Touch detection using polyvinylidene fluoride piezoelectric film

Abstract

A piezoelectric sensing module comprises a polyvinylidene fluoride (PVDF) piezoelectric film, a first electrode layer comprising a plurality of receiving electrodes arranged in a first pattern to detect the position of an input object on a touch surface using the PVDF piezoelectric film, and a second electrode layer comprising at least one common electrode. The PVDF piezoelectric film is arranged between the first electrode layer and the second electrode layer, and the second electrode layer is between the PVDF piezoelectric film and the touch surface.

Description

Technology Field

[0001] Cross-reference regarding related applications

[0002] This application claims the benefit of priority under 35 USC § 119(e) to U.S. Provisional Patent Application No. 63 / 316,904 filed on March 4, 2022, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Input devices including touch sensor devices (e.g., touchpads or touch sensor devices) are widely used in various electronic systems. A touch sensor device generally includes a sensing area represented by a surface that determines the presence, location, and / or motion of one or more input objects. Touch sensor devices can be used to provide interfaces to electronic systems. For example, touch sensor devices are often used as input devices in large computing systems (e.g., integrated into laptops or desktop computers, or as peripheral opaque touchpads). Touch sensor devices can be used in other environments with unique problems, such as different types of noise and moisture exposure. means of solving the problem

[0004] This summary is provided to introduce the selection of concepts that are further explained below in the detailed description. This summary is not intended to identify the core or essential features of the claimed technical concept, nor is it intended to be used as supplementary material to limit the scope of the claimed technical concept.

[0005] Generally, in one aspect, embodiments comprise a polyvinylidene fluoride (PVDF) piezoelectric film, a first electrode layer comprising a plurality of receiving electrodes arranged in a first pattern to detect the position of an input object on a touch surface using the PVDF piezoelectric film, and a second electrode layer comprising at least one common electrode, wherein the PVDF piezoelectric film is arranged between the first electrode layer and the second electrode layer and the second electrode layer is a piezoelectric sensing module located between the PVDF piezoelectric film and the touch surface.

[0006] Generally, in one aspect, embodiments relate to a piezoelectric input device comprising a polyvinylidene fluoride (PVDF) piezoelectric film and a first electrode layer comprising a plurality of receiving electrodes arranged in a first pattern to detect the position of an input object on a touch surface using the PVDF piezoelectric film, wherein the PVDF piezoelectric film and the first electrode layer are arranged substantially transparently beneath the touch surface, and a processing system for determining the position of the input object based on a result signal obtained from the plurality of receiving electrodes.

[0007] Generally, in one aspect, embodiments of a method for detecting a piezoelectric touch include the steps of: obtaining a first force signal from a piezoelectric sensing module comprising a polyvinylidene fluoride (PVDF) piezoelectric film; registering the start of a touch event based on a determination that the amplitude of the first force signal is greater than or equal to a first predetermined threshold; obtaining a second force signal; and registering the end of the touch event based on a determination that the amplitude of the second force signal is greater than or equal to a second predetermined threshold and that the polarities of the first and second force signals are opposite to each other.

[0008] Other aspects and advantages of the claimed technical concept will become apparent from the following detailed description and the appended claims. Brief explanation of the drawing

[0009] Specific embodiments of the disclosed technology will now be described in detail with reference to the accompanying drawings. Similar elements in the various drawings are indicated by similar reference numbers for consistency. FIG. 1 illustrates an input device according to one or more embodiments. FIG. 2 illustrates a touch sensing system according to one or more embodiments. FIGS. 3A and FIGS. 3B illustrate electrode patterns according to one or more embodiments. FIGS. 4A through 4I illustrate exemplary stack-ups of a sensing display module according to one or more embodiments. FIG. 5 illustrates a flowchart of a method for piezoelectric touch detection according to one or more embodiments. FIG. 6 illustrates an example according to one or more embodiments. Specific details for implementing the invention

[0010] In the following detailed description of embodiments of the present disclosure, a number of specific details are described to provide a more complete 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 cases, well-known features have not been described in detail to avoid making the description unnecessarily complex.

[0011] Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as adjectives for elements (i.e., any noun within the application). The use of ordinal numbers is not intended to imply or create a specific order of elements, or to restrict any element to a single element, unless explicitly stated by using terms such as "previous," "subsequent," "single," or others. Rather, the use of ordinal numbers is to distinguish elements. For example, the first element is distinguished from the second element, the first element may include one or more elements, and may be a subsequent (or preceding) element to the second element in the order of elements.

