Resistive humidity sensor with wide measurement range

Abstract

This invention discloses a resistive humidity sensor with a wide measurement range. A humidity-sensitive material and a pair of parallel electrodes are disposed on a substrate. The humidity-sensitive material is located between the electrodes, forming a humidity-sensitive resistor. The key feature is that the humidity-sensitive material is non-uniformly distributed along the length of the electrodes, causing the resistivity-humidity characteristic curve of the humidity-sensitive material to gradually change. Furthermore, the resistivity-humidity characteristic curve of the humidity-sensitive material gradually changes along the length of the electrodes, from the near end to the far end, resulting in different optimal humidity-sensing sensitivities at different locations.

Description

TECHNICAL FIELD

[0001] The present application relates to a wide measurement range resistance type humidity sensor. BACKGROUND

[0002] With the development of the times, scientific research, agriculture, heating, textiles, machine room, aerospace, power and other industrial sectors, more and more need to use humidity sensors, and the demand for product quality is higher and higher. The control of environmental temperature and humidity and the monitoring and analysis of the moisture value of industrial materials have become one of the more common technical conditions.

[0003] Conventional humidity sensors are divided into resistance type and capacitance type, and the basic form of the product is to coat the humidity sensing material on the substrate to form a humidity sensing film. After the water vapor in the air is adsorbed on the humidity sensing material, the impedance and dielectric constant of the element change greatly, thereby forming a humidity sensitive element. The humidity sensitive resistor is made by using the principle that the humidity sensitive material absorbs the moisture in the air to change its resistance value. The characteristic of the humidity sensitive resistor is that a layer of humidity sensing film is coated on the substrate, and when the water vapor in the air is adsorbed on the humidity sensing film, the resistivity and resistance value of the element change, and this characteristic can be used to measure humidity.

[0004] The characteristic parameters of the humidity sensor mainly include: accuracy, long-term stability, humidity range, sensitivity, temperature coefficient, response time, humidity hysteresis difference, humidity characteristic quantity-relative humidity characteristic curve, etc.

[0005] The accuracy of the humidity sensor should reach ±2%~±5%RH, and it is difficult to use as a measuring instrument if it cannot reach this level. It is relatively difficult for the humidity sensor to reach an accuracy of ±2%~±3%RH, and the characteristics given in the product data are usually measured at room temperature (20℃±10℃) and in clean gas. In actual use, due to the influence of dust, oil stains and harmful gases, the accuracy will decrease with the use time, and the accuracy level of the humidity sensor should be judged in combination with its long-term stability. Generally speaking, long-term stability and service life are the top problems affecting the quality of the humidity sensor, and products with an annual drift of 1%RH are rare, and generally around ±2% or even higher.

[0006] Humidity range: It refers to the maximum range of environmental humidity that the humidity sensor can accurately measure. Due to the different materials used and the different working principles of various humidity sensors, their characteristics are not suitable for the entire relative humidity range of 0~100%RH, and they usually have a relatively narrow suitable measurement range. When the measurement range exceeds the suitable measurement range, the humidity measurement error will increase rapidly, and the reliability of the measurement result will decrease rapidly.

[0007] The resistance of a component made of a humidity sensitive material is sensitive to the ambient humidity within its effective humidity sensing range. When the humidity is lower than its effective humidity sensing range, the resistance of the humidity sensitive material increases rapidly and approaches that of an insulating material. When the humidity is higher than its effective humidity sensing range, the resistance of the humidity sensitive material becomes very small. That is, the resistance of the humidity sensitive material cannot reflect the change of the ambient humidity when the ambient humidity is lower or higher than its effective humidity sensing range. Only within its effective humidity sensing range, the resistance of the humidity sensitive material can change obviously with the change of the ambient humidity. The measuring range of each sensor is usually narrow, so the appropriate measuring range should be selected according to the requirement of the measuring range.

