CN115694405A - Structure and method for generating flexoelectricity - Google Patents
Structure and method for generating flexoelectricity Download PDFInfo
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- CN115694405A CN115694405A CN202211436386.1A CN202211436386A CN115694405A CN 115694405 A CN115694405 A CN 115694405A CN 202211436386 A CN202211436386 A CN 202211436386A CN 115694405 A CN115694405 A CN 115694405A
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Abstract
The invention discloses a structure and a method for generating flexoelectric, which integrate an interdigital transducer and a thin film device on a chip, apply sine waves with the same frequency, phase and amplitude to the interdigital transducers on two sides, because no load is applied to an upper electrode of the thin film device, a dielectric layer of the thin film device generates a strain gradient under the action of periodic stretching of a surface acoustic wave, and the periodically changed strain gradient generates polarization charges, namely, the flexoelectric effect is generated. By arranging the thin film device at the antinode of the standing surface acoustic wave generated by the pair of interdigital transducers when the sine wave is applied, the thin film device at the antinode is strongly stretched under the action of the standing surface acoustic wave, and the generated flexoelectric effect is stronger. The structure of the invention can generate flexoelectric effect without damaging the surface of the thin film device, and has important significance for the application development in the aspects of flexoelectric energy acquisition, flexoelectric sensing and the like.
Description
Technical Field
The invention belongs to the field of force-electricity coupling, and particularly relates to a structure and a method for generating flexoelectricity.
Background
With the rapid development of microelectronic technology, the utilization of galvanic coupling effect to regulate and control the performance of devices in micro-nano scale has attracted extensive attention of researchers. The force-electric coupling effect includes the conventional piezoelectric coupling effect and the flexural electric coupling effect. The traditional force-electric coupling effect refers to the piezoelectric effect, which is a linear coupling between electric polarization and uniform strain. The flexoelectric effect is a high-order force electric coupling effect in the dielectric material, and generally refers to electric polarization of the dielectric material caused by nonuniform deformation, namely electric polarization caused by strain gradient. The flexoelectric effect has advantages over the piezoelectric effect in that: first, the dielectric material that produces the flexoelectric effect is no longer limited to non-centrosymmetric crystals, the flexoelectric effect is present in all dielectrics; second, the flexoelectric effect is independent of temperature; third, the flexoelectric effect is more pronounced as the device is scaled down to the nanometer scale, since the strain gradient is inversely proportional to the characteristic size of the material. Based on these advantages, the flexoelectric effect is receiving more and more attention.
At present, methods such as bending cantilever beams, bending films, using pyramid samples and trapezoid samples are utilized to generate flexoelectric effects, and the flexoelectric effects are indicated to have obvious size dependence, but the methods are all methods for generating the flexoelectric in a quasi-static state. Therefore, the flexoelectric effect generated in a dynamic mode needs to be developed, and a foundation is laid for the flexoelectric effect to regulate and control the performance of the electronic device in the dynamic and medium-high frequency directions in the future.
Disclosure of Invention
In view of the above drawbacks or needs for improvement in the prior art, the present invention provides a structure and a method for generating flexoelectric, which lay the foundation for the flexoelectric effect to regulate the performance of an electronic device in the dynamic and medium-high frequency directions.
To achieve the above object, according to a first aspect of the present invention, there is provided a structure for generating flexoelectricity, comprising: the piezoelectric transducer comprises an interdigital transducer I, an interdigital transducer II and at least one thin film device, wherein the interdigital transducer I and the interdigital transducer II are integrally arranged on the upper surface of a piezoelectric substrate; the interdigital transducer I and the interdigital transducer II are made of the same material, size and frequency;
when sinusoidal voltage signals with the same frequency, amplitude and phase are simultaneously applied to the interdigital transducer I and the interdigital transducer II, surface acoustic wave standing waves vibrating in an XY plane are generated, so that at least one thin film device is stretched periodically, and the flexoelectric effect is generated.