[0012] Generally, embodiments of the present disclosure include systems and methods for touch sensing using a polyvinylidene fluoride (PVDF) piezoelectric film. One or more embodiments of the present disclosure enable touch sensing that provides the location of an input object present in a sensing area of ​​an input device based on piezoelectric sensing. Touch sensing may further provide the amplitude of the force applied by the input object. One or more embodiments of the present disclosure do not use additional sensing technology (e.g., capacitive touch sensing) to determine the location of the input object. Accordingly, embodiments of the present disclosure have various advantages. For example, methods and systems as described reduce costs because additional touch sensing technology is not required. In addition, the described methods and systems do not have the limitations of other touch sensing technologies. For example, compared to capacitive touch sensing, methods and systems using piezoelectric touch sensing are more resistant to environmental influences such as moisture. Accordingly, embodiments of the present disclosure are suitable for wet or even underwater environments, such as touch interfaces in kitchens, bathrooms, outdoor, industrial, production, and medical environments, digital signage, and appliances. Embodiments of the present disclosure further include features that enhance robustness against noise, such as high-frequency noise and pyroelectric noise. Consequently, the probability of false touch detection (false positives and false negatives) is significantly reduced. Accordingly, embodiments of the present disclosure are highly suitable for safety-related applications, such as military, aerospace, automotive, industrial, and medical applications. In general, embodiments of the present disclosure are suitable for harsh environments and applications requiring high reliability. Detailed description follows.

[0013] FIG. 1 is a block diagram of an exemplary piezoelectric input device (100) according to one or more embodiments. The piezoelectric input device (100) may be configured to provide input to an electronic system (not shown in the drawing). As used herein, the term "electronic system" (or "electronic device") broadly refers to any system capable of processing information electronically. Some non-limiting examples of electronic systems include personal computers such as desktop computers, laptop computers, tablets, machines and medical devices having at least some degree of computing capability. Additional exemplary electronic systems include peripheral devices such as data input devices (including remote controls, mice, haptic input devices, or sensing devices including robot probes, hands, pressure measuring devices, etc.) and data output devices (including display screens and printers). Other examples include remote terminals, kiosks, and video game devices (e.g., video game consoles, portable game devices, etc.). Other examples include communication devices (including mobile phones such as smartphones) and media devices (including recorders, editors, and players such as televisions, set-top boxes, music players, digital photo frames, and digital cameras). Additionally, the electronic system can be a host or a slave of an input device.

[0014] In FIG. 1, the piezoelectric input device (100) is illustrated as a touch sensor device (e.g., "touchpad" or "touch sensor device") configured to detect input provided by one or more input objects in a sensing area (120). Examples of input objects include a stylus, fingers (140), etc.

[0015] The detection area (120) includes all space above, around, inside, and / or near the input device (100) where the input device (100) can detect user input (e.g., user input provided by one or more input objects). The sizes, shapes, and locations of specific detection areas may vary significantly depending on the embodiment.

[0016] The input device (100) may use any combination of sensor components and technologies to detect user input in 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., an asymmetric material in which polarization shifts in a positive or negative direction depending on the direction of the applied force), the charge balance of the piezoelectric material changes. By measuring the induced voltage, a touch event associated with the force load can be determined, and the applied force can be calculated.

[0017] In some piezoelectric implementations, arrays of receiving electrodes or other regular or irregular patterns are utilized to capture induced voltages at different locations of the piezoelectric material associated with the sensing area (120). Accordingly, the location of the touch event in the input area (120) can be determined.

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

[0019] In some embodiments, the processing system (110) also includes electronically readable commands, such as firmware code, software code, etc. In some embodiments, the components constituting the processing system (110) are located together near the sensing element(s) of the input device (100). In other embodiments, the components of the processing system (110) are physically separated from one or more components located elsewhere, and from one or more components located elsewhere, and from one or more components located near the sensing element(s) of the input device (100). 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 the central processing unit of the computing device and one or more ICs (possibly including associated firmware) separated from the central processing unit. As another example, the input device (100) may be physically integrated into a mobile device, and the processing system (110) may include circuits and firmware that are 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) also performs other functions, such as operating display screens (155) and driving haptic actuators.

[0020] The processing system (110) may be implemented as a set of modules that process various functions of the processing system (110). Each module may include a circuit, firmware, software, or a combination thereof that is part of the processing system (110). In various embodiments, various combinations of modules may be used. For example, as illustrated in FIG. 1, the processing system (110) may include a decision module (150) and a sensor module (160). The decision module (150) may include a function to determine whether at least one input object is in a detection area, a signal-to-noise ratio, location and / or force information of the input object, a gesture, an action to be performed based on the gesture, gestures or other information and / or other operations.

[0021] The sensor module (160) may include a function for determining touch events. For example, the sensor module (160) may include sensor circuitry coupled to receiving electrodes as further described below. The sensor module (160) may receive one or more resulting signals from receiving electrodes disposed on a piezoelectric material layer. The resulting signals may include desired signals, such as components generated by an input object applying force to the sensing area (120), and / or unwanted signals, such as noise or interference.

