High Permittivity Materials Research Articles

Fabrication and Investigation of a Lateral Insulated Gate-Bipolar-Transistor With Ultrafast Turn-Off Speed

A hole-controlled lateral insulated gate bipolar transistor (HC-LIGBT) device with an ultrafast turn-off speed is investigated and experimentally demonstrated. Utilizing a high-permittivity material as the dielectric on the novel device structure, the hole carrier movements are controlled. In the device ON-state, the anode plasma injection effect is amplified to improve the current density. In the OFF-state, the electrons in the drift region are rapidly neutralized by the hole current, after which the anode voltage is pulled to the bus voltage by the external driving circuit through a voltage couple to realize a fast turn-off speed. The ON-state current is not compromised for the switching speed. The device is fabricated with a 1 μm fully custom process using Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> as the dielectric. The test results indicate that the breakdown voltage of the device is 350 V, the ON-state current density is 155 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at an anode voltage of 2 V, and the rising edge of the voltage on the anode in the turn-off state lasts only 90 ns.

Debye Frequency-Extended Waveguide Permittivity Extraction for High Complex Permittivity Materials: Concrete Setting Process Characterization

A waveguide with central frequency 868 MHz is used in the transmission/reflection operation regime to accurately measure the behavior of the complex permittivity of high complex permittivity granular materials, and it has been frequency-extended up to 3 GHz using the Debye fit relaxation model. It is shown that for highly granular high permittivity materials, a waveguide-based transmission/reflection technique is necessary to reduce the uncertainty of the extracted permittivity values. The technique is first described and validated with isopropyl alcohol and then applied to the characterization of cement-based materials. This article provides accurate data on the evolution of the complex permittivity of concrete and mortar from the moment of pouring until air-dried condition is achieved.

Multi-bit dielectric coding metasurface for EM wave manipulation and anomalous reflection.

In this paper, a multi-bit dielectric reflective metasurface is presented for control of electromagnetic (EM) wave scattering and anomalous reflection. The unit cell is designed to act as a 1-, 2-, and 3-bit coding metasurface to attain better control of EM waves. For the 3-bit coding metasurface, the eight digital states have phase responses of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°. The top layer of the proposed metasurface consists of high permittivity material to realize a high Q factor. The proposed multi-bit coding metasurface can reflect the incident EM wave to the desired angle with more than 93% power efficiency. For radar cross section reduction applications, the discrete water cycle algorithm is utilized to obtain an optimal coding matrix for the unit cell arrangement, leading to better diffusion-like scattering, dispersion of the EM wave in all directions, and hence minimal specular reflection. The simulation and experimental results verify that the proposed metasurface is a suitable candidate for control of EM wave scattering and anomalous reflection.

Design and characterization of receive-only surface coil arrays at 3T with integrated solid high permittivity materials

A receive-only surface coil array for 3 Tesla integrating a high-permittivity material (HPM) with a relative permittivity of 660 was designed and constructed and subsequently its performance was evaluated and compared in terms of transmit field efficiency and specific absorption ratio (SAR) during transmission, and signal-to-noise ratio during reception, with a conventional identically-sized surface coil array. Finite-difference time-domain simulations, bench measurements and in-vivo neck imaging on three healthy volunteers were performed using a three-element surface coil array with integrated HPMs placed around the larynx. Simulation results show an increase in local transmit efficiency of the body coil of ~10-15% arising from the presence of the HPM. The receiver efficiency also increased by approximately 15% close to the surface. Phantom experiments confirmed these results. In-vivo scans using identical transmit power resulted in SNR gains throughout the laryngeal area when compared with the conventional surface coil array. In particular specifically around the carotid arteries an average SNR gain of 52% was measured averaged over the three subjects, while in the spine an average of 20% SNR gain was obtained.

Lighting up soft robotics.

A transparent, high-permittivity elastomeric dielectric material shows potential for light-emitting soft robots and stretchable optoelectronics that can self-heal.

