A By-Pass Sensor Package Design Enabling the Use of Microfluidics in High Flow Rate Applications

Abstract

The package design for microfluidic sensors is discussed. The MicroElectroMechanical Systems (MEMS) device covered in this paper requires a fluidic and electrical interface as well as vacuum packaging of the sensing element. By using a by-pass package design the limitations of low flow rate and high pressure drop often encountered with microfluidic products can be avoided. The MEMS device utilizes a resonating silicon microtube that is electrostatically driven and capacitively sensed. A platinum RTD is also integrated into the MEMS chip. To improve the Q of the resonator a thin-film getter has been integrated to lower the microcavity pressure. The microfluidic packaging technology lends itself to producing densitometers, chemical concentration meters and Coriolis mass flow sensors. The device has been applied to fuel cell concentration sensors for embedded Direct Methanol Fuel Cell (DMFC) systems. The DMFC systems require a methanol sensor to minimize crossover and hence optimize the water/methanol concentration over temperature and the life of the product. Other high flow rate applications include ethanol/gasoline concentration sensors for E85 vehicles and dialysis fluid monitoring. A microfluidic Coriolis mass flow sensor has been developed and applied to drug delivery to monitor the drug dose, total volume infused, drug type and concentration. Chemical and temperature compatibility of the MEMS chip and packaging materials must be considered when dealing with this wide range of applications and will be discussed in the paper.