[0022] FIG. 1 illustrates a decision module (150) and a sensor module (160), but alternative or additional modules may exist according to one or more embodiments. Exemplary alternative or additional modules may include hardware operation modules for operating hardware such as sensor electrodes and display screens (155), data processing modules for processing data such as sensor signals and position and / or force information, reporting modules for reporting information, identification modules configured to identify gestures such as mode change gestures, and mode change modules for changing operation modes. Additionally, various modules may be combined into separate integrated circuits. For example, a first module may be at least partially included in a first integrated circuit, and a separate module may be at least partially included in a second integrated circuit. Additionally, parts of a single module may span across multiple integrated circuits. In some embodiments, the processing system may perform the operations of various modules in whole.

[0023] In some embodiments, the processing system (110) directly responds to user input (or lack of user input) in the detection area (120) by generating one or more actions. Examples of actions include changing operation modes as well as 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 part of the electronic system (e.g., if such a separate central processing system exists, the central processing system of the electronic system separate from the processing system (110)). In some embodiments, the part of the electronic system processes the information received from the processing system (110) and operates according to the user input, such as facilitating a full range of actions including mode change actions and GUI actions.

[0024] In some embodiments, the input device (100) includes a touch screen interface, and the sensing area (120) overlaps with at least a portion of the active area of ​​the display screen (155). For example, the input device (100) may include substantially transparent sensor electrodes that overlap with the display screen and may provide a touch screen interface to the 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, electroluminescent (EL), or other display technology. The input device (100) and the display screen (155) may share physical elements. For example, some embodiments may utilize 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 partially or wholly by the processing system (110).

[0025] FIG. 1 illustrates the configuration of components, but other configurations may be used without departing from the scope of the present disclosure. For example, various components may be combined to form a single component. As another example, a function performed by a single component may be performed by two or more components.

[0026] FIG. 2 illustrates a piezoelectric touch sensing system (200) according to 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 by, for example, a finger (298) or any other input object. The result signal(s) (280) may be processed by a touch circuit (220) as described below.

[0027] The piezoelectric sensing module (210) may be used to provide touch detection for all or part of the sensing area (120) shown in FIG. 1. The piezoelectric sensing module (210) may also provide a display for all or part of the display screen (155). The touch circuit (220) may be a component of the processing system (110).

[0028] In one or more embodiments, the piezoelectric sensing module (210) has a plurality of layers including a display (212) or a substrate (where there is no display), various layers (214, 215, 216) for piezoelectric touch sensing, and a cover layer (218). In one embodiment, the display (212) is an OLED display. A plurality of display layers may form the display (212). For example, the OLED display may include one or more conductive layers, such as an organic light-emitting layer, an anode layer, a cathode layer, and a thin-film transistor (TFT) layer. A stack of display layers 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 microLED display, a TFT display, or any other type of display comprising corresponding layers.

[0029] In one or more embodiments, the piezoelectric touch sensing layers (214, 215, 216) comprise a receiving electrode layer (214), a piezoelectric film (215), and a common electrode layer (216). A cover layer (218) may provide a contactable surface. The functions of these layers are described later. Further details regarding these layers are provided with reference to FIGS. 4A through 4I, which illustrate other possible stack-ups that can be used to arrange the layers.

[0030] In one or more embodiments, the receiving electrode layer (214), the piezoelectric film (215), and the common electrode layer (216) are arranged in a sandwich structure in which a piezoelectric material is positioned 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 of the entire piezoelectric film (215) changes. The change in charge balance can be registered as a voltage between the receiving electrode of the receiving 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. Without departing from the scope of the invention, other piezoelectric materials, such as copolymers of PVDF, may be used. The piezoelectric film may have specific characteristics. For example, sensitivity (expressed as charge relative to the applied force) may be in the range of 5 pC / N to 40 pC / N. To obtain an increased signal-to-noise ratio (SNR), the sheet resistance of the PVDF piezoelectric film with electrodes can be kept low. The sheet resistance may be 300 ohm / sq., 100 ohm / sq., or less. Additionally, the piezoelectric film may have any thickness, for example, in the range of 5 to 200 μm. Additional layers may be added to the piezoelectric film. The additional layers may include, for example, one or more of a hard coating layer, a refractive index matching layer, and an antistatic layer. A description of the piezoelectric film is provided in PCT patent application PCT / JP2021 / 013199. The entire contents of PCT / JP2021 / 013199 are incorporated herein by reference.

[0031] In one or more embodiments, the receiving electrode layer (214) and the common electrode layer (216) both include one or more electrodes configured to detect changes in charge balance across the piezoelectric film (215). The electrodes may be made of a transparent conductive oxide (TCO), e.g., indium tin oxide (ITO), or other transparent or seemingly transparent structures such as metal nanowires, carbon nanotubes, graphene, PEDOT polymer mixtures, etc. For opaque applications, additional electrode materials may be considered. For example, metals, inorganic oxides, carbon, conductive polymers, etc. may be used. The common electrode(s) in the common electrode layer (216) may be maintained at a reference potential, e.g., signal ground, while the receiving electrode(s) in the receiving electrode layer (214) may be floating relative to the reference potential based on the charge balance across the entire piezoelectric film (215). In order to detect the location of the force applied to the piezoelectric film (215), the receiving electrode layer (214) and potentially the common electrode layer (216) may include patterned electrodes. The use of patterned electrodes to detect the location of the force applied to the piezoelectric film (215) is discussed below with reference to FIG. 3.

