A flexible sensor based on flexoelectric effect and electronic device

Abstract

The present disclosure provides a flexible sensor based on flexoelectric effect and an electronic device, the flexible sensor comprising a lower electrode layer, a flexoelectric layer and an upper electrode layer arranged in sequence; wherein the flexoelectric layer comprises a layered residual layer and a truncated cone array structure arranged on the surface of the layered residual layer, and the flexoelectric layer comprises a polyvinylidene fluoride material. The flexible sensor of the present disclosure can effectively improve the sensitivity and electrical performance, efficiently and stably output, meet the size design requirements of micro devices, and reduce the production cost.

Description

TECHNICAL FIELD

[0001] The present disclosure generally relates to the technical field of flexible electronic devices, and in particular, to a flexible sensor based on flexoelectric effect and an electronic device. BACKGROUND

[0002] With the continuous development and progress of science and technology, flexible sensors can be widely used in medical health, aerospace, industrial equipment and artificial intelligence fields. Among them, piezoelectric materials have become the most commonly used materials in the design of flexible sensors due to their characteristics of generating electric charges on the surface after being stressed (i.e. piezoelectric effect).

[0003] However, piezoelectric effect only exists in non-centrosymmetric materials, and the actual available piezoelectric material system is very limited. Piezoelectric materials also have a critical temperature, and when the temperature is higher than the critical temperature, the material will become centrosymmetric and lose the piezoelectric effect. In addition, piezoelectric materials have a size effect, and their performance will decrease or even be lost as the size decreases, and there is a critical size. These shortcomings limit the development and application of flexible sensors. Therefore, for the production of flexible sensors, it is urgent to solve the technical problems of effectively improving piezoelectric performance, increasing the range of material selection, and reducing costs. SUMMARY

[0004] In view of the above defects or shortcomings in the related art, it is desirable to provide a flexible sensor based on flexoelectric effect and an electronic device, which can effectively improve the sensitivity and electrical performance of the sensor, efficiently and stably output, and meet the size design requirements of micro devices while reducing production costs.

[0005] In a first aspect, the present disclosure provides a flexible sensor based on flexoelectric effect, the flexible sensor comprising a lower electrode layer, a flexoelectric layer and an upper electrode layer which are sequentially stacked.

[0006] The flexoelectric layer comprises a layered residual layer and a truncated cone array structure arranged on the surface of the layered residual layer, and the flexoelectric layer comprises a polyvinylidene fluoride material.

[0007] Optionally, in some embodiments of the present disclosure, the truncated cone array structure comprises any one of a truncated pyramid array structure and a truncated circular cone array structure.

[0008] Optionally, in some embodiments of the present disclosure, the truncated pyramid array structure comprises a truncated straight pyramid array structure or a truncated oblique pyramid array structure.

[0009] Optionally, in some embodiments of the present disclosure, the ratio of the length of the top edge of the cone to the length of the bottom edge of the cone in the truncated cone array structure is 0.01-0.1.

[0010] Optionally, in some embodiments of the present disclosure, the length of the flexible sensor is 24.5 um, the width of the flexible sensor is 8 um, and the thickness of the flexoelectric layer is 3 um.

[0011] Optionally, in some embodiments of the present disclosure, the elastic constant of the polyvinylidene fluoride material in the flexoelectric layer is 3.70 GPa, the density is 1.78 x 10 3 kg / m 3 , the flexoelectric coefficient tensor f 11 = 81.5 uC / m, f 21 = 13 ± 10 -3 uC / m.

[0012] Optionally, in some embodiments of the present disclosure, the material of the electrode layer includes metal aluminum.

[0013] Optionally, in some embodiments of the present disclosure, the frequency and displacement model of the flexible sensor is constructed based on Rayleigh-Ritz method.

