A large number of solar cells is metallized by printing and firing glass containing silver pastes. However, the contact formation is not fully understood so far. There is still a lack of understanding the role of the glass phase in the complex contact formation scenario because single effects could not been seperatly observed and evaluated up to now. To overcome this, an in-situ method to observe the contact formation via a contact resistance measurement was introduced. A special measuring device was applied to characterize two typical front side pastes, featuring a PbO-containing as well as a PbO-free glass frit during firing. The viscosity of the paste glass showed decisive influence for the etching of the anti-reflection coating (ARC). The ARC was opened immediately after entering the softening range of the respective glass, regardless of large differences in glass chemistry. Furthermore, the viscosity-temperature behaviour of the paste glass determines the intensity of the redox-reaction and related silver precipitation at the interface, which takes part between ARC opening and glass resolidification. The cooling slope was confirmed to have decisive influence on the final interface conductivity, because a crucial part of silver colloids can be formed here
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 we 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, we used a FEA model for finding an optimized design conforming to our sensitivity requirements, inclusive of resonance frequency. In a second step, we 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 we 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.
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