Multifunctional diode piezoelectric sensor, preparation method and wearable device

Abstract

The embodiment of the application provides a multifunctional diode piezoelectric sensor, a preparation method and a wearable device, which comprise a flexible substrate, a metal top electrode and a metal oxide conductive bottom electrode, the metal top electrode and the metal oxide conductive bottom electrode are made on the flexible substrate; the multifunctional diode piezoelectric sensor has a P-N junction diode structure, the P-N junction diode structure is between the metal top electrode and the metal oxide conductive bottom electrode; an N-type layer of the P-N junction diode structure is below a P-type layer of the P-N junction diode structure; the N-type layer of the P-N junction diode structure is a semiconductor piezoelectric material, the P-type layer of the P-N junction diode structure is an organic semiconductor; and a PET passivation layer is packaged on the upper surface of the P-type layer. The piezoelectric performance is good, the detection mode has high sensitivity, and the detection range is wide; energy collection can be performed at the same time of detection, and an external power supply is not needed.

Description

Technical Field

[0001] This invention relates to the field of flexible electronics, specifically to a multifunctional diode piezoelectric sensor, its fabrication method, and a wearable device. Background Technology

[0002] Flexible electronics has garnered significant attention as a broad scientific field, particularly when it targets wearable devices, energy harvesters, and tactile sensors. While some challenges have been overcome, considerable difficulties remain. Despite rapid technological advancements, tactile sensing and energy harvesting have not yet been effectively integrated. In fact, currently reported devices for energy harvesters or tactile sensors are considered two distinct devices operating in vastly different modes, and combining them into a single device presents a significant technical challenge. Energy harvesting technologies, especially the widely used piezoelectric energy harvesters, require storing regulated signals on specific power management circuit boards. This cumbersome process, involving rectifier circuitry, amplifiers, and management systems, results in typically very low output from these reported energy harvesters.

[0003] Furthermore, reports on flexible sensors commonly used in wearable electronics often necessitate the inclusion of critical amplification circuitry, which complicates the entire system and reduces its efficiency. Secondly, integrating multiple sensing modes onto a single device presents another technical challenge. Most of the aforementioned multifunctional sensors can combine two or at most three different sensing modes, while other sensors lag significantly behind. Summary of the Invention

[0004] This invention provides a multifunctional diode piezoelectric sensor, its fabrication method, and a wearable device. It exhibits excellent piezoelectric performance, high sensitivity in detection mode, and a wide range of applicable detection capabilities. Furthermore, it can perform energy harvesting simultaneously without requiring an external power supply.

[0005] To achieve the above objectives, in one aspect, embodiments of the present invention provide a multifunctional diode piezoelectric sensor, comprising:

[0006] A flexible substrate, a metal top electrode, and a metal oxide conductive bottom electrode, wherein the metal top electrode and the metal oxide conductive bottom electrode are fabricated on the flexible substrate;

[0007] The multifunctional diode piezoelectric sensor has a PN junction diode structure, which is located between a metal top electrode and a metal oxide conductive bottom electrode; the N-type layer of the PN junction diode structure is disposed below the P-type layer of the PN junction diode structure.

[0008] The N-type layer of the PN junction diode structure is a semiconductor piezoelectric material, and the P-type layer of the PN junction diode structure is an organic semiconductor; and the upper surface of the P-type layer is encapsulated with a PET passivation layer.

[0009] On the other hand, embodiments of the present invention provide a wearable device, the wearable device comprising: a basic device having wearable functionality, and a multifunctional diode piezoelectric sensor disposed on the basic device having wearable functionality, wherein the multifunctional diode piezoelectric sensor comprises:

[0010] The flexible substrate, located at the bottom layer, supports all parts of the entire sensor unit;

[0011] The sensor unit, located on a flexible substrate, is used to detect one or more of dynamic pressure, static pressure, humidity, and sound waves.

[0012] A passivation layer, encapsulated on the sensor unit, serves as the contact surface for detection and sensing; the passivation protective layer employs a cylindrical textured pattern to improve the sensitivity of the sensor unit.

[0013] The sensor unit is a PN junction diode structure, wherein the N-type layer of the PN junction diode structure is a semiconductor piezoelectric material, and the P-type layer of the PN junction diode structure is an organic semiconductor; the passivation layer is encapsulated on the upper surface of the P-type layer.

[0014] The wearable devices include: electronic skin and clothing.

[0015] Furthermore, embodiments of the present invention provide a method for fabricating a multifunctional diode piezoelectric sensor, comprising:

[0016] A bottom electrode is sputtered and deposited on top of a flexible substrate;

[0017] At room temperature, radio frequency sputtering of semiconductor piezoelectric material forms an N-type layer of a PN junction diode structure;

[0018] A P-type layer with a PN junction diode structure is formed by coating a biocompatible organic semiconductor onto an N-type layer.

[0019] Metal is deposited onto a P-type layer using metal evaporation or metal sputtering as a metal top electrode.

