Printed Silver Electrodes Research Articles

High-precision silver electrode based on PEN substrate with robust mechanical performance

Wearable electronics are becoming more and more popular, and in order to ensure the safety and accuracy of wearable electronics, the requirements for the refinement and stability of flexible electrodes are getting higher and higher. The reduction of the amount of ink jet and the reduction of surface charge density and electrostatic stress near the nozzle hole can significantly improve the jetting state of the ink. And nozzle voltage is a key factor that affects them. The spreading of ink droplets on the substrate and the formation of a specific pattern is a dynamic process, which is closely related to the properties of the substrate and the state of the ink droplets. In this paper, PEN is used as the substrate to print silver electrode, with its good thermal stability and good mechanical properties. In order to solve these problems and improve the accuracy of the electrode pattern on PEN substrate, a joint control method of ink drop spacing and nozzle voltage is proposed. It is found that the accuracy of the pattern increases with the increase of the drop spacing. At 45 μm, 90.91 % of the pattern accuracy with the ideal pattern can be achieved. As the nozzle voltage decreases, so does the satellite spot. And at 25 V, it can achieve satellite-free spot printing. Because this method avoids the adjustment of ink properties and the regulation of voltage waveform, this advancement provides a simpler solution for patterned high-precision printed silver electrodes based on flexible substrates. In addition, a silver electrode with a resistivity of 3.43 μΩ·cm was obtained at an annealing temperature of 160 °C. The resistivity change of the electrode only 7.58 % under 5000 times of bending. This is very rare in flexible electrodes.The silver film on the PEN substrate exhibited excellent adhesion under the tape test. XPS depth profiling was used to characterize the elemental states of the films at different depths. The results indicated that the coordination bond between the PEN substrate and the Ag film resulted in good bending resistance, which gives a persuasive explanation for the first time. This result is also due to the precise handling of the film, which also results in a homogeneous distribution of the film. It solves the problem of poor adhesion of silver electrodes based on other substrates or other preparation methods. Therefore, silver electrodes based on PEN substrates have a broad application prospect in the field of flexible wearable electronics.

High-sensitivity and energy-efficient chloride ion sensors based on flexible printed carbon nanotube thin-film transistors for wearable electronics

The advent of flexible single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) has transformed electronics, providing significant benefits like low operating voltage, reduced power consumption, cost-effectiveness, and improved signal amplification. This study focuses on leveraging these attributes to develop a novel flexible high-sensitivity and energy-efficient chloride ion sensors based on printed flexible SWCNT-TFTs utilizing polymers-sorted semiconducting SWCNTs (sc-SWCNTs) as the active layers and ion liquids-poly(4-vinylphenol as dielectric layers along with the evaporated deposition of aluminum electrodes and printed silver electrodes as the gate and source-drain electrodes, respectively. The sensors exhibit several operational advantages, including low voltage requirements (≤1 V), rapid response speed (5.32 s), significant signal amplification (Up to 702.6 %), low power consumption (0.31 μJ at 1 mmol chloride ion), good repeatability, high sensitivity for both low and high concentrations of chloride ion (up to 100 mmol/L) and excellent mechanical flexibility (No obvious changes after bending for 10,000 times with a 5 mm radius). The detection mechanism of chloride ions was analyzed using X-ray Photoelectron Spectroscopy (XPS). It was found that chloride ions react with silver nanoparticles (AgNPs) to form silver chloride (AgCl) on printed electrodes, impeding carrier transport and reducing the currents in SWCNT TFTs. Importantly, our sensors' compatibility with smart devices allows for real-time monitoring of chloride ion levels in human sweat, offering significant potential for daily health monitoring.

Fully printed memristors made with MoS2 and graphene water-based inks.

