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 various embodiments of the present invention provide a stress-relieving, second-level interconnect structure that is low-cost and accommodates TCE mismatch between low-TCE packages and PCBs. The various embodiments of the interconnect structure are reworkable and can be scaled to pitches from about 1 millimeter (mm) to about 150 micrometers (μm). The interconnect structure comprises a dielectric body element and at least one interconnection array that provides a conductive path between two electronic components. Each interconnection array comprises a plurality of wires that provide both conductivity and compliance to the overall interconnect structure. The versatility and scalability of the interconnect structure of the present invention make it a desirable structure to utilize in current two-dimensional and ever-evolving three-dimensional IC structures.

Interconnect structures and methods of making the same

Solid-state diffusion studies of lead-free solders on gold and in polymer films

In this paper, we design and analyze receiver channels of a glass interposer for a 5G small cell front end module (FEM). In RF systems, a 50 ohm impedance matching is important for RF channels to guarantee the target RF sensitivity of the RF system. Receiver channels of glass interposers for the 5G small cell FEM are designed, analyzed and characterized up to 40 GHz considering the impedance matching. Using the designed receiver channels, the glass interposer based the 5G small cell FEM is designed and analyzed up to 40 GHz.

Design and Analysis of Receiver Channels of Glass Interposers for 5G Small Cell Front End Module

This paper reports compliant microwire copper arrays, in thin polymer carriers, as an innovative approach for direct surface mount technology (SMT) attach of large silicon, glass, and low coefficient of thermal expansion organic interposers to printed wiring boards (PWBs). The microwire arrays (MWAs) are prefabricated as free-standing ultrathin carriers using standard, low-cost manufacturing processes such as laser vias and copper electroplating. Such wire array carriers are then assembled in between the interposer and the PWB as a stress-relief interlayer. The MWA interconnections show low interconnection stress and strains even without the underfills. The approach is extensible to larger interposer sizes ( $20~\textrm {mm} \times 20~{\rm mm}$ ) and finer pitch (400 $\mu \text{m}$ ), making it suitable for smart mobile systems. The parallel wire arrays that form each joint result in low resistance and inductance, and therefore, do not degrade the electrical performance. The scalability of these structures allows extendibility to finer pitch and larger interposer sizes for high-performance applications. The finite-element method was used to design the MWAs to meet the thermomechanical reliability requirements. Computational models were built in 2.5-D geometries to study the reliability of 400- $\mu \text{m}$ -pitch interconnections with a 100- $\mu \text{m}$ -thick, $20~\textrm {mm} \times 20~{\rm mm}$ silicon interposer that was SMT-assembled onto an organic PWB. The warpage, equivalent plastic strain, and projected fatigue life of the MWA interconnections are compared with those of the ball grid array interconnections. A unique set of materials and processes was used to demonstrate the low-cost fabrication of the MWAs. Copper microwires with $15~\mu \text{m}$ diameter and 50 $\mu \text{m}$ height were fabricated on both sides of a 50- $\mu \text{m}$ -thick thermoplastic polymer carrier using dry-film-based photolithography and bottom-up electrolytic plating. The copper microwire interconnections were assembled between silicon interposer and FR-4 PWB with SMT-compatible processes. Thermomechanical reliability of the interconnections was characterized by thermal cycling test from −40°C to 125 °C. The initial fatigue failure in the interconnections was identified at 700 cycles, consistent with the models.

Direct SMT Interconnections of Large Low-CTE Interposers to Printed Wiring Board Using Copper Microwire Arrays

One-dimensional ZnO nanobelt exhibits unique properties which makes it a perfect candidate for sensors in various applications In this paper, synthesis of ZnO nanobelts is described Design and fabrication of electrodes are presented Alignment of nanobelts, which is assisted by the optimized designed electrode, is discussed Dramatic improvement of the contact resistance is found after the sample is annealed at 500degC for 1 min This work lays the foundation for further fabrication, fictionalization and packaging of ZnO nanobelt based sensors

Rao Tummala

Papers

Interconnect structures and methods of making the same

Solid-state diffusion studies of lead-free solders on gold and in polymer films

Design and Analysis of Receiver Channels of Glass Interposers for 5G Small Cell Front End Module

Direct SMT Interconnections of Large Low-CTE Interposers to Printed Wiring Board Using Copper Microwire Arrays

Packaging of ZnO nanobelts as nanosensors: Synthesis, Alignment and Characterization