[0020] The above technical solution has the following advantages: good piezoelectric performance, high sensitivity in detection mode, and wide applicable detection range; it can also perform energy harvesting while detecting, without the need for an external power supply. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of a multifunctional diode piezoelectric sensor according to an embodiment of the present invention;

[0023] Figure 2 This is a flowchart illustrating a method for fabricating a multifunctional diode piezoelectric sensor according to an embodiment of the present invention;

[0024] Figure 3 yes Figure 1 The equivalent circuit;

[0025] Figure 4 Is adopted Figure 1 The design layout of a multifunctional diode piezoelectric sensor as a human body microelectronics;

[0026] Figure 5 This is a schematic diagram of the current and voltage changes caused by a butterfly landing on the top of a multifunctional diode piezoelectric sensor.

[0027] Figure 6 This is a schematic diagram illustrating the acquisition of the pulse value of a human body and the resulting voltage change using a multifunctional diode piezoelectric sensor according to an embodiment of the present invention;

[0028] Figure 7 This is a schematic diagram of the voltage change of humidity collected by the multifunctional diode piezoelectric sensor according to an embodiment of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] like Figure 1 As shown, in conjunction with an embodiment of the present invention, a multifunctional diode piezoelectric sensor is provided, comprising:

[0031] A flexible substrate, a metal top electrode, and a metal oxide conductive bottom electrode, wherein the metal top electrode and the metal oxide conductive bottom electrode are fabricated on the flexible substrate;

[0032] The multifunctional diode piezoelectric sensor has a PN junction diode structure, which is located between a metal top electrode and a metal oxide conductive bottom electrode; the N-type layer of the PN junction diode structure is disposed below the P-type layer of the PN junction diode structure.

[0033] The N-type layer of the PN junction diode structure is a semiconductor piezoelectric material, and the P-type layer of the PN junction diode structure is an organic semiconductor; and the upper surface of the P-type layer is encapsulated with a PET passivation layer.

[0034] Preferably:

[0035] The organic semiconductor of the P-type layer includes one of the following: PEDOT:PSS, P3HT, PTAA;

[0036] The semiconductor piezoelectric material of the N-type layer is ZnO;

[0037] The metal top electrode can be made from one of the following materials: gold, platinum, silver, or copper.

[0038] Materials used to fabricate metal oxide bottom electrodes include one of the following: indium tin oxide (ITO) or aluminum-doped zinc oxide (AZO).

[0039] Preferably, it has a sensing mode and an energy harvesting mode, wherein:

[0040] The sensing mode is implemented by directly reading the voltage or current of the PN junction diode structure, and using the read voltage or current of the PN junction diode structure as a sensing signal to achieve different types of sensing detection; wherein, different types of sensing detection are achieved through the PN junction diode structure in the sensing mode, and the types of sensing detection include: high-sensitivity dynamic pressure detection, humidity detection, temperature detection, and sound wave detection; and the minimum pressure detected during high-sensitivity dynamic pressure detection or sound wave detection is 0.1N;

[0041] While using the sensing mode for detection, the corresponding energy is harvested through the energy harvesting mode. The energy harvesting mode is implemented as follows: the PN junction diode structure is connected in parallel with an energy storage capacitor. After the charge generated by the detected pressure is detected by the PN diode structure, it is stored in the energy storage capacitor. The energy storage capacitor uses the stored charge to power the external circuit.

[0042] Preferably, when the semiconductor piezoelectric material of the N-type layer is ZnO, the ZnO is in the shape of a dense thin film or a one-dimensional nanowire, and the 002 unit cell orientation of the wurtzite crystal structure possessed by ZnO is adopted.

[0043] In high-sensitivity dynamic pressure detection or acoustic wave detection, when stress is applied to the PET passivation layer, the stress is polarized in two different directions in ZnO, and charge accumulates on the upper and lower surfaces of ZnO. ZnO exhibits the best piezoelectric response when oriented in a 002 unit cell.

[0044] Dense thin films or one-dimensional nanowire-shaped ZnO increase the Schottky barrier and energy storage capacitance, enabling the PN junction diode structure to detect a minimum pressure of 0.1N during high-sensitivity dynamic pressure detection or acoustic wave detection.

[0045] Preferably,

[0046] During temperature detection, water vapor is absorbed by the oxygen vacancies in ZnO, generating interfacial charges in the N-type and P-type layers. These interfacial charges form a voltage signal, which is then detected to achieve humidity sensing.

[0047] In conjunction with embodiments of the present invention, a wearable device is provided, the wearable device comprising: a basic device having wearable functionality, and a multifunctional diode piezoelectric sensor disposed on the basic device having wearable functionality, wherein the multifunctional diode piezoelectric sensor comprises:

[0048] The flexible substrate, located at the bottom layer, supports all parts of the entire sensor unit;

[0049] The sensor unit, located on a flexible substrate, is used to detect one or more of dynamic pressure, static pressure, humidity, and sound waves.

[0050] A passivation layer, encapsulated on the sensor unit, serves as the contact surface for detection and sensing; the passivation protective layer employs a cylindrical textured pattern to improve the sensitivity of the sensor unit.

[0051] The sensor unit is a PN junction diode structure, wherein the N-type layer of the PN junction diode structure is a semiconductor piezoelectric material, and the P-type layer of the PN junction diode structure is an organic semiconductor; the passivation layer is encapsulated on the upper surface of the P-type layer.

[0052] The wearable devices include: electronic skin and clothing.

