Piezoelectric films with carbon nanotube-based electrodes

Abstract

A piezoelectric element comprising a piezoelectric film and a first carbon nanotube (CNT)-based electrode layer disposed directly on at least one side of the piezoelectric film, the CNT-based first electrode layer having a sheet resistance of less than 300 ohms / sq.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 63 / 333,323, filed April 21, 2022, which is incorporated by reference in its entirety herein. [Background technology]

[0002] Piezoelectric elements may be used for applications in many fields, including but not limited to biomedicine, defense technology, nanodevices, micro electromechanical systems (MEMS), and mechanical energy harvesters (MEH). In a broad sense, piezoelectric elements may be useful in any application involving conversion between mechanical and electrical energy. Input devices including touch sensor devices (e.g., touch pads or touch sensor devices) are widely used in various electronic systems. Touch sensor devices generally include a sensing area, often bounded by a surface, in which the touch sensor device determines at least one of the presence, location, and motion of one or more input objects. Touch sensor devices may be used to provide an interface to electronic systems. For example, touch sensor devices are often used as input devices to larger computer systems (e.g., opaque touch pads integrated into or around notebook or desktop computers, or transparent touch pads integrated into touch displays, etc.). Summary of the Invention [Means for solving the problem]

[0003] This Summary is provided to introduce a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0004] In general, in one aspect, an embodiment of a piezoelectric device includes a piezoelectric film and a first carbon nanotube (CNT)-based electrode layer disposed directly on at least one side of the piezoelectric film, the CNT-based first electrode layer having a sheet resistance of less than 300 ohms / sq.

[0005] In general, in one aspect, an embodiment of a method for making a piezoelectric device includes obtaining a carbon nanotube (CNT) dispersion, coating a piezoelectric film with the CNT dispersion to obtain a CNT-based electrode layer disposed directly on the piezoelectric film, and curing the CNT-based electrode layer, wherein the CNT-based electrode layer has a sheet resistance of less than 300 ohms / sq.

[0006] In general, in one aspect, an embodiment of a piezoelectric input device includes a piezoelectric element comprising a piezoelectric film and a first carbon nanotube (CNT) based electrode layer disposed directly on at least one side of the piezoelectric film, the CNT-based first electrode layer having a sheet resistance of less than 300 ohms / sq. and forming a plurality of receiver electrodes, the piezoelectric input device further including a processing system for determining a position of the input object based on resultant signals obtained from the plurality of receiver electrodes.

[0007] Other aspects and advantages of the claimed subject matter will become apparent from the following description and the appended claims.

[0008] Certain embodiments of the disclosed technology will now be described in detail with reference to the accompanying drawings, in which, for purposes of consistency, like elements in the various drawings are designated by like reference numerals. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 illustrates an input device in accordance with one or more embodiments. [Diagram 2] FIG. 1 illustrates a touch sensing system in accordance with one or more embodiments. [Diagram 3] FIG. 1 illustrates an energy collection system in accordance with one or more embodiments. [Figure 4] FIG. 1 illustrates an actuator according to one or more embodiments. [Diagram 5] 5A, 5B, and 5C are diagrams illustrating examples of piezoelectric elements according to one or more embodiments. [Figure 6] 6A and 6B are diagrams illustrating electrode patterns according to one or more embodiments. [Figure 7] 1 illustrates a method of manufacturing a piezoelectric element according to one or more embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In the following detailed description of the embodiments of the present disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that the present disclosure may be practiced without these specific details. In other instances, well-known features have not been described in detail in order to avoid unnecessarily complicating the description.

[0011] Throughout this application, ordinal numbers (e.g., first, second, third, etc.) may be used as adjectives for elements (i.e., any noun in this application). The use of ordinal numbers is not intended to imply or create any particular order of elements, nor to limit any element to being only a single element, unless expressly disclosed, e.g., by using "before," "after," "single," and other such terms. Rather, the use of ordinal numbers is to distinguish elements. By way of example, a first element is different from a second element, and a first element may encompass two or more elements and may follow (or precede) a second element in the ordering of elements.

