A flexible elastic oxide ferroelectric thin film sensor

Abstract

The present invention discloses a flexible, elastic oxide ferroelectric thin film sensor. The sensor has a corrugated structure, comprising a gold foil, an insulating film, a parallel lower electrode, an oxide ferroelectric thin film, and parallel upper electrodes connected in sequence. The oxide ferroelectric thin film serves as the sensor's functional layer, and the "lower electrode / ferroelectric thin film / upper electrode" constitutes the sensor's basic unit. The parallel lower electrodes and the parallel upper electrodes are perpendicular to each other, forming a sensor composed of several units. The sensor has a thickness of 0.5 to 10 μm and contains a regularly arranged corrugated structure. This makes the sensor flexible, elastic, and ductile, allowing it to be transferred to the surface of human and animal skin, plant epidermis, or artificial organic or inorganic materials, and to sense strain and temperature changes in these objects.

Description

Technical Field

[0001] The present application relates to the field of ferroelectric oxide thin film sensors, and in particular to a flexible and elastic ferroelectric oxide thin film sensor. Background Art

[0002] In recent years, ultrathin, flexible, wearable epidermal electronic systems (i.e., electronic tattoos) composed of ultrathin electrodes, sensors, wireless power supplies, electronic components, and communication systems have been developed, promising to measure the wearer's heart rate, blood pressure, skin temperature, and other vital health data. As important and widely used functional materials, ferroelectric and piezoelectric materials also hold significant application prospects in flexible electronic devices and wearable electronics.

[0003] Oxide ferroelectric materials such as PZT, PMN-PT, and BaTiO3 exhibit excellent piezoelectric, dielectric, and multiferroic properties and have found widespread application in the electronics and high-end manufacturing industries, including medical ultrasound probes, ship sonar, temperature sensors, piezoelectric sensors, infrared detectors, and accelerometers. These perovskite oxide ferroelectrics are often used in ceramic or single crystal forms, resulting in rigid and inflexible samples. The booming development of flexible electronics and wearable devices requires current oxide ferroelectric films and devices to exhibit flexible bendability and elastic stretchability.

[0004] When the substrate of a ferroelectric thin film, such as PZT, is peeled off or thinned to the micro-nanoscale, the film not only exhibits superior bending resistance but also potentially exhibits piezoelectric properties similar to those of single crystals and ceramics. By peeling off a rigid substrate, such as SrTiO3, to obtain a substrate-free, free-standing ferroelectric film, or by fabricating a ferroelectric film on an ultrathin flexible substrate, the strain clamping effect of the rigid substrate on the ferroelectric film can be eliminated or effectively suppressed, allowing the piezoelectric effect of the ferroelectric film to be consistent with that of a single crystal or ceramic, thus improving the sensitivity of the piezoelectric sensor. Furthermore, the out-of-plane piezoelectric effect can be amplified through in-plane shrinkage and bending, thereby enhancing the overall performance of microelectromechanical systems (MEMS) [Di Lu et al., Synthesis of freestanding single-crystal perovskite films and heterostructures by etching of sacrificial water-soluble layers. Nature Materials 15, 1255, 2016].

[0005] However, growing oxide ferroelectric thin films on rigid substrates like Si and SrTiO3 and obtaining flexible oxide films through lift-off and transfer processes is a challenging process. Currently, flexible oxide films can only be produced on a millimeter-scale in the laboratory. The ability to fabricate flexible elastic oxide films on large areas, measuring 8 to 12 inches, and to scale up the production of flexible elastic sensor arrays remains a critical challenge in the transition of flexible electronics from the laboratory to large-scale applications. Summary of the Invention

[0006] To address the above issues, the present invention provides a novel structure for fabricating flexible, elastic ferroelectric oxide thin film sensors. This invention enables electronic devices to possess excellent ductility and flexibility, enabling arbitrary deformation, repeated stretching, bending, and even folding. To achieve these objectives, the present invention provides the following technical solutions:

[0007] A flexible elastic ferroelectric oxide thin film sensor has a wrinkled structure and comprises a gold foil, an insulating film, parallel lower electrodes, an oxide ferroelectric film, and parallel upper electrodes connected in sequence.

[0008] Preferably, the thickness of the gold foil is 50nm-500nm.

[0009] Preferably, the insulating film is selected from any one of SiO2, Al2O3, and HfO2, with a thickness of 10-200 nm and a surface roughness of less than 5 nm.

