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Optical Antennae Amplify LEDs for Fast Interconnects

Because lasers are fast—their transmission rate can reach 50 gigahertzthey are widely used for data transmission. Now researchers from the University of California at Berkeley and Bell Labs, Alcatel Lucent at Homdel in New Jersey have shown that by equipping light-emitting diodes (LEDs) with tiny antennae, they will be able to match and even surpass transmission speeds of semiconductor lasers, which would be especially useful over short distances. 

“If we push optical interconnects down to chip-scale, then we would want two things: First, the light source should be small physically, comparable to transistors, and secondly, they should be energy efficient,” says Ming Wu, who with Eli Yablonovitch, both at Berkeley, led the research team. They published this research in the February 10 issue of the Proceedings of the National Academy of Sciences.

Unlike lasers that produce intense focused beams of coherent photons by a process called “stimulated emission,” first seen in 1960, LEDs produce light by “spontaneous emission,” the ordinary light we see around us all the time.

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Coupling Microwaves to Optoelectronics With Sound

Sound is widely used for modulating light in optical communications or for controlling the output of lasers. The devices designed to do this, acousto-optic modulators, typically contain a crystal attached to a piezoelectric transducer. The sound waves propagating through the crystal modulate the intensity of light passing through it. But these devices are typically the size of a sugar cube, so integration with photonic chips is difficult. Also, their acoustic frequencies, limited to the megahertz range, make them unsuitable for high-speed optical communications.

Now, two researchers at the University of Minnesota have reported, in Nature Communications, how they overcame the frequency limitations of the transducer. They did it by reducing the size of the acoustic modulator and by integrating a nanophotonic circuit with the piezoelectric transducer on a single chip.

The logical approach was, of course, to look for a material with both good optical and piezoelectric properties. They used aluminum nitride, a piezoelectric material that fits the bill perfectly. It can easily be sputtered on silicon dioxide, has a high refractive index, and is a good conductor of sound waves. They deposited a 330-nanometer-thick layer of this material on a silicon wafer, then etched away some of the material to form a rib waveguide. The waveguide is a closed loop shaped like a racetrack; light is allowed to circulate around the elongated circle. A tiny piezoelectric interdigital transducer comprising parallel gold lines deposited on the aluminum nitrate emits sound waves in one of the racetrack’s straightaways.  

Because the gold lines in the transducer are only about 100 nanometers wide, they can generate sound waves with frequencies as high as 10 gigahertz.

“What is new in this research is that we reduce the wavelength of the sound wave to be even smaller than the wavelength of light,” says Mo Li, a coauthor of the paper and head of the electrical and computer engineering department’s nanophotonics and nanomechanics lab. The sound waves set up a traveling region of lower and higher density in the material; this region acts like a diffraction grate, bending the light sideways. Because the period of the grate is smaller than the wavelength of the light, the diffraction is very efficient.

This is not the only advantage of the on-chip design. The sound waves are, unlike conventional acoustic modulators, not bulk waves, but surface waves. “We do everything on a surface, and this is why we achieved a strong interaction between the sound and light,” Says Li.

Because they injected light into the racetrack and allowed it to resonate, the researchers were able to modulate the intensity of the light efficiently by injecting a 10-GHz signal into the acoustic wave transducer. Li explains that converting a microwave signal into modulated light will greatly increase the distance over which data-carrying microwaves can be transmitted. The light can transport the microwaves over much longer distances in optical fiber, with much lower signal loss and at a much lower cost, than transmitting them directly through air, says Li. “You only need a photodetector that can convert the light back into microwaves,” he adds.

With the recent breakthroughs in research into plasmons—surface waves of electrons induced by light on conducting surfaces—these waves’ interaction with acoustic surface waves might be an interesting new direction. “The challenge is to further reduce the sound wave to be of the same order as the wavelength of surface plasmon waves,” says Li. “This is not impossible, and you might find some interesting effects,” he says, adding that because both the sound waves and plasmons are surface waves, you will have a perfect overlap. 

Now the researchers’ goal is to increase the frequency of the sound waves to 20 GHz. Such higher frequencies will open up interesting possibilities for quantum computation, says Li. Sound waves will allow the coupling of optical qubits (photons) with phonons. Optical qubits are good for the transmission of data, while phonons, which arise at very low temperatures, are better suited for quantum processing.