[0012] In general, embodiments of the present disclosure include a piezoelectric element based on a piezoelectric film with carbon nanotube (CNT)-based electrodes and a method for manufacturing a piezoelectric element based on a PVDF piezoelectric film with CNT-based electrodes. The piezoelectric element may be used in any application involving conversion between mechanical and electrical energy. The embodiments of the present disclosure described hereinafter have various advantages. For example, as discussed in detail below, a piezoelectric element according to one or more embodiments is easy to manufacture, requires relatively few components, and has good optical transparency. This optical transparency may make the piezoelectric element suitable for use with displays. Furthermore, a piezoelectric element according to an embodiment of the present disclosure may be relatively flexible or bendable, and thus suitable for non-rigid applications. Input devices (e.g., touch or force sensing input devices) based on piezoelectric elements may have advantages over other touch sensing technologies. For example, compared to capacitive touch sensing, piezoelectric touch sensing according to one or more embodiments is more robust against environmental influences, such as moisture. Thus, piezoelectric elements according to embodiments of the present disclosure are particularly well suited for a wide range of applications and operating environments, including wet or underwater environments, applications where mechanical flexibility is required or desired, applications where optical transparency is required or desired, etc. A detailed description is provided below.

[0013] FIG. 1 is a block diagram of an example of a piezoelectric input device (100) according to one or more embodiments. The piezoelectric input device (100) may be configured for touch sensing and / or force sensing to provide input to an electronic system (not shown). The term "electronic system" (or "electronic device") as used in this document broadly refers to any system that may process information electronically. Some non-limiting examples of electronic systems include personal computers, such as desktop computers, laptop computers, tablets, machines and medical devices that have at least some computing power, and the like. Further examples of electronic systems include peripherals, such as data input devices (including remote controls, mice, tactile input devices, or sensing devices including robotic probes, hands, pressure measuring devices, and the like), and data output devices (including display screens and printers). Other examples include remote terminals, kiosks, and video game machines (such as video game consoles and portable game devices, and the like). Other examples include communication devices (including mobile phones, e.g., smart phones) and media devices (including recorders, editors, and players, e.g., televisions, set-top boxes, music players, digital photo frames, digital cameras, etc.) In addition, an electronic system may be a host or a slave to an input device.

[0014] 1, the piezoelectric input device (100) is shown as a touch sensitive device (e.g., a "touch pad" or "touch sensitive device") configured to sense input provided by one or more input objects within a sensing area (120). Examples of input objects include a stylus, a finger (140), etc.

[0015] The sensing region 120 encompasses any space on, around, in, and / or near the input device 100 in which the input device 100 may detect user input (e.g., user input provided by one or more input objects). The size, shape, and location of a particular sensing region may vary widely from embodiment to embodiment.

[0016] The input device (100) may use any combination of sensor components and technologies to detect user input within a sensing area (120). The input device (100) includes one or more sensing elements for detecting user input. The sensing elements may be piezoelectric. When a force load is applied to a piezoelectric material (e.g., a non-centrosymmetric material with a polarization that moves in a positive or negative direction according to the direction of the applied force), the charge balance in the piezoelectric material changes. By measuring the induced voltage, a touch event associated with the force load may be determined and the applied force may be calculated.

[0017] Some piezoelectric implementations use an array of receiver electrodes or other regular or irregular patterns to obtain induced voltages at different locations across a piezoelectric material associated with the sensing area (120), and the location of a touch event within the input area (120) may be determined accordingly.

[0018] In Figure 1, the processing system (110) is shown as part of the input device (100). The processing system (110) is configured to operate the hardware of the input device (100) to detect input in the sensing area (120). The processing system (110) may include some or all of one or more integrated circuits (ICs) and / or other circuit components. For example, the processing system (110) may include the circuit components described below with reference to Figure 2.

[0019] In some embodiments, the processing system (110) also includes electronically readable instructions, such as at least one of firmware code and software code. In some embodiments, the components that make up the processing system (110) are located together, such as near the sensing element(s) of the input device (100). In other embodiments, the components of the processing system (110) are physically separated, with one or more components in close proximity to the sensing element(s) of the input device (100) and one or more components elsewhere. For example, the input device (100) may be a peripheral device coupled to a computing device, and the processing system (110) may include software configured to run on a central processing unit of the computing device and one or more ICs (possibly with associated firmware) separate from the central processing unit. As another example, the input device (100) may be physically integrated within a mobile device, and the processing system (110) may include circuitry and firmware that is part of the main processor of the mobile device. In some embodiments, the processing system (110) is dedicated to implementing the input device (100). In other embodiments, the processing system (110) performs other functions as well, such as operating a display screen (155) or driving haptic actuators.

[0020] The processing system (110) may be implemented as a set of modules that handle different functions of the processing system (110). Each module may include circuitry, firmware, software, or a combination thereof that is part of the processing system (110). Different combinations of modules may be used in various embodiments. For example, as shown in FIG. 1, the processing system (110) may include a determination module (150) and a sensor module (160). The determination module (150) may include functionality for determining at least one of a signal-to-noise ratio, position information and / or force information of the input object, a gesture, an action to be taken based on the gesture or a combination of gestures or other information, and other operations when at least one input object is within a sensing area.