[0032] In one or more embodiments, the cover layer (218) provides a protective surface of the sensing display module. The cover layer (218) may be a thin glass or plastic layer having mechanical properties that transmit a force applied by an input object (e.g., a finger (298)) to the piezoelectric film (215).

[0033] In one or more embodiments, the receiving electrode layer (214), the piezoelectric layer (215), the common electrode layer (216), and the cover layer (218) are substantially transparent so that the user can see the visual content displayed by the display (212).

[0034] Now, referring to the touch circuit (220), in one or more embodiments, the touch circuit (220) receives a resulting signal (280) that reflects the charge balance of the entire piezoelectric film with respect to a reference potential (270). In one or more embodiments, a charge integrator (230) is used to convert the measured charge balance (or, the change in charge balance when a force is applied) into a voltage (force signal (290)). A low-pass filter (240) is applied to the force signal (290) to reduce or remove higher frequency noise on the force signal (290) and further avoid aliasing by an analog-to-digital converter (ADC) (260). To suppress noise without interfering with actual touch events, the cutoff frequency of the filter may be set, for example, to 20 Hz, 30 Hz, or 40 Hz. Any suitable cutoff frequency may be used. Considerations for selecting the cutoff frequency may include, for example, the reduction or elimination of power supply noise at 50 Hz or 60 Hz and / or the elimination of other high-frequency noise. A digital force signal representing the force applied to the piezoelectric film (215) may be available at the output of the ADC (260). An example of a force signal (290) obtained in response to the application of force is shown in FIG. 6.

[0035] FIG. 2 illustrates a single touch circuit (220), but in one or more embodiments, as discussed with reference to FIG. 3A and FIG. 3B, multiple touch circuits may be used with multiple receiving electrodes of the receiving electrode layer (214). Alternatively, multiplexing may be used to read multiple receiving electrodes by a single touch circuit.

[0036] In FIG. 3A, an electrode pattern (300) is illustrated. The electrode pattern includes rows of receiving electrodes (302) and columns of common electrodes (304). In the sensor pattern (300), the receiving electrodes (302) and the common electrodes (304) have rectangular shapes. The electrodes may have various shapes without departing from the disclosure. For example, interconnected diamond-shaped electrode pads may be arranged in rows or columns. Although not illustrated, a piezoelectric film (215) may be positioned between the receiving electrodes (302) placed on one side of the piezoelectric film and the common electrodes (304) placed on the other side of the piezoelectric film.

[0037] In one embodiment, the common electrodes (304) can be set to a reference potential, e.g., signal ground, while the receiving electrodes (302) are fluid. For example, a result signal can be obtained for each of the pair of receiving electrodes (302) and common electrodes (304) using a touch circuit (220).

[0038] A local voltage measurement (corresponding to the force signal (290)) is performed at the intersection of the receiving electrode (302) and the common electrode (304) to determine the local effect of the force acting on the piezoelectric film (215). This local voltage measurement area may be referred to as a "sensing element" (306). Although only a single sensing element (306) is identified in FIG. 3a, the sensing element (306) may exist at each intersection of the receiving electrode (302) and the common electrode (304). By performing a sensing operation for each sensing element (306), the local effect of the force acting on the piezoelectric film (215) can be evaluated over the entire piezoelectric film (215) (or a part thereof). The sensing operations may be performed as a scanning operation, row by row or column by column, until the entire frame of the sensing operations is completed. Each sensing operation may be performed by the touch circuit (220) as described above. The result may be a series of force signals, each representing the force at the corresponding sensing element. The location where the input object actually applies force to the piezoelectric element can be estimated later. For example, the location can be determined as being at the sensing element by using the force signal having the highest voltage or the highest voltage change over time. To increase accuracy, spatial interpolation can be performed between multiple sensing elements based on these force signals.

[0039] In FIG. 3B, an electrode pattern (350) is illustrated. The electrode pattern includes a pattern of receiving electrodes (352) and single joint electrodes (354) extending across the area of ​​the receiving electrodes (352). In the sensor pattern (350), each receiving electrode (352) is a pad that can have any shape.

[0040] In one embodiment, the common electrodes (354) can be set to a reference potential, e.g., signal ground, while the receiving electrodes (352) are fluid. For example, a result signal can be obtained for each receiving electrode (352) using a touch circuit (220).