[0014] Optionally, in some embodiments of the present disclosure, the frequency and displacement model is obtained by the following steps:

[0015] The structure of the flexible sensor is simplified as a beam model, and the displacement is assumed as

[0016] u = af(x)cosωt (1)

[0017] In formula (1), a represents the displacement amplitude corresponding to the truncated top, f(x) represents the vibration function corresponding to the beam, and ω represents the frequency;

[0018] The system potential energy expression of the beam is obtained by integration

[0019]

[0020] In formula (2), E represents Young's modulus, I represents the moment of inertia, p represents the axial force, A represents the area of the truncated top, L represents the length of the beam, and p represents the density;

[0021] Substitute the period expression, and introduce the frequency variable formula and the constant solution of the power term of the cosine function in the period, that is,

[0022]

[0023] Simplify the system potential energy expression (2) to obtain

[0024]

[0025] Let the integral terms of f be B1, B2 and B3 respectively, to obtain

[0026]

[0027] Substitute B1, B2 and B3 into the system potential energy expression (3), to obtain

[0028]

[0029] To obtain the optimal solution of the system and the minimum potential energy of the system, the first derivative of the potential energy is 0, so that

[0030]

[0031] The corresponding frequency expression is obtained by solving

[0032]

[0033] In formula (6),

[0034] ω0 represents the linear vibration frequency;

[0035] Substitute the linear expression of u into the system potential energy expression (4) to obtain

[0036]

[0037] In formula (7), ε0 represents linear expansion.

[0038] In a second aspect, the present disclosure provides an electronic device comprising the flexible sensor based on flexoelectric effect according to any one of the first aspect.

[0039] From the above technical solutions, the embodiments of the present disclosure have the following advantages:

[0040] The embodiments of the present disclosure provide a flexible sensor based on flexoelectric effect and an electronic device having the same. The flexoelectric effect is introduced by arranging a truncated cone array structure on the surface of a polyvinylidene fluoride material, so that the flexoelectric effect is not affected by symmetry constraints, i.e., the flexoelectric effect still exists at high temperatures, and the effect increases with the decrease of size, which can be improved by several orders of magnitude at the micro-nano size. Further, the sensitivity and electrical performance of the sensor are effectively improved, the output is efficient and stable, and the size design requirements of the micro device are met, and the production cost is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0041] Other features, objects and advantages of the present disclosure will become more apparent from the following detailed description of the non-limiting embodiments, made with reference to the accompanying drawings:

[0042] Figure 1 A structure schematic diagram of a flexible sensor based on flexoelectric effect provided by the embodiments of the present disclosure;

[0043] Figure 2 A partial structure schematic diagram of a flexible sensor based on flexoelectric effect provided by an embodiment of the present disclosure;

[0044] Figure 3 Another partial structure schematic diagram of a flexible sensor based on flexoelectric effect provided by an embodiment of the present disclosure;

[0045] Figure 4 Still another partial structure schematic diagram of a flexible sensor based on flexoelectric effect provided by an embodiment of the present disclosure;

[0046] Figure 5 A simulation model schematic diagram of a flexible sensor based on flexoelectric effect provided by an embodiment of the present disclosure;

[0047] Figure 6 A potential distribution schematic diagram of a flexible sensor based on flexoelectric effect provided by an embodiment of the present disclosure;

[0048] Figure 7 A piezoelectric and flexoelectric contribution schematic diagram in sensor polarization provided by an embodiment of the present disclosure;

[0049] Figure 8 A strain and strain gradient and voltage relationship schematic diagram provided by an embodiment of the present disclosure;

[0050] Figure 9 A resonant frequency changes with sensor cone upper and lower edge length ratio schematic diagram provided by an embodiment of the present disclosure;

[0051] Figure 10 A structure block diagram of an electronic device provided by an embodiment of the present disclosure.

[0052] Reference signs:

[0053] 100-flexible sensor based on flexoelectric effect, 101-lower electrode layer, 102-flexoelectric layer, 1021-layered residual layer, 1022-truncated cone array structure, 103-upper electrode layer, 200-electronic device. DETAILED DESCRIPTION

[0054] In order to enable persons skilled in the art to better understand the present disclosure scheme, the technical solutions in the embodiments of the present disclosure will be described clearly and completely below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by persons skilled in the art without creative labor are within the scope of protection of the present disclosure.

[0055] The terms "first", "second", "third", "fourth" and the like in the description and in the claims of the present disclosure, and above mentioned drawings, if any, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the use of the terms so

[0056] Moreover, the terms "comprising" and "having" and any variations thereof are intended to cover a non-exclusive inclusion, for example, a process, method, system, product or apparatus that comprises a list of steps or modules as

[0057] For the purpose of understanding and illustration, the following is described by way of example Figures 1 to 10 The flexible sensor based on flexoelectric effect and the electronic device having the same according to the embodiments of the present disclosure are described in detail.

