DC and AC Sensing Characteristics of Si-nanowire FET for Urea Detection

Abstract

Urea, a product of the urea cycle, is one of the important biomarkers for medical diagnosis. The urea concentration is specifically critical for disease diagnosis related to kidney and liver. Here, a Si-nanowire field-effect transistor (SiNW FET) was fabricated using a top-down method and characterized to detect the urea. The SiNW FET has advantages of high sensitivity, compatibility with conventional CMOS fabrication, low cost, and mass production. The devices were functionalized using 3- Aminopropyltriethoxysilane (APTES) and Glutaraldehyde (GA) to facilitate the binding of urease. DC and AC characterizations were conducted to evaluate the sensing performances. From DC characteristics, the voltage-related and current-related sensitivities were extracted with various concentrations in the range of 100 μM ~ 100 mM. Selectivity tests without urease immobilization and reaction with other types of samples were also conducted at room temperature. From the AC measurement, the ratio of VOUT (=VOUT.AFTER /VOUT.BEFORE) increases as the urea increases at the frequency to 1 kHz and then saturates at the frequency above 10 kHz. Depending on DC and AC operation, the limit of detection (LOD) is also characterized and analyzed.