Study on the Hysteresis Effect of Sodium Ion Sensing Based on the Extended Gate Field Effect Transistor

We employed the extended gate field effect transistor (EGFET) to fabricate the sodium-sensing electrode. The advantages are easy package, easy preservation, and better stability. The EGFET based on the structure of the ruthenium oxide/silicon (RuOx/Si) for measuring the sodium ion. Although EGFET has above advantages, but there is still the non-ideal effect such as hysteresis effect. In this paper, the hysteresis effect is the phenomenon that EGFET devices generally exist. When the device immersed into solution with different concentrations, and subsequently placed it to original solution, and measured the voltage difference. As the sequence is pNax→pNay→pNax→pNaz→pNax. We can obtain the voltage difference between the start point and endpoint due to the measuring sequence that is pNa1→pNa2→pNa1→pNa0→pNa1. The stability and. accuracy of device both were affected by the hysteresis effect. We used the NaCl solution and measured the devices in pNa1→pNa2→pNa1→pNa0→pNa1 with each step is 3 minutes. Finally, the hystersis width is the voltage difference between the start point and endpoint that is 1.62 mV.