Environmentally Robust Biosensor Using Field Effect Transistors of Heteroepitaxial Diamond

在本研究中，在耐电化学环境的氢端(H端)金刚石表面制备了离子敏感场效应晶体管(ISFET)，并用作生物传感器的换能器。在H端面上形成了电解质溶液栅场效应晶体管。栅极结构就是直接暴露在H端面的钻石。这种将半导体表面暴露在电解液溶液中的FET结构在世界上是首次开发出来的。与传统的ISFET相比，实现了更高的电流可控性。FET不仅在同质外延和异质外延金刚石中表现出理想的电流-电压特性，而且在更容易合成的多晶金刚石中也表现出理想的电流-电压特性。在电流-电压特性中，测量到了理想夹断和漏电流饱和。在关断状态下，漏电流极小，通断电流比大于4个数量级。场效应管在上述pH 1-14.3范围内稳定工作。FET的阈值电压与pH值无关。根据这一结果，合适的离子敏感碱基可以固定在pH不敏感的表面上，从而获得高选择性的分子识别。阈值电压与溶液中氯离子的浓度密切相关，其变化幅度为30-60 mV，随浓度变化一个数量级。在1mol/L~(-6)moL/L范围内观察到了氯离子的探测，显示了氯离子敏感场效应管的可能性。首次研制了金刚石溶液栅FET。证实了它们可在硬环境中工作，实现了对氯离子的高灵敏检测。

In this research, ion sensitive field effect transistors (ISFETs) have been fabricated on the hydrogen terminated (H-terminated) diamond surface resistant to electrochemical environment and operated as transducers of biosensors.1. The electrolyte solution gate FETs have been formed on H-terminated surfaces. The gate structure is just thet H-terminated diamond exposed to directly. This type of FET structure where semiconductor surface is exposed to electrolyte solution is firstly developed in the world. Compared with conventional ISFET, the higher current controllability is achieved.2. The FETs exhibit ideal current-voltage characteristics in not only homoepitaxial and heteroepitaxial diamonds, but also polycrystalline diamonds which is easier to synthesize. In the current-voltage characteristics, perfect pinch-off and the saturation of drain current have been measured. The leakage current at the off state is extremely small and the current ratio between on-off is more than 4 orders of magnitude. The FETs operate stably in the above mentioned characteristics between pH 1-14.3. The threshold voltages of the FETs are independent from pH values. From this result, an appropriate ion sensitive base can be immobilize on the pH insensitive surface leading to high selective molecular recognition.4. On the other hand, the threshold voltages strongly depend on the density of Cl ions in the solution and vary by 30-60 mV according to the density change by one order The Cl ion detection has been observed from 1 Mol/L to 10^<-6> Mol/L exhibiting the possibility of Cl ion sensitive FET.The diamond solution gate FET has been developed for the first time. Their operation in hard environment has been also confirmed and the highly sensitive detection of Cl ions has been achieved.