Alternative current electroluminescence (ACEL) can be identified as an efficient light-emitting technique among a number of different light emission methods. Open-air fabrication capability of the ACEL technique outshines among a few other advantages, whereas electrospinning has been widely identified as a simple, open-air fabrication for nanosized fibers. Here, the authors have combined these two techniques together and fabricated an ACEL device with electrospinning for the first time. The role of electrospinning is highlighted as a scalable fabrication technique to achieve uniform dispersion of both phosphor (ZnS:Cu) and dielectric (BaTiO3) particles. With a greenish-blue luminescence (peak wavelength, 484 nm), the proposed device has achieved a maximum brightness value of 88.55 cd/m2 and a maximum current efficiency of 7.4 cd/A with only 1 kHz sinusoidal input signal. The uniformity of nanofiber mats was evaluated with SEM and EDS analyses, TEM was used as a corroboration. The crystal structures of the active materials were confirmed with X-ray diffraction (XRD) analysis as well. With the opportunities available in both electrospinning and optoelectronic field, this can initiate newer prospects including but not limited to backlighting and smooth light emitting panels in display technology, surface emitting devices in large-area luminescence applications, e.g., in advertising or architectural aspects, and even phototherapeutic applications as well.

Researcher/Author: Wanasinghe Arachchige Dumith Madushanka Jayathilaka, Amutha Chinnappan, Ji Dongxiao, Rituparna Ghosh, Thang Q. Tran, and Seeram Ramakrishna

ACS Appl. Electron. Mater. 2021, 3, 267−276; https://doi.org/10.1021/acsaelm.0c00838

Recently, in healthcare sectors, specifically for personalized health monitoring, motion sensing, and human–machine interactions, the rising demand for stretchable and soft electronic devices is significant. In particular, stretchable, skin mountable, breathable, wearable, light weight, and highly sensitive sensors are needed for detecting subtle deformation arising from human physiological signals and have potential applications in health diagnosis. In this review, we discuss flexible, noninvasive, and wearable sensors based on micro/nanofibers with unique sensing capabilities for detecting human vital signs such as body motion, temperature, heartbeat, respiration rate, and blood glucose level, which have applications in both fitness-monitoring and medical diagnosis. Here, the latest successful examples of micro/nanofiber based flexible and wearable human vital signs monitoring sensors in the form of film, mat, yarn, fabric, textiles, etc., are outlined and discussed in detail. Discussion includes the fiber fabrication technique, sensing mechanism, device structure, sensor performance, and data processing. Some of the latest fabricated self-powered devices with integrated sensing platforms are also reviewed. Finally, this article reveals the existing challenges that are still to be overcome associated with wearable technologies for applications in health monitoring, diagnosis, and rehabilitation.

Researcher/Author: Rituparna Ghosh, Koh Yi Pin, Vundrala Sumedha Reddy, Wanasinghe Arachchige Dumith Madushanka Jayathilaka, Ji Dongxiao, William Serrano‐García, Suresh K Bhargava, Seeram Ramakrishna and Amutha Chinnappan

Appl. Phys. Rev. 7, 041309 (2020); https://doi.org/10.1063/5.0010766

extile electronics are poised to revolutionize future wearable applications due to their wearing comfort and programmable nature. Many promising thermoelectric wearables have been extensively investigated for green energy harvesting and pervasive sensors connectivity. However, the practical applications of the TE textile are still hindered by the current laborious p/n junctions assembly of limited scale and mechanical compliance. Here we develop a gelation extrusion strategy that demonstrates the viability of digitalized manufacturing of continuous p/n TE fibers at high scalability and process efficiency. With such alternating p/n-type TE fibers, multifunctional textiles are successfully woven to realize energy harvesting on curved surface, multi-pixel touch panel for writing and communication. Moreover, modularized TE garments are worn on a robotic arm to fulfill diverse active and localized tasks. Such scalable TE fiber fabrication not only brings new inspiration for flexible devices, but also sets the stage for a wide implementation of multifunctional textile-electronics.

