pH sensing characteristics of silicon nitride thin film and silicon nitride-based ISFET sensor

The pH sensing characterizations of silicon nitride (Si₃N₄) thin film, and Si₃N₄-based ISFET sensor were discussed in this paper. The Si₃N₄ thin film was fabricated with to form silicon/silicon dioxide/silicon nitride (Si/SiO₂/Si₃N₄) structure while Si₃N₄-based ISFET was fabricated and packaged as a pH sensor. Both thin film and ISFET packaged device have low pressure chemical vapor deposited silicon nitride as sensing layer. Source measure unit (SMU), the semiconductor device analyzer model Agilent B1500A and a custom made test jig was used to investigate the electrical properties for both Si₃N₄ thin film and Si₃N₄-based ISFET sensor. The measurements were carrying out in three different buffer solutions with various pH levels of 4, 7 and 10 at room temperature. The pH sensitivity of thin film and ISFET packaged device with silicon nitride were 66.9 mV/pH and 53.6 mV/pH respectively. Both have shown good linearity in chosen pH range.