Response-sensitive graphene stress sensor and preparation method thereof

Abstract

The invention provides a sensitive-response graphene stress sensor and a preparation method thereof, and relates to the technical field of graphene stress sensors. The sensor comprises a flexible light-emitting layer and a photonic lattice gel layer connected with the flexible light-emitting layer, a photonic crystal with a periodic nanostructure is embedded in the photonic lattice gel layer; when the photonic lattice gel layer is stretched, the lattice constant of the photonic crystal of the periodic nanostructure in the photonic lattice gel layer is stretched, and the wavelength of reflected light moves towards the long wave direction; when the photonic lattice gel layer is compressed, the lattice constant is reduced, and the wavelength of the reflected light moves towards the short wave direction; the graphene heterojunction light sensor is connected with the photonic lattice gel layer, the flexible light-emitting layer serves as a light-emitting source, light emitted by the flexible light-emitting layer is transmitted to the graphene heterojunction light sensor through the photonic lattice gel layer, and the graphene heterojunction light sensor collects the intensity and spectrum of transmitted light. And analyzing the intensity of the transmitted light and the strain of the spectrum sensing effect on the graphene stress sensor with sensitive response.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of graphene sensor, and particularly relates to a graphene stress sensor with sensitive response and a preparation method. BACKGROUND

[0002] As a revolutionary material, graphene has great potential in the field of sensors. Graphene pressure sensor relies on the excellent mechanical properties and piezoresistive effect of graphene. When graphene is stretched or compressed, its structure will change slightly, resulting in a measurable change in resistance. Graphene pressure sensor has the following hysteresis problem: hysteresis is essentially caused by the irreversible or slow recovery of energy dissipation of the sensing material or structure under stress. In the macro graphene assembly, the relative slip and rearrangement between graphene sheets occur under pressure. When unloaded, these sheets cannot completely recover to the original position due to van der Waals force, mechanical engagement or plastic deformation, resulting in the electrical indicators cannot return to the original value. When loaded, the wrinkles are unfolded, the conductive path is increased, and the resistance is reduced. When unloaded, due to material internal loss and viscoelasticity, the wrinkles cannot immediately and completely recover, resulting in resistance recovery hysteresis. In the multi-layer or composite structure, the contact resistance between graphene and graphene, and between graphene and electrode is very sensitive to pressure. When loaded, the number of contact points and the contact area increase, and the contact resistance decreases. When unloaded, the separation of contact points and the reduction of contact area will lag behind the release of pressure due to the adhesion of the interface and the slow recovery of the substrate, thereby producing hysteresis. SUMMARY

[0003] In order to solve the above technical problems or at least partially solve the above technical problems, the present application provides a graphene stress sensor with sensitive response and a preparation method.

[0004] In a first aspect, the present application provides a graphene stress sensor with sensitive response, comprising: a flexible light-emitting layer, a photonic lattice gel layer connected with the flexible light-emitting layer, wherein photonic crystals with periodic nanostructure are embedded in the photonic lattice gel layer; when the photonic lattice gel layer is stretched, the lattice constant of the photonic crystals with periodic nanostructure in the photonic lattice gel layer is elongated, and the wavelength of reflected light moves to the long wave direction; when the photonic lattice gel layer is compressed, the lattice constant is reduced, and the wavelength of reflected light moves to the short wave direction; a graphene heterojunction light sensor connected with the photonic lattice gel layer, wherein the flexible light-emitting layer serves as a light-emitting source, the light propagates from the photonic lattice gel layer to the graphene heterojunction light sensor, the photonic lattice gel layer changes the photonic lattice properties due to stress deformation, and affects the wavelength of reflected light; the graphene heterojunction light sensor collects the intensity and spectrum of transmitted light, and analyzes the intensity and spectrum of transmitted light to perceive the strain acting on the graphene stress sensor with sensitive response.

[0005] Further, the flexible light-emitting layer comprises: a flexible light-emitting layer substrate, the flexible light-emitting layer substrate is connected to a bottom anode layer composed of a transparent conductive oxide or a flexible silver nanowire or graphene material; the bottom anode layer is connected to a hole injection layer; the hole injection layer is connected to a hole transport layer; the hole transport layer is connected to a light-emitting layer; the light-emitting layer is connected to an electron transport layer; the electron transport layer is connected to an electron injection layer; the electron injection layer is connected to a metal cathode and an encapsulation layer; when a voltage is applied, the electrons and holes injected from the cathode and the anode recombine in the light-emitting layer, excite the organic molecules in the light-emitting layer, and emit light when returning to the ground state.

[0006] Further, the graphene heterojunction light sensor comprises: an N-type silicon substrate and a graphene layer connected to the N-type silicon substrate, a Schottky junction is formed between the N-type silicon substrate and the graphene layer; a ring-shaped silicon dioxide pedestal is arranged between the N-type silicon substrate and the graphene layer, the silicon dioxide pedestal bears the graphene layer, and an upper electrode connected to the graphene layer is arranged on the silicon dioxide pedestal, so that the photo-generated carriers separated by the Schottky junction are transmitted to an external circuit through the upper electrode; a back electrode is arranged on the lower surface of the N-type silicon substrate.

