Comparative Study of Thin-Film-Based Planar and Vertical Devices Towards Isopropyl Alcohol Sensing

Abstract

The influence of the electrode position in devices based on nanocrystalline TiO2 thin film for sensing of isopropyl alcohol has been investigated. Two types of device structure, viz. planar and vertical, with similar dimensions (length and width) were fabricated, employing Al metal electrodes. Both sensors were tested in the concentration range from 20 ppm to 400 ppm in the temperature range of 50°C to 200°C. The comparative study revealed that both sensors (planar and vertical) exhibited an optimum operating temperature of 150°C, with an optimum response of 77% and 33.08%, respectively. The response time and recovery time were found to be faster for the vertical device compared with its planar counterpart. The dissimilar sensor response of the planar and vertical devices can be understood based on the surface states and interface kinetics of the TiO2 sensing layer. An electrical model describing the modulation of the barrier height, the effect of grain boundaries (GBs), and carrier trapping at interface states at GBs was applied to understand the response time and recovery time.