Tag Archives: #MEMS

Optical Scanner Design for Adaptive Driving Beam Systems Can Lead to Safer Night Driving (Engineering)

Scientists couple adaptive driving beam technology with an electronically controllable optical scanner, enabling better road safety for drivers and pedestrians.

Car accidents are responsible for approximately a million deaths each year globally. Among the many causes, driving at night, when vision is most limited, leads to accidents with higher mortality rates than accidents during the day. Therefore, improving visibility during night driving is critical for reducing the number of fatal car accidents.

An adaptive driving beam (ADB) can help to some extent. This advanced drive-assist technology for vehicle headlights can automatically adjust the driver’s visibility based on the car speed and traffic environment. ADB systems that exist commercially are a marked improvement over manually controlled headlights, but they suffer from limited controllability. Whereas spatial light modulators, like liquid crystal pixels or digital micromirrors, can alleviate this problem, they are often expensive to implement and lead to heat loss from unutilized light power.

In a recent study published in the Journal of Optical Microsystems, researchers from Japan have come up with an alternative to conventional ADB systems: a microelectromechanical systems (MEMS) optical scanner that relies on the piezoelectric effect of electrically induced mechanical vibrations. This design consists of a thin film of lead-zirconate-titanate oxide (or PZT), which induces mechanical vibrations in the scanner in synchronization with a laser diode. The optical scanner spatially steers the laser beam to form structured light on the phosphor plate, where it is converted into bright white light. The light intensity is, in turn, modulated by the ADB controller based on the traffic, steering wheel angle, and vehicle cruising speed. University of Tokyo researcher Hiroshi Toshiyoshi, one of the authors on the paper, explains, “What is unique about this setup is that the laser beam is converted into white light at high efficiency, which reduces heating of the ADB system.”

The researchers designed the optical scanner on a single chip consisting of a bonded silicon-on-insulator wafer with the PZT layer grown on it and laminated with metal to form piezoelectric actuators. They arranged the actuators as suspensions to allow for large-angle horizontal and vertical deflections of the scanner. This, in turn, enabled two-dimensional scanning of the headlight beam. Further, they designed the modes so that they don’t react to low-frequency noise, such as from other vehicles. Their ADB system also accounts for temperature variations. Finally, they mounted the module on a vehicle and evaluated its performance for actual driving.

The researchers found that the ADB with a MEMS scanner provided the driver with better visibility, especially when it comes to seeing pedestrians. It could also reduce the glare from oncoming vehicles and reconfigure the illumination area depending on the cruising speed of the vehicle.

While this technology certainly advances drive-assist technology, it also has other potential applications in light detection and range finding, as well as inter-vehicle optical communication links, which means that the system could find use in self-driving technology of intelligent traffic systems in the future, taking us another step toward risk-free driving.

Read the original Gold Open Access article: T. Asari et al., “Adaptive driving beam system with MEMS optical scanner for reconfigurable vehicle headlight,” J. Opt. Microsys. 1(1), 014501 (2021), doi: 10.1117/1.JOM.1.1.014501

Featured image: Headlights Infographic: ADB with MEMS 2D optical scanner, based on the piezoelectric effect. © SPIE

Reference: Tomotaka Asari, Mamoru Miyachi, Yutaro Oda, Takaaki Koyama, Hiroaki Kurosu, Makoto Sakurai, Masanao Tani, Yoshiaki Yasuda, Hiroshi Toshiyoshi, “Adaptive driving beam system with MEMS optical scanner for reconfigurable vehicle headlight”, J. of Optical Microsystems, 1(1), 014501 (2021). https://www.spiedigitallibrary.org/journals/journal-of-optical-microsystems/volume-1/issue-01/014501/Adaptive-driving-beam-system-with-MEMS-optical-scanner-for-reconfigurable/10.1117/1.JOM.1.1.014501.full?SSO=1 https://doi.org/10.1117/1.JOM.1.1.014501

Provided by SPIE

Newly Developed GaN based MEMS Resonator Operates Stably Even at High Temperature (Material Science)

Promising as a highly sensitive oscillator toward 5G communication.