[0021] The sensor module (160) may include functionality for determining a touch event. For example, as described further below, the sensor module (160) may include sensing circuitry coupled to receiver electrodes. The sensor module (160) may receive one or more result signals from the receiver electrodes disposed on the layer of piezoelectric material. The result signals may include at least one of a desired signal, e.g., a component caused by an input object exerting a force at the sensing region (120), and an undesired signal, e.g., noise or interference.

[0022] Although FIG. 1 shows a decision module (150) and a sensor module (160), alternative or additional modules may be present in accordance with one or more embodiments. Examples of alternative or additional modules include a hardware operation module for operating hardware such as the sensor electrodes and the display screen (155), a data processing module for processing data such as, for example, the sensor signals and position information and / or force information, a reporting module for reporting information, an identification module configured to identify gestures such as, for example, a mode change gesture, and a mode change module for changing the operating mode. Furthermore, various modules may be combined in separate integrated circuits. For example, a first module may be at least partially included in a first integrated circuit and another module may be at least partially included in a second integrated circuit. Furthermore, portions of a single module may span multiple integrated circuits. In some embodiments, a processing system may perform the operations of the various modules as a whole.

[0023] In some embodiments, the processing system (110) responds directly to user input (or lack of user input) at the sensing area (120) by triggering one or more actions, such as changing an operational mode or graphical user interface (GUI) actions, such as cursor movement, selection, menu navigation, and other functions. In some embodiments, the processing system (110) provides information about the input (or lack of input) to a portion of the electronic system (e.g., to a central processing system of the electronic system separate from the processing system (110), if such a central processing system exists). In some embodiments, a portion of the electronic system processes the information received from the processing system (110) and acts in response to the user input, such as facilitating any action, including mode change actions and GUI actions.

[0024] In some embodiments, the input device (100) includes a touch screen interface, and the sensing region (120) overlaps at least a portion of the active area of ​​the display screen (155). For example, the input device (100) may include a substantially transparent sensor electrode overlaid on the display screen to provide a touch screen interface to an associated electronic system. The display screen may be any type of dynamic display capable of displaying a visual interface to a user, and may include any type of light emitting diode (LED), organic LED (OLED), cathode ray tube (CRT), liquid crystal display (LCD), plasma, electroluminescence (EL), or other display technology. The input device (100) and the display screen (155) may share physical components. For example, some embodiments may use some of the same electrical components for display and sensing. In various embodiments, one or more display electrodes of the display device may be configured for both display updates and input sensing. As another example, the display screen (155) may be operated in part or in whole by the processing system (110).

[0025] Turning to Figure 2, a piezoelectric touch sensing system (200) is shown in accordance with one or more embodiments. The piezoelectric touch sensing system (200) includes a piezoelectric sensing module (210). The piezoelectric sensing module (210) may output one or more result signals (280) in response to the presence or absence of a touch, such as by a finger (298) or any other input object. The result signal(s) (280) may be processed by touch circuitry (250), as described below.

[0026] The piezoelectric sensing module (210) may be used to provide touch sensing for all or a portion of the sensing area (120) shown in Figure 1. The piezoelectric sensing module (210) may also provide display for all or a portion of the display screen (155). The touch circuitry (250) may be a component of the processing system (110).

[0027] In one or more embodiments, the piezoelectric sensing module (210) has multiple layers including a display (212) or substrate (when no display is present), various layers (214, 215, 216) for piezoelectric touch sensing, and a cover layer (218). In one embodiment, the display (212) is an OLED display. Multiple display layers may form the display (212). For example, an OLED display may include an organic light-emitting layer, an anode layer, a cathode layer, one or more conductive layers that may include a thin-film transistor (TFT) layer, and the like. The display layer stack may also include a display substrate. The display substrate may be a rigid or flexible glass or plastic substrate. Alternatively, the display (212) may be a micro LED display, a TFT display, or any other type of display including the corresponding layers.

[0028] In one or more embodiments, the layers (214, 215, 216) for piezoelectric touch sensing form a piezoelectric element (220) and include a receiver electrode layer (214), a piezoelectric film (215), and a common electrode layer (216). A cover layer (218) may provide a touchable surface. The functions of these layers are described below. Further details regarding the piezoelectric element (220) are also provided below with reference to Figures 5A and 5B.

