As electronic devices get smaller and more hungry for power, Dr Rathnait Long is looking at new materials to build next-generation transistors. Claire O’Connell found out more about her career and her move from Cork to California.
Some of us remember when computers took up most of a desk and ‘mobile’ phones weren’t very mobile at all. It’s a far cry from the sylph-like laptops, tablets and smartphones we tote around now.
But as devices get slimmer and consumers demand longer battery lives, can the old stalwart silicon keep up? Long is looking at potential alternatives.
"In electronic components such as phones you have a little chip that contains millions and millions of little switches that can be on or off, and they are arranged in different configurations to do different things," explains Long, an electronic engineer from Cork. "For the last 45 to 50 years these switches [transistors] have been made with silicon as the semiconductor and silicon oxide as the insulator."
But now that devices are getting smaller and faster, silicon is getting pushed to the hilt.
"We have made the switches so small now that the materials are not acting the way they should," she says. And you can’t change the property of the material itself, so scientists are now looking at the potential for using other materials instead for both the semiconductor and the insulator."
Getting to the heart of transistors
Now based in California, where she has just completed post-doctoral research at Stanford University, Long is exploring the use of gallium-based materials in the heart of the transistors. Being able to make smaller switches with less ‘leakage’ could mean higher-performance devices and longer-lasting batteries.
"You could ask why did we not do this 45 years ago," she says. "But back then we didn’t have the tools to do what we can now."
Plus, silicon was well matched to the task in hand because from it you can grow a layer of insulating silica, or silicon dioxide, which is a good insulator, explains Long.
"We didn’t know how lucky we were with silicon," she says. "The interface between the silicon and silica is a natural one. That is not the case in these next-generation materials we are looking at now – you are slapping a totally different material on top of the semiconducting material and you are expecting them to get on well … and they don’t."
Biting the bullet
It’s a challenging problem, but it’s also the kind of question that Long was attracted to early on in her career as a scientist. She studied electronic engineering at University College Cork and did a master’s degree at Tyndall National Institute, where she helped to develop a silicon-on-insulator complementary metal oxide-semiconductor process.
From there she moved to Analog Devices in Limerick and became interested in process development, but saw that others working in the field had a PhD. So she bit the bullet and undertook doctoral research in Tyndall with Dr Paul Hurley: with funding from IRCSET (now the Irish Research Council) and Intel, she looked at indium gallium arsenide-based transistors, which could suit applications in microprocessors.
"I might be biased, but for me Tyndall was a gem," she says of her time there. "Everyone was so supportive and as an institute it has really built up a huge reputation internationally."
From Cork to California
But California also turned her head when, in 2008, Long was awarded a Fulbright scholarship to spend eight months at Stanford University.
"My attitude was changed by that programme," she recalls. "Before that I hadn’t really thought about the US, but I found that California was amazing."
New horizons in 3D
That realisation drew her to post-doctoral research at Stanford. There she looked at gallium nitride, a material more suited to applications in defence and space, where you could need devices which can operate at high power, high frequency and high temperature.
As well as being part of a busy research group, Long also enjoyed the supportive environment of California, where colleagues were willing to spend time talking about ideas and helping her with her career.
"Anybody here will have a cup of coffee with you and share their insights and it is not a big deal," she says. "And if you have any initiative at all they will grab on to you and pull you along."
She’s just about to start as a senior process engineer with Lam Research in California, where she will be looking at three-dimensional structures in the design of next-generation semiconductors.
"All the devices I have been working on to date with these new materials have been planar, where you are looking at atomic layer deposition on the top surface," she says.
"But now I’ll be looking at etching fin structures into the semiconductor itself to give you better control over the carriers in the semiconductor."
And for young students just starting out on their training, Dr Long advises them to think about engineering. "The skill set that you get and the training of your mind is fabulous," she says.
"And even if you study engineering and then go on to do something else, you will still have an approach to solving problems that will stand to you in everything that you do."
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