Air Dielectric Layer Research Articles

Multi-Channel High-Performance Absorber Based on SiC-Photonic Crystal Heterostructure-SiC Structure.

The multi-channel high-efficiency absorber in the mid-infrared band has broad application prospects. Here, we propose an SiC-photonic crystal (PhC) heterostructure-SiC structure to realize the absorber. The absorption characteristics of the structure are studied theoretically. The results show that the structure can achieve high-efficiency multi-channel absorption in the mid-infrared range. The absorption peaks come from the coupling of the dual Tamm phonon polariton (TPhP) mode formed at the interface between the two SiC layers and the photonic crystal, and the optical Tamm state (OTS) mode formed in the PhC heterostructure. By adjusting the thickness of the air dielectric layer and the period of the PhC in the heterostructure, the mode coupling intensity can be regulated; thereby, the position and intensity of the absorption peak can be adjusted. In addition, the absorption peaks of TE and TM polarized light can be controlled by changing the incident angle. Adjusting the incident angle can also control the excitation and intensity of the epsilon-near-zero (ENZ) phonon polariton mode produced by TM polarized light. This kind of light absorber may have potential applications in sensors, filters, modulators, switches, thermal radiators, and so on.

Human‐Interactive, Active‐Matrix Displays for Visualization of Tactile Pressures

AbstractHuman‐interactive displays involve the interfacing of a stimuli‐responsive sensor with a human‐readable response. Human‐readable responses include the five recognized senses, i.e., sight (vision), hearing (audition), taste (gustation), smell (olfaction), and touch (somatosensation). Vision is considered to be the most informative human stimulus so that the visualization of electrical, thermal, and mechanical data is important for various applications. Herein, the fabrication of human‐interactive displays is demonstrated in which active‐matrix arrays of pressure‐sensitive Si transistors with air dielectric layers are fully integrated with pixels of organic light‐emitting diodes (OLEDs). In this way, the luminance of the individual OLED pixels can be increased locally by pressing the display, and the luminance is dependent on the magnitude of the applied pressure. Furthermore, the air dielectric layer of transistors provides outstanding electrical properties, including high transconductance and negligible hysteresis. 3D integration of these transistors with dual‐side emissive OLED pixels is also demonstrated. Local pressing increases the light intensity of OLED pixel and then the underlaid Si channel can absorb this light successively to generate additional photocurrents from the pressure‐sensitive transistor, further enhancing its sensitivity. This human‐interactive display can visualize tactile pressure directly, suggesting the substantial promise as next generation displays for intelligent human‐machine interfacing.

Enabling Multifunctional Organic Transistors with Fine-Tuned Charge Transport.

Organic field-effect transistors (OFETs) are promising candidates for many electronic applications not only because of the intrinsic features of organic semiconductors in mechanical flexibility and solution processability but also owing to their multifunctionalities promised by combined signal switching and transduction properties. In contrast to rapid developments of high performance devices, the construction of multifunctional OFETs remains challenging. A key issue is fine-tuning the charge transport by modulating electric fields that are coupled with various external stimuli. Given that the charge transport is determined by complicated factors involving material and device engineering, the development of effective strategies to manipulate charge transport is highly desired toward state-of-the-art multifunctional OFETs. In this Account, we present our recent progress on device-engineered OFETs for sensing applications and thermoelectric studies of organic semiconductors. The interactions between organic semiconductors and the target analyte determine the performance of chemical sensors based on OFETs. We introduced gas receptors and in situ tailored molecular antenna on the surface of ultrathin active layers. The engineered interfaces enable direct and specific semiconductor-analyte interactions, as demonstrated in developed chemical sensors and biosensors with prominent sensitivity and good selectivity. In comparison with chemical stimuli, many physical stimuli such as pressure typically possess a limit effect on the charge transport properties of organic semiconductors. By utilizing the suspended-gate geometry, the carrier concentration in a conductive channel can be controlled quantitatively by the pressure dominated changes in the capacitance of an air dielectric layer, allowing for ultrasensitive pressure detection in a unique manner. More importantly, the transduced current can be further processed by a synaptic OFET, in which the proton/electron coupling interfaces contribute to the dynamic modulation of carrier concentration, thus mimicking biological synapses. The integrated pressure sensor and synaptic OFETs, namely, the dual-organic-transistor-based tactile-perception element, has exhibited promising applications in artificial intelligence elements. Aiming at revealing thermoelectric (TE) properties of organic semiconductors, we also investigated field-modulated TE performance of several high-mobility semiconductors by varying the driving electric field to the temperature gradient. This has been confirmed to offer a strategy to accelerate the search for promising TE materials from well-developed organic semiconductors. By tuning the charge transport process in the device, the functional modulation of OFETs has experienced significant progress in the preceding years. The exploration of new ways to create OFETs with more fascinating functionalities is still full of opportunities to obtain greater benefit from organic transistors.