[0029] In one or more embodiments, the receiver electrode layer (214), the piezoelectric film (215), and the common electrode layer (216) of the piezoelectric element (220) are arranged in a sandwich architecture with the piezoelectric material sandwiched between the two electrode layers. Due to the piezoelectric effect associated with the piezoelectric material, when a force load is applied to the piezoelectric film (215), the charge balance across the piezoelectric film (215) changes. This change in charge balance may be recorded as a voltage between the receiver electrode of the receiver electrode layer (214) and the common electrode of the common electrode layer (216). In one embodiment, the piezoelectric film is a polyvinylidene fluoride (PVDF) piezoelectric film. Other piezoelectric materials may be used without departing from the disclosure, such as, for example, copolymers of PVDF, polylactic acid piezoelectric biopolymers, polyurea, polyurethane, polyamide, polyacrylonitrile, polyimide, polypropylene, etc. Additional layers may be added to the piezoelectric film. The additional layers may include, for example, one or more of a hard coat layer, an index matching layer, an antistatic layer, etc. A description of the piezoelectric film is provided in PCT Patent Application No. PCT / JP2021 / 013199, the entirety of which is incorporated herein by reference.

[0030] In one or more embodiments, both the receiver electrode layer (214) and the common electrode layer (216) include one or more electrodes configured to detect changes in charge balance across the piezoelectric film (215). The electrodes may be made of transparent conductive coatings such as, for example, carbon nanotubes (CNTs), doped CNTs, a mixture of CNTs and metal nanowires (e.g., silver nanowires), conductive polymers (e.g., PEDOT:PSS), graphene, metal mesh, and the like. The common electrode(s) of the common electrode layer (216) may be held at a reference potential, such as, for example, signal ground, while the receiver electrode(s) of the receiver electrode layer (214) may float relative to a reference potential based on the charge balance across the piezoelectric film (215). To enable detection of the location of a force applied to the piezoelectric film (215), the receiver electrode layer (214) and, optionally, the common electrode layer (216) may include patterned electrodes. The use of patterned electrodes to detect the location of a force applied to the piezoelectric film (215) is described below with reference to Figures 6A and 6B.

[0031] In one or more embodiments, the cover layer (218) provides a protective surface for the sensing display module. The cover layer (218) may be a thin glass or plastic layer with mechanical characteristics that allow for the transmission of forces applied by an input object (e.g., a finger (298)) to the piezoelectric film (215).

[0032] In one or more embodiments, the receiver electrode layer (214), the piezoelectric layer (215), the common electrode layer (216), and the cover layer (218) are substantially transparent, thereby allowing a user to view the visual content displayed by the display (212).

[0033] Turning now to the touch circuitry (250), in one or more embodiments the touch circuitry (250) receives a result signal (280) reflecting the charge balance across the piezoelectric film relative to a reference potential (270). In one or more embodiments, the result signal is processed by the touch circuitry (250) to generate a touch / force signal (290) that may be indicative of a touch and / or force by an input object (298). The touch circuitry (250) may perform various operations, such as, for example, charge integration, low pass filtering, analog to digital conversion, etc.

[0034] 2 shows a single touch circuit (250), in one or more embodiments, multiple touch circuits may be used in conjunction with multiple receiver electrodes in the receiver electrode layer (214), as discussed with reference to Figures 6A and 6B. Alternatively, multiplexing may be used to read multiple receiver electrodes with a single touch circuit.

[0035] FIG. 3 illustrates an energy harvesting system according to one or more embodiments. The piezoelectric energy harvesting system (300) converts mechanical energy into electrical energy. In one embodiment, a piezoelectric element (310) including one or more piezoelectric films is used as a transducer. As will be further discussed with reference to FIG. 5C, multiple piezoelectric films may be stacked to increase the amount of electrical energy generated. The conditioning circuit (320) may convert the variable output generated by the piezoelectric element (310) into a DC voltage for the electrical load (330). The conditioning circuit (320) may include an AC / DC converter (324) and a DC / DC voltage regulator (326) controlled by a power management unit (328) for managing the power generated as a function of the power load requirements and the available power from the piezoelectric element (310). The conditioning circuit (320) may further include an impedance matching circuit (322) to ensure maximum transfer of the harvested electrical energy. The energy storage device 340 may be used to store the energy collected by the collection unit for supplying the electrical load 330 under any operating conditions. The energy storage device 340 may be, for example, a battery or a supercapacitor.