Metal/BaTiO3/β-Ga2O3 dielectric heterojunction diode with 5.7 MV/cm breakdown field

Wide and ultrawide bandgap semiconductors can provide excellent performance due to their high energy bandgap, which leads to breakdown electric fields that are more than an order of magnitude higher than conventional silicon electronics. In materials where p-type doping is not available, achieving this high breakdown field in a vertical diode or transistor is very challenging. We propose and demonstrate the use of dielectric heterojunctions that use extreme permittivity materials to achieve a high breakdown field in a unipolar device. We demonstrate the integration of a high permittivity material BaTiO3 with n-type β-Ga2O3 to enable a 5.7 MV/cm average electric field and a 7 MV/cm peak electric field at the device edge while maintaining forward conduction with relatively low on-resistance and voltage loss. The proposed dielectric heterojunction could enable improved design strategies to achieve theoretical device performance limits in wide and ultrawide bandgap semiconductors where bipolar doping is challenging.

Dielectric properties of epoxy–barium titanate composite for 5 GHz microstrip antenna design

To fulfill the demands for robust, compact microstrip antenna for wireless communication, miniaturization is necessary. To achieve this, conventional dielectric microstrip antenna substrate can be replaced with high-permittivity composite dielectric material. Epoxy–barium titanate composite has potential to be used as antenna substrate. This paper focuses on fabrication of epoxy–barium titanate composite at different filler loadings. Then, the permittivity of the composite at G-band frequencies (4–6 GHz) is measured using waveguide technique. The effect of filler concentration to permittivity is observed at 5 GHz, the intended resonant frequency of the antenna. Waveguide technique determines the complex permittivity by analyzing only the measured transmission coefficient of the material, and easily noise affected reflection coefficient is not used. The experimental results show that the permittivity of epoxy–barium titanate increases steadily as the filler volume increases. At the highest filler volume (20%), the permittivity of the composite at 5 GHz is at 6.67. The results obtained are in good agreement with theoretically predicted values.

Experimental evaluation of 3D printed spiral phase plates for enabling an orbital angular momentum multiplexed radio system.

This paper evaluates the performance of three-dimensionally (3D) printed spiral phase plates (SPPs) for enabling an orbital angular momentum (OAM) multiplexed radio system. The design and realization of the SPPs by means of additive manufacturing exploiting a high-permittivity material is described. Modes 1 and 2 SPPs are then evaluated at 15 GHz in terms of 3D complex radiation pattern, mode purity and beam collimation by means of a 3D printed dielectric lens. The results with the lens yield a crosstalk of −8 dB for between modes 1 and −1, and −11.4 dB for between modes 2 and −2. We suggest a mode multiplexer architecture that is expected to further reduce the crosstalk for each mode. An additional loss of 4.2 dB is incurred with the SPPs inserted into the communication link, which is undesirable for obtaining reliable LTE-based communications. Thus, we suggest: using lower loss materials, seeking ways to reduce material interface reflections or alternative ways of OAM multiplexing to realize a viable OAM multiplexed radio system.

Practical approaches to designing and fabricating flat lenses

This work presents two approaches to design and implement three-dimensional (3D) graded index (GRIN) flat lenses consisting of concentric annular segments. Generally, the design of GRIN flat lenses calls for segments with very specific tailored permittivity which makes the realization of the lens challenging. To meet this challenge, each segment of the lens is replaced with a three-layer structure consisting of two materials with a high and a low dielectric constant in such a way that the high permittivity layer is sandwiched between two low permittivity layers. By treating the lens segments as transmission lines and taking the effect of multiple reflections into account, the layer thicknesses are adjusted in such a way that the rays passing through different segments interfere constructively at a focal point. To further improve the focusing performance, a practical design approach is introduced in which each segment of the lens is made of a symmetric seven-layer structure using only two materials (alternating in arrangement) with a high and a low dielectric constant. This design provides the following features: (1) almost all of the incident power passes the lens without considerable reflection, (2) the lens provides a constructive interference of the incident wave at a focal point, and (3) the lens has the potential to be manufactured using available material and technology. Numerical examples are provided in which silica and silicon are utilized as low and high permittivity materials, respectively.

