AU2017101883A4

AU2017101883A4 - Flexible electronic pressure sensing device and preparation method therefor

Info

Publication number: AU2017101883A4
Application number: AU2017101883A
Authority: AU
Inventors: Jing Chen; Qinwu GAO; Hui Li; Lei Wang
Original assignee: Shenzhen Institute of Advanced Technology of CAS
Current assignee: Shenzhen Institute of Advanced Technology of CAS
Priority date: 2017-12-20
Filing date: 2017-12-20
Publication date: 2020-08-06
Anticipated expiration: 2025-12-20

Abstract

WO 2019/119286 PCT/CN2017/117390 ABSTRACT A flexible electronic pressure sensing device and fabrication method. The flexible electronic pressure sensing device comprises a flexible housing (1). The flexible housing (1) has an internal cavity (10). The internal cavity (10) comprises paralleled microchannels (101), which and are connected by two perpendicular microchannels at both ends (102). Conductive liquid metal (3) is embedded in the internal cavity (10). The flexible housing (1) is connected to at least two electrodes (2) contact with conductive the liquid metal in the microchannels(3). The fabrication method can be used for preparing the flexible electronic pressure sensing device, which is capable of measuring pressure while being completely conformal to three-dimensional complex static/dynamic surfaces. 1

Description

A flexible electronic pressure sensor and its fabrication method

TECHNICAL FIELD

[0001] This invention falls in the field of fabrication and packaging technologies of electronic pressure sensors; in particular, it relates to a flexible electronic pressure sensor and its fabrication method.

BACKGROUND

[0002] As people pay increasing attention to their health conditions, wearable devices

capable of collecting physiological parameters and analyzing states of motion in real-time are getting more popular. The sensor system, as one of the core components of the wearable devices, hinders the further development of wearable devices due to its insufficient flexibility. In the fields of real-time health monitoring, implanted medical device, smart home and skin electronic devices, flexible electronic devices with high performances are urgently needed. Most pressure sensors now in the market are made of inorganic materials, such as silicon. Due to lack of flexibility, once the sensors are deformed by stretching or bending, they will be disabled due to hardware structure damage. In the process of signal acquisition, the sensors have low sensitivity, making it susceptible to the interference of physiological noises such as breath and muscular contraction, and thus, unable to collect complete and legible data.

[0003] With the popularisation of intelligent terminals, intelligent life will be associated with our daily activities. Wearable electronic devices hold a huge market prospect. Almost all major companies of consumer electronics launched their wearable products, such as Apple Watch, Microsoft Bend, Huawei Watch, etc. In just a few years, all sorts of wearable devices emerged and their functions include pedometer, calorie consumption, dietary habit, sleep monitoring, chronic disease warning, electronic tattoo and retinal implant and so on. These devices greatly enriched our life. However, the current sensor technology applied in wearable devices is normally based on a rigid substrate, and the sensor must be embedded in the rigid package. The mechanical mismatch between the rigid sensor and complex 3-D skin surface of human impairs the user experience and results of measurements.

[0004] Currently, the flexible sensors are mainly fabricated using the following methods.

[0005] 1. Fabricate a high-density tactile sensor array using vertically-oriented zinc oxide

(ZnO) nanowire. Under tensile conditions, the zinc oxide nanowire will produce a piezoelectric effect, and the piezoelectric current will be used as grid electrical signal. Only two terminal electrodes are needed to make a skin sensor with detection sensitivity.

[0006] 2. A thin film is made of elastic and low-modulus hollow sphere polypyrrole polymer generated from heterogeneous reaction. The contact area between the thin film and the electrodes varies with the force, allowing the sensor to detect loads of various magnitudes.

[0007] 3. By structural and shape design, traditional inorganic materials such as metal and silicon can be used to make flexible and elastic conducting elements with a 3D "wave" structure. Thus, the traditional inorganic conducting materials could be extended and deformed with the extension of the flexible substrate without rupturing.

[0008] 4. Using PDMS and carbon nano tube (CNT), a small piezoresistive and interlocking arched structure array is formed. An electronic skin capable of perceiving pressure method is developed. Such sensors have a high sensitivity, and can even detect the direction and intensity of airflow.