[0010] Preferably, the oxide ferroelectric thin film is selected from any one of PZT, PMN-PT, and BaTiO3, with a thickness of 100 nm to 4 μm and a surface roughness of less than 5 nm.

[0011] Preferably, the parallel lower electrodes and the parallel upper electrodes are Au electrodes, and the thickness of the Au electrodes is 0.05-0.5 μm.

[0012] The method for preparing the flexible elastic ferroelectric oxide thin film sensor comprises the following steps:

[0013] Step 1: Transfer the gold foil to a hard substrate with a flat surface and high temperature resistance above 700°C. Use silver paste to bond and fix the four edges of the gold foil to the hard substrate to obtain a hard substrate / gold foil sample.

[0014] Step 2: Place the hard substrate / gold foil into a vacuum growth chamber and grow an insulating film on the surface of the gold foil to obtain a hard substrate / gold foil / insulating film sample;

[0015] Step 3: Using a mask or photolithography technology, a gold electrode is grown on the surface of the insulating film as a parallel lower electrode to obtain a hard substrate / gold foil / insulating film / parallel lower electrode sample;

[0016] Step 4: growing an oxide ferroelectric thin film on the surface of the parallel lower electrode in a high temperature and oxygen environment to obtain a hard substrate / gold foil / insulating film / parallel lower electrode / oxide ferroelectric thin film sample;

[0017] Step 5: Using a mask or photolithography technology, a gold electrode is grown on the surface of the insulating film as a parallel upper electrode to obtain a hard substrate / gold foil / insulating film / parallel lower electrode / oxide ferroelectric film / parallel upper electrode sample;

[0018] Step 6: removing the hard substrate from the sample to obtain a self-supporting sensor;

[0019] Step seven, bidirectionally stretch the elastomer in two directions perpendicular to each other within the surface to a maximum value, transfer the self-supporting sensor obtained in step six to the surface of the bidirectionally stretched elastomer, alternately release the stretching force of the elastomer in the two perpendicular directions and allow the elastomer to return to its original shape, the strain reduction after each release of the stretching force is less than 1%, and after the strain of the elastomer is released, the sensor forms a wrinkled structure on the surface of the elastomer, forming a flexible elastic ferroelectric oxide thin film sensor.

[0020] Preferably, in step 1, the hard substrate is one of Si, Al2O3 single crystal, and mica.

[0021] Preferably, in step 2, the growth conditions of the insulating film are: high vacuum oxygen pressure of 10 -6 -10 -5 Pa, the preferred high temperature is 600-800 degrees.

[0022] Preferably, in step four, when the oxide ferroelectric film is PZT, the growth conditions are: temperature of 600-700°C, laser energy of 70-80mj, and oxygen pressure of 13-20Pa; when the oxide ferroelectric film is PMN-PT, the growth conditions are: temperature of 600-700°C, laser energy of 70-80mj, and oxygen pressure of 13-20Pa; when the oxide ferroelectric film is BaTiO3, the growth conditions are: temperature of 700-800°C, laser energy of 70-80mj, and oxygen pressure of 3-5Pa.

[0023] Preferably, in step 3 and step 5, the growth conditions of the Au electrode are: temperature of 20-25°C, laser energy of 120-130mj, oxygen pressure of 10 -6 -10 -5 Pa.

[0024] Compared with the prior art, the advantages of the present invention are:

[0025] (1) The present invention uses all-inorganic materials to prepare a flexible elastic oxide ferroelectric thin film sensor; the ferroelectric thin film sensor prepared by the prior art by growing a lower electrode, a ferroelectric thin film, an upper electrode and other thin films on a Si substrate is rigid and has no flexibility and elasticity.

[0026] (2) The present invention uses all-inorganic materials such as PZT and PMN-PT oxide films to prepare flexible elastic oxide ferroelectric thin film sensors, and their performance is consistent with that of rigid ferroelectric thin film sensors. The existing technology grows ferroelectric films such as PVDF on flexible elastic polymer substrates and prepares polymer ferroelectric thin film sensors, and their performance is far inferior to that of rigid ferroelectric thin film sensors.

[0027] (3) The oxide ferroelectric thin film sensor prepared by the present invention can work in the range of room temperature to 200 degrees; the polymer ferroelectric thin film sensor prepared by the second prior art cannot work at high temperatures.

