Top Metal Research Articles

Compact LTCC millimeter wave bandpass filter with imbedded dielectric resonators

ABSTRACT A novel substrate-integrated low-temperature ceramic co-fired (LTCC) millimeter-wave bandpass filter operating in the Ka-band is proposed. The filter is composed of multiple layers of media and metal plane. The dielectric resonators (DRs) with high dielectric constant are embedded in LTCC dielectric cavity excavated in LTCC dielectric. The input/output (I/O) is exploited by the slot on metal plane feed by CPW （Co-Planar Waveguide）structure on the top and bottom metal planes, which make the filter able to be integrated to the other components. Simulations and measurements show that the filter has a center frequency of 35 GHz, a relative bandwidth of about 6%, an insertion loss of 1.25 dB, and a return loss of −15 dB in the passband. The filter has many advantages, such as high selectivity, wide bandwidth, low profile, small volume, and so on, which has high engineering application in 5G communications.

Design of 50-GHz Low Phase Noise VCO Employing Two-Branches DGS Resonator in 0.18-μm CMOS Technology

This letter presents a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula> -band low phase noise voltage-controlled oscillator (VCO) design using a novel integrated two-branches defected ground structure (DGS) resonator in 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> complementary metal-oxide-semiconductor (CMOS) technology. The proposed DGS resonator is realized in the top metal layer (M6) which has not only a higher quality factor than its predecessors but is also effective to reduce the length of interconnects. The measured carrier frequency and phase noise are 49 GHz and −122.05 dBc/Hz (−102.58 dBc/Hz) at 10-MHz (1-MHz) offset frequencies, respectively. The VCO core consumes 5.5 mW of dc power from the dc supply, which results in a figure of merit (FoM) of −189 dBc/Hz. The proposed VCO using the two-branches DGS resonator may give an alternative low-cost solution for designing a high-performance VCO or frequency synthesizer at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula> -band and beyond.

Ku-Band Low Phase Noise VCO Using High-Quality Factor Transformer in 0.18-μm CMOS Technology

This work introduces a low phase-noise (PN) wideband voltage-controlled-oscillator (VCO) by proposing five ports transformer in 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS technology. The proposed VCO uses five ports transformer and operates in the low band when all the pMOS–nMOS cross-coupled VCO components are activated, whereas this VCO operates in the high band using only part of the transformer, and an nMOS cross-coupled core. The transformer is designed using the top metal layer (M6) and the first inductor is meander line U-shaped center tap inductor, while the second inductor consists of two shunted octagonal loops to increase the quality ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> -) factor compared with using a single-loop inductor. The wideband switched transformer VCO achieves a measured frequency tuning range (FTR) of 16.4–17.1 GHz with a PN of −113.3 dBc/Hz at 1-MHz offset, and from 17 to 17.9 GHz with a PN of −110.3 dBc/Hz at 1-MHz offset in the low and high bands, respectively. The achieved figure-of-merit (FoM) is −189 and −186.4 dBc/Hz in the low and high bands, respectively.

Doped poly 3-methylthiophene device exhibits negative-differential resistance

Poly 3-methylthiophene (P3MT) polymer is electrochemically deposited on stainless steel substrate and a sandwich device structure (SS/P3MT/Ag) is realized by placing a top metal contact to fabricate a two-terminal device. The polymer is first doped with & dopants and then de-doped for 30 seconds. The current-voltage (I-V) measurement is carried out on a de-doped P3MT device to probe the charge-transport and negative-differential resistance (NDR). In the present experiment, NDR and Charge transport mechanism varies with the dopant. The magnitude of NDR, i.e., peak-valley current (PVCR) depends on the voltage swept and dopants. We propose the reason for anomaly NDR is dopant-induced trap-states.

High Open-Circuit Voltage Cs2 AgBiBr6 Carbon-Based Perovskite Solar Cells via Green Processing of Ultrasonic Spray-Coated Carbon Electrodes from Waste Tire Sources.