[0007] Further, a silicon dioxide oxidation layer with a certain thickness is introduced at the interface between the graphene layer and the N-type silicon substrate, and the silicon dioxide oxidation layer separates the graphene layer and the N-type silicon substrate.

[0008] Further, a flat, uniform and loose titanium dioxide covering layer with a certain thickness is coated on the graphene layer, a Schottky junction is formed at the interface between the titanium dioxide covering layer and the graphene layer; the interface between the titanium dioxide covering layer and the graphene layer and the interface between the N-type silicon substrate and the graphene layer both point to the graphene in the direction of the internal electric field of the Schottky junction; wherein, the titanium dioxide covering layer adopts an anatase titanium dioxide.

[0009] Further, the graphene heterojunction light sensor after the coated titanium dioxide covering layer is treated with nitric acid vapor for a certain period of time to provide P-type doping for the graphene.

[0010] Further, an adhesive with a certain elasticity and a certain breaking elongation is used to construct a neutral layer between the flexible light-emitting layer and the photonic crystal gel layer, and when subjected to stress deformation, the relative displacement between the flexible light-emitting layer and the photonic crystal gel layer is absorbed and compensated by the deformation of the neutral layer.

[0011] Further, the flexible light-emitting layer is designed to support a grid-like structure, a wave or a snake-like structure that can adapt to deformation, and the conductive wire of the flexible light-emitting layer and the graphene heterojunction light sensor is designed to have a wave or a snake-like structure.

[0012] In a second aspect, the present application provides a preparation method of a graphene stress sensor with sensitive response, for preparing the graphene stress sensor with sensitive response, comprising: Preparation of graphene heterojunction optical sensor, at least one graphene heterojunction optical sensor is embedded into one side of the photonic crystal gel layer, and a flexible light-emitting layer is combined to the other side of the photonic crystal gel layer.

[0013] Further, the process for preparing the graphene heterojunction optical sensor comprises: Double-side polishing of the silicon wafer; Placing the silicon wafer in a high-temperature furnace for thermal oxidation for a first time duration to form a silicon dioxide layer on the surface of the silicon wafer; Removing the silicon dioxide layer on the upper surface window of the silicon wafer and the lower surface of the silicon wafer by etching; Cleaning and nitrogen-drying the silicon wafer; Placing the cleaned and dried silicon wafer in a vapor of hydrofluoric acid with a set mass fraction for processing for a second time duration to remove the silicon dioxide layer in the upper surface window of the silicon wafer; Transferring the graphene film to the silicon wafer and drying in air; Coating an upper electrode on the graphene on the silicon dioxide base around the window; Setting a back electrode on the lower surface of the silicon wafer; Preparing an ethanol dispersion of anatase titanium dioxide nanoparticles and diluting and shaking; Taking a set amount of the diluted titanium dioxide nanoparticle dispersion and spin-coating to the graphene side at room temperature; Alternatively, the process for preparing the graphene heterojunction optical sensor comprises: Double-side polishing of the silicon wafer; Etching the silicon wafer to form a silicon substrate array with a window; Cleaning and nitrogen-drying the silicon substrate array; Soaking the silicon substrate array in ethanol and drying; Taking a set amount of an aqueous solution of graphene oxide with a set concentration and drop-coating onto the surface of the silicon substrate array, and standing at room temperature until the graphene oxide is dried into a film; Reducing the graphene oxide film-covered silicon substrate array; Treating the upper surface of the reduced device with a vapor of hydrofluoric acid with a set mass fraction for a fifth time duration to thin the silicon dioxide layer formed at the interface between the reduced graphene oxide and the silicon; Coating an upper electrode on the graphene on the silicon dioxide base around the window; Setting a back electrode on the lower surface of the silicon wafer; Preparing an ethanol dispersion of anatase titanium dioxide nanoparticles and diluting and shaking; Taking a set amount of the diluted titanium dioxide nanoparticle dispersion and spin-coating to the graphene side at room temperature.

[0014] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art: The application provides a flexible light-emitting layer, and a photonic lattice gel layer connected with the flexible light-emitting layer, wherein photonic crystals with periodic nanostructures are embedded in the photonic lattice gel layer; when the photonic lattice gel layer is stretched, the lattice constant of the photonic crystals with periodic nanostructures in the photonic lattice gel layer is elongated, and the wavelength of reflected light moves to the long-wave direction; when the photonic lattice gel layer is compressed, the lattice constant is reduced, and the wavelength of reflected light moves to the short-wave direction. Thus, the mechanical deformation of the photonic lattice gel layer is converted into optical information; the graphene heterojunction optical sensor collects the intensity and spectrum of transmitted light, analyzes the intensity and spectrum of the transmitted light, and senses the strain acting on the response-sensitive graphene stress sensor. The photoelectric detection of graphene mainly depends on the optical properties and photoelectric effect of graphene. Graphene can absorb light in a very wide range from ultraviolet to terahertz, and the energy of the photons can excite the electrons in graphene to generate photocurrent or photovoltage. The speed of photoelectric conversion is faster, and the use of graphene to detect light has significant advantages in sensitivity and response speed compared to measuring force.

