaded hole.

[0063] As one or more embodiments, a mounting hole is provided on one of the end flanges 18, and one end face of the end flange 18 is exposed outside the housing 12. The mounting hole is a through hole with a diameter of 3.2 mm for threaded connection with an M3 bolt. The mounting hole is eccentrically set on the end flange 18. The eccentric design can maximize the mounting area of ​​the bare chip under the premise of compact size.

[0064] In this embodiment, the adapter 5 is cylindrical or polygonal in shape. The dimensions of the adapter 5 need to be balanced between compactness and functionality, with the diameter or diagonal dimension generally controlled between 8-15 mm and the height between 12-25 mm. The design of this size range takes into account the following factors: (1) sufficient space is needed to accommodate the heat sink structure formed by the resistor die and wires; (2) the overall size should be as compact as possible to adapt to the space-constrained low-temperature experimental device; (3) the position of the mounting hole needs to be reserved.

[0065] As one or more implementations, the adapter 5 is cylindrical in shape, with a diameter of 10 mm and a height of 16 mm, achieving a good balance between compactness and functionality. The chip mounting area 17 on the mounting base 13 is adapted to the sensor chip 6. The width of the heat sink space is generally 0.5-3 mm, which ensures smooth winding of the wires without excessively increasing the sensor size.

[0066] The mounting base 13 and the housing 12 are made of high thermal conductivity metals such as oxygen-free copper, high-purity copper, copper alloys, or aluminum and its alloys. A metal plating layer can be applied to the surface to reduce heat radiation and prevent oxidation. The characteristics of different materials are as follows: oxygen-free copper has excellent thermal conductivity and is a commonly used material in low-temperature applications; high-purity copper also has excellent thermal conductivity; copper alloys can improve mechanical strength while maintaining good thermal conductivity; aluminum alloys are lightweight and suitable for weight-sensitive applications. In this embodiment of the invention, oxygen-free copper is preferably used as the adapter material, with a gold-plated surface to reduce heat radiation and prevent oxidation.

[0067] This embodiment also provides a wire exit hole at the connection between the outer casing 12 and the mounting base 13, through which the wire extends. The wire exit hole provides guidance and protection for the wire.

[0068] In some embodiments, the sensor chip 6 is bonded to the mounting base 13 using an adhesive material. This adhesive material is a mixture of epoxy resin and a catalyst, with a catalyst-to-epoxy resin mass ratio of 5-15:100. This ratio range is designed to account for the curing time and final performance of the epoxy resin: too little catalyst will result in incomplete curing and insufficient bond strength; too much catalyst will result in excessively rapid curing, insufficient operating time, and potentially excessive internal stress. In this embodiment, catalyst No. 24 is preferably used, mixed with epoxy resin at a mass ratio of 100:8, which is in the middle of the preferred range.

[0069] To ensure a secure bond between the sensor chip 6 and the mounting base 13, the adhesive material used is an adhesive material that has undergone degassing treatment to remove air bubbles.

[0070] When the sensor chip 6 is bonded to the mounting base 13 with adhesive material, the adhesive material is first degassed to remove air bubbles. Then, the degassed adhesive material is applied between the sensor chip 6 and the mounting base 13 and cured to form an adhesive assembly. Next, the cured adhesive assembly is subjected to thermal shock treatment to eliminate assembly stress and obtain the sensor chip assembly. After that, the wire 7 is electrically connected to the electrode 2 of the sensor chip 6 in the sensor chip assembly, and part of the wire 7 is wound in the heat sink space to form a heat sink structure. Finally, the housing 12 is fitted over the sensor chip assembly and the wire 7, connected to the mounting base 13, and the other end of the wire 7 extends out of the housing 12 to complete the sensor encapsulation. The degassing process employs vacuum mixing for 1-10 minutes to effectively remove air bubbles while ensuring sufficient processing time. Insufficient mixing time leads to incomplete bubble removal, affecting bonding quality; excessive mixing time may cause the epoxy resin to begin curing, impacting subsequent operations. The preferred degassing conditions in this embodiment are: placing the mixed epoxy resin in a vacuum mixer, evacuating, and mixing for 3 minutes to effectively remove air bubbles while ensuring sufficient processing time.

[0071] In this embodiment, an assembly mold is used to fix the sensor chip 6 onto the mounting base 13 to form a sensor chip assembly. The assembly mold is an important auxiliary tool for sensor assembly proposed in this embodiment. It is used to accurately position the sensor chip 6 and the mounting base 13 during the bonding process and to control the thickness of the adhesive layer.

[0072] The assembly mold in this embodiment includes a base 14 and a cover plate 15; both the base 14 and the cover plate 15 are provided with grooves, and the grooves match the shape of the mounting base 13; after the base 14 and the cover plate 15 are closed, the two grooves together form a positioning cavity for accommodating the mounting base 13; ensuring that the mounting base 13 remains stable during the assembly process.