[0058] Reference is made to Figure 1 which is a structural schematic diagram of a flexible sensor based on flexoelectric effect provided by the embodiments of the present disclosure. The flexible sensor 100 comprises a lower electrode layer 101, a flexoelectric layer 102 and an upper electrode layer 103 which are sequentially stacked, wherein the flexoelectric layer 102 comprises a layered residual layer 1021 and a truncated cone array structure 1022 arranged on the surface of the layered residual layer 1021, the flexoelectric layer 102 comprises polyvinylidene fluoride (PVDF) material, and the materials of the lower electrode layer 101 and the upper electrode layer 103 comprise aluminum.

[0059] It should be noted that the flexoelectric effect is a new type of force-electric coupling effect describing the interaction between strain gradient and electric polarization intensity in materials, all dielectric materials can have this force-electric coupling effect, and the material selection range is wide. Moreover, the effect is not affected by symmetry constraints, i.e., it still exists at high temperatures, and it is also related to strain gradient, which increases with the decrease of size, and can be improved by several orders of magnitude especially at micro-nano size. Therefore, the embodiments of the present disclosure introduce the flexoelectric effect by arranging the truncated cone array structure on the surface of the polyvinylidene fluoride material, so as to effectively improve the sensitivity and electrical performance of the sensor, output high efficiency and stability, meet the size design requirements of micro devices, and reduce the production cost.

[0060] In addition, the frequency and displacement model of the flexible sensor 100 can be constructed based on the Rayleigh-Ritz method, which starts from the energy angle, and the mathematical model is simple and concise in the solving process, and the solving result is effective and accurate.

[0061] Specifically, the structure of the flexible sensor 100 is simplified as a beam model for analysis, a time variable is added, and a harmonic component in vibration at a steady state is eliminated by integrating in a period T, and the displacement is assumed as

[0062] u = af(x)cosωt (1)

[0063] In formula (1), a represents a displacement amplitude corresponding to a truncated top, f(x) represents a vibration function corresponding to a beam, and ω represents a frequency. The time variable is eliminated by the assumption using a cosine function;

[0064] Thus, the unknown displacement function can be transferred to unknown coefficients, and a system potential energy expression of the beam is listed, and the following formula (2) is obtained by integration

[0065]

[0066] In formula (2), E represents Young's modulus, I represents a moment of inertia, p represents an axial force, A represents a cross-sectional area, L represents a length of the beam, and ρ represents a density;

[0067] The period expression is substituted, and a frequency variable formula and a constant solution of a power term of a cosine function in a period are introduced, that is

[0068]

[0069] Further, the system potential energy expression (2) is simplified to obtain

[0070]

[0071] Let the integral terms of f be B1, B2 and B3 respectively to obtain

[0072]

[0073] B1, B2 and B3 are substituted into the system potential energy expression (3) to obtain

[0074]

[0075] To obtain the optimal solution of the system and the minimum potential energy of the system, the first derivative of the potential energy is 0, that is

[0076]

[0077] The corresponding frequency expression is obtained by solving

[0078]

[0079] In formula (6),

[0080] ω0 represents a linear vibration frequency;

[0081] Substituting the linear expression for u into the system potential energy expression (4), we obtain

[0082]

[0083] In equation (7), ε0 represents linear expansion.

[0084] In summary, the displacement solutions obtained by Rayleigh-Ritz analysis in the embodiments of this disclosure are more accurate, and also reflect the influence of frequency and mode shape on amplitude.

[0085] The following is still in the format of Figure 1 Taking the structure of the flexible sensor 100 shown as an example, the relevant characteristics of the flexible sensor 100 will be described in detail.

