We present the multilevel fabrication and measurement of a Coulomb-blockade
device displaying tunable negative differential resistance (NDR). Applicat
ions for devices displaying NDR include amplification, logic, and memory ci
rcuits. Our device consists of two Al/AlxOy islands that are strongly coupl
ed by an overlap capacitor. Our measurements agree excellently with a model
based on the orthodox theory of single-electron transport. (C) 1999 Americ
an Institute of Physics. [S0003-6951(99)00607-5].