Search Results (56)

The anisotropic magnetoresistance (AMR) effect is widely used in microscale and nanoscale magnetic sensors. In this study, we investigate the correlation between AMR and the crystal structure, epitaxial relationship, and magnetic properties of Co₅₀Fe₅₀ thin films deposited on rigid MgO and flexible mica substrates. The AMR ratio is approximately 1.6% for CoFe films on mica, lower than the 2.5% observed in epitaxially grown films on MgO substrates. The difference is likely due to the well-defined easy axis in the single domain epitaxial thin films on MgO, which enhances the AMR ratio. Microscopic strain induced by lattice mismatch and bending on flexible substrates were determined using grazing incidence X-ray diffraction and extended X-ray absorption fine structure techniques. These results showed that neither microscopic nor macroscopic strain (below 0.5%) affects the AMR ratio on mica, suggesting its suitability for magnetic sensors in flexible and wearable devices. Additionally, investigating M-H loops under various growth temperatures, lattice mismatch conditions, and bending strains could further benefit the fabrication and integration of the micro-scale magnetic sensors in the microelectronic industry. Full article

Flexible pressure sensors can be widely utilized in healthcare, human–computer interaction, and the Internet of Things (IoT). There is an increasing demand for high-precision and high-sensitivity flexible pressure sensors. In response to this demand, a novel flexible pressure sensor with a symmetrical structure composed of MoS₂ and PDMS is designed in this paper. Simulation is conducted on the designed flexible pressure sensor. Its piezoresistive effect is analyzed, and the influence of the cavity structure on its sensitivity is investigated. Additionally, a fully symmetrical Wheatstone bridge composed of the flexible pressure sensor is designed and simulated. Its symmetrical structure improves the temperature stability and the sensitivity of the sensor. The structure can be used to convert pressure changes into voltage changes conveniently. It indicates that the sensor achieves a sensitivity of 1.13 kPa⁻¹ in the micro-pressure range of 0–20 kPa, with an output voltage sensitivity of 3.729 V/kPa. The designed flexible pressure sensor exhibits promising potential for applications in wearable devices and related fields, owing to its high sensitivity and precision. Full article

In the current era, energy resources from the environment via piezoelectric materials are not only used for self-powered electronic devices, but also play a significant role in creating a pleasant living environment. Piezoelectric materials have the potential to produce energy from micro to milliwatts of power depending on the ambient conditions. The energy obtained from these materials is used for powering small electronic devices such as sensors, health monitoring devices, and various smart electronic gadgets like watches, personal computers, and cameras. These reviews explain the comprehensive concepts related to piezoelectric (classical and non-classical) materials, energy harvesting from the mechanical vibration of piezoelectric materials, structural modelling, and their optimization. Non-conventional smart materials, such as polyceramics, polymers, or composite piezoelectric materials, stand out due to their slender actuator and sensor profiles, offering superior performance, flexibility, and reliability at competitive costs despite their susceptibility to performance fluctuations caused by temperature variations. Accurate modeling and performance optimization, employing analytical, numerical, and experimental methodologies are imperative. This review also furthers research and development in optimizing piezoelectric energy utilization, suggesting the need for continued experimentation to select optimal materials and structures for various energy applications. Full article

The emergence of novel e-textile materials that combine the inherent qualities of the textile substrate (lightweight, soft, breathable, durable, etc.) with the functionality of micro/nano-electronic materials (conductive, dielectric, sensing, etc.) has resulted in a trend toward miniaturization, integration, and intelligence in new electronic devices. However, the formation of a conductive network by micro/nano-conductive materials on textiles necessitates high-temperature sintering, which inevitably causes substrate aging and component damage. Herein, a bis-hydroxy-imidazolium chloride salt as a hard segment to synthesize a waterborne polyurethane (WPU) adhesive is designed and prepared. When used in nano-silver-based printing coatings, it offers strong adherence for coatings, reaching 16 N cm⁻¹; on the other hand, the introduction of chloride ions enables low-temperature (60 °C) chemical sintering to address the challenge of secondary treatment and high-temperature sintering (>150 °C). Printed into flexible circuits, the resistivity can be controlled by the content of imidazolium salts anchored in the molecular chain of the WPU from a maximum resistivity of 3.1 × 10⁷ down to 5.8 × 10⁻⁵ Ω m, and it can conduct a Bluetooth-type finger pulse detector with such low resistivity. As a flexible circuit, it also offers high stability against washing and adhesion, which the resistivity only reduces less than 20% after washing 10 times and adhesion. Owing to the adjustability of the resistivity, we fabricated an all-textile flexible pressure sensor that accurately differentiates different external pressures (min. 10 g, ~29 Pa), recognizes forms, and detects joint motions (finger bending and wrist flexion). Full article

