Low-loss Polymer Research Articles

Overcoming Energy Storage-Loss Trade-Offs in Polymer Dielectrics Through the Synergistic Tuning of Electronic Effects in π-Conjugated Polystyrenes.

Achieving high-performance dielectric materials remains a significant challenge due to the inherent trade-offs between high energy storage density and low energy loss. A central difficulty lies in identifying a suitable dipolar unit that can enhance the polarity and dielectric constant of the material while effectively suppressing the high energy losses associated with polarization relaxation, charge injection, and conduction. To address this, a novel strategy is proposed that introduces electron-donating and electron-withdrawing substituents on the benzene ring of polystyrene-based polymers, creating bulky dipole groups that are resistant to reorientation under an electric field. This approach mitigates relaxation losses associated with dipole reorientation and manipulates the band structure via substituent modification to suppress conduction losses. Additionally, the deformation of the π-electron cloud under an electric field enhances the dielectric constant and energy storage density. Ultimately, the optimized chlorostyrene-methyl methacrylate (MMA) copolymer exhibits an 85% discharge efficiency and an energy storage density of 18.3 J cm- 3, nearly three times that of styrene-based copolymers under the same conditions. This study introduces a new approach for designing high-energy density, low-loss polymer dielectric materials by precisely controlling electron-donating and electron-withdrawing effects to modulate the distribution of π-conjugated electron clouds.

Designing a terahertz optical sensor based on helically twisted photonic crystal fiber for toxic gas sensing

A novel helically twisted photonic crystal fiber (PCF) is designed and proposed for sensing toxic gases with refractive indices ranging from 1.00 to 1.08. The PCF consists of twelve hollow pipes arranged circularly around the hollow core to support THz radiation propagation. Low-loss polymer Topas is used as the background material of cladding. The fiber is twisted 360° over 50 cm to enhance anti-resonance in the THz region. The fundamental LP01 mode is analyzed using the finite-difference eigenmode (FDE) method. The sensor operates across four frequency bands (0.2 to 3.0 THz) with minimal transmission loss (~ 10⁻⁴ 1/cm). Key parameters such as refractive index sensitivity, relative sensitivity, resolution, and figure of merit (FOM) are evaluated. The average refractive index sensitivities are 1450, 2250, 3000, and 2550 for Bands 1 to 4, respectively, with 100% relative sensitivity across all bands. The sensor detects refractive index changes as small as 10⁻⁴. The FOM, defined as the inverse of the full width at half maximum, exceeds 30 1/RIU, reaching up to 250 1/RIU due to sharp resonance peaks. Compared to other THz sensors, this design offers enhanced performance in sensing gases like SOx, NOx, and CO, while maintaining a simple structure.

LCP-Based Low-Cost Base Station Antenna for 3.7 GHz 5G Band

This paper presents a large-scale base station antenna assembly structure that is low-cost, reliable, and easy to manufacture. The antenna element is composed of a low-loss liquid crystal polymer based on a plastic molded module and a modified wideband stacked patch antenna. The base station antenna consists of a 4 × 8 antenna module, with each module comprising 3 × 1 subarrays along with dual-polarized antenna elements. The antenna element achieved an efficiency of 91% and an impedance bandwidth of 1.14 GHz within a height of 10 mm at 3.7 GHz. Furthermore, the fabricated array antenna structure was tested and verified to have an effective isotropic radiated power of 75.6 dBm at boresight and a steering range of less than ±60°. Therefore, the proposed structure meets the required antenna and beam-forming performance for commercial 5G active antenna systems.

Self-Assembled MXene@Fluorographene Hybrid for High Dielectric Constant and Low Loss Ferroelectric Polymer Composite Films.

Modern electrical applications urgently need flexible polymer films with a high dielectric constant (εr) and low loss. Recently, the MXene-filled percolative composite has emerged as a potential material choice because of the promised high εr. Nevertheless, the typically accompanied high dielectric loss hinders its applications. Herein, a facile and effective surface modification strategy of cladding Ti3C2Tx MXene (T = F or O; FMX) with fluorographene (FG) via self-assembly is proposed. The obtained FMX@FG hybrid yields high εr (up to 108 @1 kHz) and low loss (loss tangent tan δ = 1.16 @ 1 kHz) in a ferroelectric polymer composite at a low loading level (the equivalent of 1.5 wt % FMX), which is superior to its counterparts in our work (e.g., FMX: εr = 104, tan δ = 10.71) and other studies. It is found that the FG layer outside FMX plays a critical role in both the high dielectric constant and low loss from experimental characterizations and finite element simulations. For one thing, FG with a high F/C ratio would induce a favorable structure of high β-phase crystallinity, extensive microcapacitor networks, and abundant interfacial dipoles in polymer composites that account for the high εr. For another, FG, as a highly insulating layer, can inhibit the formation of conductive networks and inter-FMX electron tunneling, which is responsible for conduction loss. The results demonstrate the potential of a self-assembled FMX@FG hybrid for high εr and low loss polymer composite films and offer a new strategy for designing advanced polymer composite dielectrics.

