Laser-Induced All-Carbon-Based Field-Effect Transistor Metasurface Unit Structure and Preparation Method

Abstract

The present invention discloses a laser-induced all-carbon-based field-effect transistor metasurface unit structure and a preparation method thereof. The metasurface unit structure includes an electromagnetic resonance layer, a flexible substrate layer, and a back gate layer. The electromagnetic resonance layer is composed of a graphene source electrode, a graphene drain electrode, and a graphene channel. The graphene source electrode and the graphene drain electrode are periodic sub-wavelength unit structures, and the graphene source electrode is connected to the graphene drain electrode through the graphene channel. The back gate layer is composed of a porous graphene gate electrode, and the back gate layer is embedded in the flexible substrate layer. The carrier concentration in the graphene channel is regulated by applying a gate-source voltage. The metasurface unit structure adopts an integrated design of a regulation unit and an external drive unit, realizing a metal-free flexible metasurface; the electromagnetic response is flexibly switched by regulating the channel impedance through the gate-source voltage.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic metamaterials, in particular to a laser-induced all-carbon-based field-effect transistor metamaterial unit structure and a preparation method thereof. Background Art

[0002] Under the background of the rapid development of modern technology, the control and modulation of electromagnetic waves have become increasingly important in fields such as communication, sensing, and imaging. As a new type of artificial material, electromagnetic metamaterials have attracted much attention due to their unique optical and electromagnetic properties. By designing sub-wavelength structural units, these electromagnetic metamaterials can achieve precise manipulation of electromagnetic waves and exhibit extraordinary performance. However, traditional electromagnetic metamaterials are usually composed of rigid materials, lacking flexibility and adaptability, which limits their potential in diverse applications. Therefore, researchers have begun to explore the use of flexible materials to achieve the bendable and deformable characteristics of metamaterials. The introduction of flexible materials enables electromagnetic metamaterials to adapt to different shapes and environments, enhancing their applicability in wearable devices, intelligent electronic products, and other new applications. Reconfigurable electromagnetic metamaterials have the ability to dynamically adjust their electromagnetic properties and can flexibly respond to different working conditions by changing their states. This reconfigurability not only enhances the functionality of electromagnetic metamaterials but also provides a new direction for the innovation of future intelligent materials and devices. Traditional electromagnetic metamaterials mainly rely on rigid substrate materials (such as silicon or metal) and discrete regulation architectures, making it difficult to meet the requirements of flexible electronic systems in bendable or stretchable scenarios: hard materials cannot achieve conformal fitting with curvature, and the cost of multi-layer lithography process is high with poor flexible compatibility; the regulation unit is separated from the external drive circuit, resulting in low system integration, high power consumption (usually > 10W / m 2 ), limited response speed; the mobility of semiconductor materials (such as silicon < 1500cm 2 / (V·s)) and the metal-semiconductor contact resistance limit the electromagnetic modulation efficiency of electromagnetic metasurfaces at high-frequency millimeter waves, resulting in insufficient phase modulation accuracy and a narrow dynamic range; these factors jointly limit the application potential of traditional electromagnetic metasurfaces. Therefore, it is urgent to develop new flexible materials and integrated manufacturing processes, and optimize the modulation architecture to improve the system integration, so as to overcome the many disadvantages of traditional electromagnetic metasurfaces and promote the new development of electromagnetic metasurface technology. Currently, a series of studies have been carried out at home and abroad to address the existing problems. Muchen Wang et al. from Wuhan University of Science and Technology developed a fully metallic metasurface with metal split-ring resonator structures, and achieved modulation in the terahertz band through laser direct writing and lithography processes; within the range of 0.8 - 1.65 THz, the polarization conversion efficiency of this metasurface exceeded 95%, and it had the characteristic of high temperature resistance (>500 °C). Imogen M. Pryce et al. from the Institute of Process Engineering designed gold planar coupled split-ring resonators (SRRs) based on a PDMS substrate; by mechanically stretching the PDMS, the researchers were able to change the gap between the SRRs, thereby adjusting the capacitance and the coupling strength between the resonators, and further achieving the adjustment of the resonant frequency; experiments proved that the resonant wavelength could be tuned within a wide range of approximately 400 nm. Changfeng Fu et al. from Northeast Petroleum University designed a graphene / VO2 dual-functional metasurface with polyimide as the dielectric layer and copper as the ground plane; through the phase change of VO2 (the conductivity increased from 10 S / m to 2×10 5 S / m), polarization conversion (PCR reached 90%) and efficient absorption (efficiency exceeded 90%) in the microwave band were achieved. Generally speaking, certain achievements have been made in the current research on the problems of traditional electromagnetic metasurfaces, showing positive progress in material innovation, structural design, and performance modulation. However, continuous efforts are still needed in aspects such as improving system integration, enhancing performance, and reducing costs. Summary of the Invention