[0073] The base 14 and cover plate 15 of the assembly mold are both cubic structures with grooves. The groove depth is 5mm. Multiple grooves are provided on the base 14 and cover plate 15 respectively, and the grooves on the base 14 and cover plate 15 are set one-to-one. This can support the bonding and assembly of multiple mounting seats 13 and sensor chips 6 at the same time, thereby improving production efficiency.

[0074] In addition, a counterweight is provided on the cover plate 15. By applying a counterweight to the cover plate 15, the thickness of the adhesive material can be controlled and short circuits of the electrodes can be prevented. The weight of the counterweight needs to be adjusted according to factors such as the viscosity of the adhesive material and the size of the bare die. If the counterweight is too light, the adhesive layer will be too thick, increasing thermal resistance and reducing the thermal response speed; if the counterweight is too heavy, too much adhesive material may be extruded, or even cause a short circuit of the electrodes. By reasonably adjusting the weight of the counterweight, the thickness of the adhesive layer can be ensured to be uniform and moderate, neither too thick nor too thin, thus ensuring good thermal conductivity and electrical insulation performance.

[0075] When bonding and fixing the sensor chip 6 and the mounting base 13 using the assembly mold, the mounting base 13 is placed in the groove of the assembly mold base 14, with the chip mounting area 17 on the mounting base 13 facing the cover plate 15. The degassed adhesive material is fully applied to the surface of the sensor chip 6, and then it is attached to the chip mounting area 17 of the mounting base 13. The cover plate 15 is then closed, and a counterweight is applied. The amount of adhesive material applied needs to be moderate; too much will cause extrusion and short circuits, while too little will result in weak adhesion. By adjusting the weight of the counterweight, the thickness of the adhesive layer can be controlled to prevent the adhesive material from being too thick or causing electrode short circuits.

[0076] The curing temperature is 50-80℃, and the curing time is 1-4 hours. The combination of curing temperature and time affects the curing quality and efficiency: too low a temperature will lead to incomplete curing; too high a temperature may cause a decrease in the performance of the epoxy resin. In this embodiment, it is preferable to place the assembled mold in a vacuum oven, evacuate the vacuum, and set the temperature to 65℃ for 2 hours for curing. The vacuum environment can further remove any residual air bubbles and improve the bonding quality.

[0077] After curing, the components need to undergo thermal shock treatment to eliminate thermal stress that may have been generated during assembly. Thermal shock treatment involves multiple consecutive thermal shocks, each including a low-temperature holding phase and a room-temperature recovery phase. During the cryogenic holding phase, the bonded components are placed in liquid helium medium and cooled for a first set time; during the room temperature recovery phase, the components that were in the cryogenic holding phase are restored to room temperature and held for a second set time. The first set time is 2 minutes, and the second set time is 2 minutes. Liquid nitrogen is used as the cooling medium, and the number of thermal shock cycles is generally 10-30 times, which can effectively eliminate the thermal stress generated during the assembly process. After the thermal shock treatment, the stability of the component in the subsequent low-temperature use process is significantly improved, thereby improving the long-term stability of the sensor.

[0078] In some embodiments, conductor 7 is made of enameled copper wire or polyimide-insulated copper wire, with a wire diameter typically of 30-40 AWG. Excessive wire diameter increases thermal conductivity error, while excessively thin wire diameter increases resistance, affecting measurement accuracy. In this embodiment, 36 AWG polyimide-insulated copper wire is preferably used. Two conductors approximately 400mm long are twisted together; twisting reduces electromagnetic interference. A 2-3mm layer of insulation is scraped off the ends of the conductors to expose the copper core, which is then electrically connected to the electrodes of the resistor plate.

[0079] Electrical connections can be made using indium soldering or cryogenic soldering. Indium has good ductility at low temperatures and will not break due to thermal expansion and contraction, making it an ideal soldering material for cryogenic sensors. This embodiment uses indium soldering, where indium wire is used to solder the conductor to the electrode of the resistor chip.

[0080] After soldering, the remaining wires are wrapped around the outer ring of the sensor chip assembly 5-20 times to form a heat sink structure, and then secured with insulating tape (such as polyimide tape). In this embodiment, 10-15 turns are preferably wrapped to achieve sufficient heat sink effect within a limited space.

[0081] Finally, attach the housing to the sensor chip assembly and wires, and connect the housing to the mounting base 13, extending one end of the wires out of the housing to complete the final encapsulation of the sensor. Care must be taken not to damage the wires during housing installation. After encapsulation, the sensor becomes a unified whole, possessing good mechanical strength and environmental adaptability.

[0082] The temperature sensor in this embodiment exhibits monotonic resistance-temperature characteristics within the temperature range of 10 mK to 45 K. By controlling the microstructure, interface characteristics, and special post-processing of the ruthenium oxide thick film, the carrier migration capability at the extremely low temperature end is significantly enhanced, achieving high-sensitivity temperature detection in a wide temperature range of 10 mK to 45 K. Furthermore, higher short-term and long-term stability is achieved through structural optimization and stress relief processes.