A simulation study on the effect of optimized high permittivity materials on fetal imaging at 3T.

PurposeOne of the main concerns in fetal MRI is the radiofrequency power that is absorbed both by the mother and the fetus. Passive shimming using high permittivity materials in the form of “dielectric pads” has previously been shown to increase the B1+ efficiency and homogeneity in different applications, while reducing the specific absorption rate (SAR). In this work, we study the effect of optimized dielectric pads for 3 pregnant models.MethodsPregnant models in the 3rd, 7th, and 9th months of gestation were used for simulations in a birdcage coil at 3T. Dielectric pads were optimized regions of interest (ROI) using previously developed methods for B1+ efficiency and homogeneity and were designed for 2 ROIs: the entire fetus and the brain of the fetus. The SAR was evaluated in terms of the whole‐body SAR, average SAR in the fetus and amniotic fluid, and maximum 10 g‐averaged SAR in the mother, fetus, and amniotic fluid.ResultsThe optimized dielectric pads increased the transmit efficiency up to 55% and increased the B1+ homogeneity in almost every tested configuration. The B1+‐normalized whole‐body SAR was reduced by more than 31% for all body models. The B1+‐normalized local SAR was reduced in most scenarios by up to 62%.ConclusionSimulations have shown that optimized high permittivity pads can reduce SAR in pregnant subjects at the 3rd, 7th, and 9th month of gestation, while improving the transmit field homogeneity in the fetus. However, significantly more work is required to demonstrate that fetal imaging is safe under standard operating conditions.

Measurement Capability of Scanning Microwave Microscopy: Measurement Sensitivity Versus Accuracy

Here, we investigate the measurement capability of a near-field scanning microwave microscope (SMM) using an atomic force microscope with several types of matching circuits for the characterization of high-permittivity dielectric materials. A fixed impedance matching circuit is generally used in SMM products. In this paper, we propose two types of passive interferometer circuits for the application of SMM systems in laboratories. Both systems are useful for operators without knowledge of microwave measurements; however, they are somewhat limited in their measurement ranges and accuracy when performing high-reflection measurements in the characterization of high-permittivity dielectric materials. Thus, we investigate the stability and the accuracy of SMMs with both setups for measurements on high-permittivity dielectric materials; here, we show that an SMM with an interferometric circuit can achieve a low data distribution and a high-dynamic range, and is, therefore, capable of quantitatively characterizing high-permittivity dielectric materials over frequencies higher than approximately 8 GHz.

Strong interface effect induced high-k property in polymer based ternary composites filled with 2D layered Ti3C2 MXene nanosheets

High permittivity property is hard to achieve in the binary polymer based nanocomposites filled with wide-band-gap semiconductors unless substantial semiconductor fillers are introduced into polymer matrices. The overload of those semiconducting nanofillers usually results in the severe reduction of the mechanical and electric breakdown properties of the composite materials. In this work, the novel ternary polymer based nanocomposites were designed and further fabricated through adding a low concentration of 2D Ti3C2 MXene nanosheets into the binary polymer based nanocomposites containing alpha-SiC nanoparticles. In comparison with the binary composites, these ternary composites could exhibit the notably improved high permittivity properties due to significantly enhanced interface interaction from the introduction of MXene nanosheets. The desirable highly maintained comprehensive electrical properties and mechanical performances have been achieved in those ternary composites. This work might open the door to the large-scale preparation of promising high-permittivity nanocomposite dielectric materials based on building the ternary composite systems.

Design of Transistors Using High-Permittivity Materials

The design and modeling of dielectric superjunction transistors using combinations of ultrahigh permittivity materials and high-mobility materials are described. We show that placing high dielectric permittivity materials in the gate–drain depletion region can reduce electric field variations by screening the field due to depleted charges. This enables simultaneously high sheet charge density and breakdown voltage for scaled field-effect transistors. Using detailed 2-D device simulation of dc and high frequency characteristics, we show that extreme dielectric constant engineering provides unique opportunities for transistor design and has the potential to perform better than state-of-the-art millimeter-wave and terahertz frequency transistors.

