LTCC ultra high isostatic pressure sensors

Piezoresistive pressure sensors using classical deformable structures such as membranes progressively run into difficulties at very high pressures (above 1 to 2 kbar), due to the decreasing ratio between the available sensing strain on the outer membrane surface and the maximal materials strain experienced on the pressurised side. Therefore, a novel "isostatic" pressure sensor concept, whereby the sensing element is immersed in the pressure fluid, has been developed. This method in principle allows the measurement of very high pressures, because materials stresses within the sensing beam are all compressive. LTCC (Low-Temperature Cofired Ceramic) beams with hermetically embedded thick-film piezoresistor bridges have been fabricated, packaged and characterised as sensor elements. The observed sensitivity is comparable to the response expected from the LTCC and piezoresistor materials properties. Key words: piezoresistivity, thick-film, LTCC, high pressure sensor.