ROMJIST Volume 23, No. 1, 2020, pp. 93-104
Bogdan Catalin SERBAN, Octavian BUIU, Nicolae DUMBRAVESCU, Cornel COBIANU, Viorel AVRAMESCU, Mihai BREZEANU, Marius BUMBAC, Cristina Mihaela NICOLESCU Optimization of Sensing Layers Selection Process for Relative Humidity Sensors
ABSTRACT: Electronic devices designed for environmental monitoring have gained an increasing importance in the last years. Parameters such as relative humidity (RH), temperature, pressure, acceleration and speed, measured by devices such as RH, temperature, pressure, and motion sensors, are at the core of the efforts for improving the environmental conditions. The employment of such devices in complex sensing systems enable their use in IoT (Internet of Things) applications, which is of paramount importance for an in-time and appropriate reaction to adverse environmental phenomena. Given all these, the need to design sensors with improved sensing performance, such high sensitivity, reduced cross-sensitivity and low response time, emerges. The aim of this paper is to introduce the Hard-Soft Acid Base (HSAB) concept as a valuable investigative tool to explain, to a certain extent, the increased sensitivity and selectivity experimentally demonstrated by different used metal oxides (MOX) and their nanocomposites to relative humidity. Based on literature data, six different case-studies of RH detection by sensing layers employing metal oxides and related composites, are highlighted and investigated in terms of HSAB theory. To support the thesis that the HSAB principle can be a useful criterion and can be taken in account when either selecting a suitable gas sensing layer (in particular, for RH detection) or optimizing his functional response, we will build our argumentation on three reasons: 1) strong RH detection capabilities of MOX layers classified as hard acids according to the HSAB theory; 2) strong ethanol, ammonia and trimethylamine detection capabilities of MOX layers classified as hard acids; 3) the significant role played by dopants classified as hard acids in the performance of MOX-based RH sensing layers.KEYWORDS: Humidity Sensor, Metal Oxide, Hard Soft Acid BaseRead full text (pdf)