Low-permittivity Dielectric Materials Research Articles

A Compact and Robust RFID Tag Based on an AMC Structure.

A platform-tolerant RFID (Radio-Frequency Identification) tag is presented, designed to operate across the entire RFID band. This tag utilizes a small Artificial Magnetic Conductor (AMC) structure as a shielding element for an ungrounded RFID tag antenna. It can be easily mounted on various surfaces, including low permittivity dielectric materials, metal objects, or even attached to the human body for wearable applications. The key features of this RFID tag include its ability to be tuned within the worldwide RFID band, achieving a maximum theoretical read range of over 11 m. Despite its advanced capabilities, the design emphasizes simplicity and cost-effective manufacturing. The design and simulations were conducted using CST Studio Suite.

An X-Band Dielectric Rod Antenna for Subdermal Tumor Heating to Assist Electroporation-Mediated DNA Delivery

An end-fire dielectric rod antenna is proposed as a heating device for integration with an array of electroporation electrodes in order to enable efficient delivery of DNA into the cells that comprise subcutaneous tumors. A 5-7 °C temperature elevation of tumors that are located near the fat-muscle boundary and 3-7 mm below the skin surface can be achieved in a short period of time without damaging surrounding tissues. This capability is demonstrated through a combination of a directional antenna applicator operating at 8 GHz, and utilization of forced air cooling of the outer surface (skin layer). The directionality of the antenna is improved by cladding its high permittivity core with 3D printed, low permittivity dielectric material. Experimental data using a pork skin-fat-muscle tissue show that the desired temperature elevation at the tumor location is obtained after 2.5 W RF illumination for 3 minutes, which is in good agreement with electro-thermal simulations. With the addition of realistic human body model parameters to the same simulation setup, the results indicate that tumors can be uniformly heated with 3 minutes of illumination at 2.5 W input power while keeping the surrounding healthy tissues at a safe temperature.

Planar Pyramid Shaped UHF RFID Tag Antenna With Polarisation Diversity for IoT Applications Using Characteristics Mode Analysis

This paper presents a novel dual polarised tag antenna design for ultra-high frequency radio frequency identification (UHF RFID) featuring polarisation or frequency band diversity using characteristic mode analysis. The proposed tag design consists of two meandered line bowtie or dipole-like structure (resembles with planar pyramid), shorting stubs, and a ground plane. The initial design comprises of an upper patch wrapped around FR 4 substrate and shorted from all side to ground plane using shorting stubs. After running the characteristic mode analysis of the initial design, the diagonal slots are created to transform the resonant behavior of corresponding characteristic modes towards lower frequency band. However, the characteristics modes of diagonal slots-based structure still shows inductive behavior in US RFID band (902 - 928 MHz). Therefore, the parallel slots having capacitive performance are etched to realise the resonance behaviour of modes in the required RFID band. The positions and dimensions of parallel slots are optimised further to achieve a better conjugate impedance match with RFID chip. Moreover, the frequency band of one or both meandered line dipole-like structures can be tuned to European UHF RFID band by varying the length of the shorting walls. The RFID chip is directly placed at the current minima to run diversity modes. The overall dimensions of the proposed tag antenna are 50×50×2 mm 3 hence making this dual polarised tag antenna low-cost and easy to fabricate due to the absence of vias, shorting pins, and any matching circuit. Additionally, the proposed tag design offers 3-dB bandwidth ranging from 900 MHz to 940 MHz (40 MHz) together with orientation insensitive 3D read range pattern. The proposed tag design achieved a read range of 5.5 m and 8.5 m on low permittivity dielectric material and 200 × 200 mm 2 metal plate, respectively.

