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

Disclosed are ferroelectric and ferromagnetic noise isolation structures that reduce electromagnetic interference and noise in integrated circuit devices and system architectures. Representative structures comprise two or more devices that are vertically disposed relative to one another, and a thin ferroelectric or ferromagnetic film layer disposed between the respective devices that isolates electromagnetic energy coupling from one device to another.

Ferroelectrics and ferromagnetics for noise isolation in integrated circuits, packaging, and system architectures

A simple and low-cost fabrication method for single-mode polymer optical waveguides with circular cores was demonstrated for fiber-to-waveguide coupling. The waveguide structure consists of trenches with semicircular cross sections, fabricated with dry film benzocyclobutene (BCB) as the bottom cladding layer, circular cores embedded inside the trenches, and another layer of dry film BCB as the top cladding layer. Simple photolithography is used to pattern both trenches in the bottom cladding layer and cores, and only one mask is used for both lithography steps. The advantages of single-mode circular waveguides on ultra-thin 3D glass interposers are discussed by comparing optical properties of those with conventional polymer waveguides with trapezoidal cross sections. To the best of the author's knowledge, this is the first demonstration of single-mode polymer waveguides with circular cross sections. Fabrication of circular-core waveguides are discussed and geometry characterization and analysis are performed.

First Demonstration of Single-Mode Polymer Optical Waveguides with Circular Cores for Fiber-to-Waveguide Coupling in 3D Glass Photonic Interposers

A method of making a gaseous discharge display and/or memory device in which no separate passivation step is required to protect the electrical conductors formed on a glass substrate. After a dielectric glass frit slurry is sprayed over the conductors and dried, the assemblage is fired in an oven to cause the dielectric to reflow and, when later cooled, to provide a smooth protective dielectric layer over the conductors. Applicants found that firing in a very wet atmosphere with neutral or oxidizing ambients causes the dielectric to reflow at a substantially lower temperature than it would in a similar but dry atmosphere. This desirably permits dielectrics of higher viscosity and consequently higher softening temperatures to now be used because the requisite firing temperature is reduced in the wet atmosphere. High viscosity dielectrics are preferred to minimize crazing of the magnisium oxide coating that is currently placed over the dielectric coating after the dielectric-substrate is cooled. Except for this reduction in firing temperature, these high viscosity dielectrics would have to be fired at temperatures over 600 DEG C., which undesirably causes warping of the soda-lime silica glass substrates currently available.

Method of sealing electrodes to glass with a glass frit

This paper presents the design, fabrication, assembly, and characterization of a fully-integrated single-chip glass BGA package at 40/80 µm off-chip I/O pitch with multilayered wiring and through-package-vias (TPVs) at 160 µm pitch. The designed test vehicle emulates an application processor package for smart mobile applications, and enables for the first time measurements of DC signal transmission from the die to the board, through the package, at this density and pitch. A daisy chain test die, 10 mm x 10 mm in size, was designed to emulate a logic processor chip comprising 5448 I/Os distributed in four peripheral rows at 40/80 µm pitch and a central area array at 150 µm pitch. The test dies were fabricated and bumped with standard Cu pillars by ASE. The glass package design included four routing layers, with blind vias (BVs) and TPVs both at 150 µm pitch, to connect 176 I/Os to the board, with BGAs at 400µm pitch. Independent multi-level test structures were added for evaluation of TPV and BV yield during fabrication, as well as partial chip-and board-level interconnection yield and reliability. The TPVs in glass were achieved by a via-first process with a high-throughput plasma etching and primer drilling method. Semi-additive processes (SAP), combined with wet chemical surface treatment methods were applied for patterning of the multi-layer wiring with a minimum of 20 µm Cu trace width at 40 µm pitch. A fan-in fan-out finger design was implemented on the top layer for bump-on-trace chip-level interconnections. Chip assembly on glass panels was carried out by high-speed thermocompression bonding with non-conductive paste (TC-NCP) with the new high-performance APAMA chip-to-substrate (C2S) bonder by Kulicke and Soffa. Yield of each process step was evaluated through fabrication and assembly by DC electrical characterization of TPV, BV and chip-level interconnection daisy chains. Die-to-substrate interconnections were characterized, demonstrating signal transmission through the fully-integrated glass package for the first time at this I/O pitch.

Design, Demonstration and Characterization of Ultra-Thin Low-Warpage Glass BGA Packages for Smart Mobile Application Processor

Highly-integrated 3D voltage regulators (IVRs) for high-power applications are developed for emerging applications such as AI computing and server. With this 3D process integration, passive components such as inductors and capacitors are embedded into substrates and placed close to the chips, resulting in short power delivery networks (PNDs) and high power efficiency. High-density tantalum capacitors are integrated with high-density magnetic-core inductors to realize IVRs with module thickness around 0.7 mm. By incorporating high-permeability magnetic materials as the cores, the inductors achieved 20X improvement in inductance as compared to air-core inductors. The high inductance allows inductors to be designed with less number of windings, resulting in low component resistance of 5 mΩ. The integrated components have package-compatible terminals that are compatible with electrolytic plating process. The terminals allow them to be connected with low-resistance vias to further reduce parasitic losses and improve the power efficiency. Short PDNs and low-resistance interconnections and low-resistance components make the demonstrated IVRs ideal for high-power density computing applications with high efficiency low-impedance power delivery networks.

Rao Tummala

Papers

Ferroelectrics and ferromagnetics for noise isolation in integrated circuits, packaging, and system architectures

First Demonstration of Single-Mode Polymer Optical Waveguides with Circular Cores for Fiber-to-Waveguide Coupling in 3D Glass Photonic Interposers

Method of sealing electrodes to glass with a glass frit

Design, Demonstration and Characterization of Ultra-Thin Low-Warpage Glass BGA Packages for Smart Mobile Application Processor

3D Packaging with Embedded High-Power-Density Passives for Integrated Voltage Regulators