CMOS compatible electrooptic plasmonic modulators are slated to be key components in chip-scale photonic circuits. In this work, we investigate detailed design and optimization protocols for electrooptic plasmonic modulators that are suitable for free-space coupling and on-chip integration. The metallic structures in the proposed devices offer simultaneous electric and optical functions. The resonance-enhanced nonlinear interaction and submicrometer-footprint of these devices meet the stringent requirements for future CMOS modulators, allowing for high-speed operation (>100 GHz) with a decent modulation depth (>3 dB) and moderate insertion loss (<3 dB) at a very low swing voltage ( approximately 1 V) and power dissipation ( approximately 1 fJ/bit). The realization of the proposed structures appears feasible with current materials and lithographic techniques.