The surge in transistor scaling and integration processes has driven the growth of wireless technology, especially low-cost millimeter-wave systems. Based on mainstream Silicon technology, System-on-Chip (SoC) has become an attractive approach to achieve the required high level of on-chip integration for modern wireless systems. However, the low resistivity (ρ=10 Ω-cm) and high relative permittivity (εr=11.9) of the silicon substrate are unsuitable for hosting antennas on it, because the Radio Frequency (RF) power is lost in the lossy silicon substrate, and some of it gets radiated in a certain undesired direction due to the surface waves. This has caused such antennas, typically known as Antenna-on-chip (AoC), to be poor radiators. Introducing an on-chip artificial magnetic conductor (AMC) between the substrate and the antenna can isolate the silicon substrate from the antenna and provide in-phase reflection, thereby improving the radiation performance. However, the drawback of conventional on- chip AMC is its relatively large thickness, which is extremely difficult to achieve on the thin silicon dioxide layer of typical CMOS processes (~10-15 μm). To resolve this problem, the embedded guiding structures have been designed between the periodic structure layer and the ground plane to realize an ultra-thin AMC which is suitable for thin oxide stack up of typical CMOS processes. Specifically, a patch-based AMC with embedded guiding structures has been designed for an on-chip monopole antenna operating at 94 GHz. The performance of the AMC has been studied for different resistivity substrates (from 10-3 to 103 Ω-cm). The AMC-backed on- chip antenna has been fabricated through an in-house CMOS-compatible process. The adhesion of the metallic layer to the substrate has been improved without using a seed layer, which is typically a low conductivity metal and has a negative impact on the radiation of the AoC. The measured input impedance and radiation performance of the AMC-backed AoC are fairly consistent with the simulations. It provides 5.85 dBi gain with the return loss of 16 dB at 94 GHz. According to the author’s best knowledge, this is the thinnest AMC-based AoC design in the literature.
|Date made available
|KAUST Research Repository