[0053] like Figure 2 As shown, in conjunction with embodiments of the present invention, a method for fabricating a multifunctional diode piezoelectric sensor is provided, comprising:

[0054] S101: A bottom electrode is sputtered and deposited on top of a flexible substrate;

[0055] S102: Forming an N-type layer of a PN junction diode structure by radio frequency sputtering of semiconductor piezoelectric material at room temperature;

[0056] S103: A P-type layer forming a PN junction diode structure is formed by coating a biocompatible organic semiconductor onto an N-type layer;

[0057] S104: Metal is deposited onto a P-type layer using metal evaporation or metal sputtering as a metal top electrode.

[0058] Preferably, step 101, which involves sputtering and depositing a bottom electrode on top of a flexible substrate, specifically includes:

[0059] At room temperature, indium tin oxide (ITO) is sputtered and deposited on a flexible PET substrate to form a transparent metal oxide conductive bottom electrode, wherein the thickness of the indium tin oxide (ITO) is 100 to 200 nm.

[0060] Step 102, which involves forming an N-type layer of a PN junction diode structure by radio frequency sputtering of a semiconductor piezoelectric material at room temperature, specifically includes:

[0061] ZnO thin films were deposited by radio frequency sputtering on a flexible substrate at room temperature, pressure of 1.6 Pa, and argon atmosphere. The sputtered ZnO thin films were then annealed at 100 degrees Celsius to obtain an N-type layer of wurtzite crystal structure ZnO with a thickness of 0.5-1 μm. The polycrystalline ZnO of the wurtzite crystal structure satisfies the preset requirements in the 002 unit cell orientation, and the peak intensity of the crystals in the 002 unit cell orientation satisfies the preset peak intensity.

[0062] Preferably, the biocompatible organic semiconductor coated on the N-type layer includes one of the following: PEDOT:PSS, P3HT, PTAA;

[0063] Step 103, which involves coating a biocompatible organic semiconductor onto the N-type layer to form a P-type layer for a PN junction diode structure, specifically includes:

[0064] When the organic semiconductor is PEDOT:PSS, PEDOT:PSS is diluted in deionized water at a ratio of 1:10 to obtain an aqueous solution of PEDOT:PSS.

[0065] A biocompatible PEDOT:PSS aqueous solution is coated onto an N-type layer by drop casting or screen printing to obtain a P-type layer, wherein the thickness of the P-type layer is thinner than that of the N-type layer; wherein the thickness of the P-type layer is 100-180 nm.

[0066] Preferably, step 104, which involves depositing metal onto a P-type layer using metal evaporation or metal sputtering as a metal top electrode, specifically includes:

[0067] At room temperature, a 100 nm thick metal is deposited on a P-type layer by metal evaporation or metal sputtering to obtain a metal top electrode; wherein the material of the metal top electrode includes one of the following: gold, platinum, silver, and copper;

[0068] The method for fabricating the multifunctional diode piezoelectric sensor further includes:

[0069] S105: A 50μm thick PET passivation layer is applied to the upper surface of the P-type layer, excluding the metal top electrode, to encapsulate the P-type layer; the PET passivation layer has cylindrical gaps to enable humidity sensing.

[0070] The technical solutions of the present invention will be described in detail below with reference to specific application examples. For technical details not described in the implementation process, please refer to the relevant descriptions above.

[0071] This invention relates to a multifunctional diode piezoelectric sensor and its fabrication process. The technical problems to be solved are:

[0072] 1. High-sensitivity multi-sensing modes. With excellent piezoelectric properties, it integrates several important sensing modes into a unique device that can accurately detect the pressure (0.1–10 Newtons) at which mosquitoes or butterflies land and take off.

[0073] 2. No complex rectifier circuit design is required. With its own power supply, most common and widely used sensors and energy harvesters are limited by their circuit design because their output voltage or current will not meet the requirements of the appropriate power management circuitry or readout circuitry used for acquisition. The PN structure (PN junction diode structure) presented in this patent overcomes such problems in the aforementioned modes because it does not require any signal rectification, making the system simple and practical.

[0074] 3. Easy to manufacture and use. Compared with existing technologies, the PN structure of this invention has a lower implementation cost. The core of the PN junction structure is a piezoelectric material, such as ZnO as an N-type material; and common P-type materials, such as PEDOT:PSS, PTAA, and nickel oxide, which are widely used due to their relatively low price. Zn is one of the essential trace elements for the human body, and PEDOT:PSS also has good biocompatibility. Therefore, this device is not only very humane and has no side effects on the human body (e.g., when used in electronic skin), but it can also protect the human body. This type of PN structure is also relatively simple to manufacture, which is another advantage that helps reduce manufacturing time and cost.

[0075] 4. High stability and high reliability. Due to the reliable and stable performance of ZnO ferroelectrics oriented in the 002 direction under strain or stress, this device can withstand nearly 20,000 high-intensity operating cycles without performance degradation.

[0076] 5. User-friendly and environmentally friendly. As mentioned earlier, in order to form the PN structure, N-type ZnO and PEDOT:PSS P-type materials are used.