2-Dimensional materials (2DMs) offer an attractive solution for the realization of high density and reliable memristors, compatible with printed and flexible electronics. In this work we fabricate a fully inkjet printed MoS2-based resistive switching memory, where graphene is used as top electrode and silver is used as bottom electrode. Memristic effects are observed only after annealing of each printed component. The printed memory on silicon shows low SET/RESET voltage, short switching times (less than 0.1 s) and resistance switching ratios of 103-105, comparable or superior to the performance obtained in devices with both printed silver electrodes on rigid substrates. The same device on Kapton shows resistance switching ratios of 102-103 and remains stable at least up to 2% of strain. The memristor resistance switching is attributed to the formation of Ag conductive filaments, which can be suppressed by integrating graphene grown by chemical vapour deposition (CVD) onto the silver electrode. Temperature-dependent electrical measurements starting from 200 K show that memristic behavior appears at a temperature of ∼300 K, confirming that an energy threshold is needed to form the conductive filament. This work shows that inkjet printing is a very powerful technique for the fabrication of 2DMs-based resistive switches onto rigid and flexible substrates.

Printed organic Schottky diode with self-assembled monolayer for 13.56 MHz band near-field communication

We demonstrate printed organic Schottky diodes for the rectification of the 13.56 MHz near-field communication carrier wave. Printed silver electrodes covered with a self-assembled monolayer of 4-methylbenzenethiol were employed for the Schottky barrier. Optimizing the conditions of the self-assembled monolayer treatment was performed to improve the rectification ratio to 106 and the forward current density to 1 A cm−2. Finally, organic half-wave and full-wave rectifiers were demonstrated with a high-frequency response of output rectifying voltage of more than 5 V at 13.56 MHz.

An integrate-and-fire neuron circuit made from printed organic field-effect transistors

Neuromorphic circuits that mimic the operation of nerve cells are promising approaches to interface with or emulate the operation of biological neural network. These types of electronic circuits have generally been realised by fabrication using well-established silicon technology but herein we report the fabrication of a simple neuromorphic circuit, specifically, an integrate-and-fire (I&F) circuit, using solution-processed OFETs. It consists of p-type organic field-effect transistors (OFETs) realised with parylene-dielectric, printed silver electrodes and a solution processed semiconductor on a flexible plastic substrate. As the behaviour of the fabricated I&F circuit is predictable by simulation, the reported process allows for customised circuit design and provides the basis to realise a variety of flexible neuromorphic circuit designs. • Neuromorphic circuits can mimic the electrical spiking of nerve cells. • A simple neuromorphic circuit made using printed organic field-effect transistors. • Performance of a printed integrate and fire circuit can be modelled by simulation.

Room temperature processed protective layer for printed silver electrodes.

Low-temperature processed printed silver electrodes pave the way for electrical connections in flexible substrates with reduced energy consumption. Despite their excellent performance and simple process, printed silver electrodes' poor stability limits their applications. This study demonstrates a transparent protective layer without thermal annealing for printed silver electrodes, which maintains its electrical properties for a long period of time. A fluoropolymer, specifically a cyclic transparent optical polymer (CYTOP), was used as a protective layer for silver. The CYTOP is room temperature processable and chemically stable against carboxyl acid. The introduction of the CYTOP film on the printed silver electrodes mitigates the chemical reaction between silver and carboxyl acid, thereby elongating its lifetime. Under heated acetic acid, the printed silver electrodes with a CYTOP protective layer maintained their initial resistance for up to 300 hours, while the electrodes without a protective layer were damaged within a few hours. A microscopic image shows that the protective layer enables printed electrodes to maintain their shape without damage. Hence, the protective layer guarantees the accurate and reliable performance of electronic devices with printed electrodes under actual operating conditions. This research will contribute to designing chemically reliable flexible devices in the near future.

Morphological Regulation of Printed Low-Temperature Conductive Ink.

The unbalanced evaporation of solvents in low-temperature sintered inks for printed electronics leads to a series of problems in the actual printing process, including printed pattern distortion, surface cracking, and the coffee ring effect, which has become a serious obstacle to this technique. Here, we present a comprehensive investigation of the influence of the solvent composition, environmental, and sintering conditions on the complicated pattern formation process of reactive silver inks. The results first showed that only inks with a certain wettability of solvents could form well-defined patterns. Then, the solvent composition and ambient humidity can be adjusted to balance the nonequilibrium evaporative flow within the liquid and thus to obtain a flat liquid film. Combined with the rapid UV sintering process, the particle size, porosity, and roughness could be controlled to produce dense and homogeneous silver films. Finally, we successfully printed silver electrodes with a smooth and dense surface (Rqs ∼ 21 nm in 0.8 × 0.8 mm2 area and less than 1% porosity) under an optimized relative humidity (RH) of 50-60% at room temperature with the solvent composition of IPA (isopropanol)/2,3-BD (2,3-butanediol) = 8:2. In addition, we also demonstrated high-performance Pr-IZO (praseodymium-doped indium-zinc oxide) thin film transistors (TFTs) with a mobility (μsat) of 2.14 cm2/V/s and Ion/Ioff ratio of over 107 using source-drain electrodes printed under optimized conditions.

