Schottky barrier-based silicon nanowire pH sensor with live sensitivity control

Abstract

We demonstrate a pH sensor based on ultrasensitive nanosize Schottky junctions formed within bottom-up grown dopant-free arrays of assembled silicon nanowires. A new measurement concept relying on a continuous gate sweep is presented, which allows the straightforward determination of the point of maximum sensitivity of the device and allows sensing experiments to be performed in the optimum regime. Integration of devices into a portable fluidic system and an electrode isolation strategy affords a stable environment and enables long time robust FET sensing measurements in a liquid environment to be carried out. Investigations of the physical and chemical sensitivity of our devices at different pH values and a comparison with theoretical limits are also discussed. We believe that such a combination of nanofabrication and engineering advances make this Schottky barrier-powered silicon nanowire lab-on-a-chip platform suitable for efficient biodetection and even for more complex biochemical analysis

Gating Hysteresis as an Indicator for Silicon Nanowire FET Biosensors

“…In order to fabricate such devices, a previously reported process was followed [32,33,42]. Nominally intrinsic, undoped silicon nanowires were grown by bottom-up means employing the vapor-liquid-solid (VLS) mechanism.…”

“…Devices with close to ideal Nernstian sensitivity were obtained using this oxide material [32,43]. Each FET had up to 10 3 parallel nanowire channels.…”

“…The Schottky barrier silicon NW transducers do not require doping, strongly simplifying the technological complexity compared to other ion-sensitive FET approaches. We have recently proven that the Schottky junctions do not impair the sensitivity of the devices, since near Nernstian sensitivity can be reached [32]. As demonstrated recently [8,[32][33][34][35], such multi-wire devices, assembled using a thin-film-transistor (TFT) format, reveal remarkably high output currents (up to~mA) preserving the high on-to-off current ratio (in average up to~10 6 ), which greatly outperform the single wire FET, mostly employed for biosensor measurements [33].…”

“…We have recently proven that the Schottky junctions do not impair the sensitivity of the devices, since near Nernstian sensitivity can be reached [32]. As demonstrated recently [8,[32][33][34][35], such multi-wire devices, assembled using a thin-film-transistor (TFT) format, reveal remarkably high output currents (up to~mA) preserving the high on-to-off current ratio (in average up to~10 6 ), which greatly outperform the single wire FET, mostly employed for biosensor measurements [33]. Thus, devices connected by NW arrays are able to deliver a broader dynamic range for the measurements and lower device-to-device variation in current and sensitivity due to the averaging of the different signals coming from the individual wires [36,37].…”

A planar Al-Si Schottky barrier metal–oxide–semiconductor field effect transistor operated at cryogenic temperatures

“…For this reason their uptake has been limited, but interest remains in areas such as low power biomedical applications [3], bio-sensing [4] and in particular, nano-devices [5]. In this letter we discuss and investigate advantages which arise at cryogenic temperature.…”