We present a new solid state rectifier, compatible with CMOS integrated circuit, suitable to direct conversion of terahertz radiation, at room temperature. The structure creates a rectenna, consists in a truncated conical helix extruded from a planar spiral and connected to a nanometric metallic whisker at one of its edges. The whisker reaches the gate of a MOS-FET transistor. Rectification can be obtained by the self-mixing effect occurring into the plasma waves generate underneath the gate. The proposed solution is easy to integrate with existing imaging systems. No need of scaling toward very scaled and costly technological node is required, since the plasma wave are not dependent on the gate extension. The remaining electronics should only provide the necessary integrated readout. A theoretical explanation of the self-mixing process, and TCAD simulations showing the onset of the DC potential are presented. An additional detector structure, the double barrier rectifier, is also presented for comparison.