Thick film accelerometers in LTCC-technology - Design optimization, fabrication, and characterization

State of the art in mechanical elements of MEMS in LTCC-technology are diaphragms and beams, e.g. for force and pressure sensors. These elements perform small strains and small deformations under loads. However a lot of sensor and actuator applications require movable elements that allow higher deformations whereas the local strains are still low. Such applications are e.g. springs, accelerometers, actuators, positioners, and valves. For an accelerometer the authors developed an approach for the fabrication of leaf springs integrated into the LTCC technology. The working principle of the accelerometer is based on a seismic mass disposed on two parallel leaf springs which carry piezoresistors connected to form a measuring bridge. In a first design optimization step, the authors used a FEA model for finding an optimized design conforming to the sensitivity requirements, inclusive of resonance frequency. In a second step, the authors performed a tolerance analysis that calculates the probability distributions of functional variables from the probability distributions of the design parameters. This enables the probability of a system failure to be deduced. In a final design step, a design of the ceramic thick film accelerometer was calculated that minimizes the system failure propability. As a result the authors obtained a design optimized with concern to a set of functional requirements and design tolerances. The results of the computations using the FEA models were compared to results of measurement data acquired from prototypes of the accelerometer.