||With the advance of science and technology, our life has become more and more convenient. We can receive large amount of information from around the world. But also because of this, a lot of civilization diseases appears in modern life (e.g., the pressure of life often accompanied by the convenient life) and will result in poor health conditions of human body. The concentration of ions in human blood not only respond directly to health condition, but also can obtain symptoms of different diseases by detecting it.|
In order to develop a novel microsystem that can detect the concentration of different ions rapidly at the same time, several different ion sensors must be integrated on one chip. A common micro reference electrode is also needed to be combined together to develop the portable micro multi-ion detection system. Five extended-gate field-effect transistor (EGFET) devices are fabricated on one chip by utilizing micro-electromechanical systems (MEMS) in this thesis. Five different ion selective membranes (ISMs) which can adsorb the appointed ions are coated on each separate gate metal electrodes of the EGFETs to develop the sodium, calcium, ammonium, chloride and potassium ion sensors array. To obtain the miniaturization and portable ion detection system, a planar solid-state Ti/Ag/AgCl/KCl-gel reference electrode (μRE) is also developed in this study. The size of the proposed μRE also fabricated by utilizing MEMS is only 9 mm (W) × 6 mm (L) × 1 mm (H). The μRE includes two parts: a Ti/Ag/AgCl electrode chip and a packaging chip with the KCl-gel injected on the backside silicon cave. On the other hand, the channel width/length ratio of the implemented EGFET device is 1000 μm/10 μm and the extended gate sensing area is 1 mm × 1 mm. Five EGFET devices are integrated on the silicon chip with a volume of 1.3 cm (W) × 1.1 cm (L) × 1 mm (H).
Based on the measurement results, the proposed multi-ion sensors array have excellent characteristics with high sensitivity (Sodium：38 mV/pNa, Calcium：36.7 mV/pCa, Chloride：56.7 mV/pCl, Ammonium：323 mV/ pNH4 at pNH4 1~1.3 and 22.2 mV/ pNH4 at pNH4 1.3~4, Potassium：48 mV/pK), high sensing linearity (Sodium：0.985, Calcium：0.941, Chloride：0.932, Ammonium：0.999 at pNH4 1~1.3 and 0.990 mV/ pNH4 at pNH4 1.3~4, Potassium：99.9%), low hysteresis voltage (Sodium：13 mV at pNa 2.6, Calcium：10 mV at pCa 2.6, Chloride：7 mV at pCl 1.3, Ammonium：15 mV at pNH4 1.3, Potassium：6 mV at pK 2), long life time (more than 30 days) and short response time (about 180 seconds). It is very suitable for the application of the portable multi-ions detection microsystem. Besides, the implemented Ti/Ag/AgCl/KCl-gel μRE has good characteristics with low drift voltage, which are almost the same as that of the commercial reference electrode. Hence, the proposed μRE can provide the multi-ions sensors array with a stable reference potential.