[0083] As one or more implementation methods, the ruthenium oxide-based thick film material in this embodiment is based on a composite system of RuO2 and glass powder. The optimized design of the resistance-temperature characteristics is achieved by adjusting the ratio of the two components. During sintering, the glass phase forms a glass network structure, and RuO2 particles are dispersed in the glass matrix to form a structure resembling... Figure 2 The conductive network shown maintains a stable carrier transport channel at extremely low temperatures, avoiding measurement failure caused by carrier freezing. By changing the mass ratio of RuO2, glass powder, and modifier (preferred range 10%–40% RuO2 powder, 45%–70% glass powder), the resistance value and temperature coefficient of the sensor can be effectively controlled, thereby optimizing the resistance-temperature characteristic curve of the sensor.

[0084] It should be noted that the thickness and microstructure of the ruthenium oxide thick film are crucial to the cryogenic sensing performance; an excessively thick film increases heat capacity, leading to a decrease in response speed; an excessively thin film will exhibit pinhole defects, affecting the repeatability and reliability of measurements. In this embodiment, the ruthenium oxide thick film thickness is 10–40 μm, more preferably 10–20 μm; within this thickness range, the thick film possesses sufficient mechanical strength while maintaining low heat capacity and rapid thermal response characteristics. The microstructure of the thick film should have uniformly distributed nanoscale grains and submicron-level pores, with a grain size preferably 50–500 nm, to ensure good carrier transport and appropriate heat exchange efficiency; this optimized microstructure effectively suppresses carrier scattering noise and is the structural basis for achieving excellent short-term stability.

[0085] It should be noted that the ruthenium oxide-based thick-film sensitive layer uses a conductive network structure formed by combining RuO2 and glass powder. In other embodiments, a small amount of oxide modifier can be introduced into this system to regulate the resistance-temperature characteristics. For example, transition metal oxides such as manganese oxide and titanium oxide, or oxides such as copper oxide, can be added to change the grain boundary barrier height and carrier concentration, thereby optimizing the sensor's response characteristics in the low-temperature region.

[0086] In this embodiment, the electrode 2 of the sensor chip 6 is fabricated using palladium-silver paste through a printing process. Compared with traditional precious metal electrodes such as gold and platinum, silver paste has advantages such as low cost, good conductivity, and strong adhesion to thick films. By optimizing the composition and sintering process of the palladium-silver paste, good ohmic contact performance with the ruthenium oxide thick film can be obtained. The electrode design takes into account both minimizing contact resistance and uniformizing electric field distribution. The electrode width on the resistive side is preferably 1.5-2 mm, and the electrode width on the back side is greater than 2 mm. This electrode design facilitates the contact of the resistive side with the adapter surface and reduces the temperature hysteresis effect. At the same time, there is sufficient space on the back side for easy soldering and assembly.

[0087] It should be noted that the electrode structure in this embodiment uses a palladium-silver paste electrode. In other embodiments, the electrode structure may also use interdigitated electrodes, parallel strip electrodes, or ring electrode structures to adapt to different current distribution requirements. In addition to silver-palladium paste, conductive pastes such as gold paste, silver paste, or platinum paste can also be used to form thick-film electrodes.

[0088] In this embodiment, the resistive surface of the sensor chip is bonded to the adapter with epoxy resin. The epoxy resin adhesive layer has good bonding strength and ultra-low temperature adaptability, which can effectively fix the sensor chip and reduce the temperature hysteresis effect during temperature cycling. The epoxy resin must have a low coefficient of thermal expansion and flexibility in ultra-low temperature environments to accommodate the thermal expansion differences in the temperature range of 10 mK to 45 K. The thickness of the epoxy resin adhesive layer is preferably 10-30 μm. Too thick a layer will increase thermal resistance and reduce response speed, while too thin a layer will affect the bonding strength or cause a short circuit. The adapter in this embodiment is made of metal material and has a gold-plated surface, which has good conductivity, oxidation resistance, and thermal expansion matching.

[0089] In other embodiments, mechanical pressing structures or other low-temperature adhesive materials can be used for encapsulation and connection. For example, varnish can be used to fix the sensor chip to a metal base, or a flexible pressing structure can be used to achieve detachable installation.

[0090] To obtain a uniform, dense thick film with appropriate pore structure, this embodiment employs a printing process to deposit a functional paste containing ruthenium oxide powder, an organic binder, and a solvent onto an insulating substrate, followed by high-temperature sintering. A segmented sintering procedure using a rapid annealing furnace is employed: first, holding at 200–400°C to remove organic components; then, pre-sintering at 400–700°C to form a preliminary framework; and finally, final sintering at 700–900°C to obtain a dense conductive network. The preferred final sintering temperature is 800–900°C, with a holding time of 10–30 minutes.

[0091] To improve the long-term stability and thermal cycling reliability of the sensor, this embodiment performs liquid nitrogen thermal shock treatment on the sintered thick film; specifically, the sintered sensor is quickly immersed in liquid nitrogen and then quickly removed, and the thermal cycling treatment is repeated multiple times; the internal stress generated during the sintering process is released and the grain boundary structure is optimized, thereby improving the stability of the device under multiple temperature cycling conditions.