Effect of Additive Manufacturing on β‐Phase Poly(Vinylidene Fluoride)‐Based Capacitive Temperature Sensors

Additive manufacturing, commonly known as 3D printing, significantly simplifies the manufacturing process for soft electronics. This work demonstrates the feasibility of a fully 3D-printed flexible poly(vinylidene fluoride) (PVdF) capacitive temperature sensor. The sensor is constructed using fused deposition modeling (FDM)-printed PVdF film as the dielectric (thickness ≈180–280 μm) sandwiched between two parallel Direct Ink Writing (DIW) printed silver electrodes (entire device thickness ≈200–380 μm). The motion of the nozzle can facilitate mechanical drawing to the molten PVdF filament, which is a necessary condition to increase the β-phase content (critical for the sensitivity of the sensor). With optimized printing parameters, the highest β-phase content (21.30%) is achieved when printing with a nozzle temperature of 200 °C and a print speed of 70 mm s−1. The research demonstrates the application of the device as a temperature sensor by applying heating-and-cooling cycles from room temperature (25 °C) up to 140 °C while measuring the capacitance as a function of frequency under different temperatures. The sensor exhibits a stable sensitivity of 3 pF °C−1 at 102 Hz and higher frequencies and improved sensitivities at frequencies higher than 102 Hz after dielectric polarization via the corona poling method.

Highly sensitive and selective H2S sensors with ultra-low power consumption based on flexible printed carbon-nanotube-thin-film-transistors

Flexible printed carbon-nanotube-thin-film-transistors (CNT-TFTs) with characteristics of low cost, low operating voltage, low power consumption, and signal amplification have great potential for emerging electronics powered by self-powered systems or low-power density thin-film solar cells. In this work, we have fabricated flexible printed CNT-TFTs using the printing process to selectively deposit semiconducting CNTs in device channels as channel materials, printed silver electrodes as side gates, and printed ion gel as the dielectric layer. The as-prepared TFTs exhibited an extremely high sensitivity to H2S (up to 1565% ppm-1) at room temperature (25 ℃) and the relative humidity (RH) of 5%, excellent signal amplification (response increased from 1% to 4045.5% towards 2 ppm H2S), ultra-low working power consumption (1.03 nW under 2 ppm H2S), excellent selectivity, fast response/recovery time (10 s/26 s) and great mechanical flexibility (stable after 10,000 times bending with 5 mm radius). The outstanding improvement of sensor characteristics was related to the enrichment and absorption of H2S by ionic liquids, and the resistor-mode device's response to 2 ppm H2S increased from ~1% to 80% after the device channel was covered by ion gel. To the best of our knowledge, our H2S sensors demonstrated the recorded low power consumption (1.03 nW) and high response (4045.4%) when exposed to 2 ppm H2S at room temperature, making our sensors a promising candidate for portable applications in gas detection.

Flexible, Piezoelectric Aluminum-Doped Zinc Oxide Energy Harvesters with Printed Electrodes for Wearable Applications

Aims: Recent advancements in sensing technology and wireless communications have accelerated the development of the Internet of Things (IoT) which promote the usage of wearable sensors. An emerging trend is to develop self-sustainable wearable devices, thus eliminating the necessity of the user to carry bulky batteries. In this work, the development of a flexible piezoelectric energy harvester that is capable of harvesting energy from low frequency vibrations is presented. The target application of this energy harvester is for usage in smart shoes. Objectives: The objectives of this research is to design, fabricate and test an energy harvester on PET substrate using Aluminum Zinc Oxide as its piezoelectric layer. Methods: The energy harvester was designed as a cantilever structure using PET/AZO/Ag layers in d33 mode which can generate large output voltages with small displacements. The electrodes were designed as an interdigitated structure in which two significant design parameters were chosen, namely the effect of gap between electrodes, g and number of interdigital electrodes (IDE) pairs, N to the output voltage and resonant frequency. Results: The sputtered AZO on PET showed c-axis orientation at 002 peak with 2 values of 34.45° which indicates piezoelectric behaviour. The silver IDE pairs were screen-printed on the AZO thin film. Functionality of the device as an energy harvester was demonstrated by testing it using a shaker. The energy harvester was capable of generating 0.867 Vrms output voltage when actuated at 49.6 Hz vibrations. Conclusion: This indicates that the AZO thin films with printed silver electrodes can be used as flexible, d33 energy harvesters.