[0028] (4) The present invention directly fabricates 3-12 inch sensor arrays on large-area gold foil. This process meets the needs of large-scale, low-cost industrial production of large quantities of sensors. Existing technologies grow oxide films on Si and SrTiO3 substrates and fabricate millimeter-scale flexible electrode / ferroelectric film / electrode structural units by peeling and transferring the oxide ferroelectric films. However, these units lack elasticity and cannot be used for mass production of sensor arrays. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the preparation process of the flexible elastic oxide ferroelectric thin film sensor of the present invention.

[0030] Figure 2 This is an optical photograph of the sensor containing wrinkles obtained in the present invention.

[0031] Figure 3 is the piezoelectric constant (d) of Examples 1 to 54 in a flat state, a bent state with a radius of 1 mm, and a stretched state with a strain of 5%. 33 ) distribution map.

[0032] Figure 4 is the piezoelectric constant (d) of Examples 1 to 54 after bending 10,000 times at a radius of 1 mm and stretching 10,000 times at a strain of 5%. 33 ) distribution map.

[0033] Figure 5 The pyroelectric coefficient distribution diagrams of Examples 1 to 54 in a flat state, a bent state with a radius of 1 mm, and a stretched state with a strain of 5%.

[0034] Figure 6Graph showing the pyroelectric coefficient distribution of Examples 1 to 54 after being bent 10,000 times at a radius of 1 mm and stretched 10,000 times at a strain of 5%.

[0035] Figure 7 Schematic diagram of the steps of biaxial pre-stretching of the elastomer and step-by-step release in the vertical direction. DETAILED DESCRIPTION

[0036] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail below in conjunction with the embodiments. The following embodiments are merely simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is subject to the claims.

[0037] In the sensor of the present invention, the oxide ferroelectric film is the functional layer of the sensor, and the "lower electrode / ferroelectric film / upper electrode" is the basic unit of the sensor. The parallel lower electrodes and the parallel upper electrodes are perpendicular to each other, forming a sensor composed of several units. The thickness of the sensor is 0.5μm to 10μm, and it contains a regularly arranged pleated structure. Therefore, the sensor has good flexibility, elasticity and ductility, and can be transferred to the surface of human and animal skin, plant epidermis, artificial organic or inorganic objects, and sense the strain and temperature changes of the above objects.

[0038] The present invention is based on the principle that gold foil is selected as a flexible substrate because gold has good elastic ductility and is not easily oxidized at high temperatures. Silver paste is used to adhere the four corners of the gold foil to a rigid substrate, ensuring that the foil is smooth and crack-free. Then, a physical deposition method is used to sequentially grow an insulating layer, a parallel lower electrode, a ferroelectric thin film layer, and a parallel upper electrode. The resulting device not only has excellent ferroelectric performance but also retains its original ferroelectric properties to the greatest extent possible when operating at high temperatures. The gold foil can be physically peeled from the rigid substrate by cutting off the four corners where the silver paste is applied, eliminating the need for complex processes such as etching. The peeled device is then transferred to a pre-stretched elastomer. Because the gold foil has high plastic ductility and the thin film grown on the gold foil is very thin, the strain of the elastomer is released, creating a wrinkled structure in the gold foil, thereby driving the expansion and contraction of the device.

[0039] Combine Figure 1 The following is a schematic diagram of the fabrication process for the flexible, elastic, ferroelectric oxide thin film sensor according to the embodiments of the present invention. A gold foil, an insulating film, a parallel lower electrode, an oxide ferroelectric film, and a parallel upper electrode are sequentially arranged on a Si substrate. The fabrication process is specifically performed using the following steps. Specific parameters for each embodiment are shown in Table 1:

[0040] Step 1: Transfer a 12-inch large-area gold foil to a 700-degree high-temperature-resistant and flat Si substrate. Use high-temperature-resistant silver paste to bond and fix the edge area of the gold foil to the Si substrate, while keeping the middle area of the gold foil smooth and flat.

[0041] Step 2: Place the Si substrate / gold foil into a vacuum growth chamber in a high vacuum and high temperature environment. The preferred high vacuum oxygen pressure is 10 -5 Pa, the preferred high temperature is 600 degrees, and a large area of uniform and continuous insulating film is grown on the surface of the gold foil to obtain a Si substrate / gold foil / insulating film sample, and the insulating film component is one of the three materials of SiO2, Al2O3, and HfO2.

[0042] Step three: In a high vacuum and high temperature environment, by physically sputtering Au metal targets, a row of parallel long Au electrodes are grown on the surface of a hard substrate / gold foil / insulating film as parallel lower electrodes. There is an insulating area between adjacent parallel Au electrodes. The thickness of the Au electrode is 0.05-0.5 μm, and a Si substrate / gold foil / insulating film / parallel lower electrode sample is obtained.

