Flexible Polyimide Films Research Articles

CuO nanoparticles embedded in laser-induced graphene for flexible planar micro-supercapacitors

Utilizing predefined electrode geometries, laser direct writing technology is employed to intricately inscribe flexible polyimide (PI) films, thereby inducing porous graphene patterned electrodes for flexible planar micro-supercapacitors (MSCs), which greatly facilitates the integration of MSCs into functional devices for power supply. Nevertheless, prevailing challenges confront current flexible MSCs relying on laser-induced graphene (LIG), including the constrained electrochemical functionality of pure LIG electrodes and the uneven incorporation of heterogeneous constituents within LIG electrodes. In light of these challenges, this study delves into the fundamental mechanism underlying the formation of polyimide (PI) films and introduces an innovative approach to uniformly integrate CuO nanoparticles into the poly (acrylic acid) (PAA) precursor solution. The subsequent imidization process culminates in the synthesis of a CuO-embedded PI film. The research progresses to the fabrication of shape-controllable CuO/LIG patterned electrodes utilizing a precision laser direct writing technique, and the subsequent construction of flexible planar MSCs. Harnessing the synergistic interactions between the dual components within the electrode, the resulting MSC possesses an impressive areal capacitance of 6.45 mF·cm-2, coupled with an energy density of 0.896 mWh·cm-2 and a power density of 0.081 mW·cm-2, thus illustrating the potential of this innovative material integration for high-performance flexible energy storage implementations.

Conformal, stretchable, breathable, wireless epidermal surface electromyography sensor system for hand gesture recognition and rehabilitation of stroke hand function

Surface electromyography (sEMG) plays a significant role in the everyday practice of clinic hand function rehabilitation. The materials and design of current typical clinic sEMG electrodes are rigid Ag/AgCl or flexible polyimide (PI) film, which cannot provide a stable interface between electrodes and skin for adequate long-term high-quality data. Thus, conformal, soft, breathable, wireless epidermal sEMG sensor systems have broad potential relevance to clinic rehabilitation settings. Herein, we demonstrate a stretchable epidermal sEMG sensor array system with optimized materials and structure strategies for hand gesture recognition and hand function rehabilitation. The optimized serpentine structures with marvelous stretchability and improved fill ratio, provide lower impedance and high-quality sEMG signals. Moreover, the easy-to-use airhole method further ensures stable and long-term contact with the skin for recording. In addition, integrated with a customized flexible wireless data acquisition system, the capability for real-time 8-channel sEMG monitoring is developed, and taking together with the CNN-based algorithm, the system can automatically and reliably realize the 7 kinds of hand gestures with an accuracy of 81.02%. Moreover, the low-cost yet high-performance epidermal sEMG sensor system demonstrated its conceptual feasibility in quantitatively evaluation of stroke patient’s hand and facilitating human-robot collaboration in hand rehabilitation by proof-of-the-concept clinical testing.

Synthesis of novel Stachytarpheta jamaicensis flower liked hexagonal boron nitride nanoribbons (SJF-BNNBs) to efficiently improve the thermal/mechanical/electrical properties of flexible polyimide films

Heat dissipation has become a bottleneck restricting large-scale integration and flexible electronic technologies. This study reports a novel fabrication strategy to prepare flexible stachytarpheta jamaicensis flower-like hexagonal boron nitride nanoribbons (SJF-BNNBs) and their composite films with polyimide (PI). The effect of synthesis conditions on the morphology of SJF-BNNBs was investigated, and the growth mechanism was proposed. The in-plane and through plane thermal conductivities of the 4 wt% SJF-BNNBs/PI composite film reach 5.98 W m−1 K−1 and 0.79 W m−1 K−1, which are 3047 % and 316 % higher than those of the pure PI film, respectively. The in-plane and through plane thermal conduction enhancement efficiencies reach 761.8 % and 78.9 %, respectively. The tensile strength of the composite film is 61.7 % higher than that of pure PI, and maintains excellent electrical insulating and thermal stability properties. Infrared imaging tests verified the excellent heat dissipation performance of the composite film as a thermal interface material and a flexible copper clad laminate substrate, where the operating temperature of device could be reduced by 17.3 °C. To the best of our knowledge, SJF-BNNBs outperform the most efficient thermally conductive electrically insulating filler and are to break the overcome of polymer composites in heat dissipation applications.