[0077] The multifunctional device based on a PN junction (PN junction diode structure) proposed in this invention has four sensing modes: high-sensitivity pressure sensing, humidity sensing, temperature sensing, and sound wave sensing. Furthermore, it exhibits excellent piezoelectric sensitivity. Therefore, this concept has broad application potential, such as electronic skin capable of detecting force, temperature, humidity, sound waves, and human pulse. Moreover, it combines these sensing functions with energy harvesting; the generated voltage signal is sufficiently large for effective detection and storage, and the harvested energy is stored in a matched supercapacitor, ultimately powering low-power electronic devices such as Radio Frequency Identification (RFID). On one hand, in human health monitoring applications, human mechanical movements (such as joint bending) can be used to harvest energy and activate RFID tags. On the other hand, the proposed sensing modes can detect heartbeats, enabling a single device to simultaneously perform sensing and energy harvesting functions.

[0078] This invention fabricates a PN junction device by combining an N-type semiconductor piezoelectric material layer with a P-type semiconductor organic polymer material layer. This device has two operating modes: sensing mode and energy harvesting mode. It can simultaneously perform energy harvesting and sensing, is self-powered, requires no external power supply, and can monitor pressure, humidity, and temperature. PEDOT:PSS and ZnO are both biocompatible materials; therefore, the fabricated PN junction device is also an environmentally friendly and user-friendly sensor / data logger. This self-powered sensor has broad applications in human health monitoring and infrastructure surveillance.

[0079] The device of the present invention (i.e., a multifunctional diode piezoelectric sensor) has a PN junction diode structure, wherein the N-type layer of the PN junction is ZnO, and the P-type layer is made of a semiconductor conductive polymer. It has a metal top electrode and a metal oxide conductive bottom electrode, and is fabricated on a flexible substrate. The multifunctional diode piezoelectric sensor has a PN junction diode structure located between the metal top electrode and the metal oxide conductive bottom electrode; the N-type layer of the PN junction diode structure is disposed below the P-type layer of the PN junction diode structure; the N-type layer of the PN junction diode structure is a semiconductor piezoelectric material, and the P-type layer of the PN junction diode structure is an organic semiconductor; and a PET passivation layer is encapsulated on the upper surface of the P-type layer.

[0080] The P-type layer can be one of organic semiconductors such as PEDOT:PSS, P3HT, PTAA, etc. The metal oxide conductive bottom electrode can be composed of indium tin oxide (ITO) or aluminum-doped zinc oxide (AZO), and the metal top electrode can be one of gold, platinum, silver, or copper.

[0081] The manufacturing process of a multifunctional diode piezoelectric sensor can be achieved through the following simple standard steps: sputtering a bottom electrode on top of a flexible substrate, RF sputtering of piezoelectric material ZnO at room temperature, spin-coating PEDOT:PSS, and finally evaporating gold as the top electrode.

[0082] PN junction devices (PN junction diode structures) can achieve various types of sensing detection in sensing mode: dynamic pressure detection, humidity detection, and sound wave detection. The sensing mode is implemented by directly reading the voltage or current of the PN junction as the sensing signal. In energy harvesting mode, the proposed PN junction device can harvest energy generated by any applied pressure or vibration. This truly combines sensing and energy harvesting, thus realizing the concept of a self-driven, battery-free sensor. The energy harvesting mode is implemented as follows: the PN junction is connected in parallel with an energy storage capacitor. The charge generated by piezoelectricity is first stored in the capacitor, and then the capacitor powers the external circuit, serving as the power source for the multifunctional diode piezoelectric sensor itself, achieving a self-driven, battery-free sensor.

[0083] The technical solution of the present invention is described in detail below:

[0084] 1. Figure 1 This is a cross-sectional schematic diagram of a PN structure formed by ZnO and PEEDOT:PSS. The PN junction structure is formed by sandwiching a (optimizable) 1μm layer of n-type piezoelectric material ZnO and a 200nm layer of p-type polymer (such as PEDOT:PSS) between the bottom and top electrodes. The bottom and top electrodes are respectively a 150-200nm thick indium tin oxide (ITO) layer and a 50-150nm thick metal layer, which can be gold, silver, platinum, copper, etc. Figure 1 The serial numbers (0)-(5) in the table represent: 0: PET substrate; 1: ITO layer; 2: N-type layer (ZnO layer); 3: P-type layer (P3HT layer, 120-180nm); 4: metal top electrode layer; 5: PET encapsulation layer (PET is polyethylene terephthalate).

[0085] 2. When any mechanical stress is applied to the device (e.g.) Figure 1 As shown in the diagram (touch the top of the structure lightly), when the N-type layer semiconductor piezoelectric material is ZnO, the stress will be polarized in two different directions, where charge will accumulate on the upper and lower surfaces of ZnO. Furthermore, ZnO, as a semiconductor piezoelectric material, can also be fabricated into dense thin films or one-dimensional nanowire shapes (abbreviated as 1D). shape Because ZnO possesses a wurtzite crystal structure, ZnO crystals oriented in the 002 direction (an industry term) of the unit cell achieve the best piezoelectric response compared to other semiconductor piezoelectric materials. However, regarding piezoelectric materials, based on the electrical properties of ZnO, comparing it under pressure and without pressure, the capacitance of this 500nm thick layer remains unchanged (because deformation is negligible relative to thickness, so the capacitance remains constant). The PN junction or Schottky barrier made of ZnO with the aforementioned properties increases the capacitance of the entire device; any change in pressure at the Schottky barrier height (SBH) leads to an increase in capacitance. Therefore, the static sensitivity of the PN junction diode structure is very high, and even a weight of approximately 1g can be detected well. On the other hand, the dynamic pressure response of the PN junction diode structure can be characterized based on the piezoelectric effect of the piezoelectric N-type material. A diode can be fabricated using PEDOT:PSS as a P-type barrier because of its high work function. Therefore, due to any applied stress or strain, not only will the charge polarize in N-type ZnO, but the height of the Schottky barrier will also change, thus enabling a very highly sensitive dynamic pressure sensor capable of detecting forces as small as 0.1 N. Based on this, the landing and takeoff of a typical butterfly weighing approximately 0.5–1 g were detected. Figure 5 This demonstrates the extraction of DC voltage when a butterfly lands on top of the sensor and takes off after a period of time.

