Heating body with step type resistance temperature characteristic and preparation method thereof

Abstract

The invention discloses a heating body with a step type resistance temperature characteristic and a preparation method thereof, the heating body comprises a substrate and a resistance body, and the resistance body is connected with the substrate; the resistance change body comprises a thinning layer and a nitriding layer, the thinning layer is connected with the substrate and is thinner than the substrate, and the nitriding layer is formed on the surface of the thinning layer. According to the resistive body, step type mutation from low resistance to high resistance can be achieved through the thinning layer and the nitriding layer, an external sensor or a control circuit is not needed, the resistive body does not need to depend on the resistance-temperature characteristic of metal, and self-adjustment of the temperature can be achieved by depending on the response of the heating body after being powered on; and due to the heat concentration design of the resistive body, the base body can also be designed into an ultra-thin structure, the energy consumed by self temperature rise is less, and the jump response time is short.

Description

Technical Field

[0001] This application relates to the field of novel tobacco heating element technology, and in particular to a heating element with step resistance temperature characteristics and its preparation method. Background Technology

[0002] In the existing field of new tobacco products, products that use resistance heating to obtain aerosols are further divided into heated cigarette devices and electronic cigarettes.

[0003] Electronic cigarettes use nickel-chromium, iron-chromium-aluminum, or iron-chromium-aluminum / stainless steel sheet etched with conductive resistive traces as the heating element, supplemented by capillary liquid guiding materials. The heating element causes the liquid e-liquid to evaporate, creating an aerosol. The resistive heating element used is extremely low-cost, low-energy, and heats up rapidly. For example, iron-chromium-aluminum can reach 1000℃ in one second. Its excessively rapid heating rate and extremely low temperature coefficient of resistance (TCR) (±20ppm / ℃) make it almost impossible for the control circuit to capture its signal in time for precise temperature control. Existing electronic cigarette devices control the temperature of the heating element by the boiling point of the liquid e-liquid; the continuous evaporation of the e-liquid carries away the heat from the heating element, preventing it from overheating.

[0004] Heated cigarette devices use heating resistors to heat solid or semi-solid tobacco mixtures and control the temperature to produce an aerosol. The heating resistors are made by coating a substrate (ceramic, glass, or pre-insulated metal) with a metal material with a high resistance-to-temperature ratio (TCR), such as palladium, and controlling the temperature using the resistance-temperature characteristics, or by using an external sensor at the resistor. The method is mature and readily available, but a drawback is that the heating resistor substrate needs sufficient strength, requiring a certain thickness. For example, the minimum thickness for metal tubes is 0.15 mm, for metal sheets 0.3 mm, and for ceramic sheets or tubes 0.5 mm. These thickness requirements not only lead to higher energy consumption by the heating resistor itself, but also result in higher costs for the heating element, making it inconvenient to incorporate into aerosol products as a consumable. Summary of the Invention

[0005] This invention provides a heating element with step resistance temperature characteristics and its preparation method, in order to solve the technical problem of the inability to accurately control the temperature of the heating element in the prior art.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows: In a first aspect, the present invention provides a heating element having a step resistance temperature characteristic, comprising a substrate and a resistive body, the resistive body being connected to the substrate; the resistive body comprising a thinning layer and a nitriding layer, the thinning layer being connected to the substrate and having a thickness less than that of the substrate, the nitriding layer being formed on the surface of the thinning layer.

[0007] Furthermore, the thickness of the substrate is 0.03 mm to 0.15 mm, and the thinning layer is obtained by reducing the thickness of the substrate, wherein the thickness of the thinning layer is 30% to 70% of the thickness of the substrate.

[0008] Furthermore, the thickness of the nitrided layer is 0.2 μm to 2 μm.

[0009] Furthermore, the nitrided layer comprises AlN and / or CrN.

[0010] Furthermore, the materials of the substrate and the resistive material are selected from iron-chromium-aluminum.

[0011] Furthermore, the resistive material is disposed in the middle region of the conductive trajectory of the heating element.

[0012] Furthermore, the heating element is provided with at least one corner, and the resistive body is provided at the corner of the heating element.

[0013] Furthermore, the number of resistive variants is at least two, wherein the thickness of the thinned layer of the two resistive variants is different, and / or the thickness of the nitrided layer of the two resistive variants is different.