Mimicking surface polaritons for unpolarized light with high-permittivity materials

Tailoring near-field optical phenomena often requires excitation of surface plasmon polaritons (SPPs) or surface phonon polaritons (SPhPs), surface waves at the interface between media with electric permittivities of opposite sign. Despite their unprecedented field confinement, surface polaritons are limited by polarization: only transverse magnetic fields enable their excitation, leaving transverse electric fields unexploited. By contrast, guided modes in positive permittivity materials occur for both linear polarizations, however, they typically cannot compete with SPPs and SPhPs in terms of confinement. Here we show that omnipolarization guided modes in materials with high-permittivity resonances can reach confinement factors similar to SPPs and SPhPs, while surpassing them in terms of propagation distance. We explore the cases of silicon carbide and transition-metal dichalcogenides near their permittivity resonances, and compare with SPhPs in silicon carbide and SPPs in silver, at infrared and visible frequencies, respectively.

Disentangling the effects of high permittivity materials on signal optimization and sample noise reduction via ideal current patterns.

To investigate how high-permittivity materials (HPMs) can improve SNR when placed between MR detectors and the imaged body. We used a simulation framework based on dyadic Green's functions to calculate the electromagnetic field inside a uniform dielectric sphere at 7 Tesla, with and without a surrounding layer of HPM. SNR-optimizing (ideal) current patterns were expressed as the sum of signal-optimizing (signal-only) current patterns and dark mode current patterns that minimize sample noise while contributing nothing to signal. We investigated how HPM affects the shape and amplitude of these current patterns, sample noise, and array SNR. Ideal and signal-only current patterns were identical for a central voxel. HPMs introduced a phase shift into these patterns, compensating for signal propagation delay in the HPMs. For an intermediate location within the sphere, dark mode current patterns were present and illustrated the mechanisms by which HPMs can reduce sample noise. High-amplitude signal-only current patterns were observed for HPM configurations that shield the electromagnetic field from the sample. For coil arrays, these configurations corresponded to poor SNR in deep regions but resulted in large SNR gains near the surface due to enhanced fields in the vicinity of the HPM. For very high relative permittivity values, HPM thicknesses corresponding to even multiples of λ/4 resulted in coil SNR gains throughout the sample. HPMs affect both signal sensitivity and sample noise. Lower amplitude signal-only optimal currents corresponded to higher array SNR performance and could guide the design of coils integrated with HPM.

Novel lateral double-diffused MOSFET with folded silicon and high-permittivity dielectric breaking silicon limit

A novel folded-accumulation LDMOS (FALDMOS) employing high-permittivity (HK) material as the partial field dielectric (HK-FALDMOS) is proposed and investigated by simulation. The device features the high-k dielectric partially replacing conventional SiO2 as the field oxide covering partial drift region and the gate electrode extending to the drain electrode. In the ON-state, the majority-carrier accumulation effect of HK-FALDMOS is more intense than that of FALDMOS, which is attributed to the larger capacitance of high-k film with the same dielectric thickness. Besides, a higher doping concentration in drift region I is obtained due to the electric field modulation effect resulting from the employed high-k film, which further reduces the specific on-resistance (Ron,sp) of the drift region I. The breakdown voltage (BV) declines slightly with the increase of permittivity of high-k film. Simulation results show that the proposed HK-FALDMOS has best-in-class Ron,sp-BV performance (9.9 mΩ mm2 with BV of 44.9 V when the relative permittivity of high-k is 8), which breaks the silicon limit of LDMOS.

