The notion of quantum-dot cellular automata (QCA) as a possible replacement
paradigm for conventional transistor-based logic is reviewed. Experiments
using metal tunnel structures demonstrating a functional QCA cell are prese
nted. It is shown that single electron tunnelling transistors used as elect
rometers verify proper switching of the QCA cell. Additionally, we provide
evidence for a QCA cell switching frequency of 14 MHz, and a calculated upp
er limit of more than 5 GHz.