Record-breaking, ultrafast devices step to protecting the grid from EMPs
New Sandia diode can shunt excess electricity in a few billionths of a
second

Date:
March 15, 2022
Source:
DOE/Sandia National Laboratories
Summary:
Scientists have announced a tiny, electronic device that can shunt
excess electricity within a few billionths of a second while
operating at a record-breaking 6,400 volts -- a significant
step towards protecting the nation's electric grid from an
electromagnetic pulse.



FULL STORY ========================================================================== Scientists from Sandia National Laboratories have announced a tiny,
electronic device that can shunt excess electricity within a few
billionths of a second while operating at a record-breaking 6,400 volts
-- a significant step towards protecting the nation's electric grid from
an electromagnetic pulse.


==========================================================================
The team published the fabrication and testing results of their device
on March 10 in the scientific journalIEEE Transactions on Electron
Devices. The team's ultimate goal is to provide protection from voltage
surges, which could lead to months-long power interruptions, with a
device that operates at up to 20,000 volts. For comparison, a household electric dryer uses 240 volts of electricity.

An electromagnetic pulse, or EMP, can be caused by natural phenomena,
such as solar flares, or human activity, such as a nuclear detonation
in the atmosphere. An EMP causes huge voltages in a few billionths of
a second, potentially affecting and damaging electronic devices over
large swaths of the country.

EMPs are unlikely, said Bob Kaplar, manager of a semiconductor device
research group at Sandia, but if one were to occur and damage the huge transformers that form the backbone of our electric grid, it could take
months to replace them and re-establish power to the affected portion
of the nation.

"The reason why these devices are relevant to protecting the grid from an
EMP is not just that they can get to high voltage -- other devices can
get to high voltage -- but that they can respond in a couple billionths
of a second," Kaplar said. "While the device is protecting the grid
from an EMP, it's at a very high voltage and thousands of amps are going through it, which is a huge amount of power. A material can only handle
so much power for a certain amount of time, but we think the material
in our diode has some advantages over other materials." A regulator
valve for the grid The new Sandia device is a diode that can shunt a record-breaking 6,400 volts of electricity within a few billionths of
a second -- a significant advancement toward being able to protect the
nation's electric grid from an EMP. The team, including Sandia electrical engineer Luke Yates, the first author on the paper, is working towards fabricating a diode able to operate at around 20,000 volts, since most
grid distribution electronics operate at around 13,000 volts.



========================================================================== Diodes are electronic components found in nearly every electronic device
and serve as one-way regulator valves, said Mary Crawford a Sandia Senior Scientist leading diode design and fabrication for the project. Diodes
allow electricity to flow in one direction through the device, but
not the other. They can be used to convert AC power into DC power,
and in this project, divert damaging high voltage away from sensitive
grid transformers.

Kaplar agreed that the diode operates somewhat like a regulator valve
in plumbing. He said, "In a regulator valve, even if you open that
valve all the way, you can't flow an infinite amount of water through
the valve. Similarly, there's a limit to how much current you can flow
through our diode. If the valve on the pipe is closed, if the pressure
reaches a certain point, it'll burst. Analogously, the diode cannot block
an infinite voltage. However, our EMP device uses the point at which the
diode can no longer block the high voltage, holds the voltage to that 'pressure,' shunting the excess current through itself, to the ground and
away from the grid equipment in a controlled, non-destructive fashion."
The voltage surges caused by EMPs are a hundred times faster than those
caused by lightning, so experts don't know if the devices designed to
protect the grid against lightning strikes would be effective against
an EMP, said Jack Flicker, a Sandia electric grid resiliency expert on
the team.

"The electric grid has a number of different protections," Flicker
added. "They range in timeframe from very fast to very slow, and they're overlaid on the electric grid to ensure that an event cannot cause a catastrophic outage of the electric grid. The fastest protection that
we typically have on the grid reacts against pulses at one millionth
of a second, to protect against lightning. For EMPs, we're talking ten billionths of a second, a hundred times faster." The new Sandia device
can react that quickly.



========================================================================== Growing perfect layers Part of what makes the diode special is that it is
made from gallium nitride, the same basic material used in LEDs, Kaplar
said. Gallium nitride is a semiconductor, like silicon. But because of
its chemical properties, it can hold off much higher voltage before it
breaks down than silicon, Crawford said.

