Ag Microflakes Research Articles

Stretchable conductors based on nanoporous Ag for flexible sensors

Conductive filler is essential to fabricate stretchable conductors for flexible electronics. In this paper, a novel kind of conductive filler, regularly nanoporous Ag (NP–Ag) is synthesized using a method called “complexation coprecipitation-rapid reduction”, which offers rapid, facile, and environment-friendly advantages. Owing to the nanoporous feature, the as-prepared conductor containing low contents of NP-Ag can exhibit excellent conductivity. Typically, the fluorine rubber-based conductor containing 45 wt% of NP-Ag can maintain a conductivity as high as 1578 S cm−1, while the composite loaded with the same content of fashionable filler (commercial Ag micro-flakes) remains non-conductive. Utilizing this conductor, a strain sensor with excellent sensitivity and repeatability can be fabricated conveniently. The synthetic advantages and regular porosity would make those microstructures a filler candidate for preparing large-area, low-cost, and high-through stretchable conductors.

Mechanochemically Assisted Synthesis of Cu–Ag Microflakes

In this work, a simple, inexpensive, and eco-friendly synthesis method of Cu−Ag microflakes has been developed. Firstly, Cu nanoparticles were synthesized by the reduction of copper nitrate in ethylene glycol at 180 °C in the presence of NaOH. The as-synthesized Cu powder was then dispersed in a mixture of ethyl alcohol and a dispersant followed by the mechanochemical treatment of the dispersion in a ball mill resulting in the formation of Cu flakes of approximately 0.2 μm thick and 2.7 μm lateral size. Next, by adding AgNO3 dissolved in H2O into the Cu particle dispersion, the bimetallic Cu−Ag microflakes were prepared. The particles so prepared were investigated by X-ray phase analysis and electron microscopy. It was shown that the Cu−Ag bimetallic particles were also flake-like in shape and similar in size to the original Cu microflakes. The effect of synthesis conditions, including parameters of mechanochemical processing, on thickness, size, and uniformity of the bimetallic microflakes was studied. The results obtained in this study were compared with those obtained by wet chemical synthesis alone. The flake-like Cu–Ag particles are supposed to be used in the manufacture of conductive pastes, adhesives, and composites for printed electronics.

Highly strong interface in Ag/Si sintered joints obtained through Ag2O–Ag composite paste

In this study, the interfacial strength and fracture behavior of Ag/Si interfaces formed by a composite paste comprising Ag2O microparticles, Ag microflakes, and terpineol is demonstrated through microscale tensile testing. This paste induces a delayed reduction of Ag2O and subsequent interconnection between the Ag grains and Si substrate. This is owing to the interface formation by the direct bonding of Ag and a layer with Ag nanoparticles intermediated bonding using the newly generated Ag nanoparticles. This characteristic interface formation helps achieve a high joint strength (>30 MPa) at a bonding temperature of 250 °C, inducing a substrate fracture at 275 °C. Microscale tensile testing reveals the high-strength Ag/Si (>200 MPa) interface formation and intrinsic fracture morphology within the Ag layer at a nanoscale; the fracture occurs in the Ag layer and not at the interface.

Enhanced sensitivity from Ag micro-flakes encapsulated Ag-doped ZnO nanorods-based UV photodetector

An innovative method of improving zinc oxide (ZnO) nanorods-based ultraviolet (UV) photodetectors was fabricated by photodeposition of silver (Ag) micro-flakes on top of Ag-encapsulated Ag-doped ZnO nanorods. Four concentrations are selected for the doping process (0, 1.7, 3.4, and 5.1 mol%). The Ag-doped ZnO nanorods are synthesized via the hydrothermal method, followed by photodeposition using AgNO3 solution, both of which are low-cost and simple. Ag doping resulted in thinner and shorter ZnO nanorods, improved crystallinity, and reduction of deep-level emissions as corroborated by field emission scanning electron microscopy, X-ray diffraction, and photoluminescence analyses. UV photodetectors fabricated from the samples showed that Ag-doped ZnO nanorods in addition to Ag micro-flakes have improved sensitivity and gain than non-doped ZnO nanorods. Excessive doping results in a higher dark current and reduced sensitivity. A proposed mechanism is given showing the source of photocurrents from Ag micro-flakes and Ag-doped ZnO nanorods.