[0086] In summary, ZnO is an oxide, so oxygen vacancies are inevitably present during its growth process, which is common to all oxide materials. However, while most oxides are insulators, ZnO is an N-type semiconductor, allowing it to be used to form PN junctions. Finally, ZnO grown along the 002 direction exhibits good piezoelectric properties, enabling it to be fabricated into PN junction diodes for measuring pressure and sound pressure. Furthermore, the oxygen vacancies have water-absorbing capabilities, altering the conductivity of zinc oxide, thus allowing for humidity measurement. Therefore, it is a multifunctional material.

[0087] Introducing a PN structure introduces an intrinsic built-in capacitance into the system. In this case, we have two types of capacitance connected in series, corresponding to the dielectric ZnO layer and the PN junction Schottky barrier, respectively. While increasing the overall capacitance of this capacitance-based pressure sensor can reduce sensitivity, it can also improve the linear behavior of the capacitance, especially in static pressure sensing. Therefore, a trade-off must be struck between these two effects depending on the application. Increasing the thickness of the p-type material (PEDOT:PSS) increases the capacitance but also reduces the device's sensitivity under static low pressure. Appropriate manufacturing techniques are needed to optimize and balance the thickness of the p-type layer.

[0088] 3. Figure 3 (a) The equivalent circuit is described first. Figure 3 (b) also describes the device's operation in energy harvesting mode. The PN junction structure can be modeled as two junction capacitances (C0, C ...). J and diffusion capacitance (C) d ) and the shunt resistor (R) that forms the junction J Parallel connection of R. S It relates to the resistance of all ohmic contacts, wires, etc. ZnO itself, as a dielectric layer, can also be represented by a simpler model, where the bulk material (C) is introduced. Z The related capacitance and resistance (R) Z ).

[0089] 4. Inspired by the structure of human skin tissue, wearable devices (such as electronic skin) are one application of this multifunctional device. Figure 4 (a) and (b) illustrate the analogy between human skin and the proposed design layout. The electronic skin, similar to human skin tissue, is primarily composed of three layers. The bottom layer is a flexible substrate that supports all parts of the sensor. The second layer, at the bottom, is the sensor unit, situated on the flexible substrate, capable of detecting one or more of dynamic / static pressure, humidity, and sound waves. The top layer is a passivation protective layer, encapsulated on the sensor unit, serving as the contact surface for sensing; it is patterned with a cylindrical texture to improve the device's sensitivity and also functions as an encapsulation layer. A schematic diagram of this structure can be found in... Figure 1 As seen in the image, a light pressure is simultaneously applied to the top of the structure. The sensor unit is a PN junction diode structure, where the N-type layer is a piezoelectric semiconductor material, and the P-type layer is an organic semiconductor; the passivation layer is encapsulated on the upper surface of the P-type layer.

[0090] 5. Figure 6This description aptly describes the device's ability to detect the human pulse in sensing mode. The detected complete signal reveals P1 and P2 peaks (peak pressures during systole and diastole, respectively) corresponding to cardiac function, allowing for further analysis and diagnosis. Multiple different locations can be selected to acquire these pulse signals, such as the wrist, neck, ankle, and elbow.

[0091] 6. Figure 7 The signal obtained through humidity is shown. It describes how the PN junction diode structure responds to humidity and how the peak voltage decreases during the sensing recovery time. Acquiring this probe signal requires no external power supply.

[0092] The manufacturing process of the device of the present invention is as follows:

[0093] a) Depositing an ITO transparent electrode on a flexible PET(0) substrate. This step can be achieved using sputtering technology. The thickness of the ITO bottom electrode is typically 100 to 200 nm, and this transparent electrode sputtered at room temperature exhibits excellent conductivity. Since the PET substrate can only withstand temperatures of approximately 150 degrees Celsius, all fabrication steps must be performed using low-temperature processes, such as room temperature.

[0094] b) ZnO of approximately 1 μm thickness was deposited by RF sputtering at room temperature under a pressure of 1.6 Pa and an argon atmosphere. XRD analysis was performed post-deposition to check the ZnO crystal orientation along the 002 direction. Since ZnO belongs to the hexagonal crystal system, the 002 orientation plays a crucial role in obtaining the optimal piezoelectric response. The intensity of this piezoelectric response is influenced by the piezoelectric coefficients in the d33 and d31 directions. The piezoelectric coefficient can be improved by optimizing the 002 orientation of the sputtered wurtzite crystal structure, resulting in a better response under applied stress.