[0003] Aiming at the problems of the traditional electromagnetic metasurface, such as the rigidity of the substrate, static response, and complex process, the present invention provides a laser-induced all-carbon-based field-effect transistor metasurface unit structure and a preparation method. Through femtosecond laser processing technology, a metasurface unit structure with micron accuracy and an all-carbon-based field-effect transistor array are synchronously processed on a flexible substrate, providing a high environmental adaptability solution for intelligent stealth, flexible radar, and wearable electromagnetic devices.

[0004] For the above purpose, the present invention adopts the following technical solutions:

[0005] In an embodiment of the present invention, a laser-induced all-carbon-based field-effect transistor metasurface unit structure is proposed. The metasurface unit structure includes: an electromagnetic resonance layer, a flexible substrate layer, and a back-gate layer. The electromagnetic resonance layer is composed of a graphene source electrode, a graphene drain electrode, and a graphene channel. The graphene source electrode and the graphene drain electrode are periodic sub-wavelength unit structures, and the graphene source electrode and the graphene drain electrode are connected by a graphene channel. The back-gate layer is composed of a porous graphene gate electrode. The back-gate layer is embedded in the flexible substrate layer, and the carrier concentration in the graphene channel is regulated by applying a gate-source voltage.

[0006] Furthermore, each metasurface unit is independently addressed to achieve dynamic regulation of local electromagnetic response.

[0007] Furthermore, the graphene source electrode and the graphene drain electrode form a highly conductive region through femtosecond laser-induced graphene technology, and its sheet resistance is less than 20 Ω / sq.

[0008] The graphene channel is a narrowband region connecting the graphene source electrode and the graphene drain electrode, and a gradient conductivity distribution is formed by adjusting the parameters of the femtosecond laser.

[0009] Furthermore, the conductivity of the graphene channel is dynamically modulated by the gate-source voltage, thereby changing its equivalent impedance and further affecting the electromagnetic response of the electromagnetic resonance layer.

[0010] Furthermore, by driving the change of the carrier concentration in the graphene channel by the gate-source voltage, the conductivity of the graphene channel is changed, and thus the equivalent dielectric constant and magnetic permeability of the electromagnetic resonance layer are dynamically adjusted.

[0011] In an embodiment of the present invention, a method for fabricating a laser-induced all-carbon-based field-effect transistor metasurface unit is also proposed. The method for fabricating the metasurface unit includes:

[0012] Disperse 5-10 wt% of BaTiO3 nanoparticles in a polyimide solution, form a film with a thickness of 20-50 μm by spin coating technology, and perform pre-curing to form a flexible substrate layer.

[0013] Use a femtosecond laser to scan the surface of the flexible substrate layer through a galvanometer system to induce a graphene channel.

[0014] By adjusting the parameters of the femtosecond laser, the graphene source electrode and the graphene drain electrode are scanned and generated on both sides of the graphene channel, and the porous graphene back-gate layer is scanned and generated on the back of the flexible substrate layer.

