Surface Of Dielectric Substrate Research Articles

An investigation of methods to enhance adhesion of conductive layer and dielectric substrate for additive manufacturing of electronics

Additive manufacturing of conductive layers on a dielectric substrate has garnered significant interest due to its promise to produce printed electronics efficiently and its capability to print on curved substrates. A considerable challenge encountered is the conductive layer’s potential peeling due to inadequate adhesion with the dielectric substrate, which compromises the durability and functionality of the electronics. This study strives to facilitate the binding force through dielectric substrate surface modification using concentrated sulfuric acid and ultraviolet (UV) laser treatment. First, polyetheretherketone (PEEK) and nanoparticle silver ink were employed as the studied material. Second, the surface treatment of PEEK substrates was conducted across six levels of sulfuric acid exposure time and eight levels of UV laser scanning velocity. Then, responses such as surface morphology, roughness, elemental composition, chemical bonding characteristics, water contact angle, and surface free energy (SFE) were assessed to understand the effects of these treatments. Finally, the nanoparticle silver ink layer was deposited on the PEEK surface, and the adhesion force measured using a pull-off adhesion tester. Results unveiled a binding force of 0.37 MPa on unmodified surface, which escalated to 1.99 MPa with sulfuric acid treatment and 2.21 MPa with UV laser treatment. Additionally, cross-approach treatment investigations revealed that application sequence significantly impacts results, increasing binding force to 2.77 MPa. The analysis further delves into the influence mechanism of the surface modification on the binding force, elucidating that UV laser and sulfuric acid surface treatment methods hold substantial promise for enhancing the binding force between heterogeneous materials in the additive manufacturing of electronics.

Dual-Polarized Nonuniform Fabry–Pérot Cavity Antenna With Flat-Topped Radiation Pattern

A method to realize the flat-topped radiation pattern of Fabry–Pérot cavity antenna is proposed based on the ray-tracing model. In the design, a nonuniform partially reflective surface of dielectric substrate is proposed to reduce the sidelobe level and get a fast roll-off in the operating frequency band. Besides, a dumb source array is added around the dual-polarized feed array to minimize the disparity of beamwidth between E- and H-plane. The antenna was calculated with the proposed method, simulated by the full-wave simulation, and validated by the experiment. Compared with the traditional array synthesis method, there is no need to design a complex feed network because each coaxial port is fed equally in phase and amplitude. In addition, based on the proposed method, the aperture size is small and the flat-topped beamwidth is flexible.

Ultrafast Growth of Highly Conductive Graphene Films by a Single Subsecond Pulse of Microwave.

Currently, graphene films are expected to achieve real applications in various fields. However, the conventional synthesis methods still have intrinsic limitations, especially not being applicable on a surface with high curvature. Herein, an ultrafast synthesis method was developed for graphene and turbostratic graphite growth by a single subsecond pulse of microwaves generated by a household magnetron. We succeeded in growing high-quality around 10-layered turbostratic graphite in 0.16 s directly on the surface of an atomic force microscope probe and maintaining a tip curvature radius of less than 30 nm. The thus-produced probes showed high conductivity and tip durability. Moreover, turbostratic graphite film was also demonstrated to grow on the surface of dielectric Si flat substrates in a full coverage. Graphene can also grow on metallic Ni tips by this method. Our microwave ultrafast method can be used to grow high-quality graphene in a facile, efficient, and economical way.

Exact dispersion relations for the hybrid plasmon-phonon modes in graphene on dielectric substrates with polar optical phonons.