[0009] 5. Piezoresistive rubber is used to fabricate a pressure sensor array based on the piezoresistive principle. The scattered circular sensor units are positioned on the flexible PET thin film, and silver is used to make the electrodes of the sensors. Due to the flexibility of the materials, the sensor array also becomes flexible.

[0010] Although the above-mentioned strain sensor possesses certain flexibility, it could not be stretched, bent or twisted at will. It lacks the flexibility of skin, and could not perfectly fit the 3D and complex static/dynamic surface while measuring the contact pressure. Even when it is integrated into the wearable devices, the mechanical mismatch between it and the human skin surface impairs the user experience. In addition, the limitations in structural design and packaging technology force us to make a trade-off between accuracy and sensitivity. It is very susceptible to interference by the physiological signals of the human body. The fabrication technology and skills of flexible sensors using carbon nano tubes and graphene remain immature, and they also face problems such as poor tolerance of high temperature, poor range of applications and service life. Summary of the Invention

Technical Issues

[0011] This invention aims at overcoming the defects of the prior art. It provides a flexible electronic pressure sensor and its fabrication method. The pressure sensor hereof possesses good stability, accuracy and precision, as well as reliability.

Solutions Technical Solutions

[0012] The technical scheme of this invention is: a flexible electronic pressure sensor, including flexible casing; the said flexible casing has an internal cavity; the said internal cavity includes multiple array channels and connecting cavity of the same end face connecting multiple said array channels; there is a liquid metal conductor in the said internal cavity and the said flexible casing has at least two electrodes linking to the said liquid metal conductor.

[0013] Optionally, the said flexible casing is made of degradable polyester material or silicone rubber material.

[0014] Optionally, liquid conductor eutectic gallium-indium is arranged in the said internal cavity.

[0015] Optionally, the said flexible casing includes the first flexible substrate and the second flexible substrate in the said internal cavity generated via involutory connection. Bulges or/and recesses conducive for the formation of the said array channel are arranged in the said first flexible substrate; the said connecting cavity is arranged in the said second flexible substrate.

[0016] This invention provides a wearable device, and the wearable device possesses the aforesaid flexible electronic pressure sensor.

[0017] This invention also provides the fabrication method of a flexible electronic pressure sensor, including the following steps:

[0018] Fabricate the flexible casing with an internal cavity, and the said internal cavity shall include multiple array channels and connecting cavities linking multiple said array channels; inject liquid metal conductor in the said internal cavity, and plug at least two electrodes on the said flexible casing, and make the said electrodes contact with the said liquid metal conductor.

[0019] Optionally, fabrication of the said flexible casing includes the following steps:

[0020] Fabricate the first mould, the second mould and the flexible material solution. Mix the flexible material solution and remove the air bubbles;

[0021] Add the said flexible material solution with air bubbles removed into the first mould to form the first flexible substrate with multiple array channels;

[0022] Add the flexible material solution with air bubbles removed into the second mould to form the second flexible substrate with connecting cavities;

[0023] Press the said first flexible substrate on the said second flexible substrate which is not solidified yet to make the first flexible substrate and the second flexible substrate connected and form the flexible casing; at the same time, link the multiple array channels and connecting cavities to form an enclosed internal cavity.

[0024] Optionally, inject the liquid metal conductor into the said internal cavity, which includes the following steps:

[0025] Insert two syringes on both sides of the said internal cavity, with one syringe containing liquid metal conductor and the other sucking out the air inside the said internal cavity. The syringe containing liquid metal conductor can then inject the liquid metal conductor inside the said internal cavity and fill the internal cavity with the liquid metal conductor, then draw out the syringes.

[0026] Optionally, plug electrodes on both sides of the said internal cavity, which includes the following steps:

[0027] Plug the two electrodes on both sides of the said internal cavity respectively, and seal the internal cavity with semi-solidified flexible material.