Overcoming oxygen inhibition in UV photolithography for the fabrication of low-loss polymer waveguides.

Perfluorinated acrylate polymer materials exhibit low absorption loss at 1310 and 1550 nm, but molecular oxygen inhibits their photocuring. We propose a novel, to our knowledge, UV photolithography method incorporating a pre-exposure process for fabricating low-loss perfluorinated acrylate polymer waveguides. During the pre-exposure process, a partially cured thin layer forms on the core layer, effectively overcoming oxygen inhibition in subsequent lithography. Furthermore, the functional group contents of the polymerized materials were characterized by a Raman spectrometer to analyze the development reaction under the pre-exposure layer. Utilizing this improved method, we fabricated a straight waveguide with a length of 21 cm. The experiments showed that the propagation losses are 0.14 dB/cm at 1310 nm and 0.51 dB/cm at 1550 nm. The inter-channel cross talk for a core pitch of 250 µm was measured as low as -49 dB at 1310 nm. Error-free NRZ data transmission over this waveguide at 25 Gb/s was achieved, showcasing the potential in optical interconnect and communication applications.

High Speed Transmission Characteristics on Glass Interposer for High Performance Computing

Electronic product becomes smaller and lighter with an increasing number of functions. The demand for high density and high integration becomes stronger. Interposers for system in package will became more and more important for advanced electronic systems. Silicon interposers with through silicon vias (TSV) and back end of line (BEOL) wiring offer compelling benefits for 2.5D and 3D system integration; however, they are limited by high cost and high electrical loss. On the other hand, glass has many properties that make it an ideal substrate for interposer substrates such as; ultra high resistivity, adjustable thermal expansion (CTE) and manufacturability with large panel size. Furthermore, glass via formation capabilities have dramatically improved over the past several years. Fully populated wafers with >100,000 through holes (50 micron diameter) are fabricated today with 300 micron thick glass. The application of glass interposer for highly integrated module requires ultra-low loss transmission characteristics as substrate material, we will build interposers with fine pitch TQVs(Through Quartz Vias) with metallization coupled with double sided routing distribution layers utilizing low loss dielectric polymer layers. This paper firstly reports high frequency characteristics of Fused Quartz Glass as core substrate for glass interposer. The basic structure will consist of coplanar waveguide (CPW) on top of a quartz substrate with TQVs connecting top to the bottom side of the circuit. In next section, measurement result of insertion loss using low loss polymer dielectrics on transmission line structure. We also demonstrate fine pitch line and space under 2um wiring on Glass. Insertion loss of ultra fine transmission lines measured by vector network analyzer. The modeling result of eye diagram discussed for 2.1D high speed applications.

Analysis and characterization of electro-optic coefficient for multi-layer polymers: dependence on measurement wavelengths.

We report a significant improvement in the measurement accuracy of electro-optic (EO) coefficients for low-loss EO polymers on substrates of sol-gel silica and indium tin oxide (ITO). Initially, we apply the standard Teng and Man reflection ellipsometric method, which results in substantial variability in the measured EO coefficients across a wavelength spectrum with changes as small as <1 nm. This variance leads to unreliable EO coefficient values ranging from a few to 70 pm/V at the 1.31 and 1.55 µm wavelengths. By adopting a transmission method for our experiments, we effectively mitigate the dependence of the measured EO coefficient on the wavelength variance of 0.2 nm. As a result, this new approach enables a more accurate and reliable measurement of the EO coefficients. This breakthrough presents a significant step forward in the field of EO research, paving the way for further exploration into the behavior and properties of EO polymers. Additionally, our findings highlight the importance of selecting an appropriate measurement method in accordance with the unique properties of the material under investigation.

Optimization of the interlayer distance for low-loss and low-crosstalk double-layer polymer optical waveguides.