[0036] FIG. 4 illustrates an actuator according to one or more embodiments. The piezoelectric actuator (400) generates a mechanical output, e.g., motion (416), in the presence of an electrical input, e.g., a voltage. The piezoelectric actuator (400) includes a piezoelectric element (410). As described below, e.g., with reference to FIG. 5A, the piezoelectric element (410) includes a piezoelectric film (412) and an electrode (414). The piezoelectric element is mechanically secured by an anchor (420). When a voltage is applied to the piezoelectric film (412), the piezoelectric material expands according to the polarization of the applied voltage, thereby causing axial bending over the length of the piezoelectric film. As will be further discussed with reference to FIG. 5C, multiple piezoelectric films may be stacked to increase the amplitude of motion and / or enable more complex motion patterns, e.g., motion in multiple dimensions, e.g., three or more dimensions including translational and / or rotational motion.

[0037] Turning to Figures 5A, 5B, and 5C, two configurations of a piezoelectric sensor are shown in accordance with one or more embodiments.

[0038] Referring to FIG. 5A, the piezoelectric element (500) includes a piezoelectric film (510), a first electrode layer (520), and a second electrode layer (530). The first electrode layer may include one or more receiver electrodes (214) or one or more common electrodes (216). Similarly, the second electrode layer may include one or more receiver electrodes (214) or one or more common electrodes (216). In one or more embodiments, the first electrode layer (520) and the second electrode layer (530) are disposed directly on the piezoelectric film (510). In one or more embodiments, at least one of the first electrode layer and the second electrode layer includes an electrode formed from a carbon nanotube (CNT) material. The CNT-based electrode may be deposited directly on the piezoelectric film (510).

[0039] Referring to FIG. 5B, the piezoelectric element (550) includes the components of the piezoelectric element (500) of FIG. 5A, plus a polyethylene terephthalate (PET) layer (570) and an adhesive (580). The PET layer (570) may be used as a substrate for depositing the second electrode layer (560). Thus, in the embodiment of FIG. 5B, only the first electrode layer (520) and not the second electrode layer (560) is deposited directly onto the piezoelectric film. The adhesive (580) may permanently bond the PET layer (570) with the second electrode layer (560) to the piezoelectric film (510). The piezoelectric element (550) may otherwise be similar to the piezoelectric element (500). In one or more embodiments, at least one of the first electrode layer and the second electrode layer includes an electrode formed from a carbon nanotube (CNT) material. The CNT-based electrode in the first electrode layer (520) may be deposited directly on the piezoelectric film (510), while the CNT-based electrode in the second electrode layer (560) may be deposited directly on the PET layer (570).

[0040] Referring to FIG. 5C, the piezoelectric element (570) includes a plurality of piezoelectric elements (500) as shown in FIG. 5A. Any number of piezoelectric elements (500) may be stacked. An adhesive (590) may mechanically connect the individual piezoelectric elements (500). To obtain a higher output voltage in response to a mechanical input, the individual piezoelectric elements (500) may be electrically connected in series. Alternatively, in configurations involving electrically driving the piezoelectric elements (570), stacking multiple piezoelectric elements (500) may increase the generated motion amplitude and / or enable more complex motion patterns, such as motion in multiple dimensions, e.g., three or more dimensions including at least one of translational and rotational motion.

[0041] A detailed discussion of the fabrication of the piezoelectric elements of Figures 5A, 5B, and 5C, including the deposition of CNT material onto the piezoelectric film and the resulting features, is provided below with reference to Figure 7. Additionally, examples of electrode arrangements in the first and second layers (520, 530, 560) are provided with reference to Figures 6A and 6B.

[0042] Turning to FIG. 6A, an electrode pattern (600) is shown. The electrode pattern includes rows of receiver electrodes (602) and columns of common electrodes (604). The receiver electrodes (602) may be located on the first or second electrode layer of the piezoelectric element of FIG. 5A, FIG. 5B, and FIG. 5C. Similarly, the common electrode (604) may be located on the first or second electrode layer of the piezoelectric element of FIG. 5A, FIG. 5B, and FIG. 5C. In the sensor pattern (600), the receiver electrodes (602) and the common electrode (604) have a rectangular shape. The electrodes may have different shapes without departing from the present disclosure. For example, interconnected diamond-shaped electrode pads may be arranged in rows or columns. Although not shown, as discussed above, the piezoelectric film (215) may be located between the receiver electrodes (602) located on one surface of the piezoelectric film and the common electrodes (604) located on the other surface of the piezoelectric film.

