Chapter 13: Nonlinear Resistors

1 INTRODUCTION

In the previous chapters we examined resistive components whose mechanical and electrical properties must remain stable during operation. To avoid degrading the performance of the electronic circuits in which they are used, it is important that changes in nominal resistance due to thermal, electrical, mechanical, and chemical factors, as well as humidity, be kept to a minimum. The techniques and materials used to satisfy this condition have already been discussed.

The introduction of signal measurement and processing technologies resulted in a demand for new components designed to measure and interact with physical parameters such as temperature and pressure, the concentration and composition of gas mixtures, and changes in voltage. A large number of these components are based on measurements of changes in resistance as a function of these parameters. To achieve the highest possible sensitivity, researchers have continued to develop materials in which conductivity variation as a function of the magnitude of the physical phenomena being measured is maximized. This approach is therefore antithetical to that used in the development of conventional resistors. In addition, the materials used must also satisfy certain criteria of selectivity. A component intended to measure the concentration of carbon dioxide gas should not be sensitive to any phenomena other than those being measured.

This chapter describes such components, which are referred to as nonlinear resistive sensors. For each type of sensor, the following elements will be described and analyzed: properties of the materials used, fabrication technologies, and applications. Among the many kinds...