This study presents a novel pH sensor platform utilizing charge-trap-flash-type metal oxide semiconductor field-effect transistors (CTF-type MOSFETs) for enhanced sensitivity and self-amplification. Traditional ion-sensitive field-effect transistors (ISFETs) face challenges in commercialization due to low sensitivity at room temperature, known as the Nernst limit. To overcome this limitation, we explore resistive coupling effects and CTF-type MOSFETs, allowing for flexible adjustment of the amplification ratio. The platform adopts a unique approach, employing CTF-type MOSFETs as both transducers and resistors, ensuring efficient sensitivity control. An extended-gate (EG) structure is implemented to enhance cost-effectiveness and increase the overall lifespan of the sensor platform by preventing direct contact between analytes and the transducer. The proposed pH sensor platform demonstrates effective sensitivity control at various amplification ratios. Stability and reliability are validated by investigating non-ideal effects, including hysteresis and drift. The CTF-type MOSFETs’ electrical characteristics, energy band diagrams, and programmable resistance modulation are thoroughly characterized. The results showcase remarkable stability, even under prolonged and repetitive operations, indicating the platform’s potential for accurate pH detection in diverse environments. This study contributes a robust and stable alternative for detecting micro-potential analytes, with promising applications in health management and point-of-care settings. Full article

Environmental heat-to-electric energy conversion presents a promising solution for powering sensors in wearable and portable devices. However, the availability of near-room temperature thermoelectric (TE) materials is highly limited, posing a significant challenge in this field. Bi₂Se₃, as a room-temperature TE material, has attracted much attention. Here, we demonstrate a large-scale synthesis of Bi₂Se₃ nanoflakes used for the microflexible TE generator. A high-performance micro-TE generator module, utilizing a flexible printed circuit, has been designed and fabricated through the process of screen printing. The TE generator configuration comprises five pairs of PN TE legs. The p-type TE leg utilizes commercially available Sb₂Te₃ powder, while the n-type TE leg employs Bi₂Se₃ nanoflakes synthesized in this study. For comparative purposes, we also incorporate commercially available Bi₂Se₃ powder as an alternative n-type TE leg. The optimal performance of the single-layer microflexible TE generator, employing Bi₂Se₃ nanoflakes as the active material, is achieved when operating at a temperature differential of 109.5 K, the open-circuit voltage (V_OC) is 0.11 V, the short circuit current (I_SC) is 0.34 mA, and the maximum output power (P_MAX) is 9.5 μW, much higher than the generator consisting of commercial Bi₂Se₃ powder, which is expected to provide an energy supply for flexible electronic devices. Full article

According to the latest literature, it is difficult to measure the multiple important physical parameters inside a proton battery stack accurately and simultaneously. The present bottleneck is external or single measurements, and the multiple important physical parameters (oxygen, clamping pressure, hydrogen, voltage, current, temperature, flow, and humidity) are interrelated, and have a significant impact on the performance, life, and safety of the proton battery stack. Therefore, this study used micro-electro-mechanical systems (MEMS) technology to develop a micro oxygen sensor and a micro clamping pressure sensor, which were integrated into the 6-in-1 microsensor developed by this research team. In order to improve the output and operability of microsensors, an incremental mask was redesigned to integrate the back end of the microsensor in combination with a flexible printed circuit. Consequently, a flexible 8-in-1 (oxygen, clamping pressure, hydrogen, voltage, current, temperature, flow, and humidity) microsensor was developed and embedded in a proton battery stack for real-time microscopic measurement. Multiple micro-electro-mechanical systems technologies were used many times in the process of developing the flexible 8-in-1 microsensor in this study, including physical vapor deposition (PVD), lithography, lift-off, and wet etching. The substrate was a 50 μm-thick polyimide (PI) film, characterized by good tensile strength, high temperature resistance, and chemical resistance. The microsensor electrode used Au as the main electrode and Ti as the adhesion layer. Full article