The interlayer distance optimized for low-loss and low-crosstalk double-layer polymer optical waveguides was investigated to enhance their transmission performance. Simulations were conducted to determine the minimal interlayer distances for double-layer optical waveguides with different core sizes. An optimal interlayer distance of 24 µm was identified for a 20 µm × 20 µm double-layer waveguide, which ensured interlayer crosstalk below -30 dB when roughness remained under 80 nm. The double-layer waveguides were fabricated employing ultraviolet lithography combined with the overlay alignment method. Based on experimental optimization, the important fabrication parameters were optimized, such as a plasma treatment time of 10 s, a core exposure dose of 500 mJ/cm2, and a cladding exposure dose of 240 mJ/cm2. Additionally, the fabricated double-layer waveguides, with an interlayer distance of 24.5 µm, exhibited low transmission losses of less than 0.25 dB/cm at 850 nm and 0.40 dB/cm at 1310 nm, respectively. The low interlayer crosstalk values were less than -52 dB at 850 nm and -60 dB at 1310 nm, respectively. The agreement between the experimental results and the simulation findings indicates that this method offers a promising approach for fabricating double-layer waveguides with good performances.

D-Band Integrated and Miniaturized Quasi-Yagi Antenna Array in Glass Interposer

An integrated and miniaturized D-band quasi Yagi antenna in glass interposer is presented. Single element, 1×2 and 1×4 test coupons are fabricated on 100-μm glass substrate with low-loss polymer buildup films and the return loss, gain and radiation pattern of the antennas are characterized. The proposed antenna utilizes a monopole radiator to achieve a higher bandwidth. Advantages of the glass substrate for beyond 5G communications in terms of enabling fine features and compact integration of other active and passive devices through chip embedding is discussed. An analysis of the substrate modes to ensure proper mode propagation in the selected stack-up is presented. Furthermore, the paper discusses the challenges in planar antenna measurements in sub-THz frequencies and it presents two measurement setups to overcome these challenges. The first is a low-cost probe-station-based measurement setup to characterize the return loss and boresight gain, and the second is a diode-detector-based setup to measure the normalized radiation pattern. The proposed antennas achieve high bandwidth covering the frequency range of 110-170 GHz, and 4.78 dBi, 8.41 dBi, and 11.04 dBi gain for the single element, 1×2 and 1×4 array, respectively.

Low Loss Vertical TiO2/Polymer Hybrid Nano-Waveguides.

This article proposes a novel demonstration of a low-loss polymer channel hybridized with a titania core leading to a nano-waveguide elongated in the normal direction to the substrate. It is aimed at using the quasi-transverse magnetic (TM) mode as the predominant mode in compact photonic circuitry. A detailed design analysis shows how a thin layer of a higher-refractive index material in a trench within the core of the waveguide can increase the confinement and reduce the propagation losses. This thin layer, produced by atomic layer deposition, covers the entire polymer structure in a conformal manner, ensuring both a reduction of the surface roughness and a stronger field confinement. The trench can be made at any place within the polymer channel and therefore its position can be tuned to obtain asymmetric modal distribution. The waveguide is demonstrated at telecom wavelengths, although the material's properties enable operation over a large part of the electromagnetic spectrum. We measured propagation losses as low as 1.75 ± 0.32 dB/cm in a 200 nm × 900 nm section of the waveguide core. All processes being mass-production compatible, this study opens a path towards easier integrated-component manufacture.

Planarized THz quantum cascade lasers for broadband coherent photonics

Recently, there has been a growing interest in integrated THz photonics for various applications in communications, spectroscopy and sensing. We present a new integrated photonic platform based on active and passive elements integrated in a double-metal, high-confinement waveguide layout planarized with a low-loss polymer. An extended top metallization keeps waveguide losses low while improving dispersion, thermal and RF properties, as it enables to decouple the design of THz and microwave cavities. Free-running on-chip quantum cascade laser combs spanning 800 GHz, harmonic states with over 1.1 THz bandwidth and RF-injected broadband incoherent states spanning over nearly 1.6 THz are observed using a homogeneous quantum-cascade active core. With a strong external RF drive, actively mode-locked pulses as short as 4.4 ps can be produced, as measured by SWIFTS. We demonstrate as well passive waveguides with low insertion loss, enabling the tuning of the laser cavity boundary conditions and the co-integration of active and passive elements on the same THz photonic chip.

Ultra-broadband LP11 mode converter with high purity based on long-period fiber grating and an integrated Y-junction.

