Low-cost flexible pressure sensor with ultrahigh sensitivity and high stability

Abstract

The invention discloses a low-cost flexible pressure sensor with ultrahigh sensitivity and high stability, which sequentially comprises a packaging layer, an electrode layer and a sensitive layer from outside to inside, and is characterized in that the sensitive layer is formed by uniformly dispersing amorphous powder FeCrMoSiB subjected to heat treatment on porous PDMS (Polydimethylsiloxane). The sensor has extremely high sensitivity due to the fact that a large number of micron-sized holes exist in the sensor, and the amorphous powder FeCrMoSiB subjected to heat treatment distributed in the micron-sized holes forms a certain conductive network; under low stress, micron-sized holes in the sensor can be greatly closed, so that the spatial arrangement mode of the amorphous powder FeCrMoSiB subjected to heat treatment is changed, a conductive network structure is further changed, the resistance and magnetic characteristics of a thin film are changed, and finally, a relatively large stress impedance response is generated; most micron-sized holes in the sensor in a high-stress interval are closed, so that the elastic modulus of the sensor is increased, and the sensor can bear higher pressure stress.

Description

Technical Field

[0001] The present invention belongs to the field of flexible pressure sensors, and particularly relates to a low-cost, ultra-sensitive and highly stable pressure sensor based on amorphous powder / porous PDMS. Background Art

[0002] Flexible wearable electronic devices have generated great interest in various practical applications due to their excellent wearability, good flexibility and outstanding sensing performance. Flexible pressure sensors can effectively detect and collect biometric data, which is of great significance for the configuration of wearable electronic devices. Therefore, the development of flexible pressure sensors is a major focus of the current development of wearable electronic products. The pressure-sensitive performance of flexible pressure sensors can usually be evaluated by several basic characteristics such as durability / stability, response / recovery rate, detection response range and sensitive response, which also provides a reference for the functional design of the sensors. In fact, cyclic stability and sensitive response are two key factors affecting the performance of the sensors.

[0003] However, currently, commonly used sensors at home and abroad generally have problems such as high cost, low sensitivity and short service life. The present invention manufactures a low-cost flexible pressure sensor with ultra-high sensitivity and up to 1000 cycles of cyclic stability by blending amorphous powder with significant stress impedance effect into the PDMS matrix and constructing a porous structure by the sugar templating method. The sensor is expected to be applied in the field of wearable flexible sensors and plays an increasingly important role in monitoring and collecting biometric data, in human-machine interaction (HMI) systems, and in human motion monitoring. The sensor also has a certain degree of flexibility. Compared with traditional rigid strain sensors, flexible pressure sensors can withstand greater external strains. Compared with traditional keyboards, joysticks and touchpads, flexible pressure sensors can be integrated onto the human body surface, making it a very promising method for measuring motion on flexible and curved surfaces. Summary of the Invention

[0004] Aiming at the problems of low sensitivity and short service life in existing sensors, the present invention proposes a low-cost flexible pressure sensor with high stability and ultra-high sensitivity.

[0005] A low-cost flexible pressure sensor with ultra-high sensitivity and high stability, from outside to inside, sequentially includes a packaging layer, an electrode layer and a sensitive layer. Among them, the sensitive layer is composed of heat-treated amorphous powder FeCrMoSiB uniformly dispersed on porous PDMS.

[0006] Preferably, the packaging layer is polydimethylsiloxane.

[0007] Preferably, the electrode layer is copper foil with a thickness of 0.01 - 0.014 mm.

[0008] Preferably, the thickness of the sensitive layer is 0.4 to 0.5 mm.

[0009] Preferably, the preparation steps of the heat-treated amorphous powder FeCrMoSiB are as follows: Under vacuum conditions, the amorphous powder FeCrMoSiB is heat-treated at 550 °C for 30 min, then mixed with a coupling agent with a mass fraction of 2% and ground for 20 min, and then dried at 80 °C for 3 hours.

