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SummaryMemory is one of the most important part for electronics. Computers and Smartphones woludn't be nearly as useful without room for lots of apps,music and videos. Devices tend to store that  information in two ways: through electric fields (think of a flash drive) or through magnetic fields (like a computer’s spinning hard disk). Each method has advantages and disadvantages. However, in the future, our electronics could benefit from the best of each. There are some questions put by Chang-Beom Eom, the Theodore H. Geballe Professor and Harvey D. Spangler Distinguished Professor of Materials Science and Engineering at the University of Wisconsin-Madison. “Can you cross-couple these two different ways to store information? Could we use an electric field to change the magnetic properties? Then you can have a low-power, multifunctional device. We call this a ‘magnetoelectric’ device.” In research published recently in the journal Nature Communications, Eom and his collaborators describe not only their unique process for making a high-quality magnetoelectric material, but exactly how and why it works. Physics graduate student Julian Irwin checks equipment in the lab of materials science and engineering Professor Chang-Beom Eom, where researchers have produced a material that could exhibit the best qualities of both solid-state and spinning disk digital storage. Magnetoeletric materialsMagnetoelectric materials,which have both magnetic and electrical functionalities,or "orders" already exist. Switching one functionality induces a change in the other.“It’s called cross-coupling,” says Eom. “Yet, how they cross-couple is not clearly understood.” Gaining that understanding, he says, requires studying how the magnetic properties change when an electric field is applied. Up to now, this has been difficult due to the complicated structure of most magnetoelectric materials. In the past,people studied magnetoelectric properties using very "complex" materials,or those that lack uniformity.In his approach,Eom simplified not only the research but the material itself. Drawing on Eom's expertise in material growth,he developed a unique process,using atomic "steps" to guide the growth of a homogenous,single-crystal thin film of bismuth ferrite. Atop that, he added cobalt, which is magnetic; on the bottom, he placed an electrode made of strontium ruthenate.  Bismuth Ferrite MaterialThe bismuth ferrite material was important because it made it much easier for Eom to study the fundamental magnetoelectric cross-coupling. Eom found that in their work,because of their single domain,they could actually see what was going on using multiple probing, or imaging, techniques.The mechanism is intrinsic. It’s reproducible — and that means you can make a device without any degradation, in a predictable way. To image the changing  electric and magnetic properties switching in real time, Eom and his colleagues used the powerful synchrotron light sources at Argonne National Laboratory outside Chicago, and in Switzerland and the United Kingdom. “When you switch it, the electrical field switches the electric polarization. If it’s ‘downward,’ it switches ‘upward,'” he says. “The coupling to the magnetic layer then changes its properties: a magnetoelectric storage device.” That change in direction enables researchers to take the next steps needed to add programmable integrated circuits — the building blocks that are the foundation of our electronics — to the material. While the homogenous material enabled Eom to answer important scientific questions about how magnetoelectric cross-coupling happens, it also could enable manufacturers to improve their electronics.Eom saied they can design a much more effective,efficient and low-power device now. 

SummaryIt has been successfully demonstrated that a nanocrystal of of perovskite can serve as a quantum emitter of light, and, when coupled with a nanophotonic cavity, can dramatically improve the efficiency of the light emission by an international research team from the University of Maryland and ETH Zurich in Switzerland.  A new device features perovskite nanocrystals and a series of nanophotonic cavities. The arrows indicate the way that the UV laser used to excite the crystals, and the light  the crystals produce, move in and out of the device. Described in the Journal Applied Physics Letters ,the resulting device and method could be used to build nanolasers and optical devices that exhibit much faster response times than currently possible. Previously, there have been other quantum emitting materials that have been coupled to nanophotonic cavities. In this area, epitaxial materials such as quantum dots have garnered the most research interest. Distinct advantage to using PerovskiteHowever, the researchers believe there are some distinct advantages to using perovskite nanocrystals instead of epitaxial materials, which involve the fairly complex deposition of a crystalline layer on a crystalline substrate.Instead of the epitaxial techniques, the perovskite nanocrystals are synthesized using inexpensive colloidal chemistry techniques. This