Radio-frequency C-V measurements with sub-attofarad sensitivity

TL;DR

This paper introduces a radio-frequency resonator technique for highly sensitive capacitance measurements of nano-scale semiconductor devices, achieving sub-attofarad sensitivity at cryogenic and room temperatures, enabling new device characterization methods.

Contribution

The paper presents a novel rf resonator approach for capacitance measurement with unprecedented sensitivity, applicable to nano-scale devices at various temperatures.

Findings

Achieved 75 zF/√Hz sensitivity at 1 kHz bandwidth with superconducting spiral inductor.

Measured capacitances consistent with Coulomb blockade periodicity.

Predicted room-temperature sensitivity of about 40 zF/√Hz with off-the-shelf components.

Abstract

We demonstrate the use of radio-frequency (rf) resonators to measure the capacitance of nano-scale semiconducting devices in field-effect transistor configurations. The rf resonator is attached to the gate or the lead of the device. Consequently, tuning the carrier density in the conducting channel of the device affects the resonance frequency, quantitatively reflecting its capacitance. We test the measurement method on InSb and InAs nanowires at dilution-refrigerator temperatures. The measured capacitances are consistent with those inferred from the periodicity of the Coulomb blockade of quantum dots realized in the same devices. In an implementation of the resonator using an off-chip superconducting spiral inductor we find sensitivity values reaching down to 75~zF/$\sqHz$ at 1~kHz measurement bandwidth, and noise down to 0.45~aF at 1~Hz bandwidth. We estimate the sensitivity of the method for a number of other implementations. In particular we predict typical sensitivity of about 40~zF/$\sqHz$ at room temperature with a resonator comprised of off-the-shelf components. Of several proposed applications, we demonstrate two: the capacitance measurement of several identical 80~nm-wide gates with a single resonator, and the field-effect mobility measurement of an individual nanowire with the gate capacitance measured in-situ.