Abstract
Electrolyte–insulator–semiconductor (EIS) sensors, used in applications such as pH sensing and sodium ion sensing, are the most basic type of ion-sensitive field-effect transistor (ISFET) membranes. Currently, some of the most popular techniques for synthesizing such sensors are chemical vapor deposition, reactive sputtering and sol-gel deposition. However, there are certain limitations on such techniques, such as reliability concerns and isolation problems. In this research, a novel design of an EIS membrane consisting of an optical material of indium gallium oxide (IGO) was demonstrated. Compared with conventional treatment such as annealing, Ti doping and CF4 plasma treatment were incorporated in the fabrication of the film. Because of the effective treatment of doping and plasma treatment, the defects were mitigated and the membrane capacitance was boosted. Therefore, the pH sensitivity can be increased up to 60.8 mV/pH. In addition, the hysteresis voltage can be improved down to 2.1 mV, and the drift voltage can be suppressed to as low as 0.23 mV/h. IGO-based membranes are promising for future high-sensitivity and -stability devices integrated with optical applications.
Highlights
The first ion-sensitive field effect transistor (ISFET) was invented by Bergveld in 1970s [1]
Results and Discussion due to plasma treatment, the crystalline structure of the as‐deposited membrane and the membrane with post-CF4 plasma treatment were monitored by using X-ray diffraction (XRD), as shown membrane with post‐CF
Ti‐doped indium gallium oxide (IGO) membranes were fabricated in the EIS structure
Summary
The first ion-sensitive field effect transistor (ISFET) was invented by Bergveld in 1970s [1]. Due to the stable performance, rapid response, compact size and low cost, semiconductor-based ion sensing membranes such as ISFETs and extended-gate field effect transistors (EGFETs) have been intensively studied [3,4]. Excellent pH-sensing membranes are crucial to develop multiple ion detection devices. Since membrane capacitance is crucial to the sensing performance, increasing the membrane capacitance values by enhancing the effective electric field passing through the membrane material is our goal. The sensitivity can be enhanced to improve the sensing performance. Incorporating possible charges near the surface may decrease the CDL and enhance the sensitivity, as the sensing equation (Equation (1)) reveals. Ti-doped IGO membranes with CF4 plasma treatment are promising for future biosensing portable devices [17,18]
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