Bottom Metal Layer Research Articles

Modulation of a multi-band tunable metamaterial with metal disk array

A multi-band metamaterial with vanadium dioxide (VO2) layer is proposed, manufactured, and measured in the terahertz (THz) band. Two absorption peaks (P1 and P2) are excited at 33.88 THz (60% amplitude, and 0.7 THz full width at half maximum (FWHM)) and 37.94 THz (76% amplitude, and 1.62 THz FWHM) at room temperature. The P1 peak is achieved based on the local surface plasmon (LSP) modes resonance, while the P2 peak is revealed by the LSP modes and the Ohmic loss of the bottom metal layer. Both P1 and P2 can be enhanced through increasing structural parameter D or reducing structural parameter P during experiments. As the temperature rises to T = 340k, the peaks P3 and P4 are obtained at 11.9 THz (80.1% amplitude, and 2.24 THz FWHM) and 23.52 THz (85.2% amplitude, and 3.83 THz FWHM). The resonance properties of P1 and P2 peaks are insensitive to temperature. The P3 peak is obtained based on the Fabry-Perot resonance between the metal disk and the lower VO2 layer, while the P4 peak is revealed by the ultra-thin Fabry-Perot resonance between the metal disk and the upper VO2 layer. The original resonance properties of the proposed metamaterial absorber can be kept stable, while the new absorption performances can be controlled through changing temperature.

Metal–Dielectric–Metal Metamaterial-Based Hydrogen Sensors in the Water Transmission Window

In this letter, we have numerically proposed design of a novel, efficient, and weather condition independent metal-dielectric-metal metamaterial-based plasmonic hydrogen sensor. In the proposed device, the top and bottom metallic layers are palladium (Pd) nanodisc array and gold thin film, separated by a sandwiched dielectric aluminum oxide layer. The presence of hydrogen reversibly changes Pd to its hydride, which leads to a change in its optical properties. Only 4% (v/v) presence of hydrogen in the air can change optical reflectance from 95% to 14% at 905 nm wavelength, center of first water transmission window, that results for a weather-resistant hydrogen sensor with ~21.3% change in optical response for 1% change in hydrogen concentration with 76.5 s of response time for remote hydrogen sensing.

Miniaturized SIW Cavity Tri-Band Filter Design

This letter presents a novel tri-band filter design using an ultraminiaturized substrate-integrated waveguide (SIW) cavity operated at evanescent mode. Two miniaturized SIW cavities in a face-to-face form are vertically stacked to build the proposed tri-band filter. The top and bottom metal layers form the cavity’s broadside walls, and the middle layer possesses three identical patches which are formed by evenly trisecting a circular patch. These patches are shorted to the cavity’s bottom wall through one, two, or four via-holes. The patches together with the host cavity exhibit three frequency-distinct resonances that create the filter’s triple passbands. The resonance frequencies are independently controlled, and six passband-edge transmission zeros are created for good selectivity. The filter size is only $0.22\,\,\lambda _{d} \times 0.22\,\,\lambda _{d}$ , and the measured in-band minimum insertion losses are 2.31, 2.25, and 3.01 dB for the first, second, and third bands, respectively. It is believed that the proposed tri-band filter has obtained the best circuit area efficiency in the SIW tri-band filter category.

Broadband metamaterial absorber with double resonant modes using single-layer substrate

A novel broadband metamaterial absorber (MA) is proposed in this paper. The element of absorber consists of square substrate, top and bottom metal layer. A circular patch is printed on the top layer and located in the center of element. Other three circular patches are located in three corners and connected with the center patch, respectively. The mechanism is analysed and discussed with the equivalent circuit and parameter study. It exhibits double resonant frequencies corresponding to different working modes and achieves broadband of good absorption. The structure has a thickness of 1.0 mm and two resonate frequencies of 7.94 GHz and 8.65 GHz. The experiment results are good agreement with the simulated ones. The simple structure shows a relative bandwidth of 19%, polarization insensitive and wide operating angle. The proposed absorber can be widely applied in national defence and civil fields due to its simple structure and good absorption characteristic.

