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.

Physics-based reliability assessment of embedded passives

Abstract: The integration of passives into boards requires research in process steps, material synthesis and characterization, thermomechanical-electrical modeling, fabrication and reliability testing. The literature available on the thermo-mechanical reliability of integral passives and its relation to system level reliability is limited. The reliability of integral passives under thermal excursions through physics-based models is presented in this paper. The thermo-mechanical failure mechanisms and their influence on system electrical parameters (R, L and C parameters) are discussed.

3D printed wearable flexible SIW and microfluidics sensors for Internet of Things and smart health applications

Abstract: In this paper, a flexible SIW wearable sensing platform is proposed with a novel 3D printing process which enables fast-prototyping customized wearable devices. The fabrication utilizes state-of-the-art SLA 3D printing that features fast prototyping of easy-to-reconfigure flexible 3D objects. Two different flexible metallization approaches are explored in this paper, which are complementary to each other and provide an excellent 3D metallization solution together. Two 3D shape SIW transmission lines are shown with a great flexibility and great potential for wearable devices. Moreover, based on a SIW slot waveguide antenna, this paper presents a proof-of-concept microfluidics sensor with sensitivity of 1.7 MHz/Er, which can be used as a wearable sensing device for real-time monitoring of body fluids. The proposed SIW-based flexible wearable devices along with the microfluidics sensors can be used in various Internet-of-Things applications, such as smart health and food quality monitoring.

Method of making a multi-layer glass-ceramic structure having copper-based internal conductors

Abstract: Die Erfindung betrifft die Herstellung gesinterter glaskeramischer Substrate, die in mehreren Ebenen miteinander verbundene Dickschicht-Leitungsmuster auf Kupferbasis enthalten. The invention relates to the production of sintered glass-ceramic substrates containing in several planes interconnected thick-film conductive patterns on the copper base. Diese Substrate werden dabei durch Brennen in einer genau uberwachten Atmosphare von Wasserstoff und H 2 O und bei Temperaturen unterhalb des Schmelzpunktes von Kupfer erhalten. These substrates are obtained here by firing in a carefully controlled atmosphere of hydrogen and H 2 O and at temperatures below the melting point of copper.

Innovative Socketable and Surface-Mountable BGA Interconnections

Abstract: This paper introduces a universal BGA technology that can reliably be used both in sockets and SMT applications. Socketing and SMT have been driving two different board-level interconnection technologies: LGA for socketing, to provide a stable and reworkable mechanical contact, and BGA for SMT, for low-temperature metallurgical bonding to the board. Enabling socketable BGAs has become critical to simplify microprocessor package designs and converge towards a unique product. The approach presented in this research involves the use of multi-layered coatings on solder spheres. These coatings consist of a diffusion barrier/noble metal combination designed based on diffusion models to meet the requirements of both applications. Standard surface finish Electroless Ni Immersion Au (ENIG) has been studied in detail as a first approach. This paper focuses on the challenges faced in plating ENIG on traditional SAC solder balls and a new process combining sputtering and electrodeposition is demonstrated as a promising alternative to uniformly coat solder spheres with a controlled thickness of ENIG without corrosion. A first demonstration of attaching these coated spheres to the package is also presented.

Structure-magnetic property correlations in nickel-polymer nanocomposites

Abstract: Epoxy matrix nanocomposites with nickel nanoparticles of two different sizes were processed and characterized to investigate their structure-magnetic prop- erty correlations. Crystal structure, morphology, density, resistivity and magnetic properties of the nanocomposites withdifferentfillercontentswerecomparedfordifferentsize scales. Nanocomposites with 25 nm nanoparticles showed higher coercivity, higher frequency stability and lower loss, though the permeability was suppressed. Coarser nickel particles (100 nm) showed a permeability of *5.5 but sta- bility only up to 200 MHz. The structure-magnetic property correlations were validated using analytical models to pro- vide valuable design guidelines for permeability and fre- quency-stability in particulate nanocomposites.

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.