Flexible pressure sensor

Abstract

The utility model relates to the field of pressure sensing, and discloses a flexible pressure sensor. The flexible pressure sensor comprises a packaging layer, a sensitive layer, a conductive layer, an electrode layer and a flexible substrate from top to bottom. When the flexible pressure sensor is under pressure, the effective contact area of the sensitive layer and the electrode layer is increased, the total cross section of a conductive path is increased, and the contact resistance is reduced, so that a pressure signal is converted into a resistance signal, and the pressure signal is detected by measuring the contact resistance value of the sensor. The flexible pressure sensor provided by the utility model has the characteristics of high sensitivity, wide pressure range and fast response speed.

Description

Technical Field

[0001] The utility model relates to the technical field of pressure detection, in particular to a flexible pressure sensor. Background Art

[0002] In the background of the Internet of Things era, with the continuous expansion of the application scenarios of flexible pressure sensors, high-performance flexible pressure sensors have developed vigorously in aspects such as human-computer interaction, electronic textiles, and smart homes, and people's demand for pressure measurement has also increased day by day. The pressure sensor undertakes the mutual connection between the external environment and the internal system and plays the role of an information transmission bridge. However, pressure sensors were usually made of rigid materials in the past and were restricted by actual applications. As an important part of the flexible electronics frontier technology, flexible pressure sensors have gradually become one of the research hotspots with the rapid development of information technology. At present, there is a contradiction that the high sensitivity and wide measurement range of flexible pressure sensors are difficult to balance. In order to meet the needs of different application scenarios, flexible pressure sensors should be able to simultaneously possess performance characteristics such as high sensitivity, wide measurement range, and high stability.

[0003] The flexible matrix of the flexible sensor has viscoelasticity, and there is contact adhesion between the sensor layer interfaces. These two problems cause hysteresis in the response of the sensor, reducing the sensitivity and accuracy of the sensor. Therefore, it is very important to design a flexible pressure sensor that takes into account the sensitivity, measurement range, and responsiveness of the sensor for pressure detection. Summary of the Utility Model

[0004] When detecting tiny pressures, the sensor needs to have extremely high measurement accuracy, be able to measure tiny physical quantity changes, and ensure the accuracy of the measurement results. In some cases, for the measurement of high-frequency pressures, the sensor is required to have a fast response speed and be able to capture the changes of the measured physical quantity in real time. However, some flexible conductive polymers of flexible sensors have elastic hysteresis, and there is contact adhesion between the sensor layer interfaces, resulting in problems such as untimely response, high signal output hysteresis, and low sensitivity of such sensors under rapid pressure changes.

[0005] To solve the above problems, the utility model improves the hysteresis in the morphological changes of the sensor, improves the sensitivity of the sensor, and accurately and efficiently realizes the measurement of pressure through solutions such as material modification and structure optimization.

[0006] The utility model discloses a flexible pressure sensor. It includes a packaging layer, a sensitive layer, a conductive layer, an electrode layer, and a flexible substrate; the upper surface of the sensitive layer adopts a pyramid structure; the material of the sensitive layer is PDMS doped with TEMs; the electrode layer adopts a planar interdigital electrode.

[0007] In order to increase the effective sensing range of the sensor and ensure the accuracy of sensor measurement within a larger pressure range, preferably, a pyramid structure is used on the upper surface of the sensitive layer. The side length of the square at the bottom of the pyramid is 0.5-0.8 mm, the height is 0.6-1.0 mm, and the spacing is 0.1-0.2 mm. Compared with the simple planar structure on the upper surface of the sensitive layer, the mechanical contact between the sensitive layer and the electrode layer changes more slowly during the process of applying and removing pressure, and reaches saturation more slowly. When the sensor senses pressure, the pyramid structure can more effectively conduct external forces, making the distribution of pressure on the sensor surface more uniform, gradually increasing the effect of pressure, and extending the sensor's response to pressure, thereby increasing the effective range of the pressure sensor.