Conventional eddy-current sensors have the advantages of being contactless and having high bandwidth and high sensitivity. They are widely used in micro-displacement measurement, micro-angle measurement, and rotational speed measurement. However, they are based on the principle of impedance measurement, so the influence of temperature drift on sensor accuracy is difficult to overcome. A differential digital demodulation eddy current sensor system was designed to reduce the influence of temperature drift on the output accuracy of the eddy current sensor. The differential sensor probe was used to eliminate common-mode interference caused by temperature, and the differential analog carrier signal was digitized by a high-speed ADC. In the FPGA, the amplitude information is resolved using the double correlation demodulation method. The main sources of system errors were determined, and a test device was designed using a laser autocollimator. Tests were conducted to measure various aspects of sensor performance. Testing showed the following metrics for the differential digital demodulation eddy current sensor: nonlinearity 0.68% in the range of ±2.5 mm, resolution 760 nm, maximum bandwidth 25 kHz, and significant suppression in the temperature drift compared to analog demodulation methods. The tests show that the sensor has high precision, low temperature drift and great flexibility, and it can instead of conventional sensors in applications with large temperature variability. Full article

The proton battery has facilitated a new research direction for technologies related to fuel cells and energy storage. Our R&D team has developed a prototype of a proton battery stack, but there are still problems to be solved, such as leakage and unstable power generation. Moreover, it is unlikely that the multiple important physical parameters inside the proton battery stack can be measured accurately and simultaneously. At present, external or single measurements represent the bottleneck, yet the multiple important physical parameters (oxygen, hydrogen, voltage, current, temperature, flow, and humidity) are interrelated and have a significant impact on the performance, life, and safety of the proton battery stack. This research uses micro-electro-mechanical systems (MEMS) technology to develop a micro oxygen sensor and integrates the six-in-one microsensor that our R&D team previously developed in order to improve sensor output and facilitate overall operation by redesigning the incremental mask and having this co-operate with a flexible board for sensor back-end integration, completing the development of a flexible seven-in-one (oxygen, hydrogen, voltage, current, temperature, flow, and humidity) microsensor. Full article

The main purpose of this study is to carry out the immediate micro-monitoring of the roll-to-roll (R2R) process of polarizing films. Therefore, a self-made flexible three-in-one (temperature, humidity, and flow) microsensor is developed. The temperature and flow sensing area are 585 μm × 450 μm, the humidity sensing area is 1065 μm × 1035 μm, and the minimum line width is 15 μm. The micro-electro-mechanical systems (MEMS) technology was applied to integrate temperature, humidity, and flow sensors on a 50 µm thick polyimide substrate. A 100 Å thick chromium (Chrome, Cr) section form the adhesion layer. A 1000 Å thick gold section forms the sensing layer. A self-made flexible three-in-one microsensor set up in a laboratory oven for immediate micro-monitoring of the R2R process of the polarizing film. Since it is not advisable to set up signal lines in a clean room, the analog signals of the sensor should be transmitted via wireless means. Thus, a monitoring module should be connected to the back end of the self-made flexible three-in-one microsensor to receive the analog signals of the sensor, convert them into digital signals, send them out in the form of wireless signals, and store the data on the server-side. Through these measures, both the R2R process and yield can be improved. Therefore, the focus of this study is the environmental monitoring of drying process ovens. However, commercially available all-in-one sensors cannot handle the temperature of high-temperature factory ovens, and commercial flow sensors are rarely used in high-temperature applications. Some are also expensive and cannot be widely distributed, so this study intends to develop an integrated sensor to measure the internal environment of the drying oven. Full article

