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Rao Tummala

Other affiliations: Qualcomm, IBM, AVX Corporation  ...read more
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.


Papers
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Journal ArticleDOI
TL;DR: In this article, the authors describe the development of three interconnection schemes for wafer-level packages (WLPs) at 100-spl mu/m pitch, involving rigid, compliant, and semicompliant interconnection technologies, extending the state of the art in each.
Abstract: According to the latest ITRS roadmap, the pitch of area array packages is expected to decrease to 100 /spl mu/m by 2009. Simultaneously, the electrical performance of these interconnections needs to be improved to support data rates in excess of 10 Gbps, while guaranteeing thermomechanical reliability and lowering the cost. These requirements are challenging, thus, needing innovative interconnection designs and technologies. This paper describes the development of three interconnection schemes for wafer-level packages (WLPs) at 100-/spl mu/m pitch, involving rigid, compliant, and semicompliant interconnection technologies, extending the state of the art in each. Extensive electrical and mechanical modeling was carried out to optimize the geometry of the interconnections with respect to electrical performance and thermomechanical reliability. It was found that the requirements of electrical performance often conflict with those of thermomechanical reliability and the final "optimum" design is a tradeoff between the two. For the three interconnection schemes proposed, it was found that the electrical requirements can be met fairly well but acceptable mechanical reliability may require organic boards with a coefficient of thermal expansion of 10 ppm/K or lower.

14 citations

Proceedings ArticleDOI
20 Jun 2011
TL;DR: In this article, a chip embedding in 1 or 2 metal layer substrates using chip-last embedding for its merits is presented, which is obtained by embedding thin-chips within the core instead of the build-up layers as has been demonstrated previously.
Abstract: This paper presents a novel technology to enable chip embedding in 1 or 2 metal layer substrates using chip-last embedding for its merits. The novel structure is obtained by embedding thin-chips within the core instead of the build-up layers as has been demonstrated previously [1]. To enable the smallest profile embedded die structure, results from the three critical elements of the technology- 1) fine lines and spaces on core, 2) small-diameter fine-pitch area-array through-holes, and 3) thermo-mechanical reliability of small diameter through-holes have been discussed in the paper. Lines and spaces as small as 7μm were demonstrated on core laminate by using build-up type processes. Copper-filled through-holes of 30–60μm diameters were successfully fabricated and shown to pass 1300 thermal cycles from −55°C to 125°C. In addition, through-hole drilling process was optimized to achieve ultra-fine pitches of 70–100μm. Comprehensive analysis of three new materials and associated fabrication processes, carried out to demonstrate the advantages and robustness of this manufacturing-friendly 1–2 metal layer chip-last embedding technology emphasizes that it is a promising technology to achieve ultra-miniaturization for future embedded systems and sub-systems.

14 citations

Journal ArticleDOI
TL;DR: In this article, a circuit topology based on unique resonator and grounding inductor is proposed to provide design freedom of locating transmission zeros at lower and upper stopbands relative to the center frequency.
Abstract: This paper presents thin-film high-rejection bandpass filters integrated into organic substrate technology called RXP. A circuit topology based on unique resonator and grounding inductor is proposed. The proposed circuit provides design freedom of locating transmission zeros at lower and upper stopbands relative to the center frequency. About 2.4 GHz narrow band $({ and 5 GHz wide band $({>}{1}~{\rm GHz})$ bandpass filters have been implemented in four-metal layer with 0.191 mm thin RXP substrate. The measured results show good agreement with simulations.

14 citations

Proceedings ArticleDOI
26 May 2015
TL;DR: In this article, a thermocompression bonding was applied to form copper interconnections with process tolerances to accommodate non-coplanarities of bumps and warpage of the substrate, without solders.
Abstract: High-throughput assembly technologies to form Copper (Cu) interconnections without solders at below 200°C, and pitch below 40µm has been a major challenge in the semiconductor industry. A unique solution has been demonstrated by Georgia Institute of Technology to overcome this grand challenge. This technology utilizes thermocompression bonding to form copper interconnections with process tolerances to accommodate non-coplanarities of bumps and warpage of the substrate, without solders. The bonding pressure applied for thermocompression was 365MPa, to enable Cu bump collapse by 3µm. As thermocompression bonders are generally force-limited to 400N, such high bonding pressures may hinder scalability of this technology to fine pitches with higher I/O densities. This paper addresses this manufacturability challenge with the novel Electroless Palladium Autocatalytic Gold (EPAG) surface finish instead of the standard Electroless Nickel Immersion Gold (ENIG) or Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG) finish, previously used to prevent Cu oxidation for bonding load reduction down to 120MPa.

14 citations

Proceedings ArticleDOI
20 Jun 2005
TL;DR: In this paper, the authors proposed reworkable nano interconnects as a new interconnect paradigm for potential low cost, highest performance and reliability, not trading one for the other.
Abstract: The decrease in feature sizes of micro-electronic devices has underlined the need for higher number of I/O's in order to increase its functionality. Being able to provide several fold increase in the chip-to-package vertical interconnect density is essential for garnering the true benefits of nanotechnology that will utilize nanoscale devices. This will spur greater interest in developing electronic packages with fine and ultra fine pitches (20-50 microns). Current approaches for chip to package interconnections are limited in terms of either pitch or electrical-mechanical trade-off in properties. For example, lead free solder interconnects fail mechanically as the pitch is brought down from current 200 micron pitch to 20 micron. Compliant leads, on the other hand, solve mechanical reliability but at the expense of electrical performance. We propose reworkable nano interconnects as a new interconnect paradigm for potential low cost, highest performance and reliability—not trading one for the other. This paper describes the design and fabrication of the first 50 micron pitch wafer level packaging test bed to demonstrate reworkable nano-interconnects. Nano-grained electroplated copper is chosen as the primary interconnect material. Reworkability was addressed by a thin, liquid lead-free solder interface between the interconnect and the package. The processing approaches for the electroplated Cu interconnect, Sn-Cu interface and the high-density substrate wiring are presented along with the simulated mechanical and electrical performance of the interconnects.

14 citations


Cited by
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Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
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 …

33,785 citations

Journal ArticleDOI
TL;DR: Shape-memory polymers as discussed by the authors are an emerging class of active polymers that can change their shape in a predefined way from shape A to shape B when exposed to an appropriate stimulus.

1,575 citations

Journal ArticleDOI
14 Feb 2008-Nature
TL;DR: This work establishes a methodology for scavenging light-wind energy and body-movement energy using fabrics and presents a simple, low-cost approach that converts low-frequency vibration/friction energy into electricity using piezoelectric zinc oxide nanowires grown radially around textile fibres.
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.

1,473 citations

Journal ArticleDOI
TL;DR: This work demonstrates the vertical and lateral integration of ZnO nanowires into arrays that are capable of producing sufficient power to operate real devices and uses the vertically integrated nanogenerator to power a nanowire pH sensor and a Nanowire UV sensor, thus demonstrating a self-powered system composed entirely of nanowiring.
Abstract: The lateral and vertical integration of ZnO piezoelectric nanowires allows for voltage and power outputs sufficient to power nanowire-based sensors.

1,465 citations

Journal ArticleDOI
TL;DR: In this paper, the authors focus on the important role and challenges of high-k polymer-matrix composites (PMC) in new technologies and discuss potential applications of highk PMC.

1,412 citations