Physics professors make developments in flexible electronics
Electronics have been getting thinner and smaller for decades, but now there is a new characteristic to expect in devices — flexibility.
The work of University scientists aims to change rigid tools such as calculators, e-readers, watches and other electronics.
Vitaly Podzorov, an associate professor in the Department of Physics, said he, along with researchers Hee Taek Yi and Szu-Ying Wang, are making strides in flexible organic electronics.
The group explores the conductive behavior of organic materials, which are mainly made of carbon and hydrogen, Podzorov said.
He said his group is trying to utilize the beneficial properties of the organic materials they know work already.
Podzorov said the softness and flexibility of the materials is because of the weak interactions between atoms, named Van der Waals interactions.
“This only results in mechanical flexibility. They are still very durable devices,” he said.
The flexibility of the device is related to its thickness. Podzorov’s group uses a necessary layer of insulation that is 40 times thinner than a human hair, said Yi, a post-doctoral student in the Department of Physics.
“When I first joined the group, we had a time-consuming process for creating components. I developed a method that makes flexible electrical components very easily,” Yi said.
He said they changed the methods used to form these materials, including creating a vacuum to form the desired component.
“It’s flexible, easy to make and cheap,” said Wang, a Ph.D. student in the Department of Chemistry. “It may have many applications based on people’s needs.”
The devices turned out to be very flexible and were easy to test, Podzorov said. They first made working devices on these flexible substrates using commercially available plastic mylar films.
“The thing is that we’re the first to experiment with flexible semiconductors,” he said.
A semiconductor is the backbone of modern electronic components. It is traditionally made from hard metals like silicon oxide or magnesium, he said.
“Before us, people were using hard substrates because they’re commercially available and conveniently flat,” he said.
He said silicon is found easily in the earth, but costly to process. In processing, the scientists need high-temperature furnaces, high-pressure vacuums and considerably expensive equipment.
What makes silicon semiconductors expensive is the purification process, he said. Keeping it pure is simple.
“You can kick Silicon with your foot and nothing would happen,” he said. “You can wash it in acetone, and it’s as good as new.”
Nobody understands the conductive organics yet because they are hard to maintain, he said.
“It’s very easy to spoil an organic sample. Many of them oxidize or degrade easily. We’re trying to work with more stable systems by creating our own,” he said.
Physical behaviors of conductive materials are very specific and somewhat predictable, he said. What they’ve discovered through experiments is the electron behavior in organic materials resembles that of inorganic materials.
“There are many groups that do computational studies on this. We don’t do this. What is more valuable for us is to experimentally show something in an unambiguous way,” he said.
The researchers are trying to design clear-cut experiments that make physical mechanisms clear, he said.
“What I like to do is something very new. It is much less explored and that makes working with new materials exciting,” he said.
He said there is no clear consensus on many physical behaviors, such as energy transport in organic materials.
In his experiments, Podzorov said he binds an electron with a metal and migrates this pair, called an exiton, into an organic material, which leads to emission of energy in the form of a photon.
The hope is to create organic materials that have simple and low processing needs, he said. Researchers hope they would eventually learn to conduct with only one molecule.
“We’re trying to figure everything out about organic materials. We’re not worried about the commercial-end of things, we are a physics department,” he said.
There is a separate experiment dedicated to testing the wear and tear of a device, he said.
“We try to find the optimal condition of organic semiconductors,” Wang said. “We need to fully understand them before we put them in devices.”
One trade-off is that organic materials transfer electricity less efficiently than traditional inorganic materials, he said.
“This is compensated by specific applications, such as flexibility, inexpensive processing, and self-generated light emission,” Podzorov said.
Podzorov said they do not want to replace inorganic materials, but improve on some existing products. For example, LCDs, an inorganic product they want to replace with organic materials, are illuminated by a white backlight, which causes glare and loses color purity.
“We’re not trying to replace silicon. This is important to understand. We’re trying to occupy some niche of applications that silicon is not doing very well on,” Podzorov said. “It’s clear that organic semiconductors won’t be able to beat silicon. And they don’t have to.”