Reconfigurable active frequency selective surface for ultra‐wideband applications

A reconfigurable active frequency selective surface (AFSS) with ultra-wideband (UWB) characteristics is presented in this article. The proposed AFSS consists of a periodic array of three metal layers and two dielectric layers. PIN diodes are arranged on the top and bottom metal layers which can rebuild the function of AFSS. The transmission bandwidth of the AFSS with OFF-state diodes is 8 to 12.5 GHz with a fractional bandwidth of 44%, and the transmission coefficient of the FSS with ON-state diodes is lower than −10 dB from 2 to 18 GHz. Additionally, the AFSS is angular stable and polarization-insensitive for both transverse electric and transverse magnetic polarizations. The simulation results show that the proposed AFSS is an effective candidate for radome applications.

Alleviation of abnormal NBTI phenomenon in LTPS TFTs on polyimide substrate for flexible AMOLED

AbstractThis letter investigates the negative‐bias temperature instability (NBTI) behavior of p‐channel low‐temperature polycrystalline silicon thin‐film transistors (LTPS TFTs) on plastic substrate. The measurements reveal that the threshold‐voltage positive shift is highly correlated to the passivation of grain boundary trap states. By applying the established phenomenon such as NBTI recovery and H diffusion from PI substrate, a new model is introduced to explain the mechanism and verified by the experiment. With the thick buffer and bottom metal layer or newly processed PI substrate, we succeeded in adjusting the NBTI behavior of LTPS TFTs on plastic substrate.

Miniaturised wideband antenna with low profile based on dual‐layer metasurface

A novel miniaturised wideband antenna based on dual-layer metasurface (MS) is proposed in this study. It is composed of three metallic and two substrate layers. The top metallic layer is the MS whose unit is a square patch etched four interlaced quarter arc-shaped slots (PQAS). The middle metallic layer is a circular ring patch. The bottom metallic layer is the MS formed by the square metal ring (SMR). The top MS with PQAS and the bottom MS with SMR are combined which serve as a radiator and ground plane of the antenna directly, not a reflector. Thus, avoiding air layer, a low profile of 0.014 λ 0 (λ 0 is the guided wavelength at 2.57 GHz) is realised. Meanwhile, the impedance bandwidth and gain of the antenna are improved. The measured results show that the −10-dB impedance bandwidth of the proposed MS antenna is from 2.57 to 4.12 GHz (the relative bandwidth is 46.3%). Furthermore, the maximum gain reaches 4.17 dBi.

Modulation of single-band to multi-band based on tunable metamaterial absorber in terahertz range

In this paper, a tunable metamaterial absorber with an absorption peak (94% amplitude at resonance frequency 11 THz) is proposed and measured at room temperature. This absorption peak is result by the bright-bright modes coupling effect on the cross shape metal particles array. The absorption peak is adjusted by changing the structural parameters P or b in experiments. It is found that this original absorption peak is not sensitive to the measured temperature. When the measured temperature is increased from 300 k to 390 k, the amplitude and resonance frequency of this absorption peak are basically retained. On the other hand, two newly resonance modes between the top and bottom metal layers are excited, which lead to two newly absorption peaks (65% amplitude at resonance frequency 21.9 THz, and 57% amplitude at resonance frequency 32.7 THz). Moreover, both newly absorption peaks can be controlled by changing the measured temperature. This tunable metamaterial absorber can both retain the original absorption properties and modulate two new absorption peaks.

Methodology for the characterization and observation of filamentary spots in HfOx-based memristor devices

Filamentary TiN/Ti/HfO2/W resistive switching devices were fabricated and electrically measured setting them in different resistance and degradation conditions. The TiN/Ti top electrode layer was then chemically removed by specifically selected reagents for the materials of these devices. This methodology caused the formation of plate-shaped microstructures in the W bottom metal layer. However, the HfO2 dielectric layer was not affected due to the selectivity of the etchants. Filamentary structures in the insulator layer of the devices were found in the center of these “microplates”. The top morphology and the size of the filaments were characterized by physical inspection techniques. The analysis of the results highlighted the correlation between the device electrical degradation, the resistance state and the physical nature of the filamentary path.