Intrinsic optical phonons and extrinsic polar optical phonons (POPs) strongly affect the graphene surface plasmons. Specifically, extraneous POPs present on the surface of an underlying substrate change the behavior of the graphene's surface plasmons sharply due to the plasmon-phonon hybridization. Here, we report modeling of exact dispersion relations for graphene's surface plasmons affected by intrinsic optical phonons and extrinsic POPs of the surface of polar dielectric substrates with one or more vibrational frequencies. In doing so, we have employed random phase approximation with modified two-dimensional polarizability (2D-Π0). The adapted Π0 addresses limitations of the previously derived plasmons dispersion, obtained using classical two-dimensional polarizability. We show the new model overcomes the unsatisfying behavior of the plasmonic dispersion relation obtained by the classical 2D-Π0 at high-wavenumbers and its inability to indicate the starting point of the mode damping. Our new simple model eliminates the complexity of the other presented models in describing the surface plasmons' behavior, specifically at high wavenumbers. Besides, we use our dispersion model to learn about the plasmon content of the hybrid modes, which is a vital value to compute output current in plasmonic graphene-based devices. The coupled-mode lifetime due to the hybrid nature depends on both plasmon and phonon lifetimes. We capture this value here. There is an excellent agreement between our theoretical results and the experimental data reported earlier. They pave the way for the exact modeling of graphene plasmons on common polar substrates and bring in the closeness of the theoretical approaches and experimental results.

Broadband linear‐to‐circular polarization reflector using anisotropic metasurface

A high-performance polarization reflector is introduced based on anisotropic metasurface. This structure can convert a linearly polarized (LP) incident electromagnetic (EM) wave into a circularly polarized (CP) reflection wave. The unit cell of the proposed metasurface is made of metallic patch imprinted on the top surface of a metal-backed single-layer dielectric substrate. The shape of this metallic patch is a combination of a deformed Jerusalem cross and two deformed L. The simulation results show that the LP incident EM wave is converted to CP reflected wave from 7 to 19.4 GHz, which the bandwidth of axis ratio less than 3 dB is 12.4 GHz and the relative bandwidth is 94%. The current distributions and equivalent circuit model are given to analyze the generation of circularly polarized waves. To verify the metasurface structure performance, a sample consisting of 24 × 24 unit cells is fabricated and measured. The experimental and simulation 3-dB AR bandwidth are basically consistent with each other, which verify the properties of the design. The proposed metasurface structure has potential application in microwave sensors and antenna design to manipulate the polarization states of EM waves.

Miniaturization of Quasi-Yagi Antenna Array with High Gain Using Split-Ring Resonators

In order to realize the miniaturization of quasi-Yagi antenna array, an antenna array with split-ring resonators (SRRs) based on two 7 units quasi-Yagi elements is designed in this paper. The radiation performance of the quasi-Yagi antenna array degrades significantly when array element spacing is reduced. After embedding SRRs on both sides of the miniaturized dielectric substrate surface, the S parameters and gain of array are significantly better than the array without SRRs, and the adjustable wave beam energy is also enhanced effectively. It indicates that the proposed antenna array with SRRs has good directional radiation performance under the miniaturize process at the operation frequency of 2.45 GHz, which could be widely applied in the fields of smart rail transportation and wireless power transfer.

Potential of Liquid-Crystal Materials for Millimeter-Wave Application

In this study, we reviewed three topics regarding the application of liquid-crystal (LC) materials to millimeter-wave (MMW) devices. It is essential to develop useful measurement methods for refractive indices of LC materials in the MMW region. Herein, a novel measurement method using optical short is demonstrated using a Si semiconductor substrate. There are two approaches to develop MMW LC devices. One is the quasi-optical approach, which involves scaling up the optical components, and the other approach involves integrating the LC materials into high-frequency electric circuits. A three-dimensional (3D) printer is used to fabricate the Fresnel lens, which is a typical quasi-optical device useful in the MMW region, where we can develop the tunable lens by introducing LC materials. A planar-type MMW waveguide is advantageous for integrating the LC materials to develop LC MMW devices using the second approach. We investigated a useful microstrip-line-type LC phase shifter by developing a novel conversion circuit to introduce the LC material onto the dielectric substrate surface. A phase shifter is an important MMW component that is used to attain a phased array antenna system, and a minimal twin antenna array is demonstrated using the microstrip-line-type LC phase shifters.