Phase composition and microwave dielectric properties of low permittivity AGeO3 (A = Mg, Zn) ceramics

It has become a focus to develop low-permittivity microwave dielectric materials to meet the needs of high-speed transmission in telecommunication devices. Here, we report two Ge-based microwave dielectric ceramics prepared using the conventional solid-state method, MgGeO3 and ZnGeO3, with low permittivity of 6.8 and 6.6, the high-quality factor of 65,200 GHz and 25,200 GHz, and negative temperature coefficient of −45 ppm/°C and −35 ppm/°C. Orthorhombic ilmenite structure of MgGeO3 can be obtained in the range of 1160–1240 °C. However, the single-phase ZnGeO3 is not available in air, and the ceramics sintered at 1040–1120 °C contain two phases of Zn2GeO4 and GeO2.

Circularly polarised periodic leaky‐wave antenna with filtering capability

A planar periodic leaky-wave antenna with filtering capability, circular polarisation, and wideband performance is presented. Seamless beam scanning from backward to forward is provided by self-matching the unit cell of the antenna over a large frequency band from 22 to 28 GHz. A wide scanning range of 84° is achieved by using a relatively low-permittivity dielectric material. Filtering capability is embedded in the antenna structure which contributes to the minimisation of the overall circuit size which is aimed in recent millimetre-wave antenna in package systems. The proposed antenna has a circular polarisation with an axial ratio of <2 dB at broadside which makes it a good candidate for peer-to-peer and peer-to-multipeer communication systems.

Li2AGeO4 (A = Zn, Mg): Two novel low-permittivity microwave dielectric ceramics with olivine structure

Two low-permittivity dielectric materials Li2AGeO4 (A = Zn, Mg) were prepared via the solid-state reaction method. X-ray diffraction analysis and Rietveld refinement indicated that both ceramics crystallize in an orthorhombic olivine structure with a space group Pmn21. Dense ceramics with high relative density and homogeneous microstructure were obtained. Li2ZnGeO4 densified at 1200 °C possessed a relative permittivity εr = 6.5, a quality factor Q × f = 35,400 GHz, and a temperature coefficient of resonant frequency. Li2MgGeO4 exhibited εr = 6.1, Q × f = 28,500 GHz, and τf = –74.7 ppm/°C when sintered at 1220 °C. Additionally, the large negative τf values of Li2AGeO4 (A = Zn, Mg) ceramics were successfully adjusted compensated by forming composite ceramics with CaTiO3 and near-zero τf values of +2.9 ppm/°C and +5.8 ppm/°C were achieved in 0.92Li2ZnGeO4-0.08CaTiO3 and 0.90Li2MgGeO4-0.10CaTiO3, respectively.

Properties of Silica-Based Aerogel Substrates and Application to C-Band Circular Patch Antenna

Silica aerogel is a lightweight and low-permittivity dielectric material that possesses attractive features for use as an antenna substrate. In this paper, we characterize the radio frequency and microwave dielectric permittivity properties of substrates composed of silica aerogel encapsulated in polymer aerogel in the frequency range from 10 MHz to 8.5 GHz. Characterized silica-based aerogel substrates show relative permittivity values varying between 1.055 and 1.25 and loss tangent values ranging from 5.08 × 10−4 to 0.0206. Silica-based aerogel substrates thus have the potential of use in designing antennas with high gain and large bandwidth. Validation is presented by characterizing the performance of a manufactured C-band circular patch antenna on silica-based aerogel substrate. The performance is also compared to a design that uses Rogers Duroid RT5880 substrate. The results reveal that the silica aerogel substrate antenna at 7.2 GHz provides 1.5 dB increase in gain, 88% enhancement in bandwidth and 68.5% reduction in mass, in comparison with the antenna on RT5880 substrate.

Thermally tunable water-substrate broadband metamaterial absorbers

The naturally occurring water has frequency dispersive permittivity at microwave frequencies and thus is a promising constituent material for broadband absorbers. Here, we develop water as the dielectric spacer in the substrate of metal-backed metamaterial (MM) absorbers. The designed substrate is a hybrid of water and a low-permittivity dielectric material. Such a design allows tight packaging of water and easy fabrication of the absorber. We obtain broadband absorption at temperatures of interest by designing the hybrid substrate and MM inclusions. Additionally, the absorption performance of the water-substrate MM absorbers could be tunable according to the environment temperature. We experimentally demonstrate the broadband and thermally tunable absorption performance. We expect that water could replace dielectric layers in other structural MM absorbers to achieve the broadband and thermally tunable absorption performance.

