Characterization of ISFET/REFET Pair Based on Inorganic Chemosensitive Layers with Surface Treatment and Post Annealing

• Main Authors: Cheng En Lue, 呂承恩
• Other Authors: C. S. Lai
• Format: Others
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/31905395171439054498

博士 === 長庚大學 === 電子工程學研究所 === 98 === To improve quality of our life, environment protection, process control of industry, food and medicine production, drinking water quality, and human health monitoring could be tested and or monitored through a multi-functional ion sensor arrays. The ion sensitive field effect transistor (ISFET) with good quality of sensing membrane, durable and miniaturized reference electrode, good stability to the interference factors, shows a high potential as a candidate for a platform for these applications. In this study, sensing membranes – tantalum oxide (Ta2O5), tantalum oxynitride (TaOxNy), and silicon nitride (Si3N4) layers with surface treatments and post annealing based on microelectronic technology were investigated to improve the sensing properties and apply for inorganic ISFET/reference field effect transistor (REFET) pair. To improve the sensing properties, the Ta2O5–electrolyte insulator semiconductor (EIS) structures were optimized through a post annealing, including: high pH sensitivity – 58.0 mV/pH, narrow hysteresis width – 0.33 mV at pH 6, low drift coefficient – 0.5-1.5 mV/h, and low light response. In addition, for the fabrication with low thermal budget, a nitridation process was used on Ta2O5 layers to form TaOxNy layers. The pH sensitivity, hysteresis, and time drift were also improved. For the development of inorganic ISFET/REFET pair, Si3N4-EIS structures with single and stacked sensing membranes were investigated. In addition, the differential sensitivity was controlled through CF4 plasma post treatment, thickness modification, post annealing temperature, and use of different substrates n- and p-type silicon wafers. The highest differential sensitivity was 39.7 mV/pH, and a pH-dependent trapping effect was proposed as the mechanism for explanation of the decrease of pH sensitivity of single layer structure. Finally, the sensing membranes and optimization methods were applied on ISFETs. Based on the achievements in this study, the ISFET/REFET pair with inorganic chemosensitive layers was optimized and could be applied for smart sensor array based on the pH sensing.