[0015] The application introduces a silicon dioxide oxidation layer with a set thickness at the interface between the graphene layer and the N-type silicon substrate, improves the Schottky junction barrier height, limits the multi-carrier current in the dark current, reduces the dark current, increases the open-circuit voltage, and improves the junction capacitance to improve the response and recovery time; and comprehensively improves the detection performance.

[0016] The application coats a flat, uniform and loose titanium dioxide cover layer with a set thickness on the graphene layer, and a Schottky junction is formed at the interface between the titanium dioxide cover layer and the graphene layer. There are two Schottky junctions in the graphene heterojunction optical sensor. One is located at the titanium dioxide / graphene interface, and the other is located at the graphene / silicon interface. The internal electric fields of the two Schottky junctions both point to the graphene and can separate the photo-generated carriers. When the incident light irradiates on the surface of the device, the electrons in the titanium dioxide absorb photon energy to jump to the conduction band to form electron-hole pairs, which are then separated by the internal electric field between the titanium dioxide / graphene interface. The holes can be injected into the loop composed of the graphene / silicon photodetector after being separated, so as to enhance the light response current. The titanium dioxide cover layer injects more carriers into the loop through the heterojunction between itself and the graphene, which can improve the short-wavelength light detection performance. After coating the titanium dioxide cover layer on the upper surface of the graphene, the surface state of the graphene is changed, which can reduce the dark current. After coating the titanium dioxide cover layer, the introduction of the titanium dioxide and graphene barrier capacitance in the graphene heterojunction optical sensor reduces the total capacitance of the graphene heterojunction optical sensor, and the time constant of the system response is also reduced, so that the response speed and recovery speed of the graphene heterojunction optical sensor after coating the titanium dioxide cover layer are faster. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate embodiments that are in accordance with the present application and, together with the description, serve to explain the principles of the application.

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without any creative effort.

[0019] Figure 1 A schematic diagram of a responsive and sensitive graphene stress sensor provided by the embodiments of the present application; Figure 2 A schematic diagram of a graphene heterojunction light sensor provided by the embodiments of the present application; Figure 3 A schematic diagram of an equivalent circuit of a graphene heterojunction light sensor provided by the embodiments of the present application; Figure 4 A flowchart of a preparation method of a responsive and sensitive graphene stress sensor provided by the embodiments of the present application; Figure 5 A flowchart of a preparation method of a graphene heterojunction light sensor provided by the embodiments of the present application; Figure 6 A flowchart of a preparation method of a graphene heterojunction light sensor provided by the embodiments of the present application.

[0020] The reference signs and meanings in the drawings are as follows: 1, flexible light-emitting layer, 2, photonic crystal gel layer, 3, graphene heterojunction light sensor, 31, N-type silicon substrate, 32, silicon dioxide base, 33, silicon dioxide oxide layer, 34, graphene layer, 35, titanium dioxide cover layer, 36, back electrode, 37, upper electrode. DETAILED DESCRIPTION

[0021] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without any creative effort fall within the protection scope of the present application.

[0022] It is to be understood that the terms "including", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises a... " does not, without more constraints, exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0023] Embodiment 1 Embodiments of the present application provide a graphene stress sensor with high sensitivity, as shown in Figure 1 comprises: a flexible light-emitting layer 1; the flexible light-emitting layer 1 is connected to a photonic crystal gel layer 2.

[0024] An example of the flexible light-emitting layer 1 comprises: a flexible light-emitting layer substrate, such as polyimide, polyethylene terephthalate, polydimethylsiloxane; the flexible light-emitting layer substrate is connected to a bottom anode, the bottom anode uses a transparent conductive oxide, such as indium tin oxide, or a flexible silver nanowire, or a graphene material; the bottom anode is connected to a hole injection layer, the hole injection layer is connected to a hole transport layer; the work function of the hole injection layer is between the anode and the hole transport layer, facilitating the injection of holes from the anode to the hole transport layer, such as using copper phthalocyanine for the hole injection layer and α-naphthylphenyl biphenyl diamine for the hole transport layer; the hole transport layer is connected to a light-emitting layer, such as using tris-8-hydroxyquinoline aluminum for the light-emitting layer; the light-emitting layer is connected to an electron transport layer, such as using 4,7-diphenyl-1,10-phenanthroline for the electron transport layer; the electron transport layer is connected to an electron injection layer, such as using lithium fluoride for the electron injection layer; the electron injection layer is connected to a metal cathode and an encapsulation layer; when a voltage is applied, the electrons and holes injected from the metal cathode and the bottom anode recombine in the light-emitting layer, exciting the organic molecules in the light-emitting layer to emit light when returning to the ground state.

[0025] An example of the flexible light-emitting layer 1 uses a flexible Micro-LED, which is a micron-level LED arranged on a flexible substrate.

[0026] To compensate for the problem of easy delamination after multiple stresses caused by the mismatch between the mechanical properties of the flexible light-emitting layer 1 and the mechanical properties of the photonic crystal gel layer 2.

