Optimizing Material Selection for High-Reliability 3D In-Mold HMI Structures: Essential Factors to Consider

Flexible and wearable pressure sensors have attracted a tremendous amount of attention due to their wider applications in human interfaces and healthcare monitoring. However, achieving accurate pressure detection and stability against external stimuli (in particular, bending deformation) over a wide range of pressures from tactile to body weight levels is a great challenge. Here, we introduce an ultrawide-range, bending-insensitive, and flexible pressure sensor based on a carbon nanotube (CNT) network-coated thin porous elastomer sponge for use in human interface devices. The integration of the CNT networks into three-dimensional microporous elastomers provides high deformability and a large change in contact between the conductive CNT networks due to the presence of micropores, thereby improving the sensitivity compared with that obtained using CNT-embedded solid elastomers. As electrical pathways are continuously generated up to high compressive strain (∼80%), the pressure sensor shows an ultrawide pressure sensing range (10 Pa to 1.2 MPa) while maintaining favorable sensitivity (0.01-0.02 kPa-1) and linearity ( R2 ∼ 0.98). Also, the pressure sensor exhibits excellent electromechanical stability and insensitivity to bending-induced deformations. Finally, we demonstrate that the pressure sensor can be applied in a flexible piano pad as an entertainment human interface device and a flexible foot insole as a wearable healthcare and gait monitoring device.

Inkjet printing is known as a main technology to manufacture flexible electronic interconnect structures due to its ability to print different types of inks on flexible substrate in a controllable and fast way. However, current inkjet printing processes on manufacturing flexible electronic interconnects still face many challenges (e.g. fracture, rough etc.). In view these serious problems, the following research has been carried out in this paper. First of all, printed a series of single ink drop array on the flexible substrate, and measured its average diameter to select the appropriate distance spacing. Second, manufactured flexible interconnect structures with different substrate-ink groups by inkjet printing. Third, made a compare on the effect with different pre-treatment of the flexible substrate. And finally, discussed the effect on surface topography and resistivity of interconnect structures with different layers, curing temperature and time. After all above experiments, we obtained flexible interconnects with uniform surface morphology and good electrical conductivity.

In this paper we discuss our progress on the HID toolkit, a collection of software modules for the Pure Data and Max/MSP programming environments that provide unified, user-friendly and cross-platform access to human interface devices (HIDs) such as joysticks, digitizer tablets, and stomp-pads. These HIDs are ubiquitous, inexpensive and capable of sensing a wide range of human gesture, making them appealing interfaces for interactive media control. However, it is difficult to utilize many of these devices for custom-made applications, particularly for novices. The modules we discuss in this paper are [hidio] 1, which handles incoming and outgoing data between a patch and a HID, and [input_noticer], which monitors HID plug/unplug events. The goal in creating these modules is to preserve maximal flexibility in accessing the input and output capabilities of HIDs, in a manner that is approachable for both sophisticated and beginning designers. This paper documents our design notes and implementation considerations, current progress, and ideas for future extensions to the HID toolkit.

The development of the plastic electronics industry has drawn great interest and inspired technology innovations in a broad area. This has stimulated the rapid development of flexible circuitry manufacturing technologies, including advances in conductive inks, printing technology and most importantly the novel curing technology - laser based curing (or Laser Direct Write). This has the ability to replace the conventional environmentally damaging and time consuming chemical etching method in current Printed Circuit Board (PCB) manufacturing.This work presented in this paper is an investigation into the Nd:YAG laser curing process at the wavelength of 532 nm of particulate silver inks. A mathematical approximation of key physical properties has been developed based on the presented experimental research for use in a finite element model (FEM) simulation. 532 nm has shown benefits in protecting the flexible substrate used from thermal damage, owing to the high transparency of the wavelength through the substrate material. In this paper, liquid-phase particulate silver ink tracks deposited on flexible substrates were irradiated by laser along the track geometry. Repetition of the laser beam scanning was found to produce a smooth and fully cured sample and further reduced the track’s electrical resistivity.The development of the plastic electronics industry has drawn great interest and inspired technology innovations in a broad area. This has stimulated the rapid development of flexible circuitry manufacturing technologies, including advances in conductive inks, printing technology and most importantly the novel curing technology - laser based curing (or Laser Direct Write). This has the ability to replace the conventional environmentally damaging and time consuming chemical etching method in current Printed Circuit Board (PCB) manufacturing.This work presented in this paper is an investigation into the Nd:YAG laser curing process at the wavelength of 532 nm of particulate silver inks. A mathematical approximation of key physical properties has been developed based on the presented experimental research for use in a finite element model (FEM) simulation. 532 nm has shown benefits in protecting the flexible substrate used from thermal damage, owing to the high transparency of the wavelength through the subst...

