Top Conductor Research Articles

Highly Miniaturized Self-Quadruplexing Antenna Based on Substrate-Integrated Rectangular Cavity

This letter introduces a novel self-quadruplexing antenna (SQA) architecture using a substrate-integrated rectangular cavity (SIRC) for compact size, wide-frequency redesignability, and high isolation responses. The proposed SQA is developed by engraving two U-shaped slots (USSs) on the top conductor of the SIRC. The USSs are excited by employing four microstrip feedlines to achieve SQA characteristics. The operating frequencies can be tuned independently according to the assumed targets, with a wide tuning range from 2.3 to 7 GHz. The dimensions of USSs are meticulously chosen to achieve high isolation and compact size. An equivalent circuit is suggested to validate the proposed SQA. Finally, the SQA operating at 2.33, 2.96, 5.43, and 6.15 GHz is fabricated and validated. As compared to the earlier SQAs, the proposed antenna offers competitive performance with a compact size of 0.124λ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (45.6% smaller than the most compact SQA reported in the literature), high isolation of 32.5 dB, and a wide tunable range from 2.3 to 7 GHz. Its measured gain is 4.31, 3.39, 6.12, and 4.34dBi at 2.33, 2.96, 5.43, and 6.15 GHz, respectively.

Interactive deformable electroluminescent devices enabled by an adaptable hydrogel system with optical/photothermal/mechanical tunability.

Deformable electroluminescent devices (DELDs) with mechanical adaptability are promising for new applications in smart soft electronics. However, current DELDs still present some limitations, including having stimuli-insensitive electroluminescence (EL), untunable mechanical properties, and a lack of versatile stimuli response properties. Herein, a facile approach for fabricating in situ interactive and multi-stimuli responsive DELDs with optical/photothermal/mechanical tunability was proposed. A polyvinyl alcohol (PVA)/polydopamine (PDA)/graphene oxide (GO) adaptable hydrogel exhibiting optical/photothermal/mechanical tunability was used as the top ionic conductor (TIC). The TIC can transform from a viscoelastic state to an elastic state via a special freezing-salting out-rehydration (FSR) process. Meanwhile, it endows the DELDs with a photothermal response and thickness-dependent light shielding properties, allowing them to dynamically demonstrate "on" or "off" or "gradually change" EL response to various mechanical/photothermal stimuli. Thereafter, the DELDs with a viscoelastic TIC can be utilized as pressure-responsive EL devices and laser-engravable EL devices. The DELDs with an elastic TIC can withstand both linear and out-of-plane deformation, enabling the designs of various interactive EL devices/sensors to monitor linear sliders, human finger bending, and pneumatically controllable bulging. This work offers new opportunities for developing next-generation EL-responsive devices with widespread application based on adaptable hydrogel systems.

Flexible and Polarization Independent Miniaturized Double-Band/Broadband Tunable Metamaterial Terahertz Filter.

In this paper, the design of a double-band terahertz metamaterial filter with broadband characteristics using a single conducting layer is presented. The design uses a structured top metallic layer over a polyimide material. The proposed design has achieved broadband band-pass transmission characteristics at the resonances of 0.5 THz and 1.65 THz, respectively. The 3-dB bandwidths for these two resonances are 350 GHz and 700 GHz, respectively, which indicates that dual-band resonance with broadband transmission characteristics was obtained. The design has achieved the same transmission characteristics for two different orthogonal polarizations, which was confirmed using numerical simulation. The design was tested for a different angle of incidences and it was observed that this results in angle-independent transmission behavior. In addition, for obtaining tunable resonant behavior, the top conductor layer was replaced by graphene material and a silicon substrate was added below the polymer layer. By varying the Fermi level of graphene, modulation in amplitude and phase was observed in numerical simulation. The physical mechanism of double-band behavior was further confirmed by surface current distribution. The proposed design is simple to fabricate, compact, i.e., the size is λ0/8, and obtained dual-band/broadband operation.

