Nickel–chromium alloy piezoresistive pressure sensor using eutectic bonding

摘要

A nickel–chromium (Ni –Cr) piezoresistive pressure sensor is presented, which has the advantages of low-cost and easy fabrication processes. In the designed sensor, Ni –Cr alloy (80:20 wt%), which can be fabricated using simple processes, is used as the strain-detecting material with a smaller but acceptable gauge factor. Eutectic-bonding technology, based on silver –tin (Ag –Sn) alloy, which contains 3.5 wt% Ag and has 20 mm thickness, is used as an alternative and easy bonding choice to complete the vacuum package. Normally, Ag –Sn alloy is mostly obtained by the electrochemical deposition method. However, here the Ag –Sn solder film is directly used as a bonding material. It reduces the fabrication difficulty of eutectic bonding of the proposed pressure sensor. By studying the processes of annealing of Ni –Cr fabrication and eutectic bonding with Ag –Sn, the authors complete the alloy piezoresistive atmosphere pressure sensor. Bonding quality is evaluated by inspection through the deflection of a diaphragm of silicon with more than 95% of the area successfully bonded. The pressure –voltage characteristic test results suggest a precision within 0.3% in square fitting. The temperature coefficient offset is 620 ppm/(u000b0;C free space optic (FSO)).