PhD Defense: "High Aspect Ratio Transmission Line Circuits Micromachined in Silicon"

Shane T. Todd

October 29th (Friday), 2:00pm
Engineering Science Building (ESB), Rm 2001

Abstract: The performance of silicon monolithic microwave integrated circuits (MMICs) has improved dramatically. The scaling down of silicon transistors has increased the maximum frequency of transistors to the point where silicon MMICs have become a viable alternative to compound semiconductor MMICs in certain applications. A fundamental problem still exists in silicon MMICs however in that transmission lines fabricated on silicon can suffer from high loss due to the finite conductivity of the silicon substrate.

A novel approach for creating low-loss transmission lines on silicon is presented in this work. Low-loss transmission lines are created on low resistivity silicon by using a micromachining method that combines silicon deep reactive ion etching (DRIE), thermal oxidation, electroplating, and planarization. Two types of high aspect ratio transmission lines are created with this method including high aspect ratio coplanar waveguide (hicoplanar) and semi-rectangular coaxial (semicoaxial). Transmission lines with impedances ranging from 20 – 80 Ω have been fabricated with minimum measured loss lower than 1 dB/cm at 67 GHz.

Advantages of the high aspect ratio transmission lines are demonstrated including low-loss over a wide impedance range, high isolation, and high coupling for coupled-line circuits. Analytical models have been developed for hicoplanar and semicoaxial transmission lines that predict the effective dielectric constant, characteristic impedance, and attenuation. The models show excellent agreement with simulations and measurements. A new method for calculating the resistance of infinitely thin conductors has been developed and utilized in the models. This method combines Wheeler’s incremental inductance rule and perturbation theory to calculate the infinitely thin conductor line resistance.

About Shane T. Todd:

Shane Todd received his B.S. (Magna Cum Laude) and M.S. degrees in electrical engineering from the University of Florida in 2003 and 2005 respectively. He is currently pursuing the Ph.D. degree in electrical and computer engineering at the University of California, Santa Barbara. His graduate study has been supported by a National Defense Science and Engineering Graduate Fellowship. His research interests include the design, modeling, fabrication, and characterization of microwave and MEMS devices.

Hosted by: Professor John Bowers