Preparation of Low Volatile Organic Compounds Silver Paste Containing Ternary Conductive Fillers and Optimization of Their Performances.

Conductive silver paste is a key material in the fields of printed circuits and printed electronic devices. However, the preparation of conductive silver paste with low-cost and volatile organic compounds (VOCs) is still a challenge. In this work, conductive silver pastes with excellent comprehensive performances were developed by using water-borne polyurethane (WPU) as the bonding phase and using the ternary mixture of Ag microflakes (Ag MFs), Ag nanowires (Ag NWs), and Ag nanoparticles (Ag NPs) as the conductive phase. WPU endowed conductive silver pastes with the adhesion along with releasing a few VOCs during the curing. Results showed that a small amount of Ag NPs or Ag NWs dramatically enhanced the electrical conductivity of silver paste paint film filled only with Ag MFs. The electrical resistivity for optimal ternary mixture conductive silver paste was 0.2 × 10-3 Ω∙cm, and the conductive phase was composed of 20.0 wt% Ag MFs, 7.5 wt% Ag NWs, and 2.5 wt% Ag NPs. Meanwhile, the adhesive strength and hardness of silver paste paint film were effectively improved by increasing the curing temperature. The optimal overall performance of the conductive silver pastes was achieved at the curing temperature of 160 °C. Therefore, this work can provide a new route for preparing conductive silver pastes with high performances.

High-performance electrically conductive adhesives with aluminum-doped zinc oxide (AZO) for various flexible electronic devices

Electrically conductive adhesives (ECAs) are a kind of attractive alternative to tin solders in microelectronics. However, fabricating high-performance, low-cost ECAs remains challenging due to the need for high-content metal fillers. This work reported a facile preparation of cost-effective ECAs composed of aluminum-doped zinc oxide (AZO) nanoparticles and silver (Ag) micro-flakes. The AZO nanoparticles could serve as a “bridge” to connect neighboring Ag micro-flakes to significantly improve the ECAs′ conductivity (from 1638.8 × 10-5 Ω⋅cm to 8.5 × 10-5 Ω⋅cm). After the aging and bonding performance tests, prototyped applications of the as-prepared ECAs for three flexible electronic devices were demonstrated sequentially: (Ⅰ) The resistance of flexible conductive film showed excellent dynamic stability after being folded for 1000 cycles, bent/released within 6 mm radius for more than 2000 cycles, or applied with 1000 kPa pressure; (Ⅱ) The coil antenna achieved fast transmission of radio frequency signal for near field communication (NFC) system; (III) The flexible heater performed efficient thermal management at 0.4–1.4 V input voltages. Therefore, the fabricated ECAs are expected to provide new opportunities for the development of novel flexible electronic devices for future applications.

A Comparative Study of Silver Microflakes in Digitally Printable Liquid Metal Embedded Elastomer Inks for Stretchable Electronics

AbstractPrinted soft conductive materials for stretchable electronics should have low electrical resistivity, high strain limit, and stable electrical properties when stretched. Previously, it has been shown that a bi‐phasic ink composed of silver (Ag) microflakes, eutectic gallium−indium (EGaIn) alloy, and styrene isoprene (SIS) block copolymer is a promising formulation for printed soft electronics and has the potential to satisfy the necessary criteria. In this study, further improvements to the ink formulation are explored, with a focus on how the choice of Ag microflakes affects the electrical and electromechanical properties of the composite. By using specific Ag microflakes, AgInGa‐SIS inks that have conductivity as high as 6.38 × 105 S m−1 and a strain limit of over 1000%, with low electromechanical coupling can be synthesized. More broadly, when comparing the composite with different silver flakes, there is a 176% relative difference in conductivity, >600% difference in strain limit, and 277% relative difference in electromechanical coupling. To demonstrate the applicability of these inks for various use cases such as wearable bioelectronics, interconnects are printed for connecting electronic breakout boards with microcontrollers that provide a stable electrical connection when stretched, and the interconnects and electrodes of a wearable electrocardiography system that monitors the heart pulses in real‐time.