A novel RF energy harvesting cube based on air dielectric antenna arrays

In this article, a new 2 × 2 circular microstrip antenna array with air dielectric layer for ambient RF energy harvesting has been proposed. Two pairs of arc-shaped slots located close to the boundary of the circular microstrip patch have been designed for achieving dual-band response and extending the frequency bandwidth. The antenna has a frequency bandwidth from 1.85 to 1.93 GHz and from 2.0 to 2.1 GHz which can cover GSM-1800 and UMTS-2100 bands. At the frequency of 1.89 and 2.05 GHz, the measured gain is 5.3 and 6.6 dBi, respectively, and high gain of 3.8-9.3 dBi has been achieved over the whole band. Also, a broadband rectifier that can cover all the bandwidths of the antenna array is designed for the rectenna, which has the maximum rectifying efficiency of 53.6%. Finally, a cube device formed of four antenna and four rectifiers is designed to harvest RF energy, whose maximum output DC voltage is 2.3 V and the maximum output power is 4 mW that can drive four LEDs and an electronic watch.

Integrated arrays of air-dielectric graphene transistors as transparent active-matrix pressure sensors for wide pressure ranges

Integrated electronic circuitries with pressure sensors have been extensively researched as a key component for emerging electronics applications such as electronic skins and health-monitoring devices. Although existing pressure sensors display high sensitivities, they can only be used for specific purposes due to the narrow range of detectable pressure (under tens of kPa) and the difficulty of forming highly integrated arrays. However, it is essential to develop tactile pressure sensors with a wide pressure range in order to use them for diverse application areas including medical diagnosis, robotics or automotive electronics. Here we report an unconventional approach for fabricating fully integrated active-matrix arrays of pressure-sensitive graphene transistors with air-dielectric layers simply formed by folding two opposing panels. Furthermore, this realizes a wide tactile pressure sensing range from 250 Pa to ∼3 MPa. Additionally, fabrication of pressure sensor arrays and transparent pressure sensors are demonstrated, suggesting their substantial promise as next-generation electronics.

LOW-PROFILE WIDEBAND CIRCULARLY POLARIZED PATCH ANTENNA USING ASYMMETRIC FEEDING

A low-proflle wideband circularly polarized aperture stacked patch (ASP) antenna without air dielectric layers is presented. The new circular ASP antenna, which is fed by two orthogonal dual-ofiset lines through an asymmetric crossed slot, delivers a wide bandwidth of 80% for the 10-dB return loss and similar input impedance characteristics for the two ports. Then, a novel broadband 90 - hybrid feed network is employed to achieve good impedance matching, balanced power splitting and consistent 90 - (§9 - ) phase shifting across the wide operating band. The two unbalanced feed lines are connected to the respective ports of the feed network comprising a three-section Wilkinson power divider and a broadband 90 - phase shifter. It is found that the proposed antenna can achieve a measured impedance bandwidth of 91.3% (2.44{6.54GHz), measured 3-dB axial ratio (AR) bandwidth of 86.4% (2.5{6.3GHz), and measured gain bandwidth of 60.9% from 3.2 to 6.0GHz for the gain > 4dBic. In addition, a comparison between the proposed wideband CP antenna and related wideband CP and ASP antennas in the literature is made.