[0041] A sensing element (356) is formed on each receiving electrode (352). The design of the electrode pattern (350) is different from the design of the electrode pattern (300), but power signals (one per receiving electrode (352)) are obtained in a similar manner.

[0042] FIGS. 3A and FIGS. 3B illustrate two types of electrode patterns, but other types of electrode patterns may be used without departing from the disclosure. Additionally, the size and / or resolution of the electrode patterns may be adjusted without departing from the disclosure.

[0043] FIGS. 4A through 4I illustrate various examples of possible stack-ups of piezoelectric sensing modules according to one or more embodiments. The stack-ups of FIGS. 4A through 4I illustrate how the aforementioned layers can be arranged and how additional layers can be included in the stack-up.

[0044] Referring to FIG. 4A, the stack-up (400) comprises a display or substrate (401), a patterned electrode (403), a piezoelectric film (404), a common electrode (405), and a cover layer (407). The display or substrate (401) may be as previously described. The patterned electrode (403) may include a set of receiver electrodes as previously described. The patterned electrode (403) may be placed directly on the piezoelectric film (404). An air gap or direct coupling may be provided between the patterned electrode (403) and the display or substrate (401). The piezoelectric film (404), the common electrode (405), and the cover layer (407) may be as previously described. In the stack-up (400), the common electrode (405) is connected to signal ground. The common electrode may be placed directly on the piezoelectric film (404). The adhesive (406) can attach a cover layer (407) to the top of the stack-up (400).

[0045] Referring to FIG. 4B, the stack-up (410) comprises the components of the stack-up (400) of FIG. 4A and additionally includes a polyethylene terephthalate (PET) layer (411) and an adhesive (412). The PET layer (411) may be used to facilitate the manufacture of the piezoelectric sensing module. Specifically, the patterned electrode (403) may be placed on the PET layer (411) instead of being placed on the piezoelectric film (404). The adhesive (412) may permanently bond the PET layer (411) having the patterned electrode (403) to the piezoelectric film (404). The stack-up (410) may otherwise be similar to the stack-up (400).

[0046] Referring to FIG. 4C, the stack-up (420) comprises the components of the stack-up (410) of FIG. 4B and additionally includes a PET layer (422) and an adhesive (421). The PET layer (422) may be used to facilitate the manufacture of the piezoelectric sensing module. Specifically, the common electrode (405) may be placed on the PET layer (422) instead of being placed on the piezoelectric film (404). The adhesive (421) may permanently bond the PET layer (422) having the common electrode (405) to the piezoelectric film (404). The stack-up (420) may otherwise be similar to the stack-up (410).

[0047] Referring to FIG. 4D, the stack-up (430) includes the components of the stack-up (400). However, the stack-up (430) includes a shielding layer (432) instead of a cover layer (407). The shielding layer (432) may be electrically conductive and may be connected to a ground potential, e.g., system or device ground. The shielding layer (432) can thus reduce possible interference from external noise that would otherwise affect the power signal. The shielding layer (432) may have mechanical properties similar to those of the cover layer (407) and may be transparent. Unlike the cover layer (407), the shielding layer (432) may be conductive. For example, the shielding layer may include a conductive coating such as an ITO coating.

[0048] Referring to FIG. 4E, the stack-up (440) includes the elements of the stack-up (430) of FIG. 4D. However, in the stack-up (440), the positions of the patterned electrode (403) and the common electrode (405) in the stack-up are opposite to each other. The stack-up (440) may otherwise be similar to the stack-up (430).

[0049] Referring to FIG. 4F, the stack-up (450) includes elements of the stack-up (440) of FIG. 4E. However, in the stack-up (450), the shielding layer (452) provides multi-directional shielding. More specifically, in the stack-up (452), the shielding layer (452) surrounds other layers (e.g., at least the patterned electrode (403), the piezoelectric film (404), and the common electrode (405)) from multiple sides. The shielding layer (452) may surround these layers from multiple or all sides.

[0050] Referring to FIG. 4G, the stack-up (460) comprises elements of the stack-up (400) of FIG. 4A and additionally includes a shielding layer (462) capable of blocking or reducing electromagnetic interference by the display (401). The shielding layer may be located between the display (401) and the layers used for touch detection (pattern electrode (403), piezoelectric film (404), and common electrode (405)). The shielding layer (462) may be electrically conductive and may be connected to a ground potential, for example, system or device ground. ITO or other conductive coatings may be used for the shielding layer (462). The shielding layer (462) may thus reduce possible interference from external noise that could otherwise affect the power signal. The shielding layer (432) may be transparent to ensure the visibility of the display (401).

[0051] Referring to FIG. 4H, the stack-up (470) comprises the elements of the stack-up (460) of FIG. 4G and additionally includes a PET layer (411) and an adhesive (412). The PET layer (411) can be used to facilitate the manufacture of the piezoelectric sensing module. Specifically, the patterned electrode (403) can be placed on the PET layer (411) instead of being placed on the piezoelectric film (404). The adhesive (412) can permanently bond the PET layer (411) having the patterned electrode (403) to the piezoelectric film (404). The stack-up (410) may otherwise be similar to the stack-up (460).

