The pleasure of owning a smartphone is the myriad ways in which it lets you be more productive and stay connected. The pain is when it inexplicably goes blank after someone (..ahem!) accidentally drops it. Similar is the ordeal if the victim is your laptop or tablet. If you are nodding your head in déjà vu, know that we have all been there.
As technology becomes more pervasive and integral to our lives, the call for more robustness becomes louder. So how do we make our electronic gadgets stronger without sacrificing their light weight and handy size? Dr. Praveen Kumar and his team from IISc have discovered that one of the answers lies in using electricity itself!
His team is developing ways to increase the strength of CNT foam to replace the standard polymer foam used inside electronic gadgets for shock absorption. CNT (short for ‘Carbon Nano Tube’) foam is a dense mesh of carbon nanotubes, routinely studied for mechanical applications. Recent experiments show that applying a voltage of 1V during a fall can increase the shock absorption capacity of CNT foam by 3 times. This new finding can be implemented in the near future because “such a small voltage is easily available in your phone or laptop battery!” says Kumar excitedly.
In the Thermo-Electro-Mechanical Behaviour Laboratory at the Indian Institute of Science, Praveen Kumar and his team design ways to improve mechanical strength of materials for a variety of applications, especially futuristic devices. They identify, investigate and engineer solutions for all possible causes for failure – such as mechanical shock, high currents and excessive heat. Why are these factors so troublesome in electronics today?
The main reason lies in miniaturization. To get smaller, multi-functional gadgets, engineers pack more transistors in an electronic chip and more chips in a circuit board. This leads to high current densities confined in a small space, which means that the longer you use them, the hotter they get. Laptops today can heat up to 60°C with continuous usage. This temperature is high enough to cause structural weakness in the environmentally-benign lead-free solders used in circuits today. Additionally, high current densities weaken the bond between regular tin-based solders and copper wires, further reducing their life.
Connection between electricity and mechanical failure is not new. Electromigration, i.e. flow of metal due to high electric currents, used to be notorious for breaking aluminium interconnect wires in integrated circuits (ICs) over 40 years ago. Aluminium was later replaced with copper, which has a higher melting point and is therefore more robust against electromigration. However, rising heat and current density in devices in last 15 years has led to the resurgence of serious electromigration problems in copper wires as well. Kumar’s group is designing solutions for these problems and also developing new materials that can withstand high currents. What sets them apart is that they have also found a way to benefit from electromigration!
“It was all serendipity”, reminisces Kumar about the experiment where they first observed that they could melt metal and control the direction of its flow using electric field. This gave birth to ‘Electro-lithography’ – a new method of creating patterns using only electric field. Conventional lithography needs UV light and masks with precisely drawn outlines to create device patterns on the semiconductor. It is one of the most expensive steps in any semiconductor device fabrication today. In comparison, electro-lithography is inexpensive and simpler to execute. All it needs is a movable electrode tip and metal.
“It is like writing with a quill,” explains Kumar, “if I keep the quill at a spot, the liquid will spread out. Instead if I move the quill, I can actually write with it.”
Using electro-lithography, Kumar and his colleagues have written patterns as small as 40 nm on semiconductors. Their research aims to provide lasting solutions and new techniques that can give us more reliable and economical electronic devices in the future.
The group also studies the effect of heat on mechanical stability for other applications – such as aeroplane turbine coatings, solar cells, etc. Bringing together students and experts from material sciences, applied physics, mechanical engineering and electrical engineering, this team is eager to explore all new aspects of mechanical reliability, material behaviour and their close connection to electricity.
After all, “some of these things start with a little bit imagination,” signs off Dr. Kumar with a smile.
About the cover picture of this article:
What you see is a high magnification image of a dense sheet of carbon nanotubes. The inset carries the image of the CNT foam used in their experiments (and which could be in our devices someday in the future!). Both the images were taken by the team during their research.
About the scientist:
Dr. Praveen Kumar is an Assistant Professor at the Department of Materials Engineering at Indian Institute of Science (IISc), Bangalore. To know more about his group’s work, do visit this detailed website.
This article was developed as a lab story for the Science Media Center at Indian Institute of Science, Bangalore, India.