Researcher/Author: Tianpeng Ding, Kwok Hoe Chan, Yi Zhou, Xiao-Qiao Wang, Yin Cheng, Tongtao Li and Ghim Wei Ho

Nature Communications volume 11, Article number: 6006 (2020); https://doi.org/10.1038/s41467-020-19867-7

This paper presents a wearable active concentric electrode for concurrent EEG monitoring and Body-Coupled Communication (BCC) data transmission. A three-layer concentric electrode eliminates the usage of wires. A common mode averaging unit (CMAU) is proposed to cancel not only the continuous common-mode interference (CMI) but also the instantaneous CMI of up to 51Vpp.The localized potentialmatching technique removes the ground electrode. An open-loop programmable gain amplifier (OPPGA) with the pseudo-resistor-based RC-divider block is presented to save the silicon area. The presented work is the first reported so far to achieve the concurrent EEGsignal recording and BCC-based data transmission. The proposed chip achieves 100 dB CMRR and 110 dB PSRR, occupies 0.044 mm2, and consumes 7.4 μW with an input-referred noise density of 26 nV/Hz.

Researcher/Author: Tao Tang, Long Yan, Jeong Hoan Park, Han Wu, Lian Zhang, Jiamin Li, Yilong Dong, Benjamin Ho Yin Lee and Jerald Yoo

IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS, VOL. 14, NO. 6, DECEMBER 2020, 10.1109/TBCAS.2020.3039353; https://ieeexplore.ieee.org/abstract/document/9265233

A 1225-Channel Neuromorphic Retinal Prosthesis (RP) SoC is presented. Existing RP SoCs directly convert light intensity to electrical stimulus, which limit the adoption of delicate stimulus patterns to increase visual acuity. Moreover, a conventional centralized image processor leads to the local hot spot that poses a risk to the nearby retinal cells. To solve these issues, the proposed SoC adopts a distributed Neuromorphic Image Processor (NMIP) located within each pixel that extracts the outline of the incoming image, which reduces current dispersion and stimulus power compared with light-intensity proportional stimulus pattern. A spike-based asynchronous digital operation results in the power consumption of 56.3 nW/Ch without local temperature hot spot. At every 5×5 pixels, the localized (49-point) temperatureregulation circuit limits the temperature increase of neighboring retinal cells to less than 1 °C, and the overall power consumption of the SoC to be less than that of the human eye. The 1225-channel SoC fabricated in 0.18 μm 1P6M CMOS occupies 15mm2 while consuming 2.7 mW, and is successfully verified with image reconstruction demonstration.

Researcher/Author: Jeong Hoan Park, Joanne Si Ying Tan, Han Wu, Yilong Dong and Jerald Yoo

IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 56, NO. 7, JULY 2021, 10.1109/JSSC.2020.3030995; https://ieeexplore.ieee.org/document/9241047

This article presents a wireless multi-channel sensor interface circuit for emerging e-skin applications. The proposed interface circuit uses a CDMA-like sensing method to simultaneously record 16-channel resistive sensors and 16-channel capacitive sensors. The code-modulated multi-channel signals are conditioned and wirelessly transmitted through an edge-encoded pulsewidth-modulation ultra-wideband (PWM UWB) transmitter in the time domain. The PWM UWB transmitter eliminates the need for digitization on the sensor node, reducing the number of data to be sent. This improves the sensing and wireless transmission efficiency.With the proposed edge-encoding technique, the PWM UWB transmitter can recover the sensor data with SNR above 70 dB despite 20% data loss under a lossy environment. Fabricated in 130-nm technology, the wireless multi-channel sensor node occupies a die area of 1.35 mm2 and consumes a power of 70 μW. It achieves an energy efficiency of 0.87 pJ/Conversion-step per channel.

Researcher/Author: Yuxuan Luo, Yida Li, Aaron Voon-Yew Thean and Chun-Huat Heng

IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 56, NO. 7, JULY 2021, 10.1109/JSSC.2020.3030995; https://ieeexplore.ieee.org/document/9241047

We have developed a 5-electrode recording system that combines an implantable electromyography (EMG) device package with transcutaneous inductive power transmission, nearinfrared (NIR) transcutaneous data telemetry and 3 Mbps Wi-Fi data acquisition for chronic EMG recording in vivo. This system comprises a hermetically-sealed single-chip, 5-electrode Implantable EMG Acquisition Device (IEAD), a custom external powering and Implant Telemetry Module (ITM), and a custom Wi-Fi-based Raspberry Pi-based Data Acquisition (RaspDAQ) and relay device. The external unit (ITM and RaspDAQ) is powered entirely by a single battery to achieve the objective of untethered EMG recording, for the convenience of clinicians and animal researchers. The IEAD acquires intramuscular EMG signals at 17.85 ksps/electrode while being powered transcutaneously by the ITM using 22 MHz near-field inductive coupling. The acquired EMG data is transmitted transcutaneously via NIR telemetry to the ITM, which in turn, transfers the data to the RaspDAQ for relaying to a laptop computer for display and storage. We have also validated the complete system by acquiring EMG signals from rodents for up to two months. Following the explantation of the devices, we have also conducted failure and histological analysis on the devices and the surrounding tissue, respectively.