[0092] In this embodiment, the number of thermal shock cycles is 10 to 20, with each immersion time being 60 to 120 seconds. To test long-term stability, the number of thermal shock cycles in this embodiment is 200, with each immersion time being 60 to 120 seconds.

[0093] To ensure the measurement accuracy of the sensor in the target application environment, this embodiment uses a dilution refrigerator and a pulse tube refrigerator for system calibration of the sensor. The dilution refrigerator calibration covers a temperature range of 10 mK to 4.5 K, providing an intrinsic reference temperature point; the pulse tube refrigerator calibration covers a temperature range of 3.5 K to 45 K. By combining steady-state and dynamic methods to perform multi-point calibration within the temperature ranges of the two refrigerators and then fitting the data, a complete resistance-temperature characteristic curve of the sensor can be obtained throughout the entire operating temperature range (10 mK to 45 K).

[0094] This embodiment uses a multi-parameter fitting model (such as an exponential decay fitting model or a polynomial fitting) to describe the resistance-temperature relationship in order to obtain the best measurement accuracy and interpolation / extrapolation capability.

[0095] This embodiment provides a ruthenium oxide-based thick-film temperature sensor suitable for ultra-low temperature environments from 10 mK to 45 K. Its overall structure sequentially includes an insulating substrate, an electrode structure, a ruthenium oxide-based thick-film sensitive layer, and an encapsulation structure for electrical connection and mechanical fixation. The sensitive layer is composed of a continuous conductive network formed by RuO2 particles dispersed in a glass matrix. The material of the ruthenium oxide-based thick-film sensitive layer is defined as a composite system of RuO2 and glass powder, preferably ranging from 10% to 40% RuO2 powder and 45% to 70% glass powder. The chip size is 5 to 9 mm in length, 3 to 5 mm in width, and 10 to 40 μm in thickness, more preferably 10 to 20 μm. The electrode structure is defined as a patch electrode prepared using palladium-silver (Pd-Ag) paste. Preferably, the electrode width on the front side (resistive side) of the sensor is 1.5 to 2 mm to facilitate adapter bonding and reduce thermal hysteresis, while the electrode width on the back side (soldering side) is greater than 2 mm, and the solder joints are located on the back side to balance low contact resistance and soldering convenience.

[0096] This embodiment constructs a RuO2-glass powder composite thick film material system, enabling the sensor to possess highly stable resistance-temperature response characteristics in the ultra-low temperature range of 10 mK to 40 K. The microscopic mechanism lies in the fact that during sintering, the glass phase forms a stable insulating network framework, within which RuO2 particles are uniformly dispersed, constructing continuous conductive channels. This composite conductive network maintains efficient carrier transport even at extremely low temperatures, thus completely avoiding the "carrier freezing" phenomenon that easily occurs in traditional semiconductor temperature sensors. Furthermore, by precisely controlling the mass ratio of RuO2 to glass powder, this embodiment allows for flexible modulation of the sensor's fundamental resistance value and temperature coefficient of resistance (TCR), ensuring that the sensor not only maintains a monotonically stable response curve throughout the entire operating temperature range but also exhibits excellent temperature sensitivity at the extremely low temperature end.

[0097] This embodiment optimizes the size of the resistive electrode by printing a larger electrode on the back side of the substrate to connect the wires. This allows the resistive surface to be highly fitted to the adapter regardless of the wire size, reducing interface thermal resistance. The smaller resistive surface not only maintains a low thermal response time but also increases long-term measurement stability. It exhibits extremely low measurement noise and excellent repeatability in low-temperature environments, meeting the requirements for high-precision cryogenic temperature measurement, and has engineering advantages such as ease of manufacturing, assembly, and testing.

[0098] This embodiment employs a composite connection structure combining a gold-plated metal adapter and indium foil, successfully solving the adapter heat conduction problem in cryogenic systems. The gold plating on the adapter surface possesses oxidation resistance and thermal conductivity, ensuring efficient thermal contact. The indium foil's excellent adhesion and ductility at extremely low temperatures perfectly fill microscopic gaps at the interface and absorb mechanical stress generated by rapid temperature changes; while achieving high-fidelity thermal anchoring and stable electrical connection between the sensor and the cryogenic platform, it also offers convenient detachability.

[0099] This embodiment achieves high-sensitivity and high-stability temperature measurement in the ultra-low temperature range by optimizing the material ratio of the ruthenium oxide-glass powder composite system, using a segmented sintering process to form a stable conductive network, designing a double-layer heterogeneous interface encapsulation structure to reduce interface thermal resistance, and introducing liquid nitrogen thermal shock post-treatment to release internal stress.

[0100] Example 2 Embodiment 2 of the present invention introduces a method for fabricating a ruthenium oxide thick film resistance temperature sensor.