In situ patterning of nickel/sulfur-codoped laser-induced graphene electrode for selective electrocatalytic valorization of glycerol

The electrocatalytic valorization of glycerol is an emerging upcycling process for the biomass utilization. In this work, nickel/sulfur-codoped laser-induced graphene (LINiSG) on flexible polyimide film was fabricated and demonstrated as a self-supported and binder-free monolithic electrode for electrocatalytic glycerol oxidation reaction (EGOR) towards the selective generation of value-added three-carbon (C3) chemicals. The laser-induced in-situ and synchronous carbonization of polysulfone and Ni precursor was demonstrated to remarkably promote both the electrochemical surface area and Ni loading of LINiSG electrode. These synergistic merits are considered as the main origin for its enhanced EGOR activity and stability, showing much smaller Tafel slope and 2-fold enhanced current density, as compared to LINiG electrode without the co-carbonization of polysulfone. The influence of experimental parameters has been systematically investigated by the product analysis, achieving an average 94.7 % C3 selectivity and 76.1 % C3 Faradaic efficiency with a high selectivity of dihydroxyacetone (ca. 67.7 %) in near-neutral conditions, which is better than most of the reported EGOR electrodes operated in near-neutral conditions. This work demonstrated the viability of using flexible self-supported and binder-free LIG electrode with rational design and preparation approach for electrocatalytic valorization of biomass.

Synergistic polyimide&ZrO2 flexible films enable low solar absorption and excellent wave-transparency

Carbon fiber epoxy resin (CFRP), as space satellite antenna materials with great application prospects to transmit and receive signals. It is necessary to ensure its normal operation through surface thermal control, which can be achieved by covering with a flexible film. Polyimide (PI) films modified by ceramics particle have been widely studied in the field of flexible devices. However, there is no research on multifunctional PI films with thermal control and wave transmission multifunctional performance. In this study, ZrO2 modified flexible PI films (PI/ZrO2 films) which can be covered on the surface of satellite antenna was prepared, and its solar absorption and wave transmission properties were studied. Prepared films exhibited excellent heat resistance and mechanical properties, and the addition of ZrO2 increased their thermal stability. The solar absorption of films with 50% ZrO2 is the lowest for 0.30, and the highest reflectance can reach to 88.4%. In addition, the maximum dielectric constant of the films was less than 2.5, and the dielectric loss was less than 0.03, showing an excellent wave transmission performance. The films can be covered on the satellite antenna, and also can be used for other space environment or wave transmission requirements.

Transparent, superhydrophobic, and flexible polyimide films with robust and durable imide/silica particles surface prepared via a sintering process

Recently, transparent superhydrophobic surfaces have attracted great interest due to their potential applications in various fields, such as skyscrapers, windows, glass doors, displays, and solar panels. However, flexible films with superhydrophobicity and transparency still face challenges in practical applications due to their lack of durability of the properties. Here, we report transparent, superhydrophobic, and flexible polyimide films with robust oligoimide/silica protrusion surface prepared by a simple sintering process, aiming to address the above issues. A transparent polyimide film (PIF) and nano-silica particles modified with an oligoimide (NSOI) were separately prepared, and the sintering between PIF and NSOI were performed to obtain PINSOI samples. Among PINSOIs, the optimal PINSOI-3 sample exhibited excellent superhydrophobicity, optical transmittance and tensile strength. After folding/torsion, sandpaper abrasion, tape peeling and acidic/basic immersion tests, its superhydrophobicity was maintained, indicating excellent mechanical and chemical durability of superhydrophobicity even under harsh conditions. Also, after a standard accelerated weathering test, its superhydrophobicity, transmittance and tensile strength were almost completely maintained, indicating the excellent weathering durability of PINSOI-3. These durability properties of PINSOI-3 could be attributed to that the sintering resulted in strong fusion between the NSOI particles and PIF by chain entanglement. PINSOI-3 showed excellent self-cleaning performance, and it can be applied as a self-cleaning film for flexible or curved solar cells and displays.