Particle-free silver inks have the advantage of low sintering temperature, high stability, and easy synthesis over traditional nanoparticle-based silver inks, which have been widely applied in the printing electronic industry. In this paper, we develop a novel particle-free and ionic liquid-assisted silver ink consisting of silver acetate and formic acid/iso-propanolamine liquid that can be used to print highly conductive silver patterns at low sintering temperatures. A variety of continuous and consistent silver circuits with a resistivity of 7.7 µΩ·cm can be printed by a dispenser machine, which is only 4.8 times bulk silver. Furthermore, the low-resistivity silver patterns can be also printed on the flexible polyimide foil, which maintains the stability of resistivity and mechanical properties after bending multiple times, demonstrating that our ionic liquid-assisted silver ink can be applied in flexible electronic devices. Besides, our particle-free silver ink can be utilized to write electric circuits directly with a ball-point pen.

Recent development of high κ dielectric oxides on (In)GaAsis reviewed in the fields of electronic structure and electric performance; this includes studies of (In)GaAssurfaces with various surface reconstructions, different orientations, and Indium contents, and of high κ/(In)GaAsinterfaces. The oxide deposition was carried out using atomic‐layer deposition (ALD) and molecular beam epitaxy (MBE) viaex‐situorin‐situmethods. For the former approach, the semiconductor surfaces prior to the oxide deposition were obtained via chemical, arsenic‐cap or annealing treatments. For the latter, the high k's were deposited on pristine freshlyMBE‐grown (In)GaAssurfaces without any treatments. Surface being treated or not clearly determines the quality of the oxide interface which delivers different interfacial electronic structure and electric performance. Without exception, theex‐situtreated samples show remnant native oxides, which are never found in thein‐situsamples. The electronic structure has been investigated using photoemission measurements, in which the photon energy was provided byX‐ray and synchrotron radiation. The discussion on high κ/(In)GaAsinterfaces has been further extended to the electrical characterization including extraction of interfacial trap densities (Dit's). Especially, the distinct electrical characteristics of the In0.2Ga0.8As metal‐oxide‐semiconductor capacitors (MOSCAPs) usingMBE‐Ga2O3(Gd2O3) andALD‐Al2O3as the gate are elucidated. Finally, a summary and bench‐marking of the recent advances on enhancement modeIII‐V(In)GaAsMOSFETsis given, which reveals the great potential of inversion‐channel (In)GaAsMOSFETsfor ultimate complementaryMOS(CMOS) applications.

Most of textile substrates are porous because they are fabricated from yarns by weaving, or knitting. Hence direct printing of electrically conductive ink to form solid patterns on textile fabrics is a challenge. One of the conductive circuitry forming methods includes the usage of the heat transfer polymer (HTP) substrate. In this study, we investigate the described fabrication process which includes the printing of electrically conductive silver ink on the HTP substrate for wearable electronics applications. The printing process on the HTP substrate using screen printing was empirically studied using our newly developed roll-to-roll pilot line for flexible hybrid electronics. The investigated materials included $60\mu \mathrm{m}$ thick HTP substrates, and a shear thinning silver ink. The test vehicles includes lenticular patterns from 200 to $700\mu \mathrm{m}$ . The results of the study show that the different line-widths towards the resistivity values of the same length printed silver patterns follow a power function equation. The study also finds that the average electrical resistance values of the printed silver on the HTP substrate are 17.3% lower than those of on the polyethylene terephthalate (PET) substrate.

Multilayer flexible metamaterials based on circular shape with negative refractive index at microwave spectrum

Recent development in silver-based ink for flexible electronics

Surface modification of an ambient UV-cured dielectric to realise electrically conducting traces

Computed Tomography (CT) is an advanced optical imaging tool for non-destructive 3D analysis of test structures compared to the conventional imaging tool Scanning Electron Microscopy (SEM). SEM has been used extensively for analyzing the via filling1, however as per the available literature the CT-scanner has not been employed for via filling analysis of through plastic vias (TPV). In this study, we have employed both the techniques for investigating the via filling and calculating the fill ratios in TPV. A non-destructive 3D imaging technique is essential for estimating the fill ratio while overcoming the loss of material that can be accrued in sectioning samples for SEM. We show that CT-Scanning achieves a better estimation of via-filling. This method can be useful for PCB/circuit designers in obtaining a higher accuracy of via-resistance (for conductive inks) and a better 3D packaging reliability (for dielectric polymers2). This technique also shows an additional advantage for scanning dielectric materials as it doesn’t require pre-processing step of metal deposition. Images from CT-Scanning and SEM have been presented in Fig. 1 (a) and (b) respectively. Vias in different samples were prepared by laser ablation using a pico-second Nd:YAG laser3. Via-filling was accomplished by screen-printing on both sides of polyethylene terephthalate (PET) using a 325 stainless-steel mesh screen and CI-1036 (silver ink) 4,5 individually and separately with DI-7540 (dielectric). Curing of all the printed inks were done at 1220C for 12 minutes individually. No treatment of the substrates was carried out before printing. A 7-mil (177 µm) thick PET with a surface energy of 28.3 mN/m was used as a substrate for this study. Samples were first freeze-dried and cut before being used for SEM whereas samples used for CT-scanning did not require any pre-processing. Three samples for each diameter were investigated through SEM and CT-Scanning. Fill ratios from SEM images was quantified using the method outlined in other studies for through silicon vias (TSV)6,7 (Fig. 1(c)). Two sections (the center and bottom of the via) of the scanned samples were inspected for measuring the thickness of deposited material that is filled in the walls of via, as illustrated in Fig. 1 (d). For the CT-scanned images the process for calculating the fill ratio was as follows. First, the image processing toolbox of MATLAB was used to mark different points on the curvature (Fig. 1(c)) and then these points were converted into cartesian coordinates. These coordinates were then fitted into a quadratic equation of second degree to obtain an equation in f(x) (where x is parallel to cross section of the via). The volume of the cured silver was then calculated by using Eq. 1 and the fill ratio was calculated using Eq. 2. Vfill= Π∫(f(x))2 dx (1) Fill ratio=Vfill/Πr2l (2) where r is the radius of the via and l is the length of the via. The fill ratios of different diameter vias are presented in Fig. 1 (e) (only CI-1036) & Fig. 1(f) (CI-1036 and DI-7540). A mean difference of 21.11% for CI-1036 and 16.44% for DI-7540 in fill ratios was observed between CT and SEM. The work aims to address the uncertainty that may occur due to sample pre-processing required for SEM. It also discusses a rigorous approach for estimation of the via fill ratio of liquid phase materials such as dielectric or conductive inks in TPVs. *Acknowledgement This work was supported in part by the National Science Foundation (IIP-1439644) through the Multi-Functional Integrated Systems Technology (MIST).