also makes it possible for these crystals to be placed on a broad range of substrates using simpler solution-deposition techniques when they are coupled to various photonic structures. The other main set of advantages for perovskites in light-emitting applications relates back to why they have become such a darling in photovoltaics: their optical and electrical properties. Perovskites exhibit a slow non-radiative decay rate and low densities of carrier-trapping defects, which contributes to their high photoluminescence efficiency at room temperature.In addition, the emission spectrum could cover the whole visible range by controlling the size and material composition, especially for the blue-green wavelengths that are otherwise difficult to access. The device operates by exciting the coupled system using a UV laser. This excites the perovskites to a higher energy level. Within a nanosecond, the exciton (an excited electron-hole pair) will decay to its ground state while transforming its energy in the form of an emitting photon. The cavity introduces more decay channels to the emitting materials, so a majority of the photons are coupled into the cavity and form the standing mode of the cavity. Finally, the researchers are able to detect the photons leaking away from the cavity, which is the emission signal. Difficult metThe problem that previous attempts have encountered in working with nanocrystal perovskites has been the material quality. “We need emitters with good photostability, so it can hold the performance when coupling to the cavities, said Yang. “Our collaborators from ETH provided perovskites that make this coupling possible.” In addition to nanolasers and faster optoelectronics, Yang believes the device they have made could increase the efficiency of existing perovskite emitting devices, such as LEDs, which could open up real-world applications in efficient illumination and displays. Before these aspirations can be realized, Yang concedes that they will need to further improve the performance and stability of the material itself. Second, it would be better to excite the material electrically rather than optically for practical use.Yang will try to realize similar devices spanning the whole visible range and the next step it to find ways to further improve and stabilize the performance and also utilizing electrical gates to excite the material in devices. Article source: Applied Physics LettersArticle edited by kynix 

SummaryPublished in the Joural Nature Materials in Nov.13,2017,reaearchers from Princeton University,the Georgia Institute of Technology and Humboldt Uniersity in Berlin is pointing the way to possibly more widespread use of organic electronics. Their research focuses on organic semiconductors,a class of materials prized for their applications in emerging technologies such as flexible electronics, solar energy conversion, and high-quality color displays for smartphones and televisions. In the short term, the advance should particularly help with organic light-emitting diodes that operate at high energy to emit colors such as green and blue.  Body“Organic semiconductors are ideal materials for the fabrication of mechanically flexible devices with energy-saving low-temperature processes,” said Xin Lin, a doctoral student in electrical engineering at Princeton and the lead author. “One of their major disadvantages has been their relatively poor electrical conductivity. In some applications, this can lead to difficulties and inefficient devices. We are working on new ways to improve the electrical properties of these organic semiconductors.” Semiconductors, typically made of silicon, are the foundation of modern electronics because engineers can take advantage of their unique properties to control electrical currents. Among many applications, semiconductor devices are used for computing, signal amplification and switching( signal switches ). They are used in energy-saving devices such as light-emitting diodes and devices that convert energy such as solar cells. In the doping process used to make semiconductors their chemical makeup is modified by adding a small amount of chemicals or impurities. By carefully choosing the type and amount of dopant, researchers are able to alter the electronic structure and electrical behaviour of the semiconductor in a number of ways. As the article shows,researchers have developed an approach for greatly increasing the conductivity of organic semiconductors,which are formed of carbon-based molecules rather than silicon atoms. The dopant, a ruthenium-containing compound, is a reducing agent, which means it adds electrons to the organic semiconductor as part of the doping process. The addition of the electrons is the key to increasing the semiconductor’s conductivity. The compound belongs to a newly introduced class of dopants called dimeric organometallic dopants. Unlike many other powerful reducing agents, these dopants are stable when exposed to air but still work as strong electron donors both in solution and solid state. Seth Marder and Stephen Barlow from the Georgia Institute of Technology, who led the development of the new dopant, called