[0028] Optionally, mix the solution of flexible material and remove the air bubbles, which include the following steps:

[0029] Put the Ecoflex series silicone rubber solution in the container of the centrifugal mixer. The revolving speed of the said centrifugal mixer shall be set at 300-400rpm for 10-15s and then raise it to 1400-1600rpm for 25-30s to get the mixed silicone rubber solution;

[0030] Add the mixed silicone rubber solution into the vacuum suction filter, and turn on the vacuum pump of the said vacuum suction filter to get the silicone rubber solution with air bubbles removed;

[0031] Forming the first flexible substrate includes the following steps:

[0032] Spray at least one layer of release agent on the said first mould, and then fill the profiled cavity of the said first mould with the silicone rubber solution with air bubbles removed using a pipette;

[0033] Put the said first mould into an oven and bake it under 80°C for 45-60min; after de-molding, the first flexible substrate with multiple array channels will be acquired;

[0034] Spray at least one layer of release agent on the surface of the said second mould, and fill the profiled cavity of the said second mould with silicone rubber solution with air bubbles removed using a pipette, and then assemble the mould;

[0035] Open the mould after the silicone rubber solution in the profiled cavity of the said second mould becomes semi-solidified and forms the second flexible substrate; and then press the first flexible substrate on the second flexible substrate, making the said first flexible substrate and the said second flexible substrate to form the connecting cavities, and the connecting cavities of the same end face with multiple said array channels via involutory connection. Beneficial Effects of the Invention

Beneficial Effects

[0036] This invention provides a flexible electronic pressure sensor and its fabrication method. The flexible electronic pressure sensor has high flexibility, good stretchability, simple geometry and thin structure, which get rid of the constraints of physical parts and allow it to fit the skin perfectly, and thus, realise measurement at any position, even joints where the deformation could be huge. Besides, when in use, this sensor mainly collects the signal of resistance variation of the liquid conductor caused by deformation of enclosed micro-array channels. The sensor has high sensitivity and strong interference resistance. It can be stretched, bent and twisted at will, making it especially suitable for the wearable devices, in particular, situations with great deformation. It can perfectly fit three-dimensional and complex static/dynamic surfaces while measuring the contact pressure with high stability, precision, accuracy and reliability. This sensor is not susceptible to interference of human body's physiological signals, and its internal cavity is enclosed, making it resistant to high temperature and giving it a wide range of applications and long service life. BRIEF DESCRIPTION OF FIGURES

Description of Figures

[0037] To better illustrate the technical scheme in this embodiment of the invention, accompanying figures required in the embodiment are briefly introduced below. Obviously, accompanying figures described below are only some embodiments of the invention. To those of ordinary skills in the art, other accompanying figures can be obtained on the basis of these figures without creative work.

[0038] Fig. 1 is a diagrammatic cross-section of the flexible electronic pressure sensor provided in this embodiment of the invention;

[0039] Fig. 2 is a diagrammatic cross-section of the flexible casing to the flexible electronic pressure sensor provided in this embodiment of the invention;

[0040] Fig. 3 is a plan sketch of the flexible electronic pressure sensor with a circular flexible casing provided in this embodiment of the invention;

[0041] Fig. 4 is a plan sketch of the flexible electronic pressure sensor with a rectangular flexible casing provided in this embodiment of the invention;

[0042] Fig. 5 is a plan sketch of the silicone rubber solution preparation in the fabrication of a flexible electronic pressure sensor provided in this embodiment of the invention;

[0043] Fig. 6 is a plan sketch of the mixing of silicone rubber solution in the fabrication of the flexible electronic pressure sensor provided in this embodiment of the invention;

[0044] Fig. 7 is a plan sketch of the flexible electronic pressure sensor provided in this embodiment of the invention after air bubbles in the silicone rubber solution are removed;

[0045] Fig. 8 is a plan sketch of the fabrication method of a flexible electronic pressure sensor provided in this embodiment of the invention when filling silicone rubber solution in the first mould;

[0046] Fig. 9 is a plan sketch of the first mould of the flexible electronic pressure sensor provided in this embodiment of the invention after it is filled with silicone rubber solution and baked;

