Innovations in Fully Integrated Reconfigurable Intelligent Surfaces: From Semiconductor Fabrication to RF Design

This paper presents a novel multi-physics (Electromagnetics based semiconductor physics) model based CMOS fabrication process enabling a new class of Reconfigurable Intelligent Surfaces (RIS) topology. By analyzing and resolving differences between CMOS/EM simulations and the actual fabrication process, the research successfully implemented varactor functionality within an innovative PIN varactor. The varactor was designed with an extended intrinsic layer, enabling forward varactor operation through electromagnetic analysis of dopant behavior. This design approach enabled the co-design of the active component and the RIS, enhancing overall performance by completely embedding the PIN varactor into the substrate layers without increasing the overall foam-factor or thickness. Based on this technology, a RIS featuring a 12 × 12 unit cell array (6λ × 6λ) was co-designed and fabricated on a 4-inch Si wafer, achieving effective beam steering. At 28 GHz, the system demonstrated a peak gain of 11.45 dB and a scanning range from 0 to 40 degrees, facilitated by 576 fully embedded active components. The proposed technique merges CMOS fabrication with mmWave EM design, introducing a novel approach to RIS design.