the ruthenium compound a “hyper-reducing dopant.” They said it is unusual, not only in its combination of electron donation strength and air stability, but in its ability to work with a class of organic semiconductors that have previously been very difficult to dope. In studies conducted at Princeton, the researchers found that the new dopant increased the conductivity of these semiconductors about a million times. The ruthenium compound is a dimer, which means it consists of two identical molecules, or monomers, connected by a chemical bond. As is, the compound is relatively stable and, when added to these difficult-to-dope semiconductors, it does not react and remains in its equilibrium state. That posed a problem because to increase the conductivity of the organic semiconductor, the ruthenium dimer needs to react with the semiconductor it and then split apart. The researchers looked for different ways to break up the ruthenium dimer and activate the doping, eventually they added energy by irradiating with ultraviolet light, which effectively excited the molecules in the semiconductor and initiated the reaction. Under exposure to the light, the dimers split into monomers, and the conductivity rose. "Once the light is turned off, one might expect the reverse reaction to occur" and the increased conductivity to disappear, Marder said. "However, this is not the case." The researchers found that the ruthenium monomers remained isolated in the semiconductor even though thermodynamics should return the molecules to their original configuration as dimers. The team's hypothesis is that the monomers are scattered in the semiconductor in such a way that it is very difficult for them to return to their original configuration and re-form the ruthenium dimer. They are, according to the team “kinetically trapped." The researchers also discovered that doping was continuously re-activated by the light produced by the device. The light activates the system more, which leads to more light production and more activation until the system is fully activated, Marder said. "This alone is a novel and surprising observation." The work was supported in part by the National Science Foundation and the U.S. Department of Energy. Article edited by kynix   

Summary As we all know,originally developed to support analogue computers,the op amp has an elegantly simple core design. The industries are contining to spare no effect in creating‘ideal op-amp'.     Simply by wiring in different feedback configurations using passives,op amp can be massaged into roles that include buffers and integrators as well has high-gain amplifiers. It is little wonder the op amp has been as successful as it has been. What's more, people in the industry expect a few core parts to do almost any job and for the circuit to be ripe for integration cause the op amp is so readily tunerable.In practice,the choice of discrete op amps has never been wider. Steve Logan, executive business manager for Maxim Integrated’s core products groups, says: “If you don’t need terribly high bandwidth, high voltage for industrial systems or very low voltage for portable designs, those are times when op amps can be integrated.”   Subtly different edge cases push designer to discrete options Op amps often interface electronics to the outside world, so they need to take account of numerous subtly different edge cases, which pushes designers to discrete options. Each variant uses a specific choice of process and circuit topology to take on a job. Logan cites the wrist-worn heart rate monitor, which measures the light reflected back from a green LED. In these systems, input current noise has a large effect on signal quality, calling for op amps that can deliver much lower levels than generic options.   Signal-Conditioning of Systems Signal-conditioning of systems can turn out to be more complex than first appears. Logan says "“One application that’s not immediately obvious is driving a high-speed, high-resolution SAR A/D converter; it can be pretty demanding circuitry. The difference between a SAR and sigma-delta is in how it takes a big gulp of current. The op amp has to settle quickly, so you are talking settling time, slew rate and total harmonic distortion. You may need multiple stages to get the settling time, along with an input buffer, plus a gain stage and filter stage in front of that. You might think at first: how tough can it be? Then it turns into a two- or three-stage op-amp circuit.”   Dwight Byrd, marketing manager at Texas Instruments, says: “As demand for further sensors and signals increases, better conditioning and amplification of the sensor becomes paramount, thus making the proliferation of op amps possible.”     Art Eck, senior product marketing manager at Microchip Technology, adds: “We see a trend toward more designer op amps: op amps that are built for a particular application or set of applications.” At the same time,Kevin Tretter,the product marketing manager of Microchip notes that changes in application needs are creating new problems for op-amp components to address. “With the rapid expansion of wireless capabilities the industry has seen over the years, the presence of electromagnetic interference is becoming a larger issue. Sensitive analogue sensor circuits commonly sit next to wireless communication modules. More and more amplifier manufacturers are trying to combat the adverse effects by implementing on-chip filtering.”   