Individually-addressable composite microneedle electrode array by mold-and-place method for glucose detection

Microneedle (MN)-based electrochemical biosensors enable minimally invasive and in situ monitoring of biomolecules from interstitial fluid (ISF) that is strongly correlated to their concentrations in the blood. When an array of MNs is used as either working or counter electrodes for electrochemical sensing, it is often difficult to have narrow spacing between them and this can lead to poor measurement accuracy due to increased resistance, low sensitivity, and slow response time. This study aims to develop a method to fabricate independently functioning MN electrodes with narrow intervals between them for high precision electrochemical sensing. A mixture of photocurable polymer (SU-8) and single-wall carbon nanotubes (SWCNTs) was optimized for pressure-assisted transfer (PAT) molding and electrical conductivity. Single composite MNs were molded by PAT molding, and then attached on pre-patterned electrodes. After the ‘mold-and-place’ of the composite MN structures, plasma etching and electropolymerization of PEDOT:PSS were performed to enhance the electrochemical activity. Prussian blue (PB) and glucose oxidase (GOx) were electrodeposited on surface-treated MNs to enable glucose detection. MN electrodes showed limit of detection (LOD) at 0.225 mM and linearity up to 20 mM. Finally, MN electrodes were constructed on a flexible polyimide film and demonstrated the feasibility of detecting glucose in an in vivo mouse study.

High throughput, spatially resolved thermal properties measurement using attachable and reusable 3ω sensors.

The 3ω method is a well-established thermal technique used to measure the thermal conductivity of materials and the thermal resistance of interfaces. It has significant advantages over other steady state and transient thermal techniques in its ability to provide spatially resolved thermal property measurements over a wide range of thermal conductivity. Despite its advantages, it has been restricted to lab-scale use because of the difficulty involved in sample preparation and sensor fabrication and is limited to non-metallic substrates. High-throughput 3ω measurements with reusable sensors have not been realized yet. In this work, we demonstrate a method of applying reusable 3ω sensors fabricated on flexible polyimide films to measure bulk and spatially resolved thermal properties. We establish the limits of thermal conductivity measurement with the method to be 1 to 200 W/mK, and within the measurement limit, we verify the method by comparing the measured thermal conductivities of standard samples with established values. From the 3ω measurements, we also determine the thermal resistance of an interlayer of thermal grease as a function of pressure and compare it against the resistance calculated from direct thickness measurements to demonstrate the ability of this method to provide spatially resolved subsurface information. The technique presented is general and applicable to both metallic and non-metallic substrates, providing a method for high-throughput 3ω measurements with reusable sensors and without considerable sample preparation.

Polyimide resins with superior thermal stability, dielectric properties, and solubility obtained by introducing trifluoromethyl and diphenylpyridine with different bulk pendant groups

Three polyimides (PI-p, PI-t, and PI-n) containing a 2,6-di(4-aminophenyl) pyridine body and different pendant groups are reported in this study. The resulting polyimide films exhibit excellent dielectric properties, with a dielectric constant of 2.91–2.62@10GHz and a dielectric loss in the range of 0.00939–0.00808@10GHz. Through computer simulation, the dielectric constant and dielectric loss of the polyimides are found to decrease with increasing pendant group volume. Moreover, the resulting strong and flexible polyimide films exhibit excellent thermal stability, with decomposition temperatures (at a 5% weight loss) in the range of 532.3–552 °C and glass-transition temperatures in the range of 343.7–376.4 °C. TGA/FTIR/MS experiments indicate that the thermal stability of the resin containing the methyl phenyl group is worse due to the degradation of the methyl group at low temperatures. In addition, the three polyimides also show excellent solubility and transparency. These superior properties indicate that the PI series is an ideal candidate material for future 5G communications.

Preparation of Flexible Wavelength-Selective Metasurface for Infrared Radiation Regulation