Costs and toxicity concerns are at the center of a heated debate regarding the implementation of perovskite solar cells (PSCs) into commercial products. The first bottleneck could be overcome by eliminating the top metal electrode (generally gold) and the underlying hole transporting material and substituting both with one single thick layer of conductive carbon, as in the so-called carbon-based PSCs (C-PSCs). The second issue, related to the presence of lead, can be tackled by resorting to other perovskite structures based on less toxic metallic components. An interesting case is that of the double perovskite Cs2 AgBiBr6 , which at present still lacks the outstanding optoelectronic performances of the lead-based counterparts but is very stable to environmental factors. In this work, the processing of carbon electrodes onto Cs2 AgBiBr6 -based C-PSCs was reported, starting from an additive-free isopropanol ink of a carbon material obtained from the hydrothermal recycling of waste tires and employing a high-throughput ultrasonic spray coating method in normal environmental conditions. Through this highly sustainable approach that ensures a valuable step from an end-of-life to an end-of-waste status for used tires, devices were obtained delivering a record open circuit voltage of 1.293 V, which might in the future represent ultra-cheap solutions to power the indoor Internet of Things ecosystem.

Plasma–induced damage in magnetic tunneling junctions

Plasma–induced damage (PID) in the fabrication of magnetic tunnel junction (MTJ) based magnetic random access memory (MRAM) is studied after the formation of MTJ devices, which excludes process effect directly from the ion beam etching and protection layer deposition. Large degradation in coercivity (Hc) of MTJs is found in comparison with that measured just after the top metal （TM） was formed, which heavily deteriorates MRAM performances. This Hc degradation is found to be mainly introduced in plasma-enhanced chemical vapor deposition (PECVD) for passivation (PA) film after TM formation. The amplitude of the degradation depends on plasma power, but independent of the composition of the PA film. Hc reduction is observed once the plasma is turned on even though no PA deposition is performed. These results suggest that the observed Hc degradation is from PID effect most likely due to the plasma charge damage (PCD) induced in the PECVD process as no direct plasma contact with MTJ devices is involved in the process. It is argued that this PCD effect is due to the charge accumulations at the interface between the free layer and MgO barrier based on electric field–modulated magnetic anisotropy effect. This is further confirmed by an experiment in which Hc degradation is largely cured through partially removing the trapped charges by an annealing process.

A Wideband Low-RCS Circularly Polarized Reconfigurable C-Shaped Antenna Array Based on Liquid Metal

A wideband low radar cross-section (RCS) circularly polarized (CP) reconfigurable patch antenna array based on liquid metal (LM) has been proposed in this article. The array was formed by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\,{\times }\,4$ </tex-math></inline-formula> CP C-shaped antenna elements fed with a sequential feeding network. The antenna element was designed with a pair of narrow slots, and a microchannel adhered to the top metal layer. The CP reconfiguration depends on the tuning of the slots by moving the LM in the channel. The patch antenna array can obtain good CP radiation and low RCS features without any extra RCS reduction structures other than the array elements. RCS reduction (RCSR) can be realized by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$180^{\circ }\,{\pm }\,37^{\circ }$ </tex-math></inline-formula> reflection phase variations between two different antenna elements under normal incidence for both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula> -polarizations. The antenna prototype has been fabricated and measured. The measured results show good agreement with simulated results.

Thermally stable and conductive nickel-incorporated gallium oxide thin-film electrode for efficient GaN microscale light-emitting diode arrays

Microscale light-emitting diodes (µLEDs) have attracted considerable attention as next-generation solid-state lighting sources owing to their reliable performance and attractive properties, such as easy miniaturization and stable operation in various movements. However, the quantum efficiency of μLEDs is lower than that of larger-size LEDs, which hinders their use in high-performance μLED display applications. Herein, a thermally stable and highly conductive GaOx thin-film as a p-type contact electrode is demonstrated by using electric-field-induced doping treatment (EDT) to achieve high-performance GaN µLEDs. The proposed GaOx electrode exhibits high transmittance (92%) and low specific contact resistance (3.5 × 10-3 Ωcm2), along with high thermal stability (over 10 years at 77 °C). Transmission electron microscopy analyses show that conductive channels are formed in the GaOx electrode based on the diffusion of metallic Ni species from the top metal because of EDT, thereby facilitating efficient hole injection into the μLED pixels with little spreading to the passivation layers. Consequently, the µLED array with the GaOx electrode exhibited a 12% higher light output power and 57% higher current level than those of a µLED array with conventional ITO electrodes. The results of this study can guide efforts dedicated to further improving the performance of ITO-based optoelectronic devices, including µLEDs.