Wideband compact phase shifter based on hybrid half-mode substrate integrated waveguide and spoof surface plasmon polariton

This paper proposes a wideband compact equal-length phase shifter based on the hybrid half-mode substrate integrated waveguide (HMSIW) and spoof surface plasmon polariton (SSPP) concept for the first time. The HMSIW transmission lines (TLs) with different widths result in different propagation constants. The difference of propagation constants between two HMSIW TLs with two different widths decreases as the frequency increases. Therefore, a wideband phase shifter cannot be designed by using this technique. In this paper, a series of half-butterfly grooves are etched on the top conductor layer of the HMSIW TL to compensate the phase shift. The combination of the SSPP and HMSIW structures provides a higher degree of freedom to keep the propagation constants difference constantly. Accordingly, a wideband response can be achieved by properly tuning the structure. Here, the dispersion characteristic of the butterfly-shaped HMSIW-SSPP can be adjusted by changing the width of the HMSIW and the radius and angle of the half-butterfly grooves. Moreover, the HMSIW-SSPP structure with half-butterfly grooves reduces both longitudinal and transverse dimensions of the proposed circuit. It has more slow-wave effects than the traditional counterpart with rectangular grooves. To validate the concept, a phase shifter is designed and fabricated on a single-layer substrate at the center frequency of 5.8 GHz covering WLAN. The simulated and measured results are in good agreement. The measured results show that the phase shifter has a fractional bandwidth of 31.7% with a phase error of , an insertion of dB, and a return loss of higher than 13.8 dB. Also, the size of the proposed phase shifter is .

Hybrid‐type stretchable interconnects with double‐layered liquid metal‐on‐polyimide serpentine structure

We demonstrate a new double-layer structure for stretchable interconnects, where the top surface of a serpentine polyimide support is coated with a thin eutectic gallium–indium liquid metal layer. Because the liquid metal layer is constantly fixed on the solid serpentine body in this liquid-on-solid structure, the overall stretching is accomplished by widening the solid frame itself, with little variation in the total length and cross-sectional area of the current path. Therefore, we can achieve both invariant resistance and infinite fatigue life by combining the stretchable configuration of the underlying body with the freely deformable nature of the top liquid conductor. Further, we fabricated various types of double-layer interconnects as narrow as 10 μm using the roll-painting and lift-off patterning technique based on conventional photolithography and quantitatively validated their beneficial properties. The new interconnecting structure is expected to be widely used in applications requiring high-performance and high-density stretchable circuits owing to its superior reliability and capability to be monolithically integrated with thin-film devices.

Investigation of on-chip integrated inductors fabricated in SOI-MUMPs for RF MEMS ICs

This paper presents for the first time implementation of zig–zag and solenoidal on-chip inductors in standard and cost effective SOI-MUMPs fabrication process. The solenoidal inductor offers high Q-factor and inductance as compared to planar zig–zag inductor. Bonding wires are used to construct the top conductor loop of the solenoidal inductor. The inductors are also characterized at elevated temperature for performance investigation in harsh environment. The mechanical resonance frequency of the inductors are characterized using the Finite element software COMSOL. The inductors are characterized using a vector network analyzer from 60 MHz to 3 GHz, and the results of both inductors are compared. The total size of the device is 2 × 0.7 mm2.

Electrostatic Supercapacitors by Atomic Layer Deposition on Nanoporous Anodic Alumina Templates for Environmentally Sustainable Energy Storage

In this work, the entire manufacturing process of electrostatic supercapacitors using the atomic layer deposition (ALD) technique combined with the employment of nanoporous anodic alumina templates as starting substrates is reported. The structure of a usual electrostatic capacitor, which comprises a top conductor electrode/the insulating dielectric layer/and bottom conductor electrode (C/D/C), has been reduced to nanoscale size by depositing layer by layer the required materials over patterned nanoporous anodic alumina membranes (NAAMs) by employing the ALD technique. A thin layer of aluminum-doped zinc oxide, with 3 nm in thickness, is used as both the top and bottom electrodes’ material. Two dielectric materials were tested; on the one hand, a triple-layer made by a successive combination of 3 nm each layers of silicon dioxide/titanium dioxide/silicon dioxide and on the other hand, a simple layer of alumina, both with 9 nm in total thickness. The electrical properties of these capacitors are studied, such as the impedance and capacitance dependences on the AC frequency regime (up to 10 MHz) or capacitance (180 nF/cm2) on the DC regime. High breakdown voltage values of 60 V along with low leakage currents (0.4 μA/cm2) are also measured from DC charge/discharge RC circuits to determine the main features of the capacitors behavior integrated in a real circuit.