Perpetual advancements in modern detection techniques have augmented the requirement of infrared camouflage; however, its development is impeded by multiband compatible regulation and curved application targets. Here, a flexible wavelength-selective metasurface based on two metal-dielectric-metal resonators is experimentally demonstrated for infrared radiation regulation with thermal management utilizing magnetic polariton. Low emissivity in atmosphere windows (infrared stealth) and high emissivity in the wavelength of 5-8 μm nonatmospheric window (radiative cooling) are simultaneously achieved. In comparison with conventional hard substrates, it is for the first time the composite wavelength-length metasurface is successfully prepared directly on a flexible polyimide film via applying polyimide double-sided tapes and S1805/LOR5A bilayer stack lift-off technology. Not only does this method successfully overcome the debonding problem of photoresist on the flexible substrate, but it also solves the bulging problem of the substrate as well as the limitation of high temperature. Besides, the temperature and infrared radiation distributions of flexible wavelength-selective metasurfaces with different curvatures are first investigated. The compared results reveal that the metasurface with larger curvature has a better infrared camouflage performance. Furthermore, the cycle stability of the flexible metasurface is tested, and the results show that the infrared radiation regulation is stable after 30 cycles with essentially no change. This study provides a guideline for preparing flexible composite metasurfaces and avoids the trouble of replacing the metal/dielectric material of the initial structure with a flexible material to improve the structure for application to curved surfaces, thus broadening implications in enhancing the effective bonding of metasurfaces to target surfaces.

Horizontally‐Oriented Growth of Organic Crystalline Nanowires on Polymer Films for In‐Situ Flexible Photodetectors with Vis‐NIR Response and High Bending Stability

AbstractVarious epitaxial mechanisms have been proposed to control the growth orientation of vapor‐deposited nanowires, yet the required lattice matching between target nanowires and supporting substrates limits their applicability. In this work, a versatile hot stamping protocol for fabricating parallel hydrophobic nanogrooves on flexible polymer films (e.g., polyimide (PI), polyethylene naphthalate (PEN), polydimethylsiloxane (PDMS)) is proposed. More interestingly, various organic small molecules, including several metal phthalocyanines (MPc, M = Cu, Zn, Fe, Ni, Co), 9,10‐bis(phenylethynyl)anthracene (BPEA), 9,10‐diphenylanthracene (DPA), and tris‐(8‐hydroxyquinoline)aluminium (Alq3), are directly assembled into horizontally‐oriented nanowires along the hot‐stamped nanogrooves on a flexible PI film, thereby breaking the lattice‐matching limitation for oriented nanowire growth. These submillimeter‐long horizontally oriented nanowires can be integrated into flexible photodetectors directly on their growth film, eliminating the need for laborious post‐growth transfer and alignment steps and the associated structural damage and contamination. Consequently, the in situ integrated flexible photodetector made of aligned CuPc nanowires maintains a stable and fast photoresponse to a spectrum in the region of 405‐980 nm even when the detector is bent to a radius of curvature of 2.5 mm and 1000 times. This work will open new opportunities to develop in situ integrated flexible devices based on organic crystalline nanowires for practical applications.

Optical and Flame-Retardant Properties of a Series of Polyimides Containing Side Chained Bulky Phosphaphenanthrene Units.

Among the multitude of polymers with carbon-based macromolecular architectures that easily ignite in certain applications where short circuits may occur, polyimide has evolved as a class of polymers with high thermal stability while exhibiting intrinsic flame retardancy at elevated temperatures via a char-forming mechanism. However, high amounts of aromatic rings in the macromolecular backbone are required for these results, which may affect other properties such as film-forming capacity or mechanical properties; thus, much work has been done to structurally derivatize or make hybrid polyimide systems. In this respect, flexible polyimide films (PI(1-4)) containing bulky 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) units have been developed starting from commercial dianhydrides and an aromatic diamine containing two side chain bulky DOPO groups. The chemical structure of PI(1-4)) was characterized by 1H NMR, 13C NMR and 31P NMR spectroscopy. The optical properties, including absorption and luminescence spectra of these polymers, were analyzed. All polyimides containing DOPO derivatives emitted blue light with an emission maxima in the range of 340-445 nm, in solvents such as N,N-dimethylformamide, N-methyl-2-pyrrolidone, chloroform, and N,N-dimethylacetamide, while green light emission (λem = 487 nm for PI-4) was evidenced in a thin-film state. The thermal decomposition mechanism and flame-retardant behavior of the resulting materials were investigated by pyrolysis-gas-chromatography spectrometry (Py-GC), scanning electron microscopy (SEM), EDX maps and FTIR spectroscopy. The residues resulting from the TGA experiments were examined by SEM microscopy images and FTIR spectra to understand the pyrolysis mechanism.

