Ultra-Thin Artificial Magnetic Conductor for Gain Enhancement of Antenna-on-Chip

Abstract

System-on-chip (SoC) has become an attractive solution to achieve highly integrated wireless systems. However, the antenna-on-chip (AoC) suffers from poor radiation due to the lossy silicon substrate in standard complementary metal–oxide–semiconductor (CMOS) processes. Artificial magnetic conductors (AMCs) with the ground plane above the silicon can enhance the radiation; however, fitting the AMC completely in the thin stack-up (~10–15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> ) is extremely challenging, particularly for frequencies below 100 GHz. In this article, metallic posts (MPs) and embedded guiding structures (EGSs) have been investigated to reduce the AMC thickness by employing the available vias and metal layers in the stack-up. An in-house CMOS-compatible process has been used to realize the AoC, where typical low-conductivity adhesion layers have been avoided to reduce the undesired losses by using the surface roughness in a unique fashion. With MP and EGS approaches, AMC thickness can be reduced by 33% and 41%, respectively. The AMC with EGS fits within an oxide of a thickness of 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> . A monopole antenna, backed by this AMC, demonstrates a gain of 5.85 dBi and a radiation efficiency of 57% at 94 GHz, bettering the gain and radiation efficiency by 9.15 dB and 42%, respectively, compared to the case without AMC.