[0010] The preparation method of the above flexible pressure sensor includes the following steps:

[0011] (1) Heat treatment of the amorphous powder FeCrMoSiB

[0012] Under vacuum conditions, the amorphous powder FeCrMoSiB is heat-treated at 550 °C for 30 min, then mixed with a coupling agent with a mass fraction of 2% and thoroughly ground, and then dried at 80 °C for 3 hours;

[0013] (2) Preparation of the sensitive layer

[0014] Put 40 - 80 parts by mass of the heat-treated amorphous powder FeCrMoSiB, 20 - 60 parts of polydimethylsiloxane (PDMS), 2 - 6 parts of curing agent, and 400 parts of caster sugar into a container, add xylene, stir for 1 h to fully mix all components evenly; place it in a mold and cure. Then put the cured film into boiling water for 3 h to dissolve the caster sugar and xylene, and then ultrasonically remove the amorphous powder that is not firmly embedded in the PDMS matrix to improve its stability, thus obtaining the sensitive layer;

[0015] (3) Encapsulation

[0016] First, weld copper wires on the electrode layer, then put the electrode layer, sensitive layer, and electrode layer into the mold in sequence. Stir the PDMS and curing agent evenly according to a mass ratio of 10:1 and pour it into the above mold, cure it, and perform demolding after curing is completed to obtain the flexible piezomagnetic sensor.

[0017] Preferably, the coupling agent is isopropyl triisostearoyl titanate.

[0018] Preferably, grind for 20 min.

[0019] Preferably, the heat-treated amorphous powder FeCrMoSiB is 80 parts.

[0020] Preferably, in step (2), cure at 80 °C for 12 h.

[0021] Preferably, in step (3), cure at 65 °C for 6 h.

[0022] Compared with the prior art, the advantages and effects of the present invention are:

[0023] (1) Compared with the current sensors, the manufacturing process of the sensor of the present invention is simple, and the raw materials used (cotton candy, PDMS, Fe-Cr-Mo-Si-B-C amorphous micron powder) are inexpensive. The cost of the sensor is low and suitable for large-scale production. Its high performance meets the market demand, and its high cost performance conforms to the market law, having broad commercial prospects.

[0024] (2) The sensor in the present invention has extremely high sensitivity, with extremely high sensitivity (6.556 kPa -1 ) in the low stress range (0 - 25 kPa), and also has high sensitivity in the stress ranges (25 - 100 kPa) and (100 - 600 kPa), which are 0.769 kPa -1 and 0.026 kPa -1 respectively. The sensor of the present invention has extremely high sensitivity because there are a large number of micron-sized pores in it, and the heat-treated amorphous powder FeCrMoSiB distributed therein forms a certain conductive network. At low stress, a large number of micron-sized pores in the sensor will close, causing a change in the spatial arrangement of the heat-treated amorphous powder FeCrMoSiB, thereby changing the conductive network structure, causing changes in the resistance and magnetic properties of the thin film, and finally generating a large stress impedance response. In the high stress range, most of the micron-sized pores in the sensor close, resulting in an increase in its elastic modulus, enabling it to withstand higher compressive stress.

[0025] (3) The present invention uses the sugar template method to construct a porous structure in the PDMS matrix, improving the sensitivity and stability of the sensor. Moreover, the cotton candy used in the sugar template method has low cost, and the process of constructing the pores is simple.

[0026] (4) The sensor in the present invention has high cyclic stability and can still return to the initial state after repeatedly applying a pressure of 2 kPa for 1000 times. This is due to the high elastic modulus of the polydimethylsiloxane matrix and the high stability of the micron pore framework structure therein. Description of the Drawings

[0027] Figure 1 is the flow chart for preparing the amorphous powder / porous PDMS sensitive layer by the sugar template method.

[0028] Figure 2 is the cross-sectional scanning electron micrograph of the amorphous powder / porous PDMS sensitive layer described in Example 3.