[0086] First, the truncated pyramid array structure 1022 in this embodiment can be, but is not limited to, any one of a truncated pyramid array structure and a truncated circular cone array structure. Further, the truncated pyramid array structure includes a truncated right pyramid array structure and a truncated oblique pyramid array structure, etc. For example, the truncated right pyramid array structure includes a truncated regular square pyramid array structure, thereby introducing flexural electrical effects and increasing the sensor output. For example... Figure 2 As shown, the truncated pyramid array structure 1022 is composed of n rows × m columns of truncated regular square pyramids. The flexible sensor 100 has a length of b (um) in the x-direction and a width of a (um) in the y-direction. Figure 3 and Figure 4 As shown, the thickness of the upper electrode layer 103 in the z-direction is h. s The thickness of the flexural electric layer 102 is h (um), and the height of the truncated square pyramid is h. d (cm), and the height of the lower electrode layer 101 is h. x (um), the distance between the truncated regular square pyramids is d. s (um), where the length of the bottom edge of each truncated square pyramid is R(um), and the length of the top edge is r(um). Optionally, in the truncated square pyramid array structure of this disclosure, the ratio of the length of the top edge r to the length of the bottom edge R can be 0.01 to 0.1.

[0087] For example, in this embodiment of the disclosure, the flexible sensor 100 may be configured with a length of 24.5 μm in the x-direction, a width of 8 μm in the y-direction, and a thickness of 3 μm for the flexoelectric layer 102; the elastic constant of the polyvinylidene fluoride material in the flexoelectric layer 102 may be selected as 3.70 GPa, and the density as 1.78 × 10⁻⁶. 3 kg / m 3 Flexural coefficient tensor f 11 =81.5uC / m, f21 = 13 ± 10 - 3 uC / m; and the truncated cone array structure 1022 is composed of 4 rows x 9 columns of truncated right tetragonal pyramids, each truncated right tetragonal pyramid has a cone bottom edge length of 1.5 (um) and a cone top edge length of 0.15 (um). Model simulation is performed using COMSOL Multiphysics finite element analysis software, as shown in Figure 5 .

[0088] The simulation results show that ① the flexible sensor 100 designed in the embodiment of the present disclosure has obvious potential distribution difference and good voltage output characteristics. For example, as shown in Figure 6 , the sensor potential distribution continuously decreases along the z direction, showing a gradient distribution from large to small. When a pressure of 50 kPa is applied to the upper electrode layer 103 and a potential of 0 is set at the lower electrode layer 101, the upper surface potential of the polyvinylidene fluoride film can be regarded as the effective output voltage of the sensor. The structure of the flexoelectric layer 102 designed in the embodiment of the present disclosure, i.e. the truncated cone array structure 1022 combined with the layered residual layer 1021, makes the maximum output voltage of the sensor 1.36 V.

[0089] ② The flexoelectric polarization effect of the flexible sensor 100 proposed in the embodiment of the present disclosure plays a dominant role in the total output polarization contribution. For example, as shown in Figure 7 , a sinusoidal excitation pressure of 50 kPa and a frequency of 40 kHz is input to the upper electrode layer 103, and the polarization behavior of the sensor is analyzed at equally spaced time points. At 25 ms, the total polarization output is less than 0.01 uC / m 2 , and the flexoelectric contribution accounts for 6.67% of the total output polarization. With the change of time, the corresponding output pressure increases, and the flexoelectric contribution gradually increases from 24.72% to 55.32%, which means that flexoelectricity plays a dominant role in the output polarization contribution of the micron-level sensor.

[0090] ③ The flexible sensor 100 designed in the embodiment of the present disclosure can increase the flexoelectric effect by adjusting the strain gradient, and ultimately improve the output. For example, the length r (um) of the top edge of the truncated tetragonal pyramid array structure and the length R (um) of the bottom edge of the truncated tetragonal pyramid are adjusted to obtain a larger strain gradient along the thickness direction. As shown in Figure 8As shown, simulation analysis compared the voltage response amplitude of the sensor within the taper ratio (r / R) range of 0.01 to 0.1. Specifically, as the taper ratio increases, the sensor's output voltage decreases from 11.2V to 1.36V, and the corresponding strain gradient decreases from 110 (1 / m) to 63 (1 / m), while the strain decreases from 0.57 to 0.15. At this point, the trends of strain and strain gradient are basically the same as those of the output voltage response, but the range of change in strain gradient is significantly larger than that of strain. This indicates that flexural conductivity has a significant scale effect; even a tiny size change of 0.01µm can cause a large change in the output response, and smaller sizes will result in larger strain gradients and potentials. This further demonstrates that to better improve device performance, the design of the truncated cone array structure 1022 should favor a sharper cone structure rather than a gentler cylindrical structure.

