Electroless Au Research Articles

Electroless Au Plating of CMOS Microelectrodes: Fabrication, Characterization, and Electrochemical Measurement

Electroless Au Plating of CMOS Microelectrodes: Fabrication, Characterization, and Electrochemical Measurement

A flexible IrO2 membrane for pH sensing

An optimized mixture of polydopamine (PDA) and polyvinyl alcohol (PVA) is employed as the surface functionalizing agent and reducing agent to encapsulate individual polypropylene (PP) fibers of polypropylene micromembrane (PPMM). The functionalized PPMM becomes hydrophilic to allow the formation of Au nuclei for subsequent electroless Au deposition. The metalized PPMM is further deposited with IrO2 nanoparticles, and evaluated as a flexible and porous pH sensor. Images from scanning electron microscope confirms the uniform formation of IrO2 nanoparticles on Au-coated PP fibers. For pH-sensing performance, the IrO2-decorated metalized PPMM reveals a super-Nernstian response for a sensing slope of -74.45 mV/pH in aqueous solutions with pH value ranging between 2 and 12. In addition, the pH-sensing performance is properly maintained after 5000 bending cycles and hysteresis is modest in an acidic environment. The cell viability test indicates a negligible bio-toxicity. Our strategy of using a conductive polymeric membrane decorated with IrO2 nanoparticles enables possible sensing applications in wearable and implantable electronics.

Fabrication of biocompatible and conductive polypropylene micromembrane as a soft and porous electrode

BackgroundWe adopt a biomimic approach to fabricate a biocompatible and conductive polypropylene micromembrane (PPMM). It usefulness as a soft electrode is validated via its large electrochemical active surface area for in-vivo and in-vitro glucose sensing. MethodsWe conduct the conformal coating of Au on polypropylene (PP) fibers of PPMM using polydopamine (PDA) and polyvinyl alcohol (PVA) as the adhesive, wetting, and reducing agent, simultaneously. The uniform coverage of PDA/PVA on individual PP fibers of PPMM renders the latter to be hydrophilic for subsequent electroless Au deposition in thickness of 150 nm encapsulating every single PP fiber. SignificantFindings The metalized PPMM exhibits impressive conductivity in both X (10.04 S/cm) and Z (1.23 × 10−2 S/cm) directions. In addition, its tensile strength and strain are similar to those of pristine PPMM. After 10,000 bending cycles, the metalized PPMM reveals negligible physical delamination. Thermogravimetric analysis shows a thermal stability of 400 °C and an effective Au loading of 5.32 mg/cm2. Electrochemical analysis indicates a large electrochemical active surface area with for enhanced glucose sensing performance. Our strategy of using the PDA/PVA for their multifunctional roles could be adopted to fabricate alternative conductive polymer membranes for many possible applications.

Electrochemical Sensing on a Nanostructured Silicon Mass Spectrometry Surface

Mass Spectrometry (MS) is a widely used analytical tool that provides quantitive information (molecule weight and intensity) of the analyte. Nanostructured silicon-based surface-assisted desorption/ionization mass spectrometry (LDI-MS) provides matrix-free and high sensitivity advantages. However, the mass spectrometer is a large and expensive tool limiting the onsite screening or point-of-care testing applications. Electrochemical sensing, on the other hand, is a simple and less-expensive detection method that can be used as portable onsite screening purposes. If the nanostructure silicon (nSi) surface can be used for electrochemical sensing, it opens the possibility of using nSi surface for both electrochemical sensing and Mass Spectrometry (MS) detection. Therefore, in this paper, we demonstrate the feasibility of using nSi surface for electrochemical sensing. Effects of the major nSi surface process parameters, including metal-assisted etching time and electroless Au decoration/deposition time to the electrochemical was evaluated.

