Engineers Use Nanowires to Create Artificial E-Skin

Engineers at the University of California, Berkeley, have developed a
pressure-sensitive electronic material from semiconductor nanowires that could
potentially be applied to robotic or prosthetic hands, according to Kuniharu
Takei, post-doctoral fellow in electrical engineering and computer sciences.

  Kuniharu Takei
  Kuniharu Takei

The artificial skin, dubbed “e-skin” by the UC Berkeley
researchers, is the first such material made out of inorganic single
crystalline semiconductors.

“The goal was to create a material system that could function
similarly to the human skin,” Ali Javey, associate professor of electrical
engineering and computer sciences and head of the UC Berkeley research team
developing the artificial skin, told O&P Business News.
“The material would be able to detect touch.”

A touch-sensitive artificial skin would help overcome a key challenge in
robotics — adapting the amount of force needed to hold and manipulate a
wide range of objects.

Humans generally know how to hold a fragile egg without breaking it. If
researchers ever wanted a robot that could unload the dishes, for instance,
they would want to make sure it does not break the wine glasses in the process.
But researchers would also want the robot to be able to grip a stock pot
without dropping it, according to Javey. Their research could potentially allow
the robot to control the strength of power used to grab any fragile material
without breaking the item, according to Takei.

“We need to know the weight of the object,” Takei said.
“If we can apply robotic hands and an eye or a camera for the robot, then
from the eyes, the robot can distinguish how heavy the object is. From those
results, we can control how strong we need to grab the object.”

and easier to process. According to Javey,
organic materials are poor semiconductors, indicating that electronic devices
made out of them would often require high voltages to operate the circuitry.
Inorganic materials, such as crystalline silicon, on the other hand, have
excellent electrical properties and can operate on low power. They are also
more chemically stable.

“But historically, they have been inflexible and easy to crack. In
this regard, works by various groups, including ours, have recently shown that
miniaturized strips or wires of inorganics can be made highly flexible —
ideal for high performance, mechanically bendable electronics and
sensors,” Javey explained.

The UC Berkeley engineers utilized an innovative fabrication technique
that works somewhat like a lint roller in reverse. Instead of picking up
fibers, nanowire “hairs” are deposited.

“We contacted printed parallel arrays of germanium/silicon
nanowires on a polyimide substrate, followed by the fabrication of field-effect
transistors on the nanowires,” Javey explained. “Next, a pressure
sensitive rubber was integrated on top of the devices through a lamination
process. The conductivity of the rubber changes upon the application of an
applied pressure, resulting in the change of underlying field effect
transistor’s output signal. By monitoring the output signal of each pixel,
we were able to map out a pressure profile.”

Researchers demonstrated the ability of the e-skin to detect pressure
from 0 to 15 kilopascals, a range comparable to the force used for such daily
activities as typing on a keyboard or holding an object. In a nod to their home
institution, the researchers successfully mapped out the letter C in Cal.

Researchers have been working on e-skin for 2 years. Next, UC Berkeley
engineers plan to integrate more sensors on the same substrate, such as thermal
sensors and develop an interface between their device and the robot. —
by Anthony Calabro


I am quite familiar with this research. This impressive piece of work
establishes a new milestone in the development of flexible sheets for tactile
sensing. The approaches appear to form a realistic foundation for important
applications in biomedicine and robotics.

— John Rogers, PhD
Principal investigator,
Frederick Seitz Materials Research Laboratory in the Department of Materials
Science and Engineering, the University of Illinois at Urbana-Champaign

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