Researcher/Author: Kian Ann Ng , Astrid Rusly, Gil Gerald Lasam Gammad, Nguyen Le, Shih-Chiang Liu, Khay-Wai Leong, Miaolin Zhang, John S. Ho, Jerald Yoo, and Shih-Cheng Yen

IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS, VOL. 14, NO. 4, AUGUST 2020; https://ieeexplore.ieee.org/document/9140303

A sensor node with system power tuning is presented for 5-order-of-magnitude adaptation to harvested power. Coordinated tuning of unified voltage/capacitive/light sensor interface, MCU and direct MPPT with no intermediate power conversion scales system power to 3.1nW at 0.3V.

Researcher/Author: Longyang Lin, Saurabh Jain, Massimo Alioto

2020 IEEE, 978-1-7281-9942-9/20; https://ieeexplore.ieee.org/document/9162898/

This article presents a 15-channel orthogonal code chopping instrumentation amplifier (OCCIA) for an areaefficient and low gain-mismatch multi-channel bio-signal acquisition. Orthogonal codes directly modulate each channel and merge into a single signal for sharing IA, while performing dynamic offset compensation with low power consumption. Digitizationbefore- demodulation (DBD) transmits the combined modulated data directly, which alleviates ripple noise, and completely removes the demodulation and TX encoding overhead from the ASIC. The proposed OCCIA in 0.18-μm 1P6M CMOS, when compared with the recent multi-channel instrumentation amplifiers (IAs), shows the smallest area (0.019 mm2/Ch.), low gain mismatch (0.43%), with the lowest power consumption (1.97 μW/Ch.) and low crosstalk (< −51.5 dB) at 490-Hz bandwidth. Index Terms—Bio-signal acquisition, demodulation-beforedigitization (DBD), instrumentation amplifier (IA), low mismatch, orthogonal code chopping (OCC).

Researcher/Author: Jeong Hoan Park, Tao Tang, Lian Zhang, Kian Ann Ng, Gil Gerald Lasam Gammad, Shih-Cheng Yen, and Jerald Yoo

IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 55, NO. 10, OCTOBER 2020; https://ieeexplore.ieee.org/document/9094180

Hierarchical porous carbons (HPCs) are highly efficient supports for various remarkable catalytic systems. However, templates are commonly utilized for the preparation of HPCs, and the postremoval of the templates is uneconomical, time-consuming, and harmful for the environment in most cases. Herein, a new humidity-induced nontemplating strategy is developed to prepare 1D HPC with rich topologies and interconnected cavities for catalysis and energy storage applications. Porous electrospun nanofibers as calcination precursors are prepared via a humidity-induced phase separation strategy. A nitrogen-doped hierarchical porous carbon nanofiber (HPCNF), loading Co/ Co3O4 hetero-nanoparticles as exemplary nonprecious-metal active substance (Co/Co3O4@HPCNF), is fabricated through the subsequent hydrothermal and pyrolysis treatment. The internal mesopore and cavity structure can be simply controlled by varying environment humidity during the electrospinning process. Benefiting from the unique topology, Co/Co3O4@HPCNF exhibits superior bifunctional activity when being used as electrocatalysts for oxygen reduction/evolution reactions. Moreover, the hybrid catalyst also demonstrates a remarkable power density of 102.5 mW cm−2, a high capacity of 748.5 mAh gZn −1, and long cycle life in Zinc–air batteries. The developed approach offers a facile template-free route for the preparation of HPCNF hybrid and can be extended to other members of the large polymer family for catalyst design and energy storage applications.

