Tag Archives: letter-pulse-tech

Directly converting electrical power to heat is easy. It regularly happens in your toaster, that is, if you make toast regularly. The opposite, converting heat into electrical power, isn’t so easy.

Researchers from Sandia National Laboratories have developed a tiny silicon-based device that can harness what was previously called waste heat and turn it into DC power. Their advance was recently published in Physical Review Applied.

This tiny silicon-based device developed at Sandia National Laboratories can catch and convert waste heat into electrical power. The rectenna, short for rectifying antenna, is made of common aluminum, silicon and silicon dioxide using standard processes from the integrated circuit industry. Credit: Photo by Randy Montoya/Sandia National Laboratories

“We have developed a new method for essentially recovering energy from waste heat. Car engines produce a lot of heat and that heat is just waste, right? So imagine if you could convert that engine heat into electrical power for a hybrid car. This is the first step in that direction, but much more work needs to be done,” said Paul Davids, a physicist and the principal investigator for the study.

“In the short term we’re looking to make a compact infrared power supply, perhaps to replace radioisotope thermoelectric generators.” Called RTGs, the generators are used for such tasks as powering sensors for space missions that don’t get enough direct sunlight to power solar panels.

Davids’ device is made of common and abundant materials, such as aluminum, silicon and silicon dioxide — or glass — combined in very uncommon ways.

Silicon device catches, channels and converts heat into power

Smaller than a pinkie nail, the device is about 1/8 inch by 1/8 inch, half as thick as a dime and metallically shiny. The top is aluminum that is etched with stripes roughly 20 times smaller than the width of a human hair. This pattern, though far too small to be seen by eye, serves as an antenna to catch the infrared radiation.

Between the aluminum top and the silicon bottom is a very thin layer of silicon dioxide. This layer is about 20 silicon atoms thick, or 16,000 times thinner than a human hair. The patterned and etched aluminum antenna channels the infrared radiation into this thin layer.

The infrared radiation trapped in the silicon dioxide creates very fast electrical oscillations, about 50 trillion times a second. This pushes electrons back and forth between the aluminum and the silicon in an asymmetric manner. This process, called rectification, generates net DC electrical current.

The team calls its device an infrared rectenna, a portmanteau of rectifying antenna. It is a solid-state device with no moving parts to jam, bend or break, and doesn’t have to directly touch the heat source, which can cause thermal stress.

Infrared rectenna production uses common, scalable processes

Because the team makes the infrared rectenna with the same processes used by the integrated circuit industry, it’s readily scalable, said Joshua Shank, electrical engineer and the paper’s first author, who tested the devices and modeled the underlying physics while he was a Sandia postdoctoral fellow.

He added, “We’ve deliberately focused on common materials and processes that are scalable. In theory, any commercial integrated circuit fabrication facility could make these rectennas.”

That isn’t to say creating the current device was easy. Rob Jarecki, the fabrication engineer who led process development, said, “There’s immense complexity under the hood and the devices require all kinds of processing tricks to build them.”

One of the biggest fabrication challenges was inserting small amounts of other elements into the silicon, or doping it, so that it would reflect infrared light like a metal, said Jarecki. “Typically you don’t dope silicon to death, you don’t try to turn it into a metal, because you have metals for that. In this case we needed it doped as much as possible without wrecking the material.”

The devices were made at Sandia’s Microsystems Engineering, Science and Applications Complex. The team has been issued a patent for the infrared rectenna and have filed several additional patents.

The version of the infrared rectenna the team reported in Physical Review Applied produces 8 nanowatts of power per square centimeter from a specialized heat lamp at 840 degrees. For context, a typical solar-powered calculator uses about 5 microwatts, so they would need a sheet of infrared rectennas slightly larger than a standard piece of paper to power a calculator. So, the team has many ideas for future improvements to make the infrared rectenna more efficient.

Future work to improve infrared rectenna efficiency

These ideas include making the rectenna’s top pattern 2D x’s instead of 1D stripes, in order to absorb infrared light over all polarizations; redesigning the rectifying layer to be a full-wave rectifier instead of the current half-wave rectifier; and making the infrared rectenna on a thinner silicon wafer to minimize power loss due to resistance.

