Amorphous boron carbon nitride as a pH sensor

Amorphous boron carbon nitride ${\mathrm{(a-BC}}_x{N}_y)$ has been used as the sensing membrane in an extended gate field effect transistor for the measurement of $p\mathrm{H}$ of solutions. The ${\mathrm{a-BC}}_x{N}_y$ material was produced by dual gun magnetron sputtering and has been found to be a stable and sensitive $p\mathrm{H}$ sensor with sensitivities in the range of $\text{40\hspace{0.17em}}\mathrm{mV}\mathrm{/p}\mathrm{H}.$ The $p\mathrm{H}$ sensitivity, however, increased with increasing carbon content of the ${\mathrm{a-BC}}_x{N}_y$ sensing membrane and reached a maximum of $\text{46\hspace{0.17em}}\mathrm{mV}\mathrm{/p}\mathrm{H}$ for a carbon concentration of 47 at. %. The response times of these sensors are close to 6 s. The drain current, which is an indicator of the $p\mathrm{H},$ remained stable (fluctuation of few microamperes) over a period of 10 min in the phosphate solution with varied $p\mathrm{H},$ demonstrating a good stability of the sensing membrane.