Whole‐Device Mass‐Producible Perovskite Photodetector Based on Laser‐Induced Graphene Electrodes

AbstractPerovskites have attracted enormous attention in optoelectronics, owing to their excellent optoelectronic properties, low‐cost constituents, and simple solution fabrication approaches. Despite significant advances in large‐scale production of perovskite films, electrode layers—indispensable components of an optoelectronic device—are typically fabricated by depositing noble metals onto perovskite films using complicated techniques, which hinder the large‐scale production of optoelectronic devices. Herein, a whole‐device mass‐producible perovskite photodetector is developed using low‐cost and high‐scalability direct laser writing (DLW) of laser‐induced graphene on a flexible polyimide (PI) film as electrodes, followed by depositing a formamidinium cesium lead triiodide perovskite film using solution methods as the sensing element. The fabricated device exhibits a broad bandwidth (from 365 to 940 nm), a decent responsivity (15.1 mA W−1) and detectivity (5.12 × 1013 Jones), a large photo‐to‐dark current ratio (47.2), and short response time (rise time = 0.4 s and decay time = 0.4 s). The device demonstrates a high humidity (relative humidity = 85%) stability, a long‐term (>48 days) stability, and a high flexibility (0°/90° bending cycles > 1000 times) after encapsulation. The developed whole‐device scalable fabrication sheds light on the mass production and commercialization of perovskite based optoelectronic devices and flexible electronics.

Room Temperature Phase Transition of W‐Doped VO2 by Atomic Layer Deposition on 200 mm Si Wafers and Flexible Substrates

AbstractThe unique structural transition of VO2 between dielectric and metallic phases has significant potential in optical and electrical applications ranging from volatile switches and neuromorphic computing to smart devices for thermochromic control and radiative cooling. Critical condition for their widespread implementation is scalable deposition method and reduction of the phase transition to near room temperature. Here, a W:VO2 process based on atomic layer deposition (ALD) is presented that enables precise control of W‐doping at the few percent level, resulting in a viable controllable process with sufficient W incorporation into VO2 to reduce the phase transition to room temperature. It is demonstrated that the incorporation of 1.63 at.% W through ALD growth leads to a state‐of‐the‐art phase transition at 32 °C with emissivity contrast between the low‐temperature and high‐temperature phase exceeding 40% in a metasurface‐based radiative cooling device configuration. The process is shown to be viable on 200 mm silicon substrates as well as flexible polyimide films. The full and self‐consistent temperature‐dependent characterization of the W‐doped VO2 using spectroscopic ellipsometry, electrical conductivity, mid‐wave infrared camera, and Fourier transform infrared emissivity, allows for a fully validated material model for the theoretical design of various smart and switchable device applications.

Synthesis and Properties of Optically Transparent Fluoro-Containing Polyimide Films with Reduced Linear Coefficients of Thermal Expansion from Organo-Soluble Resins Derived from Aromatic Diamine with Benzanilide Units.

Wholly aromatic polyimide (PI) films with good solution processability, light colors, good optical transparency, high storage modulus, and improved heat resistance were prepared and characterized. For this purpose, a multi-component copolymerization methodology was performed from a fluoro-containing dianhydride, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), a rigid dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and a fluoro-containing diamine, 2,2′-bis(trifluoromethyl)-4,4′-bis [4-(4-amino-3-methyl)benzamide]biphenyl (MABTFMB). One homopolymer, FPI-1 (6FDA-MABTFMB), and five copolymers, FPI-2~FPI-6, containing the BPDA units from 10 mol% to 50 mol% in the dianhydride moieties, were prepared, respectively. The derived PI resins showed good solubility in the polar aprotic solvents, such as N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc). The flexible PI films obtained by the solution casting procedure showed good optical properties with the transmittances higher than 74.0% at the wavelength of 450 nm. The PI films exhibited excellent thermal properties, including 5% weight loss temperatures (T5%) over 510 °C, together with glass transition temperatures (Tg) over 350.0 °C according to the peak temperatures of the loss modulus in dynamical mechanical analysis (DMA) measurements. The FPI-6 film also showed the lowest linear coefficient of thermal expansion (CTE) value of 23.4 × 10−6/K from 50 to 250 °C according to the thermomechanical analysis (TMA) measurements, which was obviously lower than that of FPI-1 (CTE = 30.6 × 10−6/K).