Flexible printed single-walled carbon nanotubes olfactory synaptic transistors with crosslinked poly(4-vinylphenol) as dielectrics

Flexible brain-inspired neuromorphic transistors are spring up in the scopes of artificial electronic skins and human-interactive electronics for wearable devices and robotic applications benefiting from the capability of synchronous recognition and processing of the external information. In this work, we reported the flexible printed single-walled carbon nanotube (SWCNT) synaptic thin film transistors (TFTs) with printed silver electrodes as source/drain and gate electrodes, and the solid state electrolyte blending ionic liquids with crosslinked-poly(4-vinylphenol) (c-PVP) as dielectric layers. Our flexible printed SWCNT synaptic transistors display excellent electrical properties, such as low operation voltages (between ±1 V), high on/off ratios (>106) and low off currents (∼10−12 A), as well good stability and good mechanical flexibility. These flexible printed SWCNT TFT devices can imitate some typical synaptic plasticities like excitatory postsynaptic current and paired-pulse facilitation. The results indicate that synaptic behaviors of flexible devices are related to weight concentrations of ionic liquids in ionic c-PVP insulators. Moreover, our synaptic transistors can imitate the olfactory neurons and show the inhibitory characteristic when triggered by under a series of electrical stimulations after exposure to NH3.

Improvement of Chemical Stability in Electrochemical Migration Resistance in Printed Silver Electrodes

印刷法を用いて作製する有機エレクトロニクスは大面積・低コストな電子デバイスを実現できるため，近年注目が集まっている研究分野である。特に，これらはフレキシブル基板上に形成することで，ヒトの肌に貼り付けて体調管理を行えるウェアラブルなヘルスケアデバイスに応用できる。一方，上記デバイスにおける印刷銀電極は，ヒトに直接貼付するため，汗や湿度に対するエレクトロケミカルマイグレーション(ECM)への耐久性が低いことが問題視されている。本研究ではECM発生時の印刷銀電極表面を解析することで，耐久性向上に対する指針を得ることを目的とした。電極表面にバリア層として自己組織化単分子膜を導入，または封止層を形成することで銀イオン生成防止によってECMの耐久性が向上することも併せて明らかにした。

Flexible and Stretchable Temperature Sensors Fabricated Using Solution-Processable Conductive Polymer Composites.

Accurate monitoring of physiological temperatures is important for the diagnosis and tracking of various medical conditions. This work presents the design, fabrication, and characterization of temperature sensors using conductive polymer composites (CPCs) patterned on both flexible and stretchable substrates through both drop coating and direct ink writing (DIW). These composites were formed using a high melting point biopolymer polyhydroxybutyrate (PHB) as the matrix and the graphenic nanomaterial reduced graphene oxide (rGO) as the nanofiller (from 3 to 12 wt%), resulting in a material that exhibits a temperature-dependent resistivity. At room temperature the composites exhibited electrical percolation behavior. Around the percolation threshold, both the carrier concentration and mobility were found to increase sharply. Sensors were fabricated by drop-coating PHB-rGO composites onto ink-jet printed silver electrodes. The temperature coefficient of resistance was determined to be 0.018 /°C for pressed rGO powders and 0.008 /°C for the 3 wt% samples (the highest responsivity of all composites). Composites were found to have good selectivity to temperature with respect to pressure and moisture. Thermal mapping was demonstrated using 6 × 7 arrays of sensing elements. Stretchable devices with a meandering pattern were fabricated using DIW, demonstrating the potential for these materials in healthcare monitoring devices.