Through improved design and greater conversion efficiency, the power output per unit area will increase. Davids thinks that within five years, the infrared rectenna may be a good alternative to RTGs for compact power supplies.

Shank said, “We need to continue to improve in order to be comparable to RTGs, but the rectennas will be useful for any application where you need something to work reliably for a long time and where you can’t go in and just change the battery. However, we’re not going to be an alternative for solar panels as a source of grid-scale power, at least not in the near term.”

Davids added, “We’ve been whittling away at the problem and now we’re beginning to get to the point where we’re seeing relatively large gains in power conversion, and I think that there’s a path forward as an alternative to thermoelectrics. It feels good to get to this point. It would be great if we could scale it up and change the world.”

Today at its Imec Technology Forum USA in San Francisco, imec, the research and innovation hub in nano-electronics and digital technology, announced that it has demonstrated ultra-low power, high-bandwidth optical transceivers through hybrid integration of Silicon Photonics and FinFET CMOS technologies. With a dynamic power consumption of only 230fJ/bit and a footprint of just 0.025mm2, the 40Gb/s non-return-to-zero optical transceivers mark an important milestone in realizing ultra-dense, multi-Tb/s optical I/O solutions for next-generation high-performance computing applications.

The exponentially growing demand for I/O bandwidth in datacenter switches and high-performance computing nodes is driving the need for tight co-integration of optical interconnects with advanced CMOS logic, covering a wide range of interconnect distances (1m-500m+). In the presented work, a differential FinFET driver was co-designed with a Silicon Photonics ring modulator, and achieved 40Gb/s NRZ optical modulation at 154fJ/bit dynamic power consumption. The receiver included a FinFET trans-impedance amplifier (TIA) optimized for operation with a Ge waveguide photodiode, enabling 40Gb/s NRZ photodetection with an estimated sensitivity of -10dBm at 75fJ/bit power consumption. High-quality data transmission and reception was also demonstrated in a loop-back experiment at 1330nm wavelength over standard single mode fiber (SMF) with 2dB link margin. Finally, a 4x40Gb/s, 0.1mm2wavelength-division multiplexing (WDM) transmitter with integrated thermal control was demonstrated, enabling bandwidth scaling beyond 100Gb/s per fiber.

“The demonstrated hybrid FinFET-Silicon Photonics platform integrates high-performance 14nm FinFET CMOS circuits with imec’s 300mm Silicon Photonics technology through dense, low-capacitance Cu micro-bumps. Careful co-design in this combined platform has enabled us to demonstrate 40Gb/s NRZ optical transceivers with extremely low power consumption and high bandwidth density,” says Joris Van Campenhout, director of the Optical I/O R&D program at imec. “Through design optimizations, we expect to further improve the single-channel data rates to 56Gb/s NRZ. Combined with wavelength-division multiplexing, these transceivers provide a scaling path to ultra-compact, multi-Tb/s optical interconnects, which are essential for next-generation high-performance systems.”

This work has been carried out as part of imec’s industrial affiliation R&D program on Optical I/O and was presented at the 2018 Symposia on VLSI Technology and Circuits (June 2018) in a “late news” paper. Imec’s 200mm and 300mm Silicon Photonics technologies are available for evaluation by companies and academia through imec’s prototyping service and the iSiPP50G multi-project wafer (MPW) service.

If your laptop or cell phone starts to feel warm after playing hours of video games or running too many apps at one time, those devices are actually doing their job.

Whisking heat away from the circuitry in a computer’s innards to the outside environment is critical: Overheated computer chips can make programs run slower or freeze, shut the device down altogether or cause permanent damage.

As consumers demand smaller, faster and more powerful electronic devices that draw more current and generate more heat, the issue of heat management is reaching a bottleneck. With current technology, there’s a limit to the amount of heat that can be dissipated from the inside out.

Researchers at the University of Texas at Dallas and their collaborators at the University of Illinois at Urbana-Champaign and the University of Houston have created a potential solution, described in a study published online July 5 in the journal Science.

