Kim K.-H., Jahan S. A., Kabir E. (2013) A review on human health perspective of air pollution with respect to allergies and asthma.

Self-powered sensors can lead to disruptive advances in self-sustainable sensing systems that are imperative for evolving human lifestyles. For the first time, we demonstrate the fabrication of a heterojunction sensor using p-type hybrid-halide perovskites (CH3NH3PbBr3) and an n-type semiconducting metal oxide thin film [InGaZnO (IGZO)] for the detection of NO2 gas and power generation. Combining the excellent photoelectric properties of perovskites and the remarkable gas-sensing properties of IGZO at room temperature, the devised sensors generate open-circuit voltage and modulate according to the ambient NO2 concentration. The major challenge in devising self-powered gas sensors is to attain harvesting capability and selectivity simultaneously, owing to perovskites reactivity in the presence of oxygen and humidity. In this work, we developed a novel approach and fabricated a heterojunction sensor using parylene-c as an additional layer to curb the cross-sensitivity and to enhance the selectivity of the sensor. Even under the low concentrations of NO2, the developed sensor exhibits remarkable sensitivity, selectivity, and repeatability. The devices are sensitive and robust even under extreme humidity conditions (80% RH) and synthetic air. The devised sensor configuration is one way to eliminate the cross-sensitivity issue of the perovskite-based devices and serves as a reference for the development of self-powered sensors.

Highly Selective Self-Powered Organic-Inorganic Hybrid Heterojunction of a Halide Perovskite and InGaZnO NO2 Sensor.


 This study uses acetylacetone (acac) as an additive to control the size of the nanostructure of solution-processed a-IGZO for ozone (O3) gas sensor applications. It is found that by adding acac, the gas response, response time, and recovery time of an IGZO gas sensor are highly improved. Under the optimal condition (4 wt%), the IGZO sensor shows a gas response of 19 and a response/recovery time of 80/120 s, against 5 ppm O3. Adding acac significantly increases the number of oxygen vacancies within an a-IGZO film so more electrons are available for reaction with the gas. The increased number of oxygen vacancies means that more dangling bonds are created, which activates the gas adsorption process. Moreover, the IGZO gas sensor has an excellent long-term stability showing negligible variation in gas response over 2 months. This method allows easy fabrication of a high-performance gas sensor that uses solution-processed a-IGZO as a sensing layer.

Increasing the Gas Response of Ozone Sensors Based on Solution-Processed InGaZnO by Tuning the Size of the Nanostructure

We investigate the effects of postdeposition annealing (PDA) ambience on the nitrogen dioxide (NO2) gas sensing performance in the Si-based field-effect transistor (FET)-type gas sensor having an indium–gallium–zinc oxide (IGZO) as a sensing material. After the IGZO thin films are deposited, the sensors are postannealed in vacuum and atmospheric ambiences. The content of oxygen vacancy in IGZO films varies depending on the PDA ambience, which changes the electrical properties and NO2 gas sensing performance of the sensors. The sensor postannealed in a vacuum ambience has more oxygen vacancy, which acts as an electrical donor, than that in an atmospheric ambience. Thus, the former has a larger coupling ratio and transconductance of the FET transducer. Also, the oxygen vacancy produces negatively charged oxygen species, increasing the response to NO2. Due to a larger response to NO2 gas and low noise, the sensor postannealed in a vacuum shows excellent signal-to-noise ratio (SNR) and limit-of-detection performances.

Effects of Postdeposition Annealing Ambience on NO2 Gas Sensing Performance in Si-Based FET-Type Gas Sensor

Theoretical Study of NO2, H2O, and CO2 Gases Adsorbed on SnO2-GeSe Monolayer

Semiconducting metal oxide gas sensors that are inexpensive, room temperature operable are imperative for toxic gas and air pollution monitoring. The heating or continuous light activation requirements are unavoidable for these types of gas sensors. This paper reports for the first time a room temperature operable solution-processed In-Ga-Zn-O thin-film transistor (TFT) gas sensor to detect NO2 without continuous light activation. The TFT sensor exhibits promising sensing and selectivity towards NO2. The devices are re-generable and require light activation only to recover after exposure to the gas. Kelvin probe force microscopy characterization studies are performed to understand in detail the sensing mechanism of the solution-processed TFT device. A novel solution-processed TFT based gas-sensitive digital indicators that yield digital output quantifying the NO2 concentration are demonstrated. One of the integrated gas-sensitive digital indicators is developed using only two InGaZnO TFTs incorporating a signal conditioning circuit and analog to digital converter. Furthermore, it paves the way for portable, compact, and inexpensive systems for various gas sensing applications, including smart cities and sustainable ecosystems.

Towards a low cost fully integrated IGZO TFT NO2 detection and quantification: A solution-processed approach

Bottom-gate bottom contact amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) were fabricated using solution processing. The nonpassivated a-IGZO-TFTs exhibited a significant threshold voltage shift, large hysteresis in the current–voltage characteristics, and degradation in the subthreshold swing. TFTs’ performance degradation is due to the interaction of its back channel with adsorbed oxygen and water molecules in the ambient air. The hydroxy-phenyl zinc porphyrin (ZnP) self-assembled monolayer (SAM) was formed on TFTs’ back channel using a low-cost solution-based approach to passivate TFTs back channel. The passivated a-IGZO-TFTs exhibited enhanced electrical characteristics and improved stability compared with nonpassivated TFTs. Passivated TFTs presented significantly reduced hysteresis up to 87% and subthreshold slope degradation up to 71%. The passivated TFTs showed excellent stability under positive (20 V) and negative (−20 V) bias stress conducted for 5000 s.

Passivation of Solution-Processed a-IGZO Thin-Film Transistor by Solution Processable Zinc Porphyrin Self-Assembled Monolayer

Metal oxide semiconductors proved their usability in environmental monitoring applications and are considered successful in detecting ionizing radiation. This work reports the feasibility of solution-processed metal oxide semiconductor thin-film transistors for radiation sensing for the first time. In particular, the effects of a wide range of gamma radiation (100Gy to 10kGy) on the performance of solution-processed amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) transistors are investigated. The current-voltage (IV) characterization (both output and transfer characteristics) of IGZO-TFTs before and after irradiation are obtained to study different parameters. The radiation-induced changes in TFT are mainly observed in the threshold voltage shift ( $\sf \Delta ~\text{V}_{th}$ ) and the increase of subthreshold swing. It is observed that up to a total dose of 1kGy, threshold voltage increases negatively ( $\sf \Delta \,\,\text{V}_{th}= -1.8\text{V}$ at 1 kGy), and beyond 1 kGy, threshold voltage increases positively ( $\Delta \,\,\text{V}_{\text{th}} =0.8\text{V}$ at 10 kGy). The XRD and AFM data of IGZO thin-film suggests minor structural and morphological changes after exposure to gamma irradiation. The corresponding sensitivity obtained with gamma irradiation is 27.78 mV/Gy (100Gy-1kGy), expressed in the threshold voltage shift. The effects of radiation-induced changes in TFTs are completely removed after storing irradiated TFTs in the vacuum at room temperature for 6 months.

Maruti B. Zalte

Papers

Towards a low cost fully integrated IGZO TFT NO2 detection and quantification: A solution-processed approach

Passivation of Solution-Processed a-IGZO Thin-Film Transistor by Solution Processable Zinc Porphyrin Self-Assembled Monolayer

A Solution Processed Amorphous InGaZnO Thin-Film Transistor-Based Dosimeter for Gamma-Ray Detection and Its Reliability