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.

Electrical characteristics analysis and comparison between through silicon via(TSV) and through glass via(TGV)

Abstract: The electrical characteristics of silicon and glass interposer channel are heavily affected by the design of through silicon via (TSV) and through glass via (TGV). In this paper, we analyzed the overall signal integrity of glass and silicon interposer channel including through package via. To compare electrical property between silicon and glass, we simulated these channels in frequency-domain and time-domain. We observed s-parameter of single and multiple via transition channel. Moreover we compared the characteristic impedance and eye diagram simulation results. Finally, we observed the change of electrical characteristics when the impedance mismatch is occurred at via pad.

Substrate Embedded Thin-Film Inductors With Magnetic Cores for Integrated Voltage Regulators

Abstract: High-density and high-frequency inductors (>5 MHz) enable miniaturization of power modules, and also integration of voltage regulator modules into the processor packages for higher efficiency and switching frequencies Several advances in magnetic materials and substrate process integration are needed to meet the performance, size, and cost requirements This paper highlights two substrate-embedded inductor approaches using magnetic paste and pre-fabricated magnetic thick laminate sheets An innovative cavity-filling process using paste printing and hot pressing is developed to integrate magnetic paste with high magnetic filler loading into the core of standard organic laminate substrates The hot-pressed metal/polymer composite magnetic cores showed a permeability of ~55 at 10 MHz The other approach utilizes pre-fabricated thick magnetic sheets with a permeability of ~93 at 10 MHz Standard panel-scale processes are adapted for high-volume manufacturing at low cost The electrical performance of the inductors from both approaches showed good correlation between the simulated and measured data Compared with air-core inductors with the same structure, the advanced thin-film inductors with magnetic sheet showed nine times improvement in inductance Both these approaches can be scaled to higher frequencies with further innovation in magnetic composites

High-density, end-to-end optoelectronic integration and packaging for digital-optical interconnect systems

Abstract: Recent progress toward implementing high-density, optical-digital building blocks necessary to accomplish efficient, end-to-end optical interconnect architecture on low cost FR-4 boards has been demonstrated. The optical interconnect system consists of fabricating an optical buffer layer separating board metallurgy from the optical lightwave circuit layer, and implementing optical links between embedded lasers and detectors. We will show an example of 1310 nm light from an edge emitting distributed-feedback or Fabry-Perot laser operating at 10 Gb/s being guided to the photodetector by a polymer waveguide. Both lasers and detector are embedded in the waveguide and all construction is built on a low-cost FR-4 board with 3 levels of metallurgy.

New structure of microelectronic packages with edge protection by coating

Abstract: Disclosed herein are edge-coated microelectronic packages comprising a microelectronic package having a top, a bottom, and an exposed edge, and a coating comprising a polymer, wherein the microelectronic package comprises a glass substrate, and wherein the coating covers at least a portion of the top, at least a portion of the bottom, and at least a portion of the exposed edge of the microelectronic package. Also disclosed herein are methods of making and using edge-coated microelectronic packages.

Reliability assessment of microvias in HDI printed circuit boards

Abstract: Accelerating adoption of CSP and flip-chip area array packaging for high performance and hand-held applications is the main driving force for high-density printed circuit boards and substrates. Ultrafine line HDI substrate technology is being developed as part of the System-on-a-Package (SOP) research and test bed efforts to meet these emerging requirements. To be adopted by industry, this novel technology must demonstrate the critical elements of high reliability and low cost processing. The high density interconnect (HDI) and microvias structures discussed in this paper, were fabricated on high Tg FR4 cores, measuring 300 mm /spl times/ 300 mm in size, and contain up to 3 metal interconnect layers. They were fabricated using a sequential build-up process, and were subject to extensive liquid to liquid thermal shock testing. Shock testing revealed that reliability failures are process defect driven and do not correlate directly to microvia geometries. 75 /spl mu/m microvias have successfully passed 2,000 cycles without failure, zero 50 /spl mu/m vias failed before 1,000 cycles, and 25 /spl mu/m microvias have passed 1,200 cycles with zero failures to date. Cross-sectioning of the failed components confirmed that failures were caused by process related defects, such as thin electrolytic copper plating. This paper discusses the reliability results of the PRC HDI microvias process, and how to improve the mechanical reliability of small photodefined microvias fabricated on similar laminates using similar processes.

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.