The material itself also responds very quickly and therefore is a good candidate to achieve the fast response needed to protect the grid from
an EMP.

Crawford and materials scientists Brendan Gunning and Andrew Allerman
made the devices by "growing" gallium nitride semiconductor layers
using a process called chemical vapor deposition, she said. First,
they heat a commercially available gallium nitride wafer to around 1,800 degrees Fahrenheit and then add vapors that include gallium and nitrogen
atoms. These chemicals form layers of crystalline gallium nitride on
the surface of the wafer.

By tweaking the ingredients and the "baking" process, the team could
produce layers with different electrical properties. By building up
these layers in a specific order, combined with processing steps, such
as etching and adding electrical contacts, the team produced devices
with the needed behavior.

"A major challenge of achieving these very high voltage diodes is the
need to have very thick gallium nitride layers," Crawford said. "The
drift regions of these devices have thicknesses of about 50 microns,
or 1/6th of a sheet of notebook paper. This may not sound like a lot,
but the growth process we use can have growth rates of only one or
two microns per hour. A second major challenge is maintaining very low densities of crystalline defects, specifically impurities or missing
atoms in the semiconductor material, throughout the growth time in order
to generate devices that work at these very high voltages." For the team
to reach their ultimate goal of a device that operates at 20,000 volts,
they will need to grow the thick layer even thicker with even fewer
defects, Crawford said. There are several other technical challenges to constructing a device that can operate at such high voltages and currents,
she added, including designs to manage the very high internal electric
fields within the devices.

Testing ultrafast diodes Once Crawford's team fabricated the devices,
Flicker and his team tested how the devices responded to fast voltage
spikes, similar to what would occur during an EMP. His challenge has been modifying a tool to measure the very fast response time of the devices.

"Developing the tools that can accurately measure the very fast responses
is very difficult," Flicker said. "If we're talking one or two billionths
of a second, they need to be able to measure even faster than that,
which is a challenge." Flicker and his team used very specialized
equipment to apply a high voltage pulse, and measure the electric pulse
that is reflected back from the diode to tell when the device turns on,
very accurately and in less than a billionth of a second.

Useful for smart transformers, solar panel converters and more Diode
devices like the Sandia gallium nitride diode can be used for other
purposes, beyond protecting the grid from EMPs, Kaplar said. These
include smart transformers for the grid, electronic devices to convert electricity from roof-top solar panels into power that can be used by
household appliances, and even electric car charging infrastructure.

Commonly, solar panel converters and electric car charging infrastructure
can handle 1,200 or 1,700 volts, he added. But operating at higher voltage allows for higher efficiencies and lower electricity losses. Another
portion of the project is to develop diodes for these types of devices
that operate at high, but not record-breaking voltage but are easier to manufacture, Kaplar said. The Naval Research Laboratory is leading this
part of the project.

Some smart transformers and electronic devices can now operate at up to
3,300 volts, Flicker said, but efficiencies would be even greater if they
could operate at 10,000 or 15,000 volts with one semiconductor device.

"We have this primary goal of protection of the electrical grid,
but these devices have other uses beyond that," Flicker said. "It's
interesting to have our application area, but know that these devices
can be used in power electronics, power converters, everything that's at
very high voltages." This research is funded by ARPA-E and the larger
project is conducted in partnership with the Naval Research Laboratory, Stanford University, National Institute of Standards and Technology,
EDYNX and Sonrisa Research.


========================================================================== Story Source: Materials provided by
DOE/Sandia_National_Laboratories. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Luke Yates, Brendan P. Gunning, Mary H. Crawford, Jeffrey
Steinfeldt,
Michael L. Smith, Vincent M. Abate, Jeramy R. Dickerson, Andrew M.

Armstrong, Andrew Binder, Andrew A. Allerman, Robert J. Kaplar.

Demonstration of >6.0-kV Breakdown Voltage in Large Area
Vertical GaN p- n Diodes With Step-Etched Junction Termination
Extensions. IEEE Transactions on Electron Devices, 2022; 1 DOI:
10.1109/TED.2022.3154665 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220315113007.htm

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