CMOS Skin Sensor for Mobile Skin Diagnosis Using an Electronic Cotton Pad

This paper presents a complementary metal-oxide semiconductor (CMOS) skin sensor for detecting hydration, sebum, and ultraviolet (UV) protection. This sensor employs pixels comprising interdigitated capacitors (IDCs) for detecting hydration and a 30 x 24 photodiode (PD) array for detecting UV protection and sebum. The 4 x 8 pixels with IDCs over the PDs are used for area efficiency; they afford reliable detection regardless of the skin contact area and a high sensitivity, which is achieved via pixel merging. For the readout of both IDCs and PDs, a column-parallel multiple-sampling analog front-end and a 9b successive approximation register analog-to-digital converter are integrated. To detect UV protection under different wavelengths of UVA and UVB, we implement the spatiotemporal delta readout of the PDs. Furthermore, a fully characterized, proof-of-concept prototype chip is fabricated using a 110-nm CMOS process. Compared with conventional skin sensors, the proposed sensor exhibits higher sensitivities of 0.25%/min and 2.32%/mL in detecting dehydration rate and sebum levels, respectively. Moreover, the sensor can detect UV protection under UVA and UVB wavelengths. Owing to its core size of 2.32 x 4.65 mm(2), the proposed sensor can potentially be integrated into cotton pads for mobile skin diagnosis

Low Temperature Combustion Processed Stable Al Doped ZnO Thin Film Transistor: Process Extendable up to Flexible Devices

We report combustion synthesis of polycrystalline Aluminium doped zinc oxide (AZO) at low temperature for next generation low cost, flexible thin film transistor (TFT) application. Solution processed AZO thin film has been characterized by X ray diffraction and atomic force microscopy to confirm crystallinity. In this research work TFT with solution processed AZO as channel layer has been fabricated on both rigid and flexible substrate which exhibits excellent electrical stability and improved field effect mobility of 1.2 cm2V-1S-1, threshold voltage of 15 V and on-off ratio of 106 as compared to pure ZnO based TFT. All the measurements have been carried out with varying Al concentration. Moreover, variation in defect density of AZO with Al concentration which essentially causes significant change in TFT’s performance is demonstrated by chemical composition and bonding state analysis using XPS. Our results suggest that low temperature solution processed AZO TFTs have a potential for low cost, flexible and transparent electronic applications

Whey Protein Isolate Film and Laser-Ablated Textured PDMS-Based Single-Electrode Triboelectric Nanogenerator for Pressure-Sensor Application

The use of biopolymers for realizing economical and eco-friendly triboelectric nanogenerators (TENGs) widens the application prospects of TENGs. Herein, an animal-sourced whey protein isolate (WPI) film, processed and prepared by a simple aqueous solution preparation and drop-casting technique, is applied to demonstrate its potential use in bio-TENGs. With the addition of formaldehyde in WPI, the films result in a free-standing and flexible film, whereas the pure WPI films are difficult to handle and lack flexibility. A TENG device based on the WPI and the laser-ablated textured polydimethylsiloxane (PDMS) for pressure-sensor application were developed. The output voltage of the TENG comprising WPI increased nearly two-fold compared to the TENG without WPI. A simple single-electrode TENG device configuration was adopted so that it could be easily integrated into a wearable electronic device. Moreover, WPI film exhibited tribo-negative-like material characteristics. This study provides new insights into the development of biocompatible and eco-friendly biopolymers for various electronic devices and sensors

Sub-Zero Temperature Sensor Based on Laser-Written Carbon

Sub-zero temperature sensors (SZTSs) have potential applications in safely storing COVID-19 vaccines. Herein, an SZTS based on laser-induced carbonization (LIC) achieved by a nanosecond infrared laser with a wavelength of 1064 nm is reported. Direct laser writing is adopted for laser-induced carbon in Kapton polyimide sheets with a thickness of 125 µm. The sensor exhibits a good linear change in resistance to sub-zero temperatures ranging from 0 to −150 °C, where the coefficient of determination adjusted R-square (R2) value is 0.99238, which indicates a good linear fit. The sensor exhibits a stable static response at all temperatures over time. The dynamic responses by controlling the liquid nitrogen gas and placing an ice cube on the sensor are also measured to validate the sensor. Notably, the electrical performance of the sensor remains stable even after 15 h. The sensor response of the LIC sample validates the 3D variable range-hopping charge transport mechanism, governed by the Mott equation with a good linear fit, which is mainly owing to disorder in its structure. LIC-based SZTSs can enable sensors that are ultra-fast to fabricate, roll-to-roll processable, economical, and more significantly, can be interfaced with flexible printed circuit boards without any additional interfacing. © 2022 Wiley-VCH GmbHFALS

Transparent and Flexible Copper Iodide Resistive Memories Processed with a Dissolution-Recrystallization Solution Technique

