Tag Archives: letter-mems-tech

Rudolph Technologies has introduced its new SONUS Technology for measuring thick films and film stacks used in copper pillar bumps and for detecting defects, such as voids, in through silicon vias (TSVs). Copper pillar bumps are a critical component of many advanced packaging technologies and TSVs provide a means for signals to pass through multiple vertically stacked chips in three dimensional integrated circuits (3DIC). The new SONUS Technology is non-contact and non-destructive, and is designed to provide faster, less costly measurements and greater sensitivity to smaller defects than existing alternatives such as X-ray tomography and acoustic microscopy.

“SONUS Technology meets a critical need for measuring and inspecting the structures used to connect chips to each other and to the outside world,” said Tim Kryman, Rudolph’s director of metrology product management. “Copper pillar bumps and TSVs are critical interconnect technologies enabling 2.5D and 3D packaging. The mechanical integrity of the interconnect and final device performance are directly dependent on tight control of the plating processes used to create copper pillar bumps. Likewise, the quality of the TSV fill is critical to the electrical performance of stacked devices. This new technology allows us to measure individual films and film stacks with thicknesses up to 100µm, and detect voids as small as 0.5µm in TSVs with aspect ratios of 10:1 or greater.”

Kryman added, “SONUS Technology builds on the expertise we developed in acoustic metrology for our industry-standard MetaPULSE systems, which are widely used for front-end metal film metrology. By offering similar improvements in yield and time-to-profitability in high volume manufacturing (HVM), SONUS offers a compelling value proposition to advanced packaging customers.”

Both MetaPULSE and SONUS systems use a laser to initiate an acoustic disturbance at the surface of the sample. As the acoustic wave travels down through the film stack, it is partially reflected at interfaces between different materials. Although the detection schemes are different, the reflected waves are detected when they return to the surface and the elapsed time is used to calculate the thickness of each layer. In the case of SONUS Technology, two lasers are used. The first laser excites the sample and the second probes for the returning acoustics. This decouples excitation and detection allowing SONUS to continuously probe the sample resulting in a much larger film thickness range. So, where MetaPULSE can measure metal films and stacks to ~10 microns, SONUS can measure films in excess of 100 microns. In addition, SONUS Technology’s use of interferometry to characterize the surface displacement provides a rich data set that can be analyzed to not only characterize film thickness, but perform defect detection.

The primary alternatives for such measurements are X-ray based tomographic analysis and acoustic microscopy. SONUS Technology’s ability to detect voids as small as half a micrometer is approximately twice as good as current X-ray techniques, which have a spatial resolution of about 1 micrometer. Acoustic microscopy can make similar measurements, but the sample must be immersed in water, which, though not strictly destructive, does effectively preclude the return of the sample to production. SONUS is both non-contact and non-destructive and is designed for R&D and high-volume manufacturing.

In the run up to the product introduction, Rudolph worked closely with TEL NEXX to develop SONUS-based process control for pillar bump and TSV plating processes. Arthur Keigler, chief technology officer of TEL NEXX, said, “We are attracted by the opportunity SONUS Technology offers our mutual customers in the advanced packaging market. The ability to measure multi-metal film stacks for Cu pillar, and then continue to use the same tool for TSV void detection offers immediate productivity and cost benefits to manufacturing and development groups alike.”

While Rudolph is initially focused on using the technology for copper pillar bump process metrology and TSV inspection, they are also investigating other applications, ranging from detecting film delamination to metrology and process control for MEMS fabrication processes.

Oxford Instruments is hosting its third series of annual seminars for the nanotechnology industry in India in November.  “Bringing the Nanoworld Together 2014” seminars are being held in Kolkata (November 24-25th) and Delhi (November 27-28th) and will showcase cutting edge nanotechnology tools and their use in multiple fields.

image004

The first day at each venue will comprise Plenary Sessions focusing on “Emerging Materials for Nanoscale Devices – Fabrication & Characterization.” Day 2 will focus on thin film processing, materials characterisation, surface science and cryogenic environments.  A wide range of topics will be covered within each technical area. This will also present an excellent opportunity for networking between all participants, including guest speakers from prestigious Indian and international institutes, speakers from the host institutes, and technical experts from Oxford Instruments.

