Photodefinable Metal Oxide Dielectrics II: Direct Fabrication of Patterned High-k Dielectrics for Low Cost RF Capacitive
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Photodefinable Metal Oxide Dielectrics II: Direct Fabrication of Patterned High-k Dielectrics for Low Cost RF Capacitive MEMS Switches Michael Romeo1, Isaac Finger1, Augustin Jeyakumar1, Guoan Wang2, John Papapolymerou2, and Clifford L. Henderson1* 1 School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, GA 30332-0100 2 School of Electrical and Computer Engineering, Georgia Institute of Technology, 777 Atlantic Drive NW, Atlanta, GA 30332-0250 * Corresponding Author: E-mail: [email protected], Phone: (404)-385-0525 ABSTRACT In this paper, recent advancements related to a novel approach for fabricating low cost capacitive radio frequency microelectromechanical (RF MEMS) switches using directly photodefinable high dielectric constant metal oxides are discussed. In this approach, a radiation sensitive metal-organic precursor is deposited via spin coating and converted patternwise to a metal oxide using exposure to ultraviolet light. The feasibility of this approach has previously been demonstrated by fabricating bridge-type and cantilever-type RF MEMS switches. These early experiments showed that the photopatterned oxides displayed dielectric breakdown strengths that were insufficient for reliable operation of MEMS switches which required actuation voltages on the order of 20 V to 30 V. Recent work has focused on developing advanced processes based on the photodefinable metal-organic approach that can produce oxides with higher dielectric breakdown strengths and higher dielectric constants. A variety of postpatterning processes, including thermal baking and oxygen plasma annealing, were investigated and the impact of such processing on the resulting dielectric properties are discussed in this paper. It is shown that a combination of thermal annealing and oxygen plasma treatment can substantially improve the dielectric breakdown strength of the metal oxides produced using the photosensitive metal-organic process.
1. INTRODUCTION Low-cost MEMS switches are prime candidates to replace the conventional GaAs FET and p-i-n diode switches in RF and microwave communication systems, mainly due to their low insertion loss, good isolation, linear characteristic and low power consumption. Various designs of capacitive RF micromechanical switches made out of nickel [1], aluminum [2,3], gold [4], and copper [5] have been so far reported in literature, with a variety of intended applications such as phase shifters, reconfigurable filters, tuners and other planar circuits. The structure of these switches consists of a lower electrode, a very thin dielectric layer, and a moveable membrane. Several studies have shown the importance of the dielectric layer in the switch performance (Cmax/Cmin ratio, isolation) and reliability [6]. In most MEMS switches reported so far, this dielectric layer is typically silicon nitride deposited with PECVD or HDICP CVD techniques [7]. A switch that uses barium strontium titanate (BST) as the dielectric layer has also been report
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