Researchers at the University of Texas at Dallas and their collaborators have created and characterized tiny crystals of boron arsenide, like the one shown here imaged with an electron microscope, that have high thermal conductivity. Because the semiconducting material efficiently transports heat, it might be used in future electronics to help keep smaller, more powerful devices from overheating. The research is described in a study published online July 5, 2018 in the journal Science. Credit: University of Texas at Dallas

Bing Lv (pronounced “love”), assistant professor of physics in the School of Natural Sciences and Mathematics at UT Dallas, and his colleagues produced crystals of a semiconducting material called boron arsenide that have an extremely high thermal conductivity, a property that describes a material’s ability to transport heat.

“Heat management is very important for industries that rely on computer chips and transistors,” said Lv, a corresponding author of the study. “For high-powered, small electronics, we cannot use metal to dissipate heat because metal can cause a short circuit. We cannot apply cooling fans because those take up space. What we need is an inexpensive semiconductor that also disperses a lot of heat.”

Most of today’s computer chips are made of the element silicon, a crystalline semiconducting material that does an adequate job of dissipating heat. But silicon, in combination with other cooling technology incorporated into devices, can handle only so much.

Diamond has the highest known thermal conductivity, around 2,200 watts per meter-kelvin, compared to about 150 watts per meter-kelvin for silicon. Although diamond has been incorporated occasionally in demanding heat-dissipation applications, the cost of natural diamonds and structural defects in manmade diamond films make the material impractical for widespread use in electronics, Lv said.

In 2013, researchers at Boston College and the Naval Research Laboratory published research that predicted boron arsenide could potentially perform as well as diamond as a heat spreader. In 2015, Lv and his colleagues at the University of Houston successfully produced such boron arsenide crystals, but the material had a fairly low thermal conductivity, around 200 watts per meter-kelvin.

Since then, Lv’s work at UT Dallas has focused on optimizing the crystal-growing process to boost the material’s performance.

“We have been working on this research for the last three years, and now have gotten the thermal conductivity up to about 1,000 watts per meter-kelvin, which is second only to diamond in bulk materials,” Lv said.

Lv worked with postdoctoral research associate Sheng Li, co-lead author of the study, and physics doctoral student Xiaoyuan Liu, also a study author, to create the high thermal conductivity crystals at UT Dallas using a technique called chemical vapor transport. The raw materials — the elements boron and arsenic — are placed in a chamber that is hot on one end and cold on the other. Inside the chamber, another chemical transports the boron and arsenic from the hot end to the cooler end, where the elements combine to form crystals.

“To jump from our previous results of 200 watts per meter-kelvin up to 1,000 watts per meter-kelvin, we needed to adjust many parameters, including the raw materials we started with, the temperature and pressure of the chamber, even the type of tubing we used and how we cleaned the equipment,” Lv said.

David Cahill and Pinshane Huang’s research groups at the University of Illinois at Urbana-Champaign played a key role in the current work, studying defects in the boron arsenide crystals by state-of-the-art electron microscopy and measuring the thermal conductivity of the very small crystals produced at UT Dallas.

“We measure the thermal conductivity using a method developed at Illinois over the past dozen years called ‘time-domain thermoreflectance’ or TDTR,” said Cahill, professor and head of the Department of Materials Science and Engineering and a corresponding author of the study. “TDTR enables us to measure the thermal conductivity of almost any material over a wide range of conditions and was essential for the success of this work.”

The way heat is dissipated in boron arsenide and other crystals is linked to the vibrations of the material. As the crystal vibrates, the motion creates packets of energy called phonons, which can be thought of as quasiparticles carrying heat. Lv said the unique features of boron arsenide crystals — including the mass difference between the boron and arsenic atoms — contribute to the ability of the phonons to travel more efficiently away from the crystals.

“I think boron arsenide has great potential for the future of electronics,” Lv said. “Its semiconducting properties are very comparable to silicon, which is why it would be ideal to incorporate boron arsenide into semiconducting devices.”

Lv said that while the element arsenic by itself can be toxic to humans, once it is incorporated into a compound like boron arsenide, the material becomes very stable and nontoxic.