[0014] Furthermore, the switching temperature of the resistive body is 300℃~1000℃.

[0015] A second aspect of the present invention provides a method for preparing the above-mentioned heating element, comprising the following steps: S1. At least one region of the substrate is partially etched to form the thinned layer; S2. Nitriding treatment is performed on the thinned layer to form the nitrided layer on the surface of the thinned layer, thereby obtaining the heating element.

[0016] Furthermore, the nitriding treatment step in step S2 specifically includes: covering the substrate with a mask, and holding the thinned area at 700℃~800℃ for 2min~30min in an ammonia atmosphere.

[0017] Further, the nitriding treatment step in step S2 specifically includes: placing the substrate in an ammonia atmosphere, and scanning the area to be thinned on the substrate using a pulsed laser to obtain the nitrided layer; the wavelength of the pulsed laser is 355nm or 532nm, and the power density of the pulsed laser is 1-10W / mm². 2 The scanning speed is 5–20 mm / s.

[0018] The heating element with step resistance-temperature characteristics provided by this invention has a substrate and a resistive body connected together. The resistive body can achieve a step change from low resistance to high resistance through a thinning layer and a nitriding layer. It does not require external sensors or control circuits, nor does it rely on the resistance-temperature characteristics of the metal. After being powered on, it can achieve self-regulation of temperature by relying on the response of the heating element itself. Moreover, due to the heat concentration design of the resistive body, the substrate can also be designed as an ultra-thin structure, which consumes less energy for heating and has a short jump response time. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of a heating element with step resistance-temperature characteristics in an embodiment of the present invention; Figure 2 for Figure 1 Schematic diagram of resistance-temperature jump after heating of the heating element; Figure 3 for Figure 1 Schematic diagram of temperature-time jump after heating by the heating element; Figure 4 This is a schematic diagram of the heating element structure with a single temperature jump in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the heating element structure with two temperature jumps according to Embodiment 2 of the present invention; Figure 6 This is a schematic diagram of a heating element structure in an embodiment of the present invention, in which the resistive body is located in the middle region; Figure 7 This is a schematic diagram of another heating element structure located in the middle region of the resistive body in an embodiment of the present invention.

[0021] Figure label: 10. Heating element; 11. Substrate; 12. Resistor; 20. Electrode. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly set on the other component; when a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to the other component.

[0024] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0025] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "a plurality of" or "several" means two or more, unless otherwise explicitly specified.

[0026] It should be noted that the structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which this application can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size should still fall within the scope of the technical content disclosed in this application, provided that they do not affect the effects and purposes that this application can produce.

[0027] This application provides a heating element with a step resistance temperature characteristic, including a substrate 11 and a resistive body 12, the resistive body 12 being connected to the substrate 11; the resistive body 12 includes a thinning layer and a nitriding layer, the thinning layer being connected to the substrate 11 and having a thickness less than that of the substrate 11, and the nitriding layer being formed on the surface of the thinning layer.

[0028] In this embodiment, the material of the thinning layer is the same as that of the substrate 11. Preferably, the thinning layer can be integral with the substrate 11. The thinning layer is obtained by etching or photolithography to reduce the thickness of the substrate 11. Specifically, the thickness of the substrate 11 is 0.03 mm to 0.15 mm, and the thickness of the thinning layer is 30% to 70% of the thickness of the substrate 11, preferably 30% to 50%. This allows for increased current density in the thinning layer, leading to preferential heating and providing a thinner region that is more easily reacted for subsequent nitriding; the reduced mechanical strength facilitates thermal stress triggering abrupt changes.

[0029] In the heating element of this application embodiment, the substrate 11 is connected to the resistivity 12. The resistivity 12 can achieve a step change from low resistance to high resistance through the thinning layer and the nitriding layer. It does not require external sensors or control circuits, nor does it rely on the resistance-temperature characteristics of metals. After being powered on, it can achieve self-regulation of temperature by relying on the response of the heating element 10 itself. Moreover, due to the heat concentration design of the resistivity 12, the substrate 11 can also be designed as an ultra-thin structure, which consumes less energy for heating and has a short jump response time.