Ultra-Broadband Polarization Conversion Meta-Surface and its Application in Polarization Converter and RCS Reduction

In this paper, an ultra-broadband and high-efficiency polarization conversion metasurface is presented in the terahertz region. The metasureface is similar to a sandwiched structure, which is composed of the top Double Split Ring Resonator (DSRR), an intermediate dielectric layer and a bottom metal layer. Both numerical simulation and theoretical calculation results demonstrate that the proposed metasurface can convert linearly co-polarized waves into cross-polarized waves in the frequency from 2.04 THz to 5.33 THz with a relative bandwidth of 89% and the polarization conversion ratio (PCR) is over 90%. Further simulation results show that the proposed metasurface is insensitive to the polarization angle, and the physical mechanism is revealed in detail by the surface current distribution. In addition, two different kinds of 2-bit coding metasurfaces are designed based on the Pancharatnam-Berry (PB) Phase. The simulated and calculated results show that the proposed PB-coding metasurface has excellent performance in flexibly controlling terahertz wave reflection and low Radar Cross Section (RCS). A 10dB RCS reduction can be achieved from 1.9 THz to 5.5 THz under normal incidence. It provides new degrees of freedom for studying terahertz wave manipulation and reducing RCS.

Design of Graphene-Based Dual-Polarized Switchable Rasorber/Absorber at Terahertz

This paper reports a dual-polarized graphene-based multi-functional device which could switch between rasorber and absorber flexibly. The only difference between rasorber and absorber is that rasorber has a transmission window with low loss. Therefore, a wideband absorber is proposed at the first step. Then, four split-ring resonators (SRRs) are introduced to the absorber, which makes the electromagnetic (EM) energy could be reflected at the certain frequency band. The state (on/off) of SRRs and absorber can be controlled by the chemical potential of graphene. To find a new pathway for this part of the reflected energy, metal ground of the absorber is replaced by a reconfigurable graphene-based frequency selective surface (FSS). The proposed FSS could be switched between FSS and metal plate by controlling the chemical potential of graphene ring embedded in the bottom metal layer. Therefore, the proposed multi-functional device could be obtained by combing the absorber with SRRs and reconfigurable FSS. When the proposed device serves as a rasorber, it has an absorption-transmission-absorption response with superior selectivity. When it performs as an absorber, it has wideband performance with high absorptive rate. It is an attractive candidate for stealth applications.

A Band-Pass Filter Based on Half-Mode Substrate Integrated Waveguide and Spoof Surface Plasmon Polaritons

In this paper, a band-pass filter based on half-mode substrate integrated waveguide (HMSIW) and double-layer spoof surface plasmon polaritons (SSPPs) consisting of two corrugated metal strips is proposed, which can realize band-pass transmission by etching periodic grooves at the top and bottom metal layers of the HMSIW. Moreover, the influences of important parameters on the performance of the proposed band-pass filter are analyzed by parametric study. By changing the key parameters, the low and high cut-off frequency can be controlled independently. The corresponding equivalent circuit of the proposed band-pass filter is put forward to explain the physical mechanism. Compared with the previous structures, this structure features smaller size, wider bandwidth and lower loss. Simulated results show that the proposed band-pass filter achieves a bandwidth (for |S11| < −10 dB and |S21| > −0.8 dB) of about 69.77% (15.6–32.1 GHz). The measured results have good agreements with the simulated ones, which verify that the proposed band-pass filter has good performances and potential applications at the microwave frequencies.

Ultra-compact quasi-elliptic bandpass filter based on capacitive-loaded eighth-mode SIW cavities

AbstractThis paper reports a novel fourth-order quasi-elliptic bandpass filter (BPF) based on capacitive-loaded eighth-mode substrate integrated waveguide (CLEMSIW) cavities. The CLEMSIW cavity is constructed by the conventional eighth-mode SIW with two dielectric substrates and three metal layers; a metal via is employed to connect the middle and bottom metal layers. The middle metal layer achieves a large loading capacitance to shift the resonance frequency. The proposed filter is designed in a quadruple scheme, and two controllable finite-transmission zeros can be realized. For the demonstration, a prototype with a center frequency of 1 GHz and a fractional bandwidth of 10% was designed, fabricated, and measured. The measured results agree well with simulated ones. The proposed filter has advantages of ultra-compact size, high selectivity, and good stopband performances.

Design and measure of a tunable reflection polarization converter based on hybrid dielectric layer metamaterials

We design and experimentally investigate of a temperature sensitive reflection polarization converter based on circular hole array metamaterial. This achieved converter consists of two metal layers (silver) and three dielectric layers (SU-8, polyimide, VO2). Measured results reveal that two polarization conversion ratio (PCR) peaks are obtained (99.1%, 99.3%) at two neighboring frequencies at normal temperature, which are derived from the cavity and electrical resonance modes, respectively. A PCR band is achieved based on the overlap of two PCR peaks, and the average conversion rate reaches 94.2%. When the measured temperature is increased, the average value of the PCR band is enhanced. Moreover, a new PCR peak is achieved with the measured temperature increasing, which is derived from a new electrical resonance mode excited between the bottom metal layer and the VO2 layer.

