Tech Briefs Magazine - November 2023 - PIT-14

Multicolored Light-Emitting Array on a Single Chip
With limitless colors, device may lead to advances in spectroscopy.
University of California, Berkeley, CA
M
ulticolored light-emitting arrays
could be useful in low-power sensing,
computing, and spectroscopy, but
too often their spectral range is limited
to a few colors due to material and
device constraints. Now, Berkeley engineers
have devised a way to produce an
economical and compact light-emitting
device with limitless colors that
could greatly increase resolution in
spectral imaging.
In a recent issue of Science Advances, a
team of researchers led by Ali Javey, Professor
of Electrical Engineering and
Computer Sciences, demonstrated the
first light-emitting array with 49 different
colors on a single chip. This novel optoelectronic
device is built on metal-oxide
semiconductor (MOS) capacitors and
uses electroluminescent materials to
generate light spanning the visible to the
infrared wavelength range.
According to Vivian Wang, lead author
and a Ph.D. student in electrical engineering
and computer sciences, this
work builds off the team's accidental discovery
many years ago: light can be generated
from semiconducting materials
by putting them on top of capacitors on
silicon wafers, instead of using diodes.
" We wanted to know what else we
could do with these light-emitting devices, "
said Wang. " After putting different
semiconducting materials on the devices,
we found that we could get them to
emit different ranges of light. This led us
to build a big array of these devices, with
all of these colors on one chip. "
Multicolored light-emitting device
arrays based on diodes, like the LEDs
commonly used in computer and television
displays, have a complex and costly
fabrication process that limits them to a
few colors. Another consideration is
size. Some semiconducting materials
cannot be grown on a single substrate,
so devices fabricated on separate chips
must be glued together, resulting in a
larger package.
The researchers, however, wanted to
easily and economically scale light-emitting
arrays to tens or hundreds of colors
14
An array of light-emitting devices with 49 different individually addressable colors. (Image: Vivian Wang)
while keeping the device size at a nanoscopic
scale. They solved this problem by
developing arrays based on electroluminescent,
alternating current-driven MOS
capacitors, instead of conventional diodes.
By using a capacitor, their new device
allows for a simpler, more compact structure.
" Unlike diodes, our device needs
only one electrode, not two, to contact
the material, " said Wang. " This makes
the fabrication process really easy because
you don't have to put an electrode
on top of the material; it just needs to fit
on a bottom electrode. "
In addition, light can be generated
from many different semiconducting
materials without requiring adjustments
to the device structure. " We don't have
to choose special kinds of electrodes for
certain kinds of materials, like you do
with a diode, " said Wang.
Fabrication is further simplified by an
automated process called microprinting,
which the researchers used to easily dispense
different color emitters on a single
chip. The emitters consist of molecular
and quantum dot materials, which
are semiconductor nanocrystals with
tunable optical and electronic properties.
Microprinting is fast and enables
the array to scale to a vast spectral range.
The device's ability to offer limitless
color options makes it highly versatile
and a good tool for spectral sensing,
which has applications in the consumer,
industrial, and medical sectors.
" If your array has only five different
colors, you can't get very fine-grained
Photonics & Imaging Technology, November 2023

Tech Briefs Magazine - November 2023

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