Reference Electrode–Insulator–Nitride–Oxide–Semiconductor Structure with Sm 2 O 3 Sensing Membrane for pH-Sensor Application

• Published in: Japanese Journal of Applied Physics 2011-04, Vol.50 (4S), p.4
• Main Authors: Wang, Jer-Chyi, Lu, Tseng-Fu, Shih, Hui-Yu, Yang, Chia-Ming, Lai, Chao-Sung, Kao, Chyuan-Haur, Pan, Tung-Ming
• Format: Article
• Language: English
• ISSN: 0021-4922; 1347-4065
• DOI: 10.1143/JJAP.50.04DL09

We investigate a reference electrode–insulator–nitride–oxide–semiconductor (RINOS) structure with a Sm 2 O 3 sensing membrane and using silicon nitride as the charge trapping layer for pH detection. The proposed RINOS device with the oxide–nitride–oxide (ONO) structure exhibits a high pH sensitivity (larger than the ideal Nernst response, ∼59 mV/pH) owing to hydrogen ion adsorption by the trapped electrons within the embedded Si 3 N 4 layer when applying a stress voltage. As the applied voltage and time increase, pH sensitivity increased. The possible sensing mechanism based on charge attraction was demonstrated using schematic band diagrams. To improve the retention of an increased sensitivity, an additional SiO 2 layer as a blocking layer between the Sm 2 O 3 and Si 3 N 4 films to form the RIONOS device was proposed. Compared with the conventional electrolyte–insulator–semiconductor (EIS) structure, the proposed RIONOS device can be used to detect ultra small pH variations owing to its high pH-sensing response.