A microfabricated electron‐tunneling accelerometer as a directional underwater acoustic sensor

Microfabricated accelerometers have been developed for a wide variety of applications; however, the principal commercial focus has been on signal detection in the milli‐g to tens or hundreds of g accelerations. The development of a microfabricated device to detect accelerations in the 10 to 100 nano‐g range is a substantial technological challenge because of the conflict between the required increase in mass (and reduction in suspension stiffness) and the small volume. In an underwater sensor, designed to be nearly neutrally buoyant, there are additional restrictions on the packaging of the sensor with regard to overall density, resistance to hydrostatic pressure, and flexibility of power and signal leads. The design goal of this project is to demonstrate a two‐axis sensor in an 8 cm3 (and 8 gram) package capable of immersion to 600 meters. The sensor must have a self noise below 100 nano‐g per root hertz from 5 to 1000 Hz. Several of these requirements have been demonstrated with an accelerometer structu...