[0043] In one embodiment, the common electrode (604) may be set to a reference potential, such as signal ground, while the receiver electrode (602) is floated. A result signal may be obtained for each receiver electrode (602) and common electrode (604) pair, such as using the touch circuitry (250).

[0044] At the intersection of the receiver electrode (602) and the common electrode (604), a local voltage measurement (corresponding to the force signal (290)) may be performed to determine the local effect of the force acting on the piezoelectric film (215). This area of ​​local voltage measurement may be termed a "sensing element" (606). Although only a single sensing element (606) is identified in FIG. 6A, there may be a sensing element (606) at each intersection of the receiver electrode (602) and the common electrode (604). By performing a sensing operation on each sensing element (606), the local effect of the force acting on the piezoelectric film (215) may be evaluated across the entirety (or a portion) of the piezoelectric film (215). The sensing operations may be performed in a scanning operation, e.g., row-by-row or column-by-column, until an entire frame of the sensing operation is completed. Each sensing operation may be performed by the touch circuitry (220) as described above. The result may be a set of touch / force signals, each indicative of a touch / force at a corresponding sensing element. The location where the input object is actually exerting a force on the piezoelectric element may then be estimated. For example, it may be determined that the location is at the sensing element having the touch / force signal with the highest voltage or highest voltage change over time. To increase accuracy, spatial interpolation between multiple sensing elements may be performed based on the corresponding force signals.

[0045] Turning to Figure 6B, an electrode pattern (650) is shown. The electrode pattern includes a pattern of receiver electrodes (652) and a single common electrode (654) that spans the area of ​​the receiver electrodes (652). The receiver electrodes (652) may be located on the first or second electrode layer of the piezoelectric elements of Figures 5A, 5B, and 5C. Similarly, the common electrode (654) may be located on the first or second electrode layer of the piezoelectric elements of Figures 5A, 5B, and 5C. Each receiver electrode (652) in the sensor pattern (650) is a pad that may have any shape.

[0046] In one embodiment, the common electrode (654) may be set to a reference potential, such as signal ground, while the receiver electrodes (652) are floated. A result signal may be obtained for each receiver electrode (652), such as using the touch circuitry (250).

[0047] A sensing element 656 is formed on each receiver electrode 652. Although the design of the electrode pattern 650 differs from the design of the electrode pattern 600, the touch / force signals (one for each receiver electrode 652) are obtained in a similar manner.

[0048] 6A and 6B show two types of electrode patterns, other types of electrode patterns may be used without departing from this disclosure. In addition, non-patterned electrodes (e.g., solid surface electrodes) may be used. Furthermore, the size and / or resolution of the electrode patterns may be scaled without departing from this disclosure.

[0049] In addition, although Figures 1, 2, 3, 4, 5A, 5B, 5C, 6A, and 6B depict configurations of components, other configurations may be used without departing from the scope of the present disclosure. For example, various components may be combined to create a single component. As another example, functions performed by a single component may be performed by two or more components. Furthermore, while piezoelectric elements are described in conjunction with touch sensing and / or force sensing, embodiments of the present disclosure relate more generally to any type of piezoelectric element, including piezoelectric sensors, energy collectors, and actuators.

[0050] FIG. 7 illustrates a method (700) of fabricating a piezoelectric element according to one or more embodiments. More specifically, FIG. 7 illustrates depositing carbon nanotube (CNT) material onto a substrate using a wet coating process. The substrate may be a piezoelectric film (e.g., a PVDF film) or another substrate, such as, for example, a PET layer. Although the various steps in FIG. 7 are provided and described sequentially, one of ordinary skill in the art will recognize that some or all steps may be performed in a different order, may be combined or omitted, and some or all steps may be performed in parallel.

[0051] In step 702, a carbon nanotube (CNT) dispersion or solution is prepared. The dispersion may be based on any liquid of any viscosity, such as water, ethanol, oil, polymer, epoxy resin, etc. Mechanical or chemical approaches may be used to generate the dispersion. Mechanical approaches include, for example, sonication and high shear mixing. Chemical approaches include covalent methods with functionalization and non-covalent methods with chemical moieties. Surfactants may be used to facilitate dispersion. In one embodiment, a nanotube solvent capable of dissolving CNT molecules is used to create a CNT solution. As an example, the carbon nanotube solvent may be an acid, such as, for example, chlorosulfonic acid (HSO3Cl), fluorosulfonic acid, fluorosulfuric acid, hydrochloric acid, methanesulfonic acid, nitric acid, hydrofluoric acid, fluoroantimonic acid, magic acid, or any other type of carborane-based acid. As another example, the nanotube solvent may be a supercritical fluid, which is a substance at a temperature and pressure above its critical point. The nanotube solvent as a supercritical fluid provides screening of electrostatic interactions between solute molecules, in this case CNT molecules, eliminating the effects of surface tension and particle-particle interactions, allowing dissolution. Once the nanotube solvent exceeds its critical point, its temperature and pressure may be adjusted to maintain maximum solubility of the CNT molecules, such that the nanotube solvent in the supercritical state may be considered non-thermal for all effective purposes. By way of example, the nanotube solvent as a supercritical fluid may include supercritical carbon dioxide.