Generation of laser-induced periodic surface structures (LIPSS) in fused silica by single NIR nanosecond laser pulse irradiation in confinement

High-quality submicron pattern formation in dielectrics by lasers is challenging, in particular with regard to large areas. Self-assembly and self-organization mechanisms, which arise from the interaction of the laser photons with the material of the sample, can provide conditions for efficient micron patterning of large surface areas. This study demonstrates the formation of submicron ripples in fused silica (SiO2) by nanosecond laser irradiation, which extends the category of lasers capable of the controllable manufacturing of laser-induced surface structures (LIPSS). A newly designed layer system was deposited on the surface of samples, comprising, on top of the dielectric substrate, an interlayer, an absorber, and a confinement layer. The samples were irradiated though the dielectric substrate with single nanosecond (λ = 1064) nm laser pulses. It was found that the period of the LIPSS can be tuned by changing the nanosecond laser energy, the confinement strength, and the laser pulse length from 5 ns to 25 ns. LIPSS with periods in the range of 400–600 nm, with a depth of up to 140 nm and with an orientation perpendicular to the polarization direction of the laser light, were found experimentally. The design of the sample finally enables an intra-pulse modification of the dielectric surface that provides temporal conditions near the dielectric substrate surface for surface plasmon polaritron (SPP) generation. The proposed mechanism of LIPSS formation thus comprises the ablation of the absorber layer and a plasma formation confined between the substrate surface and the confinement layer. This process causes a modification of the substrate surface. In consequence, temporary SPP generation occurs at the modified SiO2 surface, resulting in a lateral intensity modulation of the nanosecond laser beam within the pulse duration. This lateral intensity modulation of the laser pulse causes localized variation of the ablation, which finally results in the LIPSS found.The experimentally observed dependencies of the LIPSS period on the pulse energy, the confinement layer thickness, and the pulse length can be explained with the proposed model. The findings of this work provide a method of enabling local adjustment of the LIPSS period, which can be used in applications such as writing hierarchical structures of variable sizes.

Skin Effect Suppressed Ni–Fe/Cu Electroplated Multilayer Wiring for High Data-Rate and Low Delay-Time I/O Interface Board

This paper proposes a new application of skin effect suppression technology [1]–[4] for long wiring on high-speed & low-delay I/O board (typical wiring length; 200 to 1000 mm). This proposal will overcome the difficulty to further reduce the transmission losses on the I/O board with >50 Gbps data rate, which is currently performed by lowering dielectric substrate losses and surface smoothing of Cu conductor. A major challenge in this paper is to demonstrate the skin effect suppression by electroplated magnetic/conductor multilayer, instead of sputter-deposited thin film in literature [2]–[4], in order to meet coming cost-effective, thick (>5 μm), large area, and high throughput mass productivity requirements. High frequency (>10 GHz) estimation of complex permeability and measurements of low resistance devices are also investigated.

SELECTIVE GROWTH OF THIN CARBON FILMS ON DIELECTRICS SUBSTRATES

The method of control of the quality of thin carbon films obtained by ethanol vapor pyrolysis on the surface of dielectric substrates which was preliminary irradiated by e-beam is described. The influence of the exposure doses on the structural perfection of the obtained films was studied.

Rubrene on differently treated SiO2/Si substrates: A comparative study by atomic force microscopy, X-ray absorption and photoemission spectroscopies techniques

The performances of organic thin film transistor devices are crucially connected with electronic and structural properties at organic semiconductor/dielectric interfaces. In our studies, Silicon substrates with native SiO2 layer were made hydrophilic according to Radio Corporation of America (RCA) cleaning procedure (RCA treated SiO2, RCA/SiO2) and hydrophobic by following octadecyltrichlorosilane (OTS) modification method (OTS treated SiO2, OTS/SiO2). The surface morphology, molecular orientation and nature of interaction have been studied at rubrene/RCA treated SiO2 and rubrene/OTS treated SiO2 interfaces with increasing thickness of rubrene film from sub-monolayer to multilayer. The angle dependent near edge x-ray absorption fine structure (NEXAFS) spectroscopy and atomic force microscopy (AFM) were used to probe the evolution of molecular configuration and surface morphology of rubrene thin films respectively. The nature of interaction was investigated by X-ray photoemission spectroscopy (XPS) techniques. XPS and NEXAFS studies indicate that the rubrene molecules were physically adsorbed onto both substrates. Angle dependent NEXAFS data suggest that OTS molecules were in standing up configuration on SiO2 surface while rubrene molecules were randomly oriented on both RCA and OTS treated SiO2 substrates. On RCA/SiO2 substrate the percentage of rubrene molecules with twisted backbone was higher compared to that on OTS/SiO2 for 20nm thick films. The rubrene films were found to grow with different features onto two studied substrates due to their difference in surface energy. At lower coverage, the grain size was larger and nucleation density was smaller onto hydrophilic RCA/SiO2 surface, compared to hydrophobic OTS/SiO2. Hydrophobation of the dielectric substrate surface tends to hinder the diffusion of rubrene molecules resulting in smaller grains for hydrophobic substrate compared to hydrophilic one.