[0043] Step 4: Grow a large area of uniform oxide ferroelectric film on the surface of the Si substrate / gold foil / insulating film / parallel lower electrode sample in a high temperature and oxygen environment. The preferred high temperature is 750 degrees, the preferred oxygen pressure is 13 Pa, the ferroelectric film component is one of the three ferroelectric materials PZT, PMN-PT, and BaTiO3, and the film thickness is 100nm to 2μm to obtain a Si substrate / gold foil / insulating film / parallel lower electrode / oxide ferroelectric film sample.

[0044] Step 5. Through physical sputtering, in a high vacuum and high temperature environment, a row of long strips of Au electrodes are prepared as parallel upper electrodes on the surface of the Si substrate / gold foil / insulating film / parallel lower electrodes / oxide ferroelectric film sample, with an insulating area between adjacent upper electrodes; the parallel upper electrodes and the parallel lower electrodes are perpendicular to each other; the Si substrate / gold foil / insulating film / parallel lower electrodes / oxide ferroelectric film / parallel upper electrodes constitute an oxide film sensor array.

[0045] Step 6: Cut the four corners of the Si substrate / gold foil / insulating film / parallel lower electrode / oxide ferroelectric film / parallel upper electrode sample, remove the Si substrate from the above sample, and obtain a self-supporting sensor.

[0046] Step 7: Combine Figure 7, biaxially stretch the elastomer in two mutually perpendicular directions within the surface to a maximum value, preferably the maximum values of the stretching in the two directions are 10% and 10% respectively, and transfer the self-supporting sensor to the surface of the elastic object that has been biaxially stretched in advance. After the stretching force of the elastic object is alternately released in the above two mutually perpendicular directions, the elastic object is allowed to return to its original shape (for example, the force in the W direction is released first, and then the force in the L direction is released, and the release cycle is alternated 4-5 times). The strain reduction after each release of the stretching force is less than 1%. After the strain of the elastomer is released, the sensor forms a wrinkle structure on the surface of the elastic object, forming a flexible elastic ferroelectric oxide thin film sensor. The optical photograph of the wrinkle is as shown in FIG. Figure 2 .

[0047] Adopt ZJ-4AN type quasi-static d 33 The measuring instrument confirmed its piezoelectric performance 33 , see Table 2, and the pyroelectric coefficient P (ie dPs / dT) was measured using a pyroelectric instrument, see Table 3.

[0048] Table 1 Specific parameters of the embodiment

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069] Table 2 Piezoelectric d of ferroelectric thin film in various states in the embodiment 33 Coefficient test table (μC / N)

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078] Table 3 Pyroelectric coefficient P test table of ferroelectric film in various states (C / m 2 K)

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086] Figure 3-Figure 6 is the piezoelectric constant d of the structure measured in different states 33 And the pyroelectric coefficient P, detailed data are shown in Table 2 and Table 3.

Claims

1. A flexible elastic ferroelectric oxide thin film sensor, characterized in that: The sensor has a corrugated structure, including a gold foil, an insulating film, a parallel lower electrode, an oxide ferroelectric film, and a parallel upper electrode connected in sequence, wherein the oxide ferroelectric film is selected from any one of PZT, PMN-PT, and BaTiO3; Prepared by the following steps: Step 1: Transfer the gold foil to a hard substrate with a flat surface and high temperature resistance of over 700 degrees Celsius. Use silver paste to bond and fix the four edges of the gold foil to the hard substrate to obtain a hard substrate / gold foil sample. Step 2: Place the hard substrate / gold foil into a vacuum growth chamber and grow an insulating film on the surface of the gold foil to obtain a hard substrate / gold foil / insulating film sample; Step 3: Using a mask or photolithography technology, a gold electrode is grown on the surface of the insulating film as a parallel lower electrode to obtain a hard substrate / gold foil / insulating film / parallel lower electrode sample; Step 4: growing an oxide ferroelectric thin film on the surface of the parallel lower electrode in a high temperature and oxygen environment to obtain a hard substrate / gold foil / insulating film / parallel lower electrode / oxide ferroelectric thin film sample; Step 5: Using a mask or photolithography technology, a gold electrode is grown on the surface of the insulating film as a parallel upper electrode to obtain a hard substrate / gold foil / insulating film / parallel lower electrode / oxide ferroelectric film / parallel upper electrode sample; Step 6: removing the hard substrate from the sample to obtain a self-supporting sensor; Step 7: biaxially stretching the elastomer in two mutually perpendicular directions within the surface of the elastomer to a maximum value, transferring the self-supporting sensor obtained in Step 6 to the surface of the biaxially stretched elastomer, alternately releasing the stretching force on the elastomer in the two perpendicular directions and allowing the elastomer to return to its original shape, wherein the strain reduction after each release of the stretching force is less than 1%, and after the strain of the elastomer is released, a wrinkled structure is formed on the surface of the elastomer, thereby forming a flexible elastic ferroelectric oxide thin film sensor; Among them, in step 4, when the oxide ferroelectric film is PZT, the high temperature is 600-700 degrees; when the oxide ferroelectric film is PMN-PT, the high temperature is 600-700 degrees; when the oxide ferroelectric film is BaTiO3, the high temperature is 700-800 degrees.