The next step in the work will include trying other processes to improve the growth and properties of this material for large scale applications, Lv said.

Researchers at Kyushu University’s Center for Organic Photonics and Electronics Research (OPERA) in Japan have demonstrated a way to split energy in organic light-emitting diodes (OLEDs) and surpass the 100% limit for exciton production, opening a promising new route for creating low-cost and high-intensity near-infrared light sources for sensing and communications applications.

OLEDs use layers of carbon-containing organic molecules to convert electrical charges into light. In normal OLEDs, one positive charge and one negative charge come together on a molecule to form a packet of energy called an exciton. One exciton can release its energy to create at most one beam of light, or photon.

Illustration of the singlet fission process used to boost the number of excitons in an OLED and break the 100 percent limit for exciton production efficiency. The emitting layer consists of a mixture of rubrene molecules, which are responsible for singlet fission, and ErQ3 molecules, which produce the emission. A singlet exciton, which is created when a positive charge and a negative charge combine on a rubrene molecule, can transfer half of its energy to a second rubrene molecule through the process of singlet fission, resulting in two triplet excitons. The triplet excitons then transfer to ErQ3 molecules, and the exciton energy is released as near-infrared emission by ErQ3. Credit: William J. Potscavage Jr.

When all charges form excitons that emit light, a maximum 100% internal quantum efficiency is achieved. However, the new technology uses a process called singlet fission to split the energy from an exciton into two, making it possible to exceed the 100% limit for the efficiency of converting charge pairs into excitons, also known as the exciton production efficiency

“Put simply, we incorporated molecules that act as change machines for excitons in OLEDs. Similar to a change machine that converts a $10 bill into two $5 bills, the molecules convert an expensive, high-energy exciton into two half-price, low-energy excitons,” explains Hajime Nakanotani, associate professor at Kyushu University and co-author of the paper describing the new results.

Excitons come in two forms, singlets and triplets, and molecules can only receive singlets or triplets with certain energies. The researchers overcame the limit of one exciton per one pair of charges by using molecules that can accept a triplet exciton with an energy that is half the energy of the molecule’s singlet exciton.

In such molecules, the singlet can transfer half of its energy to a neighboring molecule while keeping half of the energy for itself, resulting in the creation of two triplets from one singlet. This process is called singlet fission.

The triplet excitons are then transferred to a second type of molecule that uses the energy to emit near-infrared light. In the present work, the researchers were able to convert the charge pairs into 100.8% triplets, indicating that 100% is no longer the limit. This is the first report of an OLED using singlet fission, though it has previously been observed in organic solar cells.

Furthermore, the researchers could easily evaluate the singlet fission efficiency, which is often difficult to estimate, based on comparison of the near-infrared emission and trace amounts of visible emission from remaining singlets when the device is exposed to various magnetic fields.

“Near-infrared light plays a key role in biological and medical applications along with communications technologies,” says Chihaya Adachi, director of OPERA. “Now that we know singlet fission can be used in an OLED, we have a new path to potentially overcome the challenge of creating an efficient near-infrared OLED, which would find immediate practical use.”

Overall efficiency is still relatively low in this early work because near-infrared emission from organic emitters is traditionally inefficient, and energy efficiency will, of course, always be limited to a maximum 100%. Nonetheless, this new method offers a way to increase efficiency and intensity without changing the emitter molecule, and the researchers are also looking into improving the emitter molecules themselves.

With further improvements, the researchers hope to get the exciton production efficiency up to 125%, which would be the next limit since electrical operation naturally leads to 25% singlets and 75% triplets. After that, they are considering ideas to convert triplets into singlets and possibly reach a quantum efficiency of 200%.

By integrating the design of antenna and electronics, researchers have boosted the energy and spectrum efficiency for a new class of millimeter wave transmitters, allowing improved modulation and reduced generation of waste heat. The result could be longer talk time and higher data rates in millimeter wave wireless communication devices for future 5G applications.