Circularly polarized wearable antenna with low specific absorption rate and high gain based on artificial magnetic conductor

Aiming at wearable electronic equipment in wireless body area network communication, we propose a circularly polarized wearable antenna based on artificial magnetic conductor (AMC) for the problem of unreliable data transmission of linearly polarized wearable antenna and reduction of transmission distance due to the low gain of antenna. The AMC of in-phase reflection reflects the backward radiation to the top to reduce the damage of the antenna to human body. And the polarization direction of the reflected wave reflected through AMC is the same as that of the main direction, which makes the radiation performance of the antenna improved. Meanwhile, the antenna is flexible and lightweight due to the use of flexible polyimide and graphene films as the substrate and conductor materials. The antenna was also simulated and the prototype was fabricated and tested. The simulation results show that the working bandwidth covers 2.4–2.48 GHz, and the peak gain is 8.09 dBi. The peak specific absorption rate of 1 g and 10 g of human tissue at an input power of 350 mW is 1.48 W kg−1 and 0.65 W kg−1, respectively, which meets the safety standards.

Development of a Flexible MEMS Sensor for Subsonic Flow.

Detection and control of flow separation is a key to improving the efficiency of fluid machinery. In this study, we developed a flexible MEMS (microelectromechanical systems) sensor for measuring the wall shear stress and flow angle in subsonic airflow. The developed sensor is made of a flexible polyimide film and a microheater surrounded by three temperature sensor pairs. The sensor measures the wall shear stress from the heater output and the flow angle from the temperature gradient around the heater. The geometry and design of the heater and temperature sensors were determined based on numerical simulations. To evaluate the validity of the sensor, we conducted an experiment to measure the wall shear stress and the flow angle in a wind tunnel in different velocities ranging from 30 m/s to 170 m/s, equivalent to Mach numbers from 0.1 to 0.5. The heater output was proportional to one-third power of the wall shear stress. Additionally, the bridge output correlating the temperature difference between two opposing temperature sensors showed sinusoidal variation depending on the flow angle. Consequently, we have clarified that the developed sensor can measure both the wall shear stress and flow direction in subsonic flow.

Flexible Copper Metal Circuits via Desktop Laser Printed Masks

AbstractA novel process is demonstrated that produces patterns of electrically conductive copper on a flexible polyimide film substrate using standard desktop laser printed toner and near room temperature aqueous chemistry. The laser toner acts as a mask to selectively block the ion exchange self‐metallization (IESM) reduction reaction that forms nanoscale silver or palladium coatings at the polyimide surface. The silver or palladium IESM coating is then used as a catalyst for electroless deposition of copper. Under appropriate conditions, the copper is deposited selectively on top of the catalyst layer. The resulting copper layer has a measured sheet resistance as low as 0.3 Ohms/sq. Electrical isolation is measured between copper traces spaced as close as 300 microns, and high conductivity is measured along traces with widths as low as 200 microns. The minimum pattern size appears to be limited primarily by the resolution of the laser toner pattern, as the IESM metal layer is observed to follow the contours of individual toner particles. The process avoids the use of high temperature, vacuum, and organic solvents and is thus suitable for very low cost prototyping or distributed manufacturing of simple electronic devices.

Local pattern growth of carbon nanomaterials on flexible polyimide films using laser scribing and its sensor application

Local pattern growth of carbon nanomaterials on flexible polyimide films using laser scribing and its sensor application

VO2 films on flexible thin polyimide films: Fabrication and characterization of electrical and optical properties in insulator-metal transition

We report on the realization of thin polyimide films on which phase transition vanadium dioxide (VO2) films grow. Biased reactive sputtering achieved b-axis-oriented growth of VO2 films on ZnO-buffered polyimide films with a thickness of 8.5 μm. By peeling off the polyimide films from a quartz substrate, stand-alone VO2/ZnO/polyimide layered films that exhibited insulator-metal transition (IMT) with nearly three orders of resistivity change were fabricated. Dependence of IMT on a mechanical curvature was investigated for demonstrating the high flexibility. Temperature-dependent optical transmittance at 1.45 μm showed a high switching ratio for infrared light in VO2/ZnO/polyimide layered films. The proposed structure can be utilized for active metasurfaces that control terahertz waves with quite low reflection loss due to its small thickness.