| AVS 60th International Symposium and Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF-ThP |
| Session: | Thin Films Poster Session |
| Presenter: | S.H. Lee, Kyungpook National University, Republic of Korea |
| Authors: | S.K. Lee, Kyungpook National University, Republic of Korea W.H. Son, Kyungpook National University, Republic of Korea S.H. Lee, Kyungpook National University, Republic of Korea Y.S. Moon, Kyungpook National University, Republic of Korea T.Y. Lee, Kyungpook National University, Republic of Korea S.Y. Choi, Kyungpook National University, Republic of Korea |
| Correspondent: | Click to Email |
The sensing membrane of the pH-ion-sensitive field-effect transistor (pH-ISFET) is a very important element in order to measure continuous monitoring of pH in systems. The Al2O3 film among the sensing membrane materials is well-known as a chemically stable dielectric material that has low leakage current, however, it is classified to be poor sensing materials because of their low sensitivity than other sensing membrane materials. The atomic layer deposition (ALD) method meets the good characteristics the Al2O3 film, because it is possible for deposition of high density, low impurity level, uniform thickness, and low pinhole density. Also, the pH-sensitivity of the pH-ISFET can be improved by thermal annealing at high-temperatures in O2 ambient after ALD deposition. In this paper, to apply continuous monitoring, the pH-ISFET with the Al2O3 sensing membrane deposited by ALD was fabricated, and its characteristics were investigated.
The n-channel field effect transistor (FET) designed for using the pH-ISFET was fabricated by the CMOS-processing technology. The thermal temperature annealing process of the Al2O3 film was carried out using a conventional furnace system in O2 ambient for 40 min at 500, 600, 700 and 800 ℃. All the measurements of pH-ISFET were carried out in a standard pH solution. The conventional reference of Ag/AgCl and liquid-junction filled with 3 M KCl electrode was used to establish the pH solution potential. The null balance circuit, which maintained constant the drain current and the drain voltage, was used to measure continuous monitoring. In the operation of pH-ISFET sensor, the change of electrochemical potential between the surface of sensing membrane and a reference electrode is generated by the establishment potential with chemical response in the pH solution. In order to ensure the shift of VT of pH-ISFET with the Al2O3 sensing membrane, the IDS–VGS curves were measured in pH 4, pH 7 and pH 10 at a constant 600 ℃, these are shown in Fig. 1. From measured results, we confirmed that the VT of the pH-ISFET was shifted from the pH values which changed the surface potential on the Al2O3 sensing membrane. In accordance with experiment results, we measured the shift of the VT on the pH-ISFETs with Al2O3 sensing membrane with respect to the difference of thermal annealing temperatures. Those results are shown in Fig. 2. Through the results of our experiments, we ascertained that the sensitivity of the pH-ISFETs with Al2O3 sensing membranes annealed at 500, 600, 700 and, 800 ℃ are about 56.7, 55.2, 50.3, and 33 mV/pH, respectively.