[0030] A complete metal sheet typically has a low resistivity. By removing a portion of the sheet using dry photolithography or wet etching, a substrate 11 of the desired shape can be obtained. (Refer to...) Figure 1 The substrate 11 can be configured in a serpentine shape. Compared to a metal sheet, the substrate 11 extends the length of the resistor and reduces its cross-sectional area, thus achieving a larger resistance value. The substrate 11 and the resistive body 12 are made of iron-chromium-aluminum alloy. The substrate 11 is preferably configured with a uniform width and rounded corners to avoid reducing etching or photolithography tolerances and to prevent uneven current density after energization. Furthermore, the heating element 10 has at least one corner, and the resistive body 12 is located at the corner. This is because the current density is relatively high at the corner when current flows.

[0031] In other embodiments, the resistive variant 12 is disposed in the middle region of the conductive trace of the heating element 10. (See also...) Figure 6 , Figure 7 The middle region refers to the middle segment when the conductive trajectory is stretched into a straight line. The middle segment includes the midpoint of the conductive trajectory. The range of the middle segment can be set according to the temperature distribution on the conductive trajectory of the heating element. The temperature of the middle segment is higher than that of the two ends near the conductive pin. When the temperature jump of the resistive part in the middle segment occurs, the effect on the temperature of the heating element is more significant. The resistive part can be set in part of the middle region without covering the middle region, or the resistive part can be set in a position outside the midpoint.

[0032] In this embodiment, at least one region of the substrate 11 is thinned and nitrided to form a resistive layer 12. The nitrided layer is formed on the surface of the thinned layer. The resistive layer 12 is preferably located at a corner of the heating element 10. (Refer to...) Figure 1 The corners of the heating element 10 are generally high-resistance regions. When the heating element 10 is energized and heated, the crystalline phase transformation of the nitride layer at a specific temperature and the synergistic effect of microcracks or interface separation in the thinning layer caused by thermal expansion achieve a step-like abrupt change from low resistance (metallic conductivity) to high resistance (insulating layer dominance). Specifically, the nitride layer includes AlN and / or CrN. The thickness of the nitride layer is 0.2 μm to 2 μm.

[0033] A sudden change in crystalline structure refers to the initial state at room temperature where the nitride layer has a crystalline structure (CrN has a face-centered cubic structure, and AlN has a hexagonal wurtzite structure), and is free from stress and cracks. The crystalline nitride layer possesses a certain degree of conductivity (belonging to semiconductor ceramics, not insulators), and its resistivity is much higher than that of the substrate 11, such as iron-chromium-aluminum, but much lower than that of amorphous or cracked nitride layers. In this case, the total resistance of the resistive body 12 is dominated by the bulk resistance of the crystalline nitride layer. This can be understood as a large resistance of the nitride layer connected in series with a small resistance of the non-nitride layer, and its total resistance is the sum of the two resistances.

[0034] When the heating element 10 is energized and the temperature reaches the phase transition point, the nitride layer transforms from a crystalline structure to an amorphous structure. The atomic arrangement of the nitride layer changes from ordered to disordered, and crystal planes and grain boundaries completely disappear. During electron transport, they are scattered by a large number of disordered atoms, causing the transport path to become drastically disordered and blocked, which is equivalent to forming countless tiny resistive barriers at the microscopic level. When the phase transition from crystalline to amorphous occurs, the bulk resistivity of the nitride layer increases by 100 to 200 times. This is the first important factor contributing to the step increase in the resistance of the resistive body 12.

[0035] In this embodiment, the resistive layer 12 further includes a transition layer between the thinned layer and the nitride layer. The transition layer is a molecular interpenetration layer between the thinned layer and the nitride layer, comprising a bottom metal layer, a middle transition layer, and a surface nitride layer. Taking the substrate 11 as an example of iron-chromium-aluminum, the coefficients of thermal expansion (CTE) of the three layers are as follows: iron-chromium-aluminum layer 13*10... -6 / ℃, transition layer CrN+AlN+FeN 8*10 -6 / ℃, the surface AlN and / or CrN layer (ceramic layer) is 4*10 -6 / ℃. The significant differences in CTE among the three lead to huge differences in thermal expansion after being heated by electricity. The FeCrAl metal substrate has the largest expansion, while the surface CrN / AlN has the smallest expansion. This mismatch in expansion will generate huge tensile stress in the surface nitrided layer. The metal substrate attempts to expand, but the surface ceramic layer prevents it from expanding, thus the surface layer is stretched.