Improvement of the Scanning Performance of the Extended Hemispherical Integrated Lens Antenna Using a Double Lens Focusing System

We demonstrate that an integrated lens antenna (ILA) with a double lens (DL) focusing system can provide simultaneously a high broadside directivity and a low scan loss over a wide angular range. The proposed DL ILA system consists of a hemispherical substrate lens and a planoconvex objective lens. A prototype of a high-gain DL ILA with lenses made of a low permittivity dielectric material is fabricated and characterized in the frequency range of 75–79 GHz. The realized scan loss in terms of gain within a ±30° field of view is <1.1 dB in both planes. The performance of the DL ILA is compared with that of two hemispherical ILAs designed to provide the best broadside directivity and the lowest scan loss, respectively.

Meta-lens design with low permittivity dielectric materials through smart transformation optics

We report here a design method based on smart transformation optics (STO) to control the range of the permittivity values of the materials required to manufacture transformation optics devices. In particular, we show that it is possible to reduce the maximum electric permittivity value required to realize a STO device with certain functionality by means of a simple conceptual elastic stretching process. We illustrate the design procedure with two types of collimator meta-lens designs, which we call warping space collimator meta-lens and half fisheye collimator meta-lens, respectively. We provide design examples of these two types of lenses with the help of COMSOL Multiphysics software. These two design examples are fabricated with commonly available dielectric materials by means of 3D printing technology. For the functional verification of these two collimator lenses, we provide measurement results obtained with transverse electric waves of frequency range 7–13GHz.

SAR imaging-based techniques for Low Permittivity Lossless Dielectric Bodies Characterization

i»?The following contribution aims to test two synthetic aperture radar (SAR)-image-based techniques to obtain geometry and constitutive parameter information about low-permittivity lossless dielectric materials. While characterization of high-permittivity dielectrics is relatively affordable in SAR images, the low amount of power reflected back by lowpermittivity bodies makes their characterization a challenging task. The first proposed technique combines two illumination angles (normal and 45) to overcome the permittivity-geometry uncertainty appearing on each independent case. The second method makes use of the relationship between reflection coefficient amplitudes between two media, which can be directly extracted from the SAR image to provide an estimation of the dielectric object permittivity. Uncertainty of both techniques can be reduced by properly combining them. We validate these methods using a simulation-based application example in the form of a millimeter-wave portal-based system for concealed-object detection.

Two-Shell Radially Symmetric Dielectric Lenses as Low-Cost Analogs of the Luneburg Lens

This communication provides guidelines for the design of two-shell radially symmetric dielectric lenses with collimating capabilities compatible with those of the classical Luneburg lens. Unlike earlier publications, it is demonstrated that such a lens can be designed using any standard low permittivity dielectric materials, provided the optimal shell thickness is selected. The lens characteristics are studied in 2-D formulation using exact series representation. A detailed description is given for lenses with radius of 10 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and core made of Rexolite. The design recommendations are then generalized for lenses with radii of 5 to 15 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and cores made of Teflon, Fused Silica and Quartz. Finally, a chart defining the optimal shell thickness for lenses made of two arbitrary dielectric materials is provided. Validity of the recommendations for design of 2-D and 3-D radially symmetric lenses is proven by comparison with optimal designs reported by other authors.

Stiffening of organosilicate glasses by organic cross-linking

Atomistic simulations show that organosilicates, used as low permittivity dielectric materials in advanced integrated circuits, can be made substantially stiffer than amorphous silica, while maintaining a lower mass density. The enhanced stiffness is achieved by incorporating organic cross-links to replace bridging oxygen atoms in the silica network. To elucidate the mechanism responsible for the enhanced stiffness, the conformational changes in the network upon hydrostatic and shear loading are examined. The structural and mechanical impact of terminal methyl groups is also assessed quantitatively and compared with continuous random network theory.