The thin film processing sessions will review the latest etch and deposition technological advances, including: ALD, Magnetron Sputtering, ICP PECVD, Nanoscale Etch, MEMS, MBE and more.

The materials characterisation, surface science and cryogenic environment sessions will cover multiple topics and technologies including: ultra high vacuum SPM, Cryofree low temperature solutions, XPS/ESCA, an introduction to atomic force microscopy (AFM), and applications such as nanomechanics, in-situ heating and tensile characterisation using EBSD, measuring layer thicknesses and compositions using EDS, and nanomanipulation and fabrication within the SEM/ FIB.  Andor Technology, a recently acquired business, will also be showcasing its high performance optical cameras and software which are used in both the physical and bio sciences.

Previous host Prof. Rudra Pratap, Chairperson at the Centre for Nano Science and Engineering, Indian Institute of Science, IISC Bangalore commented, “This seminar has been extremely well organized with competent speakers covering a variety of processes and tools for nanofabrication. It is great to have practitioners in these areas give talks and provide tips and solutions based on their experience – something that cannot be found in text books.”

Mark Sefton of Oxford Instruments Nanotechnology Tools commented, “We are demonstrating our commitment to our customers through providing these learning events, encouraging discussion and cross dissemination of ideas that is of benefit to all those attending. Not only do we provide high technology tools and excellent global service, but we want our customers to be empowered to use these systems to the best of their abilities, with the maximum information possible behind them.”

CEA-Leti and LUCIOM, which develops visible-light communication using light-emitting diodes (LEDs), have launched a project to develop high-data-rate LiFi transceivers. With this technology, LUCIOM expects to offer in mid-2015 one of the first high-data-rate bidirectional light-fidelity, or LiFi, products that can work with different LED lighting sources, and on mobile devices.

Visible light communications (VLC) has gained significant momentum in recent years, primarily because of expectations that LEDs will become predominant in the lighting market. As LiFi benefits from this rapid market penetration of LED lighting sources and their reduced cost, it will become more efficient and economical compared to wireless RF communications.

Moreover, because LEDs can be modulated at very high frequencies and their oscillations are invisible to humans, they permit information transmission at very high data rates.

Earlier this year, Leti demonstrated a new prototype for wireless high-data-rate Li-Fi transmission. The technology employs the high-frequency modulation capabilities of LED engines used in commercial lighting. It achieves throughputs of up to 10Mb/s at a range of three meters, suitable for HD video streaming or Internet browsing, using light power of less than 1,000 lumens and with direct or even indirect lighting. This technology will be adapted to meet the needs of LUCIOM’s transceivers.

LUCIOM’s technology allows the convergence of light-emitting diodes with the worldwide proliferation of mobile devices to make any LED lighting source a high-speed data transmitter that is both secure and environmentally friendly.

Based on integrated circuits and transceivers, the technology turns LED light sources into positioning beacons, which transmit signals. This allows smartphones and tablets to become LiFi enabled, thanks to a receiver that is implemented in a 3.5mm audio jack dongle. The compact size of the receiver eases the integration in the device. In addition, the audio remains accessible from the audio interface, even when the LiFi application is launched from a smartphone.

LUCIOM’s technology can be combined with the use of gyro-sensors present in smartphones and tablets to predict movement between two beacons and provide a very accurate position to the user. This way, communication between phones and smart indoor LED lighting can be used inside buildings when GPS technology is no longer effective. The localization application can also be used to provide additional personalized services or information to customers as well as information to the infrastructure manager.

In addition to these indoor-positioning applications, the company is targeting high-data-rate video transfer.The project between Leti and LUCIOM builds on their previous collaboration in which Leti developed an optical over-the-air data link for the company that allows the transmission of true HD video from a lamp to a handheld receiver.

“Our indoor geo-localization could guide shoppers through the maze of large shopping malls to the stores they are seeking, and LED lighting in museums could be used to guide visitors through an enriched tour of the displays and exhibits,” said Michel Germe, CEO of LUCIOM. “Working again with Leti, we will be able to bring new, bidirectional transceivers that enable these applications to market in 2015.”

