Effects of pH on High-Performance ZnO Resistive Humidity Sensors Using One-Step Synthesis.

Zhang Zhang,Li Li,Yu Yu

doi:10.3390/s19235267

Abstract

In this paper, we prepared a high-performance zinc oxide (ZnO) humidity sensor in an alkaline environment using one-step hydrothermal method. Experiments showed that the pH value of the precursor solution affects the performance of ZnO humidity sensors. There are abundant hydroxyl group and oxygen vacancies on the surface of ZnO with a precursor pH value of 10. Abundant hydroxyl groups on the surface of ZnO can adsorb a large number of water molecules and rich oxygen vacancies can accelerate the decomposition of water molecules, thus increasing the number of conductive ions (H3O+) and further improving the performance of the sensor. So, such a ZnO humidity sensor exhibited high sensitivity (14,415), good linearity, small hysteresis (0.9%), fast response/recovery time (31/15 s) in the range from 11% to 95% relative humidity (RH). Moreover, the ZnO-2 humidity sensor has good repeatability and can be effectively used for a long time. This study provides a new idea for the development of low-cost, high-performance and reusable ZnO resistive humidity sensors.

Highlights

In recent years, humidity sensors have played an important role in the development of medical, food preservation, environmental monitoring, semiconductor, and other industries [1,2,3,4]
Sensitive materials are a major factor to improve the performance of humidity sensors due to their different chemical structures and special functions
zinc oxide (ZnO) has become widely studied as a nano-sensing material because it is plentiful and has controllable surface morphology, wide resistivity range, good chemical stability, and thermal stability [15,16]

Summary

Introduction

Humidity sensors have played an important role in the development of medical, food preservation, environmental monitoring, semiconductor, and other industries [1,2,3,4]. With the deepening of research, humidity sensors are required to meet special characteristics, such as high sensitivity, fast response/recovery speed, low hysteresis, and long-term stability [5,6,7]. Sensitive materials are a major factor to improve the performance of humidity sensors due to their different chemical structures and special functions. The development of sensitive materials has become a hot-spot to improve humidity sensitivity. Metal oxide semiconductor materials such as ZnO, TiO2 , CuO, and Al2 O3 are widely used for sensor development due to their simple fabrication, high sensing response, good operational stability, low cost, and good portability [12,13,14,15]. ZnO has become widely studied as a nano-sensing material because it is plentiful and has controllable surface morphology, wide resistivity range, good chemical stability, and thermal stability [15,16]

Methods

Results

Conclusion