[0036] When heated by electricity, the surface nitride layer has extremely low tensile strength (approximately 200 MPa). When the temperature reaches the jump temperature, the tensile stress generated by thermal expansion exceeds the tensile strength of the nitride layer, causing microcracks to form first at defects (such as grain boundaries and vacancies) within the nitride layer. These microcracks rapidly propagate, forming an interconnected crack network. These cracks further amplify the increase in resistance in two ways: First, the microcracks penetrate the nitride layer, significantly reducing its effective conductive cross-sectional area. According to the resistance formula R=ρL / S, the decrease in the conductive cross-sectional area S directly leads to an increase in resistance R. Second, the gaps in the microcracks are filled with air or oxidation products (such as Al2O3), which have extremely high resistivity (almost like insulators). During electron transport, they need to tunnel through the cracks to continue, creating a huge contact resistance at the cracks, further increasing the total resistance at the break point.

[0037] like Figure 2 , Figure 3 The diagrams show the temperature resistance changes RT and Tt after the heating element 10 is heated. It should be noted that the above changes are based on a scenario where the input voltage remains constant. After the resistance changes at the temperature jump point, the heat generated and the heat dissipated by the heating element 10 reach an equilibrium point, achieving its own constant temperature control. Figure 2 It is a curve showing the change in resistance of the heating element with temperature. The resistance changes slowly at first, and then the resistance changes abruptly after the temperature rises to the set jump temperature. Figure 3 A fixed voltage is used to supply electrical energy to the heating element, and the temperature of the heating element gradually increases. After reaching the jump temperature, the resistance of the resistive transformer changes abruptly, and the resistance of the heating element increases significantly. The heat generated and dissipated by the heating element quickly reach an equilibrium point, and the temperature of the heating element no longer rises significantly. The difference in the coefficient of thermal expansion caused by the multilayer structure is the second important factor contributing to the step increase in the resistance of the resistive transformer 12.

[0038] In this embodiment, the phase transition point of the nitride layer from a crystalline structure to an amorphous structure is usually around 1000°C. In the field of new tobacco products, the conventional operating temperature of the heating element 10 is less than 500°C. Therefore, when applied to the field of new tobacco products, the second important factor, namely the difference in the coefficient of thermal expansion, is the main reason why the heating element 10 has a step-type resistance temperature characteristic.

[0039] In this embodiment, the resistive body 12, in addition to being located at the corner, can also extend 0.5mm to 1.0mm along the substrate 11 at both ends. This arrangement, besides ensuring sufficient area and fully considering the reliability and stability of the thermoelectric response performance, also achieves better repeatability and stable consistency in the manufacturing process. Preferably, the width of the resistive body 12 is equal to the width of the substrate 11. This width setting ensures uniform current distribution and heat conduction paths.

[0040] In some embodiments, multiple resistive layers 12 are provided. The resistive layers 12 can have thinning layers and nitriding layers with different surface areas and thicknesses to achieve multi-point control, multi-step temperature control, and increased temperature control accuracy. Specifically, the number of resistive layers 12 is at least two, wherein the thicknesses of the thinning layers of the two resistive layers 12 are different, and / or the thicknesses of the nitriding layers of the two resistive layers 12 are different. The temperature jump of the resistive layers 12 is 300℃ to 1000℃. In this case, the heating element 10 can achieve multiple temperature jumps, allowing aerosol products to be released better at different times. When the heating element 10 includes two or more temperature jump levels, the nitriding process of each thinning layer needs to be differentiated.

[0041] A second aspect of this application provides a method for preparing the above-mentioned heating element with stepped resistance-temperature characteristics, comprising the following steps: S1. At least one region of the substrate 11 is partially etched to form a thinned layer; S2. Nitriding treatment is performed on the thinned layer to form a nitrided layer on the surface of the thinned layer, thus obtaining the heating element 10.

[0042] In this embodiment, the substrate 11 is partially etched to reduce its thickness and obtain a thinned layer. After the substrate 11 is partially etched and thinned, heat treatment is performed to eliminate its stress. The heat treatment step involves immersing the substrate 11 and the thinned layer in a high-purity nitrogen atmosphere and annealing at 700°C for 20 minutes to eliminate residual etching stress and prevent premature cracking. After heat treatment, the thinned layer is nitrided. There are various methods for nitriding.

