Silicon Filled Integrated Waveguides

In this letter, we report, for the first time, a silicon-filled integrated waveguide based on a two mask integrated circuit (IC) process and substrate transfer technique. The fabrication process offers a high degree of control and repeatability on the device geometrical dimensions. Waveguide structures with cutoff frequencies of 35, 50, and 77 GHz were designed and fabricated. In the fundamental ${\rm TE}_{10}$–like operating mode, average losses as low as 0.10 dB/mm with a slow-wave factor of 2.5 were observed. The measurement results are in excellent agreement with HFSS simulations, validating the usability of these structures as a new component in mm-wave IC-designs.

I. Introduction

Modern monolithic microwave integrated circuits (MMIC's) make commonly use of planar transmission lines to transfer and process high-frequency signals. Despite their ease of fabrication, however, integrated transmission lines are prone to high losses. At millimeter wave frequencies (e.g., above 30 GHz), conductor loss alone can easily exceed several dB/cm [1]. Moreover, depending on the substrate permittivity and thickness [2], substrate surface waves may be excited leading to additional attenuation and crosstalk effects.