[0052] Referring to FIG. 4I, the stack-up (480) comprises the elements of the stack-up (470) of FIG. 4H and additionally includes a PET layer (422) and an adhesive (421). The PET layer (422) may be used to facilitate the manufacture of the piezoelectric sensing module. Specifically, the common electrode (405) may be placed on the PET layer (422) rather than on the piezoelectric film (404). The adhesive (421) may permanently bond the PET layer (422) having the common electrode (405) to the piezoelectric film (404). The stack-up (480) may otherwise be similar to the stack-up (470).

[0053] FIGS. 4A through 4I illustrate various stack-ups, but other stack-ups may be implemented without departing from the present disclosure. For example, any component shown in one of the stack-ups may also be in one of the other stack-ups.

[0054] The selection of a specific stack-up can be based on various considerations. For example, more basic stack-ups (fewer layers) may be more cost-effective and / or more compact. Other stack-ups may be easier to manufacture. For instance, instead of having electrodes directly on the surfaces of the piezoelectric film, additional PET layers may be used to support the electrodes. Additionally, certain stack-ups may be more immune to noise than others. Specifically, a shielding layer between the display and the electrode layers can reduce interference from the display. Placing the common electrode toward the top of the stack-up can reduce the impact of external electromagnetic interference on the resulting signal obtained from the patterned electrodes, such as an actively driven shield potential, if the common electrode is connected to system ground. The materials for all stack-ups can be selected to achieve a high level of transparency for transparent applications. For example, a combination of a PVDF piezoelectric film and adjacent electrode layers may have at least 90%, at least 80%, or other levels of transparency considered sufficient for a given application. Thus, the various features and benefits provided by the stack-up can be utilized in touch-display configurations without significantly impairing display quality.

[0055] Additionally, although not specifically illustrated, in one or more embodiments, the stack-up includes a thermal layer. Piezoelectric materials may exhibit thermal drift due to their pyroelectric properties. This thermal drift can affect force measurements, for example, when the temperature of the piezoelectric material increases during prolonged touch by a finger. The thermal layer may be a layer present within the stack-up (e.g., a cover layer) or a dedicated layer. To stabilize the temperature of the piezoelectric material, it may be placed on the piezoelectric film to provide a thermal barrier between the touch surface, which may come into contact with an object of a different temperature (e.g., a finger), and the piezoelectric film. The thermal layer may be designed as a thermally insulating layer that limits heat transfer to the piezoelectric film. Alternatively, the thermal layer may be designed as a heat sink or heat spreader that absorbs heat and / or conducts heat toward other components. Thermally conductive materials that can be used include, for example, metals (such as copper (Cu) and aluminum (Al)), ceramics (such as aluminum nitride (AlN), aluminum oxide (Al2O3), and silicon nitride (Si3N4)), graphite, etc. Thermal insulating materials that can be used include, for example, glass wool, rock wool, cellulose fiber, wool, etc. For applications requiring transparency, silica gel, aerogel, etc., may be used. Since the use of the thermal layer as described can reduce the presence of pyroelectric noise, other measures to address pyroelectric noise may be unnecessary. For example, it may be unnecessary to compensate for temperature changes using software processing.

[0056] FIG. 5 illustrates a flowchart of a method for piezoelectric touch detection according to one or more embodiments.

[0057] The execution of one or more steps of FIG. 5 may include one or more components of a system as described in FIG. 1, FIG. 2, FIG. 3 and FIG. 4A through 4I. Although the various steps of FIG. 5 are presented and described sequentially, those skilled in the art will recognize that some or all of the blocks may be executed in different orders, may be combined or omitted, and some or all of the blocks may be executed in parallel. Furthermore, the steps may be performed actively or passively.

[0058] In FIG. 5, the method (500) operates on force signals in one or more embodiments. Although not illustrated in FIG. 5, additional steps for acquiring force signals may be performed by performing sensing operations as described above. These sensing operations may include the step of acquiring a result signal, the step of acquiring a force signal by integrating the result signal by a charge integrator, and additionally the step of low-pass filtering and analog-to-digital converting the force signal. The sensing operations may be performed by the components illustrated in FIG. 2. The sensing operations may be performed at a set rate, e.g., 10, 100, 1,000 times per second, or any other rate. The sensing operations may be performed on any number of sensing elements as described with reference to FIG. 3A and FIG. 3B.

[0059] In step (502), a force signal baseline is obtained. The force signal baseline may reflect the force signal of non-touch conditions (i.e., when there is no input object within the detection area). Over time, non-touch conditions may be statistically detected. To quantify the noise level of the force signal baseline, the force baseline may be a single value, e.g., an offset voltage, or a range, e.g., a combination of the offset voltage and the standard deviation.

