While NASA explores the power of 3D printing in the development of the next generation space exploration vehicle, a CubeSat Trailblazer was launched in November 2013 that integrated 3D-printed structures with embedded electronics. Space provides a harsh environment necessary to demonstrate the durability of 3D-printed devices with radiation, extreme thermal cycling, and low pressure—all assaulting the structure at the atomic to macroscales. Consequently, devices that are operational in orbit can be relied upon in many terrestrial environments—including many defense and biomedical applications. The 3D-printed CubeSat module (a subsystem occupying approximately 10 % of the total volume offered by the 10 × 10 × 10-cm CubeSat enclosure) has a substrate that fits specifically into the available volume—exploiting 3D printing to provide volumetric efficiency. Based on the best fabrication technology at the time for 3D-printed electronics, stereolithography (SL), a vat photopolymerization technology, was used to fabricate the dielectric structure, while conductive inks were dispensed in channels to provide the electrical interconnect between components. In spite of the structure passing qualification—including temperature cycling, shock and vibration, and outgas testing—the photocurable materials used in SL do not provide the level of durability required for long-term functionality. Moreover, the conductive inks with low-temperature curing capabilities as required by the SL substrate material are widely known to provide suboptimal performance in terms of conductivity. To address these challenges in future 3D-printed electronics, a next generation machine is under development and being referred to as the multi3D system, which denotes the use of multiple technologies to produce 3D, multi-material, multifunctional devices. Based on an extrusion process necessary to replace photocurable polymers with thermoplastics, a material extrusion system based on fused deposition modeling (FDM) technology has been developed that integrates other technologies to compensate for FDM’s deficiencies in surface finish, minimum dimensional feature size, and porosity. Additionally, to minimize the use of conductive inks, a novel thermal embedding technology submerges copper wires into the thermoplastic dielectric structures during FDM process interruptions—providing high performance, robust interconnect, and ground planes—and serendipitously improving the mechanical properties of the structure. This paper compares and contrasts stereolithography used for 3D-printed electronics with the FDM-based system through experimental results and demonstrates an automated FDM-based process for producing features not achievable with FDM alone. In addition to the possibility of using direct write for electronic circuitry, the novel fabrication uses thermoplastics and copper wires that offer a substantial improvement in terms of performance and durability of 3D-printed electronics.

3D Printing multifunctionality: structures with electronics

The sol-gel process

A method for growing films for use in integrated circuits using atomic layer deposition and a subsequent converting step is described. In an embodiment, the subsequent converting step includes oxidizing a metal atomic layer to form a metal oxide layer. The atomic layer deposition and oxidation step are then repeated to produce a metal oxide layer having sufficient thickness for use as a metal oxide layer in an integrated circuit. The subsequent converting step, in an embodiment, includes converting the atomic deposition layer by exposing it to one of nitrogen to form a nitride layer, carbon to form a carbide layer, boron to form a boride layer, and fluorine to form a fluoride layer. Systems and devices for performing the method, semiconductor devices so produced, and machine readable media containing the method are also described.

Atomic layer deposition and conversion

Stereoregular Polymers and Stereospecific Polymerizations Edited by Giulio Natta and Ferdinando Danusso. (The Contributions of Giulio Natta and his School of Polymer Chemistry.) Vol. 1: Pp. xxii + 1 + 466. Vol.2: Pp. xx + 467–888. (Oxford, London and New York: Pergamon Press, Ltd., 1967.) 315s. net per set of two volumes. Heteroatom Ring Systems and Polymers By H. R. Allcock. Pp. xi + 401. (New York: Academic Press, Inc.; London: Academic Press, Inc. (London), Ltd., 1967.) 132s.

Advances in Polymer Science

Wearable devices that monitor muscle activity based on surface electromyography could be of use in the development of hand gesture recognition applications. Such devices typically use machine-learning models, either locally or externally, for gesture classification. However, most devices with local processing cannot offer training and updating of the machine-learning model during use, resulting in suboptimal performance under practical conditions. Here we report a wearable surface electromyography biosensing system that is based on a screen-printed, conformal electrode array and has in-sensor adaptive learning capabilities. Our system implements a neuro-inspired hyperdimensional computing algorithm locally for real-time gesture classification, as well as model training and updating under variable conditions such as different arm positions and sensor replacement. The system can classify 13 hand gestures with 97.12% accuracy for two participants when training with a single trial per gesture. A high accuracy (92.87%) is preserved on expanding to 21 gestures, and accuracy is recovered by 9.5% by implementing model updates in response to varying conditions, without additional computation on an external device. A surface electromyography biosensing system that is based on a screen-printed, conformal electrode array and has in-sensor adaptive learning capabilities can classify human gestures in real time and with high accuracy.

