Sensing characteristics of ruthenium films fabricated by radio frequency sputtering

The pH is an important parameter for analyzing the conditions in the environment, for clinical assays, and in cases of water pollution. The design of a convenient pH sensor is presented in this report. Ruthenium was investigated to fabricate a pH sensing membrane by radio frequency (R.F.) sputtering, and the reaction gas was assumed to control the sensing characteristics of the pH sensor. Additionally, the sensing membrane was deposited on a silicon substrate. This pH sensor offers many advantages, such as ease of packaging, capability of making high temperature measurements and disposability. Furthermore, this pH sensor was easily fabricated on a single chip to yield an integrated chip using semiconductor technology. According to experimental results, the ruthenium oxide membrane presented a linear pH sensitivity of 55.52 mV/pH when immersed in a standard buffer solution, the pH of which was between 1 and 12, at room temperature. The ruthenium nitride membrane presented a linear pH sensitivity of 57.05 mV/pH when immersed in a standard buffer solution, the pH of which was between 1 and 13, at room temperature. The reaction gas influenced the structure of the sensing membrane and the ruthenium nitride membrane had higher pH sensing range than the ruthenium oxide. Furthermore, the structure of the sensing film was appropriate for fabrication of the sensing chip using semiconductor processes, especially in micro-electro-mechanical systems (MEMS).