Rao Tummala

Bio: Rao Tummala is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: Interposer & Capacitor. The author has an hindex of 43, co-authored 623 publications receiving 11663 citations. Previous affiliations of Rao Tummala include Qualcomm & IBM.

Co-integration of High-Bandwidth Photonic and Electronic RDL on 2.5D Glass Interposers Using Low Optical Absorption Photoimageable Dielectric Polymer

Abstract: Integration of single mode waveguides for high-bandwidth photonic interconnections and fine line RDL structures for high-bandwidth electronic interconnections on 2.5D glass interposers was demonstrated. Both structures were fabricated using the same benzocyclobutene (BCB) based low optical absorption photoimageable dielectric polymer. This material has low optical absorption, which is suitable for optical waveguides, and simulation shows that the size of the BCB based waveguide cores is close to the size of fiber cores, which enables improved fiber-to-waveguide direct coupling and reduces coupling loss due to mode mismatch. This material also has low dielectric loss, high glass transition temperature and high-temperature stability. Embedded trench RDL was developed using this material to realize fine line structures for 2.5D interposers and scale RDL beyond the limits of semi-additive process. Using one material system to fabricate both structures reduces the complexity of fabrication. This paper describes the fabrication process improvements, and the geometry characterization and analysis of electronic and photonic RDL on glass interposers.

Crystallization in copper-containing solder glasses

Abstract: Durch Erhitzen oberhalb 750°C werden in Cu-haltigen Bleiglasern betrachtliche Mengen an Cu+-Ionen erzeugt, die wahrend fortdauernder Erwarmung eine braunen CuzO-Niederschlag im Glas bilden.

Microwave design & characterization of a novel Nano-Cu based ultra-fine pitch chip-to-package interconnect

Abstract: This paper presents design and characterization of nano-Cu based ultra-fine pitch chip-to-package interconnects for microwave frequencies. Transitions are designed with this new interconnect and characterized up to 40 GHz in packaging configurations such as chip-on-chip and chip-on-package.

High Reliability and High Performance 30μm Through-Package-Vias in Ultra-Thin Bare Glass Interposer

Abstract: This paper presents, for the first time, the thermo-mechanical reliability and the electrical performance of 30μm through package vias (TPVs) formed by Corning in ultra-thin low-cost bare glass interposers and metallized directly by sputter seed and electroplating. In contrast to glass interposers with polymer coated glass cores reported previously, this paper reports on direct metallization of thin and uncoated glass panels with fine pitch TPVs. The scalability of the unit processes to large panel sizes is expected to result in bare glass interposers at 2 to 10 times lower cost than silicon interposers fabricated using back end of line (BEOL) wafer processes. The thermo-mechanical reliability of 30μm TPVs was studied by conducting accelerated thermal cycling tests (TCT), with most via chains passing 1000 cycles from −55°C to 125°C. The high-frequency behavior of the TPVs was characterized by modeling, design and measurement up to 30 GHz.

I and i

Abstract: 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 …

Microfibre–nanowire hybrid structure for energy scavenging

Abstract: 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.

Self-powered nanowire devices.

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