Successful Flight of Angara-A5 Rocket Marks New Era for Russia's Ambitions in Space

The little-noticed launch of a Russian rocket just before last Christmas deserves a lot more attention. A new model of a space booster called the Angara-A5 blasted off from the Plesetsk space center in northwestern Russia, and its launch says a lot about the often unclear state of the Russian space industry.

Although it took years of agonizing delays and redesigns to get the medium class booster—on par with the most powerful rockets currently produced by the United States, Japan, and Europe—the Angara-A5 flew flawlessly on its maiden launch: It was the most powerful rocket ever launched from anywhere in Europe, and the first rocket launched from Europe to send a payload into 24-hour geosynchronous orbit.

Politically, it was a demonstration that Russia’s uncomfortable dependence on the Baikonur spaceport in independent Kazakhstan is being significantly reduced. In recent years that dependence has been more worrisome: fears in Kazakhstan of a Crimea-style Russian annexation of ethnic-Russian-inhabited northern provinces make it more likely that a less hospitable government will succeed that of aging strong-man President Nursultan Nazarbayev.

But the technological implication of the flight is the most profound, and it is this: however much the Russian space industry has been suffering under a string of military generals performing reorganizations or enhancing discipline for inadequate quality control, Russian aerospace engineers still have what it takes to expand their capabilities. They are rocket builders, and by the ultimate judgment of spaceflight, they can still build magnificent rockets.

The Angara-A5 uses the RD-191 rocket engine. The RD-191 burns kerosene and liquid oxygen and is an upgraded version of the RD-170 engines used on the short-lived Energia heavy-lift booster. At sea level, the RD-191 can produce a thrust of 196 tons. Its specific impulse—a general measure of engine performance—is a respectable 311 seconds (for comparison, the space shuttle main engines had a specific impulse of 363 seconds at sea level, using the more powerful, but trickier to use, liquid hydrogen as a fuel). Together, the five engines of the Angara-A5 produce a total thrust of 980,000 kilograms.

The Angara booster family was designed more than twenty years ago with the intent of replacing a hodge-podge of boosters developed from earlier military ballistic missile programs. The goal was to transition from self-igniting hypergolic propellants to less toxic propellants, such as kerosene and liquid oxygen. With a first stage consisting of from one to five (or possibly more) standardized core units—each long and narrow enough to be transported by rail—and a standardized selection of upper stages, the system was supposed to allow operation of different models of booster from the same standardized launch pad.

Built by the Khrunichev State Research and Production Space Center, the Angara family currently has two booster components, designated URM (universal rocket module) #1 (for the first stage) and #2 (for use as a middle stage). The light Angara-A1 uses a single URM-1 (plus a small upper stage), and can put a 3.8 ton payload into low-Earth-orbit; the medium Angara-A3, currently in development, will use three URM-1s to send 14.6 tons aloft; and the heavy Angara-A5 (using five URM-1’s) is rated for 24 tons. There is already a plan for an Angara-A7, which would be capable of boosting 35 tons.

Vladimir Nesterov, the chief designer of the Angara booster family, boasted of the value of this standardization in an interview published in January in the Moscow newspaper Argumenty Nedeli: “Different classes of Angara are assembled in the same launch support facility and are checked and transported to a common launch complex for all three rockets,” he told a reporter. “This is a colossal savings from the standpoint of operating expenses. Not a single world space system currently has such advantages.”

The launch of the Angara-A5 on 22 December demonstrated the approach, using the same pad—and the same, mostly-military, launch crew—as an earlier Angara-A1 test launch six months earlier. Other one-vehicle-type-only pads have already been shut down, and their launch crews dispersed, in anticipation of a complete transition to the Angara family.

This transition is causing the Russians some concern however. The next test flight of the Angara-A5 is still a year away, and the reallocation of payloads to the booster has been slowed by major budget cuts forced by the drop in oil prices.   

Nesterov made some imprudent boasts about his rocket system in the Argumenty Nedeli interview: “Angara provides the most important thing,” he explained, “gaining independent access to space. From Russian territory we will have the opportunity of launching all types of launch vehicles and ensuring insertion of all payloads into those orbits which are necessary.”