[0015] Beneficial effects:

[0016] The all-metal metasurface developed by Muchen Wang et al. at Wuhan University of Science and Technology, while achieving efficient control in the terahertz band and possessing high-temperature resistance, suffers from its rigid metal substrate, which cannot be bent, and the high cost of multi-layer photolithography. This directly hinders its application in flexible integrated applications and fails to meet the current demand for thinner and wearable devices. Imogen M. Pryce et al. from the School of Processing Engineering developed a gold planar coupled split-ring resonator based on a PDMS substrate. However, this device relies heavily on MEMS template photolithography for mid-infrared reflectivity modulation, resulting in slow response speed and low phase modulation accuracy. This severely limits its performance in optical applications where response speed and modulation accuracy are critical. The graphene / VO2 dual-functional metasurface designed by Changfeng F's team at Northeast Petroleum University relies solely on PI film for flexibility, resulting in poor bending tolerance. At high frequencies, contact resistance increases, significantly increasing power consumption, which not only reduces energy efficiency but also can lead to a series of problems such as device overheating. This invention, based on a laser-induced, all-carbon-based approach, offers significant advantages. In terms of materials and integration, laser-induced graphene is used to achieve conductor-semiconductor integration, which is beneficial to reducing contact resistance and effectively solving the problems of high dielectric loss of traditional flexible substrates and the difficulty of all-metal or liquid crystal structures to be compatible with flexible electronic systems. In terms of control mechanism, all-carbon-based field-effect transistors control the carrier concentration through gate-source voltage, which can achieve dynamic reconstruction and thus phase modulation, surpassing the slow response speed of traditional mechanical stretching or thermal tuning. In terms of process cost, femtosecond laser direct writing of all-carbon-based structures does not require masks, and can achieve large-area rapid processing, greatly reducing costs, and completely getting rid of the complex and high-cost dilemma of multi-layer lithography or MEMS processes. In terms of environmental adaptability, all-carbon-based materials are corrosion-resistant, can withstand high tensile strain, are suitable for extreme environments, and perfectly solve the problem of easy oxidation of metals or VO2. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the structure of the all-carbon-based field-effect transistor based on femtosecond laser induction of the present invention;

[0018] Figure 2 Schematic diagram of the structure of the metasurface unit of the present invention;

[0019] Figure 3 Schematic diagram of the porous graphene morphology of the present invention;

[0020] Figure 4 This is a diagram showing the relationship between the laser power and the square resistance of graphene in the present invention. DETAILED DESCRIPTION

[0021] The principles and spirit of the present invention will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are provided merely to enable those skilled in the art to better understand and then design the present invention, rather than limiting the scope of the present invention in any way. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0022] Those skilled in the art know that the embodiments of the present invention can be designed as a structure, a device, a preparation method or a computer program product. Therefore, the present disclosure can be specifically designed in the following forms: completely hardware, completely software (including firmware, resident software, microcode, etc.), or a combination of hardware and software.

[0023] According to the embodiments of the present invention, a laser-induced all-carbon-based field-effect transistor metasurface unit structure is proposed. Through femtosecond laser processing technology, a metasurface unit structure with micron accuracy and an all-carbon-based field-effect transistor array are synchronously processed on a flexible substrate, providing a high environmental adaptability solution for intelligent stealth, flexible radar and wearable electromagnetic devices.

[0024] The principles and spirit of the present invention will be explained in detail below with reference to several representative embodiments of the present invention.

