Integrating sensors and electronics - New challenges for silicon

The integration of sensors with signal-processing systems offers striking advantages over older discrete-sensor, hybrid-system approaches. Carrier-domain magnetometers are examples of sensors that can be built without modifying conventional silicon planar processing. These devices offer remarkable sensitivity, linearity, and versatility for magnetic sensing. Extensions of conventional IC technology, such as anisotropic etching of silicon single crystals to produce micromechanical structures, greatly enlarge possibilities for the development of integrated sensors. A very promising new approach is to use polycrystalline silicon as a mechanical material and to form microstructures using oxide etching-- thus avoiding anisotropic etches. This technology is employed to construct a vibrating-beam vapor sensor in which a microbeam is mechanically resonated by electrical excitation. Active thin films which function as stress transducers (through the piezoelectric effect), or as heat sensors (through the pyroelectric effect) can also be fabricated together with silicon ICs. Examples of this technology include a sensitive cantilever accelerometer (employing the piezoelectric effect) and a single-chip flow sensor (using the pyroelectric effect) in thin films on chip with NMOS ICs. RF sputtering in a reactive atmosphere provides highly oriented ZnO films for these applications.