[0052] In one or more embodiments, additional components are added to the dispersion or solution. For example, silver nanowires may be mixed into the dispersion or solution. Any amount of silver nanowires may be added. For example, silver nanowires may be added to reach a concentration anywhere between 0.01 mg / ml and 0.1 mg / ml. In one or more embodiments, doping of the CNTs may be performed. Doping may be performed on the CNTs before preparing the CNT solution or dispersion. Any type of doping may be performed. For example, at least one of iodine vapor doping, HNO3 vapor doping, SOCl2 vapor doping, and MoO3 vapor doping may be performed. Doping and / or adding components to the dispersion or solution may be performed for any reason. In one or more embodiments, doping and / or adding components to the dispersion or solution is performed to lower the resistance of the CNTs.

[0053] In step 704, a substrate, such as a piezoelectric film, is coated with the CNT nanotube dispersion or solution to form an electrode layer on the substrate. Any type of coating method may be used, such as spray coating, screen printing, spin coating, blade coating, dip coating, vacuum filtration coating, etc. The choice of coating method may depend on the desired type of electrode layer. For example, screen printing may be more suitable for producing patterned electrodes, while spin coating may be more suitable for producing homogeneous non-patterned electrodes. The choice of coating method may further depend on the viscosity of the CNT dispersion or solution. Step 504 may be performed on one or both sides of the piezoelectric film.

[0054] In step 506, the carbon nanotube coating (706) is cured. Any type of curing method that is not detrimental to the piezoelectric film may be used. For example, curing at elevated temperature is performed while the temperature is kept below the Curie temperature of the piezoelectric material of the piezoelectric film. For example, curing at room temperature or at a slightly elevated temperature, e.g., 60-70°C, may be performed.

[0055] Additional steps may be performed without departing from the present disclosure. For example, an electrical interface may be created to the electrode(s) of the electrode layer(s) upon completion of curing of the CNT coating. The electrical interface may include contact pads on the surface of the electrode layer(s). Additionally, assembly operations may be performed to integrate the piezoelectric element with other components. Assembly operations may include steps such as, for example, gluing or otherwise attaching additional layers to the piezoelectric element.

[0056] Fabrication of piezoelectric elements according to embodiments of the present disclosure may have various advantages. In particular, because a wet coating process is used, the piezoelectric material of the piezoelectric film may maintain its piezoelectricity. Thus, no significant heat is applied, unlike other processes, such as physical vapor deposition (PVD) used to deposit tin doped iridium (ITO). In addition, the wet coating process is cost-effective compared to the PVD process. Furthermore, a high level of transparency of the electrode may be achieved with the CNT-based electrode. An additional advantage may be that unlike ITO films, which are known to be hard and brittle, the CNT-based electrode may have a high level of flexibility and durability. Furthermore, the CNT-based electrode is known to be environmentally stable, thus reducing the cost of meeting environmental standards.

[0057] The following examples of piezoelectric elements according to embodiments of the present disclosure provide performance characteristics, although embodiments of the present disclosure are not limited to these examples.

[0058] In one embodiment, the piezoelectric film has certain characteristics, such as the charge in response to an applied force, i.e., the piezoelectric coefficient d 31 The sensitivity (expressed as ) may be greater than 10 pC / N or greater than 20 pC / N. In addition, the piezoelectric film may have any thickness, such as in the range of 10 to 200 μm. The optical transmittance of the piezoelectric film may be at least 90% or at least 95%. The optical haze optical transmittance of the piezoelectric film may be less than 10% or <5%.

[0059] In one embodiment, the CNT-based electrode has certain characteristics. For example, the sheet resistance across the CNT-based electrode may be kept low to obtain an increased signal-to-noise ratio (SNR). The sheet resistance may be less than 300 ohms / sq., less than 100 ohms / sq., or less than 50 ohms / sq. The optical transmittance of the CNT-based electrode layer may be at least 90% or at least 95%. The optical haze optical transmittance of the CNT-based electrode layer may be less than 10% or less than <5%.