An Integration Technology for RF and Microwave Circuits Based on Interconnect Programming

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A configurable integration technology suitable for implementing application specific radio-frequency (RF) and microwave circuits is presented. This postfabrication integration scheme is compatible with complementary metal–oxide–semiconductor (CMOS) technology and utilizes room temperature deposited Parylene-N as low loss and low permittivity dielectric material. Interconnect lines, inductors, and transmission lines fabricated on top of arrays of prefabricated 0.13 <formula formulatype="inline"><tex Notation="TeX">$\mu{\hbox {m}}$</tex></formula> and 90 nm CMOS transistors coated with Parylene-N are configured to design interconnect programmable RF and microwave circuits. The technology is used to demonstrate three proof of concept interconnect programmable narrowband amplifiers. These amplifiers have center frequencies of 5.5, 6.4, and 18 GHz with forward gain <formula formulatype="inline"><tex Notation="TeX">${\rm S}_{21}$</tex></formula> of 16.6, 11, and 18.7 dB, respectively. Fabrication simplicity and programmable nature of this technology compared to standard application specific integrated circuit (ASIC) fabrication lowers the cost and time to market of individual ASIC chip. </para>

Study on the composite and properties of Y 2O 3–TiO 2 microwave dielectric ceramics

Various high and low permittivity dielectric material systems were studied frequently. However, middle permittivity dielectric ceramics with ɛ r values ranging from 40 to 80 were seldom reported. For adapting to the development of microwave communication technology, a new Y 2O 3–TiO 2 system ceramic was investigated in this paper. The effects of different k values on the properties of Y 2O 3– kTiO 2 ( k = 1, 1.5, 2, 2.5) microwave dielectric ceramics were studied by impedance analyzer, network analyzer, X-ray diffraction apparatus (XRD) and scanning electron microscope (SEM). It is shown that the major crystal phases of the samples are pyrochlore except when k value is 1. The ceramic with a optimal composition (Y 2O 3:TiO 2) sintered at 1460 °C exhibits the best dielectric properties: ɛ r ≈ 54, tan δ ≈ 9.0 × 10 −4 (1 MHz); ɛ r ≈ 54, Q· f = 6565.8 GHz (4.65 GHz), τ f = −31 ppm/°C.

The effect of growth temperature on the nanostructure and dielectric response of BaTiO 3 ferroelectric films

BaTiO 3 ferroelectric films were grown on Si/SiO 2/Ti/Pt/Au/Pt templates at different temperatures in the range 560–680 °C by pulsed laser deposition. Cross section scanning electron microscopy images and atomic force microscopy surface morphology analysis reveal films with columnar structure and in-plane grain size distribution, in the range 10–60 nm, depending on growth temperature. Low-field dielectric measurements were performed as functions of temperature in the range 40–500 K and external dc field up to 400 kV/cm. The apparent permittivity of ferroelectric films grown at 680 °C shows Curie–Weiss behavior above 400 K with Curie temperature and Curie–Weiss constant 240 K and 1 · 10 5 K, respectively. The films grown at lower temperatures reveal a decrease of Curie temperature down to − 80 K, reduced values of apparent permittivity and loss tangent, and broadening of maximum of temperature dependence of apparent permittivity. The film grown at 590 °C demonstrates state of the art combination of temperature stability (temperature coefficient of apparent permittivity 300 ppm/K in the range 50–350 K), high tunability of apparent permittivity (up to 60% at room temperature), and relatively low loss tangent (less than 0.05 in the frequency range up to 10 GHz). The change in apparent permittivity and its temperature dependence, with variation of growth temperature are analyzed using two different composite models. The first model assumes the film to be a composite with vertical inclusions of low permittivity dielectric material associated with grain boundaries. This model may explain the observed decrease of permittivity with decreasing growth temperature, but not the shift of Curie temperature. The second model assumes a layered type of composite with low permittivity material associated with the film/electrode interfaces, and allows explanation of the Curie temperature shift.

