U-shaped stacked structure monolithic transformer for efficiency improvement

Abstract

This article presents a novel monolithic transformer (TF) structure, which is designed to improve TF efficiency by enhancing the quality factor of the metal trace. When the number of thick metal layers is limited in semiconductor technology, it is necessary to use thin metals that have lower quality factors to form the TF coil, which degrades TF efficiency. To overcome this limitation, supplementary walls of metal and a via are connected along both sides of the thin metal to form a U-shaped metal trace, which in turn improves the quality factor and TF efficiency. The proposed structure does not require additional metal layers, other than the metal layers used in the TF configuration. Thus, the proposed structure is widely applicable to all semiconductor technologies, including those that provide only a small number of metal layers. To assess and validate this proposed structure, we fabricated a set of TFs including conventional structures using gallium arsenide (GaAs) technology, which is the most widely used technology in mobile power amplifier (PA) fabrication. The proposed structure was successfully demonstrated to effectively improve the TF efficiency by as much as 8.6% and 6.5% in comparison to a conventional planar structure and a stacked structure, respectively.