[0043] In some embodiments, the nitriding process in step S2 specifically includes: taking a mask and covering it on the substrate 11, and keeping the thinned area at 700°C to 800°C for 2 min to 30 min in an ammonia atmosphere.

[0044] In this embodiment, the mask can be a high-temperature resistant type, such as a stainless steel mask or a ceramic mask. The mask covers the substrate 11, exposing only the thinned layer, which facilitates nitriding treatment of the thinned area. The nitriding treatment can be performed in an ammonia atmosphere or an N2 / H2 atmosphere. After nitriding, the mask is removed, ultrasonically cleaned with acetone, and dried. This method is suitable for the mass production of heating elements.

[0045] Both ammonia and N2 / H2 can achieve nitriding of thinned layers in materials such as iron-chromium-aluminum. However, for the baking temperature of 300℃ to 450℃ required in the field of new tobacco, ammonia is preferred because of its high nitrogen concentration and fast reaction kinetics, allowing the formation of a dense AlN layer at 700℃ to 800℃. During the nitriding process, although Al in FeCrAl reacts preferentially, the activity of N2 is too low, and almost no AlN is formed below 800℃. The temperature must be further increased, but at high temperatures (>900℃), the substrate 11 and the thinned layer will suffer severe recrystallization and embrittlement. At room temperature, the electrical resistance is too high (due to the reduction of grain boundaries). When the substrate 11 is too thin, the trajectory may be deformed (thermal stress + creep).

[0046] In other embodiments, the nitriding process in step S2 specifically includes: placing the substrate 11 in an ammonia atmosphere, and scanning the area to be thinned on the substrate 11 using a pulsed laser to obtain the nitrided layer; the wavelength of the pulsed laser is 355nm or 532nm, and the power density of the pulsed laser is 1-10W / mm². 2 The scanning speed is 5–20 mm / s.

[0047] This application employs a laser-assisted nitriding method to prepare the nitrided layer. The specific operation includes: placing the substrate 11 in an ammonia atmosphere chamber; focusing a pulsed laser of the aforementioned wavelength onto the thinning layer; controlling the laser power density and scanning speed; and precisely controlling the thickness and composition of the nitrided layer by adjusting the laser energy density and the number of scans. This method eliminates the need for a physical mask, achieves micron-level positioning accuracy, and is suitable for high-precision prototypes or small-batch production. It is particularly suitable for differentiated nitriding of different functional regions in devices with multi-level temperature variations.

[0048] In some embodiments, the heating element 10 needs to achieve multiple temperature jumps to allow for better aerosol release at different times. When the heating element 10 includes two or more temperature jumps, the nitriding process parameters of each resistive body 12 need to be set differently. For example, the heating element 10 needs to have two temperature jump zones, with the first jump zone temperature T1 at 300–360°C and the second jump zone T2 at 380–450°C. During the nitriding process, in an NH3 atmosphere, the first jump zone uses a lower nitriding temperature (730–760°C) and a shorter time (3–5 minutes) to form a thinner nitriding layer (0.2–0.4 μm), causing it to fail conductively at a lower temperature. The second jump zone uses a higher nitriding temperature (770–800°C) and a longer time (6–9 minutes) to form a thicker and denser nitriding layer (0.5–0.8 μm), requiring higher thermal stress to trigger the jump. Through the aforementioned differentiated nitriding, multi-level, ordered, and programmable self-temperature response can be achieved on the same device.

[0049] The above technical solution will be further illustrated below through specific embodiments.

[0050] Example 1 The heating element 10, with a single-temperature step, is made of a thin sheet of iron-chromium-aluminum alloy. A substrate 11 with a serpentine trajectory is etched to form a thickness of 0.08 mm, a total width of 7.92 mm, a trajectory width of 0.72 mm, a spacing between trajectories of 0.72 mm, a single trajectory length of 12 mm, a total trajectory extension of 72 mm, and a resistance of 1.85 ohms. The formed serpentine trajectory includes 5 corners. (Refer to...) Figure 4 Corners 1, 3, and 5 are far from the input end of the heating element 10, while corners 2 and 4 are close to the input end. There are three temperature-sensitive points (points 2, 3, and 4). A resistive material 12 is placed at one of the corners, and a thinned layer is obtained after a reduction depth of 0.025 mm. A nitrided layer with a thickness of 0.3 μm AlN is formed on the surface of the thinned layer after local nitriding treatment. Electrodes 20 are placed at both ends of the substrate, using a relatively wide trajectory. The switching temperature of the heating element 10 is 350℃.