[0095] c) Annealing the ZnO sputtered on the flexible substrate at 100 degrees Celsius improves the 002 crystal orientation and peak intensity in that orientation of the resulting wurtzite ZnO polycrystalline material. This further enhances the piezoelectric properties of the device, as they correspond to the piezoelectric properties of the ZnO film. Obtaining a well-aligned hexagonal polycrystalline ZnO with good 002 crystal orientation is challenging and requires careful control of the sputtering conditions.

[0096] d) Coating a biocompatible p-type layer, such as PEDOT:PSS, by drop coating or screen printing. Some preparation is usually required for PEDOT:PSS because its acidity can etch other materials (metals, oxides), especially the PSS component. Preparation of PEDOT:PSS is as follows: Since PEDOT:PSS is water-soluble, dilute it with deionized water at a ratio of 1:10. Only a few drops of PEDOT:PSS are sufficient for drop coating or screen printing on ZnO. The thickness of this p-type layer is thinner than the piezoelectric layer, approximately 100-180 nm. PET / ITO surfaces are relatively hydrophobic, making it difficult to coat PEDOT:PSS on them, while a thick layer of ZnO on ITO has better surface hydrophilicity and forms a suitable bond between the N-type and P-type materials.

[0097] e) Deposit a 100 nm thick copper layer as the top electrode. The top electrode can be made of gold or a combination of copper and silver, but copper, with its good binding energy and practicality, is generally chosen. The deposition of this copper electrode must be performed at a low temperature (below 150 degrees Celsius) to prevent mechanical deformation or damage to the PET substrate. This process can be accomplished at room temperature using metal evaporation or sputtering deposition.

[0098] f) Finally, a 50 μm thick PET passivation layer is used to encapsulate the PEDOT:PSS layer on top of the device. PEDOT:PSS is water-soluble, and this passivation helps reduce static charge and protect the P-type layer. Furthermore, since the humidity sensing mechanism relies on filling oxygen vacancies in the ZnO layer, a cylindrical textured pattern is applied to the passivation layer to achieve humidity sensing. This helps the device accurately detect oxygen transmitted to the device through the cylindrical holes, while filtering out water to protect the P-type layer. PEDOT:PSS itself, as a P-type material, influences the humidity sensing mechanism, and its enhanced oxygen absorption results in a larger amplitude and higher response voltage signal compared to pure ZnO humidity sensors.

[0099] The rational device structure design enables a simple and rapid fabrication process, which is one of the advantages of this invention. Fabrication can be completed quickly in less than a day, and it also allows manufacturers to have a better and easier understanding of the fabrication process so that they can improve the product in the future.

[0100] Replacement methods for components or steps in the technical solution of this invention:

[0101] The proposed concept of forming a PN structure by utilizing piezoelectric semiconductor materials as sensing and collecting devices may require modifications and replacements in device design and layout, particularly in some manufacturing steps. The N-type material in the device is ZnO, a ferroelectric piezoelectric material, which can be replaced by various other N-type semiconductor materials, such as PZT piezoelectric ceramics. However, PZT is rigid and bulky, potentially posing flexibility challenges for such devices. In this sense, ZnO exhibits better flexibility compared to PZT. Theoretically, PZT has higher piezoelectric coefficients d33 and d31 than ZnO, improving device response and output signal, but its lack of flexibility may pose challenges for wearable applications.

[0102] Furthermore, given that the P-type material in the PN structure is PEDOT:PSS, it is a biocompatible material. Regardless of user-friendliness and biocompatibility, it can be replaced with various P-type materials to form the PN junction, such as nickel oxide. In this case, the efficiency and output of the device in energy harvesting mode play a crucial role. Due to the conductivity of certain given materials, the current may be lower, and the output response signal may be imperfect, both of which directly affect the output power and thus the efficiency. Therefore, material selection needs to be optimized according to the specific application scenario; different applications may employ different N-type or P-type materials.

[0103] Regarding the device fabrication steps mentioned in the preceding section, since various mature fabrication technologies are currently available, some alternatives can be used. For example... Figure 1 The second layer in device fabrication is the deposition of a thick ZnO film, which can be easily accomplished via RF sputtering. Solution-based ZnO spin-coating followed by annealing can be considered an alternative to sputtering. Similarly, solution-based ZnO spin-coating requires optimization of the crystal orientation of the ZnO polycrystalline material during annealing. Another method for ZnO deposition is to first sputter a very thin seed layer, such as 5 nm, and then deposit ZnO on top of the seed layer via solution spin-coating, which facilitates the crystallization of ferroelectrics.

[0104] Figure 1 The third layer is a PEDOT:PSS coating, which can be accomplished using several alternative techniques, such as spin coating, screen printing, drop coating, and blade coating.

[0105] Figure 1 The fourth layer is a metal vapor deposition as the top contact, which can also be simply replaced with some other metal thin film tape. While this type of tape does not achieve good atomic bonding and reaction, the device efficiency may be lower. Another potentially more practical method compared to metal evaporation is sputter deposition of the top electrode.