[0060] In step (504), a force signal is acquired. The acquired force signal may be the most recent force signal available during the operation of the piezoelectric touch sensing system illustrated in FIG. 2. The force signal may be adjusted for a force signal baseline. For example, an offset voltage may be subtracted.

[0061] In step (506), a test is performed to determine whether the amplitude of the force signal exceeds a first predetermined threshold. The first predetermined threshold can be set so that it can be used to distinguish the touch event from other events considered as noise. Accordingly, if the force baseline indicates low baseline noise, a lower threshold may be appropriate, whereas if the baseline noise is higher, a higher threshold may be required. If the amplitude of the force signal exceeds the first predetermined threshold, the execution of the method may proceed to step (508). Alternatively, if the amplitude of the force signal does not exceed the first predetermined threshold, the execution of the method may continue by returning to step (504) to acquire a new force signal or returning to step (502) to determine a new force baseline. The execution of step (506) is illustrated in the example shown in FIG. 6.

[0062] In step (508), the start of a touch event is registered based on a force signal exceeding a first predetermined threshold. That is, it is concluded that a touch is present in the sensing area of ​​the piezoelectric input device.

[0063] In step (510), a power signal is obtained. Step (510) can be performed similarly to step (504).

[0064] In step (512), a test is performed to determine whether the amplitude of the force signal exceeds a second predetermined threshold. Similar to the first predetermined threshold, the second predetermined threshold may be set with reference to baseline noise. If the amplitude of the force signal exceeds the second predetermined threshold, the execution of the method may proceed to step (514). Alternatively, if the amplitude of the force signal does not exceed the first predetermined threshold, the execution of the method may continue by returning to step (510) to acquire a new force signal. The execution of step (512) is illustrated in the example shown in FIG. 6.

[0065] In step (514), a test is performed to determine the polarity of the force signal (i.e., whether the amplitude of the force signal is positive or negative is determined). If the polarity of the force signal is the same as the polarity of the force signal that caused the start of the touch event (step (508)), the method may proceed to the execution of step (516). Otherwise, the method may proceed to the execution of step (518).

[0066] In step (516), the start of another touch event is registered. This touch event may be the result of increased touch force. An example is provided below with reference to FIG. 6.

[0067] In step (518), the termination of a touch event is registered based on a force signal exceeding a second predetermined threshold and the polarity of the force signal obtained in step (510) being opposite to the polarity of the force signal obtained in step (504). That is, it is concluded that the touch event initiated by the execution of step (508) is terminated. If multiple touch events are detected (e.g., after the execution of step (516)), the multiple touch events may be considered terminated based on the execution of step (518).

[0068] Steps (502) through (518) can be performed repeatedly, for example, within a loop, to enable continuous detection of touch events over time.

[0069] The described steps are for detecting touch events, but other steps may also be performed. For example, steps may be performed to determine the location of the touch detected within the detection area and / or to determine the force amplitude of the touch detected.

[0070] FIG. 6 illustrates an example of touch event detection according to one or more embodiments. The example (600) is based on a force profile (610) showing a force that can be applied by an input object within a sensing area over time. Between times t0 and t1, the force increases from 0 to F1, which may correspond to a finger beginning to touch a piezoelectric input device within the sensing area. The force remains constant until t2, which may correspond to a finger continuing to touch the piezoelectric input device. Between times t2 and t3, as the touch by the finger becomes stronger, the force increases to F2. The force remains constant until t4, and between t4 and t5, when the touch by the finger ends, the force decreases to 0.

[0071] Example (600) also includes a force signal profile (620). The force signal profile (620) corresponds to a force signal (i.e., voltage) acquired by a piezoelectric input device while exposed to the force profile (610). The force signal acquired from the piezoelectric material responds with a noticeable downward transient for the initial touch. Referring again to FIG. 5, the downward transient exceeds a first predetermined threshold, resulting in the detection of the start of a touch event. The transient decreases as the force is maintained constant. A smaller downward transient may be observed in response to the force adjustment between t2 and t3. The smaller downward transient is in the same direction as the initial downward transient and thus can trigger the detection of a second touch event. When the finger stops applying pressure to the piezoelectric input device within the sensing area, a noticeable upward transient occurs. In the method of Fig. 5, the upward transient results in detecting the end of the touch event.

[0072] Although only a few exemplary embodiments have been described in detail above, those skilled in the art will readily understand that many modifications are possible from the exemplary embodiments without departing materially from the invention. Accordingly, all such modifications are intended to be included within the scope of the disclosure as defined in the following claims. In the claims, any means-plus-function clauses are intended to include structures described as performing the function(s) cited herein and equivalents thereof. Similarly, any step-plus-function clauses in the claims are intended to include acts described as performing the function(s) cited herein and equivalents thereof. It is the applicant's express intention that 35 USC § 112(f) not apply to any limitations in any of the claims herein, except where the words "means for" or "step for" are explicitly used in the claim in conjunction with the relevant function.