[0047] Fig. 10 is a plan sketch of the second mould in the fabrication of the flexible electronic pressure sensor provided in this embodiment of the invention after it is filled with silicone rubber solution and assembled;

[0048] Fig. 11 is a plan sketch of thefirst flexible substrate and the second flexible substrate in the fabrication of a flexible electronic pressure sensor provided in this embodiment of the invention when they are pressed fit;

[0049] Fig. 12 is a profile of the flexible electronic pressure sensor obtained using the fabrication method of the flexible electronic pressure sensor provided in this embodiment of the invention. DETAILED DESCRIPTION

Embodiment of the invention

[0050] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention is further described in detail below with reference to the accompanying figures and embodiments. It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention; it is not intended to limit the present invention.

[0051] It should be noted that when one component is "fixed on" or "arranged on" another component, it can be directly attached to another component, or there can be a middleware. When one component is "connected to" another component, it could be directly linked to another component, or there can be a middleware.

[0052] It should also be noted that the terms used in this embodiment of the invention to represent orientations, such as left, right, upper and lower are only relative concepts or refer to the normal service condition of the product, they shall not be deemed as restrictive.

[0053] As shown in Fig. 1 and Fig. 2, this embodiment of the invention provides a flexible electronic pressure sensor, including flexible casing 1. Flexible casing 1 can be made of silicone rubber material (such as the Ecoflex series). The said flexible casing 1 has an internal cavity in which its length and cross section can deform when there is an external force. The internal cavity 10 is an enclosed cavity. Inside the said internal cavity 10, there is a liquid metal conductor 3, which will fill up the internal cavity 10. The said internal cavity 10 has multiple array channels (micro-array channels) 101 and connecting cavities 102 linking the same end face of multiple said array channels 101. The array channels 101 can be aligned horizontally or longitudinally with a uniform interval, or, they can be crisscrossed (i.e. it forms a cross). Certainly, the array channels 101 can also be formed by the column cavity or hemisphere cavity of matrix arrangement. At least two electrodes 2 connecting to the said liquid metal conductor will be fixed at both ends of the flexible casing 1. The ends of electrodes 2 will make contact with liquid metal conductor 3 inside the internal cavity 10. When in use, the external load will alter the shape (length and cross section) of the internal cavity 10, and thus changes the resistance of the liquid metal conductor 3. The electrodes 2 on both ends can connect with amplifying module or constant current supply module; add a constant current supply on electrodes 2 on both ends. The resistance signal from the liquid metal conductor 3 will be converted to a voltage signal which can be easily measured, and strain values can be obtained after analyzing the voltage signal. When in use, this sensor mainly collects the signal of resistance variation of the liquid metal conductor 3 in the internal cavity 10, it has a high sensitivity, stretchability and thin structure, allowing it to integrate with any flexible actuator. This sensor has high sensitivity and strong interference resistance, and can work normally when the strain of this flexible sensor reaches 300%. It can be stretched, bent and twisted at will, making it especially suitable for the wearable devices, in particular, situations with great deformation. It can perfectly fit three-dimensional and complex static/dynamic surfaces while measuring the contact pressure with high stability, precision, accuracy and reliability. This sensor is not susceptible to interference of human body's physiological signals, and its internal cavity 10 is enclosed, making it resistant to high temperature and giving it a wide range of applications and long service life.

[0054] Optionally, each flexible casing 1 can have one or at least two internal cavities 10, with two or at least two electrodes 2 arranged in each internal cavity 10.

[0055] Optionally, the height of both the array channel 101 and the connecting cavity 102 can be smaller than 1mm.

[0056] Optionally, the overall height of the internal cavity 10 can be smaller than 1mm.

[0057] Optionally, the thickness of the flexible electronic pressure sensor can be smaller than 1mm, i.e. the thickness of the flexible casing 1 can be smaller than 1mm, making it very suitable to be applied in smart wearable devices. The flexible casing 1 can be flat. As shown in Fig 3 and Fig. 4, the shape of the flexible casing 1 can be polygonal (such as rectangular), circular and abnormally shaped.