Imprint lithography enabling ultra-low loss coaxial interconnects

Processing techniques have been demonstrated to fabricate a novel structure with smooth transitions, metallic shielding, and encapsulated air dielectric layers using sacrificial polymers and the three-dimensional patterning capabilities of imprint lithography. This innovative structure incorporates encapsulated air dielectrics with copper shielding. A semicircular stamp was fabricated to create the circular base of the coaxial transmission line using the reflow properties of solder, and imprinting the stamp produced smooth rounded terminations. Copper shielding was electroplated and a sacrificial photosensitive polycarbonate was patterned using a unique interaction with the copper. The polycarbonate was over-coated with a epoxycyclohexyl polyhedral oligomeric silsesquioxane (POSS) layer and then thermally decomposed to form an air cavity. A center conductor was patterned using photolithography and electro-deposition. The half-coaxial line was aligned with a sample with the top portion of the copper shielding and bonded in the imprinter to complete the structure. Imprint lithography also demonstrated the capability to planarize surfaces which simplified the buildup process, and complex structures were fabricated with a comparable number of registration steps to traditional transmission lines. The mechanical integrity of the air-clad transmission lines was also evaluated using nano-indentation.

Air-Gap Transmission Lines on Organic Substrates for Low-Loss Interconnects

The fabrication of low-loss transmission line structures with an air dielectric layer is described. The channels are characterized at low frequency (10 and 100 kHz) using capacitance and loss tangent and at high frequency (500 MHz to 10 GHz) using -parameter measurements. The incorporation of an air gap resulted in structures with effective dielectric constants between 1.5-1.8 and significantly lower loss tangents. The fabrication technique could be used to create more complicated air gap transmission line structures for use in monolithic microwave integrated circuits.

Structure and Thermal Properties of Thin Film Poly(α‐methylstyrene) Deposited via Plasma‐Enhanced Chemical Vapor Deposition

AbstractPlasma‐enhanced (PE) CVD from α‐methylstyrene is a dry method for synthesizing directly patternable sacrificial materials for generating pores or air dielectric layers. Films deposited at low power excitation (40 W) decompose between 65 °C and 75 °C, leave minimal residue following a 400 °C anneal for 2 h, and have spectroscopic signatures of linear poly(α‐methylstyrene) (PaMS) as determined by nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. Increased plasma excitation power leads to cross‐linking and increased residue after annealing. All films also contain hydroxyl and carbonyl groups after exposure to air. Significant C–O–C inclusion occurs under continuous plasma excitation but not under pulsed‐plasma conditions.

Low-loss microwave cavity using layered-dielectric materials

Loss measurements have been carried out on a cylindrical pillbox cavity whose metallic flat end walls have been replaced by an ordered sequence of high purity sapphire and air dielectric layers. The loss of the TE01 mode at 18.99 GHz was substantially lowered. An improvement in cavity Q for this mode from 8.30×103 to 531×103 was observed. These experimental results closely reproduce two independent theoretical simulations. All measurements were taken at 30 °C.

Propagation of Short Radio Waves in a Normally Stratified Troposphere

Experiments of the past decade give stronger fields well beyond the horizon than are calculated by the 4/3 airless earth approximation. Post-war work on the theory of the WKB approximation for wave propagation in slowly varying inhomogeneous media, and the peculiar results for eigenvalues of the bilinear refractive index proffle offer valuable clues in the search for an oversight in conventional propagation theory. If the absolute value as well as the gradient of the refractive index at the earth's surface be specified, with a refractive index profile which tapers to vacuum at some arbitrarily large height, then allowed modes of the wave equation permit the field to be calculated within, just beyond, and well beyond the horizon, in agreement with many vhf and microwave experiments. Modes thus calculated are supported by ordinary coherent molecular scattering in normal air dielectric layer. At times, superrefraction and macroscopic turbulence are additional mechanisms for propagation deep into the shadow of the earth bulge.