Researcher/Author: Lidong Tian, Dongxiao Ji, Shan Zhang, Xiaowei He, Seeram Ramakrishna and Qiuyu Zhang

Small 2020, 16, 2001743; https://doi.org/10.1002/smll.202001743

Living organisms are capable of sensing and responding to their environment through reflex-driven pathways. The grand challenge for mimicking such natural intelligence in miniature robots lies in achieving highly integrated body functionality, actuation, and sensing mechanisms. Here, somatosensory light-driven robots (SLiRs) based on a smart thin-film composite tightly integrating actuation and multisensing are presented. The SLiR subsumes pyro/piezoelectric responses and piezoresistive strain sensation under a photoactuator transducer, enabling simultaneous yet non-interfering perception of its body temperature and actuation deformation states. The compact thin film, when combined with kirigami, facilitates rapid customization of low-profile structures for morphable, mobile, and multiple robotic functionality. For example, an SLiR walker can move forward on different surfaces, while providing feedback on its detailed locomotive gaits and subtle terrain textures, and an SLiR anthropomorphic hand shows bodily senses arising from concerted mechanoreception, thermoreception, proprioception, and photoreception. Untethered operation with an SLiR centipede is also demonstrated, which can execute distinct, localized body functions from directional motility, multisensing, to wireless human and environment interactions. This SLiR, which is capable of integrated perception and motility, offers new opportunities for developing diverse intelligent behaviors in soft robots.

Researcher/Author: Xiao-Qiao Wang, Kwok Hoe Chan, Yin Cheng, Tianpeng Ding, Tongtao Li, Sippanat Achavananthadith, Selman Ahmet, John S. Ho and Ghim Wei Ho

Advanced Materials, Volume32, Issue21; https://doi.org/10.1002/adma.202000351

Terahertz (THz) signals, mainly generated by photonic or electronic approaches, are being sought for various applications, whereas the development of magnetic source might be a necessary step to harness the magnetic nature of electromagnetic radiation. We show that the relativistic effect on the current driven domain-wall motion induces THz spin-wave emission in ferrimagnets. The required current density increases dramatically in materials with strong exchange interaction and rapidly exceeds 1012Am−2, leading to the device breakdown and thus the lack of experimental evidence. By translating the collective magnetization oscillations into voltage signals, we propose a three-terminal device for the electrical detection of THz spin wave. Through material engineering, a wide frequency range from 264 GHz to 1.1 THz and uniform continuous signals with improved output power can be obtained. As a reverse effect, the spin wave generated in this system is able to move the ferrimagnetic domain wall. Our work provides guidelines for the experimental verification of THz spin wave, and could stimulate the design of THz spintronic oscillators for wideband applications as well as the all-magnon spintronic devices.  

Researcher/Author: Zhifeng Zhu, Kaiming Cai, Jiefang Deng, Venkata Pavan Kumar Miriyala, Hyunsoo Yang, Xuanyao Fong, Gengchiau Liang  

PHYSICAL REVIEW APPLIED 13, 034040 (2020); https://doi.org/10.1103/PhysRevApplied.13.034040

The generation and detection of ultrafast spin current, preferably reaching a frequency up to terahertz, is the core of spintronics. Studies have shown that the Weyl semimetal WTe2 is of great potential in generating spin currents. However, the prior studies have been limited to the static measurements with the inplane spin orientation. In this work, we demonstrate a picosecond spin-photocurrent in a Td-WTe2 thin film via a terahertz time domain spectroscopy with a circularly polarized laser excitation. The anisotropic dependence of the circular photogalvanic effect (CPGE) in the terahertz emission reveals that the picosecond spinphotocurrent is generated along the rotational asymmetry a-axis. Notably, the generated spins are aligned along the out-of-plane direction under the light normally incident to the film surface, which provides an efficient means to manipulate magnetic devices with perpendicular magnetic anisotropy. A spin-splitting band induced by intrinsic inversion symmetry breaking enables the manipulation of a spin current by modulating the helicity of the laser excitation. Moreover, CPGE nearly vanishes at a transition temperature of ∼175 K due to the carrier compensation. Our work provides an insight into the dynamic behavior of the anisotropic spin-photocurrent of Td-WTe2 in terahertz frequencies and shows a great potential for the future development of terahertz-spintronic devices with Weyl semimetals.

