The Ion Sensitive Field Effect Transistor (ISFET)

离子敏感场效应晶体管(ISFET)是一种化学传感器，其基本结构与MOSFET相同。然而，有几个显著的差异。ISFET的栅极由被监测的溶液和电化学参比电极取代。栅电介质，通常是二氧化硅，作为离子敏感膜运行，溶液的pH值控制表面电位。此外，电极电势由能斯特方程定义。与离子敏感电极(ISE)相比，ISFET体积更小，功耗更低，而且没有玻璃膜，更稳定，更不易老化。大多数电子元件都是通过设计、制造和测试过程开发的。计算机辅助工具可以在ISFET的设计步骤中发挥重要作用。虽然这些程序最初是为设计和模拟电子电路而开发的，但也可以用于设计硅基化学和生物传感器。标准的cmos通常在微制造过程中使用自对准工艺，其中栅极在源区和漏区之前制造。然而，对于ISFET来说，在不破坏薄栅氧化层的情况下移除栅电极似乎是不切实际的。在测试方面，灵敏度和线性范围等特性需要作为传感元件进行反复校准。最后，虽然ISFET最初是为测量pH而开发的，但它有许多应用，如生物传感和环境监测。

The Ion Sensitive Field Effect Transistor (ISFET) is a chemical sensor with the same basic structure as a MOSFET. However, there are a few significant differences. The gate of an ISFET is replaced by the solution being monitored and an electrochemical reference electrode. The gate dielectric, generally SiO2, operates as an ion-sensitive membrane, with the pH of the solution controlling the surface potential. Furthermore, the electrode potential is defined by the Nernst equation. Compared with Ion Sensitive Electrodes (ISE), ISFETs are smaller, consume less power, and without the glass membrane, they are also more stable and less prone to ageing.Most electronic components are developed through design, manufacture, and testing processes. Computer-aided tools can play an essential role in the design steps of ISFETs. Although initially developed for the design and simulation of electronic circuits, these programmes can be used to design silicon-based chemical and biological sensors. Standard CMOS usually uses a self-aligned process during the microfabrication process, where the gate electrode is fabricated before the source and drain regions. However, for an ISFET, removing the gate electrode afterwards without damaging the thin gate oxide seems impractical. In terms of testing, characteristics such as sensitivity and linearity range require repeated calibration as a sensing element. Finally, although the ISFET was originally developed for pH measurement, it has many applications, such as biosensing and environmental monitoring.