[0060] Although only a few example embodiments have been described in detail above, those skilled in the art will readily recognize that many modifications are possible in these example embodiments without substantially departing from the present invention. Accordingly, all such modifications are intended to be included within the scope of the present disclosure as defined in the following claims. Any means-plus-function clause in the claims is intended to encompass structures described herein as performing the described function(s) and equivalents of those structures. Similarly, any step-plus-function clause in the claims is intended to encompass acts described herein as performing the described function(s) and equivalents of those acts. It is the express intent of the applicants not to invoke 35 U.S.C. 112(f) on any limitation of any claim herein, unless the claim expressly uses the words "means for" or "step for" with the relevant function.

Claims

1. A piezoelectric film; a first carbon nanotube (CNT)-based electrode layer disposed directly on at least one side of the piezoelectric film, the CNT-based first electrode layer having a sheet resistance of less than 300 ohms / sq.

2. The piezoelectric film is selected from the group consisting of polyvinylidene fluoride (PVDF) piezoelectric films, PVDF copolymer films, polylactic acid piezoelectric biopolymer films, polyurea films, polyurethane films, polyamide films, polyacrylonitrile films, polyimides, and polypropylene films; The piezoelectric element according to claim 1 .

3. the piezoelectric film having a light transmittance of at least 90%; The piezoelectric element according to claim 1 .

4. the piezoelectric film having an optical haze of less than 5%; The piezoelectric element according to claim 1 .

5. The piezoelectric film has a thickness in the range of 10 μm to 200 μm. The piezoelectric element according to claim 1 .

6. The piezoelectric film has a piezoelectric coefficient d ３１ having The piezoelectric element according to claim 1 .

7. the first CNT-based electrode layer comprises silver nanowires; The piezoelectric element according to claim 1 .

8. The first CNT-based electrode layer is ３ , SOCl ２ , and MoO ３ 2. The piezoelectric element of claim 1, doped with at least one selected from the group consisting of:

9. the first CNT-based electrode layer has a light transmittance of at least 90%; The piezoelectric element according to claim 1 .

10. the first CNT-based electrode layer having an optical haze of less than 5%; The piezoelectric element according to claim 1 .

11. the piezoelectric element is selected from the group consisting of a sensing device, an energy harvester, and an actuator; The piezoelectric element according to claim 1 .

12. further comprising a second CNT-based electrode layer disposed directly on the piezoelectric film. The piezoelectric element according to claim 1 .

13. 1. A method for manufacturing a piezoelectric element, comprising the steps of: Obtaining a carbon nanotube (CNT) dispersion; coating a piezoelectric film with the CNT dispersion to obtain a CNT-based electrode layer directly disposed on the piezoelectric film; and curing the CNT-based electrode layer. The method, wherein the CNT-based electrode layer has a sheet resistance of less than 300 ohms / sq.

14. The coating comprises one selected from the group consisting of spray coating, screen printing, spin coating, blade coating, dip coating, and vacuum filtration coating; The method of claim 13.

15. the curing step comprises exposing the CNT-based electrode layer to a temperature below the Curie temperature of the piezoelectric film. The method of claim 13.

16. The step of obtaining the CNT dispersion includes adding at least one selected from the group consisting of silver nanowires, metal meshes, conductive polymers, and graphene to the CNT dispersion; The method of claim 13.

17. The step of obtaining the CNT dispersion comprises using iodine, HNO ３ , SOCl ２ , and MoO ３ doping the CNT dispersion with at least one selected from the group consisting of: The method of claim 13.

18. 1. A piezoelectric input device, comprising: The piezoelectric element includes: A piezoelectric film; a first carbon nanotube (CNT) based electrode layer disposed directly on at least one side of the piezoelectric film, the CNT-based first electrode layer having a sheet resistance of less than 300 ohms / sq. and forming a plurality of receiver electrodes, the piezoelectric input device further comprising: a processing system for determining a position of the input object based on resultant signals obtained from the plurality of receiver electrodes.

19. The piezoelectric film is selected from the group consisting of polyvinylidene fluoride (PVDF) piezoelectric films, PVDF copolymer films, polylactic acid piezoelectric biopolymer films, polyurea films, polyurethane films, polyamide films, polyacrylonitrile films, polyimides, and polypropylene films; 20. The piezoelectric input device of claim 18.

20. the first CNT-based electrode layer comprises silver nanowires; 20. The piezoelectric input device of claim 18.

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