Fabrication, response and stability of miniature piezoresistive force-sensing thick-film cantilevers

Miniature ceramic cantilevers have been successfully applied to the fabrication of simple and low-cost piezoresistive thick-film force-sensing cells, using different thick-film and LTCC (low-temperature co-fired ceramic) substrates. The availability of thin substrates for some materials allows much improved sensitivity compared to classical thick-film technology, with LTCC also featuring rather low substrate elastic modulus and fine structurability. However, practical applicability may be hindered by processing difficulties, such as printing and handling very thin fired substrates, or, in the case of co-fired tapes, warpage during firing. Also, signal drift is observed with some devices. In this work, we show that most of the previously-observed signal drift in some LTCC sensors is not due to self-heating, and therefore stems from defects such as micro-cracks within the ceramic cantilevers or plastic deformations in internal conductors. In a second step, we explore manufacturability of thick-film cantilevers on very thin substrates, and show that it is possible to print a single-sided design on substrates with thickness as low as 45 µm, although a lower limit of ~100 µm, depending on substrate material, is more practical.