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3D Structuration of LTCC / Thick-Film Sensors and Fluidic Devices
Keywords: Mesosystems, Sacrificial layers, LTCC
Thick-film and LTCC (Low Temperature Cofired Ceramic) technologies are now recognised as valid platforms for the fabrication of novel devices at the mesoscale for sensor, actuator, fluidic, electrical and packaging applications. In the field of sensors, especially, they allow the fabrication of sensitive, yet robust devices. This work reviews and comments, with an emphasis on sensor technology, different sacrificial layer material types, which may be formulated as tapes or as pastes, used to structure LTCC and thick-film devices: 1) organic / carbon materials that burn out during firing; 2) inert setter tape-type inorganic materials mechanically removed after firing; 3) inorganic substances removed by chemical dissolution after firing. These sacrificial layer techniques are compared with more traditional alternative / complementary structuration methods, such as laser cutting / punching, adhesive bonding, soldering, brazing and glass sealing. While sacrificial layer techniques in principle provide a much more straightforward route towards 3D integration, each of the three sacrificial material classes has its difficulties: 1) organic / carbon materials: process and design sensitivity; 2) inert inorganic materials: difficult complete removal – risk of damage of very fine structures and of particles left behind; 3) etchable inorganic materials: formulation as a compromise between sintering, chemical etching rate, chemical compatibility with other layers and (when cofired) shrinkage compatibility. In practice, no single structuration method is optimal for every application. This is and exemplified through various sensors and related devices developed at EPFL and elsewhere. Processing conditions of carbon and chemically etchable inorganic pastes are are also discussed, with the aim of obtaining useful and reproducible sacrificial materials.
Thomas Maeder, Research Scientist
Laboratoire de Production Microtechnique, Ecole Polytechnique Fédérale de Lausanne
Lausanne CH-1015,

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