Environmentally Robust Biosensor Using Field Effect Transistors of Heteroepitaxial Diamond

在本研究中，离子敏感场效应晶体管（isfet）被制作在氢端（h端）金刚石表面耐电化学环境，并作为生物传感器的换能器。在h端表面上形成了电解质溶液栅极场效应管。栅极结构只是将h端金刚石直接暴露出来。这种半导体表面暴露于电解质溶液中的FET结构在国际上尚属首次。与传统的ISFET相比，具有更高的电流可控性。fet不仅在同外延和异质外延金刚石中具有理想的电流-电压特性，而且在更容易合成的多晶金刚石中也具有良好的电流-电压特性。在电流-电压特性中，测量了完全掐断和漏极电流饱和。关断时漏电流极小，通断电流比大于4个数量级。fet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，可以将合适的离子敏感碱固定在pH不敏感的表面上，从而实现高选择性的分子识别。另一方面，阈值电压强烈依赖于溶液中Cl离子的密度，并根据密度变化一个数量级而变化30-60 mV。从1 Mol/L到10^<-6> Mol/L的范围内观察到Cl离子检测，显示出Cl离子敏感FET的可能性。首次研制出了金刚石溶液栅场效应晶体管。它们在恶劣环境下的工作也得到了证实，并实现了对Cl离子的高灵敏度检测。

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.