Bi-Phasic Ag-In-Ga-Embedded Elastomer Inks for Digitally Printed, Ultra-Stretchable, Multi-layer Electronics.

A bi-phasic ternary Ag-In-Ga ink that demonstrates high electrical conductivity, extreme stretchability, and low electromechanical gauge factor (GF) is introduced. Unlike popular liquid metal alloys such as eutectic gallium-indium (EGaIn), this ink is easily printable and nonsmearing and bonds strongly to a variety of substrates. Using this ink and a simple extrusion printer, the ability to perform direct writing of ultrathin, multi-layer circuits that are highly stretchable (max. strain >600%), have excellent conductivity (7.02 × 105 S m-1), and exhibit only a modest GF (0.9) related to the ratio of percent increase in trace resistance with mechanical strain is demonstrated. The ink is synthesized by mixing optimized quantities of EGaIn, Ag microflakes, and styrene-isoprene block copolymers, which functions as a hyperelastic binder. When compared to the same composite without EGaIn, the Ag-In-Ga ink shows over 1 order of magnitude larger conductivity, up to ∼27× lower GF, and ∼5× greater maximum stretchability. No significant change over the resistance of the ink was observed after 1000 strain cycles. Microscopic analysis shows that mixing EGaIn and Ag microflakes promotes the formation of AgIn2 microparticles, resulting in a cohesive bi-phasic ink. The ink can be sintered at room temperature, making it compatible with many heat-sensitive substrates. Additionally, utilizing a simple commercial extrusion based printer, the ability to perform stencil-free, digital printing of multi-layer stretchable circuits over various substrates, including medical wound-dressing adhesives, is demonstrated for the first time.

Fully Integrated Design of a Stretchable Solid-State Lithium-Ion Full Battery.

A solid-state lithium-ion battery, in which all components (current collector, anode and cathode, electrolyte, and packaging) are stretchable, is introduced, giving rise to a battery design with mechanical properties that are compliant with flexible electronic devices and elastic wearable systems. By depositing Ag microflakes as a conductive layer on a stretchable carbon-polymer composite, a current collector with a low sheet resistance of ≈2.7 Ω □-1 at 100% strain is obtained. Stretchable electrodes are fabricated by integrating active materials with the elastic current collector. A polyacrylamide-"water-in-salt" electrolyte is developed, offering high ionic conductivity of 10-3 to 10-2 S cm-1 at room temperature and outstanding stretchability up to ≈300% of its original length. Finally, all these components are assembled into a solid-state lithium-ion full cell in thin-film configuration. Thanks to the deformable individual components, the full cell functions when stretched, bent, or even twisted. For example, after stretching the battery to 50%, a reversible capacity of 28 mAh g-1 and an average energy density of 20 Wh kg-1 can still be obtained after 50 cycles at 120 mA g-1 , confirming the functionality of the battery under extreme mechanical stress.

Ag microflake-reinforced nano-Ag paste with high mechanical reliability for high-temperature applications

A silver (Ag) composite paste was fabricated based on Ag nanoparticles (NPs) and Ag microflakes (MFs). Robust interconnections were achieved after sintering in the temperature range of 150–225 °C. The shear strengths of the Ag MF + NP joints before and after thermal shock from − 50 to 150 °C for 1000 cycles were 155.7 ± 14.5 MPa and 78.4 ± 20.8 Mpa, respectively. The results show that the Ag composite paste not only has similar sintering properties to the Ag NP pastes but also exhibited superior mechanical reliability due to the addition of the Ag MFs. In addition, the sintered properties of different Ag pastes were discussed in terms of the coating organics, thermal behaviour and microstructure. The fracture modes after the shearing tests were analysed in detail. The Ag composite paste provides a potential solution for high-temperature applications.

Highly Conductive Ag Paste for Recoverable Wiring and Reliable Bonding Used in Stretchable Electronics.