“LUCIOM was one of the first companies to see that LEDs and LiFi can offer a powerful, secure and highly energy-efficient communications alternative to WiFi,” said Leti CEO Laurent Malier. “With Leti’s first proof of concept developed earlier this year and its expertise in RF communications, we expect data-transmission rates in excess of 100Mb/s with traditional lighting based on LED lamps.”

Graphene is a semiconductor when prepared as an ultra-narrow ribbon – although the material is actually a conductive material. Researchers from Empa and the Max Planck Institute for Polymer Research have now developed a new method to selectively dope graphene molecules with nitrogen atoms. By seamlessly stringing together doped and undoped graphene pieces, they were able to form ”heterojunctions” in the nanoribbons, thereby fulfilling a basic requirement for electronic current to flow in only one direction when voltage is applied – the first step towards a graphene transistor. Furthermore, the team has successfully managed to remove graphene nanoribbons from the gold substrate on which they were grown and to transfer them onto a non-conductive material.

Graphene possesses many outstanding properties: it conducts heat and electricity, it is transparent, harder than diamond and extremely strong. But in order to use it to construct electronic switches, a material must not only be an outstanding conductor, it should also be switchable between ”on” and ”off” states. This requires the presence of a so-called bandgap, which enables semiconductors to be in an insulating state. The problem, however, is that the bandgap in graphene is extremely small. Empa researchers from the ”nanotech@surfaces” laboratory thus developed a method some time ago to synthesise a form of graphene with larger bandgaps by allowing ultra-narrow graphene nanoribbons to ”grow” via molecular self-assembly.

Graphene nanoribbons made of differently doped segments

The researchers, led by Roman Fasel, have now achieved a new milestone by allowing graphene nanoribbons consisting of differently doped subsegments to grow. Instead of always using the same ”pure” carbon molecules, they used additionally doped molecules – molecules provided with ”foreign atoms” in precisely defined positions, in this case nitrogen. By stringing together ”normal” segments with nitrogen-doped segments on a gold (Au (111)) surface, so-called heterojunctions are created between the individual segments. The researchers have shown that these display similar properties to those of a classic p-n-junction, i.e. a junction featuring both positive and negative charges across different regions of the semiconductor crystal, thereby creating the basic structure allowing the development of many components used in the semiconductor industry. A p-n junction causes current to flow in only one direction. Because of the sharp transition at the heterojunction interface, the new structure also allows electron/hole pairs to be efficiently separated when an external voltage is applied, as demonstrated theoretically by theorists at Empa and collaborators at Rensselaer Polytechnic Institute The latter has a direct impact on the power yield of solar cells. The researchers describe the corresponding heterojunctions in segmented graphene nanoribbons in the recently published issue of “Nature Nanotechnology.”

Transferring graphene nanoribbons onto other substrates

In addition, the scientists have solved another key issue for the integration of graphene nanotechnology into conventional semiconductor industry: how to transfer the ultra-narrow graphene ribbons onto another surface? As long as the graphene nanoribbons remain on a metal substrate (such as gold used here) they cannot be used as electronic switches. Gold conducts and thus creates a short-circuit that “sabotages” the appealing semiconducting properties of the graphene ribbon. Fasel’s team and colleagues at the Max-Planck-Institute for Polymer Research in Mainz have succeeded in showing that graphene nanoribbons can be transferred efficiently and intact using a relatively simple etching and cleaning process onto (virtually) any substrate, for example onto sapphire, calcium fluoride or silicon oxide.

Graphene is thus increasingly emerging as an interesting semiconductor material and a welcome addition to the omnipresent silicon. The semiconducting graphene nanoribbons are particularly attractive as they allow smaller and thus more energy efficient and faster electronic components than silicon. However, the generalized use of graphene nanoribbons in the electronics sector is not anticipated in the near future, due in part to scaling issues and in part to the difficulty of replacing well-established conventional silicon-based electronics. Fasel estimates that it may still take about 10 to 15 years before the first electronic switch made of graphene nanoribbons can be used in a product.