The new co-design technique allows simultaneous optimization of the millimeter wave antennas and electronics. The hybrid devices use conventional materials and integrated circuit (IC) technology, meaning no changes would be required to manufacture and package them. The co-design scheme allows fabrication of multiple transmitters and receivers on the same IC chip or the same package, potentially enabling multiple-input-multiple-output (MIMO) systems as well as boosting data rates and link diversity.

Researchers from the Georgia Institute of Technology presented their proof-of-concept antenna-based outphasing transmitter on June 11 at the 2018 Radio Frequency Integrated Circuits Symposium (RFIC) in Philadelphia. Their other antenna-electronics co-design work was published at the 2017 and 2018 IEEE International Solid-State Circuits Conference (ISSCC) and multiple peer-reviewed IEEE journals. The Intel Corporation and U.S. Army Research Office sponsored the research.

Georgia Tech researchers are shown with electronics equipment and antenna setup used to measure far-field radiated output signal from millimeter wave transmitters. Shown are Graduate Research Assistant Huy Thong Nguyen, Graduate Research Assistant Sensen Li, and Assistant Professor Hua Wang. (Credit: Allison Carter, Georgia Tech)

“In this proof-of-example, our electronics and antenna were designed so that they can work together to achieve a unique on-antenna outphasing active load modulation capability that significantly enhances the efficiency of the entire transmitter,” said Hua Wang, an assistant professor in Georgia Tech’s School of Electrical and Computer Engineering. “This system could replace many types of transmitters in wireless mobile devices, base stations and infrastructure links in data centers.”

Key to the new design is maintaining a high-energy efficiency regardless whether the device is operating at its peak or average output power. The efficiency of most conventional transmitters is high only at the peak power but drops substantially at low power levels, resulting in low efficiency when amplifying complex spectrally efficient modulations. Moreover, conventional transmitters often add the outputs from multiple electronics using lossy power combiner circuits, exacerbating the efficiency degradation.

“We are combining the output power though a dual-feed loop antenna, and by doing so with our innovation in the antenna and electronics, we can substantially improve the energy efficiency,” said Wang, who is the Demetrius T. Paris Professor in the School of Electrical and Computer Engineering.  “The innovation in this particular design is to merge the antenna and electronics to achieve the so-called outphasing operation that dynamically modulates and optimizes the output voltages and currents of power transistors, so that the millimeter wave transmitter maintains a high energy efficiency both at the peak and average power.”

Beyond energy efficiency, the co-design also facilitates spectrum efficiency by allowing more complex modulation protocols. That will enable transmission of a higher data rate within the fixed spectrum allocation that poses a significant challenge for 5G systems.

“Within the same channel bandwidth, the proposed transmitter can transmit six to ten times higher data rate,” Wang said. “Integrating the antenna gives us more degrees of freedom to explore design innovation, something that could not be done before.”

Sensen Li, a Georgia Tech graduate research assistant who received the Best Student Paper Award at the 2018 RFIC symposium, said the innovation resulted from bringing together two disciplines that have traditionally worked separately.

“We are merging the technologies of electronics and antennas, bringing these two disciplines together to break through limits,” he said. “These improvements could not be achieved by working on them independently. By taking advantage of this new co-design concept, we can further improve the performance of future wireless transmitters.”

The new designs have been implemented in 45-nanometer CMOS SOI IC devices and flip-chip packaged on high-frequency laminate boards, where testing has confirmed a minimum two-fold increase in energy efficiency, Wang said.

The antenna electronics co-design is enabled by exploring the unique nature of multi-feed antennas.

“An antenna structure with multiple feeds allows us to use multiple electronics to drive the antenna concurrently. Different from conventional single-feed antennas, multi-feed antennas can serve not only as radiating elements, but they can also function as signal processing units that interface among multiple electronic circuits,” Wang explained. “This opens a completely new design paradigm to have different electronic circuits driving the antenna collectively with different but optimized signal conditions, achieving unprecedented energy efficiency, spectral efficiency and reconfigurability.”

The cross-disciplinary co-design could also facilitate fabrication and operation of multiple transmitters and receivers on the same chip, allowing hundreds or even thousands of elements to work together as a whole system. “In massive MIMO systems, we need to have a lot of transmitters and receivers, so energy efficiency will become even more important,” Wang noted.