Cerium doped strontium titanate with stable high permittivity and low dielectric loss

High permittivity materials continue to arouse considerable interest due to their applications in the field of high performance capacitors. However it is still a challenge to make material both with stable high permittivity and low dielectric loss. Here, the Sr1-3x/2CexTiO3 (SCT) ceramics are synthesized via solid-state reaction process and sintering in air. The sample (x = 0.01) exhibits a high permittivity of ∼7000 and low dielectric loss of ∼0.007 at room temperature and 1 kHz. Moreover, the dielectric properties are stable over a very broad temperature and frequency range. Further investigations reveal that the high permittivity is related to the defect chemistry caused by the trace Ce ions doping. The Ti3+ ions substitute the Ti4+ ions lead to the Ti-O octahedral off-center, which make a certain contribution to improve the permittivity. The low dielectric loss is owing to the fact that the defects are more likely to be in the form of defect clusters in the Ce doped SrTiO3 monophase solid solutions. The appropriate defect chemistry design suppresses the dielectric loss relaxation peak of Sr1-xCexTiO3 (x = 0.01) caused by the motion of oxygen vacancies.

Miniaturized VHF/UHF Dual-Band Circularly Polarized Four-Element Sequential-Rotation Array Antenna Based on Alternately Overlapped Bent Radiation-Coupled Dual-L Antenna Elements

This communication presents a novel miniaturized circularly polarized (CP) very high frequency/ultrahigh frequency dual-band four-element sequential-rotation array antenna for SATCOM applications. The dual-band operation is realized by using radiation-coupled dual-L antenna as the array element. Four elements are bent and alternately overlapped in a sequential-rotation manner, which effectively reduces the array antenna’s size while ensures that elements do not touch each other to maintain dual resonance. This results in a compact design which makes better use of the limited space to achieve good performances. Furthermore, since it does not rely on dielectric materials, particularly high permittivity materials, to reduce the resonance length, the proposed array antenna is both lightweight and low cost when compared with conventional miniaturized CP antennas operating at similar frequencies and having close performances. A prototype working at 295/355 MHz is designed, fabricated, and measured, whose weight is 786 g and effective size is $0.197{\lambda } \times 0.197{\lambda } \times 0.068{\lambda }$ at 295 MHz. The measured bandwidth of the main body for active reflection coefficient $\le -9.5$ dB is 5.6 MHz (1.9%) and 7.2 MHz (2%) for the lower and higher bands, respectively. The measured gain, axial ratio, and efficiency of the proposed array antenna are better than 4.5 dBi, 1.15 dB, and 71% within ±2 MHz bandwidth for both bands.

Novel lead – free relaxor ferroelectric based on Mg1−xSrxTiO3 (MTO:Sr) nanostructured for radar absorbing applications

Abstract Novel relaxor ferroelectric based electromagnetic wave shielding at microwave frequency materials, containing Sr doped MgTiO3, were developed and investigated. The structural and morphological characteristics of the products were analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The samples were found to sensitive to Sr doping level and the presence of Sr was confirmed. The optical band gap of pure MgTiO3, 1% Sr doped, 3% Sr doped and 5% Sr doped MgTiO3 was estimated to be 3.75, 4.02, 4.06 and 4.10 eV, respectively. The microwave dielectric properties of Sr-doped MgTiO3 as a function of microwave frequency in the range of 1–20 GHz were examined. With Sr - doping, the microwave dielectric properties of the MgTiO3 is improved considerably. The applicability of as fabricated Sr doped MgTiO3 for electromagnetic wave shielding effectiveness at microwave frequency was studied. The dependence of the polarization of MgTiO3 as a function of Sr content was examined in details. This makes the Sr doped MgTiO3 good candidates for uses as high permittivity materials and it will be versatile for various electromagnetic wave shielding applications at microwave frequency.

Microwave absorbing and shielding properties of inhomogeneous conductors and high-loss dielectrics

Microwave dielectric spectra of the relaxor ferroelectric PbMg1/3Nb2/3O3 single crystals, (Nb + In) co-doped rutile ceramics, inhomogeneous conducting polyaniline pellets, composites of poly(ethylene terephthalate) and multi-walled carbon nanotubes were used for calculation of transmission and reflection spectra of the material slabs in the free space and estimation of absorbing and shielding properties of the materials. Studied high-permittivity high-loss materials with a strong and broad dielectric dispersion in the microwave range were shown to have a high potential for microwave shielding and absorbing applications. Broadband (two decades of frequency) 40 dB shielding and high attenuation constant were demonstrated in the microwave range.