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.

Laser-drilling formation of through-glass-via (TGV) on polymer-laminated glass

Abstract: A three-dimensional (3D) glass integrated passive device (IPD) is an evolutionally advanced configuration to dramatically reduce the electronics form factor and manufacturing cost of current IPDs by introducing ultra-thin glass with through-glass-vias (TGVs). A defect-free TGV formation technology in polymer-laminated glass substrates is required to realize a highly reliable 3D glass IPD. This paper discusses mechanisms of each defect formation in the use of several types of lasers to explore suitable technology for defect-free drilling in polymer-laminated glass.

Nanomagnetic structures for inductive coupling and shielding in wireless charging applications

Abstract: This paper presents materials modeling, design, processing, integration and characterization of a new class of nanomagnetic structures for coupling and shielding in wireless charging and power conversion applications. Wireless power transfer applications such as wireless charging, operating at 6.78 MHz, require high-performance magnetic materials for enhancing the coupling between transceiver and receiver coils as well as for suppressing electromagnetic interference (EMI) shielding. This research describes two novel magnetic structures for coupling inductors and ultra-thin EMI shields. A novel vertically aligned magnetic composite structure was demonstrated for the coupling inductor. This structure is shown to result in permeabilities of above 500 and loss tangent of 0.01, which enhances the coupling inductance by 3–5x at 6.78 MHz, and also enhances the power-transfer efficiency by 2x. The second part of this paper presents the modeling, design and fabrication of nanomagnetic structures for ultra-thin EMI shields in wireless power transfer applications. The ultra-thin EMI shields for wireless power transfer described in this research can achieve greater than 20dB attenuation at 6.78 MHz even for 3–5µm shield thickness.

Hydrothermal Barium Titanate Thin-Film Characteristics and their Suitability as Decoupling Capacitors

Abstract: System integration and miniaturization demands are driving integrated thin film capacitor technologies towards ultrahigh capacitance densities for noise-free power supply, power conversion and efficient power management. Hydrothermal route can deposit crystalline ferroelectric films at low temperatures of less than 150 C. It is hence an attractive route for integrating high permittivity thin film capacitors on organic, silicon or flex substrates. However, hydrothermal films are not commercialized so far because of their inferior insulation characteristics. Embedded hydroxyl groups are attributed to be the cause for high leakage currents, temperature dependent properties and lower Breakdown Voltages (BDVs). This paper discusses the dielectric characteristics such as capacitance density, leakage currents and Temperature Coefficient of Capacitance (TCC) of hydrothermal barium titanate films and correlates them to the embedded water and OH groups, film morphology, stoichiometry and crystallinity. With thermal treatment, majority of the OH groups can be removed leading to improved insulation characteristics. The room temperature I-V characteristics agreed with ionic conduction models for films baked at 160 C while higher baking temperatures of above 300 C resulted in Poole-Frenkel type conduction. A brief perspective is provided on the suitability of hydrothermal thin film capacitors for power supply applications.

Glass Panel Packaging, as the Most Leading-Edge Packaging: Technologies and Applications

Abstract: The semiconductor and systems landscape are changing dramatically. As Moore's law begins to come to an end for many reasons that include minimal increase in transistor performance and in computer performance from node to node but at higher power, the industry has begun to shift to interconnections, referred to as Moore's law for Packaging. This focus addresses both the need for homogeneous and heterogeneous integrations by interconnecting smaller chips and smaller components with higher performance at lower cost and interconnecting them as multichip in 2.5 and 3D architectures. This is also called extending Moore's law, not in a single chip but with multiple chips interconnected horizontally and vertically. This strategy is very consistent with the dramatic and emerging changes in electronic systems such as in HPC, AI and a new era of self-driving and electric cars that potentially think and drive better than humans. This requires device, packaging, and computing architecture paradigms with an entirely different vision and strategy than transistor scaling alone. Packaging, which can be viewed broadly as system scaling, is now viewed as replacing Moore's law for enabling better devices and better systems, unlike in the past. Glass packaging is being developed by Georgia Tech and its industry partners, as the most leading-edge packaging, consistent with the above systems needs in cost, performance, functionality, reliability, and miniaturization. This paper describes the critical glass packaging technologies, their R&D and commercialization status as well as all the current and future applications. It compares and contrasts glass packaging against other leading-edge technologies such as Si and embedded packaging.

Dielectric–electrode interactions in glass and silicon-compatible thin-film (Ba,Sr)TiO3 capacitors

Abstract: This paper investigates the role of electrode–dielectric interactions, and barrier materials on leakage current, breakdown voltage, yield and reliability of thinfilm (Ba,Sr)TiO3 capacitors on silicon and glass substrates. The first part of the paper investigates the electrode–dielectric interactions with sputtered Cu and Ni electrodes to identify the mechanisms that lead to high leakage current and low yield. The second part of the paper presents lanthanum nickel oxide as a viable solution to overcome the problems with sputtered Cu and Ni electrodes. A combination of low leakage current, high yield and capacitance densities was achieved with the oxide electrode 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.