Graphene nanoribbons for photovoltaic components

Photovoltaic components could also one day be based on graphene. In a second paper published in Nature Communications, Pascal Ruffieux – also from the Empa “nanotech@surfaces” laboratory – and his colleagues describe a possible use of graphene strips, for instance in solar cells. Ruffieux and his team have noticed that particularly narrow graphene nanoribbons absorb visible light exceptionally well and are therefore highly suitable for use as the absorber layer in organic solar cells. Compared to “normal” graphene, which absorbs light equally at all wavelengths, the light absorption in graphene nanoribbons can be increased enormously in a controlled way, whereby researchers “set” the width of the graphene nanoribbons with atomic precision.

Sandwiching layers of graphene with white graphene could produce designer materials capable of creating high-frequency electronic devices, University of Manchester scientists have found. The researchers have demonstrated how combining the two-dimensional materials in a stack could create perfect crystals capable of being used in next generation transistors.

Hexagonal boron nitride (hBN), otherwise known as white graphene, is one of a family of two-dimension materials discovered in the wake of the isolation of graphene at the University in 2004. Manchester researchers have previously demonstrated how combining 2D materials, in stacks called heterostructures, could lead to materials capable of being designed to meet industrial demands.

Now, for the first time, the team has demonstrated that the electronic behaviour of the heterostructures can be changed enormously by precisely controlling the orientation of the crystalline layers within the stacks.

The researchers, led by University of Manchester Nobel laureate Sir Kostya Novoselov, carefully aligned two graphene electrodes separated by hBN and discovered there was a conservation of electron energy and momentum.

The findings could pave the way for devices with ultra-high frequencies, such as electronic or photovoltaic sensors.

The research was carried out with scientists from Lancaster and Nottingham Universities in the UK, and colleagues in Russia, Seoul and Japan.

Professor Laurence Eaves, a joint academic from the Universities of Manchester and Nottingham, said: “”This research arises from a beautiful combination of classical laws of motion and the quantum wave nature of electrons, which enables them to flow through barriers

“We are optimistic that further improvements to the device design will lead to applications in high-frequency electronics.”

Professor Vladimir Falko, from Lancaster University, added: “Our observation of tunnelling and negative differential conductance in devices made of multilayers of graphene and hexagonal boron nitride demonstrates potential that this system has for electronics applications.

“It is now up to material growers to find ways to produce such multilayer systems using growth techniques rather than mechanical transfer method used in this work.”

Move over, graphene. An atomically thin, two-dimensional, ultrasensitive semiconductor material for biosensing developed by researchers at UC Santa Barbara promises to push the boundaries of biosensing technology in many fields, from health care to environmental protection to forensic industries.

Based on molybdenum disulfide or molybdenite (MoS2), the biosensor material — used commonly as a dry lubricant — surpasses graphene’s already high sensitivity, offers better scalability and lends itself to high-volume manufacturing. Results of the researchers’ study have been published in ACS Nano.

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. - Photo Credit: Peter Allen

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. – Photo Credit: Peter Allen

“This invention has established the foundation for a new generation of ultrasensitive and low-cost biosensors that can eventually allow single-molecule detection — the holy grail of diagnostics and bioengineering research,” said Samir Mitragotri, co-author and professor of chemical engineering and director of the Center for Bioengineering at UCSB. “Detection and diagnostics are a key area of bioengineering research at UCSB and this study represents an excellent example of UCSB’s multifaceted competencies in this exciting field.”

The key, according to UCSB professor of electrical and computer engineering Kaustav Banerjee, who led this research, is MoS2’s band gap, the characteristic of a material that determines its electrical conductivity.

Semiconductor materials have a small but nonzero band gap and can be switched between conductive and insulated states controllably. The larger the band gap, the better its ability to switch states and to insulate leakage current in an insulated state. MoS2’s wide band gap allows current to travel but also prevents leakage and results in more sensitive and accurate readings.

