Research Output
FET with underlap structure for biosensing applications
Electrical label-free sensing of cardiac troponin biomarker: FET-based integration with substrate-gate coupling
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Publication
This paper presents the numerical simulation of an underlap field effect transistor (FET) device architecture on silicon‐on‐insulator (SOI) substrate for biosensing applications. By using the Silvaco ATLAS device simulator, this work is aimed to elucidate the effects of the different gate lengths, the presence of interface charge on the underlap sensing region, and also the effects of different gate biases (i.e. singlegate biasing, synchronous doublegate biasing and asynchronous doublegate biasing) on the magnitude of drain current (ID) of the simulated device. It is found that shorter gate length with the positive charges (on the n‐p‐n structure), at the sensing channel area increased the electron concentration at the channel and substrate/buried oxide interface. In asynchronous doublegate with a +3V of back‐gate supply and synchronous double‐gate, both increased the ID at different magnitude level and off‐current. Thus, depending on the biomolecule charges, the substrate biasing can be altered to improve the device’s sensitivity.
Publication
Acute myocardial infarction (AMI) is a leading cause of death worldwide despite the existence of therapy’s advances. Therefore, an early diagnosis method by using cardiac biomarkers is essential to enable correct countermeasures. Cardiac Troponin I (cTnI) is one of the cardiac biomarkers for early diagnosis of AMI and considered as ‘gold standard’ for cardiac muscle injury determination. The detection of cTnI through an electrical-based biosensor allows label-free detection by converting biomolecular binding event into a significant electrical signal via a semiconductor transducer. It utilizes conductivity to specify the existence of biomolecules. One of the electrical-based biosensors known as field-effect transistor (FET)-based biosensor has drawn much attention for owning the concept of charge transduction; thus, allows early, high sensitivity, high selectivity, and rapid diagnosis of the specific cardiac biomarker at low concentrations. In this work, the zinc oxide (ZnO)-FET biosensor coupled with substrategate has been designed and fabricated for the detection of cTnI biomarker. ZnO thin film, as n-type biocompatible semiconductor material, and also as transducer was deposited via sol-gel and spin coating techniques between p-type source and drain terminal on SOI substrate, forming a p-n-p junction, a device capable of bio-sensing application. The surface morphology of the thin film was characterized by using atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). The thin film, which demonstrated hexagonal wurtzite phase as shown by X-ray diffraction (XRD) analysis appropriate for biomolecules interaction. The surface of the ZnO thin film was immobilized with cTnI monoclonal antibody (MAb-cTnI) as biological receptor via covalent binding technique for capturing cTnI biomarker. The process was validated by Fourier transform-infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The device structure was simulated in Silvaco Atlas 2D-simulator, to elucidate its electrical characteristic, by means of hole and electron concentration in the channel and buried oxide/substrate interface, respectively. The device demonstrated a new strategy via electrical characterization with the introduction of substrate-gate coupling that enhanced the formation of hole conduction layer at the channel between drain and source region. Finally, the biosensor shown significant increment in relative changes of drain current level in a linear range of 6.2 to 16.5 % with the increase of positively charge cTnI biomarker concentrations from 1 ng/ml to 10 μg/ml. The device sensitivity of the detection is at 2.51 %·(g/ml)-1 with limit of detection (LOD) down to 3.24 pg/ml.