[0029] Figure 3 is the impedance change trend of the flexible pressure sensor based on the amorphous powder / porous PDMS described in Example 3 when repeatedly applying a pressure of 2 kPa for 1000 times.

[0030] Figure 4 Sensitivity graph of the amorphous powder / porous PDMS flexible pressure sensor described in Example 3 in different stress ranges.

[0031] Figure 5 Physical diagram of the sensitive layer of amorphous powder / porous PDMS prepared by the sugar template method described in Example 3. Detailed implementation method

[0032] The present invention will be described in detail below.

[0033] Caster sugar plays a role in constructing a porous skeleton in the fabrication of this sensor. As Figure 1 shown, when the sensitive layer solidifies, sugar particles will form a certain sugar skeleton. By dissolving the sugar skeleton with boiling water, a porous structure is constructed in the sensitive layer.

[0034] Comparative Example 1

[0035] Preparation of an amorphous powder / PDMS flexible pressure sensor without a porous structure:

[0036] Step 1: Put commercially available Fe-Cr-Mo-Si-B micron amorphous powder into a thin round tube with an outer diameter of 20 mm, an inner diameter of 18 mm, a wall thickness of 1 mm, and a length of 16 cm. Then turn on the mechanical pump to evacuate for 5 minutes and perform processing and shrinkage sealing to isolate air. Then put it into a muffle furnace and heat-treat it at 550 °C for 30 minutes. Subsequently, mix the heat-treated amorphous powder with a coupling agent (titanium isopropyl triisostearate) with a mass fraction of 2% and grind it in an agate mortar for 20 minutes. Finally, put the ground amorphous powder into a constant-temperature blast drying oven and dry it at 80 °C for 3 hours.

[0037] Step 2: Add 80 parts by mass of amorphous powder, 20 parts of polydimethylsiloxane (PDMS), and 2 parts of curing agent to a beaker in sequence, and then stir with a magnetic stirrer for 1 h to fully mix all components evenly. Pour the evenly mixed mixture into a mold of 10 mm * 10 mm * 1 mm, then put it into a constant-temperature blast drying oven and cure it at 80 °C for 12 h. Then put the cured film into boiling water at 100 °C to dissolve the sugar particles and xylene. The whole dissolution process should last for 3 h. Finally, ultrasonically remove the amorphous powder that is not firmly embedded in the PDMS matrix to improve its stability.

[0038] Step 3: Select 0.14 mm copper foil as the upper and lower electrode layers of the sensor, and weld a 20 cm long copper wire on the copper foil with a temperature-adjustable soldering iron. Cut the copper foil, the non-porous sensitive layer, and the copper foil into a size of 1 cm * 1 cm and place them in the mold in sequence. Then, prepare PDMS and the curing agent in a ratio of 10:1, stir them in a magnetic stirrer for 1 h to make them fully mixed and uniform, and finally pour them into the mold and place them in a constant temperature blast drying oven for drying. The curing temperature is 65 °C, the curing time is 6 h, and demolding is carried out after curing is completed.

[0039] The performance of the sensor was tested by an impedance analyzer (LCR Meter IM3536 made by HIOKI) and an electronic universal tester (UTM4304GD made by SUNS), and the results are listed in Table 1.

[0040] Example 1

[0041] Preparation of an amorphous powder / porous PDMS flexible pressure sensor with 40 parts of amorphous powder added:

[0042] Step 1: Put commercially available Fe-Cr-Mo-Si-B micron amorphous powder into a thin round tube with an outer diameter of 20 mm, an inner diameter of 18 mm, a wall thickness of 1 mm, and a length of 16 cm. Then turn on the mechanical pump to evacuate for 5 min and then perform processing and compression sealing to isolate air. Then place it in a muffle furnace and heat-treat it at 550 °C for 30 min. Subsequently, mix the heat-treated amorphous powder with a coupling agent (isopropyl triisostearoyl titanate) with a mass fraction of 2% and grind it in an agate mortar for 20 min. Finally, put the ground amorphous powder into a constant temperature blast drying oven and dry it at 80 °C for 3 hours.

