A flow sensor capable of measuring flow rate, fluid type, fluid pressure, fluid presence, and flow direction has been demonstrated. This research activity demonstrates a very simple cap fabrication and assembly process that enabled the realization of a flow sensor with multiple sensing capabilities. A surface micromachined process is employed to fabricate the pressure sensors as well as the cap that defines the fluid channel. The sensor was configured in a way to successfully demonstrate two differential pressure sensing modes (i.e. sensors within the cavity and sensors in the flow channel). Both flow rate and viscosity measurements are based on the differential pressure sensing principle. Fluid presence is determined using an interdigitated structure which can also sense the fluid type based on permittivity of the fluid. The flow rate measured successfully has been as low as 0.01 ml/hr and showed very good linearity when compared to the theoretical model. The diameter of the pressure sensor diaphragm utilized was as low as 100 microns and depended on the flow rate required to measure.

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This paper examines the engineering challenges created by integrated surface micromachining, which is the combination of MEMS and electronics on the same silicon substrate. It then goes on to explore the future trends in this area from both the technical challenges as well as an applications and business perspective. The low level signals that are detectable and processed make dimensional changes in the nanometer range a common aspect of this technology. The mechanical engineer is faced with structures that have millimeter dimensions with deflections from 10 nanometers to subnanometer ranges. It is therefore possible to sense acceleration, magnetic forces, and acoustic energy as well as steer light in a fully intergrated system on a chip. The applications from a technical perspective seem endless however the need to develop both a process and a product make the time to market a significant consideration. The paper concludes by highlighting promising areas such as communications, displays, and sensing, for future development from both a technical and business perspective.

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