[0051] The method for manufacturing the heating element 10 includes the following steps: 1. Material preparation: Select 600mm wide Fe-20Cr-4.5Al (wt.%) iron-chromium-aluminum alloy cold-rolled strip with a thickness of 0.08mm and cut it into 600mm long sheets; 2. Photolithography or etching to obtain substrate 11: Arrange the design files in an array to fit a material size of 600mm*600mm. Use ultraviolet lithography technology to form a serpentine trajectory on the sheet according to the design files. The trajectory is 0.72mm wide, 0.72mm apart, 12mm long in a single segment, and 70mm long in a total unfolded length. The design resistance is 1.85Ω.

[0052] 3. Secondary shallow etching for thinning: At corner 3 in the middle of the serpentine trajectory of the substrate 11 (this is the high-temperature area heated by the heat source 10), photoresist is coated, and a mask protects the remaining area. A secondary shallow etching is performed on this corner area, controlling the depth to 0.03 mm (i.e., 37.5% of the original thickness), resulting in a thinned layer. The length of the thinned layer covers the entire corner radius and extends 0.5 mm along the substrate 11.

[0053] 4. Annealing: Anneal at 700℃ for 20 minutes in a high-purity nitrogen atmosphere to eliminate residual etching stress and prevent early cracking.

[0054] 5. Nitriding treatment: Use a stainless steel micromask to cover the non-thinned areas, exposing only the locally thinned areas. Place the sample in a tube furnace and nitrid at 750°C for 5 minutes under an NH3 atmosphere to form an AlN layer of approximately 0.3 μm thickness.

[0055] 6. Cleaning and drying: After removal, ultrasonically clean with acetone and dry.

[0056] The power supply device is connected to the two electrodes 20 of the heating element 10 in this embodiment, and the heating element 10 is powered by a fixed voltage of 4.2V. The temperature jump of the third corner resistive body 12 is 350°C, which is detected by a contact temperature sensor or an infrared temperature detector.

[0057] Example 2 The heating element 10, with two temperature settings, is made of a thin sheet of iron-chromium-aluminum alloy. A substrate 11 with a serpentine trajectory is etched to form a thickness of 0.08 mm, a total width of 7.92 mm, a trajectory width of 0.72 mm, a spacing between trajectories of 0.72 mm, a single trajectory length of 12 mm, a total trajectory extension of 72 mm, and a resistance of 1.85 ohms. The formed serpentine trajectory includes 5 corners. (Refer to...) Figure 5 Corners 1, 3, and 5 are far from the input end of the heating element 10, while corners 2 and 4 are close to the input end. There are three temperature-sensitive points (points 2, 3, and 4). Resistor bodies 12 are placed at corners 2 and 4, and after thinning to a depth of 0.025 mm, thinned layers are obtained. A nitrided layer with a thickness of 0.3 μm AlN is formed on the surface of the thinned layer after local nitriding treatment. Electrodes 20 are placed at both ends of the substrate, using a relatively wide trajectory. The switching temperatures of the heating element 10 are 350℃ and 400℃.

[0058] The method for manufacturing the heating element 10 includes the following steps: 1. Material preparation: Provide FeCrAl thin sheets with a thickness of 0.08mm, composition: Fe-20Cr-4.5Al (wt.%).

[0059] 2. Photolithography and wet etching: Ultraviolet photolithography is used to form a serpentine trajectory on the sheet. The trajectory width is 0.72mm, the spacing between trajectories is 0.72mm, the length of a single segment is 12mm, the total unfolded length is 70mm, and the designed resistance is 1.85Ω.

[0060] 3. Partial semi-etching (first level), such as Figure 5 .

[0061] Photoresist was applied to the second corner of the serpentine trajectory, and a mask was used to protect the remaining areas. This corner area was then subjected to a second shallow etching, with the depth controlled to 0.03 mm (i.e., 37.5% of the original thickness), serving as the first transition zone.

