Electrical Characterization of Semiconductor Oxide-Based Gas Sensors Using Impedance Spectroscopy: A Review

F. SCHIPANI; D. R. MILLER; M. A. PONCE; C. M. ALDAO; S. A. AKBAR; P. A. MORRIS

Reviews in Advanced Sciences and Engineering

American Scientific Publishers

Lugar: Valencia; Año: 2016 vol. 5 p. 86 - 105

Impedance spectroscopy is essential in understanding the physical and chemical processes that affect the electronic behavior of semiconducting metal oxide-based gas sensor materials, but is often overlooked or avoided by researchers because of the complexity of proper data interpretation. These metal oxide nanomaterials are promising as resistive-type gas sensors because they have the potential to meet the critical need that has developed for low-power, low-cost, portable gas sensors. However, the mechanisms that determine these materials? gas-sensing performance is still not understood well enough to advance the field toward bottom-up design for specific applications. Direct current (DC) measurements give information on the device performance such as sensitivity, selectivity and response time. Alternating current (AC) measurements are a lesser-used approach that can give the same information, but also allow the varying contributions from the bulk, surfaces and interfaces, grain boundaries, electrode contacts and even substrate to be quantified, whether we work with polycrystalline materials or single-crystal structures such as nanowires and nanorods. With this technique it is possible to extract fundamental information about intergranular potential energy barrier height, width and dono concentration changes in different atmospheres and temperatures. The equivalent circuit method is the most common method of relating the impedance data to the physical system. However, the main weakness of this method is that the ideal circuit elements used in the fitting can be connected in many different ways to fit the same signal. To properly apply this technique, the model development should consider both the impedance measurement and the physical and chemical characteristics of the system being studied. This review presents a detailed description of impedance spectroscopy techniques for fundamental analysis of materials behavior in gas sensing applications, including proper data interpretation and types of fitting models commonly used, to enable researchers to better apply these techniques toward understanding of their materials systems.