[0058] Optionally, the said flexible casing 1 is made of degradable polyester material or silicone rubber material. In this embodiment, the flexible casing 1 uses the Ecoflex series silicone rubber material as the basic material. In specific applications, Ecoflex manufactured by BASF company of Germany can be used, its monomers are adipic acid, terephthalic acid and 1, 4-butanediol.

[0059] Optionally, liquid conductor eutectic gallium-indium is added in the said internal cavity 10 as the liquid metal conductor. Of course, other liquid metal conductors can also be used. Electrodes 2 can be inserted into the front end of the internal cavity 10 to contact with the liquid metal conductor 3 inside from the two ends in the lengthwise direction of the flexible casing 1 or the two ends of the internal cavity 10. The electrodes 2 and the flexible casing 1 can be sealed with sealing material to further improve its reliability. The sealing material can be silicone rubber solution material (Ecoflex).

[0060] Optionally, the said flexible casing 1 includes the first flexible substrate 11 and the second flexible substrate 12 formed via involutory connection in the said internal cavity. Inside the said first flexible substrate 11, there is a bulge or/and recess conducive for the formation of the said array channel 101; there is a connecting cavity 102 in the second flexible substrate 12 and the said connecting cavity 102 is fixed on the upper end of the second flexible substrate 12. Once the first flexible substrate 11 and the second flexible substrate 12 involute (sealed bonding), an enclosed internal cavity 10 can be formed by connecting the array channel 101 and the connecting cavity 102. The first flexible substrate 11 and the second flexible substrate 12 can be spliced together to form a flexible casing 1 with an internal cavity 10

[0061] Optionally, multiple columnar bumps aligned in matrix can be formed in the first flexible substrate 11, and the intervals between various columnar bumps can form the array channel 101. Or, multiple depressions aligned in a matrix can be formed in the first flexible substrate 11, and these depressions can connect to form the array channel 101. It is understood that the array channel 101 can be formed in different ways.

[0062] In tensile experiment of this flexible electronic pressure sensor, it shows high sensitivity, and the signals collected show good linearity and repeatability. It has high stability, precision, accuracy and reliability. The sensor can work normally when the strain reaches 300%. It can attach to complex and three-dimensional dynamic and static curved surfaces, such as human joints with great deformation (elbow joint, knee joint), and shows a good skin affinity. The sensing device has almost no effect on normal work and study of the users. It is thus an ideal flexible sensor for wearable devices.

[0063] This invention also provides a wearable device. Said wearable device is equipped with the aforesaid flexible electronic pressure sensor. The wearable device can be a smartwatch, smart bracelet, smart glasses, smart clothing, VR helmet, etc. By adopting the flexible electronic pressure sensor, its thickness is smaller than 1mm and shows an excellent elasticity. It can work normally when its tensile strain reaches 300%; it is comparable to human skin. Besides, a biocompatible material, Ecoflex is used as the basic material. It thus causes no discomfort to the users when integrated into wearable devices. Further, the sensor collects resistance signals from the enclosed interval cavity 10, and thus eliminates the interference of outside noise. The data collected is more accurate. The internal cavity 10 fabricated with photo etching technique greatly improves the sensitivity of the sensor. Certainly, the flexible electronic pressure sensor provided in this embodiment of the invention can be applied in other devices; it also belongs to the scope of protection of the invention.

[0064] This embodiment of the invention also provides the fabrication method of a flexible electronic pressure sensor. As shown in Fig. 5 to Fig. 12, it includes the following steps:

[0065] Prepare flexible casing 1 with an enclosed internal cavity 10, said internal cavity 10 includes multiple array channels 101 and multiple connecting cavities 102 on the same end face connecting the multiple said array channels 101. Inject liquid metal conductor 3 into said internal cavity 10 and plug electrodes 2 on both ends of said flexible casing 1. Liquid metal conductor 3 can fill up the entire internal cavity 10, and the ends of electrodes 2 will contact with liquid metal conductor 3.