Nano-Programmable Logics Based on Double-Layer Anti-Facing Memristors.

The memristor, as theorized by Chua in 1971 (L. Chua, IEEE Trans. Circuit Theory 18, 507 (1971)), is a two-terminal device whose resistance state is based on the history of charge flow brought about as a result of the voltage applied across its terminals. High-density regular fabrics for nanoscale memristors, such as crossbar arrays, are emerging architectures for system-on-chip (SoC) implementation, which provide both simplified structure and improved performance (W. H. Yu, et al., IEEE Trans. VLSI 20, 1012 (2012)). The advantage of using memristors as the switching devices within crossbar arrays is their nanoscale switching capability, which specifically changes their resistance state between high and low. In this paper, we propose a new nano-programmable logic array (PLA) device in the form of an on anti-facing double-layer memristor array. The PLA is composed of an AND plane and an OR plane merged onto the same layer. The AND and OR planes are stacked vertically such that each layer forms a crossbar architecture; thus, a cross section reveals two anti-facing memristors with 5 layers: the bottom metal layer, a memristive layer, the intermediate metal layer, an anti-facing memristive layer, and the top metal layer. The intermediate metal layer provides its output at the AND plane which is the input of the OR plane, and as such, the input and output nodes of the two logic functions are shared. Thus, the proposed architecture reduces the propagation delay of the AND plane by 70% by sharing the OR plane input wires. Additionally, the anti-facing architecture makes it easy to determine appropriate values for the pull-up and pull-down registers of the PLA.

Ultra-broadband wide-angle perfect absorber in the visible regime through a thin grating–insulator–metal structure

A new thin grating-insulator-metal (GIM) structure with ultra-broadband wide-angle perfect absorption is proposed, and a general approach to this kind of multilayered structure is investigated based on the rigorous coupled-wave analysis method and the transfer matrix method. On the basis of this approach, the electromagnetic field distributions in each layer and optical diffraction coefficients are derived theoretically. Compared with a metal–insulator–metal (MIM) structure, the GIM structure consisting of a metal grating on top of a low-loss dielectric layer and a bottom metal layer can achieve a higher absorption with the smaller thickness that attributes to the extraordinary optical transmission of the top grating layer and the cavity resonance of the middle insulator layer. By optimizing the structural and material parameters, the materials from top to bottom are selected as Mn-Al2O3-Mn, whose thicknesses are 10 nm, 65 nm, and 70 nm, respectively. With these optimum parameters, better performance with average absorption over 95% in the visible regime is obtained. Furthermore, this structure retains near-perfect broadband absorption for large incidence angles and different polarizations. The conclusions presented here could have potential applications in optical devices, such as optical displacement detection and visible light absorption.

Ultrathin flexible transmission metamaterial absorber

As an important branch of metamaterial-based devices, metamaterial absorber (MA) has aroused great interest and made great progress in the past several years. By manipulating the magnetic resonance and the electric resonance simultaneously, the effective impedance of MA will match the free space impedance, thus resulting in a perfect absorption of incident waves. Due to the advantages of thin thickness, high efficiency and tunable property, MA has been widely concerned in energy-harvesting and electromagnetic stealth. Since the first demonstration of MA in 2008, many MAs have been extensively studied in different regions, such as microwave frequency, THz, infrared frequency and optical frequency. At the same time, the absorber has been extended from the single-band to the dual-band, triple-band, multiple-band and broadband. In recent years, the dual-band absorber has received significant attention and has been widely studied. So far, however, most of MAs are composed of a bottom continuous metallic layer, which prevents electromagnetic waves from penetrating and makes electromagnetic waves absorbed or reflected. In this paper, an ultrathin flexible transmission absorber with a total thickness of 0.288 mm is designed and fabricated, which can be conformally integrated on an object with a curved surface. The absorber consists of three layers of structure: the bottom is a one-dimensional grating type metal line, the middle is the medium layer, and the surface metal layer is composed of two different sizes metal lines in parallel. Simulation and experimental results show that the absorptions of TE wave are 97.5% and 96.0% respectively at the two frequency points of 5 GHz and 7 GHz. The transmission of the TM wave above 90% is maintained from 3 GHz to 6.5 GHz. We also simulate the spatial electric field distribution and magnetic field distribution at two resonant frequencies, and explain the electromagnetic absorption mechanism of the proposed structure for TE wave. Secondly, when the incident angle increases to 60 degrees, the performance of the absorber is substantially unaffected, exhibiting good wide-angle characteristics. In addition, through the analysis of structural parameters, two absorption peaks of the proposed absorber can be independently adjusted, resulting in a flexible design. In conclusion, we propose both theoretically and experimentally a polarization-controlled transmission-type dual-band metamaterial absorber that can absorb the TE waves and transmit the TM wave efficiently, which has important applications in the case requiring bidirectional communication.