[0043] Step 2: Add 40 parts by mass of amorphous powder, 60 parts of polydimethylsiloxane (PDMS), 6 parts of curing agent, and 400 parts of granulated sugar (commercially available, Baizuan) to the beaker in sequence, then add xylene, and stir with a magnetic stirrer for 1 h to make each component fully mixed and uniform. Pour the uniformly mixed mixture into a mold of 10 mm * 10 mm * 1 mm, then place it in a constant temperature blast drying oven and cure it at 80 °C for 12 h. Then put the cured film into boiling water at 100 °C to dissolve the sugar particles and xylene. The whole dissolution process should last for 3 h. Finally, ultrasonically remove the amorphous powder that is not firmly embedded in the PDMS matrix to improve its stability.

[0044] Step 3: Select 0.14 mm copper foil as the upper and lower electrode layers of the sensor, and solder a 20 cm long copper wire on the copper foil with a temperature-adjustable soldering iron. Cut the copper foil, the non-porous sensitive layer, and the copper foil into a size of 1 cm * 1 cm and place them in the mold in sequence. Then, prepare PDMS and curing agent in a ratio of 10:1, stir them in a magnetic stirrer for 1 h to make them fully mixed and uniform, and finally pour them into the mold and place them in a constant-temperature forced-air drying oven for drying. The curing temperature is 65 °C, the curing time is 6 h, and demolding is carried out after curing is completed.

[0045] The performance of the sensor was tested by an impedance analyzer (LCR Meter IM3536 made by HIOKI) and an electronic universal tester (UTM4304GD made by SUNS), and the results are listed in Table 1.

[0046] Example 2

[0047] Preparation of an amorphous powder / porous PDMS flexible pressure sensor with 60 parts of amorphous powder added:

[0048] Other steps are the same as in Example 1, except that the mass fraction of the amorphous powder Fe-Cr-Mo-Si-B is changed from 40 parts to 60 parts, the mass fraction of polydimethylsiloxane (PDMS) is changed from 60 parts to 40 parts, the mass fraction of the curing agent is changed from 6 parts to 4 parts, and the number of parts of 400 parts of granulated sugar remains unchanged, to obtain the flexible pressure sensor. The performance of the sensor was tested by an impedance analyzer (LCR Meter IM3536 made by HIOKI) and an electronic universal tester (UTM4304GD made by SUNS), and the results are listed in Table 1.

[0049] Example 3

[0050] Preparation of an amorphous powder / porous PDMS flexible pressure sensor with 80 parts of amorphous powder added:

[0051] Other steps are the same as in Example 1, except that the mass fraction of the amorphous powder Fe-Cr-Mo-Si-B is changed from 40 parts to 80 parts, the mass fraction of polydimethylsiloxane (PDMS) is changed from 60 parts to 20 parts, the mass fraction of the curing agent is changed from 6 parts to 2 parts, and the number of parts of 400 parts of granulated sugar remains unchanged, to obtain the flexible pressure sensor. The performance of the sensor was tested by an impedance analyzer (LCR Meter IM3536 made by HIOKI) and an electronic universal tester (UTM4304GD made by SUNS), and the results are listed in Table 1.

[0052] The physical picture of the sensitive layer of the sensor prepared in this example is as Figure 5 shown, and the electron micrograph of the sensitive layer of the sensor is asFigure 2 As shown, it has a sponge-like porous structure, which is caused by the dissolution of the sugar skeleton, effectively changing the spatial arrangement of the amorphous powder in the polydimethylsiloxane (PDMS) matrix, enabling the conductive network constructed by the amorphous powder to undergo significant structural changes under a small external stress, thereby enhancing the impedance response sensitivity of the sensor. Figure 3 Figure [3] shows the impedance change trend of the amorphous powder / porous PDMS flexible pressure sensor when a pressure of 2 kPa is repeatedly applied 1000 times. It can be seen that the impedance ratio of the sensor can still return to the initial state after the pressure of 2 kPa is repeatedly applied 1000 times, demonstrating that the sensor has good cyclic stability. As Figure 4 shown, the sensor has extremely high sensitivity of 6.556 kPa in the low stress range of 0 - 25 kPa -1 , and also has high sensitivities of 0.769 kPa -1 , 0.026 kPa -1 in the stress ranges of 25 - 100 kPa and 100 - 600 kPa respectively.