[0101] A method for fabricating a ruthenium oxide thick-film resistance temperature sensor, used to fabricate the ruthenium oxide thick-film resistance temperature sensor described in Example 1, includes the fabrication of a sensor chip and the sequential packaging and assembly of the fabricated sensor chip; wherein, The fabrication process of the sensor chip includes: Ruthenium oxide particles 4 were mixed with a glass powder matrix to prepare a ruthenium oxide-based thick film sensitive layer slurry; The prepared ruthenium oxide-based thick film sensitive layer paste was coated onto an insulating substrate using a screen printing process. Electrodes were fabricated on both sides of a ruthenium oxide-based thick film sensitive layer on an insulating substrate using palladium-silver paste; A segmented sintering process was performed on an insulating substrate with electrodes and a ruthenium oxide-based thick film sensitive layer to obtain a ruthenium oxide thick film conductive network structure. The obtained ruthenium oxide thick film conductive network structure was subjected to liquid nitrogen thermal shock treatment to release internal stress, resulting in a ruthenium oxide thick film resistance temperature sensor chip. In the process of packaging the prepared sensor chip, the surfaces of the sensor chip and the adapter are cleaned, and the resistive side of the sensor chip is attached to the surface of the adapter. The wires are soldered to the electrode surface of the sensor chip using an electronic spot welding machine. The wires are wrapped around the surface of the adapter and then fixed with varnish. The other end of the wires is soldered to the aviation pin using tin-lead soldering to complete the packaging of the sensor chip. After the prepared sensor chip is packaged, the sensor needs to be assembled. The specific process is as follows: the sensor chip is fixed on the mounting base to form a sensor chip assembly; wires are wound around the outside of the formed sensor chip assembly; and a housing is placed over the sensor chip assembly and wires; one end of the wire is connected to the sensor chip, and the other end extends out of the housing.

[0102] As one or more embodiments, the segmented sintering process involves holding at 200-400°C to remove organic components; pre-sintering at 400-700°C to form a preliminary framework; and final sintering at 700-900°C for 10-30 minutes to form a dense ruthenium oxide thick film conductive network structure.

[0103] As one or more implementation methods, the liquid nitrogen thermal shock treatment is carried out using automated equipment, which includes a linear stepper motor and a liquid nitrogen Dewar to control the thermal shock process; wherein the number of thermal cycles is 10 to 20 or 200, and the immersion time in liquid nitrogen each time is 60 to 120 seconds.

[0104] As one or more embodiments, the mass ratio of ruthenium oxide particles to glass powder matrix is ​​(10%–40%): (45%–70%); the prepared ruthenium oxide-based thick film sensitive layer slurry also includes at least one oxide modifier selected from manganese oxide, titanium oxide, and copper oxide.

[0105] As one or more embodiments, an adhesive material is used to fix the sensor chip onto a mounting base to obtain an adhesive assembly; the obtained adhesive assembly is subjected to thermal shock treatment to obtain a sensor chip assembly; the thermal shock treatment of the obtained adhesive assembly includes multiple consecutive thermal shocks, each thermal shock including a low temperature holding stage and a room temperature recovery stage; in the low temperature holding stage, the adhesive assembly is placed in a cooling medium to cool for a first set time; in the room temperature recovery stage, the adhesive assembly after the low temperature holding stage is restored to room temperature and held for a second set time.

[0106] As one or more embodiments, this embodiment prepares a ruthenium oxide-based sensitive layer paste by uniformly mixing RuO2 and glass powder at a preferred mass ratio of 2:5. The paste is then uniformly coated onto an alumina ceramic insulating substrate using screen printing. Electrodes are fabricated on both sides of the thick film using palladium-silver paste through a combination of printing and partial hand-coating processes. The overlap between the electrodes and resistors on the resistive side (front) is controlled to be at least 0.2 mm to ensure good ohmic contact and facilitate subsequent adapter bonding. The printed substrate is then placed in a rapid annealing furnace for segmented, precise sintering. The sintering process is as follows: holding at 250°C for 30 minutes to fully remove the organic binder, followed by pre-sintering at 450°C for 30 minutes to form a preliminary network framework, and finally, final sintering at 850°C for 20 minutes. This results in a thick-film conductive network structure with a thickness of approximately 15 μm, uniform grain size, and dense, coherent structure.

[0107] In this embodiment, the sensor chip is bonded to the surface of a gold-plated metal adapter using cryogenically low-temperature compatible epoxy resin, minimizing the adhesive layer thickness while ensuring insulation. After assembly, the sensor undergoes 15 rapid thermal shock cycles in liquid nitrogen to effectively eliminate residual internal stress generated during manufacturing and packaging. A system combining a dilution refrigerator and a pulse tube refrigerator is used to perform complete calibration of the sensor within both systems. The sensor prepared in this embodiment exhibits excellent and monotonic resistance-temperature sensitivity in the cryogenic region while maintaining extremely high short-term stability.

[0108] This embodiment innovatively employs a segmented sintering process using a rapid annealing furnace, supplemented by the synergistic effect of liquid nitrogen thermal shock post-treatment and a low-stress encapsulation structure. Compared to traditional chain sintering furnaces, segmented sintering in a rapid annealing furnace offers advantages such as rapid heating and cooling and precise temperature control. This not only facilitates efficient debugging and iteration of sintering curves but also promotes the formation of a uniform and stable conductive network within the material. Combined with post-treatment and encapsulation processes, this method effectively releases residual stress accumulated during thick film fabrication and heals microscopic defects, fundamentally improving the long-term stability of the device in extremely low-temperature environments.

