This paper presents an on-chip patch antenna designed for 226-244 GHz frequency range. A 130-nm SiGe BiCMOS technology with Cu back-end-of-line process is used to fabricate this antenna. The antenna patch is realized with the thickest layer of aluminium on top-most metal layer of the technology. The lowest thin metal layer from the back-end-of-line acts as ground plane for the antenna, shielding the antenna from the thick bulk silicon of the IC technology, which would make the antenna less efficient. The thin substrate narrows the antenna bandwidth, but it provides moderate radiation efficiency. A proximity-coupled feed patch with a slot in it provides a measured bandwidth of 18 GHz, a broadside measured realized gain of 3 dBi, and a simulated radiation efficiency of 34.5 %.