[0062] 4. Partial semi-etching (second level), such as Figure 5 .

[0063] Photoresist was applied to the corner area (4) of the serpentine trajectory, and a mask was used to protect the remaining areas. This corner area was then subjected to a second shallow etching, with the depth controlled to 0.02 mm (i.e., 25% of the original thickness), serving as the second transition zone.

[0064] 5. Stress annealing: Anneal at 700℃ for 20 minutes in a high-purity nitrogen atmosphere to eliminate residual etching stress and prevent early cracking.

[0065] 6. Selective nitriding (Level 1): Cover all areas except the second corner region with a stainless steel micromask. Place the sample in a tube furnace and nitrid at 750°C for 4 minutes under an NH3 atmosphere to form an AlN layer approximately 0.3 μm thick.

[0066] 7. Selective nitriding (second stage): Replace the mask to cover all areas except the fourth corner region. Place the sample in a tube furnace and nitrid at 780°C for 7 minutes under an NH3 atmosphere to form an AlN / CrN composite layer with a thickness of approximately 0.6 μm.

[0067] 8. Cleaning and drying: After removal, ultrasonically clean with acetone and dry.

[0068] The power supply device is connected to the two electrodes 20 of the heating element 10 in this embodiment, and the heating element 10 is powered by a fixed voltage of 4.2V. The temperature jump of the second corner resistive body 12 is 350°C and the temperature jump of the fourth corner resistive body 12 is 400°C, as detected by a contact temperature sensor or an infrared temperature detector.

[0069] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A heating element with a step-type resistance-temperature characteristic, characterized in that: The material includes a substrate and a resistive layer, the resistive layer being connected to the substrate; the resistive layer includes a thinned layer and a nitrided layer, the thinned layer being connected to the substrate and having a thickness less than that of the substrate, and the nitrided layer being formed on the surface of the thinned layer.

2. The heating element with step-temperature resistance characteristics according to claim 1, characterized in that, The thickness of the substrate is 0.03 mm to 0.15 mm, and the thinning layer is obtained by reducing the thickness of the substrate. The thickness of the thinning layer is 30% to 70% of the thickness of the substrate.

3. The heating element with stepped resistance-temperature characteristics according to claim 1, characterized in that, The thickness of the nitrided layer is 0.2 μm to 2 μm.

4. The heating element with step-type resistance-temperature characteristics according to claim 1, characterized in that, The nitrided layer comprises AlN and / or CrN.

5. The heating element with stepped resistance-temperature characteristics according to any one of claims 1 to 4, characterized in that, The matrix and the resistive material are selected from iron-chromium-aluminum.

6. The heating element with stepped resistance-temperature characteristics according to any one of claims 1 to 4, characterized in that, The resistive material is disposed in the middle region of the conductive trajectory of the heating element.

7. The heating element with stepped resistance-temperature characteristics according to any one of claims 1 to 4, characterized in that, The heating element has at least one corner, and the resistive body is disposed at the corner of the heating element.

8. The heating element with stepped resistance-temperature characteristics according to any one of claims 1 to 4, characterized in that, The number of resistive variants is at least two, wherein the thickness of the thinned layer of the two resistive variants is different, and / or the thickness of the nitrided layer of the two resistive variants is different.

9. The heating element with stepped resistance-temperature characteristics according to any one of claims 1 to 4, characterized in that, The switching temperature of the resistive body is 300℃~1000℃.

10. A method for preparing a heating element with stepped resistance-temperature characteristics according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. At least one region of the substrate is partially etched to form the thinned layer; S2. Nitriding treatment is performed on the thinned layer to form the nitrided layer on the surface of the thinned layer, thereby obtaining the heating element.

11. The preparation method according to claim 10, characterized in that, The nitriding process in step S2 specifically includes: covering the substrate with a mask and holding the thinned area at 700°C to 800°C for 2 to 30 minutes in an ammonia atmosphere.

12. The preparation method according to claim 10, characterized in that, The nitriding process in step S2 specifically includes: placing the substrate in an ammonia atmosphere, and scanning the area to be thinned on the substrate using a pulsed laser to obtain the nitrided layer; the wavelength of the pulsed laser is 355nm or 532nm, and the power density of the pulsed laser is 1-10W / mm². 2 The scanning speed is 5–20 mm / s.

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