Liwen Sang, independent scientist at International Center for Materials Nanoarchitectonics, National Institute for Materials Science (also JST PRESTO researcher) developed a MEMS resonator that stably operates even under high temperatures by regulating the strain caused by the heat from gallium nitride (GaN).

Figure 1. The device processing for the double-clamped GaN bridge resonator on Si substrate. Figure Caption: (1) The as-grown GaN epitaxial film on Si substrate. Except for the AlN buffer layer, no strain removal layer is used. (2) Spin coating of the photoresist on the GaN-on-Si sample. (3) Laser lithography to define the pattern for the double clamped bridge configuration. (4) Plasma etching to remove the GaN layer without photo resist. (5) Chemical etching to release Si under the GaN layer. Therefore, the air gap is formed. (6) The final device structure of the double clamped bridge resonator. We use the laser doppler method to measure the frequency shift and resolution under different temperatures. © Liwen Sang

High-precision synchronization is required for the fifth generation mobile communication system (5G) with a high speed and large capacity. To that end, a high-performance frequency reference oscillator which can balance the temporal stability and temporal resolution is necessary as a timing device to generate signals on a fixed cycle. The conventional quartz resonator as the oscillator has the poor integration capability and its application is limited. Although a micro-electromechanical system (MEMS)*1 resonator can achieve a high temporal resolution with small phase noise and superior integration capability, the silicon (Si)-based MEMS suffers from a bad stability at higher temperatures.

In the present study, a high-quality GaN epitaxial film was fabricated on a Si substrate using metal organic chemical vapor deposition (MOCVD)*2 to fabricate the GaN resonator. The strain engineering was proposed to improve the temporal performance. The strain was achieved through utilizing the lattice mismatch and thermal mismatch between GaN and Si substrate. Therefore, GaN was directly grown on Si without any strain-removal layer. By optimizing the temperature decrease method during MOCVD growth, there was no crack observed on GaN and its crystalline quality is comparable to that obtained by the conventional method of using a superlattice strain-removal layer.

Figure 2. (a) The temperature coefficient of frequency (TCF) of the GaN resonator at different temperature; (b) The quality factor of the GaN resonator at different temperature
The temporal stability of a resonator is defined by temperature coefficient of frequency (TCF). TCF indicates a change of the resonance frequency with changing temperature. For the Si MEMS resonator, its intrinsic TCF is ~ -30ppm/K. Several methods were proposed to reduce the TCF of Si resonator, but the quality factors of the system were greatly degraded. The quality factor of a resonator in the system can be used to determine the frequency resolution. A high quality factor is required for the accurate frequency reference. The developed GaN resonator in this work can simultaneously achieve a low TCF and high quality factor up to 600 K. The TCF is as low as -5 ppm/K. The quality factor is more than 105, which is the highest one ever reported in GaN system. © Liwen Sang

The developed GaN-based MEMS resonator was verified to operate stably even at 600K. It showed a high temporal resolution and good temporal stability with little frequency shift when the temperature was increased. This is because the internal thermal strain compensated the frequency shift and reduce the energy dissipation. Since the device is small, highly sensitive and can be integrated with CMOS technology, it is promising for the application to 5G communication, IoT timing device, on-vehicle applications, and advanced driver assistance system.

The research was supported by JST’s Strategic Basic Research Program, Precursory Research for Embryonic Science and Technology(PRESTO). This result was presented at the IEEE International Electron Devices Meeting (IEDM2020) held online on December 12-18, 2020, titled “Self-Temperature-Compensated GaN MEMS Resonators through Strain Engineering up to 600 K.”

(1) Micro-electro mechanical systems (MEMS)

A device where mechanical components, sensors, actuators, and electrical circuit are integrated on a substrate, such as semiconductor, glass, or organic material through microfabrication technology. For the main component, three-dimensional shape and movable structures are built through etching.

(2) Metal organic chemical vapor deposition (MOCVD)

A useful crystal growth method to build a wafer for compound semiconductors. Organometallic compounds of the Group III and Group V are simultaneously provided to the heated crystalline surface of the substrate to achieve epitaxial growth.

