高性能離子感應電晶體之可靠度研究及應用

Abstract

本論文提出使用二氧化鋯（ZrO2）作為離子感應場效電晶體（ISFET）之感應層，並嘗試去調控溫度與製程參數對ISFET的影響，當我們可以得到一個穩定的感測靈敏度則因為漂移效應所造成的水合深度就可獲得，當我們瞭解漂移效應後，我們提出兩種方法來解決此種負面效應。 在第二章中先描述離子感應場效電晶體（ISFET）的理論跟模型，例如，表面鍵結分離模型、Gouy-Chapman理論、Gouy-Chapman-Stern理論、與漂移理論。 在第三章的研究裡，氧化鋯成功的應用在離子感應場效電晶體（ISFET）裡，成為酸鹼感測層，再利用HP4156A以定電流量測方式後，可得到相當高的反應範圍，其感測靈敏度介於56.7∼58.3 mV/pH之間。這裡所使用的氧化鋯薄膜是使用直流濺鍍方式所沈積的，此薄膜對氧化層跟矽晶都具有相當好的吸附特性，當感測環境加入1莫耳體積濃度的氯化鈉容液以後，感應靈敏度會有些微的減少，不過還是具有相當好的線性度及52.5 mV/pH的靈敏度。 在論文的第四章中，我們利用參考場效電晶體（REFET）來控制溫度跟製程差異的影響，當我們利用參考場效電晶體（REFET）校正輸出訊號後，就可以得到一個相當穩定的的感應靈敏度並可以得到以二氧化矽為感測層的離子感應場效電晶體（ISFET）的初始本質漂移（intrinsic drift），更進而定義出因為漂移影響所造成的水合層厚度。從實驗的結果來看，用二氧化矽感測層所做成的離子感應場效電晶體（ISFET）水合深度大約為50奈米，而實驗當中所測出來的感測反應也很穩定，大約處於28∼32 mV/pH之間，使用這方法可以很簡單的找出水合深度，這將對探討漂移效應的真正機制有所助益。 當我們暸解漂移現象以後，我們就試著設計兩種方法來減少這個效應，其中一種方法是在第五章，在這章節當中，我們提出漂移跟閘極電壓的關係，從而設計出一種簡單且便宜的方法來解決漂移問題。我們利用參考電極來施加不同的定電壓在感測層上面，就可以很明顯的看出閘極的飄移電壓跟應力電壓的強烈相關性，當閘極電壓控制在0.5伏特，就可以使得以二氧化矽為感測層的離子感應場效電晶體之飄移電壓從原來的十小時飄移56.12 mV變為2.94 mV，其改善百分率高達94.8％。又當閘極電壓被控制在-1伏特的時候，就可以使得以二氧化鋯為感測層的離子感應場效電晶體（ISFET）之飄移電壓從原來的十小時飄移-57.94 mV變為0.76 mV，其改善百分率高達98.7％。 另一個解決方法提出於本論文的第六章中，其方法為利用參考感應場效電晶體（REFET）來減少飄移效應，首先是利用銨電漿去處理一個以二氧化鋯為感應薄膜的離子感應場效電晶體（ISFET），以得到一個簡單且跟互補金屬氧化電晶體相容的參考感測場效電晶體（REFET）來量測酸鹼性。這是一個獨創且具有很高的可塑性，可以整合離子感應場效電晶體（ISFET）到化學微系統，應用於生物體分析或整合到單晶片系統當中。當我們利用4156A以定電流量測方式時，可以同時得到離子感應場效電晶體（ISFET）、參考感應場效電晶體（REFET）及兩者間的差值感應靈敏度。這個以二氧化鋯為感測層的離子感應場效電晶體（ISFET）具有很高的離子感測能力，其範圍介於56.7∼58.3 mV/pH間，其變異度為3％，又參考感應場效電晶體（REFET）具有較小的離子感測能力，其範圍介於27.6∼29 mV/pH間，其變異度為5％。當我們使用離子感應場效電晶體/參考感應場效電晶體(ISFET/REFET)差值電壓對的時候，可以得到一個非常穩定的差值感應靈敏度，其範圍介於29.1∼29.3 mV/pH間，其變異度為0.7％。這個結果告訴我們，這個研究不僅使得離子感應場效電晶體（ISFET）可以整合到微系統當中，也可以增加感應靈敏度的穩定性。

This dissertation proposes to use zirconium oxide as a membrane of ion-sensitive field effective transistor (ISFET), and to control the effects of temperature and process deviation. When a stable sensitivity and intrinsic drift of SiO2 gate ISFET can be found, the thickness of hydration layer that is introduced by the drift effect will be found, too. After we understand the drift effect, we also propose two methods to solve the unwanted effect. In Chapter 2, theories and models of ISFET are described, including site-dissociation model, Gouy-Chapman theory, Gouy-Chapman-Stern theory, and drift model. Chapter 3 describes the application of the zirconium oxide (ZrO2) membrane as a pH-sensitive layer for ISFETs. It exhibited an excellent response range of 56.7~58.3 mV/pH from the fixed current measurement using HP4156A. The ZrO2 membrane prepared by direct current (DC) sputtering was used as a pH-sensitive film that showed good surface adsorption with oxide and silicon. The pH sensitivities slightly decreased in 1 M NaCl solution; however, the device showed a perfect linear response of 52.5 mV/pH. In Chapter 4, a reference field effective transistor (REFET) is used to control the effects of temperature and process deviation. After the calibration of REFET, a very stable sensitivity and intrinsic drift of SiO2 gate ISFET can be obtained. It can be used to define the thickness of hydration layer that is introduced by the drift effect. Results of this study will show that the thickness of hydration is about 50 nm in SiO2 membrane ISFET. It exhibits a stable response of 28~32 mV/pH from the fixed current measurement by HP4156A. This method is a really simple way to find the thickness of hydration layer, and it will be useful in the study of the real mechanism in drift effect. When we understand the phenomenon of drift, we try to design two methods to reduce this effect. One is in Chapter 5. A simple and cheap way to solve the drift problem is presented which describes the relation of drift and gate voltage. Constant various gate voltages are biased in sensing layers with reference electrode. It obviously shows a strong relation of gate drifts and gate stress voltages. When the gate voltage is controlled as 0.5 V, the drift voltage of SiO2 gate ISFET will decrease from 56.12 to 2.94 mV in ten hours measurement. The improvement of drift voltage reaches 94.8%. When the gate voltage is controlled as -1 V, the drift voltage of ZrO2 gate ISFET will also decrease from -57.94 to 0.76 mV. The improvement of drift voltage reaches 98.7%. Another one in Chapter 6 of the thesis is using REFET to reduce the drift effect. A simple CMOS compatible REFET for pH detection by post NH3 plasma surface treatment of a ZrO2 membrane ISFET has been developed. It is a novel study that has latent capacity to integrate the ISFET devices into a chemical micro system for in vivo analysis or become a part of lab-on-a-chip. With the fixed current measurement by HP4156, we can get not only the individual sensitivities of ISFET and REFET, but also the differential sensitivities of ISFET/REFET pair. The ZrO2 membrane ISFET exhibits an excellent response of 56.7~58.3mV/pH with deviation of 3% and the REFET shows a small response of 27.6~29 mV/pH with a deviation of 5%. Using this ISFET/REFET differential pair, we can get a very stable differential sensitivities of 29.1~29.3 mV/pH with a small deviation of 0.7%. This result indicates that the research not only makes the ISFET integrate into a micro system in a simple way possible, but also increases the stability of sensitivity.