Integration Challenges for Chemical Mechanical Polishing of Cu/Low-κ Interconnects

AbstractThe drive for improved performance of microelectronic devices has led to the prevalence of copper metallization and the aggressive development of low-permittivity (low-κ) dielectric materials for use as interlayer dielectrics in BEOL interconnect structures. Progressive scaling of metal line widths coupled with the need to incorporate ultra low-κ (ULK) dielectrics, with κ&lt;2.2, presents numerous challenges for integration and reliability. Perhaps the most significant challenge for the 90nm technology node and beyond is successful planarization of Cuinterconnect structures by chemical mechanical polishing (CMP). The present paper will discuss the general integration challenges and key structural reliability issues for chemical mechanical polishing of Cu-interconnects incorporating ULK dielectric materials.

Electrostrictive Strain in Low-Permittivity Dielectrics

A single-beam interferometer capable of resolving displacements on the order of 10−4 A was used to examine the field-induced displacement in several low-permittivity dielectric materials. The experimental principle and procedures of the single-beam interferometer are described in this article. The importance and the accuracy of the Maxwell stress and the thermal stress corrections are also discussed. We present in this article the field-induced strains and the apparent electrostrictive coefficients of several common dielectric materials, including Al2O3, BeO, MgO, AlN ceramics, and SiO2 glass. Under application of an electric field, these common ceramic materials become thicker in the field direction, while glasses and glass-ceramics get thinner. The magnitude of the displacements varies between 10−2 to 10−3 A under 1 MV/m electric field. By comparison, the field-induced displacements in these common electronic materials are approximately 3 to 5 orders of magnitude smaller than those observed in relaxor materials, such as PMN and PVDF, and soft polymers.

Electrostriction measurements on low permittivity dielectric materials

To measure the electrostrictive effects in low permittivity materials, extremely sensitive instrumentation is required. A modified compressometer for resolving fractional changes in capacitance on the order of 10 −6 is used in this work, along with a modified single beam interferometer capable of sub-angstrom resolution in displacement. For the compressometric method, a high sensitivity capacitance bridge, GenRad 1615, is coupled with two lock-in amplifiers to detect attofarad (10 −18F) level capacitance changes caused by in-phase cyclic uniaxial stresses on samples. The interferometer is a Michelson –Morley type instrument modified to detect changes in interference fringe intensity for very small changes in path length. The measurements confirmed by both techniques are used to establish a set of reliable and accurate data of electrostriction coefficients for low permittivity materials. Using these recent data, along with widely accepted data on ferroelectric materials and soft polymers, the linear relationship between electrostriction coefficient (Q) and the ratio of elastic compliance over dielectric permittivity ( s/ε 0ε r) is obtained. This leads to an effective way to predict the electrostriction coefficient in dielectric materials.

Multimode solution for the reflection properties of an open-ended rectangular waveguide radiating into a dielectric half-space: the forward and inverse problems

Open-ended rectangular waveguides are extensively used in nondestructive dielectric material evaluation. The dielectric properties of an infinite-half space of a material are calculated from the measured reflection properties referenced to the waveguide aperture. This calculation relies on a theoretical and numerical derivation of the reflection coefficient likewise referenced to the waveguide aperture. Most of these derivations assume the dominant mode field distribution across the waveguide aperture. However, when dealing with low permittivity and low loss dielectric materials, there may exist significant errors when calculating the dielectric properties from the measured reflection coefficient. These errors have also shown to be more significant in the upper frequency portion of a waveguide band. More accurate results are obtained when higher order modes are considered in addition to the dominant waveguide mode. However, most studies incorporating higher-order modes have used various approximations when calculating the reflection properties and have not provided a full discussion on the influences of dielectric properties of the infinite-half space and the frequency of operation. This paper gives a rigorous and exact formulation in which the dominant mode and the evanescent higher-order modes are used as basis functions to obtain the solution for the reflection coefficient at the waveguide aperture. The analytic formulation uses Fourier analysis in addition to the forcing of the necessary boundary conditions at the waveguide aperture. The solution also readily accounts for the complex contributions of both TE and TM higher-order modes. Finally, the influences of the dielectric properties of the infinite-half space and the frequency of operation are investigated.