electrical engineering (5)

Thermo Limits


A radical reimagining of information processing could greatly reduce the energy use—as well as greenhouse gas emissions and waste heat—from computers. Credit: vchal/Getty Images

Topics: Climate Change, Computer Science, Electrical Engineering, Global Warming, Semiconductor Technology, Thermodynamics

In case you had not noticed, computers are hot—literally. A laptop can pump out thigh-baking heat, while data centers consume an estimated 200 terawatt-hours each year—comparable to the energy consumption of some medium-sized countries. The carbon footprint of information and communication technologies as a whole is close to that of fuel used in the aviation industry. And as computer circuitry gets ever smaller and more densely packed, it becomes more prone to melting from the energy it dissipates as heat.

Now physicist James Crutchfield of the University of California, Davis, and his graduate student Kyle Ray have proposed a new way to carry out computation that would dissipate only a small fraction of the heat produced by conventional circuits. In fact, their approach, described in a recent preprint paper, could bring heat dissipation below even the theoretical minimum that the laws of physics impose on today’s computers. That could greatly reduce the energy needed to both perform computations and keep circuitry cool. And it could all be done, the researchers say, using microelectronic devices that already exist.

In 1961 physicist Rolf Landauer of IBM’s Thomas J. Watson Research Center in Yorktown Heights, N.Y., showed that conventional computing incurs an unavoidable cost in energy dissipation—basically, in the generation of heat and entropy. That is because a conventional computer has to sometimes erase bits of information in its memory circuits in order to make space for more. Each time a single bit (with the value 1 or 0) is reset, a certain minimum amount of energy is dissipated—which Ray and Crutchfield have christened “the Landauer.” Its value depends on ambient temperature: in your living room, one Landauer would be around 10–21 joule. (For comparison, a lit candle emits on the order of 10 joules of energy per second.)

‘Momentum Computing’ Pushes Technology’s Thermodynamic Limits, Phillip Ball, Scientific American

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Strain and Flow...


Topography of the two-dimensional crystal on top of the microscopically small wire indicated by dashed lines. Excitons freely move along the wire-induced dent, but cannot escape it in the perpendicular direction. (Courtesy: Florian Dirnberger)

Topics: Applied Physics, Condensed Matter Physics, Electrical Engineering

Using a technique known as strain engineering, researchers in the US and Germany have constructed an “excitonic wire” – a one-dimensional channel through which electron-hole pairs (excitons) can flow in a two-dimensional semiconductor like water through a pipe. The work could aid the development of a new generation of transistor-like devices.

In the study, a team led by Vinod Menon at the City College of New York (CCNY) Center for Discovery and Innovation and Alexey Chernikov at the Dresden University of Technology and the University of Regensburg in Germany deposited atomically thin 2D crystals of tungsten diselenide (fully encapsulated in another 2D material, hexagonal boride nitride) atop a 100 nm-thin nanowire. The presence of the nanowire created a small, elongated dent in the tungsten diselenide by slightly pulling apart the atoms in the 2D material and so inducing strain in it. According to the study’s lead authors, Florian Dimberger and Jonas Ziegler, this dent behaves for excitons much like a pipe does for water. Once trapped inside, they explain, the excitons are bound to move along the pipe.

Strain guides the flow of excitons in 2D materials, Isabelle Dumé, Physics World

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Stop-Motion Efficiency...


A team of researchers created a new method to capture ultrafast atomic motions inside the tiny switches that control the flow of current in electronic circuits. Pictured here are Aditya Sood (left) and Aaron Lindenberg (right). Courtesy: Greg Stewart/SLAC National Accelerator Laboratory

Topics: Applied Physics, Electrical Engineering, Nanotechnology, Semiconductor Technology

A new ultrafast imaging technique that captures the motion of atoms in nanoscale electronic devices has revealed the existence of a short-lived electronic state that could make it possible to develop faster and more energy-efficient computers. The imaging technique, which involves switching the devices on and off while taking snapshots of them with an electron diffraction camera, could also help researchers probe the limits of electronic switching.

“In general, we know very little about the intermediate phases materials pass through during electronic switching operations,” explains Aditya Sood, a postdoctoral researcher at the US Department of Energy’s SLAC National Accelerator Laboratory and lead author of a paper in Science about the new method. “Our technique allows for a new way to visualize this process and therefore address what is arguably one of the most important questions at the heart of computing – that is, what are the fundamental limits of electronic switches in terms of speed and energy consumption?”