Having large numbers of elements working together becomes more practical at millimeter wave frequencies because the wavelength reduction means elements can be placed closer together to achieve compact systems, he pointed out. These factors could pave the way for new types of beamforming that are essential in future millimeter wave 5G systems.

Power demands could drive adoption of the technology for battery-powered devices, but Wang says the technology could also be useful for grid-powered systems such as base stations or wireless connections to replace cables in large data centers. In those applications, expanding data rates and reducing cooling needs could make the new devices attractive.

“Higher energy efficiency also means less energy will be converted to heat that must be removed to satisfy the thermal management,” he said. “In large data centers, even a small reduction in thermal load per device can add up. We hope to simplify the thermal requirements of these electronic devices.”

In addition to those already mentioned, the research team included Taiyun Chi, Huy Thong Nguyen and Tzu-Yuan Huang, all from Georgia Tech.

Toshiba Electronic Devices & Storage Corporation (“Toshiba”) announces the launch of a new analog output IC photocoupler that enables high-speed communications in automotive applications – especially electric vehicles (EV) and hybrid electric vehicles (HEV).

The new TLX9309 consists of a high-output GaAlAs light emitting diode (LED) that is optically coupled to a high-speed detector. The detector consists of a photodiode and a transistor integrated onto a single chip. A Faraday shield has been integrated onto the photodetector chip to provide enhanced levels of common-mode transient immunity – typically up to 15kV/μs, an important parameter in electrically noisy automotive environments.

By separating the photodiode and amplification transistor, the collector capacitance is reduced, reducing propagation delays and making the open-collector TLX9309 faster than transistor output devices. In fact, propagation delay times are guaranteed to be between 0.1μs and 1.0μs, with the difference between high to low and low to high transition (|tpLH-tpHL|) being no more than 0.7μs, making the device suitable for high-speed communications such as inverter control or as an interface to intelligent power modules (IPM).

Electrically, the device offers 3750Vrms of isolation with 5.0mm of creepage and clearance for safety isolation. It operates from a supply in the range -0.5 to 30V DC and can drive up to 25mA at output voltages up to 20V. The current transfer ratio is in the range 15-300%.

The TLX9309 is packaged in a 3.7mm x 7.0mm x 2.2mm RoHS compliant 5-pin SO6 package and operates over the temperature range -40°C to +125°C. The device is AEC-Q101 qualified for use in automotive applications.

The TLX9309 is now in mass production.

ROHM today announced the availability of a CMOS op-amp featuring the lowest noise in the industry optimized for industrial applications requiring high-accuracy sensing, such as accelerometers used in sonar systems, and optical sensors that handle ultra-small signals.

In recent years, in addition to IoT devices, sensors are being adopted in a variety of applications from portables and vehicle systems to industrial equipment, to improve functionality and provide advanced control. Used to detect and convert various environmental and physical changes into signals, sensors demand high accuracy, but at the same time peripheral sensor circuitry is trending towards lower voltages to achieve greater power savings.

Op-amps are configured at the rear stage to amplify the analog sensor output, but because sensor signals are so weak it is necessary to implement noise countermeasures to ensure high-accuracy transmission. In response, ROHM developed a high noise tolerant op-amp for the automotive market utilizing a vertically integrated production system that leverages original analog design technologies and processes. ROHM has introduced an op-amp that delivers the industry’s best performance against external noise optimized for consumer devices and industrial equipment.

The LMR1802G-LB, developed utilizing ROHM’s analog technology covering circuit design, processes, and layout, reduces input equivalent noise voltage density by half (2.9nV/√Hz at 1kHz, 7.8nV/√Hz at 10Hz) compared to conventional products, significantly improving the detection performance of sensor signals. In addition, best-in-class phase margin (68°) and capacitive load tolerance (500pF) provide excellent stability (difficult to oscillate, easy to handle). This enables accurate amplification of voltages in the order of µV, ensuring support for industrial and consumer applications requiring high-precision sensing.