[0025] Figure 1 It is a schematic diagram of the all-carbon-based field-effect transistor structure induced by femtosecond laser according to the present invention. As Figure 1 shown, the all-carbon-based field-effect transistor induced by femtosecond laser consists of the following core parts: The graphene source (Source) and the graphene drain (Drain) are designed as periodic sub-wavelength unit structures, directly serving as the electromagnetic resonance layer. The back-gate layer composed of a porous graphene gate (Gate) is embedded in the BaTiO3 / PI flexible substrate layer (Insulator). The graphene source (Source) and the graphene drain (Drain) form a highly conductive region through femtosecond laser-induced graphene (LIG) technology, with a sheet resistance less than 20 Ω / sq, which not only has the function of an electrode but also has electromagnetic resonance characteristics. The graphene channel (Channel) is a narrowband region connecting the graphene source (Source) and the graphene drain (Drain), and a gradient conductivity distribution is formed by adjusting the parameters of the femtosecond laser. As Figure 4 shown, it can guide the phase delay of electromagnetic waves, and its process uniqueness and functional design exceed the conventional. The conductivity of the graphene channel (Channel) can be dynamically modulated by an external bias voltage (gate-source voltage V G ), thereby changing its equivalent impedance, and further affecting the electromagnetic response of the electromagnetic resonance layer, such as the resonance frequency and phase delay. In terms of the functional coupling mechanism, through electro-magnetic collaborative regulation, the gate-source voltage (V G), driving the change of the carrier concentration in the graphene channel, resulting in the change of the conductivity of the graphene channel, and then dynamically adjusting the equivalent dielectric constant and permeability of the electromagnetic resonance layer. In addition, through the gate-source voltage V G between the gate and the source, controlling the current between the graphene source and the graphene drain, achieving the purpose of controlling the carrier concentration in the graphene channel. Through the gate-source voltage V G directly controls the electromagnetic characteristics of the graphene channel, improves the gate structure of the traditional field-effect transistor (FET) (changing from the top gate to the back gate), and realizes the effective integration of the metasurface unit and the driving circuit.

[0026] As Figure 2 shown, the all-carbon-based field-effect transistor metasurface unit based on femtosecond laser induction includes an electromagnetic resonance layer, a BaTiO3 / PI flexible substrate layer 1, and a back gate layer 5. The electromagnetic resonance layer is composed of periodically arranged graphene microstructures induced by femtosecond laser. This layer is composed of a graphene source 2, a graphene drain 3, and a graphene channel 4, where the graphene source 2 and the graphene drain 3 are connected to the graphene channel 4; the back gate layer 5 is composed of a porous graphene gate, and the back gate layer 5 is embedded in the BaTiO3 / PI flexible substrate layer 1, and the carrier concentration in the graphene channel 4 is regulated by applying a gate-source voltage.

[0027] As Figure 3 shown, the morphology of the porous graphene has a specific surface area as high as 420 m 2 / g, which is much larger than that of the actual ordinary graphene powder of 336.7 m 2 / g and that of graphene oxide of 60 m 2 / g. The porous structure is more fully exposed, and the effective active area is increased to 2-3 times that of the traditional film.

[0028] The porous graphene back gate layer 5 is generated by in-situ carbonization of the PI substrate induced by femtosecond laser. It has both a high specific surface area and nanoscale pores, can trigger local surface plasmon resonance, significantly enhance the response ability to electromagnetic waves, and can be used to achieve dynamic electromagnetic regulation. This porous structure not only improves the electric field response efficiency, but more importantly, serves the electromagnetic regulation function of the metasurface.

[0029] In the metasurface array, each metasurface unit can be independently addressed, thus realizing the dynamic regulation of the local electromagnetic response. This design aims at the "pixel-level" precise regulation requirement of the metasurface and needs to break through problems such as micro-nano signal isolation.

[0030] The present invention extends the gate-source voltage regulation from carrier concentration control to electromagnetic parameter regulation, dynamically changing the equivalent dielectric constant and magnetic permeability through conductivity, involving the "conductivity-electromagnetic response" cross-physical field coupling relationship, which requires multidisciplinary knowledge integration and experimental calibration, and is not a simple application of common sense.