Studying Knotless Screen Patterns for Fine-line Screen Printing of Si-Solar Cells

Flatbed screen printing is the dominating process in industry for metallization of silicon solar cells. It offers high throughput rates, high flexibility of printing pattern, and an overall very cost-effective production compared with other printing technologies. However, the ongoing demand for an optimization of printed silver electrode shape creates an increasing challenge to paste and screen development. The recent trend of so called “knotless” screens with a screen angle of 0° offers an increased paste transfer, therefore, better electrode conductivity, which leads to an improved solar cell efficiency. The disadvantage of this screen architecture is a reduced screen lifetime and low production yield. This article presents a systematic simulation of screen pattern to investigate screen angles, which allow for an improved knotless screen architecture. Therefore, different types of wire crossings have been defined, simulated, and experimentally verified by microscope images. For example, when 14.036°, 18.435°, and 26.565° are used, knotless screen pattern openings emerge without showing any of the disadvantages of regular 0°-knotless screens. For this reason, statistical screen lifetime estimations are carried out by modeling the intersection lengths of all mesh wires and the emulsion edge across the screen opening. Furthermore, a detailed analysis on manufacturing tolerances is given, showing that the 26.565° screen angle offers the best compromise between challenges during manufacturing and potential performance in production of Si-solar cells.

Overcoming Electrochemical Instabilities of Printed Silver Electrodes in All-Printed Ion Gel Gated Carbon Nanotube Thin-Film Transistors.

Silver ink is the most widely used conductive material for printing electrodes in the fabrication of all-printed ion gel gated transistors because of their high conductivity and low cost. However, electrochemical instability of printed silver electrodes is generally one of the biggest issues, whether it is in air where silver gets oxidized or in a moisture environment where electrochemical migration occurs. Notwithstanding, the electrochemical stability of printed silver electrodes in ion gel medium has not been studied so far. In this work, we studied the electrochemical instabilities of printed silver electrodes in fully printed ion gel gated single-walled carbon nanotube (SWCNT) thin-film transistors (TFTs) and developed some strategies to overcome these issues. All-printed ion gel-based p-type SWCNT TFTs were employed to investigate the impact of electrochemical instabilities on the electrical behavior of printed SWCNT TFTs. The results have demonstrated that printed silver was unstable at anodic and cathodic polarization because of the corrosion by the ionic liquid. Besides, anodic corrosion of silver source/drain electrodes was shown to be responsible for the electrical failure of printed SWCNT TFTs in both the linear and saturated regime. These issues were completely resolved when preventing printed silver electrodes from coming into direct contact with ion gels. For example, ion gels were partially printed in device channels to avoid contacting the printed silver source and drain electrodes. At the same time, silver side-gate electrodes were replaced by inkjet-printed PEDOT:PSS electrodes to avoid gate electrode-related instabilities. Consequently, all-printed electrochemically stable SWCNT TFTs fabricated were obtained with enhanced performance of higher ION/IOFF ratios (105 to 106), smaller subthreshold slopes (∼70 mV/dec), and smaller hysteresis (ΔV = 0.025 V) at gate voltages from 1.2 to -0.5 V. Additionally, the polarity of all-printed SWCNT TFTs was converted from the p-channel to ambipolar while achieving lower leakage currents.

Use of surface photo-reactive nanometal printing for polymer thin-film transistors: contact resistance and short-channel effects

Abstract

Excimer laser sintereing of silver nanoparticles electrodes for fully solution processed organic thin film transistors

Printing and related processing technologies of electronic materials have become an essential part in the production of many components of today's electronics. Laser processing of metal based inks in particular has received a great attention and can eliminate the need of the conventional high temperature sintering methods. Here, silver nanoparticles ink was printed using a drop on demand (DOD) printer and cured to produce highly conductive silver patterns. The printed silver nanoparticles were sintered using excimer laser and thermal treatment. The effects of curing parameters such as energy density, scan speed and annealing temperature on the surface morphology and electrical performance of the inkjet printed structures were investigated. The results revealed strong dependence of the morphology and electrical performance of the printed samples on the process parameters namely the laser fluence and the scanning speed. The production of discontinuous samples and laser ablation of silver sintered patterns at some treatment stages were also noticed. Moreover, using optimized sintering conditions, highly conductive patterns similar to those thermally treated were produced. The printed conductive patterns were then successfully utilized as S/D electrodes for organic thin film transistors. The fully solution processed transistors with printed silver electrodes exhibited excellent ohmic contact characteristics with mobility and on/off ratio in the range of 10−2 cm2/V·s and 103, respectively. The results indicate that, in addition to the various material processing uses, excimer laser can also be used as a sintering tool for printed metallic nanoparticles in the roll-to-roll manufacturing processes.

