Memristive devices showing negative differential resistance in part of their I-V curve are interesting circuit elements for novel computing paradigms since they can generate signal amplification even in a two-terminal device. To enable the integration of such devices into highly integrated systems in the future, we need to tailor and tightly control the parameters of the I-V curve such as the threshold voltage. In this paper we show the state of the art in optimizing NDR devices based on niobium oxide. Moreover, we show examples of how the devices can be applied to electronic circuits.