Empowerment of Water-Evaporation-Induced Electric Generators via the Use of Metal Electrodes.

As water rises in the pores of a partially immersed porous film due to capillary action, it carries along ions that are dissociated from the pore walls, generating a streaming current and potential. The water and current flows are sustained due to water evaporation from the unsubmerged surfaces. Traditionally, inert graphite (C) electrodes are used to construct water-evaporation-induced generators (WEIGs) that harness this electricity. WEIGs are environmentally friendly but have weak power outputs. Herein, we report on C/metal WEIGs that feature C top electrodes and metal bottom electrodes, as well as metal/metal WEIGs. Operating in a NaCl solution that facilitates the Galvanic corrosion of the metal (Cu, steel, and Al) electrodes, these Galvanic WEIGs outperform a C/C WEIG by thousands of times in power output. Equally interestingly, the asymmetric environments and potential differences between the two electrodes of a WEIG facilitate metal corrosion and fabrication of compact Galvanic WEIGs. This study clearly shows that one should choose electrodes with caution for the construction of true WEIGs.

A Shared-Aperture Dual-Band High-Efficiency Antenna Based on Groove Gap Waveguide

A shared-aperture dual-band antenna at 2.4 GHz Wi-Fi and Ku-bands is proposed in this letter. The antenna in the high-frequency band is featured by a slotted cavity configuration based on the gap waveguide technology. The slotted antenna consists of 3 × 3 slots incorporated into the top metal of the cavity. The periodic structure is loaded into the proposed antenna, which reduces the resonant frequency of the cavity. The top metal of the cavity is enlarged and four shorted screws are loaded, which achieve four half-mode cavities operated in the Wi-Fi band. Two antennas (slotted cavity antenna and dual-band antenna) are designed, fabricated, and tested. Measured results show that a −10 dB impedance bandwidth of 18.3% (13.15–15.8 GHz), a 3 dB gain bandwidth of 17.7% (13.1–15.65 GHz), and a peak gain of 14.8 dBi are realized for the cavity antenna. The impedance bandwidth of the proposed dual-band antenna covers 2.4–2.5 and 13.4–16.2 GHz. A 2 dB gain bandwidth of 16.4% (13.4–15.8 GHz) is realized. Owing to an all-metal structure that exhibits no dielectric loss, the radiation efficiency of the antenna is better than −1 dB in the whole working band. The proposed antenna shows the characteristics of high gain, high efficiency, and low cost, which is suitable for simultaneous satellite communication and Internet of Things applications.

A multi-band terahertz plasmonic absorber based on fan-like metasurface

A plasmonic absorber composed of a sandwich structure based on a fan-like metasurface with three blades has been proposed. The multiple resonance modes are analyzed based on the finite-difference time-domain (FDTD) method by comparing electric field distributions between the unit of absorber with three blades and one individual blade, which proved that the three blades of metasurface can separately excite three absorption peaks in terahertz (THz) band. The influence of the geometry configurations on the resonance modes have also been studied, including radius of blades, the thickness of the top metal layer, and period of unit. The resonance frequencies can be easily tuned by changing the radius of metasurface unit. The proposed plasmonic absorber has potential for THz imaging and sensing applications.

Reflective type metasurface for generating and regulating vortex beam at two frequencies

We proposed a reflective type metasurface to generate and control vortex beams at two operating frequencies. The proposed metasurface consists of the top metal pattern, the polyimide dielectric layer and the bottom metal plate. Under incident left circularly polarized (LCP) terahertz wave, the deflected vortex beam with topological charges (l=−1, l=2), split vortex beams with topological charges (l=1, l=−2), split vortex beam with topological charge (l=−1) and deflected vortex beam with topological charge (l=−2) are generated at two frequencies of 0.38 THz and 1.14 THz. The simulation results are good consistent with the theoretical calculation expectations. The designed metasurface can independently regulate terahertz wave vortex beams at two frequencies, which provides a new design idea for multi-functional devices in terahertz frequency region.

