An ultralow power suspended gas sensor with in-plane heater and nano gap sensor electrodes is presented. The heater and sensing electrodes, separated by 1-μm air gap, are processed using single lithography step with standard micro-fabrication techniques. Controlled electromigration is used to create a nanogap in the middle of the sensing electrode. The sol-gel grown ZnO is dispensed using a picoliter dispenser to bridge the nanogap electrode, created by electromigration, to get required metal oxide film as a sensing element. The gap between the electrode and heater is optimized by electrothermal simulation to obtain desired temperature profile on ZnO. The resulting device exhibits excellent sensing performance for hydrogen (~86% at 20 ppm) at 0.5 mW. A detailed characterization was carried out to analyze the performance of the device. This unique, in-plane structure is superior compared with the conventional out of plane structure in terms of the power efficiency and ease of processing.

Semiconducting metal oxide gas sensors typically operate at a high temperature and consume hundreds of milliwatts of power. Therefore there is great demand for the development of a low-power gas-sensing technology that can sensitively and selectively detect the gas analytes present in the atmosphere. We report an ultralow-power nanosensor array platform, integrated with an independently controlled nanoheater of size 4 μ m × 100 nm, which consumes ∼1.8 mW power when operated continuously at 300 °C. The heaters exhibit a fast thermal response time of less than 1 μ s, and can be utilized to operate in duty cycle mode, leading to power saving. The active area of the nanosensor is 1 μ m × 200 nm, defined by sensing electrodes with a nanogap of ∼200nm, leading to small form factor. As a proof of concept, each of the sensing elements in the array is functionalized with different sensing materials to demonstrate a low-power, sensitive and selective multiplexed gas-sensing technology for the simultaneous detection of CO (∼93.2% for 3 ppm at 300 °C), CO ₂ (∼76.3% for 1000 ppm at 265 °C), NO ₂ (∼2301% for 3 ppm at 150 °C) and SO ₂ (∼94% for 3 ppm at 265 °C). The technology described here uses scalable crossbar architecture for sensor elements, thus enabling the integration of additional sensing materials and making it customizable for specific applications.

In this work, we report microwave-assisted deposition of NiO for application as room- temperature NO₂ sensor. The synthesis conditions are varied to arrive at the optimum film for sensing NO₂. The optimum NiO film shows response of 4991% at 3 ppm NO₂ at room temperature with short response and recovery times of 30 s and 45 s, respectively. X-ray diffraction reveals the cubic structure of the NiO film with slightly preferred orientation and scanning electron microscopy shows high porosity in the film, both contributing to the enhanced sensing performance. The microwave-synthesized NiO shows an order of magnitude stronger response to NO₂ (3 ppm) at room temperature operation than does optimized, DC-reactive-sputtered NiO operating at 175°C. To the best of our knowledge, this is the first report on room temperature detection of NO₂ by a microwave-synthesized NiO film. The detection limit of the NiO film is 200 ppb with good selectivity against interfering gases. The sensor demonstrates an ultra-low power consumption of 0.2 μW, making it suitable for solar-powered pollution-monitoring.

In this paper, we present a novel approach of fabricating a low-cost and low power gas sensor array on flexible acetate sheets for sensing CO, SO ₂ , H ₂ and NO ₂ gases. The array has four sensor elements with an integrated microheater which can be individually controlled enabling the monitoring of four gases. The thermal properties of the microheater characterized by IR imaging are presented. The microheater with an active area of 15 µ m × 5 µ m reaches a temperature of 300 °C, consuming 2 mW power, the lowest reported on flexible substrates. A sensing electrode is patterned on top of the microheater, and a nanogap (100 nm) is created by an electromigration process. This nanogap is bridged by four sensing materials doped with platinum, deposited using a solution dispensing technique. The sensing material characterization is completed using energy dispersive x-ray analysis. The sensing characteristics of ZnO for CO, V ₂ O ₅ for SO ₂ , SnO ₂ for H ₂ and WO ₃ for NO ₂ gases are studied at different microheater voltages. The sensing characteristics of ZnO at different bending angles is also studied, which shows that the microheater and the sensing material are intact without any breaking upto a bending angle of 20°. The ZnO CO sensor shows sensitivity of 146.2% at 1 ppm with good selectivity.

A elegant extremely flexible Fan-Out Wafer-Level Packaging (FOWLP) based fully integrated bipolar multi-channel (up to 12 channels) surface electromyography (sEMG) device and assembly is demonstrated for intraoperative neurological monitoring (IONM) for complex spine surgeries and post-op physiological monitoring. It includes twenty gold-capped vertically corrugated flexible dry copper electrodes, Bluetooth wireless data transfer, a multichannel sEMG data acquisition and processing dielet, rechargeable energy storage and an ergonomic reusable adhesive for ease of use. This completely biocompatible and wearable system is highly flexible, thin (1 mm), light weight (< 5 g) and can be used to monitor neuro-muscular activations for IONM as well as for general physiological monitoring.

In this work we report on plasma oxidation of palladium (Pd) to form reliable palladium/palladium oxide (Pd/PdO _x ) core–shell sensor for ppb level H ₂ S detection and its performance improvement through nanostructuring using hole-mask colloidal lithography (HCL). The plasma oxidation parameters and the sensor operating conditions are optimized to arrive at a sensor device with high sensitivity and repeatable response for H ₂ S. The plasma oxidized palladium/palladium oxide sensor shows a response of 43.1% at 3 ppm H ₂ S at the optimum operating temperature of 200 °C with response and recovery times of 24 s and 155 s, respectively. The limit of detection (LoD) of the plasma oxidised beam is 10 ppb. We further integrate HCL, a bottom-up and cost-effective process, to create nanodiscs of fixed diameter of 100 nm and varying heights (10, 15 and 20 nm) on 10 nm thin Pd beam which is subsequently plasma oxidized to improve the H ₂ S sensing characteristics. The nanostructured Pd/PdO _x sensor with nanodiscs of 100 nm diameter and 10 nm height shows an enhancement in sensing performance by 11.8% at same operating temperature and gas concentration. This nanostructured sensor also shows faster response and recovery times (15 s and 100 s, respectively) compared to the unstructured Pd/PdO _x counterpart together with an experimental LoD of 10 ppb and the estimated limit going all the way down to 2 ppb. Material characterization of the fabricated Pd/PdO _x sensors is done using UV–vis spectroscopy and x-ray photoemission spectroscopy.