He waxed defiant: “Even if their own ‘Yatsenyuk’ [the Ukrainian Prime Minister] comes to power now in Kazakhstan, this no longer threatens us with anything.  We now have the full capability of performing all space missions from Plesetsk Cosmodrome.”

In reality, that won’t be for the rest of this decade. Plans to build a second Angara pad at a new cosmodrome in eastern Siberia have been postponed, and there’s no near-term way to build enough Angara vehicles to restore the capabilities provided by Proton booster launch facilities at Baikonur should they get shut down for diplomatic reasons.

It may satisfy the current fever of defiant nationalism now gripping Russia to insult Kazakhstan. But it seems imprudent to telegraph to any potentially hostile post-Nazarbayev leadership that they will lose the important bargaining chip of access to Baikonur, especially when, for now, they still have that chip.

Nonetheless, these prospects don’t diminish the importance of the success of the Angara-A5 launch, and there are even more significant international angles to it. In January, Khrunichev reached agreement with the US commercial space cargo delivery contractor Orbital Sciences Corporation to deliver an upgraded version of the RD-191 engine to Orbital (as a replacement for another Russian engine that exploded on liftoff late last year).

The entangled co-dependencies of the world’s space programs continues to be as messy as ever, but they have proven unexpectedly robust so far—and the resilient skill of the Russian rocket builders is an enduring sinew in that partnership.

Europe's Reusable Spaceplane Completes First Test Flight

A splashdown in the Pacific Ocean concluded the first successful test flight of Europe’s reusable spacecraft technology yesterday. The car-size Intermediate eXperimental Vehicle (IXV) could pave the way for a full-size reusable spaceplane. This would launch on Europe’s Vega rocket and eventually return to Earth by landing like an aircraft on a runway.

The now-retired U.S. space shuttle fleet marked the world’s first concerted attempt to create reusable spacecraft technology, which should result in cost savings. But the shuttle infamously failed to keep overall mission costs down. (Since then, NASA has developed a smaller, robotic spaceplane for the U.S. Air Force called the X-37B that can automatically undergo reentry through the Earth’s atmosphere and land by itself.) The European Space Agency’s IXV spaceplane prototype represents a way for Europe to develop the reentry expertise needed for reusable spacecraft that launch aboard rockets and land like gliders.

“Europe is excellent at going to orbit,” said Giorgio Tumino, project manager for ESA, in a BBC News interview. “We also have great knowhow in operating complex systems in orbit. But where we are a bit behind is in the knowledge of how to come back from orbit.”

The European test spaceplane—with a length of five meters and a weight of almost two tons—had no problems returning to Earth during its maiden voyage. It launched aboard a Vega rocket from Europe’s spaceport in Kourou, French Guiana on Feb. 11, reached an altitude of 412 kilometers, and reentered the Earth’s atmosphere from its suborbital flight path.

During descent, the spaceplane used aerial maneuvers to slow down from hypersonic to supersonic speed. After gliding through the atmosphere it then deployed parachutes in order to slow its descent for the final splashdown in the Pacific Ocean just west of the Galapagos islands.

The entire mission cost about 150 million euros (US $170 million) not including the cost of the Vega rocket, according to SPACE.com. It represents an “intermediate” step leading up to the Programme for Reusable In-Orbit Demonstrator for Europe (PRIDE), which would develop a full-size reusable spaceplane—if it receives funding from ESA.

Spaceplanes aren’t the only way to go for reusable spacecraft, however. The private spaceflight firm SpaceX has been trying to test reusability in its Falcon 9 rocket by having the rocket’s first stage return to Earth and land upright on a platform at sea—with mixed results so far.

Cosmic Ray Particles Will Reveal the Molten Hearts of Fukushima Daiichi's Reactors

In the radioactive ruins of the Fukushima Daiichi nuclear power plant, engineers are testing a new sensor technology. The goal is to see through layers of steel and concrete to determine the location of nuclear fuel at the hearts of three melted-down reactors

The sensor technology makes use of muons, subatomic particles generated when cosmic rays collide with molecules in Earth’s upper atmosphere. About 10,000 muons reach every square meter of our planet each minute, and they whiz through most substances largely unimpeded. However, their progress can be blocked by heavy elements like uranium and plutonium.