[0027] In an example scheme, a neutral layer is constructed using an adhesive with high elasticity and elongation at break, such as silicone, and when stressed and deformed, the deformation of the neutral layer absorbs and compensates for the relative displacement between the flexible light-emitting layer and the photonic crystal gel layer. In another example scheme, the flexible light-emitting layer is designed to support a grid-like structure, a wave or a snake structure with strong deformation adaptation capability, and the flexible light-emitting layer and the lead wire of the graphene heterojunction light sensor are designed to be a wave or a snake structure.

[0028] The photonic crystal gel layer 2 is embedded with photonic crystals with periodic nanostructures; when the photonic crystal gel layer is stretched, the lattice constant of the photonic crystals with periodic nanostructures inside is elongated, and the wavelength of the reflected light moves to the long-wave direction; when the photonic crystal gel layer is compressed, the lattice constant decreases, and the wavelength of the reflected light moves to the short-wave direction.

[0029] The photonic crystal gel layer 2 connects the graphene heterojunction light sensor 3, the flexible light-emitting layer 1 serves as a light-emitting source, the emitted light propagates through the photonic crystal gel layer 2 to the graphene heterojunction light sensor 3, the photonic crystal gel layer 2 changes its photonic crystal properties due to stress deformation, affecting the wavelength of the reflected light; the graphene heterojunction light sensor 3 collects the intensity and spectrum of the transmitted light and analyzes the intensity and spectrum of the transmitted light to perceive the strain acting on the response-sensitive graphene stress sensor.

[0030] In an example, an elastic skeleton is added to the photonic crystal gel layer 2 to enhance the deformation recovery performance of the photonic crystal gel layer 2.

[0031] As shown in Figure 2 The graphene heterojunction light sensor 3 includes an N-type silicon substrate 31 and a graphene layer 34 connected to the N-type silicon substrate, and a Schottky junction is formed between the N-type silicon substrate 31 and the graphene layer 34; specifically, because the Fermi level of silicon is higher, electrons will flow from the N-type silicon substrate side to the graphene side, making the electrons on the side of the N-type silicon substrate close to the contact interface fewer and fewer, leaving a positive space charge layer with a positive charge; electrons gradually accumulate on the graphene side, forming a negative space charge layer, and due to the recombination of electrons and holes between the positive and negative charge layers, the number of internal carriers is extremely small, forming a depletion layer. With the accumulation of positive and negative charges, an internal electric field that gradually increases will be formed at the junction interface, and the Fermi level of the N-type silicon substrate will gradually flatten with the Fermi level of the graphene, until the carrier motion reaches equilibrium.

[0032] A surrounding silicon dioxide pedestal 32 is arranged between the N-type silicon substrate 31 and the graphene layer 34, the silicon dioxide pedestal 32 carries the graphene layer 34, and an upper electrode 37 connected to the graphene layer 34 is arranged on the silicon dioxide pedestal 32, so that the photo-generated carriers separated by the Schottky junction are effectively transmitted to the external circuit through the upper electrode 37; a back electrode 36 is arranged on the lower surface of the N-type silicon substrate 31, and the back electrode 36 is an indium-gallium alloy or a Ti / Au electrode. The Schottky junction region formed between the graphene layer 34 and the N-type silicon substrate 31 is the effective working region of the photodetector; when incident light irradiates the Schottky junction surface, the valence electrons in the N-type silicon substrate absorb photon energy to jump to the conduction band, forming electron-hole pairs. Under the action of the internal electric field, the electron-hole pairs are separated, the holes enter the external circuit through the graphene layer 34 and the upper electrode 37 along the direction of the internal electric field, and the electrons are transmitted in the circuit through the N-type silicon substrate 31 and the back electrode 36.

[0033] For ease of understanding, the graphene heterojunction light sensor is described by using an equivalent circuit of the graphene heterojunction light sensor. As shown in Figure 3 the equivalent circuit of the graphene heterojunction light sensor includes a junction capacitance C1, an ideal diode D1, a photocurrent source, a dark current source, a noise current source, and a shunt equivalent resistance R2 in parallel, a load resistance RL, and a resistance R1 and a parallel component in series.

[0034] The junction capacitance C1 includes a barrier capacitance and a diffusion capacitance, which are the main factors affecting the response time. The barrier capacitance is caused by the change in the number of space charges in the barrier region due to the storage and removal of majority carriers in the barrier region. The diffusion capacitance is caused by the accumulation of minority carriers in the heterojunction diffusion region. In the graphene heterojunction light sensor, the directional motion of the photo-generated carriers excited by light radiation causes a photocurrent I1, and the photocurrent source generates an equivalent photocurrent I1, which is the light response output. In the absence of light, the graphene heterojunction light sensor generates a dark current I2 due to background radiation, diode saturation current, leakage current and other factors, and the dark current source generates an equivalent dark current I2. The noise current I3 is generated in the circuit by uncontrollable noise sources in the environment, and the noise current source generates an equivalent noise current I3. The shunt equivalent resistance R2 is caused by the defects of the material itself and the problems in the processing and assembly process, which causes the shunt of the photocurrent, and the shunt of the photocurrent is equivalent to a shunt equivalent resistance R2. The defects of the material itself, such as impurities or regions with high conductivity in the N-type silicon substrate. The resistance R1 includes: the resistance of graphene and silicon itself; the transmission resistance of current in the heterojunction; the contact resistance between graphene and silicon; the contact resistance between the upper electrode, the back electrode and the circuit. The resistance R1 affects the short-circuit current, and the resistance R1 should be as small as possible to improve the responsivity. The load RL is provided by the current or voltage measurement circuit.