Vertical Interconnections by Electroless Au Deposition on Electroless Ni Immersion Au Surface Finish

Electroless Au is used to vertically connect copper pillars with electroless Ni immersion Au surface finish on two stacked chips by a microfluidic electroless interconnection process. A very low bonding temperature of 50°C and a pressure-less bonding process can be achieved. The vertical interconnections are formed by a forced flow of electroless Au plating solution through a microchannel so that the reduced Au atoms self-assemble between the gaps of facing copper pillars to complete the interconnections. The deposited Au grains span the entire gap across the two copper pillars, suggesting that the rate-limiting step is more likely to be the nucleation rather than the growth of the Au grains. Four-point probe measurements show that the average resistance of the electroless-Au-bonded interconnections is low. Mechanical shear testing reveals that the bonding of the interconnections is strong. Furthermore, it is demonstrated that this process is capable of accommodating a high degree of pillar misalignment.

Electrical Resistance of Cu-Cu Interconnection Using Electroless Ni(P) and Au Plating

Electrical Resistance of Cu-Cu Interconnection Using Electroless Ni(P) and Au Plating

Interdiffusion during heteroepitaxial Au growth on Pd thin films by electroless Au plating (ELGP) at room temperature

Electroless Au plating (ELGP) on Pd thin films is performed. The ELGP time dependence on the surface morphology is investigated by a scanning electron microscope. Continuous nucleation and growth of hemispherical Au islands are observed as the plating time increases. Heteroepitaxial growth of the electroless plated Au on the Pd surface is confirmed by cross-sectional scanning transmission electron microscope images. Cross-sectional energy-dispersive X-ray spectroscopy reveals interdiffusion between the Pd atoms and the plated Au atoms at room temperature, which allows the formation of Au–Pd alloys. The heteroepitaxial Au growth on Pd is significant for reducing contact resistance of Au/Pd structures.

Single-molecule single-electron transistor (SM-SET) based on π-conjugated quinoidal-fused oligosilole and heteroepitaxial spherical Au/Pt nanogap electrodes

A single-molecule single-electron transistor (SM-SET) consisting of a π-conjugated quinoidal-fused oligosilole derivative, Si-2, of radius 0.75 nm and heteroepitaxial spherical (HS) Au/Pt nanogap electrodes is demonstrated. Si-2 with two inner silicon atoms and two ethylenethiol groups at both ends is chemisorbed by an S–Au bond between HS-Au/Pt nanogap electrodes fabricated by combining electron-beam lithography and electroless Au plating. An ideal Coulomb staircase, Coulomb oscillation, and Coulomb diamond were observed using the 1.5 nm Si-2 SM-SET, which were supported by theoretical results based on the orthodox model.

Heteroepitaxial spherical electroless Au-plated Pt-based nanogap electrodes of radius 5 nm and gap separation 0.7 nm

Heteroepitaxial growth is demonstrated by electroless Au plating (ELGP) on polycrystalline Pt surface and initial ultrafine-linewidth Pt nanogap electrodes, confirmed by scanning transmission electron microscope cross-sectional images, atomic-resolution scanning electron microscope images, and energy-dispersive X-ray spectroscopy elemental maps. The gap between a pair of spherical multidomain heteroepitaxial Au on Pt electrodes of radius 5 nm is controlled to a value as small as 0.7 nm by the self-termination mechanism of ELGP without short circuit. The heteroepitaxial spherical Au/Pt nanogap electrodes are found to be robust against annealing at temperatures up to 573 K.

Improved uniformity of Ni/Au coating on circuits by electroless plating

ABSTRACTCyanide-free electroless plating was used to deposit nickel/gold coating on the patterned circuits with fine-pitch. The relationship among the controlled process parameters, the skip plating, over-plating and pit forming were investigated. Results show that due to the uniform discharge sputtering, the copper layer is failed to be deposited around BVHs and lines of Al2O3 samples. The skip plating is mainly caused by the self-oxide and the leakage sputtering with copper. Excess Pd activation may result in over-plating during plating nickel. With enhancing the uniformity of the substrate materials and raising the annealing temperature, the number of pits decreases significantly. The thickness of the Au coating can reach up to 2 µm with the smooth coating surface and without the spillover. The electroless plating Au progress can be used to fine-pitch selective area plating.

Novel Pd-catalyzed electroless Au deposition method using a sulfite solution

A novel method is reported for the electroless deposition of Au using nanoscale Pd catalysts in a sulfite solution. A uniform and high quality Au film was generated.