[0008] For example, the appropriate humidity measuring range (effective humidity sensing range) of some humidity sensors meeting the requirement of accuracy is 10-30% RH, and the error is ±2% RH. When the humidity is out of the range of 10-30% RH, the resistance of the humidity sensitive material is either very large or very small, and it is difficult to accurately reflect the ambient humidity. The appropriate humidity measuring range (effective humidity sensing range) of some other humidity sensors is 30-55% RH, and the measuring value is also unreliable when the humidity is out of this range. The effective humidity sensing range of some other humidity sensors is 70-90% RH. Figure 1 The above situation is shown. It is difficult to manufacture humidity sensors with a wide effective humidity sensing range in practice.

[0009] In order to expand the measuring range, the industry usually uses a combination of multiple sensors and multiple measuring circuits, microprocessors to form a humidity sensor with a wide measuring range. A series of humidity values are obtained by simultaneously measuring the multiple combination sensors by the multiple measuring circuits, and the microprocessor determines which humidity value has the highest accuracy within its appropriate range by a complex algorithm, and takes the value with the highest accuracy and discards the other measuring values. The structure and resistance-humidity characteristics of the combination humidity sensor are shown in Figure 2 The price of a high-precision humidity sensor is very high, and a single one can cost hundreds or even thousands of yuan, as shown in Figure 3

[0010] The pressure on the manufacturing cost, accuracy, measuring range and other aspects forces researchers to make further research.

[0011] In order to solve the above technical problems, the present application is proposed as follows. SUMMARY

[0012] The present application aims to provide a resistance type humidity sensor with a wide measuring range, which can achieve a wide humidity measuring range while maintaining accuracy, and further reduce the manufacturing cost and the complexity of the humidity sensor. The specific technical solution to achieve the purpose of the present application is: ​

[0013] A wide-range resistance-type humidity sensor comprises a humidity-sensitive material, a substrate, and a pair of electrodes; the pair of electrodes and the humidity-sensitive material are prepared on the substrate. The humidity-sensitive material is characterized by having a water absorption property, and the absorption of water in ambient air causes the resistivity to change with the water content.

[0014] The pair of electrodes can be located above the humidity-sensitive material or below the humidity-sensitive material.

[0015] That is, in some embodiments, the humidity-sensitive material is prepared on the substrate first, and then the pair of electrodes is prepared on the humidity-sensitive material.

[0016] In some embodiments, the pair of electrodes is prepared on the substrate first, and then the humidity-sensitive material is prepared on the substrate with the pair of electrodes.

[0017] Preferably, the pair of electrodes is prepared on the substrate first, and then the humidity-sensitive material is prepared on the substrate with the pair of electrodes; in this way, the pair of electrodes is arranged between the humidity-sensitive material and the substrate, and the surface of the humidity-sensitive material is completely exposed to the environment without being covered by the electrodes. In such an embodiment, the sensitivity of the humidity sensor can be higher.

[0018] In the present application, the pair of electrodes are two "parallel" electrodes, for example, two parallel straight-line electrodes, or comb-shaped electrodes, or interdigital electrodes, or double helix structure electrodes.

[0019] In order to achieve a wide-range humidity measurement range, the core technical means adopted by the present application is:

[0020] In the length direction of the electrodes, the resistivity-humidity characteristic curve of the humidity-sensitive material gradually changes.

[0021] The "in the length direction of the electrodes, the resistivity-humidity characteristic curve of the humidity-sensitive material gradually changes" means that:

[0022] If the lead-out end of any electrode in the pair of electrodes on the substrate for connecting the measurement circuit is defined as the proximal end, and the other end of the electrode away from the proximal end is defined as the distal end, then: from the proximal end to the distal end, the resistivity-humidity characteristic curve of the humidity-sensitive material gradually changes.

[0023] At the proximal end, the humidity-sensitive material can be selected to be sensitive to low-humidity air at this position; at the distal end, the humidity-sensitive material can be selected to be sensitive to high-humidity air at this position; and the humidity-sensitive material at the intermediate position is sensitive to medium-humidity air.

[0024] It is worth noting that in the above example, the humidity sensitive material is not simply divided into three sections from the proximal end to the distal end, but only for the purpose of facilitating the understanding of the core concept of the present application.

[0025] More specifically, in the present application, the resistivity-humidity characteristic curve of the humidity sensitive material gradually changes in the length direction of the electrode, i.e. from the proximal end to the distal end, so that the humidity sensitive material at different positions responds to different ambient humidity.