A wearable biosensing system with in-sensor adaptive machine learning for hand gesture recognition

This invention relates generally to uses of novel nanomaterial composition and the systems in which they are used, and more particularly to nanomaterial compositions generally comprising carbon and a metal, which composition can be exposed to pulsed emissions to react, activate, combine, or sinter the nanomaterial composition. The nanomaterial compositions can alternatively be utilized at ambient temperature or under other means to cause such reaction, activation, combination, or sintering to occur.

Electrical, plating and catalytic uses of metal nanomaterial compositions

A system and method for synthesizing nanopowder which provides for precursor material ablation from two opposing electrodes (31, 32) that are substantially axially aligned and spaced apart within a gaseous atmosphere, where a plasma (37, 38) is created by a high power pulsed (34) electrical discharge between the electrodes (31, 32), such pulse being of short duration to inertially confine the plasma, thereby creating a high temperature and high density plasma having high quench and/or reaction rates with the gaseous atmosphere for improved nanopowder synthesis.

Radial pulsed arc discharge gun for synthesizing nanopowders

A novel and industrially scalable technique is presented for curing metal nanoparticle based films in which an uncured film is made conductive by exposure to a brief, intense pulse of light from a xenon flash lamp. This technology heats and fuses the metal nanoparticles without significantly heating the substrate. Since the technique is broadcast by nature, no critically aligned optics are required. By nature of their high surface to mass ratio, high absorptivity, poor thermal conductivity, and low thermal mass, the nanoparticles are heated by the pulsed light source without significantly heating the substrate or other thermally sensitive components. This allows a complex pattern to be instantly cured even on low temperature substrates. Data from both silver and copper based films are presented. Sheet resistances as low as 20 mΩ/□ and resistivities as low as 4X bulk have been attained with silver. Sheet resistances as low as 150 mΩ/□ and resistivities as low as 40X bulk have been attained with copper. Typical substrates are cellulose and PET and typical films are 0.5-5 microns thick. In addition to silver, this technology enables the printing of copper conductive patterns with high speed printing techniques as the short time of heating fuses the particles before they have the opportunity to significantly oxidize. Thus, no reducing or inert atmosphere is required to cure the film and attain high conductivities.

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Broadcast Photonic Curing of Metallic Nanoparticle Films

Photonic Curing uses flashlamps to thermally process a thin film at high temperature on a low temperature substrate without damaging it. This has utility in printed electronics, where high temperature curing is generally equated to electronic performance and high speed processing is equated to low cost. Three significant processing advantages are realized over previous technologies: 1. Inexpensive (and flexible) polymer substrates can now be used in place of expensive, rigid substrates while achieving similar performance. 2. Thin films can be cured quickly enough to keep up with high speed printing processes in a small footprint, thus making it suitable for in-line placement with existing print systems. 3. The transient nature of the process has enabled the creation of new types of films on low temperature substrates, including those created by the photonic modulation of high temperature chemical reactions. In this paper we discuss the mechanisms of the process and model it using a thermal diffusion simulation. The simulation has been integrated into a 4 th generation highspeed processing tool yielding predictive results.

https://briefs.techconnect.org/wp-content/volumes/Nanotech2011v2/pdf/1234.pdf

Mechanisms of Photonic Curing™: Processing High Temperature Films on Low Temperature Substrates

To avoid high temperatures and long curing times, both of which are impractical in the manufacture of flexible printed electronic devices, we fabricated new electrically conductive adhesives using vinyl ester resin and silver micro-flakes and introduced an intense pulse of light to cure the adhesives under an ambient atmosphere at room temperature. The electrically conductive vinyl ester resin–silver micro-flake adhesives can absorb intense pulsed light, which initializes the double bonds in the resin to successfully achieve crosslinking and curing. This curing process, known as photonic curing, can be completed within a second under an ambient atmosphere at room temperature, over a large area. A typical curing time was 140 ms without any photosensitizers or photoinitiators in the adhesives. The cured conductive adhesives had low bulk resistivity, e.g., 7.54 × 10−6 Ω cm and high bonding strength, e.g., 6.75 MPa. Thus, the combination of photonic curing and electrically conductive vinyl ester resin–silver micro-flake adhesives has great potential for printed electronics, which require low temperature and fast processes based on flexible devices.

Kurt A. Schroder

Papers

Electrical, plating and catalytic uses of metal nanomaterial compositions

Radial pulsed arc discharge gun for synthesizing nanopowders

Broadcast Photonic Curing of Metallic Nanoparticle Films

Mechanisms of Photonic Curing™: Processing High Temperature Films on Low Temperature Substrates

Ultra-fast photonic curing of electrically conductive adhesives fabricated from vinyl ester resin and silver micro-flakes for printed electronics