Demand for Futher Sensors A lot of designs call for sensors to be added but for boards to be shrunk cause increasing noise is partly a by-product of the shrinking size of many designs as well ass the recent focus on making systems more aware of their surrounding environment.   Byrd notes: “Where the biggest driver in further technology trends comes in is package size. Previously, an SC-70 package was considered one of the smallest one-channel op amps available. Now, SOT553 is becoming commonplace.”   Logan says the trend continues all the way to wafer-level packages, measuring just more than 1mm on the longer side. Such tiny packages support the idea of an ‘analogue insurance policy’, where op amps and similar parts provide additional conditioning and protection such as buffering to integrated mixed-signal SoCs. “For a little extra size and cost, you can add these functions and make them more robust. The wafer-level package lets you do that.”   Renesas subsidiary Intersil Engineer Tom Kugelstadt said there is otential for circuit-level advances that could reduce the need for op-amp proliferation and so aid integration. “The biggest inevitable tradeoff is between low-power and high-bandwidth, or high-speed. In general, high-speed amplifiers require the fast charging and discharging of the gate capacitances of the internal transistors. This requires increases in bias and supply currents, which often leads to increased offset current and voltages. While high-speed op amps have improved significantly in these parameters, they still tower a magnitude above their low-speed, precision counterparts.“However, there are circuit topologies that aim for increased precision while trading only a minute portion of their high-speed performance. These designs, known as composite amplifiers, consist of a precision amp in open-loop and a high-speed amp in a closed-loop differentiator configuration.”   Complesity of Picking Right Op-amp The multiple novel circuit topologies that have appeared over the past few decades to deal with problems such as temperature drift and power consumption can have unexpected side effects that designers need to take into account. That adds to the complexity of picking the right op amp.   Logan points to the use of chopper-stabilised amplifiers. “These are great for low offsets, but push the noise out to a single frequency. One that pushes it out to 60kHz is great for DC, but if you have signals that reach 50kHz, you start to get into the noise skirt. These are nuanced things you might not see immediately from the datasheet.”   Frequency-related interactions often need careful examination, says Byrd, and datasheets should show them. “If the output impedance is relatively low and unchanging over a frequency range, it is normally indicative that the op amp will be more stable than one that does have a wide varying output impedance. The output impedance will be interacting directly with the op amp load, and normally a capacitor, it would create various filters as the frequency and therefore the output impedance changes.”   Kugelstadt says interactions with manufacturing choices at the PCB level can introduce unforeseen issues. “High-precision designs using auto-zeroing amplifiers can suffer in precision from asymmetric circuit design. Here, the solder joints around the amplifier form thermocouples that contribute more differential input voltage than the specified offset in the data sheet. Customers unfamiliar with this pitfall blame the device manufacturer for overstating its device performance. The remedy is good application support, such as including layout guidelines in the application section of the data sheet.”   Design Issues TI marketing manager Ying Zhou points out that the need to consider how the op amp is designed, particularly if the op amp is being co-opted for a secondary purpose. “If a dual- or quad-channel op amp is already used elsewhere on the board, sometimes the engineers would assign the left channels for comparator functions,” she says.Although many op amps have input clamping diodes to protect the input transistors but these can affect their behaviour as comparators. Zhou says ‘mux friendly’ versions of op amps that remove the clamps make them more suitable for use as comparators.   Logan notes: “Getting an evaluation kit and putting it on the board is a great thing to do. There is a lot of pin compatibility out there, so you can easily drop another one in to check its performance. But, you do have the issue of having a lot to choose from.”   The industry continues to strive to create the ‘ideal op amp’ and, although we continually get closer to that ideal, there will always be design trade-offs among speed, noise, power usage, size, et cetera. These trade-offs, coupled with continually growing application specific needs, will continue to drive a variety of amplifier types.”  