[0026] In the above paragraph, the resistivity-humidity characteristic curve of the humidity sensitive material gradually changes in the length direction of the electrode means that the properties of the humidity sensitive material continuously change, rather than being obviously divided into several sections.

[0027] Of course, in some embodiments of the present application, the humidity sensitive material can also be obviously divided into several sections with different properties in the length direction of the electrode, i.e. from the proximal end to the distal end, and different sections have different resistivity-humidity characteristic curves.

[0028] In the present application, in order to achieve that the resistivity-humidity characteristic curve of the humidity sensitive material gradually changes in the length direction of the electrode, i.e. from the proximal end to the distal end, so that the humidity sensitive material at different positions responds to different ambient humidity, the composition and / or specific surface area and / or nanoscale size and / or microstructure of the humidity sensitive material at different positions are used.

[0029] For example, in some embodiments, the composition of the humidity sensitive material gradually changes in the length direction of the electrode, so that the composition of the humidity sensitive material at different positions is different, resulting in that the resistivity-humidity characteristic curve of the humidity sensitive material gradually changes.

[0030] Since different humidity sensitive materials have different humidity sensitive properties, i.e. each humidity sensitive material has its own resistivity-humidity characteristic curve, when the composition of the humidity sensitive material at different positions changes, the resistivity-humidity characteristic curve of the humidity sensitive material gradually changes in the length direction of the electrode.

[0031] The resistivity-humidity characteristic curve of the humidity sensitive material gradually changing can make the humidity sensitive resistance between a pair of electrodes be able to sensitively respond to a wide range of humidity changes.

[0032] Of course, in the present application, the humidity sensitive material can also be an organic composite material, or an inorganic composite material, or an organic / inorganic composite material. These humidity sensitive materials are all composite materials, and the resistivity of the composite material changes with humidity.

[0033] In the present application, the composite material refers to a composite of humidity-sensitive nanomaterials and non-humidity-sensitive nanomaterials.

[0034] Alternatively, the composite material refers to a composite of highly humidity-sensitive nanomaterials and low humidity-sensitive nanomaterials.

[0035] In the present application, the composite material can be a composite nanomaterial with a core-shell structure, or a mixture of different nanomaterials, or other structural forms.

[0036] As a common knowledge in the art, the change in the composition of the humidity-sensitive nanomaterial, or the change in the specific surface area, or the change in the nanoscale size, or the change in the microstructure, will all result in a change in the resistivity-humidity characteristic curve of the humidity-sensitive material, and thus the sensitive response to different humidity of the air.

[0037] In the present application, from the proximal end to the distal end, the pair of electrodes are sensitive to different ambient humidity due to the different positions of the humidity-sensitive materials.

[0038] Therefore, when the humidity sensor is located in an environment with low humidity, not all the humidity-sensitive materials at any position between the pair of electrodes can respond sensitively to the change in humidity, and thus exhibit a sensitive change in resistance. Instead, the humidity-sensitive material at a certain position x has the best humidity-sensing sensitivity relative to the humidity, and thus the resistance at position x can change sensitively with humidity.

[0039] However, in the above case, not all the humidity-sensitive materials except at the above position x cannot respond to the change in ambient humidity. In fact, they will also respond to the change in humidity to some extent, but the humidity-sensing sensitivity is relatively low or very low. Therefore, in the whole, it is mainly the resistance at position x that can change sensitively with humidity.

[0040] When the ambient humidity changes significantly, the humidity-sensitive material at position x no longer has the best humidity-sensing sensitivity relative to the new humidity, but the humidity-sensitive material at another position x' has the best humidity-sensing sensitivity relative to the new humidity. In this case, the resistance of the humidity-sensitive material at position x will change with humidity no longer significantly due to exceeding its optimal humidity-sensing range, and in the whole, it is mainly the resistance at position x' that changes sensitively with humidity.

[0041] When the humidity sensitive material between the pair of electrodes of the whole humidity sensor is set by a pre-selected way, the resistivity-humidity characteristic curve of the humidity sensitive material presents gradual change in the length direction of the electrode, i.e. from the proximal end to the distal end, so that the humidity sensitive material at different positions responds to different ambient humidity from the proximal end to the distal end.