140 GHz Frequency Selective Surface Based on Hexagon Substrate Integrated Waveguide Cavity Using Normal PCB Process

A frequency selective surface (FSS) based on hexagon substrate integrated waveguide (HSIW) technology is proposed in this letter and designed at the center frequency of 140 GHz. The periodic element comprises a HSIW cavity and two circular slots etched on the top and bottom conductor claddings of the cavity. Based on the hexagon cavity, this type of FSS has a better polarization stability and a closer element arrangement compared with square cavity FSS and circular cavity FSS, respectively. Besides, circular slots are better than polygonal slots which have round corners at their corners when fabricated using normal printed circuit board process. Thus, the HSIW FSS can achieve a good and stable performance at terahertz band. The proposed structure is fabricated and the measured result has a good agreement with the simulated one.

Double Dielectric Slab-Loaded Air-Filled SIW Phase Shifters for High-Performance Millimeter-Wave Integration

Phase shifters based on double dielectric slab-loaded air-filled substrate-integrated waveguide (SIW) are proposed for high-performance applications at millimeter-wave frequencies. The three-layered air-filled SIW, made of a low-cost multilayer printed circuit board process, allows for substantial loss reduction and power handling capability enhancement compared with the conventional dielectric-filled counterpart. It is of particular interest for millimeter-wave applications that generally require low-loss transmission and high-density power handling. Its top and bottom layers may make use of a low-cost standard substrate, such as FR-4, on which baseband analog or digital circuits can be implemented so to obtain very compact, low cost, and self-packaged millimeter-wave integrated systems compared with the systems based on rectangular waveguide while achieving higher performance than the systems based on the conventional SIW. In this paper, it is demonstrated that transmission loss can be further improved at millimeter-wave frequencies with an additional polishing of the top and bottom conductor surfaces. Over Ka-band, an improvement of average 1.56 dB/m is experimentally demonstrated. Using the air-filled SIW fabrication process, dielectric slabs can be implemented along conductive via rows without any additional process. Based on the propagation properties of the obtained double dielectric slab-loaded air-filled SIW, phase shifters are proposed. To obtain a broadband response, an equal-length compensated phase shifter made of two air-filled SIW structures, offering a reverse varying propagation constant difference against frequency, is proposed and demonstrated at Ka-band. Finally, a single dielectric slab phase shifter is investigated for comparison and its bandwidth limitation is highlighted.

Frequency Selective Surface With Miniaturized Elements Based on Quarter-Mode Substrate Integrated Waveguide Cavity With Two Poles

A frequency selective surface (FSS) with miniaturized elements based on a quarter-mode substrate integrated waveguide (QMSIW) is proposed and investigated in this paper. The periodic element includes the QMSIW cavity and two L-type slots etched on the top and bottom conductor claddings of the cavity. The slot not only performs as the equivalent magnetic wall of the QMSIW FSS element but also provides a pole near the resonant frequency of the QMSIW cavity to improve the passband characteristics of the FSS. In this case, the size of the conventional FSS element can be reduced by 65% at the same operation frequency while keeping a similar performance. Based on this miniaturized element, the frequency interval between the passband and the first parasitic passband can increase 2.7 times compared with that of a conventional SIW FSS. As an example, an X-band QMSIW FSS is designed, fabricated, and measured. Besides, it is insensitive to the incident angle and polarization of the incident wave. Such a miniaturized FSS element can also be employed in the design of a multiband FSS with controllable transmission zeroes.

A -Band Packaged Antenna on Organic Substrate With High Fault Tolerance for Mass Production

A grid array antenna working around 145 GHz is proposed in this paper. The antenna is built on liquid crystal polymer (LCP) and designed for the $D$ -band antenna-in-package application. The intrinsic softness of the LCP material is a limiting factor of the antenna’s aperture size. A 0.5-mm-thick copper core is used to compensate. By doing this, the rigidness of the antenna is effectively improved, compared with an antenna without the copper core. Wet etching is used to realize the patterns on the top and bottom conductor. Compared with a low-temperature cofired ceramic counterpart, we obtain a considerable cost reduction with acceptable performance. The proposed antenna has an impedance bandwidth of 136–157 GHz, a maximum gain of 14.5 dBi at 146 GHz, and vertical beams in the broadside direction between 141 and 149 GHz. The fabrication procedures of the antennas are introduced, and a parametric study is carried out, which shows the antenna’s robustness against fabrication tolerances, such as the not-well-controlled etching rate and the substrate surface roughness. This makes the antenna a promising solution for mass production.

