TABLE OF CONTENTS Sensing is by no means a modern invention. There are numerous historical accounts describing the measurement of physical parameters most notably, distance, weight, time, and temperature. Early Chinese attempts at making compasses date back to the twelfth century with the use of lodestone, a naturally occurring magnetic ore. Modern sensing methods derive their utility from the wealth of scientific knowledge accumulated over the past two centuries. We owe our intimate familiarity with electrostatics and capacitance to the work of Charles Augustin de Coulomb of France and John Priestly of England in the late eighteenth century and observe that Lord Kelvin's discovery of piezoresistivity in 1856 is recent in historical terms. What distinguishes these modern techniques is the ability to sense with greater accuracy and stability; what makes them suitable for MEMS is their scalable functionality.
The objective of modern sensing is the transducing of a specific physical parameter, to the exclusion of other interfering parameters, into electrical energy. Occasionally, an intermediate conversion step takes place. For example, pressure or acceleration are converted into mechanical stress, which is then converted to electricity. Infrared radiation in image sensors is often converted into heat and then sensed as an electrical voltage or a change in electrical resistance. Perhaps the most common of all modern sensing techniques is temperature measurement using the dependence of various material properties on temperature. This effect is pronounced in the electrical resistance of metals. The rate at which the resistance rises with...