[0042] In the specific implementation, in order to realize that the humidity sensitive material at different positions responds to different ambient humidity, the composition of the humidity sensitive material gradually changes from the proximal end to the distal end along the electrode direction.

[0043] It is known that the humidity sensitive material with different compositions, the material with different micro-nano structures, and the material with different specific surface areas all exhibit different optimal humidity sensing ranges. The specific sensing range can be reasonably selected for the humidity sensitive material at the proximal end and the distal end according to actual conditions.

[0044] Through the above setting, the same humidity sensor can respond to a wide humidity change range, and further realize a wide humidity measurement range. As can be seen from the core idea of the present application, the present application provides a wide measurement range resistance type humidity sensor, which realizes a wide humidity measurement range while maintaining accuracy, and further reduces manufacturing cost and complexity of the humidity sensor.

[0045] So far, the inventor has described the working principle, technical scheme, and technical effect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 Resistivity-humidity characteristic of a humidity sensor made of different humidity sensitive materials.

[0047] Figure 2 Resistivity-humidity characteristic of a multi-piece combined humidity sensor, which belongs to the prior art.

[0048] Figure 3 Part of the high-end humidity sensor quotation screenshot of a certain procurement website.

[0049] Figure 4 A humidity sensor using a comb-shaped electrode. DETAILED DESCRIPTION

[0050] In order to facilitate understanding of the present application, the technical scheme of the present application will be specifically introduced below in combination with examples.

[0051] A wide measurement range resistance type humidity sensor, comprising humidity sensitive material, substrate, and a pair of electrodes; the pair of electrodes and the humidity sensitive material are prepared on the substrate.

[0052] The humidity-sensitive material is characterized by having water absorption properties, and the change in resistivity with moisture content is caused by the absorption of moisture in the ambient air.

[0053] The humidity-sensitive material is an organic composite material, or an inorganic composite material, or an organic / inorganic composite material. The resistivity of the humidity-sensitive material changes with humidity.

[0054] In some embodiments of the present application, the humidity sensor comprises a humidity-sensitive material, a substrate, and a pair of electrodes; the pair of electrodes is located on the front surface of the substrate material; the humidity-sensitive material is prepared on the front surface of the substrate including the pair of electrodes. The pair of electrodes is covered with the humidity-sensitive material.

[0055] In some other embodiments of the present application, the humidity sensor comprises a humidity-sensitive material, a substrate, and a pair of electrodes; the pair of electrodes is located on the front surface of the substrate material; the humidity-sensitive material is prepared on the front surface of the substrate. The pair of electrodes is prepared on the humidity-sensitive material, so that the humidity-sensitive material has a portion of the electrodes leaking out.

[0056] In the present application, the pair of electrodes can be various types, such as interdigital electrodes, for example, meander-shaped electrodes, for example, comb-shaped electrodes; the pair of electrodes can also be snake-shaped electrodes, meander-shaped electrodes. Figure 4 A humidity sensor with interdigital electrodes is shown.

[0057] Preferably, the surface area of the electrodes is 1 / 3 to 2 / 3 of the surface area of the humidity-sensitive material.

[0058] In all embodiments of the present application, the following characteristics are present: along the length direction of the electrodes, the resistivity-humidity characteristic curve of the humidity-sensitive material gradually changes, specifically:

[0059] The proximal end of any electrode in the pair of electrodes defined on the substrate is the lead-out end for connecting the measurement circuit, the other end of the electrode away from the proximal end is the distal end, and the length of any point on the electrode away from the proximal end along the electrode direction is , then the surface resistivity-humidity function of the humidity-sensitive material at point is , the partial derivative of the surface resistivity with respect to humidity represents the humidity sensitivity of the surface resistivity at point x with respect to humidity, then represents the function curve between the humidity sensitivity of the humidity-sensitive material and humidity h, the peak of the function curve represents the optimal humidity sensitivity of the humidity-sensitive material at point x, then: from the proximal end to the distal end, the the peak of the function curve gradually moves with ; in the above formula R represents the surface resistivity of the humidity-sensitive material, Indicates humidity.