Low-Profile Broadband Absorbers Based on Capacitive Surfaces

Low-profile and broadband absorbers based on capacitive surfaces are proposed and implemented. First, the impedance of a dielectric substrate and capacitive surface is analyzed separately to characterize the surface impedance. The capacitive surfaces are therefore achieved with the combination of two ring resonators and used to design a three-fold and four-fold symmetric absorber. The resulting absorbers, with the thickness of about 0.076 $\;{\lambda _L}$ at the lowest operating frequency, exhibit good absorption at −10 dB return loss over the fractional bandwidth of 82.5%–117.4%. For demonstration, one prototype of the proposed absorber was fabricated and measured, and good agreement is observed.

The Design of a Wideband Microwave Absorber Based on Resistively Single Square-Loop Arrays

A non-magnetic microwave absorber was proposed, for which the-10dB absorbing bandwidth would operate over all the X-band with a total thickness of 4 mm. The designed structure was composed by resistively single square-loop FSS on the surface of metal-backed dielectric substrate. The influence of the substrate and FSS was discussed for absorption optimization. Besides, the current distribution of the FSS was investigated to explain the principle of resonance. Good accordance of the experimental results and the simulated results has been achieved, indicating the feasibility of our designed structure and the reliability of the simulated method.

High-performance and high-sensitivity applications of graphene transistors with self-assembled monolayers

Charge impurities and polar molecules on the surface of dielectric substrates has long been a critical obstacle to using graphene for its niche applications that involve graphene's high mobility and high sensitivity nature. Self-assembled monolayers (SAMs) have been found to effectively reduce the impact of long-range scatterings induced by the external charges. Yet, demonstrations of scalable device applications using the SAMs technique remains missing due to the difficulties in the device fabrication arising from the strong surface tension of the modified dielectric environment. Here, we use patterned SAM arrays to build graphene electronic devices with transport channels confined on the modified areas. For high-mobility applications, both rigid and flexible radio-frequency graphene field-effect transistors (G-FETs) were demonstrated, with extrinsic cutoff frequency and maximum oscillation frequency enhanced by a factor of ~2 on SiO2/Si substrates. For high sensitivity applications, G-FETs were functionalized by monoclonal antibodies specific to cancer biomarker chondroitin sulfate proteoglycan 4, enabling its detection at a concentration of 0.01fM, five orders of magnitude lower than that detectable by a conventional colorimetric assay. These devices can be very useful in the early diagnosis and monitoring of a malignant disease.

The effect of sol–gel preparation conditions on structural characteristics and magnetic properties of M-type barium hexaferrite thin films

We have shown the possibility to obtain M-type barium hexaferrite thin films with thickness of ~200–450 nm on the surface of dielectric α-Al2O3 substrates with low microwave dielectric loss (tan δ ~ 10−4 GHz) by a sol–gel method. For the production of high-dense homogeneous thin films of M-type barium hexaferrite (BaFe12O19, BHF) with nanorod-like grains and a uniform distribution of iron and barium ions, we have studied the synthesis conditions for thermally stable film-forming solutions with high concentrations of barium ions. Films with a c-axis magnetic texture were obtained by spin-coating the former solutions on α-Al2O3 substrates and annealing at temperatures between 473 and 1073 K. The resulting textured M-type BHF films have demonstrated the following magnetic parameters: H c⊥ = 334 kA/m, H c|| = 167 kA/m; M s⊥ = 0.005 emu, M s|| = 0.003 emu for the films’ thickness of ~200 nm, and H c⊥ = 360 kA/m, H c|| = 338 kA/m; M s⊥ = 0.009 emu, M s|| = 0.007 emu for the films’ thickness of ~450 nm. These M-type BHF thin films can serve as a promising basis for further development of multilayer microwave resonant elements.

