Integration of CMOS electronic circuits and electromechanical resonators has been pursued for a long time by many different research groups and even foundries. This would improve the overall performance of electromechanical oscillators and sensors. However, the postprocessing on the CMOS substrates that is necessary to attain this integration increases the production cost so much that it becomes not interesting in most cases. We present here a method of embedding a nano electromechanical resonator within a CMOS substrate by making use of the metal layers and intermetal dielectrics to build a phononic cage that stops most acoustic energy from being lost, and thus the resonator quality factor can reach values of more than 3000 at a frequency of 3.37 GHz, taking the particular case of a 65-nm node. Our results show that the performance of the integrated resonator, both in terms of quality factor and electromechanical coupling will improve when moving to smaller nodes, thus setting the roadmap for future hybrid systems.