Additive manufacturing of conductive interconnects has become essential in the electronic industry due to the requirements of having smaller electronic components with high performance and producing functional electronics that meet the applications demand. Thus, fabricating conductive lines and patches is key to reduce the challenges of mechanical and thermal reliability associated with advanced electronic technologies. In this work, high-resolution conductive interconnects were fabricated by aerosol jet printing (AJP) across different substrates using a novel particle-free silver ink. The conductivity of the metallic ink was assessed after post-processing at various curing conditions and methods. The printing process parameters of the particle-free ink were optimized to yield high-quality printed features and to investigate the printed film’s continuity on a non-flat surface, including printing from the top of a silicon die to a flexible substrate. The current carrying capacity of the printed particle-free silver ink on NEA 123 material was evaluated and compared against a commonly used nanoflake-based silver ink by performing a current sweep increasing the current by 5mA every 10 seconds until failure. In this research, conductive interconnects with sub-micron thickness have been obtained. Photonic curing using PulseForge system was found to improve the conductivity at energy density of 3.22 J/cm2 to four times the conductivity of a conventional convection oven curing. The enhancement in conductivity appears to be due to the changes in the film’s microstructure, forming metallic connections between the needle-shaped crystallized grains as revealed by X-ray microtomography. The particle-free ink can be used for irregular surfaces with smooth transitions between the electronic components. Furthermore, the current carrying capacity tests show the printed interconnect’s resistivity increased and then reduced during the test before failure; the failure of the particle-free ink occurred at 2.022 x 105 ± 0.2 A/cm2 compared to 0.99 x 105 ± 0.18 A/cm2 for the nanoflake-based silver ink which makes the particle-free ink an attractive material for high-power electronics applications. Our findings assist the application of flexible hybrid electronics and electronic packaging by providing significant guidelines for electronics manufacturers.

In recent years, there is a meteoric rise in the prevalence of electronic wearables, and flexible wearables have attracted tremendous attention in human–machine interfaces due to their high biocompatibility, functionality, conformability, and low‐cost. Flexible magnetic smart skin is part of this rapidly progressing field of flexible wearable electronics, which has paved the way for a new path for human perceptual development, as they may form a new perception, also known as magnetic sense, that is, the capacity to detect and interact with magnetic fields. In this review, the concept of the magnetic smart skin is defined: magnetoelastomers and flexible magnetic sensors. In magnetoelastomers, different sources of magnetic field, structures, and applications are summarized by recent and renowned research. In flexible magnetic sensors, different flexible substrates, sensor types, and applications are also summarized. This review further concludes by discussing the outlook and current challenges of magnetic smart skin in human–machine interfaces.

Radar cross section (RCS) reduction is thoroughly studied among electrical engineers so as to attain stealth capabilities of any object of interest. One particular kind of absorber which is in high demand is of the transparent and flexible kind. Transparent absorbers find their applications in various defence related applications such as in wind shield of aircraft and vehicles. Manufacturing of transparent metamaterial absorbers is a challenge as it is always a trade off between electrical performance and maintaining optical transparency. In this paper the authors present a technique of optimizing the electrical and optical performance of transparent absorber manufactured with commercially available Polyethylene Terephthalate (PET) coated Indium Tin Oxide (ITO) sheets.

Graphether, a two-dimensional oxocarbon monolayer, has attracted wide attention due to its excellent mechanical, thermal, and electrical performance. Armchair-edged graphether nanoribbons (AGENRs) are investigated through first-principles calculations. It is found that symmetry plays a key role in band structures, which could trigger an indirect–direct transition of the bandgap, following the odd–even parity of the nanoribbon. Furthermore, the asymmetrical electronic structure caused by edge hydrogen passivation would induce semiconducting–metallic transition. Our findings imply that the electronic structure properties of AGENRs could be modulated by symmetry, which may throw light on the band engineering of related devices and the design of heterostructures.