Block-Copolymer-Based Au/Ag Nanoring Arrays with Widely Tunable Surface Plasmon Resonance

We demonstrate a simple route for fabricating Au/Ag nanoring arrays with widely tunable surface plasmon resonce using PS-b-P2VP copolymer templates. Ring-shaped Au dotted arrays are prepared by incorporating Au precursors into the PS-b-P2VP templates. Subsequently, electroless Au plating process enables us to make continuous Au nanoring structures, in which localized surface plasmon spectra cover the range from visible to near-IR regions. Finally, when the Au nanoring arrays are combined with silver-mirror reaction, Au/Ag bimetallic nanoring structures which can also tune the surface plasmon band are successfully fabricated on a wafer scale.

Metal nanoparticle-enhanced photocurrent in GaAs photovoltaic structures with microtextured interfaces.

The photocurrent enhancement effect caused by Au and Ag nanoparticles for GaAs-based photovoltaic structures of surface barrier or p-n junction type with microtextured interfaces has been investigated in dependence on the conditions of nanoparticles deposition and, respectively, on the shape and local dielectric environment of obtained nanoparticle arrays. Three nanoparticle deposition methods have been checked: 1) photoinduced chemical deposition of Au from aqueous AuCl3 solution forming nanowires on the ridges of quasigrating-type surface microrelief, 2) deposition of Ag nanoparticles from colloidal suspension on the GaAs substrate covered with poly(vinylpyridine), and 3) drop and dry deposition of Au/SiO2 core-shell nanoparticles from aqueous colloid solution. The comprehensive investigation of optical reflectance, photoelectric, and electrical characteristics of the fabricated barrier structures has shown the highest photovoltaic parameters for surface microrelief of quasigrating-type and electroless Au nanoparticle deposition. The analysis of characteristics obtained allowed us also to define the mechanisms of the total photocurrent enhancement.

Corrosion Studies on Gold-Plated Electrical Contacts

Long-term reliability of electrical connectors are influenced by the type of plating and plating process. In this paper, the authors look for a viable alternative to 400-nm ENIG + EG (electroless Ni, immersion Au + electroless Au) for microelectronic package substrates. In alignment with historical work, the authors choose NiPdAu (electroless Ni, electroless Pd, immersion Au) as the alternative plating with about 85% reduction in Au thickness. The investigation was mainly on contact resistance degradation due to corrosion between the package substrate and socket contacts. Corrosion studies were based on experiments leading to gold wearout and exposure to corrosive test environment, including temperature, humidity, and mixed flowing gas. The scope of investigation was limited to connectors that are infrequently mated once they are shipped to an end user from the assembly factory.

Fabrication of a membrane probe card using transparent film for three-dimensional integrated circuit testing

We fabricated a novel membrane probe card using a transparent film for the chip-level testing of a three-dimensional integrated circuit (3D-IC). In this membrane probe card, 20-µm-pitch Ni–Au contact bumps and Ti–Au wirings were formed on a biaxially oriented poly(ethylene naphthalate) (PEN) film. This probe card was fabricated using a low-temperature (lower than 100 °C) process, which included through-hole formation by a laser beam, photolithography, Ar plasma irradiation to improve the adhesion between the PEN film and the metal wiring, Ti–Au sputtering, Au electroplating, Ni electroplating, and electroless Au plating. The probe card has three characteristics: (1) fine pitch probes. (2) small-gap alignment between the probe card and the tested chip owing to transparency of the probe card, which offers high accurate probing. (3) damageless (low-load) probing owing to the compliancy of the PEN film. Using this probe card, we performed pre-bond testing of a 10-mm-square chip with Cu–SnAg bumps. The probing to 20-µm-pitch, 1,000 Cu–SnAg bumps and the pre-bond testing of thin Si chips were realized without causing damage to the chip even when chip was very thin (50 µm thick).