WIDEBAND FREQUENCY SELECTIVE SURFACE WITH A SHARP BAND EDGE BASED ON MUSHROOM-LIKE CAVITY

A wideband frequency selective surface (FSS) with a sharp band edge is proposed. The periodic cell includes a mushroom-like cavity and four L-type slots etched on the top and bottom conductor claddings of the cavity. The measured results show that the proposed FSS operates at X band with a 12.5% bandwidth (7.85-8.90 GHz), in which the insertion loss is less than 3 dB. Comparing with the FSSs based on substrate integrated waveguide cavity, the proposed FSS not only realizes high selectivity, but also realizes a 55.8% reduction in cell size.

Electrohydrodynamic Direct-Write Multi-Layer Micro Circuit on Flexible Substrate

Electrohydrodynamic Direct-Writing (EDW) provides a simple and rapid way to print micro/nanostructures from viscoelastic solution, which meets the demand in the development of all-printed organic electronics. Overlapped printing of different functional materials to build up multi-layer devices displays excellent advantages in the flexible electron. The 3D multi-layer devices as well as flat interconnection can be fabricated on the flexible substrate directly via EDW technology. The technology of EDW utilized stable charged jet to print orderly conductive and insulator micro/nanostructure. Silver ink is used to print conductor connection, and polyvinylpyrrolidone (PVP) solution is used to fabricate insulator layer. Multi-layer interconnection can be printed layer by layer on the polyimide (PI) flexible insulator substrate. The resistance of top and bottom conductor connection was 6.1Ω and 5.9Ω, respectively. The insulator layer demonstrated excellent insulation characteristics between the bottom and top silver interconnection.

Ultrawide band CBCPW to stripline vertical transition in multilayer LCP substrates

This article presents an improved design of conductor-backed coplanar waveguide (CBCPW)-to-stripline (SL) vertical transition in multilayer liquid crystal polymer substrates. The CBCPW and SL is designed on the top and second conductor layers, respectively, and electrically connected with each other through micro-vias. The reported transition is optimized using High Frequency Simulation Software, and the simulated results predict low loss over an ultrawide bandwidth. To validate our design, a CBCPW-to-SL-to-CBCPW transition was fabricated and characterized. The back-to-back transition shows an insertion loss of less than 2.5 dB and a return loss of less than −10 dB over a frequency band from DC to 78 GHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1481–1484, 2015

Electrohydrodynamic direct—writing of conductor—insulator-conductor multi-layer interconnection

A multi-layer interconnection structure is a basic component of electronic devices, and printing of the multi-layer interconnection structure is the key process in printed electronics. In this work, electrohydrodynamic direct-writing (EDW) is utilized to print the conductor—insulator—conductor multi-layer interconnection structure. Silver ink is chosen to print the conductor pattern, and a polyvinylpyrrolidone (PVP) solution is utilized to fabricate the insulator layer between the bottom and top conductor patterns. The influences of EDW process parameters on the line width of the printed conductor and insulator patterns are studied systematically. The obtained results show that the line width of the printed structure increases with the increase of the flow rate, but decreases with the increase of applied voltage and PVP content in the solution. The average resistivity values of the bottom and top silver conductor tracks are determined to be 1.34 × 10−7 Ω·m and 1.39 × 10−7 Ω·m, respectively. The printed PVP layer between the two conductor tracks is well insulated, which can meet the insulation requirement of the electronic devices. This study offers an alternative, fast, and cost-effective method of fabricating conductor—insulator—conductor multi-layer interconnections in the electronic industry.

Half-Mode Buried Corrugated Substrate Integrated Waveguide

A half-mode buried corrugated substrate-integrated waveguide is proposed. Its dominant mode propagation behavior is almost identical to that of the half-mode substrate-integrated waveguide but offers a floating top conductor thereby permitting active devices connected to its longitudinal open-edge to be biased without the need for extra biasing chokes. The corrugations comprise open-circuit stubs buried in the substrate that are connected to the top wall of the waveguide by vias. These stubs are quarter-wave in length at a frequency twice the dominant mode cut-off frequency. The corrugations and vias are used to obtain an electric wall. Burying stubs in the substrate results in a low stub input impedance over a wide bandwidth which allows a monomode bandwidth of 3:1 to be obtained. Experiments for waveguides with a TE0.5,0 mode cut-off frequency of 2.8 GHz demonstrate its effectiveness.