Preferably, the at least one thin-film device is located at an antinode of the standing surface acoustic wave, and the following relational expression is satisfied with the positions between the interdigital transducer I and the interdigital transducer II:
Δx＝n(a+b)
wherein a represents the width of the interdigital transducer fingers; b represents the inter-finger spacing of the interdigital transducers; and deltax represents the distance between the central point of the last interdigital electrode of the interdigital transducer I and the central point of the nth thin film device, and n is an integer.
Preferably, the thickness of the dielectric layer of the thin film device is 10 nm-20 nm.
Preferably, the thin-film device has a size smaller than a wavelength of the surface acoustic wave.
Preferably, the electrode materials of the interdigital transducer I and the interdigital transducer II are Cr and Au.
Preferably, the upper surface of the piezoelectric substrate is a polished surface, and the lower surface is a rough surface.
Preferably, the material of the piezoelectric substrate is LiNbO with 64-degree Y-direction cutting and X-direction propagation 3 And (5) a single chip.
According to a second aspect of the present invention there is provided a method of producing flexoelectricity for use with a structure as described in the first aspect, comprising:
sinusoidal voltage signals with the same frequency, amplitude and phase are simultaneously applied to the interdigital transducer I and the interdigital transducer II to generate surface acoustic wave standing waves vibrating in an XY plane, so that at least one thin film device is stretched periodically, and the flexoelectric effect is generated.
The thin film device (3) at the antinode of the standing wave is connected with a measuring instrument by a method of inserting a needle by a probe station, and a voltage signal generated under the action of the flexural electricity is measured by the measuring instrument.
Preferably, the measuring instrument is an oscilloscope.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
1. the structure and the method for generating the flexoelectric provided by the invention integrate the interdigital transducers and the thin film device on a chip, apply sine waves with the same frequency, phase and amplitude to the interdigital transducers at two sides, because no load is applied to the upper electrode of the thin film device, a dielectric layer of the thin film device generates a strain gradient under the action of periodic stretching of surface acoustic waves, and the periodically changed strain gradient generates polarization charges, namely, the flexoelectric effect is generated, thereby providing a new idea for the flexoelectric effect to regulate and control the performance of the electronic device in the dynamic and medium-high frequency directions. In addition, the method provided by the invention can generate the flexoelectric effect through the structure without damaging the surface of the thin film device, and has important significance for the application development in the aspects of flexoelectric energy acquisition, flexoelectric sensing and the like.
2. According to the structure and the method for generating the flexoelectric, at least one thin film device is arranged at the antinode of the standing wave of the surface acoustic wave generated by the interdigital transducer I and the interdigital transducer II when the sinusoidal wave with the same frequency, phase and amplitude is applied, the thin film device at the antinode is strongly stretched under the action of the surface acoustic wave, and the generated flexoelectric effect is stronger.
3. According to the structure and the method for generating the flexoelectric, provided by the invention, the size of the thin film device unit is smaller than the wavelength of the surface acoustic wave, no load is applied to the upper electrode of the thin film device, a dielectric layer of the thin film device generates a strain gradient under the periodic stretching action of the surface acoustic wave, the strain gradient can cause electric polarization, and when the unit size of the thin film device is smaller than the wavelength of the surface acoustic wave, the generated electric polarization cannot be mutually counteracted.
4. The structure and the method for generating the flexoelectric can design the interdigital transducers with different frequencies, and the wavelength determines the size of the strain gradient, so that the flexoelectric effect generated by the high-frequency surface acoustic wave standing wave with smaller wavelength is stronger, the wavelength of the surface acoustic wave standing wave can be changed by changing the frequency of the interdigital transducers, the intensity of the flexoelectric effect is changed, and the performance of the electronic device can be regulated and controlled in the dynamic and medium-high frequency directions through the flexoelectric effect.
Drawings
Fig. 1 is a schematic structural diagram of a flexoelectric generation according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
An embodiment of the present invention provides a structure for generating a flexoelectric, as shown in fig. 1, including: the piezoelectric transducer comprises an interdigital transducer I2 and an interdigital transducer II 4 which are integrally arranged on the upper surface of a piezoelectric substrate 1, and at least one thin film device 3 positioned between the interdigital transducer I2 and the interdigital transducer II 4; the interdigital transducers I2 and II 4 are made of the same material and size, and have the same frequency;
when the interdigital transducers I2 and II 4 are simultaneously applied with sinusoidal voltage signals with the same frequency, amplitude and phase, surface acoustic wave standing waves 5 vibrating in an XY plane are generated, so that at least one thin film device 3 is periodically stretched, and the flexoelectric effect is generated.
