Investigation of sensing mechanism in nanogap embedded FET biosensor and its application

Abstract

In this thesis, investigations of a nanogap embedded field effect transistor biosensor including device structure, operational principle, detection of purified biomolecules, applicability to real serum sample, noise source, and sensitivity improvement were discussed. The nanogap embedded field effect transistor biosensor is fabricated by CMOS process. Overall structure of the device is a ring-gate FET which is easy to fabricate compared to a conventional planar FET because of absence of isolation process. Due to the use of CMOS process and its structure, nanogap embedded field effect transistor can be produced massively and cheaply which is a suitable property for a disposable biosensor in POCT system. An operational principle of nanogap embedded field effect transistor was explained by dielectric constant effect and charge effect. The dielectric constant effect is one of the most important characteristic which differentiates the nanogap embedded field effect transistor from nanowire-based biosensor and ion-sensitive field effect transistor biosensor. A noise source which was originated from the device fabrication process was characterized and it was concluded that effects of the noise source are negligible. DNA was used to characterize the fabricated biosensor and it was concluded that the device can be used as a biosensor. Based on the analysis which was acquired during the DNA detection, C-reactive protein in human serum was successively detected. In addition, the nanogap embedded field effect transistor showed good enough false-positive and false-negative test result which means that the device can be commercialized. Two methods to improve the device performance were suggested. The first method is to measure substrate current instead of threshold voltage. With this measurement scheme, SNR of the biosensor was improved. Another method is to use of passivation layer. With depositing a CYTOP passivation layer except sensing site, high sensitivity can be achieved.