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.

Electrochemical Biosensors and Microfluidics in Organic System-on-Package Technology

Abstract: A nanobioelectronic system-on-package (SOP) with integrated electrochemical sensors, microfluidic channels and microneedles was demonstrated with organic compatible processes. A novel amperometric glucose sensor based on carbon nanotubes/glassy carbon working electrodes and glucose oxidase enzyme encapsulated in a sol-gel derived zirconia/nafion matrix was developed to demonstrate the biosensing. The sol-gel chemistry provides an attractive way to immobilize the sensitive biomolecules on the electrode at low temperatures. The amperometric measurements were carried out with a three-electrode system. SU8 epoxy based thick microfluidic channels were built over the electrode layer and then the enzyme was immobilized, followed by sealing of the channel with a PDMS membrane using a low temperature bonding process (60degC). The enzyme-catalyst reaction was recorded as the release of electrons from the oxidation of glucose into gluconolactone, hydrogen peroxide and subsequently into water. The results indicate that the response time is within few seconds. The current varied from 1 muA to 2.5 muA as the glucose concentration was increased from 5 mM to 20 mM. Finally, a compatible microneedle technology is demonstrated to enable transdermal fluid injection into the device for real-time health monitoring. Nanobio SOP with recent advances in nanobiosensing, nanomedicine, low-cost polymer-based high-density packaging, mixed-signal electronics can lead to the portable, reliable and cost effective biomedical devices of the future.

Evaluation of liquid crystal polymers for high performance SOP application

Abstract: Electronic devices increasingly rely on new materials with improved properties such as lower coefficient of thermal expansion (preferably close to silicon), higher modulus, lower permittivity and dielectric loss, lower moisture absorption better thermal conductivity, higher dimensional stability, and most importantly reduced warpage particularly after the build-up process. Liquid crystal polymers (LCPs) have led to increasing interest for the packaging community due to their superior thermal and electrical properties. The targeted applications areas for LCPs are RF packaging, due to their low loss and low dielectric constant over a wide frequency range (Fukutake and Inoue, 2002; Fukutake, 1998; Jayaraj et al, 1995; Lawrence, 2000; Jayaraj et al, 1996; Yue et al, 1999,), near hermitic plastic sealing due to superior moisture barrier properties (Jayaraj et al, 1997), flex circuits and microvia laminates for high density interconnection (Corbett et al, 2000; Yue and Chan, 1998). This paper is focused toward possible application of LCP as a dielectric material for lamination on PWB and other engineered organic substrates. Commercially available LCP samples were analyzed using a variety of thermal analysis techniques. Based on thermal properties such as coefficient of thermal expansion (CTE), thermal degradation temperature and modulus, samples were selected for applications as a dielectric material. It is expected that a low CTE dielectric such as LCP will further reduce the dielectric film stress even when the CTE of the chip is matched with that of the substrate.

BaTiO3 Films by Low-Temperature Hydrothermal Techniques for Next Generation Packaging Applications

Abstract: This work reports synthesis, characterization and integration of sub-micron thick nano-grained barium titanate films on organic Printed Wiring Boards (PWB). Barium titanate films were synthesized on titanium foils at 95∘C. SEM of films revealed 80 nm grains. The films were characterized using XRD, FTIR and Raman spectroscopy. As-synthesized films exhibited high capacitance densities and dielectric loss. The films were treated with oxygen plasma to reduce entrapped hydroxyl groups and this resulted in improved dielectric properties. The plasma treated films exhibited a capacitance density of 1 μ F/cm2 and a dielectric loss of 0.06. The high frequency dielectric properties were extracted from s-parameter measurements on CPW structures on these films and were found to be stable up to 8 GHz.

Magnetic and Dielectric Property Studies in Fe- and NiFe-Based Polymer Nanocomposites

Abstract: Metal–polymer composites were investigated for their microwave properties in the frequency range of 30–1000 MHz to assess their application as inductor cores and electromagnetic isolation shield structures. NiFe and Fe nanoparticles were dispersed in epoxy as nanocomposites, in different volume fractions. The permittivity, permeability, and loss tangents of the composites were measured with an impedance analyzer and correlated with the magnetic properties of the particle such as saturation magnetization and field anisotropy. Fe–epoxy showed lower magnetic permeability but improved frequency stability, compared to the NiFe–epoxy composites of the same volume loading. This is attributed to the differences in nanoparticle’s structure such as effective metal core size and particle-porosity distribution in the polymer matrix. The dielectric properties of the nanocomposites were also characterized from 30 MHz to 1000 MHz. The instabilities in the dielectric constant and loss tangent were related to the interfacial polarization relaxation of the particles and the dielectric relaxation of the surface oxides.

System Scaling With Nanostructured Power and RF Components

Abstract: The emergence of smartphones and other smart systems is driving new trends in electronics scaling that goes beyond transistors or active devices, to include all the system components such as packaging substrates, passive components, thermal structures, power sources, and the system interconnections. Current system components are at milliscale, creating a $10^{3}$ to $10^{6}$ scaling gap with the packaging interfaces at microscale, and transistors at nanodimensions. With current microstructured materials, component miniaturization also degrades performance metrics such as efficiency, tolerance or precision, thermal and frequency stability. Nanostructured materials and processes can potentially miniaturize these system components, while simultaneously enhancing the performance. These nanostructured components are assembled close to the active devices, resulting in ultraminiaturized and ultrathin systems with 3-D integration of passives with actives. This paper shows the impact of nanostructured materials toward enhancing the performance and miniaturization of power and radio-frequency (RF) passive components in emerging smart systems. Opportunities for nanostructured materials in improving the power density and efficiency of capacitors and inductors in power-supply modules are reviewed in the first part of the paper. The impact of nanostructured magnetic, dielectric and magneto-dielectric films on emerging RF subsystems is illustrated in the last part of the paper.

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.