[0053] Table 1

[0054] Serial number Highest sensitivity Sensing range Comparative example 1 <![CDATA[0.005 kPa -1 > 0 - 35 MPa Example 1 <![CDATA[3.1025 kPa -1 > 0 - 0.6 MPa Example 2 <![CDATA[3.1801 kPa -1 > 0 - 0.6 MPa Example 3 <![CDATA[3.9575 kPa -1 > 0 - 0.6 MPa . It should be noted that there may be some inaccuracies in the original text. For example, in the description of impedance values, the units seem to be incomplete or incorrect. You may need to check and correct the original text for a more accurate translation.

Claims

1. A low-cost flexible pressure sensor with ultra-high sensitivity and high stability, Characterized in that, From the outside to the inside, it successively includes a packaging layer, an electrode layer and a sensitive layer, wherein the sensitive layer is composed of heat-treated amorphous powder FeCrMoSiB uniformly dispersed on porous PDMS.

2. The flexible pressure sensor according to claim 1, Characterized in that, The packaging layer is polydimethylsiloxane.

3. The flexible pressure sensor according to claim 1, Characterized in that, The electrode layer is a copper foil with a thickness of 0.01 - 0.014 mm.

4. The flexible pressure sensor according to claim 1, Characterized in that, The thickness of the sensitive layer is 0.4 - 0.5 mm.

5. The flexible pressure sensor according to claim 1, Characterized in that, The preparation steps of the heat-treated amorphous powder FeCrMoSiB are as follows: Under vacuum conditions, the amorphous powder FeCrMoSiB is heat-treated at 550 °C for 30 min, then mixed with a coupling agent with a mass fraction of 2% and ground for 20 min, and then dried at 80 °C for 3 hours.

6. The preparation method of the flexible pressure sensor according to any one of claims 1 - 5, Characterized in that, It includes the following steps: (1) Heat treatment of amorphous powder FeCrMoSiB Under vacuum conditions, the amorphous powder FeCrMoSiB is heat-treated at 550 °C for 30 min, then mixed with a coupling agent with a mass fraction of 2% and thoroughly ground, and then dried at 80 °C for 3 hours; (2) Preparation of the sensitive layer Put 40 - 80 parts by mass of the heat-treated amorphous powder FeCrMoSiB, 20 - 60 parts of PDMS, 2 - 6 parts of curing agent, and 400 parts of caster sugar into a container, add xylene, stir for 1 h to make each component fully mixed and uniform; place it in a mold, cure, and then put the cured film into boiling water for 3 h to dissolve the caster sugar and xylene, and then ultrasonically remove the amorphous powder that is not firmly embedded in the PDMS matrix to improve its stability, thus obtaining the sensitive layer; (3) Packaging First, weld copper wires on the electrode layer, successively put the electrode layer, the sensitive layer, and the electrode layer into a mold, stir PDMS and the curing agent evenly according to a mass ratio of 10:1, then pour it into the above mold, cure, and after curing is completed, demold to obtain the flexible piezomagnetic sensor.

7. The method according to claim 6, Characterized in that, The coupling agent is isopropyl triisostearoyl titanate.

8. The method according to claim 6, Characterized in that, The heat-treated amorphous powder FeCrMoSiB is 80 parts.

9. The method according to claim 6, Characterized in that, In step (2), cure at 80 °C for 12 h.

10. The method according to claim 6, Characterized in that, In step (3), cure at 65 °C for 6 h.

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