Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Penn Develops Computer Model That Will Help Design Flexible Touchscreens

04.09.2013
Electronic devices with touchscreens are ubiquitous, and one key piece of technology makes them possible: transparent conductors.

However, the cost and the physical limitations of the material these conductors are usually made of are hampering progress toward flexible touchscreen devices.


Researchers simulate electrical resistances (lines) to match experimental data (points) and extract the contact resistance.

Fortunately, a research collaboration between the University of Pennsylvania and Duke University has shown a new a way to design transparent conductors using metal nanowires that could enable less expensive — and flexible — touchscreens.

The research was conducted by graduate student Rose Mutiso, undergraduate Michelle Sherrott and professor Karen Winey, all of the Department of Materials Science and Engineering in Penn’s School of Engineering and Applied Science. They collaborated with graduate student Aaron Rathmell, and professor Benjamin Wiley of Duke’s Department of Chemistry.

Their study was published in the journal ACS Nano.

The current industry-standard material for making transparent conductors is indium tin oxide, or ITO, which is deposited as two thin layers on either side of a separator film. Contact, in the form of a fingertip or a stylus, changes the electrical resistance between the two ITO layers enough so that the device can register where the user is touching. While this material performs well, its drawbacks have led industrial and academic researchers to look for alternatives.

“There are two problems with ITO; indium is relatively rare, so its cost and availability are erratic, and, more importantly for flexible devices, it’s brittle,” Winey said. “We’d like to make touchscreens that use a network of thin, flexible nanowires, but predicting and optimizing the properties of these nanoscale networks has been a challenge.”

Metal nanowires are increasingly inexpensive to make and deposit; they are suspended in a liquid and can easily be painted or sprayed onto a flexible or rigid substrate, rather than grown in vacuum as is the case for ITO. The challenge stems from the fact that this process forms a random network, rather than a uniform layer like ITO.

A uniform sheet’s overall quality in this context depends on only two parameters, both of which can be reliably derived from the bulk material’s properties: its transparency, which should be high, and its overall electrical resistance, which should be low. To determine the electrical properties for a network of nanowires, however, one needs to know the nanowires’ length and diameter, the area they cover and a property known as contact resistance, which is the amount of resistance that results from electrons traveling from one wire to another. The details of how these four independent parameters impact the electrical and optical properties of nanowire networks have been unclear.

“What this means is that people will synthesize nanowires, deposit them in a network, measure the network’s overall electrical resistance and optical properties and then claim victory when they get a good one,“ Winey said. “The problem is that they don’t know why the good ones are good, and, worse, they don’t necessarily know why the bad ones are bad.”

For example, low overall resistance could be the result of a particular synthesis method that produced a few unexpectedly long nanowires, or a processing method that reduced the contact resistance between nanowires. Without a way of isolating these factors, researchers can’t determine which combination of parameters will be most successful.

Winey’s group has previously worked on simulating nanowire networks in three-dimensional nanocomposites, particularly the number of nanowires it takes to ensure there is a connected path from one end of the system to the other. Duke’s Wiley took note of this work and contacted Winey, asking her if she would be interested in developing two-dimensional simulations that could be applied to data from silver nanowire networks his group had fabricated.

With Wiley’s group able to provide the nanowire length, diameter and area fraction of their networks, Winey’s team was able to use the simulation to work backward from the network’s overall electrical resistance to uncover the elusive contact resistance. Alternative methods for finding the contact resistance are laborious and incompatible with typical network processing methods.

“Once we have reliable and relevant contact resistances, we can start asking how we can improve the overall sheet resistance by changing the other variables,” Mutiso said. “In playing with this simulation, we can see how much better our networks get when we increase the length of the nanowires, for example.”

The Penn team’s simulation provides further evidence for each variable’s role in the overall network’s performance, helping the researchers home in on the right balance of traits for specific applications. Increasing the coverage area of nanowires, for example, always decreases the overall electrical resistance, but it also decreases optical transparency; as more and more nanowires are piled on the networks appear gray, rather than transparent.

“For specific applications and different types of nanowires, the optimal area fraction is going to be different,” Winey said. “This simulation shows us how many nanowires we need to apply to reach the Goldilocks zone where you get the best mix of transparency and resistance.”

Future collaborations between Winey’s team at Penn and the Wiley group at Duke will use this simulation to test the effect of different processing techniques on nanowires, pinpointing the effect various post-deposition processing methods has on contact resistance and ultimately on overall sheet resistance.

“We can now make rational comparisons between different wires, as well as different processing methods for different wires, to find the lowest contact resistance independent of nanowire length, diameter and area fraction,” Winey said. “Now that we know where all the levers are, we can start adjusting them one at a time.”

In the next generation of modeling studies, the Penn team will consider several additional parameters that factor into the performance of nanowire networks for transparent conductors, including nanowire orientation, to mimic nanowire networks produced by various continuous deposition methods, as well as the degree to which individual nanowires vary in length or diameter.

The research was supported by the National Science Foundation and Penn’s Materials Science Research and Engineering Center.

Michelle Sherrott is now a doctoral student in materials science at the California Institute of Technology.

Media Contact:Evan Lerner | elerner@upenn.edu | 215-573-6604

Evan Lerner | EurekAlert!
Further information:
http://www.upenn.edu

More articles from Power and Electrical Engineering:

nachricht Researchers pave the way for ionotronic nanodevices
23.02.2017 | Aalto University

nachricht Microhotplates for a smart gas sensor
22.02.2017 | Toyohashi University of Technology

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Stingless bees have their nests protected by soldiers

24.02.2017 | Life Sciences

New risk factors for anxiety disorders

24.02.2017 | Life Sciences

MWC 2017: 5G Capital Berlin

24.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>