The limitations of graphene

While graphene has attracted wide interest as a biosensor due to its two-dimensional nature that allows excellent electrostatic control of the transistor channel by the gate, and high surface-to-volume ratio, the sensitivity of a graphene field-effect transistor (FET) biosensor is fundamentally restricted by the zero band gap of graphene that results in increased leakage current, leading to reduced sensitivity, explained Banerjee, who is also the director of the Nanoelectronics Research Lab at UCSB.

Graphene has been used, among other things, to design FETs — devices that regulate the flow of electrons through a channel via a vertical electric field directed into the channel by a terminal called a “gate.” In digital electronics, these transistors control the flow of electricity throughout an integrated circuit and allow for amplification and switching.

In the realm of biosensing, the physical gate is removed, and the current in the channel is modulated by the binding between embedded receptor molecules and the charged target biomolecules to which they are exposed. Graphene has received wide interest in the biosensing field and has been used to line the channel and act as a sensing element whose surface potential (or conductivity) can be modulated by the interaction (known as conjugation) between the receptor and target molecules that results in net accumulation of charges over the gate region.

However, said the research team, despite graphene’s excellent characteristics, its performance is limited by its zero band gap. Electrons travel freely across a graphene FET — hence, it cannot be “switched off” — which in this case results in current leakages and higher potential for inaccuracies.

Much research in the graphene community has been devoted to compensating for this deficiency, either by patterning graphene to make nanoribbons or by introducing defects in the graphene layer — or using bilayer graphene stacked in a certain pattern that allows band gap opening upon application of a vertical electric field — for better control and detection of current.

Enter MoS2, a material already making waves in the semiconductor world for the similarities it shares with graphene, including its atomically thin hexagonal structure, and planar nature, as well as what it can do that graphene can’t: act like a semiconductor.

“Monolayer or few-layer MoS2 have a key advantage over graphene for designing an FET biosensor: They have a relatively large and uniform band gap (1.2-1.8 eV, depending on the number of layers) that significantly reduces the leakage current and increases the abruptness of the turn-on behavior of the FETs, thereby increasing the sensitivity of the biosensor,” said Banerjee.

‘The best of everything’

Additionally, according to Deblina Sarkar, a PhD student in Banerjee’s lab and the lead author of the article, two-dimensional MoS2 is relatively simple to manufacture.

“While one-dimensional materials such as carbon nanotubes and nanowires also allow excellent electrostatics and at the same time possess band gap, they are not suitable for low-cost mass production due to their process complexities,” she said. “Moreover, the channel length of MoS2 FET biosensor can be scaled down to the dimensions similar to those of small biomolecules such as DNA or small proteins, still maintaining good electrostatics, which can lead to high sensitivity even for detection of single quanta of these biomolecular species,” she added.

“In fact, atomically thin MoS2 provides the best of everything: great electrostatics due to their ultra-thin body, scalability (due to large band gap), as well as patternability due to their planar nature that is essential for high-volume manufacturing,” said Banerjee.

The MoS2 biosensors demonstrated by the UCSB team have already provided ultrasensitive and specific protein sensing with a sensitivity of 196 even at 100 femtomolar (a billionth of a millionth of a mole) concentrations. This protein concentration is similar to one drop of milk dissolved in a hundred tons of water. An MoS2-based pH sensor achieving sensitivity as high as 713 for a pH change by one unit along with efficient operation over a wide pH range (3-9) is also demonstrated in the same work.

“This transformative technology enables highly specific, low-power, high-throughput physiological sensing that can be multiplexed to detect a number of significant, disease-specific factors in real time,” commented Scott Hammond, executive director of UCSB’s Translational Medicine Research Laboratories.

Biosensors based on conventional FETs have been gaining momentum as a viable technology for the medical, forensic and security industries since they are cost-effective compared to optical detection procedures. Such biosensors allow for scalability and label-free detection of biomolecules — removing the step and expense of labeling target molecules with florescent dye. “In essence,” continued Hammond, “the promise of true evidence-based, personalized medicine is finally becoming reality.”

“This demonstration is quite remarkable,” said Andras Kis, professor at École Polytechnique Fédérale de Lausanne in Switzerland and a leading scientist in the field of 2D materials and devices.

