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.

Material and process set for fabrication of molecular matrix print head

Abstract: A method for fabricating a molecular matrix print head for use in nonimpact electrolytic printers. Green ceramic sheets are stacked and laminated, then embossed with insulators and screened with ruthenium dioxide. The assembly is then co-sintered at less than 1000° C. and the resulting structure smoothed by lapping and finished in a convention fashion.

Glass in Electronic Packaging and Integration: High Q Inductances for 2.35 GHz Impedance Matching in 0.05 mm Thin Glass Substrates

Abstract: This work demonstrates 50 µm (2.0 mil) thin SCHOTT glass AF32eco as a RF substrate. Superior electrical performance and miniaturized component or package size in both vertical and lateral dimensions compared to traditional components and two-dimensional (2D) packages are shown to be feasible with the 3D fabrication approach with such thin glass. Vias with a diameter of 50µm are made at SCHOTT using laser structuring. Either sides of the glass substrates are coated with a thin layer of a polymer dielectric. The through-holes are re-opened and metallization processes are performed to simultaneously create a thick copper metallization on both surfaces as well as on the vias to make them conducting. The metallization is structured with semi-additive patterning using photolithography and etching to obtain solenoid inductors for matching networks of filter elements. The magnetic field of the components is mainly parallel to the glass substrate. Inductances with 1.7 nH and 1.9 nH are designed and fabricated using different structures for shielding. The performance metrics of the demonstrated glass-integrated passive devices (IPDs) and modules were characterized. Excellent correlation between modeling and measured results were observed. Characterization of the inductances revealed quality factors (Q-values) of 60 and more at 2.35 GHz. The Q-values of the inductances are confirmed by three independent measurement methods and correspond well to field simulation results. The basic building blocks demonstrated in this paper can lead to a new generation of ultra-thin 3D RF modules with substrate-embedded matching networks and filters, superior performance and lower cost compared to laminate and FO-WLP based approaches.

Integration of precision resistors and capacitors with near-zero temperature coefficients in silicon and organic packages

Abstract: This paper reports novel material and process technologies for near-zero Temperature-Coefficient Resistors (TCR) and zero temperature coefficient of capacitance (TCC) capacitors and their integration into organic or silicon packages for precision RF components. A new concept of self-compensating resistors, leading to zero TCR was explored and demonstrated for the first time, using heterogeneous resistor stack structures consisting of metal layers with positive TCR and semiconducting oxide layers with negative TCR. Zero TCC capacitors were demonstrated with a film-stack consisting of ceramic nanocomposites of positive TCC and negative TCC. In both cases, the film thickness was designed such that there is internal compensation in temperature deviation, which results in zero temperature-coefficient. Material models were developed for the film-stack to design the films for zero temperature-coefficient.

Tailoring the temperature coefficient of capacitance (TCC), dielectric loss and capacitance density with ceramic-polymer nanocomposites for RF applications

Abstract: High-K inorganic materials generally show high loss or high TCC or both, making them unsuitable for RF capacitor applications where high Q, tolerance and thermal stability are critical. Most polymers do not have the required total set of attributes, making it extremely challenging to integrate high-performance RF thin film capacitors in organic packages and boards. In this paper, we demonstrate a strategy to tailor the properties of polymeric composite materials and satisfy all the RF capacitor requirements. With this strategy, it is feasible to meet low TCC and low loss while increasing the capacitance density or permittivity to miniaturize RF components.

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.