[0008] In order to reduce the adhesion between the sensitive layer and the electrode layer and further reduce the hysteresis of the sensor output, preferably, the sensitive layer uses polydimethylsiloxane (PDMS) uniformly doped with thermal expansion microspheres (TEMs) as a matrix with a thickness of 1.0 to 1.5 mmmm. PDMS is a kind of soft, compressible silicone rubber solid with mature preparation technology. It has good flexibility and elasticity, can remain stable with the deformation of the sensor, and is not easy to break. However, this type of viscoelastic material has hysteresis in recovery after being subjected to pressure, which limits its application in flexible sensors. Therefore, thermal expansion microspheres (TEMs) with good elasticity are added to modify PDMS during the cross-linking process, so that the modified PDMS can quickly return to its original state after being deformed by pressure, reducing the influence of the inherent viscoelasticity of the elastic matrix on the deformation of the sensor, thereby effectively suppressing the hysteresis of the sensor output and ensuring the reliability of the data during sensor measurement.

[0009] In order to improve the conductivity between the sensitive layer and the electrode layer of the sensor and improve the sensitivity of the sensor, optionally, the conductive layer material is copper. Copper has good conductivity. In the pressure measurement of the pressure sensor, good conductivity can ensure the fast and stable transmission of electrical signals. The sensor can respond quickly to changes in pressure and accurately convert pressure signals into electrical signal outputs, further enhancing the sensor's ability to detect tiny pressure changes, thereby increasing the demand for high-precision pressure measurement of pressure detection sensors. The thickness is set to 0.2-0.3mm because this thickness range ensures the effect of enhancing the conductivity between the sensitive layer and the electrode layer without taking up too much space or increasing the weight of the sensor.

[0010] In order to further improve the sensitivity of the sensor, preferably, the electrode layer adopts a planar interdigitated electrode. The interdigitated electrode finger length is 10 to 15 mm, and the interdigital spacing is 0.35 to 0.5 mm. Longer electrode fingers can collect signals more widely, and the interdigitated electrode structure can provide a more uniform electric field distribution, thereby improving the measurement accuracy of the sensor. The sensing of the flexible pressure sensor mainly relies on the contact resistance formed between the electrode layer and the sensitive layer. The contact resistance will change relatively significantly with the change of pressure. The contact and separation states between the sensitive layer and the electrode layer can be collected more accurately, and the amplification effect of the mechanical deformation between the sensitive layer and the electrode layer is more obvious. Therefore, the flexible pressure sensor has a relatively high sensitivity. This high sensitivity helps to improve the accuracy of sensor measurement. The sensor can detect small pressure changes more accurately, improving the accuracy of pressure measurement.

[0011] Preferably, the encapsulation layer is made of a polyimide (PI) film with a thickness of 0.3 to 0.8 mm. The function of the PI film is:

[0012] (1) Protective circuit: PI has good chemical stability, which ensures the normal operation of the internal circuit of the sensor and prevents water molecules from entering the sensor and causing circuit short circuit in a humid environment.

[0013] (2) PI film has high mechanical strength and good flexibility. The sensor can detect pressure and maintain structural integrity under large external forces. The thickness is set to 0.3-0.8 mm, which can adapt to the bending deformation of the sensor and facilitate the sensor to detect pressure on surfaces with different degrees of curvature.

[0014] Preferably, a polyurethane (PU) film is used as the flexible substrate, with a thickness of 0.2 to 0.6 mm. The function of the PU film is:

[0015] (1) The PU film has good flexibility and can adapt to the curved surface, ensuring that the sensor fits the object being measured, thereby improving the accuracy of the sensor's pressure detection signal.

[0016] (2) The PU film is wear-resistant, which enables the sensor to maintain stable performance under frequent use and extend the service life of the sensor.

[0017] (3) PU film is chemically stable, and the sensor is not easily affected by humid environments such as rain, ensuring the reliability and stability of the sensor.

[0018] The present utility model provides a flexible pressure sensor. The flexible pressure sensor utilizes the piezoresistive effect. Its current flows into the conductive layer of the sensor from the positive electrode of the electrode layer and then transfers along the plane, and finally flows out from the negative electrode of the electrode layer. By measuring the contact resistance of the sensor, the detection of the pressure signal is realized. Combining the improvement of the viscoelasticity of the flexible matrix and the adhesion phenomenon of the contact existing between the sensor delamination interfaces, a flexible pressure sensor with high sensitivity, low hysteresis and wide range is prepared.

