Extended base H+-ion sensitive bipolar junction transistor with SnO2/ITO glass sensing membrane

In this study, an extended base bipolar junction transistor (EBBJT) as an H⁺ ion sensitive device have been investigated. The SnO₂/ITO glass, fabricated by sputtering SnO₂ on the conductive ITO glass, is used as a pH-sensitive membrane for electrode, which is connected with a commercial bipolar junction transistor (BJT) device. The experimental data show that this structure has a linear pH response, about 57-60 mV/pH in the ion concentration range between pH 2 and 10, and hysteresis effect is about 4.2 mV. The thermal stability of EBBJT has been validated by the experimental results on pH values ranging from 2 to 10 in a temperature range of 25°C to 55 °C. In addition, it is easier to fabricate and package the sensitive membrane structure and the measurement is simple for the application of disposable biosensor without complex temperature compensation.