DNA Origami Substrates for Highly Sensitive Surface-Enhanced Raman Scattering

DNA nanotechnology holds great promise for the fabrication of novel plasmonic nanostructures and the potential to carry out single-molecule measurements using optical spectroscopy. Here, we demonstrate for the first time that DNA origami nanostructures can be exploited as substrates for surface-enhanced Raman scattering (SERS). Gold nanoparticles (AuNPs) have been arranged into dimers to create intense Raman scattering hot spots in the interparticle gaps. AuNPs (15 nm) covered with TAMRA-modified DNA have been placed at a nominal distance of 25 nm to demonstrate the formation of Raman hot spots. To control the plasmonic coupling between the nanoparticles and thus the field enhancement in the hot spot, the size of AuNPs has been varied from 5 to 28 nm by electroless Au deposition. By the precise positioning of a specific number of TAMRA molecules in these hot spots, SERS with the highest sensitivity down to the few-molecule level is obtained.

Impedance Spectroscopy of Highly Ordered Nano-Porous Electrodes Based on Au–AAO (Anodic Aluminum Oxide) Structure

Electrochemical measurements using the microelectrodes are increasingly utilized for the label-free detection of the small amount of biological materials such as DNA, protein, and cells. However, the interfacial electrode impedance increases and may hinder the detection of weak signals as the size of electrode decreases. To enhance the measurement sensitivity while reducing the electrode size, in this study, microelectrodes employing a nanoporous structure were fabricated and characterized by using electrical impedance spectroscopy. We made the highly ordered honeycomb nanoporous structure of Anodic Aluminum Oxide (AAO) by electrochemical anodizing and formed Au layer on the surface of AAO (Au/AAO) by electroless Au plating method. The electrical characteristics of the fabricated Au/AAO electrodes were evaluated by using de Levie's model derived for the pore electrodes. As a result, the interfacial electrode impedance of the fabricated Au/AAO electrodes was 2-3 order lower than the value of the planar electrodes at frequencies below 1 kHz. It implies this nanoporous electrode could be directly applied to label free detection of biomaterials.

Silicon–Nitride-Passivated Bottom-Up Single-Electron Transistors

We report the elaboration of SiNx-passivated chemically assembled single-electron transistors (SETs) by bottom-up processes involving electroless Au plating and the chemisorption of Au nanoparticles. With a Au top-gate electrode, the SiNx-passivated SETs showed a clear Coulomb diamond at 9 K and the top-gate capacitance was 17 times larger than the side-gate capacitance. Moreover, Coulomb oscillation and the Coulomb diamond were observed even at 160 K. Thus, planar technology is applicable to chemically assembled SETs.

Development and characterization of a 3D GaAs X-ray detector for medical imaging

Conventional semiconductor X-ray detectors for medical imaging have either a planar or a pixelated structure. The options available for detection materials are limited by the natural trade-off between the absorption of incident photons and the collection of free charge carriers with these two structures. This trade-off can be avoided by using az 3D structure, in which electrodes are drilled into the detector's volume. This article describes a prototype 3D semiconductor detector, using semi-insulating GaAs. A laser drilling technique was used to create electrodes in the volume of the material. The holes created were characterized by scanning electron microscopy. Electrode contacts were created using electroless Au deposition. The manufacturing process and the first gamma counting results obtained with 241Am and 57Co sources are presented. The system is capable of individual photon-counting without energy discrimination but requires further development to improve efficiency.

Electroless nanoworm Au films on columnar porous silicon layers

A characterization study of nanoworm Au thin films fabricated onto Si (100) using an intermediate columnar porous silicon (PSi) layer is presented. The Au thin films are resistant to peeling in different buffers and solvents. Adhesion arises from the presence of a diffused Au nucleation layer in the channeled PSi, which can be observed even at short electroless Au deposition times. For longer deposition times, a gold surface film grows from piled and aggregated Au crystals, providing high surface area. X-ray absorption spectroscopy studies revealed differences in the Au L3 absorption edge that can be ascribed to the induced nanoworm structure. The optical behavior of the Au grown on the surface has also been studied by light reflectance spectroscopy and related to the characteristic Au intra-band absorption. Such surfaces could enhance the performance of electric or optical devices with sensitivity limited by surface area availability.