Ionic conductive hydrogels used as flexible wearable sensor devices have attracted considerable attention because of their easy preparation, biocompatibility, and macro/micro mechanosensitive properties. However, developing an integrated conductive hydrogel that combines high mechanical stability, strong adhesion, and excellent mechanosensitive properties to meet practical requirements remains a great challenge owing to the incompatibility of properties. Herein, we prepare a multifunctional ionic conductive hydrogel by introducing high-modulus bacterial cellulose (BC) to form the skeleton of double networks, which exhibit great mechanical properties in both tensile (83.4 kPa, 1235.9% strain) and compressive (207.2 kPa, 79.9% strain) stress–strain tests. Besides, the fabricated hydrogels containing high-concentration Ca²⁺ show excellent anti-freezing (high ionic conductivities of 1.92 and 0.36 S/m at room temperature and −35 ${}^{\circ }$C, respectively) properties. Furthermore, the sensing mechanism based on the conductive units and applied voltage are investigated to the benefit of the practical applications of prepared hydrogels. Therefore, the designed and fabricated hydrogels provide a novel strategy and can serve as candidates in the fields of sensors, ionic skins, and soft robots. Full article

Laser-induced graphene (LIG) films and their derivatives have been regarded as one of the most outstanding functional flexible electrodes in the past decade, which will transform society and enable new devices and developments. The aim of this Special Issue is to provide a scientific platform for scholars in the LIG field to present their recent research towards a deeper understanding of forming mechanism, structure/ morphology, properties and behaviors of LIG films. This Special Issue gives readers the possibility to gain new insights into the applications of LIG films in flexible electronics, including mechanical/temperature/gas/electrochemical sensors, micro-supercapacitors, actuators, electrocatalysis, solid-state triboelectric nanogenerators, Joule heater, etc. We believe that the papers published in this Special Issue will provide a useful guidance for the manufacturing of nanostructured LIG electrodes in flexible electronics. Full article

The reactions of vanadium redox flow batteries (VRFBs) are quite complex and the internal environment is strongly acidic. The internal voltage, current, temperature and flow distribution play a very important role in the performance of a VRFB. The VRFB, which was developed by our R&D team, encountered easy leakage of electrolytes during assembly. Additionally, the strongly acidic environment can easily cause aging or failure of these VRFBs and of the micro-sensor. Therefore, this research was aimed at the need for real-time micro-diagnosis inside the VRFB. The use of micro-electro-mechanical systems (MEMS) technology was proposed so as to develop a flexible, integrated (current, voltage, flow and temperature), micro-sensor, and a durability test was conducted after packaging. Further, we performed real-time monitoring of the VRFBs. The main finding was that the encapsulation contributed to the stability of the micro-sensor without any failure due to excessive flow impacting the sensor. In the end we successfully used a 3D printed package to protect the micro-sensor. Full article

The high-pressure proton exchange membrane water electrolyzer (PEMWE) used for hydrogen production requires a high-operating voltage, which easily accelerates the decomposition of hydrogen molecules, resulting in the aging or failure of the high-pressure PEMWE. As the high-pressure PEMWE ages internally, uneven flow distribution can lead to large temperature differences, reduced current density, flow plate corrosion, and carbon paper cracking. In this study, a new type of micro hydrogen sensor is developed with integrated flexible seven-in-one (voltage; current; temperature; humidity; flow; pressure; and hydrogen) microsensors. Full article

Bismuth telluride-based thin films have been investigated as the active material in flexible and micro thermoelectric generators (TEGs) for near room-temperature energy harvesting applications. The latter is a class of compact printed circuit board compatible devices conceptualized for operation at low-temperature gradients to generate power for wireless sensor nodes (WSNs), the fundamental units of the Internet-of-Things (IoT). CMOS and MEMS compatible micro-TEGs require thin films that can be integrated into the fabrication flow without compromising their thermoelectric properties. We present results on the thermoelectric properties of (Bi,Sb)₂(Se,Te)₃ thin films deposited via thermal evaporation of ternary compound pellets on four-inch SiO₂ substrates at room temperature. Thin-film compositions and post-deposition annealing parameters are optimized to achieve power factors of 2.75 mW m⁻¹ K⁻² and 0.59 mW m⁻¹ K⁻² for p-type and n-type thin films. The measurement setup is optimized to characterize the thin-film properties accurately. Thin-film adhesion is further tested and optimized on several substrates. Successful lift-off of p-type and n-type thin films is completed on the same wafer to create thermocouple patterns as per the target device design proving compatibility with the standard MEMS fabrication process. Full article