臨場共製之REFET與ISFET對於感測氧化層厚度調變的飄移特性之研究

Abstract

本論文係利用電漿輔助化學氣象沈積的二氧化矽當作離子感測電晶體的感測材料，以及利用濺鍍的五氧化二鉭當作參照電晶體的感測材料，來研究其感測度及飄移特性。由此兩種材料製成的感測電晶體的感測度顯示，其感測特性主要是由材料的表面特性所影響。但是其飄移特性則是由材料的塊材特性所決定。飄移現象的產生是因為感測層材料表面的水合作用，以及氫離子在水合層中的殘留所造成。電漿輔助化學氣象沈積的二氧化矽材料會導致嚴重的水合作用，因此以此材料當作感測層的離子感測電晶體相對於其他材料的離子感測電晶體而言，會產生明顯的閘極電壓飄移現象。六小時的量測結果顯示，電漿輔助化學氣象沈積的二氧化矽材料層的水合深度大約是500埃，並且最大的閘極電壓飄移是81毫伏。

The ISFETs of PECVD SiO2 as the sensing membrane and the REFETs with a sensing layer of sputtered Ta2O5 were fabricated to study the sensitivity and the drift characteristics. The sensitivity characteristics of SiO2-gate ISFETs and Ta2O5-gate REFETs showed that the pH responses were dependent on the surface characteristics of materials. But the drift characteristics were dependent on the characteristics of the material bulks. The drift phenomenon was due to the hydration effect of the sensing layer surface and the contamination of hydrogen ions in the hydrated layer. PECVD deposited SiO2 can lead to a critical hydration effect such that the gate voltage drift of a PECVD SiO2-gate ISFET is obvious relative to other ISFETs with sensing layers of different materials. In the measurement with duration of 6 hours, the hydration depth of a PECVD SiO2 layer was about 500□ and the maximum gate voltage drift of a PECVD SiO2-gate ISFET was 81mV.