“At present, the scientific community worldwide is actively seeking practical applications of 2D semiconductor materials such as MoS2 nanosheets. Professor Banerjee and his team have identified a breakthrough application of these nanomaterials and provided new impetus for the development of low-power and low-cost ultrasensitive biosensors,” continued Kis, who is not connected to the project.

Wei Liu and Xuejun Xie from UCSB’s Department of Electrical and Computer Engineering and Aaron Anselmo from the Department of Chemical Engineering also conducted research for this study. Research on this project was supported by the National Science Foundation, the California NanoSystems Institute at UCSB and the Materials Research Laboratory at UCSB, a National Science Foundation MRSEC.

Analog Devices, Inc. today introduced the first and only MEMS gyroscope specified to withstand temperatures of up to 175 degrees Celsius commonly encountered by oil and gas drilling equipment.

The ADXRS645 MEMS (micro-electromechanical) gyroscope provides vibration immunity and a minimum rotational measurement range of ±2,000°/sec, which are critical performance criteria for drilling tools operating in harsh, high-temperature environments. The ability to accurately sense angular rotation prevents drill string damage by detecting the difference between drill head rotation and the motor turning the drill. The ADXRS645 allows rig operators in the oil and gas industries to extend the life of their equipment and reduce costly downtime by ensuring that the drill string is operating properly.

The ADXRS645 joins ADI’s portfolio of precision high-temperature components designed for drilling applications, including the ADXL206 ±5g precision MEMS accelerometer, the AD8229 ultra-low-noise instrumentation amplifier, the ADR225 2.5-V band gap voltage reference and the AD8634 dual amplifier with rail-to-rail outputs, all of which are specified to operate at 175 degrees Celsius and higher.

The down-hole drilling industry is adopting a multitude of sensors to better understand the motion of the drill string below the surface to better optimize operations, prevent drill damage, and increase productivity. Other approaches to rotational measurement, such as the use of magnetometers, are susceptible to drill vibration, are unable to precisely capture fast-changing rotational speeds and their readings can be impacted by ferrous material or metal casings used in the well.

Nanoparticles, engineered materials about a billionth of a meter in size, are around us every day. Although they are tiny, they can benefit human health, as in some innovative early cancer treatments, but they can also interfere with it through viruses, air pollution, traffic emissions, cosmetics, sunscreen and electronics.

A team of researchers at Washington University in St. Louis, led by Lan Yang, PhD, the Das Family Career Development Associate Professor in Electrical & Systems Engineering, and their collaborators at Tsinghua University in China have developed a new sensor that can detect and count nanoparticles, at sizes as small as 10 nanometers, one at a time. The researchers say the sensor could potentially detect much smaller particles, viruses and small molecules.

The research appears in the Proceedings of the National Academy of Sciences online Early Edition Sept. 1, 2014.

Yang and her colleagues have created the Raman microlaser sensor in a silicon dioxide chip to find individual nanoparticles without the need to “dope” the chip with chemicals called rare-earth ions to provide optical gain for the microlaser. Incorporating additions to the microresonator creates the need for more processing steps and increased costs and invites biocompatibility risks. In addition, the use of rare-earth ions requires specific “pump” lasers matching the energy transitions of the ions to generate optical gain, so for different rare-earth ions, different pump lasers must be used. Using the Raman process loosens the requirement of specific wavelength bands for pump lasers because Raman gain can be obtained using pump at any wavelength band, Yang says.

“This gives us the advantage of using the same dopant-free sensor at different sensing environments by tailoring the lasing frequency for the specific environment, for example, at the band where the environment has minimum absorption, and for the properties of the targeted nanoparticles by just changing the wavelength of the pump laser,” says Sahin Kaya Ozdemir, PhD, a research scientist in Yang’s group and the first author of the paper.

Yang’s team integrated Raman lasing in a silica microcavity with the mode splitting technique pioneered by her group to develop a new, powerful sensor that more readily detects nanoparticles. The technology will benefit the electronics, acoustics, biomedical, plasmonics, security and metamaterials fields.

Yang’s microsensor is in a class called whispering gallery mode resonators (WGMRs) because it works similarly to the renowned whispering gallery in London’s St. Paul’s Cathedral, where a person on one side of the dome can hear a message spoken to the wall by another person on the other side. Yang’s device does much the same thing with light frequencies rather than audible ones.

