1 - Introduction

Advanced technologies enabled not only miniaturization and integration, but the improvement of reliability and low-cost mass production. The former area needs low-cost sensors, and the latter one requires high-reliability types. The great technical possibilities and the relatively low cost of microprocessor-based systems have also turned the most important requirements into other directions. A few years ago, properties conventionally expected were as follows: good linearity, small hysteresis, small offset, low temperature drift, low interference effects, good interchangeability, good long-term stability and reliability Among these requirements, only the last one should be assured nowadays, but even this can be missed in some cases. Linearity and other errors can be compensated or handled using microprocessor-based systems and additional sensors (e.g., temperature sensors for temperature compensation). On the other hand, the most important new requirements are as follows:

• low cost,
• physical compatibility with IC and packaging/interconnection technologies in order to be able to integrate
sensors into arrays, as well as together with signal-processing units,
• electrical compatibility with microprocessors: it is desirable to provide digital or pseudo digital output,
• increasing demand on multifunction sensors and integrated sensor arrays because of the necessity for compensating interference effects.