ABSTRACT
A nanopore is an analytical tool with single molecule sensitivity. For detection, a nanopore relies on the electrical signal that develops when a molecule translocates through it. However, the detection sensitivity can be adversely affected by noise and the frequency response. Here, we report measurements of the frequency and noise performance of nanopores =8 nm in diameter in membranes compatible with semiconductor processing. We find that both the high frequency and noise performance are compromised by parasitic capacitances. From the frequency response we extract the parameters of lumped element models motivated by the physical structure that elucidates the parasitics, and then we explore four strategies for improving the electrical performance. We reduce the parasitic membrane capacitances using: (1) thick Si(3)N(4) membranes; (2) miniaturized composite membranes consisting of Si(3)N(4) and polyimide; (3) miniaturized membranes formed from metal-oxide-semiconductor (MOS) capacitors; and (4) capacitance compensation through external circuitry, which has been used successfully for patch clamping. While capacitance compensation provides a vast improvement in the high frequency performance, mitigation of the parasitic capacitance through miniaturization offers the most promising route to high fidelity electrical discrimination of single molecules.
ABSTRACT
We have fabricated and tested the performance of sub-50nm gate nMOSFETs to assess their suitability for mixed signal applications in the super high frequency (SHF) band, i.e. 3-30GHz. For a 30nm×40 µm×2 device, we found f(T) =465GHz at V(ds)=2V, V(g)=0.67V, which is the highest cut-off frequency reported for a MOSFET produced on bulk silicon substrate so far. However, our measurements of f(max) and noise figure indicate that parasitics impose limitations on SHF operation. We also present a high-frequency ac model appropriate to sub-50nm gate length nanotransistors, which incorporates the effects of the parasitics. The model accurately accounts for measurements of the S and Y parameters in the frequency range from 1 to 50GHz.
ABSTRACT
We describe a prospective strategy for reading the encyclopedic information encoded in the genome: using a nanopore in a membrane formed from an MOS-capacitor to sense the charge in DNA. In principle, as DNA permeates the capacitor-membrane through the pore, the electrostatic charge distribution characteristic of the molecule should polarize the capacitor and induce a voltage on the electrodes that can be measured. Silicon nanofabrication and molecular dynamic simulations with atomic detail are technological linchpins in the development of this detector. The sub-nanometer precision available through silicon nanotechnology facilitates the fabrication of the detector, and molecular dynamics provides us with a means to design it and analyze the experimental outcomes.