[0066] Specifically, the preparation of the said flexible casing 1 includes the following steps:

[0067] Prepare the first mould 41, the second mould 42 and the flexible material solution; mix the flexible material solution and remove the air bubbles;

[0068] Add the said flexible material solution with air bubbles removed into the first mould 41 to form the first flexible substrate 11 with multiple array channels 101;

[0069] Add the flexible material solution with air bubbles removed into the second mould 42 to form the semi-solidified second flexible substrate 12 with connecting cavities 102;

[0070] Press said first flexible substrate 11 on the said second flexible substrate (second flexible substrate 12) which is not fully solidified yet, and thus form flexible casing 1 with the first flexible substrate 11 and the second flexible substrate 12 linking together; at the same time, connect multiple array channels 101 with the connecting cavities 102 to form an enclosed internal cavity 10;

[0071] Specifically, injecting liquid metal conductor 3 into said internal cavity 10 includes the following steps:

[0072] Insert two syringes on both sides of the said internal cavity 10, with one syringe containing liquid metal conductor 3 and the other sucking out air inside the said internal cavity 10. The syringe containing liquid metal conductor 3 can then inject the liquid metal conductor 3 into the said internal cavity 10 and fill the internal cavity 10 with the liquid metal conductor 3, then draw out the syringes.

[0073] Specifically, inserting electrodes 2 on both ends of said flexible casing 1 (internal cavity 10) includes the following steps:

[0074] Insert the two electrodes 2 on the opposite sides of said internal cavity 10, and use the same semi-solidified flexible material to seal the electrodes 2 and the flexible casing 1.

[0075] Specifically, mixing the flexible material solution and removing the air bubbles include the following steps:

[0076] Put the Ecoflex series silicone rubber solution in the container of the centrifugal mixer. The revolving speed of the said centrifugal mixer shall be set at 300-400rpm for 10-15s and then raise it to 1400-1600rpm for 25-30s to get the mixed silicone rubber solution;

[0077] Add the mixed silicone rubber solution into the vacuum suction filter, and turn on the vacuum pump of the said vacuum suction filter to get the silicone rubber solution with air bubbles removed; it can be appreciated that the flexible material solution is not limited to silicone rubber solution.

[0078] Forming the first flexible substrate 11 includes the following steps:

[0079] Spray at least one layer of release agent (ease release 200 release agent) on the surface of said first mould 41, and then fill the profiled cavity of the said first mould 41 with the silicone rubber solution with air bubbles removed using a pipette;

[0080] Transfer the first mould 41 with its profiled cavity filled with silicone rubber solution without air bubbles to an oven, and bake it under 80°C for 45-60min (e.g. 46-59min). Remove the mould to get the first flexible substrate 11;

[0081] Forming the second flexible substrate 12 includes the following steps:

[0082] The second mould 42 includes an upper mould 421 and a lower mould 422. Spray at least one layer of release agent on the surface of the profiled cavity of the lower mould 422 of said second mould 42. Fill the profiled cavity of the lower mould 422 of said second mould 42 with silicone rubber solution without air bubbles using a pipette, and then assemble the upper mould 421 and the lower mould 422;

[0083] When the silicone rubber solution in the profiled cavity of said second mould 42 becomes semi-solidified and forms the second flexible substrate 12, open the mould (remove the upper mould 421) and press the first flexible substrate 11 on the second flexible substrate 12. After the first flexible substrate 11 and the second flexible substrate 12 perfectly seal together, let it stand under room temperature for 45-60min to allow said first flexible substrate 11 and said second flexible substrate 12 to bond and become the flexible casing 1, and form the internal cavity 10.

[0084] In specific applications, the following flow can be used as a reference:

[0085] Prepare the first mould 41 via photoetching (using SU-8 photoresist); liquid metal conductor eutectic gallium-indium (EGaln); Ecoflex series materials with a high flexibility and ease release 200 release agent. Specifically, it includes the following steps:

[0086] Step 1: as shown in Fig. 5 and Fig. 6, take Ecoflex 1A and B with equal mass, and put them in the container of the centrifugal mixer to fully and uniformly mix the silicone rubbers. The revolving speed of the said centrifugal mixer shall be set at 300-400rpm for 10-15s (12-14s) and then raise it to 1400-1600rpm for 25-30s.