[0109] To address the frequent heat treatments in cryogenic measurements, this embodiment designs an automated liquid nitrogen thermal shock post-processing system and an epoxy resin low-stress encapsulation structure. Controlled alternation of hot and cold temperatures releases internal material stress in advance. The automated thermal shock system employs a linear stepper motor and a liquid nitrogen Dewar, enabling the implementation of the target thermal shock process via microcontroller programming. This overcomes the problems of cumbersome manual operation and insufficient repeatability in traditional testing. The epoxy resin encapsulation effectively buffers the physical deformation caused by differences in the thermal expansion coefficients of different materials. The combination of these two systems significantly reduces thermal strain and performance drift caused by multiple temperature cycles, ensuring that the sensor maintains highly stable resistance-temperature response characteristics even after repeated cryogenic thermal cycles.

[0110] To verify the effectiveness of this embodiment, the cryogenic sensor using the packaging method of this embodiment was tested at low temperature, and a sensor using the traditional method (resistive surface far from the adapter + manual indium soldering + conventional thick epoxy resin bonding + no wire winding) was used as a control.

[0111] like Figure 9 and Figure 10 The thermal hysteresis test results show that the conventionally packaged sensor exhibits significant separation in its temperature rise and fall curves within the 3.2K-45K temperature range, indicating large thermal hysteresis. In contrast, the sensor packaged using this embodiment shows almost complete overlap in its temperature rise and fall curves, demonstrating the significant effect of the ultra-thin epoxy layer and optimized structure on improving thermal response.

[0112] The sensor in this embodiment was subjected to 200 liquid nitrogen thermal shocks and then tested in a dilution refrigerator. Figure 11 The reliability and low-temperature performance tests shown exhibit a smooth, continuous, and uninterrupted RT curve throughout the temperature drop from 45 K to 10 mK, indicating extremely reliable solder joint connections. Especially in the extremely low temperature range below 0.1 K, the resistance value still monotonically and steadily increases with decreasing temperature, without any curve distortion or decrease in sensitivity due to heat leakage from the conductors, fully demonstrating the effectiveness of the wound heat sink structure.

[0113] To verify the performance of the temperature sensor proposed in this embodiment, a comprehensive performance test was conducted on the temperature sensor proposed in this embodiment, including sensitivity and thermal response tests.

[0114] (1) Sensitivity test and thermal response performance test This embodiment proposes a temperature sensor suitable for low-temperature measurements in the mK to tens of K temperature range, with a measurement range of 10 mK to 45K. Within this temperature range, the sensor's resistance value exhibits a monotonic change with temperature, and an accurate temperature-resistance curve can be obtained through calibration. Thermal response time is an important indicator for evaluating the performance of a temperature sensor; poor thermal response results in poor overlap of the actual temperature-resistance curve. This invention effectively shortens the thermal response time through the following design: (1) the bare resistor sheet is directly in contact with the mounting base through the adhesive layer, resulting in a short heat conduction path; (2) the adapter uses a high thermal conductivity metal material, resulting in high heat conduction efficiency; (3) the wire heat sink structure reduces the impact of wire heat transfer on the measurement.

[0115] Figure 12 The figure shows the temperature rise and fall (RT) curves of the sensor proposed in this embodiment in the pulse tube experiment. It can be seen that the resistance value changes significantly within the test temperature range, and the sensitivity meets the measurement requirements. The overlap between the temperature rise and fall data is good, indicating that it can quickly track temperature changes and has good thermal response performance.

[0116] (2) Stability test The more stable a sensor is at a fixed temperature, the better its stability. Figure 13 The figure shows the temperature control curve of the sensor proposed in this embodiment in the pulse tube experiment. The test results show that the sensor can maintain a stable resistance at the temperature control point without significant drift, and the sensor performance is stable and reliable.

[0117] This embodiment effectively reduces the impact of wire heat transfer on measurement accuracy by setting up a heat sink space to form a heat sink structure, significantly improving thermal response performance; it uses assembly mold positioning and counterweight control to ensure uniform adhesive layer thickness, avoid short circuits, and improve product consistency; it eliminates assembly stress through thermal shock treatment to improve long-term stability; the overall structure is compact and suitable for space-constrained applications; the sensor is suitable for low-temperature measurements in the mK to tens of K temperature range, with a measurement range of 10 mK to 45K, and can be used in ultra-low temperature applications such as quantum computing, condensed matter physics experiments, or deep space exploration.

[0118] Example 3 Embodiment 3 of this invention introduces a full-temperature-range calibration method for a ruthenium oxide thick-film resistance temperature sensor.

