Nanowell Field-Effect Transistors for Highly Sensitive Molecular Detection

We report a novel, highly sensitive bio-molecular sensor device, a nanowell FET. Its unique structure contains a 25 nm size nanowell in the center of a 35-40 nm wide silicon FinFET. Two extremely narrow, 3-4 nm wide silicon channels are formed on each side of the nanowell. These channels act as enhanced molecular sensing areas. The electrolytically gated nanowell FET exhibits a near-ideal subthreshold swing (SS) of 66 mV/dec, an on-state current of >1.8 mA/μm, peak transconductance of >3.8 mS/μm and hysteresis free characteristics. The nanowell is chemically modified to allow for the binding of target biomolecules. The binding leads to a shift of the FET threshold voltage (V
th
), i.e. the signal. Through both end-point and real-time measurements, we obtain a signal of ~40 mV for an estimated number of approximately ten 20-base single-stranded DNA molecules (20T ssDNA). This is a major enhancement compared to our previously demonstrated finFET-based biosensor (~20 mV for ~40 molecules). The nanowell acts as a nanoscale region with an enhanced sensitivity towards molecular charges. Moreover, binding inside the nanowell potentially becomes self-limiting at single-molecule level. These features are major advantages for single molecule sensing.