Based on this discrepancy, several research teams around the world are developing systems that use muons the same way your dentist uses x-rays. By placing muon detectors near a Fukushima reactor building and determining where the particles’ progress is being blocked, researchers can produce a map of the globs of melted uranium fuel inside the reactor.

There’s a critical need for such maps. The 40-year decommissioning of the Fukushima Daiichi power plant is well underway: Robots are busily surveying and decontaminating the shattered reactor buildings, and workers are removing spent fuel rods from pools. But the hardest step is yet to come. Someday, TEPCO workers will have to remove the melted nuclear fuel that glooped at the bottom of the three reactors’ pressure vessels, leaked through fissures and weak spots, and pooled in unknown nooks and crannies.

Before TEPCO can remove this highly radioactive fuel, the company must first figure out its exact location inside the melted-down reactors. That’s a big challenge, as it will be many years before robots or heavily protected humans are able to remove the tops of the reactor vessels to drop down radiation-shielded cameras. What’s more, those cameras still won’t be able to locate the fuel that seeped out through the bottoms of the presure vessels. 

That’s where the muons come in. TEPCO is first testing a system developed by Japan’s High Energy Accelerator Research Organization, putting the device near the heavily damaged Reactor 1. This system uses a “muon permeation” method; essentially just determining where muons are blocked in their progress by uranium. According to an email from TEPCO, this first test is just to serve as a proof of principle, and won’t produce detailed maps of the melted fuel’s location. 

Another system is under development by the U.S. company Decision Sciences, using a “muon scattering” method invented at Los Alamos National Lab in the early 2000s. This method places muon detectors on two sides of an object of interest, and tracks the trajectory of muons as they enter and leave the object. Because some muons interact with uranium nuclei and ping away in new directions, mapping this scattering can create a more precise map of a uranium blob’s location and contours.  Toshiba, a contractor for TEPCO, has enlisted Decision Sciences to develop its system for Fukushima Daiichi. That device will be tested later this year at Reactor 2. 

Li-Fi-like System Would Bring 100-Gbps Speeds Straight to Your Computer

The light that zips data across the Internet’s backbone used to stop a long way from the data’s final destination. Now it goes all the way to your home. Why not go the last step and take the light all the way to the computer or TV, projecting it through the air over the last few meters and only converting it to an electronic signal at the end? Oxford University is doing just that with a system that takes light from the fiber, amplifies it, and beams it across a room to deliver data at more than 100 gigabits per second.

Such indoor optical wireless probably wouldn’t replace Wi-Fi, says Ariel Gomez, a Ph.D. student in photonics at Oxford University who describes the system in IEEE Photonics Technology Letters. But with a potential for data rates of 3 terabits per second and up, it could certainly find its uses. Wi-Fi, by contrast, tops out at about 7 Gb/s. And with light, there’s no worry about sticking to a limited set of radio frequencies. “If you’re in the optical window, you have virtually unlimited bandwidth and unlicensed spectrum,” Gomez says.

To accomplish this, they’d install a base station on the ceiling of a room, which would project the light toward the computer and also receive data heading out from the computer to the Internet.

The trick, of course, is getting the light beam exactly where it needs to go. An optical fiber makes for a target that’s only 8 or 9 micrometers in diameter, after all. The team, which also included researchers from University College, London, accomplished this using so-called holographic beam steering at both the transmitter and receiver ends. These use an array of liquid crystals to create a programmable diffraction grating that reflects the light in the desired direction. The device is similar to that used in projectors, says Dominic O’Brien, a photonics engineer at Oxford who directed the work.

It’s important to use transceivers with a wide field of view to make the alignment task easier, particularly because the device relies on wavelength division multiplexing, which splits the signal into slightly different colors of light. Like a prism, the diffraction grating of the beam steerer bends each wavelength a different amount. With a 60° field of view, the team was able to transmit six different wavelengths, each at 37.4 Gb/s, for an aggregate bandwidth of 224 Gb/s. With a 36° field of view, they managed only three channels, for 112 Gb/s.

The system requires a direct line of sight, and for now the receiver must be in a fixed position. The next step, O’Brien says, is to develop a tracking and location system so that a user could place a laptop at a random spot on a table and have the system find it and create a link.