[0119] A full-temperature-range calibration method for a ruthenium oxide thick-film resistance temperature sensor employs segmented equipment collaborative calibration. Specifically, a dilution refrigerator is used to cover the extremely low temperature range of 10 mK to 4.5 K, while a pulse tube refrigerator is used to cover the temperature range of 3.5 K to 45 K. Within these two calibration segments, multi-point data are acquired using a combination of steady-state and dynamic methods. A multi-parameter fitting model (preferably an exponential decay fitting model or a polynomial fitting model) is then used to construct a complete resistance-temperature (RT) characteristic curve, achieving high-precision temperature inversion over a wide temperature range.

[0120] For cryogenic environments, this embodiment features customized heat leakage suppression and mechanical packaging design. Regarding mechanical packaging and thermal coupling, the sensor chip is mounted on a custom-designed gold-plated oxygen-free copper thermal anchoring platform. This platform is tightly bonded to the mixing chamber cold plate of the dilution refrigerator via threaded mechanical connections to achieve extremely low interfacial thermal resistance and rapid thermal equilibrium. For multi-stage thermal anchoring at cryogenic temperatures, the temperature sensing lead uses 127 μm diameter phosphor bronze wire, leveraging its low thermal conductivity to significantly reduce heat leakage through the solid along the lead into the cryogenic region. To completely eliminate parasitic heat load, the lead undergoes multi-stage thermal anchoring treatment before reaching the sensor: sequentially at the 40 K cold plate, 4 K cold plate, 1 K distillation chamber cold plate, and mixing chamber cold plate of the refrigerator, the lead is firmly and evenly laid and fixed using cryogenically compatible varnish, ensuring that the lead temperature is gradually cooled to ambient temperature. In terms of measurement circuit configuration, a standard four-wire connection method is adopted to completely eliminate measurement errors caused by the resistance of long leads. Simultaneously, to avoid Joule heating interference from the sensor itself at extremely low temperatures affecting the true temperature measurement, the measurement excitation current is strictly controlled below 10 μA. In practical applications, two sensors are installed at different locations on the cold plate to provide temperature control feedback and a temperature cross-comparison standard. During the cooling test of the dilution refrigerator, the sensor responded rapidly. When the mixing chamber temperature stabilized at approximately 50 mK, the temperature reading deviation caused by the self-heating effect was successfully suppressed to within 0.1 mK. This scheme is highly suitable for precision temperature measurement systems with stringent requirements for long-term stability and extreme accuracy, such as those used in ultra-low temperature physics experiments and quantum computing.

[0121] For the ultra-wide cryogenic range of 10 mK to 45 K, this embodiment combines the advantages of multi-point calibration using both steady-state and dynamic methods, and introduces a preferred multi-parameter fitting model, enabling high-precision reconstruction of the sensor's complete resistance-temperature (RT) characteristic curve. This not only significantly eliminates systematic errors under the target temperature measurement environment, but also significantly enhances the reliability of interpolation and extrapolation of the calibration curve over a wide temperature range, providing a high-precision benchmark for cryogenic environments.

[0122] The detailed steps are the same as the working principle of the ruthenium oxide thick film resistance temperature sensor provided in Example 1, and will not be repeated here.

[0123] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0124] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0125] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A ruthenium oxide thick-film resistance temperature sensor, characterized in that, The device includes a sensor chip, an adapter, and wires. The resistive surface of the sensor chip is bonded to the adapter with epoxy resin. The adapter includes a mounting base and a housing. The housing is fitted over the mounting base, and a heat sink space is formed between the housing and the mounting base. The sensor chip and the wires are both disposed within the heat sink space. The sensor chip is connected to the mounting base, and the wires are wound around the sensor chip and the mounting base. One end of the wire is connected to the sensor chip, and the other end extends out of the housing. The sensor chip includes an insulating substrate, electrodes disposed on the insulating substrate, and a ruthenium oxide-based thick film sensitive layer covering the electrodes and connected to the insulating substrate. The ruthenium oxide-based thick film sensitive layer employs a composite system of ruthenium oxide particles and a glass powder matrix. The resistance-temperature characteristics of the temperature sensor are optimized by adjusting the ratio of ruthenium oxide particles to the glass powder matrix. The ruthenium oxide particles are dispersed in the glass matrix to form a continuous conductive grid, which constitutes the ruthenium oxide-based thick film sensitive layer. The sensor chip's packaging structure employs a double-layer heterogeneous interface connection.

2. The ruthenium oxide thick-film resistance temperature sensor as described in claim 1, characterized in that, The mounting base adopts a fixed column, and end flanges are respectively provided at both ends of the fixed column, forming a heat sink space between the outer shell, the fixed column and the two end flanges; the fixed column is provided with a chip mounting area for placing the sensor chip.

3. The ruthenium oxide thick-film resistance temperature sensor as described in claim 1, characterized in that, The electrode is connected to an aviation pin via a wire, which is wound around the surface of the adapter to form an integrated heat sink. The wire and the electrode are connected using electronic spot welding technology to form an alloy solder joint at the connection point. The wire is fixed with varnish, and the thickness of the varnish coating on the adapter surface is less than 0.05 mm. The electronic spot welding technology uses a dual-pulse mode including a first pulse and a second pulse. The current of the first pulse is 1000~1200 A and the pulse width is 3 ms. The current of the second pulse is 800~1000 A and the pulse width is 5 ms. The pressure of the electrode is 2 N. The diameter of the alloy solder joint is 150 μm.