[0091] ④ The flexible sensor 100 designed in this embodiment can output stably within a certain frequency range. For example... Figure 9 As shown, the sensor output is related to the resonant frequency, which is defined by changing the ratio of the length of the top edge to the length of the bottom edge of the truncated pyramid array structure (i.e., r / R = 0.01–0.1). Using a linear first-order resonant frequency of 39.97 kHz (ratio = 0.1) as the fundamental frequency, the influence of different ratios on the rate of change of the resonant frequency ranges from 0.035% to 0.07%. As the ratio decreases, the range of resonant frequency variation becomes smaller, indicating that in the designed sensor structure, the gradient change corresponding to the flexural effect has little impact on the resonant frequency, while ensuring that the collector maintains a stable output state within a certain frequency range.

[0092] Based on the foregoing embodiments, this disclosure provides an electronic device. Please refer to... Figure 10 This is a structural block diagram of an electronic device provided in an embodiment of the present disclosure. The electronic device 200 includes... Figures 1 to 9 The flexible sensor 100 based on the flexoelectric effect in the corresponding embodiment.

[0093] The flexible sensor based on the flexoelectric effect and the electronic device having it provided in this disclosure introduce the flexoelectric effect by setting a truncated pyramidal array structure on the surface of polyvinylidene fluoride (PVDF) material. This allows it to remain unaffected by symmetry constraints, meaning the flexoelectric effect persists even at high temperatures. Furthermore, this effect increases with decreasing size, reaching several orders of magnitude at micro- and nano-scale dimensions. Consequently, this effectively improves the sensor's sensitivity and electrical performance, provides efficient and stable output, meets the design requirements for micro-device size, and reduces production costs.

[0094] It should be noted that the above examples are only used to illustrate the technical solutions of the present disclosure, rather than limit them; although the present disclosure has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A flexible sensor based on the flexoelectric effect, characterized in that, The flexible sensor comprises a lower electrode layer, a flexural electrode layer, and an upper electrode layer stacked sequentially. The flexural electric layer includes a layered residual layer and a truncated quadrangular pyramidal array structure disposed on the surface of the layered residual layer, and the flexural electric layer includes polyvinylidene fluoride material. In the truncated quadrangular pyramid array structure, the ratio of the length of the top edge of the pyramid to the length of the bottom edge of the pyramid is 0.01 to 0.1; The flexible sensor has a length of 24.5 μm, a width of 8 μm, and a thickness of 3 μm for the flexoelectric layer. The elastic constant of the polyvinylidene fluoride material in the flexural layer is 3.70 GPa, and the density is 1.78 × 10⁻⁶. 3 kg / m 3 The flexural coefficient tensor is f 11 =81.5uC / m, f 21 =13±10 -3 uC / m; The frequency and displacement model of the flexible sensor is constructed based on the Rayleigh-Ritz method, including: The structure of the flexible sensor is simplified to a beam model, and the displacement is assumed to be u=af(x)cosωt (1) In equation (1), a represents the displacement amplitude corresponding to the top of the truncated section, f(x) represents the vibration function of the beam, and ω represents the frequency. The system potential energy expression of the beam is obtained through integration. In equation (2), E represents Young's modulus, I represents moment of inertia, p represents axial force, A represents cross-sectional area, L represents beam length, and ρ represents density. Substituting into the periodic expression, and introducing the frequency variable and the constant solution of the cosine function power term within the period, i.e. Simplifying the system potential energy expression (2), we get Let the integral terms of f be B1, B2, and B3, then we get Substituting B1, B2, and B3 into the system potential energy expression (3), we obtain To obtain the optimal solution of the system and the minimum potential energy of the system, the first derivative of the potential energy must be 0. The solution yields the corresponding frequency expression as follows: In equation (6), ω0 represents the linear vibration frequency; Substituting the linear expression for u into the system potential energy expression (4), we obtain In equation (7), ε0 represents linear expansion.

2. A flexible sensor based on the flexoelectric effect according to claim 1, characterized in that, The electrode layer is made of aluminum.

3. An electronic device, characterized in that, The electronic device includes a flexible sensor based on the flexoelectric effect as described in claim 1 or 2.

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