In this paper, it presents the fully CMOS biomedical sensor with in situ gold reference electrode in the chip. The traditional Ag/AgCl reference electrode is too large to form a biomedical microsystem. Using the on chip gold reference electrode to replace the Ag/AgCl reference electrode has been studied. The ISFET device with native aluminum oxide is used to detect the hydrogen ions. The shape of gold reference electrode is important to get the stable results. To place the surrounding gold reference electrode nearby the sensing membrane is better than the bar-type gold electrode. The sensitivity and linearity of this pH sensor with in situ surrounding gold reference electrode are 56mV/pH and 0.975, respectively. This work demonstrates the optimum gold electrode could be integrated into CMOS-based biomedical sensors and performs the good results.
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