Micromachined Vlsi-Compatible Sensors.

Usually a silicon substrate contains circuitry alone. The special attributes of small micromachined sensors use the substrate as a mechanical material, providing sensor circuitry and packaging in one co-fabricated unit. This research concerns silicon microchip pressure sensors on ultrathin polymer films. In this flexible technology, wafer substrates have their circuitry completed by the usual IC fabrication techniques, as well as appropriate mechanical etching for the sensor. The wafer bears a polymer coating and is etched into discreet islands. The lead wires, which connect the individual elements on the islands to each other and to the outside world, are totally encapsulated (a co-fabricated micro-ribbon cable). Together with the sensing elements they provide a flexible multipurpose sensor assembly. These solid state sensors offer cost effective batch fabrication processes, reducing costs while achieving a high degree of uniformity. Additionally, conformal silicon -based sensors offer advantages in size, robustness and customizing. Two types have been investigated: piezoresistive diaphragm structures and planar pressure sensitive capacitors. Both are compatible with NMOS and CMOS VLSI fabrication processes and offer either single elements or flexible conformable arrays. In the course of this research, which was initially directed toward the development of improved robotic tactile sensors, it has become evident that the technology used to produce these sensors has a far greater range of applications. Some of those directed toward composite technology, acoustics, optics and microwaves will be discussed. Also reported is the investigation of material properties and technologies necessary to change typically specified device films into those suitable for micromechanical work.