[0060] In all embodiments, preferably, the pair of electrodes are gold electrodes or silver electrodes.

[0061] In some embodiments, a pair of electrodes is prepared using a vapor deposition process.

[0062] In some embodiments, a pair of electrodes is prepared using a radio frequency magnetron sputtering process.

[0063] In all embodiments, preferably, the humidity-sensitive material is a hydrophobic material to prevent the humidity-sensitive sensing layer from peeling off due to dissolution in water at high humidity conditions.

[0064] The humidity sensor also includes a resistance measurement module, which monitors the change in resistance of the humidity-sensitive material between a pair of electrodes, thereby obtaining the ambient humidity value.

[0065] In this invention, the humidity-sensitive material can be a single-component humidity-sensitive material, but the microscopic properties of the humidity-sensitive material gradually change along the length of the electrode.

[0066] In some implementations, the humidity-sensitive material is an organic material.

[0067] In some embodiments, the humidity-sensitive material is an inorganic material; in other embodiments, the humidity-sensitive material is an organic / inorganic composite material.

[0068] In a humidity sensor, the humidity-sensitive material is non-uniformly distributed along the length of the electrodes, from the proximal end to the distal end. The peak value of the function curve varies with Gradually moving, from different locations This can be achieved by changing one or more of the components, specific surface area, nanoscale size, and microstructure of the humidity-sensitive material.

[0069] In some embodiments, along the length of the electrode, i.e. from the proximal end to the distal end, the humidity-sensitive material is clearly divided into multiple segments with different properties, and different segments have different resistivity-humidity characteristic curves.

[0070] In some embodiments, the humidity-sensitive material is selected as a nanoparticle material. Along the length of the electrode, the specific surface area of ​​the humidity-sensitive material nanoparticle material is set to gradually change, so that the specific surface area of ​​the humidity-sensitive material at different locations is different, resulting in a gradual change in the resistivity-humidity characteristic curve of the humidity-sensitive material.

[0071] For example, along the length direction of the electrode, three segments of humidity sensitive material are coated in sequence, the three segments of humidity sensitive material are in sequence: TiO2 nanorod with a diameter of 100 nm, TiO2 nanorod with a diameter of 200 nm, and TiO2 nanorod with a diameter of 400 nm.

[0072] The change in the diameter of the TiO2 nanorod at the microscale brings different resistivity-humidity characteristic curves, so that the humidity sensor composed of three different segments of TiO2 nanorod can respond to a wider humidity change range than any single-diameter TiO2 nanorod sensor.

[0073] In some embodiments, the humidity sensor with a wide measurement range can also be caused by the change in the composition of the humidity sensitive material.

[0074] For example, along the length direction of the electrode, three segments of humidity sensitive material are coated in sequence, the three segments of humidity sensitive material are in sequence: In2O3 nanomaterial, TiO2 nanowire, and PdCl2 nanomaterial.

[0075] For another example, along the length direction of the electrode, from the proximal end to the distal end, there is an increasing amount of WO3 nanomaterial and a decreasing amount of CeO2 nanomaterial, so that the ratio of WO3 nanomaterial to CeO2 nanomaterial changes continuously along the length direction of the electrode, and the humidity sensor with a wide measurement range is caused by the change in the composition of the humidity sensitive material.

[0076] In some embodiments, the humidity sensitive material is a hydrophobic material. For example, in the present application, an organic / inorganic composite humidity sensitive material is further proposed, i.e., the humidity sensitive material is a mixture formed by adding 5-8% by weight of cuprous oxide, 4-7% by weight of zinc oxide, and 4-8% by weight of 4-epoxypropanoxycarbazole to phenyl benzoate and then stirring strongly;

[0077] As an example, the precursor solution of the humidity sensitive material is a hydrophobic oily mixture composed of cuprous oxide, zinc oxide, 4-epoxypropanoxycarbazole (CAS No.: 53-95-2), and phenyl benzoate;

[0078] Preferably, the cuprous oxide is 1-10 μm of granular cuprous oxide, and the zinc oxide is 0.5-5 μm of rod-shaped zinc oxide.