[0035] In one embodiment, a silicon dioxide oxidation layer 33 of a certain thickness is introduced at the interface between the graphene layer 34 and the N-type silicon substrate 31, which separates the graphene and the N-type silicon substrate.

[0036] After introducing the silicon dioxide oxidation layer, the barrier height is increased according to the following Schottky barrier height equation: ; wherein, is the Schottky barrier height with the silicon dioxide oxidation layer; is the Schottky barrier height without the silicon dioxide oxidation layer; is the additional barrier height brought by the silicon dioxide oxidation layer; m is the effective electron mass for tunneling; is the average tunneling barrier height of the silicon dioxide oxidation layer; is the thickness of the silicon dioxide oxidation layer; is the Boltzmann constant; T is the absolute temperature; is the reduced Planck constant.

[0037] After increasing the barrier height, the multi-carrier current in the dark current, which is formed by the carriers that cross the barrier due to thermal emission, is limited, and the dark current is reduced. After introducing the silicon dioxide oxidation layer, the dark current is greatly reduced, the photocurrent changes little, the ratio of the response current to the dark current is increased, and the detection performance is greatly improved.

[0038] According to the following open-circuit voltage equation, the open-circuit voltage is increased after introducing the silicon dioxide oxidation layer: ; wherein, is the open-circuit voltage; n is the ideal factor; q is the elementary charge, is the short-circuit current density, is the Richardson constant.

[0039] According to the relationship between the open-circuit voltage and the photocurrent, the reverse saturation current ; wherein, is the reverse saturation current, S is the area between the graphene and the silicon dioxide oxidation layer; the barrier is increased, the reverse saturation current is reduced, the open-circuit voltage is increased, and the increase in the open-circuit voltage is conducive to improving the output characteristics.

[0040] The introduction of the silicon dioxide oxide layer improves the junction capacitance to improve the response and recovery time. The response time and recovery time are mainly affected by the junction capacitance. When light, photo-generated carriers are first injected into the barrier region, the response increases rapidly, and then as the carrier injection increases, a part of the carriers diffuse away, and a part of the carriers increase the carrier accumulation at the boundary of the depletion layer, the response begins to gradually slow down until it reaches a stable state; without light, the excess carriers at the boundary of the depletion layer first recombine, the charges in the barrier region are less affected, and the response decreases slowly, and then due to the disappearance of the photo-generated voltage, the width of the barrier region increases, the carriers in the barrier region move out, and the response rapidly decreases; after the introduction of the silicon dioxide oxide layer, an interface layer capacitance is connected in series in the equivalent circuit, which reduces the total capacitance and reduces the time constant, which is beneficial to shorten the response time and recovery time.

[0041] The graphene layer 34 is coated with a flat, uniform, loose titanium dioxide covering layer 35 of a certain thickness, and a Schottky junction is formed at the interface between the titanium dioxide covering layer 35 and the graphene layer 34; the interface between the titanium dioxide covering layer 35 and the graphene layer 34 forms a Schottky junction, and the internal electric field of the Schottky junction formed between the N-type silicon substrate and the graphene layer points to the graphene layer; wherein the titanium dioxide covering layer adopts an anatase titanium dioxide.

[0042] Different wavelengths of light have different photon energies. In theory, for all incident photons with photon energy greater than the width of the silicon band gap, if their energy is absorbed and converted into photo-generated carriers, the quantum efficiency is independent of the wavelength of the incident light. However, when light with high photon energy shines on its surface, most of it will be strongly absorbed by the free electrons and other oscillators inside the graphene, eventually converting into heat loss. The remaining to the interface between graphene and silicon, at the upper interface of silicon, is strongly absorbed, and at the upper interface of silicon, due to the influence of the interface state, the utilization rate of photon energy is also not high. Therefore, after the wavelength of the incident light is less than a certain wavelength threshold, and the frequency is higher than a certain frequency threshold (the photon energy is only related to the frequency), the quantum efficiency begins to gradually decrease. This results in poor detection performance of short-wavelength light.