[0106] The technical fields to which this invention pertains are: flexible electronics, nanotechnology, microelectronics, and sensors; specifically, it can be used in: tactile sensors, wearable energy harvesters, electronic skin, vibration generators, wearable electronic devices, etc. Details are as follows:

[0107] The sensing modes used in wearable devices and electronic skin help simulate almost all the essential functions of human skin. Simultaneously, the sensing modes can also be used for vital sign monitoring, such as pulse signals. The device's energy harvesting mode collects energy from human movement to activate low-power RFID readout circuits, enabling wireless transmission of the detected signals. Both modes can operate simultaneously, allowing for the introduction of battery-free devices into numerous fields. For example, an elbow patch for measuring blood pressure, when applied to the elbow, can harvest the mechanical energy of arm flexion and simultaneously monitor the pulse.

[0108] In the realm of wearable devices, such as clothing, shoes can be used to specifically measure factors like foot pressure, maximum pressure area, and humidity for each individual. This allows for the custom production of specialized smart shoes for athletes in various competitions. They can also be considered personalized foot covers to enhance comfort and provide foot care. The feet are often considered the body's second heart, and healthy feet generally impact overall health.

[0109] In some remote areas, vibration-based infrastructure (such as bridges) requires some form of fault detection, in which case sensors can be used. However, the cost of regular battery replacements and maintenance in such systems can be cumbersome. The concept of a device that can simultaneously perform sensing and energy harvesting, as proposed above, is perfectly suited for these infrastructures used to monitor for faults.

[0110] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process may be rearranged without departing from the scope of this disclosure. The appended method claims provide elements of various steps in an exemplary order and are not intended to limit the scope to the specific order or hierarchy described.

[0111] In the above detailed description, various features are combined together in a single embodiment to simplify this disclosure. This approach to disclosure should not be construed as reflecting an intention that embodiments of the claimed subject matter require more features than are explicitly stated in each claim. Rather, as reflected in the appended claims, the invention is presented with fewer features than all of the features of the single disclosed embodiment. Therefore, the appended claims are hereby explicitly incorporated into the detailed description, wherein each claim stands alone as a preferred embodiment of the invention.

[0112] The disclosed embodiments have been described above to enable any person skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments without departing from the spirit and scope of this disclosure. Therefore, this disclosure is not limited to the embodiments given herein, but is consistent with the broadest scope of the principles and novel features disclosed in this application.

[0113] The foregoing description includes examples of one or more embodiments. It is certainly impossible to describe all possible combinations of components or methods in order to describe the above embodiments, but those skilled in the art will recognize that further combinations and arrangements of the various embodiments are possible. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the term "comprising" as used in the specification or claims is interpreted in a manner similar to the term "including," as interpreted when used as a conjunction in the claims. Additionally, the use of any term "or" in the specification of the claims is intended to mean "non-exclusive or."

[0114] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multifunctional diode piezoelectric sensor, characterized in that, include: A flexible substrate, a metal top electrode, and a metal oxide conductive bottom electrode, wherein the metal top electrode and the metal oxide conductive bottom electrode are fabricated on the flexible substrate; The multifunctional diode piezoelectric sensor has a PN junction diode structure, which is located between a metal top electrode and a metal oxide conductive bottom electrode; the N-type layer of the PN junction diode structure is disposed below the P-type layer of the PN junction diode structure. The N-type layer of the PN junction diode structure is a semiconductor piezoelectric material, and the P-type layer of the PN junction diode structure is an organic semiconductor; and a PET passivation layer is encapsulated on the upper surface of the P-type layer. The aforementioned multifunctional diode piezoelectric sensor has sensing modes, wherein: The voltage or current of the PN junction diode structure is read as a sensing signal to realize different types of sensing detection; wherein, different types of sensing detection are realized in sensing mode through the PN junction diode structure, and the types of sensing detection include: high-sensitivity dynamic pressure detection, humidity detection or sound wave detection. In high-sensitivity dynamic pressure detection or acoustic wave detection, when stress is applied to the PET passivation layer, the stress is polarized in two different directions of ZnO, and charges accumulate on the upper and lower surfaces of ZnO. ZnO has the best piezoelectric response when the 002 unit cell is oriented; and the minimum pressure detected by high-sensitivity dynamic pressure detection or acoustic wave detection is 0.1N. During humidity detection, water vapor is absorbed by the oxygen vacancies in ZnO, generating interfacial charges in the N-type and P-type layers. These interfacial charges form a voltage signal, which is then detected to achieve humidity sensing.

2. The multifunctional diode piezoelectric sensor according to claim 1, characterized in that: The organic semiconductor of the P-type layer includes one of the following: PEDOT:PSS, P3HT, PTAA; The semiconductor piezoelectric material of the N-type layer is ZnO; The metal top electrode can be made from one of the following materials: gold, platinum, silver, or copper. Materials used to fabricate metal oxide bottom electrodes include one of the following: indium tin oxide (ITO) or aluminum-doped zinc oxide (AZO).

3. The multifunctional diode piezoelectric sensor according to claim 1, characterized in that, It also features an energy harvesting mode, including: While using the sensing mode for detection, the corresponding energy is harvested through the energy harvesting mode. The energy harvesting mode is implemented as follows: the PN junction diode structure is connected in parallel with an energy storage capacitor. After the charge generated by the detected pressure is detected by the PN diode structure, it is stored in the energy storage capacitor. The energy storage capacitor uses the stored charge to power the external circuit.