4. A ruthenium oxide thick-film resistance temperature sensor as described in claim 1, characterized in that, The electrode is a patch resistor electrode made of palladium-silver paste. By optimizing the composition and sintering process of the palladium-silver paste, ohmic contact characteristics with the ruthenium oxide-based thick film sensitive layer are obtained. The design of the electrode takes into account both minimizing contact resistance and uniformizing electric field distribution. The electrode width on the resistive side is 1.5mm~2mm, and the electrode width on the back side is greater than 2mm.

5. A ruthenium oxide thick-film resistance temperature sensor as described in claim 1, characterized in that, The composite system of ruthenium oxide particles and glass powder matrix consists of 10%–40% ruthenium oxide particles and 45%–70% glass powder matrix.

6. A ruthenium oxide thick-film resistance temperature sensor as described in claim 1, characterized in that, The dual-layer heterogeneous interface used in the packaging structure includes an epoxy resin bonding structure between the sensor chip and the adapter, and an indium foil connection structure between the adapter and the external low-temperature cold plate. The adapter is a gold-plated metal adapter, and the gold-plated metal adapter is made of oxygen-free copper. The thickness of the indium foil is set to 0.05mm~0.2mm, and it is used to fill the microscopic interface gap between the gold-plated metal adapter and the low-temperature cold plate.

7. A method for fabricating a ruthenium oxide thick-film resistance temperature sensor, used to fabricate a ruthenium oxide thick-film resistance temperature sensor as described in any one of claims 1-6, characterized in that, This includes the fabrication of sensor chips and the sequential packaging and assembly of the fabricated sensor chips; among which, The fabrication process of the sensor chip includes: Ruthenium oxide particles were mixed with a glass powder matrix to prepare a ruthenium oxide-based thick film sensitive layer slurry; The prepared ruthenium oxide-based thick film sensitive layer paste was coated onto an insulating substrate using a screen printing process. Electrodes were fabricated on both sides of a ruthenium oxide-based thick film sensitive layer on an insulating substrate using palladium-silver paste; A segmented sintering process was performed on an insulating substrate with electrodes and a ruthenium oxide-based thick film sensitive layer to obtain a ruthenium oxide thick film conductive network structure. The obtained ruthenium oxide thick film conductive network structure was subjected to liquid nitrogen thermal shock treatment to release internal stress, resulting in a ruthenium oxide thick film resistance temperature sensor chip. In the process of packaging the prepared sensor chip, the surfaces of the sensor chip and the adapter are cleaned, and the resistive side of the sensor chip is attached to the surface of the adapter. The wires are soldered to the electrode surface of the sensor chip using an electronic spot welding machine. The wires are wrapped around the surface of the adapter and then fixed with varnish. The other end of the wires is soldered to the aviation pin using tin-lead soldering to complete the packaging of the sensor chip. After the prepared sensor chip is packaged, the sensor needs to be assembled. The specific process is as follows: the sensor chip is fixed on the mounting base to form a sensor chip assembly; wires are wound around the outside of the formed sensor chip assembly; and a housing is placed over the sensor chip assembly and wires; one end of the wire is connected to the sensor chip, and the other end extends out of the housing.

8. The method for fabricating a ruthenium oxide thick-film resistance temperature sensor as described in claim 7, characterized in that, The segmented sintering process involves holding the temperature at 200~400℃ to remove organic components. Pre-sintering is carried out at 400~700℃ to form a preliminary skeleton; final sintering is carried out at 700~900℃ and held for 10~30 minutes to form a dense ruthenium oxide thick film conductive network structure.

9. The method for fabricating a ruthenium oxide thick-film resistance temperature sensor as described in claim 7, characterized in that, The liquid nitrogen thermal shock treatment is carried out using automated equipment, which includes a linear stepper motor and a liquid nitrogen Dewar to control the thermal shock process. The number of thermal cycles is 10-20 or 200, and the immersion time in liquid nitrogen is 60-120 seconds each time. The mass ratio of ruthenium oxide particles to glass powder matrix is ​​(10%-40%):(45%-70%). The prepared ruthenium oxide-based thick film sensitive layer slurry also includes at least one oxide modifier selected from manganese oxide, titanium oxide, and copper oxide.

10. The method for fabricating a ruthenium oxide thick-film resistance temperature sensor as described in claim 7, characterized in that, A sensor chip is fixed to a mounting base using an adhesive material to obtain an adhesive assembly; the obtained adhesive assembly is subjected to thermal shock treatment to obtain a sensor chip assembly; the thermal shock treatment of the obtained adhesive assembly includes multiple consecutive thermal shocks, each thermal shock including a low temperature holding stage and a room temperature recovery stage; in the low temperature holding stage, the adhesive assembly is placed in a cooling medium to cool for a first set time; in the room temperature recovery stage, the adhesive assembly after the low temperature holding stage is restored to room temperature and held for a second set time.

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