It is understood that in the present embodiment, the thin-film device 3 is used, which is composed of a lower electrode (Pt), a functional layer (dielectric layer, such as SiO) and a bottom electrode (Pt), in this order 2 ；HfO 2 ) And an upper electrode (W). The thickness of the lower electrode is 100nm; the thickness of the functional layer is 10nm; the width of the upper electrode was 100 μm.
And the thin film device 3 is positioned between the interdigital transducer I2 and the interdigital transducer II 4, and on the propagation direction of the surface acoustic wave generated by the interdigital transducer I2 and the interdigital transducer II 4.
Preferably, a conductive adhesion layer is arranged between the thin-film device 3 and the piezoelectric substrate 1, the conductive adhesion layer and the piezoelectric substrate 1 form a covalent bond, and simultaneously the conductive adhesion layer and the lower electrode of the thin-film device 3 form a metal bond.
Preferably, the size of the thin-film device 3 is smaller than the wavelength of the surface acoustic wave.
The finger width and finger pitch of the interdigital transducer are both 100 μm. A two-interdigital transducer produces a surface acoustic wave wavelength λ =2 × (finger width + finger pitch) =400 μm, a surface acoustic wave frequency f = v/T, v being a surface acoustic wave velocity of about 4000m/s, and thus a surface acoustic wave frequency of 10MHz. The interdigital transducers on two sides generate surface acoustic waves, and the surface acoustic waves which are transmitted in opposite directions are superposed in the area between the interdigital transducers on two sides to form surface acoustic wave standing waves. Because no load is applied to the upper electrode of the thin film device 3, and the size of the thin film device 3 is smaller than the wavelength of the surface acoustic wave, a strain gradient is generated on the dielectric layer of the thin film device 3 under the periodic stretching action of the surface acoustic wave, and polarization charges are generated on the periodically changed strain gradient, namely, the flexoelectric effect is generated.
Integrate interdigital transducers and at least one thin-film device 3 of different frequencies (namely two interdigital transducers and at least one thin-film device 3 all are located the upper surface of piezoelectric substrate 1) on same piezoelectric substrate 1, apply the equal same sine wave signal of frequency, amplitude, phase place simultaneously to a pair of interdigital transducers on same piezoelectric substrate 1, because reverse piezoelectric effect, be located the interdigital transducers of at least one thin-film device 3 both sides all produce the surface acoustic wave, and the surface acoustic wave of opposite propagation superposes in the region between the interdigital transducers of both sides to region formation sound surface standing wave between the interdigital transducers of both sides under the effect of sound surface standing wave, at least one thin-film device 3 can receive periodic tensile. Because no load is applied to the upper electrode of the thin-film device 3, under the action of the periodic stretching of the surface acoustic wave, the dielectric layer of the thin-film device 3 is subjected to non-uniform strain, that is, the dielectric layer of the thin-film device 3 generates a strain gradient, and the periodically changed strain gradient generates polarization charges, that is, a flexoelectric effect is generated.
And the thin-film device 3 has a size smaller than the surface acoustic wave wavelength. The interdigital transducer on the piezoelectric substrate 1 generates surface acoustic waves, no load is applied to an upper electrode of the thin film device 3, non-uniform strain can be generated on a dielectric layer of the thin film device 3 under the effect of periodic stretching of the surface acoustic waves, and polarization charges can be generated by the gradient of the strain which changes periodically, namely, the flexoelectric effect is generated. According to the invention, the surface acoustic wave and the thin film device 3 are integrated on a chip to generate a flexoelectric effect, so that a new idea is provided for the flexoelectric effect to regulate and control the performance of the electronic device in the dynamic and medium-high frequency directions.