[0019] The present utility model has the following advantages:

[0020] 1. The pressure acquisition range is large. The surface of the sensitive layer adopts a pyramid structure, which makes the pressure effect gradually increase to extend the response of the sensor to the pressure.

[0021] 2. The response time of the output signal is fast. By doping TEMs with high elasticity in PDMS, the inherent viscoelasticity of the elastomer is reduced, effectively improving the hysteresis in the morphological change of the sensor.

[0022] 3. The sensitivity is high. By adopting planar interdigital electrodes in the electrode layer, the change of the contact resistance is relatively obvious. Thus, the flexible pressure sensor has relatively high sensitivity. Description of the Drawings

[0023] The following further describes the present utility model in conjunction with the drawings and examples:

[0024] Figure 1 is the structural schematic diagram of the flexible pressure sensor;

[0025] Figure 2 is the structural schematic diagram of the pyramid adopted on the upper surface of the sensitive layer;

[0026] Figure 3 is the schematic diagram of the planar interdigital electrode;

[0027] Figure 4 is the test chart of the deformation-pressure response characteristic curve of the sensor with 5% TEMs content;

[0028] Among them, 1 is the encapsulation layer, 2 is the sensitive layer, 3 is the conductive layer, 4 is the electrode layer, and 5 is the flexible substrate. Specific Embodiments

[0029] To further explain the technical means adopted by the present utility model to achieve the predetermined utility model purpose, the following is described in detail in conjunction with the drawings and preferred embodiments:

[0030] Figure 1 is the structural schematic diagram of the flexible pressure sensor. The structure of the flexible sensor from top to bottom is successively the encapsulation layer 1, the sensitive layer 2, the conductive layer 3, the electrode layer 4, and the flexible substrate 5.

[0031] In order to increase the effective sensing range of the pressure of the sensor and be more suitable for the detection of high-precision pressure. Specifically, the upper surface of the sensitive layer 2 adopts a pyramid structure. The side length of the square at the bottom of the designed pyramid is 0.5 mm, the height is 0.7 mm, and the spacing is 0.2 mm. Figure 2 It is a schematic diagram of the pyramid structure. As the pressure increases, the pyramid structure will guide the pressure to concentrate on the pyramid structure, making the pressure distribution on the sensor surface more uniform during measurement. In order to reduce the influence of the too-fast pressure speed on the sensor, reduce the measurement error, and improve the reliability of the data, a pyramid structure is designed on the surface of the sensitive layer 2, so that the effect of the pressure gradually increases, thereby prolonging the response of the sensor to the pressure and improving the reliability of the pressure measurement data of the sensor.

[0032] In order to suppress the influence of the matrix viscoelasticity on the response speed of the sensor and further reduce the hysteresis of the sensor output. Specifically, TEMs are uniformly doped in the PDMS elastomer of the sensitive layer 2 of the sensor, and the thickness is 1.5 mm. The thermally expandable microspheres of TEMs inside the PDMS, with their good elasticity, can accelerate the release of the residual stress inside the flexible matrix, reduce the contact adhesion between the sensitive layer 2 and the electrode layer 4, enable the sensor to respond more quickly to external pressure changes, and improve the sensitivity of the sensor to minute pressure changes. Figure 4 It is a test chart of the deformation-pressure response characteristic curve of the sensor with 5% TEMs content; the formation of a porous structure by TEMs inside the PDMS makes the PDMS respond more quickly under pressure, enables the sensor to respond more promptly under rapid pressure changes, and ensures that the measurement data of the sensor will not be inaccurate due to the too-fast pressure change speed during pressure measurement, thereby improving the stability and reliability of the measurement data of the sensor.

[0033] In order to improve the accuracy of the measurement of the flexible pressure sensor, specifically, the material of the conductive layer 3 is copper, and the thickness is 0.3 mm. Copper has good electrical conductivity, which can improve the electrical conductivity between the sensitive layer 2 and the electrode layer 4 of the sensor. This enables the sensor to convert the measured pressure signal into an electrical signal more quickly, improves the sensitivity of the sensor, especially when measuring minute pressure changes, and improving the electrical conductivity between the sensitive layer 2 and the electrode layer 4 of the sensor is beneficial to further enhancing the ability of the sensor to detect minute pressure changes.

