Feedback Lock-in: A versatile multi-terminal measurement system for electrical transport devices

TL;DR

The paper introduces a versatile multi-terminal measurement system called feedback lock-in that allows dynamic, programmable electrical contact configurations and sensitive measurements without preamplifiers, demonstrated on advanced materials.

Contribution

A novel feedback lock-in system combining digital control and software lock-in techniques for flexible, multi-terminal electrical measurements without preamplifiers.

Findings

Achieved differential measurement sensitivity comparable to commercial lock-in amplifiers.

Enabled multi-terminal measurements on twisted bilayer graphene and SrTiO3 quantum point contacts.

Demonstrated a new current-biased measurement mode on a ballistic graphene device.

Abstract

We present the design and implementation of a measurement system that enables parallel drive and detection of small currents and voltages at numerous electrical contacts to a multi-terminal electrical device. This system, which we term a feedback lock-in, combines digital control-loop feedback with software-defined lock-in measurements to dynamically source currents and measure small, pre-amplified potentials. The effective input impedance of each current/voltage probe can be set via software, permitting any given contact to behave as an open-circuit voltage lead or as a virtually grounded current source/sink. This enables programmatic switching of measurement configurations and permits measurement of currents at multiple drain contacts without the use of current preamplifiers. Our 32-channel implementation relies on commercially available digital input/output boards, home-built voltage preamplifiers, and custom open-source software. With our feedback lock-in, we demonstrate differential measurement sensitivity comparable to a widely used commercially available lock-in amplifier and perform efficient multi-terminal electrical transport measurements on twisted bilayer graphene and $SrTiO_3$ quantum point contacts. The feedback lock-in also enables a new style of current-biased measurement which we demonstrate on a ballistic graphene device.