Claims

Claim 1 A piezoelectric sensing module comprising: a polyvinylidene fluoride (PVDF) piezoelectric film; a first electrode layer comprising a plurality of receiving electrodes arranged in a first pattern to detect the position of an input object on a touch surface using the PVDF piezoelectric film; and a second electrode layer comprising a single patternless solid common electrode that completely spans to cover an area including the plurality of receiving electrodes, wherein the PVDF piezoelectric film is arranged between the first electrode layer and the second electrode layer, and the second electrode layer is located between the PVDF piezoelectric film and the touch surface. Claim 2 A piezoelectric sensing module according to claim 1, wherein at least one common electrode is one selected from the group consisting of signal ground potential and device ground potential. Claim 3 A piezoelectric sensing module according to claim 1, further comprising a shielding layer, wherein the shielding layer is on the device ground potential. Claim 4 In paragraph 3, the shielding layer at least partially surrounds the PVDF piezoelectric film, the first electrode layer, and the second electrode layer, forming a piezoelectric sensing module. Claim 5 In paragraph 3, the shielding layer is a piezoelectric sensing module located between the first electrode layer and the display screen within the stack-up. Claim 6 A piezoelectric sensing module according to claim 1, further comprising a thermal layer arranged within a stack-up between the PVDF piezoelectric film and the touch surface, wherein the thermal layer is one selected from the group consisting of a thermally insulating material and a heat spreader material. Claim 7 A piezoelectric sensing module according to claim 1, wherein the plurality of receiving electrodes are directly disposed on the PVDF piezoelectric film. Claim 8 A piezoelectric sensing module according to claim 1, further comprising a display screen disposed within a stack-up below the PVDF piezoelectric film. Claim 9 A piezoelectric sensing module according to claim 1, wherein the combined transparency of the PVDF piezoelectric film, the first electrode layer, and the second electrode layer is at least 80%. Claim 10 A piezoelectric sensing module according to claim 1, wherein the touch surface provides a buttonless touch interface for one selected from the group consisting of home appliances, automotive applications and industrial applications. Claim 11 A piezoelectric input device comprising: a polyvinylidene fluoride (PVDF) piezoelectric film; a first electrode layer comprising a plurality of receiving electrodes arranged in a first pattern to detect the position of an input object on a touch surface using the PVDF piezoelectric film; and a second electrode layer comprising a single patternless solid common electrode that completely covers an area including the plurality of receiving electrodes, wherein the PVDF piezoelectric film and the first electrode layer are arranged beneath the touch surface within a substantially transparent stack-up; and a processing system for determining the position of the input object based on result signals obtained from the plurality of receiving electrodes. Claim 12 In claim 11, the processing system comprises a charge integrator for determining a force signal from a result signal obtained from one of the plurality of receiving electrodes; and a low-pass filter for reducing noise on the force signal, a piezoelectric input device. Claim 13 In claim 11, the piezoelectric input device further comprises a display screen disposed within the stack-up below the PVDF piezoelectric film, wherein the piezoelectric sensing module comprises the above-mentioned piezoelectric sensing module. Claim 14 A piezoelectric input device according to claim 11, wherein the piezoelectric sensing module further comprises a shielding layer disposed between the touch surface and the first electrode layer. Claim 15 A method for detecting a piezoelectric touch, the method comprises: obtaining a first force signal from a piezoelectric sensing module comprising a polyvinylidene fluoride (PVDF) piezoelectric film, a first electrode layer comprising a plurality of receiving electrodes arranged in a first pattern to detect the position of an input object on a touch surface using the PVDF piezoelectric film, and a second electrode layer comprising a single patternless solid common electrode that completely covers an area including the plurality of receiving electrodes—the PVDF piezoelectric film and the first electrode layer are arranged beneath the touch surface in a substantially transparent stack-up—; registering the start of a touch event based on a determination that the amplitude of the first force signal is greater than or equal to a first predetermined threshold; obtaining a second force signal; and registering the end of the touch event based on a determination that the amplitude of the second force signal is greater than or equal to a second predetermined threshold and the polarities of the first and second force signals are opposite to each other. Claim 16 A method according to claim 15, further comprising the step of determining a power signal baseline. Claim 17 A method according to claim 16, further comprising the step of adjusting the first and second force signals with respect to the force signal baseline. Claim 18 A method according to claim 15, wherein the step of acquiring the first force signal comprises: receiving a result signal from a receiving electrode disposed on the PVDF piezoelectric film; and integrating the result signal to acquire the first force signal. Claim 19 A method according to claim 18, further comprising the step of low-pass filtering the first power signal. Claim 20 A method according to claim 15, further comprising the step of converting the first power signal from analog to digital.

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