We report an ultra-broadband LP11 mode converter with high purity based on integrated two shunt-wound long-period fiber gratings (LPFGs) and an adiabatic Y-junction, together with a high-order-mode bandpass filter. Two shunt-wound LPFGs are inscribed by CO2 laser in a two-mode fiber to achieve a 10 dB bandwidth of 50 nm and 51 nm at resonance wavelengths of 1530 nm and 1570 nm, respectively. Meanwhile, the Y-junction fabricated by lithography can be operated over S + C+L band to combine the converted LP11 mode. The presented ultra-broadband mode converter is able to achieve a mode conversion efficiency of 95%, together with a wavelength-dependent loss of less than 3 dB over the S + C+L band. This device has low modal crosstalk of 17 dB between the LP01 and LP11 modes, because most of the residual LP01 mode is further filtered by a high-order-mode bandpass filter at the output port of the Y-junction. The insertion loss of mode converter is estimated to be lower than 2.7 dB, due to the use of low loss polymer material during the fabrication. The proposed ultra-broadband LP11 mode converter with high purity is promising for the application of ultra-broadband mode-division-multiplexing transmission systems.

Customizing MRI-Compatible Multifunctional Neural Interfaces through Fiber Drawing.

Fiber drawing enables scalable fabrication of multifunctional flexible fibers that integrate electrical, optical and microfluidic modalities to record and modulate neural activity. Constraints on thermomechanical properties of materials, however, have prevented integrated drawing of metal electrodes with low-loss polymer waveguides for concurrent electrical recording and optical neuromodulation. Here we introduce two fabrication approaches: (1) an iterative thermal drawing with a soft, low melting temperature (Tm) metal indium, and (2) a metal convergence drawing with traditionally non-drawable high Tm metal tungsten. Both approaches deliver multifunctional flexible neural interfaces with low-impedance metallic electrodes and low-loss waveguides, capable of recording optically-evoked and spontaneous neural activity in mice over several weeks. We couple these fibers with a light-weight mechanical microdrive (1g) that enables depth-specific interrogation of neural circuits in mice following chronic implantation. Finally, we demonstrate the compatibility of these fibers with magnetic resonance imaging (MRI) and apply them to visualize the delivery of chemical payloads through the integrated channels in real time. Together, these advances expand the domains of application of the fiber-based neural probes in neuroscience and neuroengineering.

Silacyclobutane‐functionalized cyclosiloxanes as photoactive precursors for high thermal stability, low dielectric constant and low dielectric loss polymers

AbstractLow dielectric photoactive materials have significant potential as components in future microelectronics. Although a number of photosensitive groups have been used to construct photopatternable materials, it remains challenging to introduce these groups into polymer chains via facile yet controlled polymerization techniques. The present work demonstrates the synthesis of a new class of photoactive cyclosiloxane monomers having hybrid siloxane‐carbosilane main chains. These compounds can be cured by applying ultraviolet radiation and heat to promote the reaction of the silacyclobutene units and form hyper‐cross‐linked cyclosiloxanes. The cured resins show high thermal stability (with T5% values in the range of 460–550°C), low dielectric constants (2.36–2.76 at 10 MHz) and low dielectric losses (10−3 at 10 MHz). Thus, these polymers could possibly be used as high‐performance dielectric materials.

Real-time ultrasound sensing with a mode-optimized photonic crystal slab.

Integrated photonic sensors can provide large scale, flexible detection schemes. Photonic crystal slabs (PCSs) offer a miniaturized platform for wideband, sensitive ultrasound detection by exploiting the photoelastic effect in water. However, poor modal overlap with the sensing medium and non-negligible absorption loss of the aqueous medium have previously limited PCS sensor performance. In this study, we detail the development and optimization of a PCS-based acoustic sensor by adding to it a low-loss high-index polymer cladding layer. Exploiting a mode-optimized TM-like optical resonance present in a PCS, with high bulk index sensitivity (>600nm/RIU) and quality factor Q (>8000), we demonstrate real-time ultrasound sensing at a noise equivalent pressure of 170 Pa (1.9Pa/Hz). The PCS sensor is backside-coupled to an optical fiber, which, along with its intensity-based ultrasound-sensing architecture, will allow us to scale up easily to a 2D array. This work paves the way to a sensitive compact ultrasound detector for photoacoustic-based diagnostics and monitoring of tissue.