[0079] Preferably, the weight percentage of cuprous oxide is 5-8%, the weight percentage of zinc oxide is 4-7%, and the weight percentage of 4-epoxypropanoxycarbazole is 3-6%, and the rest is phenyl benzoate.

[0080] Here, the hydrophobicity of phenyl benzoate and 4-epoxypropanoxycarbazole is utilized. Cuprous oxide and zinc oxide are used as humidity-sensitive materials.

[0081] In the above example, by means of coating, the content of cuprous oxide is gradually increased and the content of zinc oxide is gradually decreased from the proximal end to the distal end along the length direction of the electrode.

[0082] In the various embodiments described in the specification, the technical means adopted are not mutually conflicting, i.e. can be freely combined to form different technical solutions. These possible permutations and combinations of technical solutions are all deemed to have been described in the original application file of the present application. Unless a particular statement is made, certain technical means are technically contradictory and cannot coexist in the same technical solution. The above is merely a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A resistive humidity sensor with a wide measurement range, comprising a humidity-sensitive material and a pair of parallel electrodes disposed on a substrate, wherein the humidity-sensitive material is located between the pair of electrodes to form a humidity-sensitive resistor, characterized in that: The humidity-sensitive material is distributed non-uniformly along the length direction of the electrode, so that the resistivity-humidity characteristic curve of the humidity-sensitive material gradually changes. The "so that the resistivity-humidity characteristic curve of the humidity-sensitive material gradually changes" along the length direction of the electrode means that: The lead-out end of any one of the pair of electrodes defined on the substrate for connecting the measuring circuit is the proximal end, the other end of the electrode away from the proximal end is the distal end, and the length of any point on the electrode away from the proximal end along the direction of the electrode is The surface resistivity of the humidity-sensitive material at point The surface resistivity-humidity function of the humidity-sensitive material at point The partial derivative of the surface resistivity with respect to humidity The humidity sensitivity of the surface resistivity with respect to humidity at point x, then The function curve of the humidity sensitivity of the humidity-sensitive material with respect to humidity h, The peak value of the function curve represents the optimal humidity sensitivity of the humidity-sensitive material at point x, then: from the proximal end to the distal end, the The peak value of the function curve gradually moves with ; in the above formula R The surface resistivity of the humidity-sensitive material is The humidity is Along the length direction of the electrode, i.e. from the proximal end to the distal end, the resistivity-humidity characteristic curve of the humidity-sensitive material gradually changes, so that the humidity-sensitive material at different positions has different optimal humidity sensing sensitivities.

2. The humidity sensor of claim 1, wherein: The humidity sensitive material is arranged to be non-uniformly distributed from proximal to distal, such that the humidity sensitive material has a peak value of the functional curve that moves gradually from a position where one or more of the composition, specific surface area, nanoscale dimensions, microstructure of the humidity sensitive material is different.

3. The humidity sensor of any one of claims 1-2, wherein: First, the humidity-sensitive material is prepared on the substrate, and then a pair of electrodes is made on the humidity-sensitive material.

4. The humidity sensor of any one of claims 1-2, wherein: First, a pair of electrodes is prepared on the substrate, and then the humidity-sensitive material is prepared on the substrate with the pair of electrodes.

5. The humidity sensor of any one of claims 1-2, wherein: Along the length direction of the electrode, i.e. from the proximal end to the distal end, the humidity-sensitive material is obviously divided into multiple segments with different properties, and different segments have different resistivity-humidity characteristic curves.

6. The humidity sensor of any one of claims 1-2, wherein: Along the length direction of the electrode, the resistivity-humidity characteristic curve of the humidity-sensitive material continuously changes, i.e. the properties of the humidity-sensitive material continuously change, rather than being obviously divided into several segments.

7. The humidity sensor of any one of claims 1-2, wherein: The humidity-sensitive material is a hydrophobic material to avoid the humidity-sensitive sensing layer from peeling off due to dissolution in water under high humidity.

8. The humidity sensor of any one of claims 1-2, wherein: The surface area of the electrode is 1 / 10-2 / 3 of the surface area of the humidity-sensitive material.

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