[0034] In order for the flexible pressure sensor to have a high sensitivity, specifically, in the part of the electrode layer 4, a planar interdigital electrode is adopted, the finger length of the interdigital electrode is 15 mm, and the interdigital spacing is 0.5 mm. Figure 3It is a schematic diagram of planar interdigital electrodes. The interdigital electrodes adopt a rectangular specification, and the anodes and cathodes are arranged in a cross pattern. The use of planar interdigital electrodes in electrode layer 4 has a more obvious amplification effect on the mechanical deformation between the sensitive layer 2 and electrode layer 4. When the pressure applied to the sensor increases, the contact area between the sensitive layer 2 and electrode layer 4 will increase with the increase in pressure, and its contact resistance will rapidly decrease. When the pressure applied to the sensor decreases, the contact area between the sensitive layer 2 and electrode layer 4 will decrease with the decrease in pressure, and its contact resistance will rapidly increase. By measuring the contact resistance value of the sensor, the detection of pressure signals is achieved, thereby improving the sensitivity of the pressure sensor and making the measurement accuracy of the pressure signal by the sensor more accurate.

[0035] To improve the measurement accuracy of the sensor, the length of the interdigital electrode fingers is 15 mm. The longer electrode fingers can collect signals more widely.

[0036] To further improve the measurement accuracy of the sensor, the interdigital spacing is 0.5 mm. The interdigital electrode structure can provide a more uniform electric field distribution, especially when the interdigital spacing is small, making the relationship between the output signal and the input signal of the sensor more linear.

[0037] To improve the reliability and stability of the flexible pressure sensor during long-term operation, specifically, the encapsulation layer 1 uses a PI film with a thickness of 0.5 mm, enabling the sensor to adapt to bending deformation, facilitating pressure measurement on surfaces with different bending degrees, and at the same time protecting the internal circuit of the sensor from the influence of environmental humidity such as rainwater, thus extending the service life of the sensor.

[0038] For the wear resistance and reliability of the flexible pressure sensor, specifically, a polyurethane (PU) film is used as the flexible substrate 5 of the sensor, with a thickness of 0.5 mm. The good wear resistance of the PU film ensures that the sensor can maintain stable performance under frequent use and is not easily affected by a humid environment, ensuring the reliability of the sensor and further improving the accuracy of signal acquisition.

[0039] The above is a specific description of the preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent deformations or substitutions without departing from the spirit of the present invention, and these equivalent deformations or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A flexible pressure sensor, characterized in that: It comprises a packaging layer, a sensitive layer, a conductive layer, an electrode layer and a flexible substrate; the upper surface of the sensitive layer adopts a pyramid structure; the material of the sensitive layer is PDMS doped with TEMs; and the electrode layer adopts a planar interdigitated electrode.

2. A flexible pressure sensor according to claim 1, characterized in that: The square bottom side length of the pyramid on the upper surface of the sensitive layer is 0.5-0.8 mm, the height is 0.6-1.0 mm, and the spacing is 0.1-0.2 mm.

3. A flexible pressure sensor according to claim 1, characterized in that: The material of the sensitive layer is PDMS doped with TEMs, and the thickness is 1.0-1.5 mm.

4. The flexible pressure sensor according to claim 1, characterized in that: The conductive layer is made of copper and has a thickness of 0.2 to 0.3 mm.

5. The flexible pressure sensor according to claim 1, characterized in that: The electrode layer adopts a planar interdigitated electrode with a finger length of 10 to 15 mm and an interdigitated distance of 0.35 to 0.5 mm.

6. The flexible pressure sensor according to claim 1, characterized in that: The encapsulation layer is made of PI film with a thickness of 0.3-0.8 mm.

7. The flexible pressure sensor according to claim 1, characterized in that: The flexible substrate is made of PU film with a thickness of 0.2-0.6 mm.

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