Ultrafast electron diffraction camera

Sood and colleagues at SLACStanford UniversityHewlett Packard LabsPennsylvania State University, and Purdue University chose to study devices made from vanadium dioxide (VO2) because the material is known to transition between insulating and electrically conducting states near room temperature. It thus shows promise as a switch, but the exact pathway underlying electric field-induced switching in VOhas long been a mystery, Sood tells Physics World.

To take snapshots of VO2’s atomic structure, the team used periodic voltage pulses to switch an electronic device made from the material on and off. The researchers synchronized the timing of these voltage pulses with the high-energy electron pulses produced by SLAC’s ultrafast electron diffraction (UED) camera. “Each time a voltage pulse excited the sample, it was followed by an electron pulse with a delay that we could tune,” Sood explains. “By repeating this process many times and changing the delay each time, we created a stop-motion movie of the atoms moving in response to the voltage pulse.”

This is the first time that anyone has used UED, which detects tiny atomic movements in a material by scattering a high-energy beam of electrons off a sample, to observe an electronic device during operation. “We started thinking about this subject three years ago and soon realized that existing techniques were simply not fast enough,” says Aaron Lindenberg, a professor of materials science and engineering at Stanford and the study’s senior author. “So we decided to construct our own.”

‘Stop-motion movie of atoms’ reveals short-lived state in nanoscale switch, Isabelle Dumé, Physics World

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Gold Anniversary...


Images are from the article, link below

Topics: Electrical Engineering, Materials Science, Nanotechnology, Solid-State Physics

It's not exactly a wedding anniversary, but it is significant.

Fifty years ago this month, Intel introduced the first commercial microprocessor, the 4004. Microprocessors are tiny, general-purpose chips that use integrated circuits made up of transistors to process data; they are the core of a modern computer. Intel created the 12 mm2 chip for a printing calculator made by the Japanese company Busicom. The 4004 had 2,300 transistors—a number dwarfed by the billions found in today’s chips. But the 4004 was leaps and bounds ahead of its predecessors, packing the computing power of the room-sized, vacuum tube-based first computers into a chip the size of a fingernail. In the past 50 years, microprocessors have changed our culture and economy in unimaginable ways.

The microprocessor turns 50, Katherine Bourzac, Chemical & Engineering News

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Scrofulous Signaling...


FIG. 1. Schematics of pulse sequences for spin-locking measurement with (a) two π/2 pulses and (b) two composite pulses. (c) Schematics of a SCROFULOUS composite pulse composed of three pulses. (d) Evolution of the spin state in the Bloch sphere. The spin state is initialized to the |0⟩ state by the first laser pulse. (e) The first π/2 pulse rotates the spin by 90∘ to the (−y)-direction. A y-driving microwave field is applied parallel to the spin in the rotation frame. (f) The second π/2 pulse rotates the spin by 90∘ to the (−z)-direction in the pulse sequence pattern A, or (g) the second −π/2 pulse rotates the spin by −90∘ to the z-direction in the pulse sequence pattern B. Finally, the spin state is read out from the PL by applying the second laser pulse. (h) Schematics of the experimental setup.

Topics: Applied Physics, Electrical Engineering, Materials Science, Optics

We present results of near-field radio-frequency (RF) imaging at micrometer resolution using an ensemble of nitrogen-vacancy (NV) centers in diamond. The spatial resolution of RF imaging is set by the resolution of an optical microscope, which is markedly higher than the existing RF imaging methods. High sensitivity RF field detection is demonstrated through spin locking. SCROFULOUS composite pulse sequence is used for manipulation of the spins in the NV centers for reduced sensitivity to possible microwave pulse amplitude error in the field of view. We present procedures for acquiring an RF field image under spatially inhomogeneous microwave field distribution and demonstrate a near-field RF imaging of an RF field emitted from a photolithographically defined metal wire. The obtained RF field image indicates that the RF field intensity has maxima in the vicinity of the edges of the wire, in accord with a calculated result by a finite-difference time-domain method. Our method is expected to be applied in a broad variety of application areas, such as material characterizations, characterization of RF devices, and medical fields.</em>

Near-field radio-frequency imaging by spin-locking with a nitrogen-vacancy spin sensor, Shintaro Nomura1,a), Koki Kaida1, Hideyuki Watanabe2, and Satoshi Kashiwaya3, Journal of Applied Physics

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