Preferably, the amplitude of the sinusoidal voltage signal does not exceed the maximum withstand voltage of the piezoelectric substrate 1. In this embodiment, the non-polished surface of the piezoelectric substrate 1 is pasted on a circuit board, and a printed circuit channel on the circuit board and the interdigital transducers are wired, and a sinusoidal voltage signal with an amplitude of 1V and a frequency of 10MHz is simultaneously applied to the two pairs of interdigital transducers.
Preferably, at least one thin-film device 3 is located at an antinode of the standing surface acoustic wave 5 (i.e. the at least one thin-film device 3 is disposed in a direction in which the interdigital transducer on the piezoelectric substrate 1 generates surface acoustic wave propagation), and the positions between the interdigital transducer i 2 and the interdigital transducer ii 4 satisfy the following relation:
Δx＝n(a+b)
wherein a represents the width of the interdigital transducer fingers; b represents the inter-finger spacing of the interdigital transducers; and deltax represents the distance between the central point of the last interdigital electrode of the interdigital transducer I and the central point of the nth thin-film device 3, and n is an integer.
Specifically, the thin film device 3 and the interdigital transducer are integrated on a chip, so that the thin film device 3 is located at an antinode of the standing acoustic wave 5, the thin film device 3 located at the antinode is strongly stretched under the action of the acoustic surface wave, and the generated flexoelectric effect is stronger.
Preferably, the thickness of the dielectric layer of the thin-film device 3 is 10nm to 20nm.
In particular, the thickness of the thin-film device 3 is in the order of nanometers. Since the strain gradient is inversely proportional to the characteristic dimension of the material, the flexoelectric effect is more pronounced when the device is scaled down to the nanometer scale.
Preferably, the electrode materials of the interdigital transducers I2 and II 4 are Cr/Au.
Specifically, the electrode material of the interdigital transducer is Cr/Au, and the thickness is generally 50nm-100nm.
The metal Cr serves as an adhesion layer between the Au and the piezoelectric substrate 1, namely, the metal Cr can increase the adhesion between the metal film Au and the substrate.
Preferably, the contact surfaces of the interdigital transducers i 2 and ii 4 and the piezoelectric substrate 1 (i.e. the upper surface of the piezoelectric substrate 1) are polished surfaces, and the lower surface of the piezoelectric substrate 1 is a rough surface.
Specifically, the upper surface of the piezoelectric substrate 1 is a polished surface, which is favorable for propagation of surface acoustic waves and reduces loss. The lower surface of the piezoelectric substrate 1 is a rough surface, which is beneficial to reducing reflection of surface acoustic waves.
Preferably, the material of the piezoelectric substrate 1 is LiNbO with 64-degree Y-direction cutting and X-direction propagation 3 Single crystal wafers, i.e. 64 ° YX-LiNbO 3 。
Specifically, liNbO 3 The single chip has large electromechanical coupling coefficient and small insertion loss. In LiNbO 3 The interdigital transducer is prepared on the polished surface of the single chip, so that the propagation loss of the surface acoustic wave can be reduced.
In this embodiment, the piezoelectric substrate 1 is made of 64 ° YX-LiNbO 3 The size is 30 multiplied by 15 multiplied by 0.5mm, and the single side is polished.
An embodiment of the present invention provides a method for generating a flexoelectric, which is applied to the structure described in any of the above embodiments, and includes:
sinusoidal voltage signals with the same frequency, amplitude and phase are simultaneously applied to the interdigital transducer I2 and the interdigital transducer II 4 to generate surface acoustic wave standing waves 5 vibrating in an XY plane, so that the at least one thin film device 3 is periodically stretched, and the flexoelectric effect is generated.
Specifically, sinusoidal voltage signals with the same frequency and amplitude are applied to the interdigital transducers on the two sides in a time-consuming mode, due to the inverse piezoelectric effect, the interdigital transducers on the two sides can generate surface acoustic waves, and the surface acoustic waves which are transmitted in opposite directions are superposed in an area between the interdigital transducers on the two sides, so that surface acoustic wave standing waves are formed.
Preferably, the method further comprises: measuring a voltage signal generated by the thin film device 3 under the flexoelectric effect by a measuring instrument; preferably, the measuring instrument is an oscilloscope.
