There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Shape-memory polymers

Nanodevices don't use much energy, and if the little they do need can be scavenged from vibrations associated with foot steps, heart beats, noises and air flow, a whole range of applications in personal electronics, sensing and defence technologies opens up. Energy gathering of that type requires a technology that works at low frequency range (below 10 Hz), ideally based on soft, flexible materials. A group working at Georgia Institute of Technology has now come up with a system that converts low-frequency vibration/friction energy into electricity using piezoelectric zinc oxide nanowires grown radially around textile fibres. By entangling two fibres and brushing their associated nanowires together, mechanical energy is converted into electricity via a coupled piezoelectric-semiconductor process. This work shows a potential method for creating fabrics which scavenge energy from light winds and body movement. A self-powering nanosystem that harvests its operating energy from the environment is an attractive proposition for sensing, personal electronics and defence technologies1. This is in principle feasible for nanodevices owing to their extremely low power consumption2,3,4,5. Solar, thermal and mechanical (wind, friction, body movement) energies are common and may be scavenged from the environment, but the type of energy source to be chosen has to be decided on the basis of specific applications. Military sensing/surveillance node placement, for example, may involve difficult-to-reach locations, may need to be hidden, and may be in environments that are dusty, rainy, dark and/or in deep forest. In a moving vehicle or aeroplane, harvesting energy from a rotating tyre or wind blowing on the body is a possible choice to power wireless devices implanted in the surface of the vehicle. Nanowire nanogenerators built on hard substrates were demonstrated for harvesting local mechanical energy produced by high-frequency ultrasonic waves6,7. To harvest the energy from vibration or disturbance originating from footsteps, heartbeats, ambient noise and air flow, it is important to explore innovative technologies that work at low frequencies (such as <10 Hz) and that are based on flexible soft materials. Here we present a simple, low-cost approach that converts low-frequency vibration/friction energy into electricity using piezoelectric zinc oxide nanowires grown radially around textile fibres. By entangling two fibres and brushing the nanowires rooted on them with respect to each other, mechanical energy is converted into electricity owing to a coupled piezoelectric–semiconductor process8,9. This work establishes a methodology for scavenging light-wind energy and body-movement energy using fabrics.

http://www.nanoscience.gatech.edu/zlwang/paper/2008/08_nat_1.pdf

Microfibre–nanowire hybrid structure for energy scavenging

The lateral and vertical integration of ZnO piezoelectric nanowires allows for voltage and power outputs sufficient to power nanowire-based sensors.

http://www.nanoscience.gatech.edu/zlwang/paper/2010/10_NN_01.pdf

Self-powered nanowire devices.

Fundamentals, processes and applications of high-permittivity polymer–matrix composites

The chemical structure and electrical properties of anodized titania are investigated for their application as conformal ultra-thin dielectrics on high surface area titanium electrodes. The chemical structure is studied by XPS depth profiling for the first time along with the role of anodization conditions on dielectric thickness, leakage current, and capacitance densities. Different leakage current models were used to identify the defect mechanisms in the titania film formed at different voltages. EDS and structural SEM studies were performed to investigate the morphology and structure of the titania films. This research also demonstrates the fabrication and characterization of high-density capacitors using high surface area titanium metal electrodes, conformal high K, and thin-film dielectric of titania. High-permittivity and thin-film titania dielectric was grown on high surface area titanium anodes using anodization, while conducting polymer was used as the cathode. The fabricated capacitor showed 7.15 µF cm−2 at 100 kHz which corresponded to 7.5X enhancement in surface area compared to planar thin-film capacitors. This is the first demonstration of high-density capacitors using high surface area titanium anodes along with high-permittivity and thin-film titania as the dielectric.

XPS depth profiling and leakage properties of anodized titania dielectrics and their application in high-density capacitors

Nanomagnetics provide unique opportunities to address the fundamental limitations of traditional electronic materials for miniaturization of RF and power components, while simultaneously enhancing their performance. This paper demonstrates nanomagnetic films and processes for power inductors and EMI shield applications. A DC-RF co-sputtering process was developed to synthesize cobalt-based nanogranular films with superior properties compared to microscale magnetic materials. The benefits of this material for miniaturized power inductors are demonstrated with analytical models. The second part of the paper demonstrates miniaturization of electromagnetic interference (EMI) shields with nanomagnetic film-stacks.

Nanomagnetic Thinfilms for Advanced Inductors and EMI Shields in Smart Systems

Reliability of through-package vias (TPVs) in 100- ${\mu }\text{m}$ glass, prefabricated with an innovative via-first process, is investigated through systematic modeling, design, fabrication, and reliability characterization. Finite element models were built to assess the impact of this novel process on stress and strain distribution in TPV structures. Thermomechanical simulations were carried out to provide design guidelines for reliable TPVs. In order to experimentally validate the predictions from simulations, test samples containing metallized TPVs with 60 ${\mu }\text{m}$ diameter were fabricated with 100- ${\mu }\text{m}$ thick glass. To assess the reliability of TPVs, daisy chains were fabricated and subjected to thermal cycling between −55 °C and 125 °C. TPV daisy chain resistances were measured at regular thermal cycling intervals to detect initiation of failures during reliability characterization. As predicted from mechanical modeling, changes in resistance were experimentally observed to be less than the chosen failure criterion, indicating no failures. Detailed mechanical failure analysis by scanning electron microscopy revealed elimination of delamination and crack failures in contrast to those observed in via-first bare glass interposers. This is attributed to the reduced stress and enhanced adhesion with the polymer layers.

Reliability of Through-Package-Vias From via-First Processing With Ultra-Thin Glass

A sintering process is described using a glass-ceramic slurry containing an alloy powder or flakes selected from a group of alloys consisting of: ______________________________________ Fe--Cr Cu--TiFe--Cr--Ni Ag--TiCr--Al Nb--AlNi--Cr Cu--AlNi--Al Cu--Al--CrFe--Al______________________________________ The slurry is molded and later is sintered in a steam atmosphere at a temperature of about 1000° C. to yield a glass-ceramic substrate toughened against crack propagation and useful in the packaging of semi-conductor device chips.

Toughened glass ceramic substrates for semiconductor devices subjected to oxidizing atmospheres during sintering

The new trends in automotive electronics such as autonomous driving, in-car infotainment, and all-electric cars, require an entirely different electronic vision and technologies than are pursued today for automotive industry. Georgia Tech proposes system scaling as a new frontier to address the upcoming era of automotive challenges. It also proposes an innovative 3D system package architecture taking into account electrical, mechanical and thermal designs as well as new digital, RF, sensors, radar millimeter-wave and power technologies. It proposes highly innovative large panel-based, ultra-thin glass packaging with many innovations in electrical, thermal, mechanical designs, materials, processes, wiring lithography, fine-pitch and high-throughput assembly and highly-conductive through-Cu vias for signal, power and heat transfer. Such an approach is proposed to lead to highly-functional sub-systems for integration of disparate set of technologies at lowest cost, in smallest ultra-miniaturized size with shortest interconnections with lowest power consumption.

Rao Tummala

Papers

XPS depth profiling and leakage properties of anodized titania dielectrics and their application in high-density capacitors

Nanomagnetic Thinfilms for Advanced Inductors and EMI Shields in Smart Systems

Reliability of Through-Package-Vias From via-First Processing With Ultra-Thin Glass

Toughened glass ceramic substrates for semiconductor devices subjected to oxidizing atmospheres during sintering

New era in automotive electronics, a co-development by Georgia tech and its automotive partners