Multi-Wire Tri-Gate Silicon Nanowires Reaching Milli-pH Unit Resolution in One Micron Square Footprint

Abstract

The signal-to-noise ratio of planar ISFET pH sensors deteriorates when reducing the area occupied by the device, thus hampering the scalability of on-chip analytical systems which detect the DNA polymerase through pH measurements. Top-down nano-sized tri-gate transistors, such as silicon nanowires, are designed for high performance solid-state circuits thanks to their superior properties of voltage-to-current transduction, which can be advantageously exploited for pH sensing. A systematic study is carried out on rectangular-shaped nanowires developed in a complementary metal-oxide-semiconductor (CMOS)-compatible technology, showing that reducing the width of the devices below a few hundreds of nanometers leads to higher charge sensitivity. Moreover, devices composed of several wires in parallel further increase the exposed surface per unit footprint area, thus maximizing the signal-to-noise ratio. This technology allows a sub milli-pH unit resolution with a sensor footprint of about 1 µm2, exceeding the performance of previously reported studies on silicon nanowires by two orders of magnitude.

Selective layer-free blood serum ionogram based on ion-specific interactions with a nanotransistor

“…A 0D ISFET can be seen as a model system to study and exploit ion-specific surface effects because it is more sensitive than typical ISFETs to ions in a wide concentration range 47 . Furthermore, the full theoretical ion sensitivity may be reached because the sensor is not degraded by pH sensitivity 29 . The dimensions of the device remain large compared to the Debye screening length (< 1 nm in blood serum).…”

“…Usual semi-empirical models such as the Nikolski-Eisenman equation do not lead to equation (2), because the presence of multiple species induces a competitive rather than an additive contribution to ψ 0 (refs. 7,29 ; the most dominant species determines ψ 0 at equivalent association constants; Fig. 3a,b and Methods).…”

“…One common aspect of these issues relates to the so-called selective layer, which is designed to capture an analyte selectively. Addition of a thin organic selective layer to sense analytes other than H 3 O + disrupts the high durability and precision of metal oxide -covered miniaturized pH sensor devices 20,[26][27][28][29][30] . A fundamentally different approach would be to take advantage of non-covalent specific surface interactions to perform selective-layer-free measurements of analytes in unknown solutions with a versatile and mass-fabricationcompatible device.…”

A 12.8 k Current-Mode Velocity-Saturation ISFET Array for On-Chip Real-Time DNA Detection

“…Large-signal biasing of the solution is provided by a reference Ag/AgCl electrode obtained by galvanostatic oxidation on silver tubes as proposed in [29]. Following the oxidation process, an aluminium wire was soldered on both tubes and connected to a voltage reference to be used for biasing.…”

AC and Phase Sensing of Nanowires for Biosensing

“…Nanowire sensors are very low cost (disposable) sensors since fabrication can be performed using standard top-down processes, based on mature photolithography, thin film deposition and plasma etching [ 7 , 8 , 9 , 10 ]. However, a typical readout system is bulky and expensive requiring a complex setup and skilled personnel.…”