Najla S. Khan

Graduation Semester and Year

2009

Language

English

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering

Department

Electrical Engineering

First Advisor

Donald Butler

Abstract

Over the past decade, a multitude of micro-electro-mechanical (MEMS) devices have been developed and commercialized due to their low power consumption, reduced cost and compact size. In recent years, significant advancements in technology have extended MEMS development towards radio frequency, microwave and millimeter wave applications. The need for micro-machining and MEMS based systems for RF and microwave applications arises from the inherent limitations of existing RF devices. Motivation for incorporating MEMS based fabrication technologies into microwave and millimeter wave systems can be classified into three main categories: precision, system integration and performance. As frequency increases, the size of RF components decreases. [1] For this reason, it is crucial that the dimensions of the RF components remain in the sub-millimeter range, necessitating high precision fabrication techniques. Such precision is only achievable through the micro-machining methodology. For a complete useful RF application, these components also need to operate properly when integrated with other analog functions such as filters, oscillators or mixers. The micro-machined RF components are fully compatible with complete system integration. Finally, the performance of these devices is also notable. Due to their capability of achieving a high quality factor or Q, reducing insertion loss and increasing bandwidth, RF MEMS devices have gained largely popularity in recent years. Such devices, especially resonators, can also be fabricated to achieve very high Q (in the tens of thousands range) for frequencies up to and beyond 10 MHz. [2]A key limitation in commercializing RF MEMS devices, such as resonators, is the reliability factor. Reliability requirements of different MEMS devices are specific and unique to the type and purpose of their application. Understanding the reliability of RF devices stems primarily from the knowledge of their failure behavior and mechanisms, which are: stiction, delamination, dampening and mechanical failure over a long period of time. [2] Unfortunately, at the time of this writing, there has not been enough research and development to fully understand these reliability issues. This research focuses on some of the factors of mechanical failure by investigating the effect of the changes in the elastic properties on the resonant and damping characteristics of the resonator beam. In an attempt to eliminate this mechanical failure, both the linear and non-linear behavior of RF MEMS resonators are investigated and a strategy is developed to improve the performance through both modeling and understanding the complete dynamics of RF MEMS devices. The complete resonator dynamics is investigated with the aid of the Agilent Advanced Systems (ADS) and MathCAD software packages. Furthermore, an amplifier circuit is designed which is integrated with the resonator model via wire bond and then characterized using an Agilent E5071C Series Network Analyzer. This improves the Q-factor (between 100 and 150) and the S21 parameter (between 10 dB and 25 dB) of the resonator significantly. Without the amplifier circuit, Q-factor is found to be between 10 and 50 and S21 between -40 and -60 dB. Thus, this model is an innovative method of reducing undesired insertion loss, thereby, improving the performance of the resonator model.

Disciplines

Electrical and Computer Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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