Researcher/Author: Mengji Chen, Kyusup Lee, Jie Li, Liang Cheng, Qisheng Wang, Kaiming Cai, Elbert E. M. Chia, Haixin Chang, Hyunsoo Yang  

ACS Nano 2020, 14, 3539−3545; https://doi.org/10.1021/acsnano.9b09828

EEG recording technology creates the opportunity to sense and discover potential
fluctuation in the human brain. Quantitative analysis based on various EEG
sensor nodes provide vital information on the patient’s mental and physiological
status. However, conventional multi-channel work requires wire connections and
thus suffers from huge environmental interference, which makes it difficult to be
wearable and durable for daily EEG monitoring. Some work tried to solve the
problem of common mode interference from power line coupling by using a
common mode charging pump (CMCP) technique, which cancels out a certain
amount of common mode voltage. However, the charging speed of the capacitor
makes it unsuitable when coupled common mode potential changes over time
and environment. Some work proposed a floating power system with an onchip
frequency-controlled LDO, while it requires all channels tied together to
average out the common mode potential and forced a power plane to be shared
by all of them, which works for implantable neural recording system instead of a
widespread distributed EEG recording system. Moreover, a conventional EEG
recording system requires a separate reference electrode, which introduces more
connection wires and extra interferences. For the active electrode, which
removes the input connection wires to reduce common mode interference, the
potential difference between circuit ground and human body is another essential
issue, a driven-right leg circuit is used in leads to extra wire/interference and
stability issue. Work in proposed in-ear EEG AFE with BCC transmission,
however, concurrent signal recording/BCC transmission is not reported.

 

Researcher/Author: Tao Tang, Long Yan, Jeong Hoan Park, Han Wu, Lian Zhang, Ho Yin Benjamin Lee, Jerald Yoo

2020 IEEE International Solid-State Circuits Conference, 978-1-7281-3205-1; https://ieeexplore.ieee.org/document/9063054

Constructing heterointerfaces between metals and metal compounds is an attractive strategy for the fabrication of high performance electrocatalysts. However, realizing the high degree of fusion of two different metal components to form heterointerfaces remains a great challenge, since the different metal components tend to grow separately in most cases. Herein, by employing carboxyl-modified carbon nanotubes to stabilize different metal ions, the engineering of abundant Ni|MnO heterointerfaces is achieved in porous carbon nanofibers (Ni|MnO/CNF) during the electrospinning–calcination process. Remarkably, the resulting Ni|MnO/ CNF catalyst exhibits activities that are among the best reported for the catalysis of both the oxygen reduction and oxygen evolution reactions. Moreover, the catalyst also demonstrates high power density and long cycle life in Zn–air batteries. Its superior electrochemical properties are mainly ascribed to the synergy between the engineering of oxygen-deficient Ni|MnO heterointerfaces with a strong Ni/Mn alloying interaction and the 1D porous CNF support. This facile anchoring strategy for the initiation of bimetallic heterointerfaces creates appealing opportunities for the potential use of heteronanomaterials in practical sustainable energy applications.

Researcher/Author: Dongxiao Ji, Jianguo Sun, Lidong Tian, Amutha Chinnappan, Tianran Zhang, Wanasinghe Arachchige Dumith Madushanka Jayathilaka, Rituparana Gosh, Chinnappan Baskar, Qiuyu Zhang, and Seeram Ramakrishna

Adv. Funct. Mater. 2020, 30, 1910568, 10.1002/adfm.2019105683; https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.201910568

Electroluminescence (EL), the light emission under an applied electrical potential, is one of several key light emitting techniques applied over a vast range of applications. Alternative Current Electroluminescent (ACEL) is one of the major light emitting techniques discussed under EL. Even though it possesses some intrinsic advantages over Light Emitting Diodes (LEDs) and Light Emitting Cells (LEC), it has not been thoroughly discussed like LEDs and most of the time has been kept under the shadow of LEDs. On the other hand, flexible light emitting devices have become an emerging trend in the field as they are widely applied in consumer electronics and wearable devices, where an ACEL technique can make a significant impact for their development. This review discusses the ACEL technique in detail covering different device architectures, materials and fabrication methods highlighting the use of electrospinning techniques. In the second part, the review briefly summarizes research works in the flexible light emitting field, covering both optical and mechanical performances.

Researcher/Author: Wanasinghe Arachchige Dumith Madushanka Jayathilaka, Amutha Chinnappan, Ju Nie Tey, Jun Wei and Seeram Ramakrishna

J. Mater. Chem. C, 2019, 7, 5553; https://doi.org/10.1039/C9TC01267B