[0043] The band gap of anatase titanium dioxide is about 3.2eV, and the band gap of rutile titanium dioxide is about 3.0eV, corresponding to the light wavelength in the range of 387~413nm. The valence electrons of titanium dioxide are excited into the conduction band by the incident photon energy of 387~413nm, thereby forming electron-hole pairs. If the electron-hole pairs are effectively separated and enter the detection circuit, the utilization of the energy of the light with shorter wavelength will be greatly improved, thereby improving the photoelectric detection performance of the graphene heterojunction optical sensor. After the introduction of the titanium dioxide covering layer 35, two Schottky junctions exist in the graphene heterojunction optical sensor. One is located at the titanium dioxide / graphene interface, and the other is located at the graphene / silicon interface. The internal electric fields of the two Schottky junctions both point to the graphene and can separate the photo-generated carriers. When the incident light irradiates on the surface of the device, the electrons in the titanium dioxide absorb the photon energy and jump to the conduction band, forming electron-hole pairs. The electron-hole pairs are then separated by the internal electric field between the titanium dioxide / graphene, and the holes can be injected into the circuit composed of the graphene / silicon photodetector, thereby achieving the enhancement of the light response current. Since the titanium dioxide itself is not conductive, the electrons separated by the electric field will accumulate on the upper surface of the titanium dioxide covering layer and be coupled with the holes on the lower surface of the titanium dioxide covering layer to reach equilibrium. The titanium dioxide covering layer injects more carriers into the circuit through the heterojunction between itself and the graphene, thereby improving the short-wavelength light detection performance. After the upper surface of the graphene is coated with the titanium dioxide covering layer, the surface state of the graphene is changed, thereby reducing the dark current. After the coating of the titanium dioxide covering layer, the introduction of the titanium dioxide and graphene barrier capacitance in the graphene heterojunction optical sensor reduces the total capacitance of the graphene heterojunction optical sensor, and the time constant of the system response is also reduced. Therefore, the response speed and recovery speed of the graphene heterojunction optical sensor after the coating of the titanium dioxide covering layer are faster.

[0044] The lifetime of the carriers in the anatase titanium dioxide is longer than that in the rutile titanium dioxide, which is more conducive to performance improvement. In the present application, anatase titanium dioxide nanoparticles are used. The nanoparticles have a large specific surface area, which is conducive to interaction with light and can be dispersed in a dispersant for easy preparation of a coating layer. The size of the anatase titanium dioxide nanoparticles is between 3~5nm.

[0045] The graphene heterojunction optical sensor after the coating of the titanium dioxide covering layer is treated with nitric acid vapor for a set period of time to provide P-type doping for the graphene. The loose structure of the titanium dioxide covering layer can effectively transmit the nitric acid vapor through the titanium dioxide covering layer to the surface of the graphene, thereby playing a P-type doping role. After the P-type doping of the graphene, the potential barrier can be further improved, and the dark current can be further reduced.

[0046] Example 2 As Figure 4 , Figure 5 andFigure 6 As shown, the embodiment of the present application provides a preparation method of a graphene stress sensor with sensitive response, and the graphene stress sensor with sensitive response is prepared by the method, which comprises the following steps. The graphene heterojunction light sensor is prepared, at least one graphene heterojunction light sensor is embedded into one side of the photonic crystal gel layer, and a flexible light-emitting layer is combined to the other side of the photonic crystal gel layer.

[0047] The process of preparing the graphene heterojunction light sensor comprises the following steps. The silicon wafer is polished on both sides. The silicon wafer is placed in a high-temperature furnace for thermal oxidation for a first time length to form a silicon dioxide layer on the surface of the silicon wafer; after the thermal oxidation for the first time length, the thickness of the silicon dioxide layer formed on the surface of the silicon wafer reaches 300 nm.

[0048] The silicon dioxide layer on the upper surface window of the silicon wafer and the lower surface of the silicon wafer is removed by etching, which comprises the following steps: photoresist is coated on the upper surface of the silicon wafer, a mask plate is used to shield the upper surface of the silicon wafer, ultraviolet light is irradiated, the photoresist in the area corresponding to the window of the mask plate is removed, and the photoresist in the unirradiated part is reserved; the processed silicon wafer is placed in a hydrofluoric acid solution to remove the silicon dioxide layer on the upper surface window of the silicon wafer and the lower surface of the silicon wafer.

[0049] The silicon wafer is cleaned and dried with nitrogen, which comprises the following steps: the prepared silicon wafer is placed in acetone for ultrasonic cleaning for 15 min to remove the attachments on the surface of the silicon wafer; the surface of the silicon wafer is rinsed with isopropyl alcohol, and then dried with nitrogen.

[0050] The cleaned and dried silicon wafer is placed in a hydrofluoric acid vapor with a set mass fraction for a second time length to remove the silicon dioxide layer in the upper surface window of the silicon wafer. Specifically, the silicon wafer is placed in a hydrofluoric acid vapor with a mass fraction of 40% for 10 s to remove the silicon dioxide layer in the upper surface window of the silicon wafer.

[0051] The silicon wafer is placed in air for a third time length to form a silicon dioxide oxidation layer introduced between the graphene and the N-type silicon substrate on the upper surface window of the silicon wafer; after the oxidation for the third time length, a 2 nm thick silicon dioxide oxidation layer is formed on the upper surface window of the silicon wafer.

[0052] The graphene film is transferred to the silicon wafer and dried in air. An upper electrode is coated on the graphene on the silicon dioxide base on the window; specifically, silver glue is coated on the graphene on the silicon dioxide base on the window, and a silver lead wire is drawn out as the upper electrode.

[0053] A back electrode is arranged on the lower surface of the silicon wafer; in one embodiment, Ti / Au with thicknesses of 10 nm / 50 nm is evaporated on the lower surface of the silicon wafer as the back electrode; in one embodiment, an indium-gallium alloy back electrode is coated on the lower surface of the silicon wafer.