Direct growth of nanocrystalline hexagonal boron nitride films on dielectric substrates

Atomically thin hexagonal-boron nitride (h-BN) films are primarily synthesized through chemical vapor deposition (CVD) on various catalytic transition metal substrates. In this work, a single-step metal-catalyst-free approach to obtain few- to multi-layer nanocrystalline h-BN (NCBN) directly on amorphous SiO2/Si and quartz substrates is demonstrated. The as-grown thin films are continuous and smooth with no observable pinholes or wrinkles across the entire deposited substrate as inspected using optical and atomic force microscopy. The starting layers of NCBN orient itself parallel to the substrate, initiating the growth of the textured thin film. Formation of NCBN is due to the random and uncontrolled nucleation of h-BN on the dielectric substrate surface with no epitaxial relation, unlike on metal surfaces. The crystallite size is ∼25 nm as determined by Raman spectroscopy. Transmission electron microscopy shows that the NCBN formed sheets of multi-stacked layers with controllable thickness from ∼2 to 25 nm. The absence of transfer process in this technique avoids any additional degradation, such as wrinkles, tears or folding and residues on the film which are detrimental to device performance. This work provides a wider perspective of CVD-grown h-BN and presents a viable route towards large-scale manufacturing of h-BN substrates and for coating applications.

The application of micro-milling technology in the processing of micro-strip antenna

The main objective of this study is to investigate the feasibility of machining the copper layer for micro-strip antenna with micro-milling technology and to find the optimal machining parameters. The main properties of the micro-strip antenna are related to the geometry accuracy of the copper layer attached to the dielectric substrate surface. In this paper, micro-milling technology is utilised to machine the copper layer for microstrip antenna. The milling process is divided into two steps: roughing and finishing milling. The influence of the micro-milling cutting parameters on the geometry quality of copper is investigated. The results show that micro-milling of copper layer on polyimide is feasible, reasonable micro-milling cutting parameters can improve the processing efficiency, ameliorate the surface quality and extend the tools' life. The main contribution of this paper to the related literature is to provide a new method to machining the copper layer for micro-strip antenna.

Measuring the surface purity of substrates by the tribometry method

A tribometric device designed for rapid monitoring of the concentrations of atomic and molecular contaminants on the surfaces of semiconductor and dielectric substrates within the range of 10−7–10−10 g/cm2 is described. The method is based on measurements of the static and sliding friction coefficients between the investigated surfaces. The arrangement of interacting substrates forming a point contact and allowing elimination of disturbances in the crystal structure in the slip region at loads in the range of 0–3.7 N and angles between the substrates of 0–15° is shown.

All-Solution-Processed Low-Voltage Organic Thin-Film Transistor Inverter on Plastic Substrate

In this paper, all-solution-processed low-voltage organic thin-film transistor inverters on polyethylene naphthalate plastic substrate were achieved in the bottom-gate bottom-contact device configuration. In the devices, 6,13-bis(triisopropylsilylethynyl)-pentacene blended with polystyrene was used as the channel layer, and ultraviolet cross-linked polyvinyl alcohol was used as the gate dielectric layer. With optimized inkjet jetting process parameters and a proper polymer dielectric substrate surface, fine silver electrodes were formed as the source, drain, and gate electrodes. The maximum processing temperature was 150°C. The devices show promising performance with a mobility of 0.8 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /(V·s), a subthreshold swing of 100 mV/decade and an ON/OFF ratio of about 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> . The fabricated diode-load inverter has a high dc voltage gain up to 67.3 at a supply voltage of 3 V.

Nonuniformity of the pressure wave formed during electric explosion of a foil

Temporal waveforms of pressure amplitude in various regions of a flat electrically exploded foil (EEF) have been measured. The results of measurements have been used to reconstruct the temporal evolution of spatial pressure profiles generated by the EEF. The measurements were performed using quartz pressure sensors arranged in various (central and peripheral) regions of the free surface of a dielectric substrate glued to the foil. The obtained data show that the electric explosion starts at the edges of a foil, which is followed by stronger pressure buildup in the central axial region of the EEF.