Fundamental constraints imposing power-frequency trade-offs in conventional electronics have stimulated research on alternative technologies for millimeter-wave and sub-millimeter-wave applications. In this work, we use the picosecond threshold firing of nanoplasma switches to demonstrate on-chip millimeter-wave modulators that rely on a single metal layer. We show amplitude shift keying (ASK) modulation with self-synthesized carrier frequencies up to 66 GHz (limited by the bandwidth of our experimental setup), with output power of 30 dBm. These all-metal nanoplasma modulators are low cost, and generally compatible with different platforms, from CMOS and III-V compounds to flexible substrates. Our work paves the way towards future terahertz communication circuits with large output powers, which otherwise are not practical using high-power amplifiers at frequencies over 100 GHz. In a more general context, the proposed all-metal circuits can potentially synthesize arbitrarily-shaped ultra-wide-band (UWB) signals with applications in advanced wireless communications, radars, and imaging systems.