Substrate Integrated Plasmonic Waveguide for Microwave Bandpass Filter Applications

In this paper, we numerically and experimentally demonstrate a substrate integrated plasmonic waveguide (SIPW) concept and its application in microwave bandpass filters. This SIPW consists of double arrays of slots etched on the top and bottom metal layers of a substrate integrated waveguide (SIW) to support spoof surface plasmon polariton (SSPP) modes with low and high cutoff frequencies. The simulated results show that by tuning the parameters of the SIPW's unit cell, the dispersion characteristics can be engineered at will. Then, we propose a sharp roll-off microwave bandpass filter based on this SIPW. This filter has a passband from 7.5 to 13.0 GHz with high return loss and low insertion loss. Furthermore, to demonstrate the independent tuning of the passband of the filter, we also design two microwave bandpass filters with passbands of 9.2-13.0 GHz and 7.5-10.5 GHz by decreasing the distance between two rows of via holes and increasing the slot length, respectively. Finally, to experimentally validate the filter designs, we fabricate and measure three prototypes and find that the experimental results are in excellent agreement with the simulations. This SIPW concept may have extensive potential applications in the development of various plasmonic integrated functional devices and circuits.

Experimental and simulated verification of a frequency and amplitude tunable metamaterial absorber

In this paper, a dual band absorption characteristic of metamaterial absorber with three dielectric layers (SU-8 layer, VO2 layer, Al2O3 layer) is proposed and experimental confirmed in terahertz region. These absorption peaks are originated from cavity resonance and electrical resonance, respectively. Impedance matching phenomenon between the proposed metamaterial absorber and free space is achieved at resonance frequencies of absorption peaks. In order to reveal the effect of geometrical parameters on absorption peaks, two groups of experiments are carried out. It is found that the cavity and electrical resonance absorption peaks show a shifted to higher frequency with the radius of holes array increasing. However, for the increase in the VO2 layer thickness, the cavity and electrical resonance absorption peaks show a shifted to lower frequency. Absorption property is improved through optimizing structural parameters at room temperature condition. Moreover, measured results demonstrate that the cavity and electrical resonance absorption peaks show a shifted to higher frequency with the temperature increasing. Absorption intensities are tuned from 81% (25 °C) to 51% (97 °C) and 83% (25 °C) to 52% (97 °C), respectively. A new low-frequency absorption peak is achieved because that a new electrical resonance mode is effectively excited between the VO2 layer and bottom metal layer. The proposed metamaterial absorber with tunable property shows the applications possibility in sensing and detecting based on external stimulus (such as heat, or light) leading to the absorption spectrum change.

Characterizations of reconfigurable infrared metamaterial absorbers.

We propose four types of metamaterial absorbers (MAs) to have tunable absorption resonance and polarization-dependent/independent, single-band, and dual-band switch characterizations. By tailoring four types of MAs with different heights between top and bottom metal layers, absorption resonance can be modified at a 5.92μm wavelength, and the absorption intensity can be attenuated gradually. These characteristics of MA devices can be potentially used in a variable optical attenuator (VOA). By changing the distance between the top unit cells of four devices, the resonances can be tuned in the range of a 1.74μm wavelength with an exponential relationship. All absorption intensities can be maintained over 90%. Furthermore, MA devices also possess single-band and dual-band switch characterizations by controlling the polarization angle of incident light, which helps the MA to have the potential in a multifunctional switch. By comparing the range of switch ratios, it can be spanned 1.76 for dual-band switch function. This Letter provides a strategy to open an avenue for VOA, absorber, detector, sensor, and switch applications in the IR wavelength range.