Physics

Dr. Rudra Pratap
IISC Bangalore

Research usually originates from simple curiosity — curiosity to understand a phenomenon or search a solution for a nagging problem. In either case, the methods of scientific research let us dive into the mystries of the universe in amazingly systematic manner. It is the systematic study of nature’s mystries that demystify what usually puzzles us first. But is that the end of scientific research? More often than not, our understadning of a phenomenon leads to understanding of other connected phenomena; and soon enough, we have enough information to create something new. This is how we invent new technologies. While serendipity has a role to play in our discoveries, technology is rarely serendipitous; it is usually a result of scientific rigor and systemtic hard work. In this talk I present some examples of the this journey of turning science into technology.

The first example concerns turning the dreaded phenomenon of electromigration into a desirable tool for material transport at the nanoscale. Electromigration is an electric field driven phenomenon in which metal atoms in a metallic thin film or line are dislodged randomly from their places due to the electron wind force when current flows through the film/line. This phenomenon has mostly played spoil-sport in semiconductor industry by breaking interconnects and creating severe reliability problems for dense circuits. We have worked on developing precise control on the electromigration process. We show that by controlling electromigration, one can harness its power to transport material at nanoscales. First, we show that with a feedback control loop on resistance change in a thin metallic line, we can control the electromigration process to produce a localized nanoscale inhomogenization that results in a percolation network enhancing the piezoresistive sensitivity of the metallic line by a few orders of magnitude. We also show, with many experiments on thin chromium films, that controlled electromigration can be used to melt the metal and drive its flow, thus transporting the metal to form certain patterns on micro and nanoscales. The material transport process is complex because of the underlying physics of the multi-phase flow. The mixture of three phases — solid, liquid and air — coupled with an electric field, provides enough number of process variables that, if controlled precisely, can be used for rapid patterning of metal films. After a thourough understanding of how solid and liquid electromigration processes work, we turn our understanding into a fascinating technology that we call Electrolithography.

The second example concerns the study of a natural transuder for loud sound production from a very small source. We are all familiar with the loud song produced by tiny field crickets. We have studied the mechanism used by the field crickets to produce sound (crickets do not have vocal cords like human beings or other animals). It is a fascinating micro-mechanical mechanism with three distinct parts—an actuator (the stridulation of wings), a frequency multiplier, and a resonator (the harp embedded in the wings). We subsequently use our understanding of this bioacoustic transducer to design tiny MEMS (Micro-Electro-Mechanical Systems) speakers that produce similar sound. Thus we turn our curiosity driven research on cricket song to a technology for producing micro-speakers.

About the speaker

Dr. Rudra Pratap is a Professor and the Founding Chairperson of the Centre for Nano Science and Engineering (CeNSE), and an associate faculty of the Department of Mechanical Engineering at the Indian Institute of Science, Bangalore. He holds a Ph.D. degree from Cornell University, a B. Tech. from the Indian Institute of Technology, Kharagpur, India. Prior to joining IISc in 1996, he taught at the Sibley School of Mechanical and Aerospace Engineering, Cornell University, for two and a half years. He has been at the Indian Institute of Science, Bangalore, India, since 1996. He was also an invited professor at EPFL, Lausanne, Switzerland, during 2004-2005.

His research interests include MEMS and NEMS, vibroacoustics, nonlinear dynamics and mechanobiology. He has published more than 150 papers in journals and international conferences. He has several MEMS patents to his credit. He is a member of the Vision Group on Nanotechnology of Karnataka State and a member of the Working Group on Nanotechnology, Ministry of Communication and Information Technology, Government of India. He is an Associate Editor of the IEEE Journal of Microelectromechanical Systems and the Journal of the Institute of Smart Structures and Systems (ISSS). He is recipient of the M. Hetényi Award from the American Society of Experimental Mechanics and VASVIK Award for Industrial Research. Dr. Pratap is an elected Fellow of the National Academy of Engineering.