The limits to silicon modulator bandwidth and power consumption are explored. Traditional electrical interconnects provide insufficient bandwidth (~10Gb/s) and consume far too much power (~10pJ/bit) for future high performance computing applications. Microphotonic devices closely integrated with advanced CMOS electronics have the potential to dramatically lower intra- and inter-chip communication power consumption while greatly increasing available bandwidth. Our recent results confirm the significant advantages offered by microphotonic communication links. We have broken the 100fJ/bit barrier by demonstrating 4-micron diameter microdisk modulators achieving 10Gb/s data transmission with a bit-error-rate below 10-12 and a measured power consumption of only 85fJ/bit. Through rigorous simulation and experimentation, we consider ultimate limits to silicon modulator bandwidth and power consumption.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.