Brien is a member of the Ultra-Parallel Visible Light Communications project, with colleagues at the Universities of Edinburgh, Strathclyde, St. Andrews, and Cambridge. One of their goals is to develop LiFi, which uses the light that’s also illuminating a room as a way to send data signals. He says LiFi usually refers to schemes based on visible wavelengths of light, whereas this system relies on infrared light at 1550 nm, which is used in telecommunications.

All these technologies—Wi-Fi, LiFi, optical wireless—may wind up being part of how people link devices to the Internet. “The world of communications is a world where everybody always wants more bandwidth,” O’Brien says.

SpaceX Drone Platform Landing Scrubbed

Update, 12 January: The Falcon 9 rocket’s first stage pulled off a nice water splashdown despite the rough weather. “Rocket soft landed in the ocean within 10m of target & nicely vertical!” Musk tweeted. “High probability of good droneship landing in non-stormy weather.”

A huge storm forced private spaceflight firm SpaceX to cancel a pioneering demonstration of rocket science during today’s successful launch of a Falcon 9 rocket. The original plan to perform a test landing of SpaceX’s reusable rocket technology at sea was scrubbed as three-story high waves crashed over the decks of a drone ship struggling to hold its landing pad in position in the Atlantic Ocean.

Originally, the Falcon 9 rocket’s first stage would have tried for a pinpoint landing on the drone ship using rocket burns, guidance fins and four landing legs. But the extreme weather, coupled with just three of the drone ship’s four engines working, made that scenario impossible. The backup plan for the test of the Falcon 9 rocket’s return to Earth involved trying for a “soft landing” in rough seas, according to a SpaceX announcementan action with very little probability of survival for the rocket.

“Mega storm preventing droneship from remaining on station, so rocket will try to land on water,” Elon Musk tweeted. “Survival probability <1%.”

SpaceX has made reusable rockets a key part of its goal to dramatically reduce the cost of flying to space. The private spaceflight firm points out that most launch costs currently come from building rockets designed to fly just one time. Perfecting the ability to return rockets to Earth could make the Falcon 9 heavy rockets—each costing about as much as a commercial airliner—almost as reusable as aircraft.

“If one can figure out how to effectively reuse rockets just like airplanes, the cost of access to space will be reduced by as much as a factor of a hundred,” says Elon Musk, founder and CEO of SpaceX. “A fully reusable vehicle has never been done before. That really is the fundamental breakthrough needed to revolutionize access to space.”

Getting a Falcon 9 rocket’s first stage back to Earth for a pinpoint landing aboard a drone ship at sea is no joke even in calm weather. The 14-story tall rocket stage uses hypersonic grid fins and three rocket burns to stabilize itself as it reenters the Earth’s atmosphere—a process that SpaceX has described as “trying to balance a rubber broomstick on your hand in the middle of a wind storm.” If all goes well, the rocket stage uses four landing legs to touch down upon the drone ship that serves as SpaceX’s oceangoing landing pad.

The latest Falcon 9 rocket launch was delayed from its initial scheduled launch on Sunday night because of a malfunction in the U.S. Air Force radar system being used to track the rocket during ascent, according to The Orlando SentinelA possible Monday launch was also pushed back because of bad weather.

SpaceX previously conducted two soft water landing tests with the Falcon 9 first stage in 2014. But the first 10 January landing attempt on the drone ship ended in a crash when the grid fins that guided the rocket’s descent ran out of hydraulic fuel just short of landing. The SpaceX team responded by upping the hydraulic fuel load by 50 percent for the latest attempt, according to Elon Musk’s Twitter account.

 The second attempt to land on the drone ship will actually be much more difficult than the first because, Musk tweeted, because the rocket reentered the atmosphere following a deep space mission. That means the Falcon 9 first stage endured almost double the force and four times the heat compared with the first hard landing attempt that followed a low-orbit space station resupply mission.

The latest Falcon 9 heavy rocket launch carried a Deep Space Climate Observatory (DSCOVR) satellite designed to help monitor space weather such as potentially dangerous solar storms. Previous Falcon 9 rockets have also ferried supplies to the International Space Station. In the future, the Dragon crew capsule aboard the rockets may also carry NASA astronauts to the orbital outpost.

Falcon 9 launches currently cost about $65 million to $70 million. If SpaceX can stick the rocket landing, it could lower costs to somewhere between $30 million to $40 million, said Marco Caceres, director of space studies at the Teal Group Corporation consultancy, in a Technology Review interview. 