One of the main differences between early resonators and the novel resonator, known as a morphology dependent resonator, was they didn’t use mirrors to reflect light. Yang’s WGMR is an actual mini-laser that supports “frequency degenerate modes,” patterns of excitation inside the mini-laser’s doughnut-shaped ring that are of the same frequency. One portion of light beamed by the Raman laser goes counterclockwise, another goes clockwise. When a particle lands on the ring and scatters energy between these modes, the single Raman lasing line splits into two lasing lines with different frequencies.

When a Raman laser beam is generated in the resonator, it likely will encounter a particle, such as a virus nanoparticle, on the circle. When the beam initially sees the particle, the beam splits into two, generating two lasing lines that serve as reference to the other to form a self-referenced sensing technique.

“Our new sensor differs from the earlier whispering gallery sensors in that it relies on Raman gain, which is inherent in silica, thereby eliminating the need for doping the microcavity with gain media, such as rare-earth ions or optical dyes, to boost detection capability,” Ozdemir says. “This new sensor retains the biocompatibility of silica and could find widespread use for sensing in biological media.”

“It doesn’t matter what kind of wavelength is used, once you have the Raman laser circulating inside and there is a molecule sitting on the circle, when the beam sees the particle it will scatter in all kinds of directions,” Yang says. “Initially you have a counterclockwise mode, then a clockwise mode, and by analyzing the characterization of the two split modes, we confirm the detection of nanoparticles.”

In addition to the demonstration of Raman microlasers for particle sensing, the team says their work shows the possibility of using intrinsic gain mechanisms, such as Raman and parametric gain, instead of optical dyes, rare-earth ions or quantum dots, for loss compensation in optical and plasmonic systems where dissipation hinders progress and limits applications.

Spin-charge converters are important devices in spintronics, an electronic which is not only based on the charge of electrons but also on their spin and the spin-related magnetism. Spin-charge converters enable the transformation of electric into magnetic signals and vice versa. Recently, the research group of Professor Jairo Sinova from the Institute of Physics at Johannes Gutenberg University Mainz in collaboration with researchers from the UK, Prague, and Japan, has for the first time realised a new, efficient spin-charge converter based on the common semiconductor material GaAs.

Comparable efficiencies had so far only been observed in platinum, a heavy metal. In addition, the physicists demonstrated that the creation or detection efficiency of spin currents is electrically tunable in a certain regime. This is important when it comes to real devices. The underlying mechanism, that was revealed by theoretical works of the Sinova group, opens up a new approach in searching and engineering spintronic materials. These results have recently been published in the journal Nature Materials.

Spintronics does not only make use of the electron’s charge to transmit and store information but it takes also advantage of the electron’s spin. The spin can be regarded as a rotation of the electron around its own axis, and generates a magnetic field like a small magnet. In some materials, electron spins spontaneously align their direction, leading to the phenomenon of ferromagnetism which is well known e.g. in iron. Additionally, “spin-up” or “spin-down” directions can be used to represent two easily distinguishable states – 0 and 1 – used in information technology. This is already used for memory applications such as computer hard discs.

Making use of electron spin for information transmission and storage, enables the development of electronic devices with new functionalities and higher efficiency. To make real use of the electron spin, it has to be manipulated precisely: it has to be aligned, transmitted and detected. The work of Sinova and his colleagues shows, that it is possible to do so using electric fields rather than magnetic ones. Thus, the very efficient, simple and precise mechanisms of charge manipulation well established in semiconductor electronics can be transferred to the world of spintronic and thereby combine semiconductor physics with magnetism.

Spin-charge converters are essential tools for that. They can transform charge currents into spin currents, and vice versa. The main principle behind these converters is the so called spin-Hall effect. Jairo Sinova had already been involved in the prediction and discovery of this relativistic phenomenon in 2004.

