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Micro-machined high capacity silicon load cells

The aim of the research presented in this thesis is to improve the performance of high capacity conventional load cells or force sensors by using silicon as the base material. Silicon is used because it offers the possibility of realising small, light, low cost and high performance mechanical sensors. The goal is to measure loads up to 1000 kg with an accuracy of about ±0.03 % of the full-scale output (fso). From an analysis it appears that high capacity silicon load cells need a spring element which is compressed, because otherwise the chip will break under loading. In order to eliminate for the effect of changes of the position of the loading point on the chip, the choice is made to make a sensing system which integrates the force distribution on the chip (distributed sensing). For these kind of chips a package is designed in which the influence of side forces are eliminated. Three different sensing principles are investigated: piezoresistive, capacitive and resonating. Of these principles the following aspects are discussed: sensitivity, noise level, temperature coefficient of the offset, temperature coefficient of the sensitivity, long-term stability, possibility for distributed sensing and costs.