There are limits to how accurately you can measure things. Think of an X-ray image: it is likely quite blurry and something only an expert physician can interpret properly. The contrast between different tissues is rather poor but could be improved by longer exposure times, higher intensity, or by taking several images and overlapping them. But there are considerable limitations: humans can safely be exposed to only so much radiation, and imaging takes time and resources.

A well-established rule of thumb is the so-called standard quantum limit: the precision of the measurement scales inversely with the square root of available resources. In other words, the more resources – time, radiation power, number of images, etc. – you throw in, the more accurate your measurement will be. This will, however, only get you so far: extreme precision also means using excessive resources.

A team of researchers from Aalto University, ETH Zurich, and MIPT and Landau Institute in Moscow have pushed the envelope and came up with a way to measure magnetic fields using a quantum system – with accuracy beyond the standard quantum limit.

An artificial atom realised from superconducting strips of aluminum on a silicon chip can be employed for the detection of magnetic fields. Credit: Babi Brasileiro / Aalto University

The detection of magnetic fields is important in a variety of fields, from geological prospecting to imaging brain activity. The researchers believe that their work is a first step towards of using quantum-enhanced methods for sensor technology.

‘We wanted to design a highly efficient but minimally invasive measurement technique. Imagine, for example, extremely sensitive samples: we have to either use as low intensities as possible to observe the samples or push the measurement time to a minimum,’ explains Sorin Paraoanu, leader of the Kvantti research group at Aalto University.

Their paper, published in the prestigious journal npj Quantum Information shows how to improve the accuracy of magnetic field measurements by exploiting the coherence of a superconducting artificial atom, a qubit. It is a tiny device made of overlapping strips of aluminium evaporated on a silicon chip – a technology similar to the one used to fabricate the processors of mobile phones and computers.

When the device is cooled to a very low temperature, magic happens: the electrical current flows in it without any resistance and starts to display quantum mechanical properties similar to those of real atoms. When irradiated with a microwave pulse – not unlike the ones in household microwave ovens – the state of the artificial atom changes. It turns out that this change depends on the external magnetic field applied: measure the atom and you will figure out the magnetic field.

But to surpass the standard quantum limit, yet another trick had to be performed using a technique similar to a widely-applied branch of machine learning, pattern recognition.

‘We use an adaptive technique: first, we perform a measurement, and then, depending on the result, we let our pattern recognition algorithm decide how to change a control parameter in the next step in order to achieve the fastest estimation of the magnetic field,’ explains Andrey Lebedev, corresponding author from ETH Zurich, now at MIPT in Moscow.

‘This is a nice example of quantum technology at work: by combining a quantum phenomenon with a measurement technique based on supervised machine learning, we can enhance the sensitivity of magnetic field detectors to a realm that clearly breaks the standard quantum limit,’ Lebedev says.

There are limits to how accurately you can measure things. Think of an X-ray image: it is likely quite blurry and something only an expert physician can interpret properly. The contrast between different tissues is rather poor but could be improved by longer exposure times, higher intensity, or by taking several images and overlapping them. But there are considerable limitations: humans can safely be exposed to only so much radiation, and imaging takes time and resources.

A well-established rule of thumb is the so-called standard quantum limit: the precision of the measurement scales inversely with the square root of available resources. In other words, the more resources – time, radiation power, number of images, etc. – you throw in, the more accurate your measurement will be. This will, however, only get you so far: extreme precision also means using excessive resources.

A team of researchers from Aalto University, ETH Zurich, and MIPT and Landau Institute in Moscow have pushed the envelope and came up with a way to measure magnetic fields using a quantum system – with accuracy beyond the standard quantum limit.

The detection of magnetic fields is important in a variety of fields, from geological prospecting to imaging brain activity. The researchers believe that their work is a first step towards of using quantum-enhanced methods for sensor technology.

‘We wanted to design a highly efficient but minimally invasive measurement technique. Imagine, for example, extremely sensitive samples: we have to either use as low intensities as possible to observe the samples or push the measurement time to a minimum,’ explains Sorin Paraoanu, leader of the Kvantti research group at Aalto University.