[0054] Preparation of anatase titanium dioxide nanoparticles ethanol dispersion, and dilution to a set concentration of 0.2 mg / mL. A certain amount of diluted titanium dioxide nanoparticle dispersion is spin-coated onto the graphene side at room temperature. Specifically, 2 μL of diluted titanium dioxide nanoparticle dispersion is taken; spin-coated onto the graphene side at room temperature.

[0055] Another process for preparing a graphene heterojunction optical sensor includes: Silicon wafer double-sided polishing.

[0056] Etching the silicon wafer to generate a silicon substrate array with windows includes: coating photoresist on the upper surface of the silicon wafer, shielding the upper surface of the silicon wafer with a mask plate, and removing the photoresist in the area corresponding to the window of the mask plate by ultraviolet light irradiation, and retaining the photoresist that has not been irradiated; etching the silicon wafer to generate a silicon substrate array with windows.

[0057] Washing and nitrogen blowing dry the silicon substrate array; place the silicon substrate array in acetone and ultrasonically clean for 15 min to remove the attachments on the surface of the silicon substrate array; after washing is completed, take out the silicon substrate array, rinse the surface of the silicon wafer with isopropanol, and then dry with nitrogen.

[0058] Soak the silicon substrate array in ethanol and dry; soak the silicon substrate array in ethanol for 30 min, then take it out and dry.

[0059] Prepare a graphene oxide aqueous solution with a set concentration; an example concentration of the graphene oxide aqueous solution is 0.25 mg / mL.

[0060] Drop 5 μL of the graphene oxide aqueous solution onto the surface of the silicon substrate array, and use the surface tension of the droplet to completely cover the surface of the silicon substrate array.

[0061] Reduce the graphene oxide film-coated silicon substrate array; specifically, place the graphene oxide film-coated silicon substrate array in a tube furnace, and heat it to a set reduction temperature under the protection of argon and hydrogen with a flow ratio of 20:1 for a fourth duration. Treat the upper surface of the reduced device with a hydrofluoric acid vapor with a set mass fraction for a fifth duration to thin the silicon dioxide layer formed at the interface between the reduced graphene oxide and the silicon. Specifically, take out the reduced device and treat the upper surface of the device with a 40% mass fraction hydrofluoric acid vapor for 10 s to thin the silicon dioxide layer formed at the interface between the reduced graphene oxide and the silicon. An upper electrode is coated on the graphene on the silicon dioxide base around the window; specifically, silver glue is coated on the graphene on the silicon dioxide base around the window, and a silver lead wire is drawn out as the upper electrode.

[0062] A back electrode is arranged on the lower surface of the silicon wafer; in one embodiment, Ti / Au with thicknesses of 10 nm / 50 nm is evaporated on the lower surface of the silicon wafer as the back electrode; in one embodiment, an indium-gallium alloy back electrode is coated on the lower surface of the silicon wafer.

[0063] An anatase titanium dioxide nanoparticle ethanol dispersion liquid is prepared and diluted to a set concentration and shaken, and the set concentration is, for example, 0.2 mg / mL. A set amount of the diluted titanium dioxide nanoparticle dispersion liquid is spin-coated on the graphene side at room temperature; specifically, 2 μL of the diluted titanium dioxide nanoparticle dispersion liquid is taken; and the graphene side is spin-coated at room temperature.

[0064] The above description is merely a specific implementation of the present application, and enables those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A sensitive graphene stress sensor, characterized in that, include: Flexible light-emitting layer (1). A photonic lattice gel layer (2) is connected to the flexible light-emitting layer (1), wherein a photonic crystal with a periodic nanostructure is embedded in the photonic lattice gel layer; when the photonic lattice gel layer is stretched, the lattice constant of the photonic crystal with the periodic nanostructure inside it is stretched, and the wavelength of the reflected light shifts to the long wavelength direction; when the photonic lattice gel layer is compressed, the lattice constant decreases, and the wavelength of the reflected light shifts to the short wavelength direction; The graphene heterojunction optical sensor (3) is connected to the photonic lattice gel layer (2). The flexible light-emitting layer (1) serves as the light source. The emitted light rays propagate through the photonic lattice gel layer (2) to the graphene heterojunction optical sensor (3). The photonic lattice gel layer changes its photonic lattice properties due to stress deformation, which affects the wavelength of the reflected light. The graphene heterojunction optical sensor (3) collects the intensity and spectrum of the transmitted light and analyzes the intensity and spectrum of the transmitted light to sense the strain of the sensitive graphene stress sensor.

2. The graphene stress sensor with high responsiveness according to claim 1, characterized in that, The flexible light-emitting layer (1) includes: a flexible light-emitting layer substrate, a bottom anode made of transparent conductive oxide or flexible silver nanowires or graphene material connected to the flexible light-emitting layer substrate; a hole injection layer connected to the bottom anode; a hole injection layer connected to the hole transport layer; a hole transport layer connected to the light-emitting layer; a light-emitting layer connected to the electron transport layer; an electron transport layer connected to the electron injection layer; and an electron injection layer connected to the metal cathode and the encapsulation layer. When a voltage is applied, electrons and holes injected from the cathode and anode recombine in the light-emitting layer, exciting the organic molecules of the light-emitting layer, which emit light when returning to the ground state.