Stretchable wiring and stretchable bonding between a rigid chip/component and a stretchable substrate are two key factors for stretchable electronics. In this study, a highly conductive stretchable paste has been developed with commercial Ag microflakes and poly(dimethylsiloxane), which can be used to fabricate stretchable wirings and bondings under a low curing temperature of 100 °C with printing method. Herein, recoverabilities as to recovery time and recovery resistance of the wirings are defined and discussed. The effect of Ag composition and the tensile strain rate on the recoverability of the wirings are also examined. The wiring with a low resistivity of 8.7 × 10-5 Ω cm shows much better recoverability than nanowire-based wirings due to the flake nature of the Ag particles. When stretched to 50 and 100% of strain, the resistance of the patterned wiring increases by only 10 and 110%, respectively. Moreover, the resistance of the wiring during 20% tensile cyclic test remains within 1.1 times even after 1000 cycles, thus demonstrating significant durability. The paste was utilized to fabricate conductive tracks and stretchable bondings to assemble a rigid chip to fabricate a stretchable demo. When stretched to 50% of strain, resistance of the wiring was increased by 90%. It is anticipated that the newly developed paste will be used to fabricate various stretchable wirings, bondings, and packaging structures by a simple printing process, thus enabling mass production of stretchable electronic devices.

Highly Conductive and Stretchable Ag Nanodendrite-Based Composites for Application in Nanoelectronics

Stretchable flexible conductive composites have received considerable attention recently. In this study, highly conductive and stretchable composites were synthesized using Ag microflakes (AgMFs), ...

Thermal Fatigue Behavior of Silicon-Carbide-Doped Silver Microflake Sinter Joints for Die Attachment in Silicon/Silicon Carbide Power Devices

We studied the thermal fatigue behavior of submicron silicon carbide particle (SiCp)-doped silver (Ag) microflake sinter joints for die attachment in next-generation power devices. Si dummy chips and direct bonded copper substrates with various metallization schemes were bonded using SiCp-doped Ag microflakes under mild conditions (250°C, 30 min, 0.4 MPa). The SiCp was distributed homogeneously in the porous Ag network and inhibited morphological evolution during thermal cycling tests. The shear strength of as-sintered pure Ag and SiCp-added joints was ∼50 MPa and 35 MPa, respectively. Thermal cycling tests from −40°C to 250°C were conducted for up to 1000 cycles (hours) to characterize the thermostability of the bonded joints. After 1000 cycles, joints with and without SiCp experienced bonding degradation, with shear strength of ∼25 MPa and 20 MPa, respectively. Thus, after 1000 cycles, the shear strength of pure Ag and SiCp-doped joints decreased by 58% and 42%, respectively, compared with their maximum value. Coarsening of porous Ag occurred in pure Ag joints. SiCp addition inhibited morphological evolution of SiCp-doped joints during thermal cycling. However, vertical cracks generated by thermal stress were observed in joints both with and without SiCp, which may limit long-term reliability.

Ternary Ag/epoxy adhesive with excellent overall performance.

Excellent electrical conductivity (EC) generally conflicts with high lap shear strength (LSS) for electrically conductive adhesives (ECAs) since EC increases while LSS decreases with increasing conductive filler content. In this work, the ECAs with the excellent overall performance are developed based on the ternary hybrid of Ag microflakes (Ag-MFs), Ag nanospheres (Ag-NSs), and Ag nanowires (Ag-NWs). First, a low silver content adhesive system is determined. Then, the effects of the relative contents of Ag fillers on the EC and the LSS are studied. It is shown that a small amount of Ag-NSs or Ag-NWs can dramatically improve the EC for the Ag-MF/epoxy adhesives. The Ag-NSs and Ag-NWs with appropriate contents have a synergistic effect in improving the EC. Meanwhile, the LSS of the as-prepared adhesive with the appropriate Ag contents reaches an optimal value. Both the EC and the LSS of the as-prepared ternary hybrid ECA with a low content of 40 wt % Ag are higher than those of the commercial ECAs filled with the Ag-MF content over 60 wt %. Finally, the ternary hybrid ECA with the optimal formulation is shown to be promising for printing the radio frequency identification tag antennas as an immediate application example.