2. The sensor according to claim 1, wherein The thickness of the gold foil is 50nm-500nm; the insulating film is selected from any one of SiO2, Al2O3, and HfO2, with a thickness of 10-200nm and a surface roughness of less than 5nm; the thickness of the oxide ferroelectric film is 100nm-4mm and a surface roughness of less than 5nm; the parallel lower electrode and the parallel upper electrode use Au electrodes, and the thickness of the Au electrodes is 0.05-0.5μm.

3. The method for preparing a sensor according to claim 1 or 2, wherein: The steps include: Step 1: Transfer the gold foil to a hard substrate with a flat surface and high temperature resistance of over 700 degrees Celsius. Use silver paste to bond and fix the four edges of the gold foil to the hard substrate to obtain a hard substrate / gold foil sample. Step 2: Place the hard substrate / gold foil into a vacuum growth chamber and grow an insulating film on the surface of the gold foil to obtain a hard substrate / gold foil / insulating film sample; Step 3: Using a mask or photolithography technology, a gold electrode is grown on the surface of the insulating film as a parallel lower electrode to obtain a hard substrate / gold foil / insulating film / parallel lower electrode sample; Step 4: growing an oxide ferroelectric thin film on the surface of the parallel lower electrode in a high temperature and oxygen environment to obtain a hard substrate / gold foil / insulating film / parallel lower electrode / oxide ferroelectric thin film sample; Step 5: Using a mask or photolithography technology, a gold electrode is grown on the surface of the insulating film as a parallel upper electrode to obtain a hard substrate / gold foil / insulating film / parallel lower electrode / oxide ferroelectric film / parallel upper electrode sample; Step 6: removing the hard substrate from the sample to obtain a self-supporting sensor; Step 7: biaxially stretching the elastomer in two mutually perpendicular directions within the surface of the elastomer to a maximum value, transferring the self-supporting sensor obtained in Step 6 to the surface of the biaxially stretched elastomer, alternately releasing the stretching force on the elastomer in the two perpendicular directions and allowing the elastomer to return to its original shape, wherein the strain reduction after each release of the stretching force is less than 1%, and after the strain of the elastomer is released, a wrinkled structure is formed on the surface of the elastomer, thereby forming a flexible elastic ferroelectric oxide thin film sensor; Among them, in step 4, when the oxide ferroelectric film is PZT, the high temperature is 600-700 degrees; when the oxide ferroelectric film is PMN-PT, the high temperature is 600-700 degrees; when the oxide ferroelectric film is BaTiO3, the high temperature is 700-800 degrees.

4. The method according to claim 3, wherein In step 1, the hard substrate is one of Si, Al2O3 single crystal, and mica.

5. The method according to claim 3, wherein In step 2, the growth conditions of the insulating film are: high vacuum oxygen pressure of 10 -6 -10 -5 Pa, high temperature is 600-800 degrees.

6. The method according to claim 3, wherein In step 4, when the oxide ferroelectric film is PZT, the growth conditions are: laser energy of 70-80mj, oxygen pressure of 13-20Pa; when the oxide ferroelectric film is PMN-PT, the growth conditions are: laser energy of 70-80mj, oxygen pressure of 13-20Pa; when the oxide ferroelectric film is BaTiO3, the growth conditions are: laser energy of 70-80mj, oxygen pressure of 3-5Pa.

7. The method according to claim 3, wherein In step 3 and step 5, the growth conditions of Au electrode are: temperature 20-25 degrees, laser energy 120-130mj, oxygen pressure 10 -6 -10 -5 Pa.

Images