Ultra-Compact Low Loss Polymer Wavelength (De)Multiplexer With Spot-Size Convertor Using Topology Optimization

Polymer waveguides are considered to be good candidates for optical interconnects application due to their advantages such as flexibility, good compatibility, and versatility for realizing 3D and micro structures. However, constrained by the limited degrees of freedom provided by template-based design approaches, there lacks a satisfying solution which achieves small footprint and low loss simultaneously. Inverse design has been proposed to improve the performance. However, most inverse design methods target at silicon-based optical devices optimization which has a relatively high refractive index difference. In this paper, we demonstrate an ultra-compact low loss polymer wavelength (de)multiplexer with spot-size conversion structure to interposing Si and optical fiber using gradient-based topology optimization and downhill simplex method. The 2-channel wavelength (de)multiplexer displays an excess propagation loss of 0.84 dB and 1.06 dB at 1310 nm and 1550 nm, respectively, with a total footprint of 245 × 35 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The 4-channel wavelength (de)multiplexer for coarse wavelength division multiplexing applications with 20 nm spacing (1270, 1290, 1310, and 1330 nm) with an excess waveguide propagation loss of 1.72 dB within 271 × 50 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> has also been demonstrated and all the output ports of the polymer wavelength demultiplexing structure achieved a conversion efficiency over 90%.

Correlating Charge-Transfer State Lifetimes with Material Energetics in Polymer:Non-Fullerene Acceptor Organic Solar Cells.

Minimizing the energy offset between the lowest exciton and charge-transfer (CT) states is a widely employed strategy to suppress the energy loss (Eg/q - VOC) in polymer:non-fullerene acceptor (NFA) organic solar cells (OSCs). In this work, transient absorption spectroscopy is employed to determine CT state lifetimes in a series of low energy loss polymer:NFA blends. The CT state lifetime is observed to show an inverse energy gap law dependence and decreases as the energy loss is reduced. This behavior is assigned to increased mixing/hybridization between these CT states and shorter-lived singlet excitons of the lower gap component as the energy offset ΔECT-S1 is reduced. This study highlights how achieving longer exciton and CT state lifetimes has the potential for further enhancement of OSC efficiencies.

Low loss single-mode polymer optical waveguide with circular cores

We experimentally demonstrate that the Mosquito method is capable of fabricating single-mode polymer optical waveguides with multiple cores while maintaining an identical mode-field diameter among them. The Mosquito method we developed is a technique to form circular cores in polymer waveguides using a commercially available microdispenser and multi-axis syringe scanning robot. However, the core shape tends to deteriorate from a circle because of the monomer flow due to the needle scan. We also demonstrate both theoretically and experimentally for the first time in this paper that the needles with a tapered outer form or just titled straight needles enable to form cores with a high circularity even if those cores are dispensed on any heights from the substrate surface.

Toward enhancing dielectric properties and thermal conductivity of f-Cu/PVDF with PS as an interlayer

ABSTRACT Flaky Cu (f-Cu) particles with surface modification by polystyrene (PS) coating layer were incorporated into poly(vinylidene fluoride) (PVDF), to obtain high dielectric constant (k) and thermal conductivity (TC) but low dielectric loss polymer composites. The results confirm the formation of a layer PS shell outside of the f-Cu, and indicate that the PVDF composites with f-Cu@PS particles exhibit superior dielectric properties compared with pristine f-Cu/PVDF. The improved dielectric performance can be attributed to the insulating PS interlayer preventing the f-Cu from direct contact with each other and meanwhile hindering the long-range electron migration. The dielectric properties of composites can be tuned through finely tailoring the PS shell’ thickness. Additionally, the f-Cu@PS/PVDF composites display slightly higher TC than the raw f-Cu/PVDF, owing to the suppressed thermal interfacial resistance and improved interfacial compatibility between the fillers and matrix. The obtained f-Cu@PS/PVDF composites with enhanced high-k and TC but low loss are promising materials for potential applications in microelectronic and electrical industries.

Quasi-Optical Characterization of Low-Loss Polymers at 300 GHz for Vacuum Window Applications

We report on the measurements of the complex refractive index of a number of low-loss polymers using a quasi-optical vector network analyzer operating in the frequency range of 210–370 GHz. The process of extracting both the real and imaginary parts of the refractive indexes is presented in this article, along with the method of error estimation. The measured refractive indexes of 25 different material samples, as well as the estimated error and the loss tangents of thicker samples, are tabulated. For selected materials, loss tangents have also been confirmed using the method of intersecting lines, which measures the additional input noise to a superconductor–insulator–superconductor receiver due to the dielectric sample. The data obtained from this work will be useful for the design of low-loss vacuum windows for cryogenic receivers operating in the 300-GHz range.