Resonant perfect absorption of molybdenum disulfide beyond the bandgap

Light absorption and radiation are fundamental processes in optical science and engineering. Materials with perfect absorption properties play an important role in numerous optical applications. Following the meteoric rise of MoS2 material, global opportunities and challenges coexist due to its extremely weak light–matter interaction capability beyond its energy band. In this work, we designed a kind of sandwich resonance structure and investigated MoS2 as a perfect absorber in the infrared spectrum that should be transparent according to the optical band theory. The infrared absorption properties of W or Au/MoS2/Au models at 800 nm–2400 nm were systematic simulated. By optimizing the structural parameters, the resonant wavelength of perfect absorption can be modulated from 830 nm to 1700 nm with angle insensitivity and polar independence. Moreover, we discovered that the bandwidth of absorption exceeding 50% of the W-top model reaches 500 nm, while that of the Au-top model is less than 100 nm, indicating that the top metal material has a great influence on the resonance absorption spectrum. Our work provides a practical route for enhancing and manipulating the light–matter interactions of low-dimensional materials beyond their own band gaps, which will be critical in the future design and implementation of optoelectronic devices and systems.

Polarization-insensitive and absorption-tunable ultra-broadband terahertz metamaterial absorbers based on multiple resonant rings

A polarization-insensitive and absorption-tunable ultra-broadband terahertz metamaterial absorbers based on multiple split resonance rings (SRRs) are designed. The single-layer structure is composed of top metal SRRs, intermediate dielectric layer and bottom metal plate. The mechanism of perfect absorption is explained by analyzing the distribution of electric field and surface current at the resonance points. The ultra-broadband absorption is realized by superposing numerous continuous single-band absorption. By optimizing the structural parameters, the results show that the designed structure can realize ultra-broadband absorption with average absorptance of 95.1% in the frequency range of 1.33 to 2.43 THz, with the bandwidth 1.1 THz. The absorptance of proposed absorber hardly changes under different polarization angles of the incident wave, which shows that the proposed asymmetric structure can also have the characteristics of polarization-insensitive. The absorption-tunable characteristic is obtained by replacing the bottom metal plate with phase change material VO2. By changing the ambient temperature in the range of 338 K to 358 K, in which the VO2 can be changed between the metal phase and the insulated phase, so as to realize the tunability of absorption. The results show that the designed absorbers can be widely used in many fields, such as terahertz switches and temperature sensors.

Si nanowire-based micro-capacitors fabricated with metal assisted chemical etching for integrated energy storage applications

Metal-Insulator-Semiconductor micro-capacitors for on-chip energy storage were fabricated and characterized. The capacitors were based on Si nanowires fabricated by Metal Assisted Chemical Etching. 1.2 μm long nanowires with 100 nm average diameter were created leading to an effective area increase of 6.28, as compared to a flat surface. Nanowires were chemically treated to reduce surface roughness and electronic states and were coated by a HfO2 layer, deposited by Atomic Layer Deposition, to act as the dielectric. Al and Cu were deposited as two possible top metal electrodes. The use of Al as the top electrode was shown to create a parasitic interface oxide between the metal and the dielectric, reducing the measured capacitance. The use of Cu was shown to significantly reduce this problem, leading to more efficient devices. Capacitors with 5.4 μF/cm2 capacitance and 8.9 × 10−7 A/cm2 leakage current at −2.5 V were demonstrated along with a cutoff frequency of 104 Hz. These values make the demonstrated capacitors very attractive for on-chip energy storage applications.

Low-loss fiber grating coupler on thin film lithium niobate platform

A grating coupler with a high coupling efficiency and low back reflections is designed and demonstrated on the thin film lithium niobate platform, which facilitates an efficient interface between a lithium niobate ridge waveguide and a standard single mode fiber. The excellent performances of the present grating coupler are enabled by a cavity-assisted grating structure and a top metal mirror, even though a uniform grating is adopted as the diffractive element. Experimentally, a coupling loss of −0.89 dB at 1552 nm is demonstrated with a 1-dB bandwidth of 45 nm. Low back reflections of &amp;lt;−16.5 dB to the waveguide and &amp;lt;−13.7 dB to the fiber are also achieved from 1536 to 1579 nm.

Enhanced circular dichroism of cantilevered nanostructures by distorted plasmon.