But the SpaceX goal of eventually reducing costs by 100-fold could mean even cheaper space access. For instance, a $65 million Falcon 9 launch translates into roughly $2,240 per pound of payload for launches to low Earth orbit. A 100-fold drop in cost could mean Falcon 9 delivering payloads to low Earth orbit at a cost of just $22 per pound. (SpaceX’s even bigger Falcon Heavy rocket could theoretically drop the cost to just $10 per pound with a high enough flight rate, according to Popular Mechanics.)

Cheaper space launches could pave the way for much cheaper space missions supporting Earth-centric projects such as SpaceX’s plans to provide global Internet access through a network of satellites. They would also bring SpaceX one step closer to enabling founder Elon Musk’s dream of sending humans to colonize Mars.

A New Material For Wearable Spintronic Devices

Researchers in South Korea have taken a step towards wearable devices based on spintronics. They have made a stretchy thin film that retains its useful electric and magnetic properties even when highly curved.

While conventional electronic circuits exploit an electron’s charge-carrying property, spintronics harnesses the quantum mechanical property of electrons known as spin. The premise is that you can flip electrons’ spin by applying a small voltage in special multiferroic materials.

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U.S. Defense Department Chief Engineer: We Want Your Help With 2030's Tech

The U.S. Department of Defense has been responsible, in one way or another, for a huge number of technological innovations. Over the past half century or so, defense research (or funding) has resulted in ubiquitous technology like GPS, unmanned aircraft, and even the Internet itself. For decades, it’s been at the forefront of science and technology research, but the world is changing. Or at this point, it may be more accurate to say that the world has changed: innovation now happens at the speed of startups. In other words, far faster than the government is used to, comfortable with, or prepared for.

It's not like the DoD hasn't realized that it’s starting to get left behind, but understanding that and doing something about it are very different things for an organization with so much inertia. To try to shake things up a bit, DoD is trying something outside of its comfort zone—actively soliciting ideas from anyone who will talk to them about what kinds of technologies are going to be critical for the military in 2030. They want to hear from you, even if you send them your ideas on a cocktail napkin. Seriously.

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Molybdenum Disulfide Shows Promise For High-Temperature Electronics

Electronics and sensors that relay information from inside jet engines and deep oil and gas wells could improve efficiency and save millions of dollars. Researchers have been looking for cost-effective electronic circuits that would work in those extreme-temperature environments.

Now a team from the University of Calfornia at Riverside and Rensselaer Polytechnic Institute has found that the two-dimensional electronic material molybdenum disulfide (MoS2) is a promising candidate for high-temperature transistors. They have made MoS2 thin-film transistors that work at temperatures exceeding 220 °C and remain stable over two months of operation. The results are published in the Journal of Applied Physics.

Conventional silicon logic chips typically break down past 350 °C. Though researchers are pursuing silicon carbide and gallium nitride circuits as an alternative for extreme environments, these materials “hold promise for extended high-temperature operation, [but] are still not cost-effective for high volume applications," said Alexander Balandin, a professor of electrical and computer engineering at UCR, in a press release.

Molybdenum disulfide, which is found as the mineral molybdenite, is an abundant, naturally occurring material. It can be synthesized by chemical vapor deposition and could also be made into solutions that serve as inks for printable electronics. Researchers have been pursuing its development, along with graphene, as the material of choice for post-silicon electronics.

The reason MoS2 transistors work well at high temperatures is because of the material’s wide bandgap of 1.9 electron volts (silicon’s is 1.1 eV). That wide bandgap keeps high temperatures from driving electrons into the conduction band, causing an undesired flow of current.

Transistors made of silicon carbide—which has an even wider bandgap, in excess 3 eV—can work at over 500 °C, but those devices have yet to be tested for longevity. A University of Utah team recently made plasma transistors for nuclear reactor electronics that function at temperatures as high as 790 °C, but those would be impractical and expensive for other applications.

To be competitive with silicon and silicon carbide, Balandin and his team will have to show that MoS2 transistors work at even higher temperatures. One challenge with making transistors that are resistant to extreme heat is designing other components (chip packaging, interconnect metals, and contacts, for example) that can survive the harsh environment.

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