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.

A digital-optical system-on-package module architecture for high performance multiprocessors

Abstract: This paper reports on the progress toward implementing optical-digital building blocks necessary to accomplish a system-on-package module architecture for high-performance multiprocessors. In this architecture, the memory access delay (MAD) bottleneck is minimized by using a 3-D distributed shared memory field in which high speed optical interconnects deliver data to and from each processor in a cluster to each memory controller/MX-DMX in the field, each memory controller being connected to a small cluster of main memory via a short, high aggregate speed copper bus that essentially matches the intrinsic MAD of the DRAM chip.

RF Device Integration on Glass Interposer toward 3D-IPAC Packages

Abstract: 3D Integrated Passive and Actives Component (IPAC) is a new concept of ultra-miniaturized and highly functional sub-systems, which enables one to achieve higher RF functionality in a single module. As the first step, this paper demonstrates the concept of integrating passive components using 100μm ultra-thin glass and small Through Package Vias (TPVs) by ArF excimer laser. Passive low pass filters (LPF) for WLAN in thin dielectrics on glass were designed using circuit simulator and EM solver. The LPFs were fabricated using low-cost panel based processes, and then assembled onto the Printed Wiring Board (PWB). The filters on either side of the glass interposer were measured at the board level, and the results corroborated well with EM simulations. The measurement results showed low insertion loss (about −1dB) and high rejection (<−20dB). The integration of passive components using double-side and ultra-thin glass interposers with small TPVs, enables one to shrink RF module size.

Low Temperature (≪100°C) deposited pyrochlore films with high capacitance (200 nF/cm 2 ), low loss (∼0.003) and low TCF (≪100 ppm/C) for integrating RF components

Abstract: We demonstrate polymer ceramic composites and pyrochlore based thin film capacitors for embedded RF capacitors. Unlike perovskites such as barium titanate, pyrochlores have low loss and stable properties with temperature and frequency while retaining a moderately high dielectric constant. Hence, these are ideally suited for RF capacitor components both as fillers in polymers and as ultrathin films. Unfortunately, pyrochlores are generally formed at above 400 C making them difficult for organic compatible integration either on BCB build-up layers on Si or traditional organic substrates. In this report, we report new energy irradiation processes that can form pyrochlores at temperatures less than 100 C. The process starts by depositing a thin layer of Ti by e- beam evaporation, followed by hydrothermally converting it to barium titanate. The film is then converted into a pyrochlore phase at less than 100 C by oxygen ion irradiation. The phase transformation results were confirmed with XRD and SEM. By a combination of wet chemical treatment followed by oxygen ion irradiation, this technique shows the feasibility of depositing a low TCC (<100 ppm/C), low loss (0.003-0.005) and high capacitance density film (200 nF/cm2) directly on plastic substrates at temperatures less than 100 C. The films show BDVs greater than 10 volts and adequate leakage current behavior that is suitable for biased RF circuits.

Novel Ceramic Composite Substrates for High-Density and High Reliability Packaging

Abstract: This paper presents the development and evaluation of a large-area carbon-silicon carbide (C-SiC) based composite board material that has the advantages of organic boards in terms of large-area processability and machinability at potentially low-cost while retaining the high stiffness (> 200 GPa) and Si-matched coefficient of thermal expansion (CTE) (~ 2.5 ppm/degC) of ceramics. Test vehicles were fabricated using C-SiC boards for assessing ultra-fine pitch solder joint reliability without underfill as well as the reliability of high-density wiring with microvias on the board. Finite element reliability models were developed to simulate the thermomechanical behavior of test vehicles. From the finite-element simulations as well as accelerated reliability tests, the high stiffness low-CTE C-SiC boards did not show any premature solder joint fatigue failure or dielectric cracking. Furthermore, the C-SiC boards show minimal via-pad misalignment and support the multilayer buildup structure required to achieve very high wiring density. The modeling and experimental results suggest that the low-cost large-area ceramic matrix composite (C-SiC) has superior thermomechanical properties, and is, therefore, a promising candidate substrate material for the emerging microelectronic systems.

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.