Chiral structures have a wide range of applications, such as biometric identification, chemical analysis, and chiral sensing. The simple fabrication process of chiral nanostructures that can produce a significant circular dichroism (CD) effect remains a challenge. Here, a three-dimensional (3D) cantilever-shaped nanostructure, which inherits the chiral advantages of 3D nanostructures and simplicity of 2D nanostructures, is proposed. The nanostructure can be prepared by the combination of one-time electron beam lithography and oblique-angle deposition and consists of a thin metal film with periodic holes such that two hanging arms were attached to the edges of holes. The length of the cantilever and the height difference between the two arms can be adjusted by controlling the tilt angle of beam current during the deposition processes. Numerical calculations showed that the enhancement of CD signal was achieved by plasmon distortion on the metal film by the lower hanging part of the cantilever structure. Furthermore, signals can be actively adjusted using a temperature-sensitive polydimethylsiloxane (PDMS) material. The angle between the lower cantilever and the top metal film was regulated by the change in PDMS volume with temperature. The results provide a new way to fabricating 3D nanostructures and a new mechanism to enhance the CD signal. The proposed nanostructure may have potential applications, such as in ultra-sensitive detection and remote temperature readout, and is expected to be an ultra-compact detection tool for nanoscale structural and functional information.

In situ and ex situ processes for synthesizing metal multilayers with electronically conductive interfaces

A number of technological applications and scientific experiments require processes for preparing metal multilayers with electronically and thermally conductive interfaces. We investigate how in situ vs ex situ synthesis processes affect the thermal conductance of metal/metal interfaces. We use time-domain thermoreflectance experiments to study thermal transport in Au/Fe, Al/Cu, and Cu/Pt bilayer samples. We quantify the effect of exposing the bottom metal layer to an ambient environment prior to deposition of the top metal layer. We observe that for Au/Fe, exposure of the Fe layer to air before depositing the top Au layer significantly impedes interfacial electronic currents. Exposing Cu to air prior to depositing an Al layer effectively eliminates interfacial electronic heat currents between the two metal layers. Exposure to air appears to have no effect on interfacial transport in the Cu/Pt system. Finally, we show that a short RF sputter etch of the bottom layer surface is sufficient to ensure a thermally and electronically conductive metal/metal interface in all materials we study. We analyze our results with a two-temperature model and bound the electronic interface conductance for the nine samples we study. Our findings have applications for thin-film synthesis and advance fundamental understanding of electronic thermal conductance at different types of interfaces between metals.

Optimization of Fully Integrated Al Nanohole Array-Based Refractive Index Sensors for Use With a LED Light Source

Plasmonic nanohole arrays that are directly structured into the top metallization of vertical Ge-on-Si PIN photodiodes can be used to sense refractive index changes. This concept can pave the way to fully integrated biosensors with small footprint and high sensitivities. Here, we show that by optimizing the layer structure of the Ge-on-Si PIN photodiode as well as the geometry of the nanohole arrays, we can achieve high and narrow optical responsivity peaks with Fano-resonance lineshapes. We used an iterative, simulation-based approach in order to optimize the photodiode layer structure as well as the nanohole geometry and compared the predictions to measurement results obtained from fabricated devices. Our fabricated device shows large peak shifts upon changes in the superstrate refractive index. Finally, we argue that the improved device setup can have potential applications in a sensor system that uses an LED light source and estimate the limit of detection to be 2.2&#x00B7;10^&#x2212;5 RIU.

Anisotropic Charge Transport Enabling High-Throughput and High-Aspect-Ratio Wet Etching of Silicon Carbide.

Wet etching of silicon carbide typically exhibits poor etching efficiency and low aspect ratio. In this study, an etching structure that exploits anisotropic charge carrier flow to enable high-throughput, external-bias-free wet etching of high-aspect-ratio SiC micro/nano-structures is demonstrated. Specifically, by applying a catalytic metal coating at the bottom surface of a SiC wafer while introducing patterned ultraviolet light illumination from its top surface, spatial charge separation across the wafer is achieved, i.e., photogenerated electrons are channeled to the bottom to participate in the reduction reaction of an oxidant in the etchant solution, while holes flow to the top to trigger oxidation of SiC and subsequent etching. Such design largely suppresses recombination-induced charge losses, and when used in combination with a top metal catalyst mask, the structure yields a remarkable vertical etching rate of 0.737µmmin-1 and an aspect ratio of 3.2, setting new records for wet-etching methods for SiC.