[0087] Step 2: as shown in Fig. 6 and Fig. 7, add the mixed silicone rubber solution into the vacuum suction filter, and turn on the vacuum pump of the said vacuum suction filter to remove all air bubbles in the solution.

[0088] Step 3: as shown in Fig. 8, spray a layer of release agent on the surface of the first mould 41, and fill the profiled cavity of the mould with the silicone rubber solution obtained in Step 2 using a pipette.

[0089] Step 4: move the first mould 41 filled with silicone rubber solution in Step 3 to an oven, and bake it under 80°C for 45-60min to get the first flexible substrate 11, as shown in Fig. 9.

[0090] Step 5: spray a layer of release agent on the surface of the profiled cavity of second mould 42, fill the profiled cavity of the lower mould 422 using a pipette and assemble the upper mould 421 and the lower mould 422, as shown in Fig. 10.

[0091] Step 6: when the second flexible substrate 12 produced in Step 5 becomes semi-solidified, gently press the demoulded first flexible substrate 11 on the second flexible substrate 12. After they perfectly seal together, let them stand under room temperature for 45-60min to get the flexible casing 1, as shown in Fig. 11. Take the lower mould 422 out of the flexible casing 1.

[0092] Step 7: insert two micro-syringes on two opposite sides of the flexible casing 1 and probe into the two ends of the internal cavity 10, with one syringe suck out the air inside the internal cavity 10 and guide the liquid conductor EGaIn. The other syringe continuously injecting the liquid conductor (EGaIn) into the internal cavity 10. It is also acceptable to vacuum the internal cavity 10 first, and then inject the liquid conductor into the internal cavity 10. When the entire internal cavity 10 is filled with the liquid conductor (EGaIn), insert the electrodes 2 and take a small quantity of silicone rubber solution (obtained in Step 2) to seal the ends (intervals between the electrodes 2 and the sidewalls of the flexible casing 1), and obtain the flexible and stretchable electronic strain sensor, as shown in Fig. 12. This preparation method is simple and can realise volume production, and thus improves the time and cost-effectiveness. It is particularly suitable for the field of wearable devices, especially situations with great deformations.

[0093] This embodiment of the invention provides a flexible electronic pressure sensor and its fabrication method. The strain sensor uses highly flexible Ecoflex material as the basic material. This flexible electronic pressure sensor is extremely thin and its thickness can be smaller than 1mm, and it shows outstanding flexibility and elasticity. It can work normally when the tensile strain reaches 300% and can be integrated into almost all complex 3D surfaces. Besides, the dimensions (both height and width of the cross-section can be smaller than 1mm) of the micro-array channel 101 are small. Thus, even a minute pressure will lead to deformation of the micro-array, and thus resistance variation. Meanwhile, the signals of resistance variation collected come from the liquid conductor sealed inside the micro-array, giving this pressure sensor relatively high sensitivity and anti-noise capabilities. This invention uses biocompatible materials, making it especially suitable to be integrated into wearable electronics contacting skin surfaces. This preparation method is simple and can realise volume production, and thus improves the time and cost-effectiveness. In the pressure test, the flexible electronic pressure sensor provided in this embodiment of the invention shows high sensitivity, and the signals collected demonstrate good repeatability on the graphs, the measurements are quite accurate. It can easily fit human's 3D skin surfaces without causing any discomfort; it can measure pressures even at the knee joint where the deformation can be huge. It has a good skin affinity, and causes almost no effect on normal work and study of the users. It is an ideal flexible sensor for wearable devices

[0094] The above description is only an embodiment of the present invention; it is not intended to limit the scope of the invention. Any modifications, equivalent substitutions or improvements with the spirit and principle of this invention shall be included in the scope of protection of the invention.

