M.Sc Thesis

M.Sc StudentKatz Shlomo Eric
SubjectElectromagnetic Applications of CMOS-MEMS
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROFESSOR EMERITUS Yael Nemirovsky


The rapid growth in recent years of wireless communications applications - including cell phones, wireless internet, and GPS - has spurred the development of CMOS analog and RF circuits which can be integrated with digital logic on a single chip, a goal known as “System-on-chip” (SoC). However, CMOS technology has deficiencies which complicate its use for high-frequency analog circuits, including low substrate resistivity and significant parasitic capacitances.

One method for overcoming these problems is the use of MEMS (Micro-Electro-Mechanical Systems) technology. Using MEMS, circuits may be micromachined to create specially shaped structures, with more flexibility and possibilities than is possible in CMOS processes alone. This work presents two applications in which MEMS is used to optimize the electromagnetic performance of CMOS designs.

In the first application, MEMS post-processing is used to improve the performance of an RF-CMOS transformer. Parasitic elements in inductors and transformers are often a limiting factor in the performance of RF-CMOS analog circuits. A front-side etching process was applied to a transformer fabricated in a commercially available RF-CMOS process, removing oxide and substrate material from around the transformer metal. Physical measurements and HFSS simulation results indicate substantial improvement in the transformer figures of merit. The improvement obtained is similar to that obtained by other MEMS methods, and is achieved with less cost and complexity than is necessary for the alternative methods.

In the second application, a novel antenna for terahertz radiation detection was designed based on CMOS-SOI-MEMS technology. A pixel array whose design derives from frequency-selective-surface considerations is suspended above a quarter-wavelength resonant cavity. The pixel design differs from the conventional approach of antenna-coupled bolometers in that radiation is directly absorbed in the antenna, rather than inducing current which is dissipated in a discrete resistive element. This leads to higher sensitivity, as more radiation is absorbed in each pixel rather than being scattered and reabsorbed by adjacent pixels. Simulations showed that up to 80% of incident radiation in the 0.5-1.5THz band was absorbed by our pixel designs. The absorbing traces in our micromachined pixel design are suspended and thermally isolated, with the goal of enabling uncooled passive terahertz imaging.