Fully Printed Infrared Photodetectors from PbS Nanocrystals with Perovskite Ligands.

Colloidal nanocrystals from PbS are successfully applied in highly sensitive infrared photodetectors with various device architectures. Here, we demonstrate all-printed devices with high detectivity (∼1012 cm Hz1/2/W) and a cut-off frequency of >3 kHz. The low material consumption (<0.3 mg per detector) and short processing time (14 s per detector) enabled by the automated printing promises extremely low device costs. To enable all-printed devices, an ink formulation was developed based on nanocrystals stabilized by perovskite-like methylammonium iodobismuthate ligands, which are dispersed in a ternary solvent. Fully inkjet printed devices based on this solvent were achieved with printed silver electrodes and a ZnO interlayer. Considerable improvements were obtained by the addition of small amounts of the polymer poly(vinylpyrrolidone) to the ink. The polymer improved the colloidal stability of the ink and its film-formation properties and thus enabled the scalable printing of single detectors and detector arrays. While photoconductors were shown here, the developed ink will certainly find application in a series of further electronic devices based on nanocrystals from a broad range of materials.

Inkjet-printed silver as alternative top electrode for lead zirconate titanate thin films

In the present work, we describe direct patterning of silver top electrodes on polycrystalline Pb(Zr0.53Ti0.47)O3 (PZT) thin films via inkjet printing. The films were first deposited on platinized silicon via chemical solution deposition. Individual nanosilver ink droplets were then printed on the PZT surface to create round top electrodes with tunable diameter from 75 to 93 μm. Printing parameters and strategy were optimized for deposition of homogeneous electrodes. High quality of the printed silver electrodes sintered at 350 °C is confirmed via measurements of the direct piezoelectric response and polarization loops of PZT thin films, whose results are comparable to the ones obtained for sputtered platinum top electrodes, with e31,f = −4.1 C m−2, Pr ∼20 μC cm−2 and Ec ∼55 kV cm−1.

Inkjet Printed Nanoparticle Electrochemical Platform for Breast Cancer Detection

Inexpensive disposable sensor platforms have the ability to revolutionize personalized cancer diagnostics. Monitoring levels of specific biomarker proteins in serum can provide further insight into a patient’s disease status enabling for physicians to diagnose and treat patients on the spot. Electrochemical sensors are among the most popular for point –of-care use due to ease of detection, low instrumentation cost, and the ability to be miniaturized and automated. A typical electrochemical cell consists of a counter, working, and reference electrodes. Miniaturization and production cost of electrodes have been improved by patterning electrodes on a substrate surface. Common methods however, are time consuming and costly therefore limiting rapid prototyping. Described here is an inexpensive commercially scalable way to integrate these electrodes on a single test chip to detect clinically relevant breast cancer biomarker Human Epidermal Growth Factor Receptor 2 (HER-2) in serum. The sensor platform consists of an inkjet printed gold nanoparticle -working 8-electrode array (WEA) and counter electrode (CE), along with an inkjet printed silver electrode that was chlorinated with bleach to produce a Ag/AgCl quasi-reference electrode (RE). The WEA featured an excellent nanostructured surface to build immunoassays. Therefore, capture antibodies were bound to a chemically modified surface on the WEA and placed into a simple microfluidic device. A full sandwich immunoassay was assembled following a simultaneous injection of HER-2, biotinlyated antibody, and polymerized horseradish peroxide labels into the microfluidic device housing the WEA. A clinically relevant detection limit of 12 pg mL-1 was achieved in a total assay time of under 20 mins. Excellent reproducibility and sensitivity of the biosensor were observed through recovery assays preformed in human serum, containing hundreds to thousands of competing proteins. Following this rapid assay protocol these sensor platforms could easily be adapted for multiplex detection of a panel of proteins for breast cancer screening