Copyright © 2022 American Chemical Society. This study explores a class of resistive memory candidates -simple binary halides -and demonstrates their efficacy in switching between high-and low-resistive states. Herein, copper halide, particularly copper iodide (CuI), is investigated for its resistive switching efficacy when sandwiched between indium tin oxide (ITO) and silver electrodes on flexible polyethylene terephthalate (PET) substrates. CuI is deposited on ITO-coated PET using an innovative dissolution-recrystallization technique, in which a deposition temperature of 80 & DEG;C is sufficient to eliminate the carrier solvent-acetonitrile-and impart considerable densification of CuI for effective memory characteristics. The PET/ ITO/CuI is transparent (> 90%), and the PET//ITO/CuI/Ag devices display states of notably low-and high-resistive states with a ratio of more than 10 within a voltage biasing range of -2.5 to +2.5 V. Additionally, the devices exhibit similar resistive states under bending stress. Halides (in particular, CuI) are, thus, introduced as a class of active materials for transparent and flexible resistive memories.11Nsciescopu

Highly Exfoliated MWNT–rGO Ink-Wrapped Polyurethane Foam for Piezoresistive Pressure Sensor Applications

The fabrication of pressure sensors based on reduced graphene oxide (rGO) as the sensing material is challenging due to the intrinsic hydrophobic behavior of graphene oxide inks as well as the agglomeration of graphene oxide flakes after reduction. Hydrazine (a reducing agent) and a dual-component additive comprising benzisothiazolinone and methylisothiazolinone in appropriate proportion were used to synthesize a rGO ink with a hydrophilic nature. Utilizing this hydrophilic rGO ink mixed with multiwalled carbon nanotubes (MWNTs), a very simple, low-cost approach is demonstrated for the fabrication of a pressure sensor based on polyurethane (PU) foam coated with the MWNT–rGO ink (MWNT–rGO@PU foam). The MWNT–rGO@PU foam-based devices are shown to be versatile pressure sensors with the potential to detect both small-scale and large-scale movements. At low pressure (below 2.7 kPa, 50% strain), the formation of microcracks that scatter electrical charges results in a detectable increase in resistance suitable for detecting small-scale motion. At a higher pressure, the compressive contact of the coated faces of the PU foam results in a sharp decrease in resistance suitable for monitoring of large-scale motion. Moreover, these sensors exhibit good flexibility and reproducibility over 5000 cycles. The versatility of this sensor has been demonstrated in a wide range of applications, such as speech recognition, health monitoring, and body motion detection. The significant advantages of this sensor are that its cost is low, it is easy to fabricate, and it has a versatility that renders it favorable to health-monitoring applications

Highly Exfoliated MWNT–rGO Ink-Wrapped Polyurethane Foam for Piezoresistive Pressure Sensor Applications

The fabrication of pressure sensors based on reduced graphene oxide (rGO) as the sensing material is challenging due to the intrinsic hydrophobic behavior of graphene oxide inks as well as the agglomeration of graphene oxide flakes after reduction. Hydrazine (a reducing agent) and a dual-component additive comprising benzisothiazolinone and methylisothiazolinone in appropriate proportion were used to synthesize a rGO ink with a hydrophilic nature. Utilizing this hydrophilic rGO ink mixed with multiwalled carbon nanotubes (MWNTs), a very simple, low-cost approach is demonstrated for the fabrication of a pressure sensor based on polyurethane (PU) foam coated with the MWNT–rGO ink (MWNT–rGO@PU foam). The MWNT–rGO@PU foam-based devices are shown to be versatile pressure sensors with the potential to detect both small-scale and large-scale movements. At low pressure (below 2.7 kPa, 50% strain), the formation of microcracks that scatter electrical charges results in a detectable increase in resistance suitable for detecting small-scale motion. At a higher pressure, the compressive contact of the coated faces of the PU foam results in a sharp decrease in resistance suitable for monitoring of large-scale motion. Moreover, these sensors exhibit good flexibility and reproducibility over 5000 cycles. The versatility of this sensor has been demonstrated in a wide range of applications, such as speech recognition, health monitoring, and body motion detection. The significant advantages of this sensor are that its cost is low, it is easy to fabricate, and it has a versatility that renders it favorable to health-monitoring applications

Laser-Processed Nature-Inspired Deformable Structures for Breathable and Reusable Electrophysiological Sensors toward Controllable Home Electronic Appliances and Psychophysiological Stress Monitoring

Physiological monitoring through skin patch stretchable devices has received extensive attention because of their significant findings in many human-machine interaction applications. In this paper, we present novel nature-inspired, kiri-spider, serpentine structural designs to sustain mechanical deformations under complex stress environments. Strain-free mechanical structures involving stable high areal coverage (spiderweb), three-dimensional out-of-plane deformations (kirigami), and two-dimensional (2D) stretchable (2D spring) electrodes demonstrated high levels of mechanical loading under various strains, which were verified through theoretical and experimental studies. Alternative to conventional microfabrication procedures, sensors fabricated by a facile and rapid benchtop programmable laser machine enabled the realization of low-cost, high-throughput manufacture, followed by transferring procedures with a nearly 100% yield. For the first time, we demonstrated laser-processed thin (10 μm) flexible filamentary patterns embedded within the solution-processed polyimide to make it compatible with current flexible printed circuit board electronics. A patch-based sensor with thin, breathable, and sticky nature exhibited remarkable water permeability >20 g h-1 m-2 at a thickness of 250 μm. Moreover, the reusability of the sensor patch demonstrated the significance of our patch-based electrophysiological sensor. Furthermore, this wearable sensor was successfully implemented to control human-machine interfaces to operate home electronic appliances and monitor mental stress in a pilot study. These advances in novel mechanical architectures with good sensing performances provide new opportunities in wearable smart sensors. © 2019 American Chemical Society.FALS