Their paper, published in the prestigious journal npj Quantum Information shows how to improve the accuracy of magnetic field measurements by exploiting the coherence of a superconducting artificial atom, a qubit. It is a tiny device made of overlapping strips of aluminium evaporated on a silicon chip – a technology similar to the one used to fabricate the processors of mobile phones and computers.

When the device is cooled to a very low temperature, magic happens: the electrical current flows in it without any resistance and starts to display quantum mechanical properties similar to those of real atoms. When irradiated with a microwave pulse – not unlike the ones in household microwave ovens – the state of the artificial atom changes. It turns out that this change depends on the external magnetic field applied: measure the atom and you will figure out the magnetic field.

But to surpass the standard quantum limit, yet another trick had to be performed using a technique similar to a widely-applied branch of machine learning, pattern recognition.

‘We use an adaptive technique: first, we perform a measurement, and then, depending on the result, we let our pattern recognition algorithm decide how to change a control parameter in the next step in order to achieve the fastest estimation of the magnetic field,’ explains Andrey Lebedev, corresponding author from ETH Zurich, now at MIPT in Moscow.

‘This is a nice example of quantum technology at work: by combining a quantum phenomenon with a measurement technique based on supervised machine learning, we can enhance the sensitivity of magnetic field detectors to a realm that clearly breaks the standard quantum limit,’ Lebedev says.

A Tokyo Institute of Technology research team has shown copper nitride acts as an n-type semiconductor, with p-type conduction provided by fluorine doping, utilizing a unique nitriding technique applicable for mass production and a computational search for appropriate doping elements, as well as atomically resolved microscopy and electronic structure analysis using synchrotron radiation. These n-type and p-type copper nitride semiconductors could potentially replace the conventional toxic or rare materials in photovoltaic cells.

Thin film photovoltaics have equivalent efficiency and can cut the cost of materials compared to market-dominating silicon solar panels. Utilizing the photovoltaic effect, thin layers of specific p-type and n-type materials are sandwiched together to produce electricity from sunlight. The technology promises a brighter future for solar energy, allowing low-cost and scalable manufacturing routes compared to crystalline silicon technology, even though toxic and rare materials are used in commercialized thin film solar cells. A Tokyo Institute of Technology team has challenged to find a new candidate material for producing cleaner, cheaper thin film photovoltaics.

(a) This is a copper and Copper Nitride. (b) Theoretical Calculation for P-type and N-type Copper Nitride. (c) Direct Observation of Fluorine Position in Fluorine-doped Copper Nitride. (a) An image of thin film copper plates before and after reacting with ammonia and oxygen. Copper metal has been transformed to copper nitride. (b) Copper insertion for an n-type semiconductor and fluorine insertion for a p-type semiconductor. (c) Nitrogen plotted in red, fluorine in green, and copper in blue. Fluorine is located at the open space of the crystal as predicted by the theoretical calculation. Credit: Advanced Materials

They have focused on a simple binary compound, copper nitride that is composed of environmentally friendly elements. However, growing a nitride crystal in a high quality form is challenging as history tells us to develop gallium nitride blue LEDs. Matsuzaki and his coworkers have overcome the difficulty by introducing a novel catalytic reaction route using ammonia and oxidant gas. This compound, pictured through the photograph in figure (a), is an n-type conductor that has excess electrons. On the other hand, by inserting fluorine element in the open space of the crystal, they found this n-type compound transformed into p-type as predicted by theoretical calculations and directly proven by atomically resolved microscopy in figures (b) and (c), respectively.

All existing thin film photovoltaics require a p-type or n-type partner in their makeup of a sandwich structure, requiring huge efforts to find the best combination. P-type and n-type conduction in the same material developed by Matsuzaki and his coworkers are beneficial to design a highly efficient solar cell structure without such efforts. This material is non-toxic, abundant, and therefore potentially cheap–ideal replacements for in use cadmium telluride and copper indium gallium diselenide thin film solar cells. With the development of these p-type and n-type semiconductors, in a scalable forming technique using simple safe and abundant elements, the positive qualities will further bring thin film technology into the light.