Provided by Japan Science and Technology Agency

Symptoms All In Your Head—Or In Your Gut? Maybe A Little Of Both (Medicine)

Anyone who has experienced “butterflies in the stomach” before giving a big presentation will be unsurprised to learn there is a physical connection between their gut and their brain. Neuroscientists and medical professionals call this connection the “gut-brain axis” (GBA); a better understanding of the GBA could lead to the development of treatments and cures for neurological disorders such as depression and anxiety, as well as for a range of chronic auto-immune inflammatory diseases such as irritable bowel syndrome (IBS) and rheumatoid arthritis.

A graphical abstract of the gut-brain axis (left) and the 3D-printed in vitro platform (right).

Right now, these conditions and diseases are primarily diagnosed by patients’ reports of their symptoms. However, neuroscientists and doctors are investigating the GBA in order to find so-called “biomarkers” for these diseases. In the case of the GBA, that biomarker is likely serotonin.

By targeting this complex connection between the gut and the brain, researchers hope they can uncover the role of the gut microbiome in both gut and brain disorders. With an easily identifiable biomarker such as serotonin, there may be some way to measure how dysfunction in the gut microbiome affects the GBA signaling pathways. Having tools that could increase understanding, help with disease diagnosis, and offer insight into how diet and nutrition impacts mental health would be extremely valuable.

With $1 million in National Science Foundation funding, a team of University of Maryland experts from engineering, neuroscience, applied microbiology, and physics has been making headway on building a platform that can monitor and model the real-time processing of gut microbiome serotonin activity. Three new published papers detail the progress of the work, which includes innovations in detecting serotonin, assessing its neurological effects, and sensing minute changes to the gut epithelium.

In “Electrochemical Measurement of Serotonin by Au-CNT Electrodes Fabricated on Porous Cell Culture Membranes” (https://www.nature.com/articles/s41378-020-00184-4), the team developed a platform that provides access to the specific site of serotonin production. The platform included a porous membrane with an integrated serotonin sensor on which a model of the gut lining can be grown. This innovation allowed researchers to access both top and bottom sides of the cell culture–important because serotonin is secreted from the bottoms of cells. The work is the first to demonstrate a feasible method for detection of redox molecules, such as serotonin, directly on a porous and flexible cell culture substrate. It grants superior access to cell-released molecules and creates a controllable model gut environment to perform groundbreaking GBA research without the need to perform invasive procedures on humans or animals.

The team’s second paper, “A Hybrid Biomonitoring System for Gut-Neuron Communication” (https://ieeexplore.ieee.org/document/9123494), builds on the findings of the first: the researchers developed the serotonin measuring platform further so it could assess serotonin’s neurological effects. By adding and integrating a dissected crayfish nerve model with the gut lining model, the team created a gut-neuron interface that can electrophysiologically assess nerve response to the electrochemically detected serotonin. This advance enables the study of molecular signaling between gut and nerve cells, making possible real-time monitoring of both GBA tissues for the first time.

Finally, the concept, design, and use for the entire biomonitoring platform is described in a third paper, “3D Printed Electrochemical Sensor Integrated Transwell Systems” (https://www.nature.com/articles/s41378-020-00208-z). This paper delves into the development of the 3D-printed housing, the maintenance of a healthy lab-on-a-chip gut cell culture, and the evaluation of the two types of sensors integrated on the cell culture membrane. The dual sensors are particularly important because they provide feedback about multiple components of the system–namely, the portions that model the gut lining’s permeability (a strong indicator of disease) and its serotonin release (a measure of communication with the nervous system). Alongside the electrochemical sensor–evaluated using a standard redox molecule ferrocene dimethanol–an impedance sensor was used to monitor cell growth and coverage over the membrane. Using both these sensors would allow monitoring of a gut cell culture under various environmental and dietary conditions. It also would enable researchers to evaluate changes to barrier permeability (a strong indicator of disease), and serotonin release (a measure of communication with the nervous system).

References: Ramiah Rajasekaran, P., Chapin, A.A., Quan, D.N. et al. 3D-Printed electrochemical sensor-integrated transwell systems. Microsyst Nanoeng 6, 100 (2020). https://doi.org/10.1038/s41378-020-00208-z

Provided by University Of Maryland