- 學位論文
強化離子敏感型場效電晶體特性之混模信號處理晶片
ISFET Performance Enhancement by Mixed-Mode Signal Processing
摘要
摘 要 離子敏感型場效電晶體由Bergveld於1970年所發明，其為一結合化學感測膜與金屬氧化物場效電晶體之固態元件，可用來選擇性量測電解液中離子的濃度，為一阻抗轉換元件。其結合金屬氧化物半導體場效電晶體低輸出阻抗及離子敏感電極之動作原理，具有快速的反應時間、高敏感性、整批處理的能力、體積小及單一晶片電路整合之潛力，並與標準CMOS製程技術相容。過去三十年，離子敏感型場效電晶體已廣泛地被討論，包括製造方法、特性分析與量測。研究顯示離子敏感型場效電晶體具有許多不理想效應，包括與溫度之相依性、時漂及遲滯，這些因素限制了以此電晶體為感測元件之量測系統的準確度。 單一晶片設計為積體電路設計之趨勢，本論文首先整合傳統閘極浮接讀出電路、類比數位轉換器、兩點校正演算法及七段顯示驅動電路，實現一酸鹼度感測器系統。同時，配合一分離式臨界電壓萃取晶片，進行溫度效應補償。此酸鹼感測計運用於居家環境污染監測，如自來水、地下水及河水之量測，獲得與商用產品一致的結果。 為了擷取感測器偵測離子濃度之電氣訊號，離子敏感型場效電晶體必須搭配一類比讀出電路。本論文提出一種新的架構，建構一適用標準CMOS製程技術實現之橋式源極浮接組態氫離子訊號讀出電路。本電路架構是將參考電極接地，利用源極電壓感測氫離子濃度的變化。其優點為具有寬廣訊號操作範圍，適用於不同架構如增強型、空乏型或不同感測薄膜之離子感測場效電晶體；由於參考電極接地，相較於傳統的閘極感測讀出電路，本架構只需單一參考電極，即可適用於以離子敏感型場效電晶體為基礎之多重感測器或感測器陣列訊號讀出電路。另外，本電路具有內嵌式低通濾波器，可強化離子敏感型場效電晶體本身或電源所造成電磁波之干擾。 當離子敏感型場效電晶體與讀出電路製作於同一晶片，離子敏感型場效電晶體會受基體效應之影響。本論文提出一種新的設計方法，建構一降低基體效應影響之讀出電路，解決離子敏感型場效電晶體整合讀出電路實現於標準CMOS製程技術之難題。另外，採用差動組態輸出，可同時補償離子敏感型場效電晶體時漂及溫漂之不理想效應。本方法不須複雜的硬體電路及軟體計算，不須溫度感測器，並且適用於所有的離子敏感型場效電晶體感測器。
並列摘要
Abstract Silicon-based semiconductor micro sensors are now able to react to the ion concentration (activity). The ISFET has features of rapid reaction time, high sensitivity, batch processing, small size and single chip integration. Furthermore, it can be implemented by CMOS technology. These advantages make it the first choice for VLSI electrochemistry bio-inspired applications. ISFET has been characterized and measured, indicating drawbacks related to: thermal dependency, long-term drift and hysteresis. To enhance the accuracy in biomedical related research, it is necessary to find a compensation method to cancel or reduce these effects. In this thesis, a single chip implementation of an ISFET-based pH-meter system and a discrete temperature compensation chip have been successfully designed, fabricated and tested. The two-point calibration circuitry based on the response of standard pH4 and pH7 buffer solution has been implemented by using Algorithmic State Machine (ASM) hardware algorithms. For homeland environmental applications, the system provide rapid, easy to use, and cost-effective on-site testing on the quality of water, such as drinking water, ground water and river water. The processor has a potential usage in battery-operated and portable devices in environmental monitoring applications compared to commercial hand-held pH meter. In order to capture the response of the ISFET sensors, it is necessary for the ISFET to be accompanied by an analog readout interface. This study devises a new integrated ISFET electronic interface circuit embedded with noise rejection capability. In addition, an approach to enhance accuracy of the output signal obtained from ISFET interface electronics due to the body effect is proposed. The scheme allows reduction of influence of body effect. Using only one ISFET with a differential output configuration, we obtained temperature dependency and long-term drift as well as common noise compensation. Simulation and experimental results show a great effect on monolithic ISFET integration in CMOS technology.