4. The multifunctional diode piezoelectric sensor according to claim 1, characterized in that, When the semiconductor piezoelectric material of the N-type layer is ZnO, ZnO is in the shape of a dense thin film or a one-dimensional nanowire, and the 002 unit cell orientation of the wurtzite crystal structure possessed by ZnO is adopted. Dense thin films or one-dimensional nanowire-shaped ZnO increase the Schottky barrier and energy storage capacitance, enabling the PN junction diode structure to detect a minimum pressure of 0.1N in high-sensitivity dynamic pressure detection or acoustic wave detection.

5. A wearable device, characterized in that, The wearable device includes: a basic piece of equipment with wearable functionality, and a multifunctional diode piezoelectric sensor as described in claim 1 disposed on the basic piece of equipment with wearable functionality, wherein the multifunctional diode piezoelectric sensor includes: The sensor unit, situated on a flexible substrate, is used to detect one or more of dynamic pressure, static pressure, humidity, and sound waves. Specifically, in high-sensitivity dynamic pressure or sound wave detection, when stress is applied to the PET passivation layer, the stress polarizes in two different directions in ZnO, and charges accumulate on the upper and lower surfaces of ZnO. ZnO exhibits optimal piezoelectric response when oriented in a 002 unit cell. Furthermore, the minimum pressure detected in high-sensitivity dynamic pressure or sound wave detection is 0.1 N. In humidity detection, water vapor is absorbed through oxygen vacancies in ZnO, generating interfacial charges in the N-type and P-type layers. These interfacial charges form a voltage signal, which is then detected to achieve humidity sensing. A passivation layer, encapsulated on the sensor unit, serves as the contact surface for detection and sensing; the passivation protective layer employs a cylindrical textured pattern to improve the sensitivity of the sensor unit. The sensor unit is a PN junction diode structure, wherein the N-type layer of the PN junction diode structure is a semiconductor piezoelectric material, and the P-type layer of the PN junction diode structure is an organic semiconductor; the passivation layer is encapsulated on the upper surface of the P-type layer. The wearable device includes: electronic skin or clothing.

6. The method for fabricating a multifunctional diode piezoelectric sensor according to claim 1, characterized in that, The steps of fabricating a multifunctional diode piezoelectric sensor: A bottom electrode is sputtered and deposited on top of a flexible substrate; At room temperature, radio frequency sputtering of semiconductor piezoelectric material forms an N-type layer of a PN junction diode structure; A P-type layer with a PN junction diode structure is formed by coating a biocompatible organic semiconductor onto an N-type layer. Metal is deposited onto a P-type layer using metal evaporation or metal sputtering as a metal top electrode; The method of forming an N-type layer with a PN junction diode structure by radio frequency sputtering of semiconductor piezoelectric material at room temperature specifically includes: ZnO thin films were deposited by radio frequency sputtering on a flexible substrate at room temperature, pressure of 1.6 Pa, and argon atmosphere. The sputtered ZnO thin films were then annealed at 100 degrees Celsius to obtain an N-type layer of wurtzite crystal structure ZnO with a thickness of 0.5-1 μm. The polycrystalline ZnO of the wurtzite crystal structure satisfies the preset requirements in the 002 unit cell orientation and the peak intensity of the crystals in the 002 unit cell orientation satisfies the preset peak intensity.

7. The method for fabricating a multifunctional diode piezoelectric sensor according to claim 6, characterized in that, The method of sputtering and depositing a bottom electrode on top of a flexible substrate specifically includes: At room temperature, indium tin oxide (ITO) is sputtered and deposited on a flexible PET substrate to form a transparent metal oxide conductive bottom electrode, wherein the thickness of the indium tin oxide (ITO) is 100 to 200 nm.

8. The method for fabricating a multifunctional diode piezoelectric sensor according to claim 6, characterized in that, The biocompatible organic semiconductor coated on the N-type layer includes one of the following: PEDOT:PSS, P3HT, PTAA; The process of coating a biocompatible organic semiconductor onto an N-type layer to form a P-type layer for a PN junction diode structure specifically includes: When the organic semiconductor is PEDOT:PSS, PEDOT:PSS is diluted in deionized water at a ratio of 1:10 to obtain an aqueous solution of PEDOT:PSS. A biocompatible PEDOT:PSS aqueous solution is coated onto an N-type layer by drop casting or screen printing to obtain a P-type layer, wherein the thickness of the P-type layer is thinner than that of the N-type layer; wherein the thickness of the P-type layer is 100-180 nm.

9. The method for fabricating a multifunctional diode piezoelectric sensor according to claim 6, characterized in that, The method of using metal evaporation or metal sputtering to deposit metal onto a P-type layer as a metal top electrode specifically includes: At room temperature, a 100 nm thick metal is deposited on a P-type layer by metal evaporation or metal sputtering to obtain a metal top electrode; wherein the material of the metal top electrode includes one of the following: gold, platinum, silver, and copper; The method for fabricating the multifunctional diode piezoelectric sensor further includes: A 50 µm thick PET passivation layer is applied to the upper surface of the P-type layer, excluding the metal top electrode, to encapsulate the P-type layer; the PET passivation layer has cylindrical gaps to enable humidity sensing.

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