The spin-Hall effect appears when an electric field drives electrons through a semiconductor plate. Taking a look at the classical Hall effect that is known from undergraduate physics, the interaction of moving electrons and an external magnetic field forces the electrons to move to one side of the plate, perpendicular to their original direction. This leads to the so called Hall voltage between both sides of the plate. For the spin-Hall effect electron-spins are generated by irradiating the sample with circularly polarised light. The electron spins are then parallel or antiparallel, and their direction is perpendicular to the plate and the direction of movement. The moving electron spins are now forced to one or the other side of the plate, depending on the spin orientation. The driving force behind this is the so called spin-orbit coupling, a relativistic electromagnetic effect which influences moving electron spins. This leads to the separation of both spin orientations.

To make practical use of this effect, it is essential to get a highly efficient spin separation. Up to now, platinum has been the most efficient spin-charge converter material, as it is a heavy metal, and the spin-orbit coupling of heavy metals is known to be especially strong due to the large amount of protons (positive charge) in their core.

Now, Sinova and his colleagues have shown that gallium-arsenide (GaAs), a very common and widely used semiconductor material, can be an as efficient spin-charge converter as platinum, even at room temperature, which is important for practical applications. Moreover, the physicists have demonstrated for the first time that the efficiency can be tuned continuously by varying the electric field that drives the electrons.

The reason for this – as theoretical calculations of the Sinova group have shown – lies in the existence of certain valleys in the conduction band of the semiconductor material. One can think of the conduction band and its valleys as of a motor highway with different lanes, each one requiring a certain minimum velocity. Applying a higher electric field enables a transition from one lane to the other.

Since the spin-orbit coupling is different in each lane, a transition also affects the strength of the spin-hall effect. By varying the electric field, the scientists can distribute the electron spins on the different lanes, thus varying the efficiency of their spin-charge converter.

By taking into account the valleys in the conduction band, Sinova and his colleagues open up new ways to find and engineer highly efficient materials for spintronics. Especially, since current semiconductor growth technologies are capable of engineering the energy levels of the valleys and the strength of spin-orbit coupling, e.g. by substituting Ga or As with other materials like Aluminum.

ROHM has recently established a process for MEMS utilizing thin-film piezoelectric elements, and implemented the industry’s first foundry business that integrates product design and manufacturing processes, from wafer pulling to mounting, in order to meet a variety of customer needs.

Piezoelectric elements, which possess the inherent property of generating a voltage when pressure is applied, are incorporated into a wide variety of electronic devices, from conventional inkjet printheads to autofocus systems in infrared and standard cameras. Combining these elements with MEMS technology, which is commonly used in accelerometers and gyroscopes, makes it possible to simplify design and reduce the size of processing controllers, contributing to increased performance, lower costs, and greater end-product miniaturization. In addition, the energy-saving characteristics of the piezoelectric element itself, which requires very little power during standby, are garnering increased attention – particularly in the sensor market where explosive growth is expected.

We have already begun conducting joint development of piezoelectric MEMS products based on customer requirements and gradually expanding our production lines to accommodate growth markets, such as industrial inkjet printers, sensors, and wearable devices. Going forward ROHM will continue to integrate piezoelectric elements with MEMS technology in order to achieve greater miniaturization and energy savings.

However, in the device creation of piezoelectric MEMS, thin-film deposition that possesses high piezoelectric properties and precision fabrication and molding of micro-piezoelectric elements are difficult to realize. Furthermore, high-precision processing is required for the MEMS drive block, and additional knowledge and expertise – along with the cultivation of new technologies – are needed in order to support next-generation applications and emerging markets.

In response to these challenges, ROHM is actively engaged in the research of thin-film piezoelectric elements. Based on the findings of Professor Isaku Kanno of the Graduate School of Engineering at Kobe University on evaluation measurement methods for thin-film piezoelectric elements, and by taking advantage of development synergy created by combining the collective production technologies of the entire ROHM Group, which includes ROHM’s ferroelectric technology cultivated for long-term memory, LAPIS Semiconductor’s high-sensitivity MEMS/mounting technology, and Kionix’s MEMS miniaturization technology, we were able to establish a manufacturing process at LAPIS Semiconductor Miyazaki and provide piezoelectric MEMS optimized for a variety of markets and applications.