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

Rapid changes in the semiconductor industry will continue toward higher functionality that leads to higher input/outputs (I/O) counts, pushing packaging towards higher density architectures. In the next two to three years, the I/O pitch will fall within 100 μm for area array die and 30 μm for periphery die. That raises an important question to the packaging industry: How will the rapid shrinkage of the I/O pitch affect the package substrate for chip attaching? The answer is sub-10 micron copper line technology. Theoretical and experimental studies on the limitations of using mercury i-line ultraviolet photolithography have been carried at the Packaging Research Center at Georgia Tech. Furthermore, ultra fine copper line routing substrates are demonstrated for flip chip attaching by using semi-additive metallization process.

Proximity Lithography in Sub-10 Micron Circuitry for Packaging Substrate

Ultra-thin, panel embedded packages in glass and laminate substrates with embedded copper heat-spreaders with near-zero thermal interface resistance are demonstrated for the first time. This unique package addresses the thermal dissipation requirements of 30W-100W power amplifiers by embedding the IC in the glass substrate and direct metallization with large copper heat spreaders. This package also demonstrates a solution to mitigate the stresses induced from copper-glass CTE mismatch using built-in stress buffers. Ultra-low loss dry film polymers used to embed the IC and serve as the RDL dielectrics result in low loss at GHz frequency bands.

Integrated Copper Heat Spreaders in Glass Panel Embedded Packages with Near-Zero Thermal Interface Resistance

Wetting of glass-to-metal and glass-to-ceramic in water-vapour atmospheres

Land grid arrays (LGAs) and ball grid arrays (BGAs) constitute the board-level interconnect technologies for a large number of packaged ICs. These technologies are used in socketing and surface mount (SMT) applications, respectively. The concept of socketable BGA packages, with solder spheres coated with a barrier layer/noble metal coating, was introduced to develop a single package design for processor ICs that are used in both socketing and SMT applications. While this concept has previously been demonstrated, the feasibility of these packages in socketing conditions has not yet been studied. This article assesses the applicability of these packages in socketing by subjecting the packages to thermal aging at a temperature of 120 °C. The change in microstructure with thermal aging along with the consumption of the barrier layer was understood. The joint shear strength evolution with thermal aging and the contamination of the top surface of the spheres was studied by the X-ray photoelectron spectroscopy (XPS) analysis. It was found that the trend for experimental consumption of the barrier layer closely follows the theoretical model predictions. Solid-state solder wicking of the Sn57.6Bi0.4Ag (SBA) solder joint due to creep was confirmed at high homologous temperature for the solder. This, along with grain coarsening over time, led to a decrease in the joint shear strength from 33.5 to 16 MPa. Polymer collars are suggested as a potential solution to prevent the solder wicking and make the package feasible for socketing applications.

Thermal Aging Reliability of Socketable BGA Packages With Ni–Au-Coated SAC305 Spheres

In this paper, a large 2.5D glass interposer is demonstrated with 50 um chip-level interconnect (FLI), 3/3 um line and space (L/S) escape routing, and six metal layers, which are targeted for JEDEC high bandwidth memory (HBM). Our routing design suggests that double sided panel processing with 3/3 um L/S can accommodate required signal lines for HBM. Then, 3/3 um L/S transmission lines on 25mm × 30mm glass interposers with 300 um core thickness can be realized by utilizing semi additive process. Finally, 10mm × 10m dies with daisy chains can be successfully bonded to 25mm × 30mm glass interposer with 6 metal lines using copper microbumps with SnAg solder caps.

Rao Tummala

Papers

Proximity Lithography in Sub-10 Micron Circuitry for Packaging Substrate

Integrated Copper Heat Spreaders in Glass Panel Embedded Packages with Near-Zero Thermal Interface Resistance

Wetting of glass-to-metal and glass-to-ceramic in water-vapour atmospheres

Thermal Aging Reliability of Socketable BGA Packages With Ni–Au-Coated SAC305 Spheres

Design and demonstration of large 2.5D glass interposer for high bandwidth applications