Plating reliability and high frequency testing of DuPont™ GreenTape™ 9K7 LTCC

Low Temperature Co-fired Ceramic (LTCC) with low dielectric loss is suitable for use on microwave and millimeter wave circuits. Thick film gold or silver conductors are used as metallization on LTCC substrates. Gold prices are increasing at a rapid rate, so efforts were made to lower the dependency on gold by substituting silver with Ni/Au surface finishes as the top conductor. The external thick film silver conductors were plated using a standard Electroless Nickel Immersion Gold (ENIG) process. The Ni/Au surface finishes provides substantial improvement to fretting corrosion, environmental protection, contact resistance, wire bond strengths, solder ability and solder joint reliability. The reliability testing of DuPont™ GreenTape™ 9K7 LTCC with Ni/Au surface finishes is being conducted. The reliability test methods &amp; conditions were chosen from well-established industry standard test protocols. This paper reports the reliability and high frequency testing results on the ENIG plated GreenTape™ 9K7 LTCC system.

SUBSTRATE INTEGRATED WAVEGUIDE FREQUENCY-AGILE SLOT ANTENNA AND ITS MULTIBEAM APPLICATION

A new technique for designing the substrate integrated waveguide (SIW) frequency-agile slot antenna is presented in this paper. Similar to the metallic waveguide counterpart, the SIW is a uniconductor guided-wave structure and inherently di-cult in the electronically tunable applications. To solve this problem, a single slot etched on the top conductor layer of a conventional antenna is instead of two slots to construct an isolated area, which is convenient for the DC bias. The electric length of slots can then be adjusted through two shunt varactors welded near the center of slot. As such, a SIW frequency-agile slot antenna is realized and fabricated to cover the frequency of 2:30 » 2:74GHz with difierent bias voltages. Experiments verify our theory analysis and design process. Then, a frequency-agile multibeam antenna is developed to cover several frequency bands while switching between four difierent radiation patterns pointing at difierent spatial locations for each frequency. It presents an excellent candidate for software and cognitive radio system applications.

Surface Properties of Laser-etched LTCC Ceramic

In the LTCC process, metal layers are usually deposited by screen printing conductor material on unfired tape substrate. Despite being widely used, this method has certain disadvantages, such as limited resolution of the printing process. An alternative method of producing conductor patterns is to deposit a uniform conductor paste layer on the substrate and the use a Nd:YAG laser to selectively ablate the conductor material, producing a desired pattern. This method allows achieving a higher patterning precision and also eliminates photochemical process of screen preparation, which makes it an attractive choice for rapid prototyping applications. Laser ablation step can be performed either post-firing (for a top conductor layer) or pre-firing (which allows for patterning buried layers). The aim of this paper is to investigate surface properties of LTCC ceramics processed by laser etching. Precision optical imaging and SEM are used to determine etched surface properties, and EDS analysis is used to determine its chemical composition. Effectiveness of conductor removal is investigated by comparing surface resistivity and metal content in raw and etched samples.

A metallic buried interconnect process for through-wafer interconnection

In this paper, we present the design, fabrication process and experimental results of electroplated metal interconnects buried at the bottom of deep silicon trenches with vertical sidewalls. A manual spray-coating process along with a unique trench-formation process has been developed for the electroplating of a metal interconnection structure at the bottom surface of the deep trenches. The silicon etch process combines the isotropic dry etch process and conventional Bosch process to fabricate a deep trench with angled top-side edges and vertical sidewalls. The resulting trench structure, in contrast to the trenches fabricated by wet anisotropic etching, enables spray-coated photoresist patterning with good sidewall and top-side edge coverage while maintaining the ability to form a high-density array of deep trenches without excessive widening of the trench opening. A photoresist spray-coating process was developed and optimized for the formation of electroplating mold at the bottom of 300 µm deep trenches having vertical sidewalls. A diluted positive tone photoresist with relatively high solid content and multiple coating with baking between coating steps has been experimentally proven to provide high quality sidewall and edge coverage. To validate the buried interconnect approach, a three-dimensional daisy chain structure having a buried interconnect as the bottom connector and traces on the wafer surface as the top conductor has been designed and fabricated.