[0031] Targeting the electromagnetic control needs of metasurface units, this invention introduces two-dimensional periodic patterned scanning and a barium titanate enhancement phase, achieving a one-step process of "material synthesis-device formation-patterning." This significantly improves fabrication efficiency compared to traditional CVD processes and avoids the damage associated with traditional transfer processes. This process not only simplifies the workflow but also enables precise control of micro-nanostructures through laser path programming, offering substantial, application-oriented improvements over previously applied flexible array fabrication methods.

[0032] The femtosecond laser-induced in-situ carbonization process of the present invention has a processing rate of 175-300 mm / s, which is significantly higher than the graphene growth rate of the traditional CVD process. It does not require the substrate pretreatment, high-temperature heating and cooling, and multi-step transfer process required by the traditional CVD process (such as wet etching of copper foil, which takes an additional 2-4 hours). The number of process steps is reduced by more than 60%, which significantly improves the preparation efficiency and avoids transfer damage, highlighting the high efficiency and advancement of the present invention in industrial production.

[0033] It should be noted that although several layers of the laser-induced all-carbon-based field-effect transistor metasurface unit structure are mentioned in the above detailed description, this division is merely exemplary and not mandatory.

[0034] Based on the same inventive concept, the present invention also proposes a laser-induced method for preparing a full-carbon field-effect transistor metasurface unit. The implementation of this method can refer to the implementation of the above structure, and the repeated parts will not be repeated.

[0035] The laser-induced method for preparing a full-carbon-based field effect transistor super-surface unit of the present invention comprises:

[0036] 5-10 wt% of BaTiO3 nanoparticles are dispersed in a polyimide solution, and a thin film with a thickness of 20-50 μm is formed by spin coating, which is then pre-cured to form a flexible substrate layer 1. Dispersion refers to a state in which the BaTiO3 nanoparticles cannot dissolve in the polyimide solution and can only be evenly dispersed in the polyimide solution.

[0037] Use a femtosecond laser (wavelength of 1030 nm, pulse width of 500 fs, power range of 15 - 25 W) to scan on the surface of the flexible substrate layer through a galvanometer system to induce a graphene channel 4; the graphene channel 4 is also part of the electromagnetic resonance layer, and generally requires a relatively high electron mobility and a low defect density to ensure good electrical conductivity; using a higher laser power and an appropriate scanning speed can promote the formation of graphene and ensure its structural quality and electronic properties;

[0038] By adjusting the parameters of the femtosecond laser (power of 10 - 15 W, scanning speed of 100 mm / s), scan on both sides of the graphene channel to generate a graphene source electrode 2 and a graphene drain electrode 3; the graphene source electrode 2 and the graphene drain electrode 3 generally require good electrical contact, but too high laser energy may cause the graphene layer in the electrode area to be too thick or have defects, thereby reducing the electrical contact performance; using a lower laser power in the electrode area can reduce the thermal influence and ensure that the formed graphene layer has good contact performance; scan on the back of the flexible substrate layer 1 to generate a porous graphene back gate layer 5.

[0039] It should be noted that although the operations of the preparation method of the present invention are described in a specific order in the above embodiments and the accompanying drawings, however, this does not require or imply that these operations must be performed in that specific order, or that all the shown operations must be performed to achieve the desired result. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step for execution, and / or one step may be decomposed into multiple steps for execution.

[0040] The laser-induced all-carbon-based field-effect transistor metasurface unit structure and preparation method proposed by the present invention have the following advantages:

[0041] The all-metal metasurface developed by Muchen Wang et al. from Wuhan University of Science and Technology, although achieving efficient modulation in the terahertz band and having high-temperature resistance, its rigid metal substrate cannot be bent, and the multi-layer lithography process is costly, which directly leads to difficulties in its flexible integration applications and cannot meet the current requirements for device thinning and wearability. Imogen M. Pryce et al. from the California Institute of Technology, based on the gold planar coupled split-ring resonator on a PDMS substrate, highly rely on MEMS template lithography when adjusting the reflectivity in the mid-infrared band, resulting in a sluggish response speed and a very low phase modulation accuracy, which severely limits its performance in optical field applications with strict requirements for response speed and modulation accuracy. The graphene / VO2 dual-functional metasurface designed by the Changfeng F team from Northeast Petroleum University has flexibility only relying on the PI film, with severely insufficient bending tolerance, an increase in contact resistance at high frequencies, and a significant increase in power consumption, which not only reduces the energy utilization efficiency but may also bring a series of problems such as device overheating. The present invention is based on a laser-induced all-carbon-based solution, with very significant advantages. In terms of materials and integration, the conductor-semiconductor integration is achieved through laser-induced graphene, which is beneficial to reducing the contact resistance and effectively solves the problems of high dielectric loss of traditional flexible substrates and the difficulty of compatibility between all-metal or liquid crystal structures and flexible electronic systems. In terms of the modulation mechanism, the all-carbon-based field-effect transistor can achieve dynamic reconstruction by regulating the carrier concentration through the gate-source voltage, thereby performing phase modulation, exceeding the slow response speed of traditional mechanical stretching or thermal tuning. In terms of process cost, the femtosecond laser direct writing of all-carbon-based structures does not require a mask, can achieve large-area and rapid processing, and the cost is significantly reduced, completely getting rid of the dilemma of the complexity and high cost of multi-layer lithography or MEMS processes. In terms of environmental adaptability, all-carbon-based materials are corrosion-resistant, can withstand high tensile strains, are suitable for extreme environments, and perfectly solve the problem of easy oxidation of metal or VO2 metasurfaces.

[0042] Although the spirit and principles of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the specific embodiments disclosed, and the division of each aspect does not mean that the features in these aspects cannot be combined for benefits. This division is only for the convenience of expression. The present invention aims to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0043] Regarding the limitations on the protection scope of the present invention, those skilled in the art should understand that based on the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. Laser-induced all-carbon-based field-effect transistor metasurface unit structure, characterized in that: The metasurface unit structure includes: an electromagnetic resonance layer, a flexible substrate layer and a back gate layer. The electromagnetic resonance layer is composed of a graphene source, a graphene drain and a graphene channel. The graphene source and the graphene drain are periodic subwavelength unit structures, and the graphene source and the graphene drain are connected by a graphene channel; the back gate layer is composed of a porous graphene gate, and the back gate layer is embedded in the flexible substrate layer. By applying a gate-source voltage, the carrier concentration in the graphene channel is regulated, so that the conductivity of the graphene channel changes, and the equivalent dielectric constant and permeability of the electromagnetic resonance layer are dynamically adjusted; the conductivity of the graphene channel is dynamically modulated by the gate-source voltage, thereby changing its equivalent impedance, and thus affecting the electromagnetic response of the electromagnetic resonance layer.

2. The laser-induced all-carbon-based field-effect transistor metasurface unit structure according to claim 1, characterized in that: Each metasurface unit is independently addressed to achieve dynamic regulation of local electromagnetic response.

3. The laser-induced all-carbon-based field-effect transistor metasurface unit structure according to claim 1, characterized in that: The graphene source and the graphene drain are formed into a highly conductive region by femtosecond laser induced graphene technology, and the square resistance thereof is less than 20Ω / sq; The graphene channel is a narrow band region connecting the graphene source and the graphene drain, and a gradient conductivity distribution is formed by adjusting the parameters of the femtosecond laser.

4. A laser-induced method for preparing a super-surface unit of a fully carbon-based field effect transistor, characterized in that: The super surface unit preparation method comprises: 5-10 wt% of BaTiO3 nanoparticles are dispersed in a polyimide solution, a film with a thickness of 20-50 μm is formed by spin coating, and pre-cured to form a flexible substrate layer; A femtosecond laser is used to scan the surface of a flexible substrate through a galvanometer system to induce graphene channels. By adjusting the parameters of the femtosecond laser, the graphene source and drain are generated by scanning on both sides of the graphene channel, and the porous graphene back gate layer is generated by scanning on the back side of the flexible substrate layer.

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