Article provided by University of Illinois at Urbana-ChampaignArticle edit by kynix A new methord to make Green LEDs more brighter and more efficient have been developed by researchers who at the University of lllinois at Urbana Champaign.  Researchers have created gallium nitride(GaN) cubic crystals grown on a silicon substrate that are capable of producing powerful green light for advanced solid-state lighting. "This work is very revolutionary as it paves the way for novel green wavelength emitters that can target advanced solid-state lighting on a scalable CMOS-silicon platform by exploiting the new material, cubic gallium nitride," said Can Bayram, an assistant professor of electrical and computer engineering at Illinois who first began investigating this material while at IBM T.J. Watson Research Center several years ago. "The union of solid-state lighting with sensing (e.g. detection) and networking (e.g. communication) to enable smart (i.e. responsive and adaptive) visible lighting, is further poised to revolutionize how we utilize light. And CMOS-compatible LEDs can facilitate fast, efficient, low-power, and multi-functional technology solutions with less of a footprint and at an ever more affordable device price point for these applications."  GaN was formed ethier hexagonal or cubic typically. HExagonal GaN is thermodynamically stable and is by far the more conventional form of the semiconductor. However, hexagonal GaN is prone to a phenomenon known as polarization, where an internal electric field separates the negatively charged electrons and positively charged holes, preventing them from combining, which, in turn, diminishes the light output efficiency. Until now, the only way researchers were able to make cubic GaN was to use molecular beam epitaxy, a very expensive and slow crystal growth method when compared to the widely used metal-organic chemical vapor deposition (MOCVD) method that Bayram used. Bayram and his graduate student Richard Liu made the cubic GaN by using lithography and isotropic etching to create a U-shaped groove on Si (100). This non-conducting layer essentially served as a boundary that shapes the hexagonal material into cubic form. "Our cubic GaN does not have an internal electric field that separates the charge carriers—the holes and electrons," explained Liu. "So, they can overlap and when that happens, the electrons and holes combine faster to produce light."  At the end, Bayram and Liu still believe their cubic GaN method may lead to LEDs free from the "droop" phenomenon that has plagued the LED industry for years. For LED lighting color like green, blue, or ultra-violet LEDs , their light-emission efficiency declines as more current is injected, which is characterized as "droop." "Our work suggests polarization plays an important role in the droop, pushing the electrons and holes away from each other, particularly under low-injection current densities," said Liu, who was the first author of the paper, ""Maximizing Cubic Phase Gallium Nitride Surface Coverage on Nano-patterned Silicon (100)", appearing Applied Physics Letters. Having better performing green LEDs will open up new avenues for LEDs in general solid-state lighting. For example, these LEDs will provide energy savings by generating white light through a color mixing approach. Other advanced applications include ultra-parallel LED connectivity through phosphor-free green LEDs, underwater communications, and biotechnology such as optogenetics and migraine treatment. Having better performing green LEDs will open up new avenues for LEDs in general solid-state lighting. For example, these LEDs will provide energy savings by generating white light through a color mixing approach. Other advanced applications include ultra-parallel LED connectivity through phosphor-free green LEDs, underwater communications, and biotechnology such as optogenetics and migraine treatment. 

There are a good news that ERP Power LLC,one of the leading provider of small,smart and connected LED drivers for the lighting industry,lanched the world's smallest programmable output drivers with wireless communication for indoor lighting applications on 25.Oct.,2017 and demonstrated it on 27-30th,Oct.,2017 at Hongkong.  According to Michael Archer,the CEO of ERP,"ERP is accelerating the Internet of Lights by embedding intelligence, connectivity and dimming into a very small footprint,every LED luminaire design engineer who has held our driver in their hand simply says ‘Wow!' and comments on the industry-leading combination of compact size, extensive dimmer compatibility, and high efficiency at competitive cost. There is no longer a need to compromise the creative style or capabilities of new lighting fixture designs." The UL Class P next generation ERP driver design is one-fifth smaller than similar capacity drivers in the industry; programmable for flexible deployment in a broad range of constant current applications; connected with wired and wireless controls; and high efficiency to reduce electricity consumption. The new ERP drivers are designed in California and built to last with a 5-year limited warranty. Now The patent-pending power electronics design includes 30W/40W/50W models which help LED lighting fixture manufacturers meet the technical requirements of ENERGY STAR®, California Title 24 and the DesignLights Consortium (DLC) specifications.  Programmable OutputCustomers can deploy a single driver across multiple lighting fixtures if the power output is programmable. This lowers inventory costs in the customer's supply chain. The ERP next generation driver output is high efficiency and fully programmable in a wide range of output currents while maintaining efficiency of 90% from 50-100% of load with power factor greater than 0.9 and THD less than 20%. ERP’s programmable LED drivers with integrated Bluetooth® mesh communications make dimming, scheduling, and ambient scene control as simple as a swipe of your finger or the sound of your voice. The secure, plug-and-play, Bluetooth® mesh wireless controls architecture leverages a turnkey solution of app, cloud, and firmware pre-integrated with proven LED drivers designed to last for the lifetime of the installation.  Tri-Mode DimmingExtensive dimmer compatibility is provided through ERP Power's unique Tri-Mode Dimming™ feature which provides TRIAC, ELV & 0-10 V support and dim-to-off along with options for alternative linear and logarithmic dimming profiles from 1-100%.  Wireless ConnectivityOther wireless controls based on Wi-Fi, ZigBee, or IEEE 802.15.4 are available in addition to wired controls protocol support for DALI, DMX, Lutron and others.