Claims

Patent Claims

[Claim 1] A flexible electronic pressure sensor, comprising a flexible casing, wherein the said flexible casing has an internal cavity; the internal cavity comprises a plurality of array channels and a connecting cavity that communicates with the plurality of array channels; a liquid metal conductor is provided in the internal cavity; and the flexible casing is connected with at least two electrodes which are in connection with a liquid conductor or a semi-liquid conductor.
[Claim 2] The flexible electronic pressure sensor as in Claim 1, wherein said flexible casing comprises a first flexible substrate and a second flexible substrate connected in an assembled way to form the internal cavity; bulges or/and recesses for forming the array channels are formed on the inner wall of the first flexible substrate; and the connecting cavity is formed at the second flexible substrate.
[Claim 3] The flexible electronic pressure sensor as in Claim 1 or Claim 2, wherein the flexible casing is made of biodegradable polyester or silicone rubber.
[Claim 4] The flexible electronic pressure sensor as in Claim 1 or Claim 2, wherein liquid metal conductor eutectic gallium-indium is provided in the internal cavity.
[Claim 5] A wearable device, wherein the wearable device has the flexible electronic pressure sensor according to any one of Claims 1-4.
[Claim 6] A fabrication method of a flexible electronic pressure sensor, comprising the following steps: fabricating a flexible casing with an internal cavity, the internal cavity comprising a plurality of array channels and a connecting cavity that communicates with the plurality of array channels; injecting a liquid metal conductor into the internal cavity, and inserting at least two electrodes in the flexible casing in such a way that the electrodes contact the liquid metal conductor.
[Claim 7] The fabrication method of a flexible electronic pressure sensor as in Claim 6, wherein fabricating the flexible casing comprises the following steps: fabricating a first mould, a second mould and a flexible material solution, stirring the flexible material solution, and removing air bubbles; adding the stirred flexible material without air bubbles into the first mould to form the first flexible substrate with a plurality of array channels; adding the stirred flexible material without air bubbles into the first mould to form the second flexible substrate with the accommodating cavity; pressing the first flexible substrate on the incompletely solidified second flexible substrate so that the first flexible substrate and the second flexible substrate are integrally connected to form the flexible casing, and at the same time, the plurality of array channels and the connecting cavity form an enclosed internal cavity.
[Claim 8] The fabricating method of a flexible electronic pressure sensor as in Claim 7, wherein injecting the liquid metal conductor into the internal cavity comprises the following steps: inserting two syringes at the two ends of the internal cavity, wherein one syringe contains the liquid metal conductor inside and the other extracts the air in the internal cavity; injecting liquid metal conductor into the internal cavity using the syringe with the liquid metal conductor so that the internal cavity is full of the liquid metal conductor; and removing the syringes.
[Claim 9] The fabrication method of a flexible electronic pressure sensor as in Claim 6, wherein inserting two electrodes at the two ends in the internal cavity comprises the following steps: respectively inserting the two electrodes at the two ends in the internal cavity, and sealing the electrodes and the flexible casing using the same semi-solidified flexible material.
[Claim 10] The fabrication method of a flexible electronic pressure sensor as in Claim 7, wherein stirring the flexible material solution and removing air bubbles comprises the following steps: putting Ecofex series silicone rubber solution in an container of a centrifugal mixer, letting the centrifugal mixer work at a revolving speed of 300-400 rpm for 10-15 s and subsequently work at a revolving speed of 1,400-1,600 rpm for 25-30 s to obtain the mixed silicone rubber solution; placing the mixed silicone rubber solution in a vacuum filtration device, and starting the vacuum pump of the vacuum filtration device to obtain a silicone rubber solution without air bubbles;

Forming the first flexible substrate includes the following steps: spraying at least one layer of release agent onto the surface of the first mould, then injecting the silicone rubber solution without air bubbles into profiled cavity of the first mould using a pipette; moving the first mould into an oven, baking at 80 °C for 45-60 min, and releasing the mould to obtain the first flexible substrate with a plurality of array channels; filling the silicone rubber solution without air bubbles into a profiled cavity of the second mould using the pipette, then closing the second mould; opening the second mould after the silicone solution in the profiled cavity of the second mould is semi-solidified to form the second flexible substrate, then pressing the first flexible substrate onto the second flexible substrate so that the first flexible substrate and the second flexible substrate are connected in an assembled way to form a connecting cavity that communicates with the same end faces of a plurality of array channels.