A 3D-printed contactless RF voltage and current probe for micrometre resolution inspection of integrated circuits

Abstract

As a result of current trends in miniaturisation and the need for faster electronic circuits, integrated circuit (IC) design has become more complex. Closely packed conductors carrying radiofrequency (RF) signals are subjected to parasitic coupling, complicating the IC design and validation. Prototyping of such devices is supported by contact probes that make an ohmic connection to contact pads. These pads take up valuable space and may interfere with the design. Alternatively, near-field probing techniques, that utilise capacitive and inductive coupling, have been employed for local RF voltage and current characterisation. In this research, such a near-field probe is developed through a multiscale 3D-printing process. It contains a miniaturised conductive loop, enclosing an area of 12.5µm2, and a conductive tip with an apex radius of 100nm. A model-based approach, that makes use of the discrepancy between parasitic long-range, and local short-range contributions to the measurement signal, is expanded to conduct both RF voltage and current measurements with increased spatial resolution. With this approach, combined contactless RF-voltage and RF-current measurements were executed demonstrating a measurement bandwidth from 1 to 23GHz. Capacitively coupled RF-voltage measurements achieved a spatial resolution of 8µm, while the spatial resolution of inductively coupled current measurements was only simulated. The simulation shows an expected spatial resolution of 3µm.