3. The graphene stress sensor with a sensitive response according to claim 1, characterized in that, The graphene heterojunction photosensor (3) includes: an N-type silicon substrate (31) and a graphene layer (34) connected to the N-type silicon substrate (31), a Schottky junction is formed between the N-type silicon substrate (31) and the graphene layer (34); a surrounding silicon dioxide platform (32) is disposed between the N-type silicon substrate (31) and the graphene layer (34), the silicon dioxide platform (32) supports the graphene layer (34), and an upper electrode (37) connected to the graphene layer (34) is disposed on the silicon dioxide platform (32) so that photogenerated carriers separated by the Schottky junction are transmitted to the external circuit through the upper electrode (37); a back electrode (36) is disposed on the lower surface of the N-type silicon substrate (31).

4. The graphene stress sensor with a sensitive response according to claim 3, characterized in that, A silicon dioxide oxide layer (33) of a set thickness is introduced at the interface between the graphene layer (34) and the N-type silicon substrate (31), the silicon dioxide oxide layer (33) separating the graphene layer (34) and the N-type silicon substrate (31).

5. The graphene stress sensor with a sensitive response according to claim 3, characterized in that, A flat, uniform, and loose titanium dioxide capping layer (35) of a set thickness is coated on the graphene layer (34). A Schottky junction is formed at the interface between the titanium dioxide capping layer (35) and the graphene layer (34). The internal electric field directions of the Schottky junction formed at the interface between the titanium dioxide capping layer (35) and the graphene layer (34) and the Schottky junction formed between the N-type silicon substrate (31) and the graphene layer (34) are all pointing towards the graphene. The titanium dioxide capping layer (35) is anatase titanium dioxide.

6. The graphene stress sensor with a sensitive response according to claim 5, characterized in that, The graphene heterojunction optical sensor coated with titanium dioxide was treated with nitric acid vapor for a set time to provide P-type doping to the graphene.

7. The graphene stress sensor with a sensitive response according to claim 3, characterized in that, A neutral layer is constructed between the flexible light-emitting layer and the photonic lattice gel layer using an adhesive with set elasticity and set elongation at break. When subjected to stress and deformation, the deformation of the neutral layer absorbs and compensates for the relative displacement between the flexible light-emitting layer and the photonic lattice gel layer.

8. The graphene stress sensor with a sensitive response according to claim 3, characterized in that, The flexible light-emitting layer is designed to support a mesh-like structure, wave-like structure, or serpentine structure that adapts to deformation, and the wires of the flexible light-emitting layer and the graphene heterojunction optical sensor are designed to be wave-like or serpentine structures.

9. A method for preparing a responsive graphene stress sensor, used to prepare the responsive graphene stress sensor according to any one of claims 1-8, characterized in that, include: A graphene heterojunction optical sensor is fabricated by embedding at least one graphene heterojunction optical sensor into one side of a photonic lattice gel layer and attaching a flexible light-emitting layer to the other side of the photonic lattice gel layer.

10. The method for preparing the responsive graphene stress sensor according to claim 9, characterized in that, The process of fabricating a graphene heterojunction optical sensor includes: Silicon wafers are polished on both sides; The silicon wafer is placed in a high-temperature furnace for thermal oxidation for a first duration to generate a silicon dioxide layer on the surface of the silicon wafer. The silicon dioxide layer at the window on the upper surface of the silicon wafer and the silicon dioxide layer on the lower surface of the silicon wafer are removed by etching; Clean and dry the silicon wafers with nitrogen gas; After cleaning and drying, the silicon wafer is placed in hydrofluoric acid vapor with a set mass fraction for a second time to remove the silicon dioxide layer in the window on the upper surface of the silicon wafer. The graphene film was transferred onto a silicon wafer and dried in air. Electrodes are coated onto graphene on a silicon dioxide substrate around the window; a back electrode is disposed on the lower surface of the silicon wafer; Prepare an ethanol dispersion of anatase titanium dioxide nanoparticles and dilute and shake well; take a set amount of the diluted titanium dioxide nanoparticle dispersion and spin-coat it onto one side of graphene at room temperature. Alternatively, the process of fabricating a graphene heterojunction optical sensor includes: Silicon wafers are polished on both sides; Etching silicon wafers creates a silicon substrate array with windows; Clean and dry the silicon substrate array with nitrogen gas; The silicon substrate array was immersed in ethanol and then dried. A set amount of graphene oxide aqueous solution of a set concentration was drop-coated onto the surface of a silicon substrate array and left to stand at room temperature until the graphene oxide dried and formed a film. The silicon substrate array coated with graphene oxide film is subjected to reduction treatment; The upper surface of the reduced device was treated with hydrofluoric acid vapor of a set mass fraction for a fifth time to reduce the thickness of the silicon dioxide layer formed at the interface between the reduced graphene oxide and silicon. Electrodes are coated onto graphene on a silicon dioxide substrate around the window; a back electrode is disposed on the lower surface of the silicon wafer; Prepare an ethanol dispersion of anatase titanium dioxide nanoparticles and dilute and shake well; Take a set amount of the diluted titanium dioxide nanoparticle dispersion and spin-coat it onto one side of the graphene at room temperature.

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