Specifically, for example, when the at least one thin film device 3 is located at an antinode of a standing wave, the thin film device 3 located at the antinode of the standing wave is connected with an oscilloscope by a probe station needle inserting method, and since no load is applied to the upper electrode of the thin film device 3, a strain gradient is generated in the dielectric layer of the thin film device 3 under the effect of the periodic stretching of the surface acoustic wave, the strain gradient causes electric polarization, and a sinusoidal voltage signal generated by the thin film device 3 can be measured by the oscilloscope.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A structure for generating flexoelectricity, comprising: the piezoelectric transducer comprises an interdigital transducer I (2) and an interdigital transducer II (4) which are integrally arranged on the upper surface of a piezoelectric substrate (1), and at least one thin film device (3) which is positioned between the interdigital transducer I (2) and the interdigital transducer II (4); the material, the size and the frequency of the interdigital transducer I (2) and the interdigital transducer II (4) are the same;
when sinusoidal voltage signals with the same frequency, amplitude and phase are simultaneously applied to the interdigital transducer I (2) and the interdigital transducer II (4), surface acoustic wave standing waves (5) vibrating in an XY plane are generated, so that the thin film device (3) is periodically stretched, and the flexoelectric effect is generated.
2. A structure for generating a flexoelectric according to claim 1, wherein the thin film device (3) is located at the antinode of the standing surface acoustic wave (5), and the positions of the interdigital transducer i (2) and the interdigital transducer ii (4) satisfy the following relation:
Δx＝n(a+b)
wherein a represents the width of the interdigital transducer fingers; b represents the inter-finger spacing of the interdigital transducers; and deltax represents the distance between the central point of the last interdigital electrode of the interdigital transducer I and the central point of the nth thin-film device (3), and n is an integer.
3. A structure for generating a flexoelectric according to claim 1 or 2, wherein the thickness of the dielectric layer of the thin film device (3) is 10nm to 20nm.
4. A flexoelectric generating structure according to claim 1 or 2, wherein said thin film device (3) has a size smaller than the wavelength of said surface acoustic wave.
5. A structure for generating a flexoelectric power according to claim 1, wherein the electrode materials of the interdigital transducer i (2) and the interdigital transducer ii (4) are Cr and Au.
6. A structure for generating a flexoelectric according to claim 1 or 5, wherein the upper surface of the piezoelectric substrate (1) is a polished surface and the lower surface is a rough surface.
7. A structure for generating a flexoelectric according to claim 1, wherein the material of the piezoelectric substrate (1) is 64 ° Y-cut, X-propagating LiNbO 3 And (3) a single wafer.
8. A method of producing flexoelectric, applied to a structure according to any one of claims 1 to 7, comprising:
sinusoidal voltage signals with the same frequency, amplitude and phase are simultaneously applied to the interdigital transducer I (2) and the interdigital transducer II (4) to generate surface acoustic wave standing waves (5) vibrating in an XY plane, so that the thin film device (3) is stretched periodically, and the flexoelectric effect is generated.
9. A method of generating a flexoelectric according to claim 8, further comprising: the thin film device (3) at the antinode of the standing wave is connected with a measuring instrument by a method of inserting a needle by a probe station, and a voltage signal generated under the action of the flexural electricity is measured by the measuring instrument.
10. A method of producing flexoelectricity according to claim 8, wherein said measuring instrument is an oscilloscope.
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| CN202211436386.1A CN115694405A (en) | 2022-11-16 | 2022-11-16 | Structure and method for generating flexoelectricity |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116317694A (en) * | 2023-05-18 | 2023-06-23 | 南京航空航天大学 | Method for regulating and controlling frequency and potential distribution of piezoelectric device by using flexoelectric effect |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116317694A (en) * | 2023-05-18 | 2023-06-23 | 南京航空航天大学 | Method for regulating and controlling frequency and potential distribution of piezoelectric device by using flexoelectric effect |
| CN116317694B (en) * | 2023-05-18 | 2023-08-04 | 南京航空航天大学 | Method for regulating and controlling frequency and potential distribution of piezoelectric device by using flexoelectric effect |
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