Mechanical Characterization of Atomic Layer Deposited (ALD) Alumina for Applications in Corrosive Environments
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1222-DD02-14
Mechanical Characterization of Atomic Layer Deposited (ALD) Alumina for Applications in Corrosive Environments Kuang-Shun Ou1, I-Kuan Lin2, Ping-Hsing Wu1, Zhi-Kai Huang1, Kuo-Shen Chen1+, and Xin Zhang2 1. Department of Mechanical Engineering, National Cheng-Kung University, Tainan, Taiwan, R.O.C. 2. Department of Mechanical Engineering, Boston University, Boston, MA, U.S.A. + Corresponding Author, email: [email protected] ABSTRACT In this work, thin ALD alumina films were fabricated for evaluating their capabilities as a barrier material for corrosive environments. The fracture toughness and the corrosion-resisting properties after fatigue cycle of these thin ALD alumina films have been characterized. Indentation tests indicate that the ALD alumina/Al structures could enhance both the yield strength of the metal and the effective fracture toughness of the coated ALD alumina films and this result could be useful for designing nanocomposite structures. However, the test results also indicate that the interfacial strength of the ALD/Al structures was prone to degrade under fatigue loading under corrosive environment. This could potentially be a problem for the long term reliability of related devices operated under a harsh environment. In addition, the strong correlation between indentation behavior and fatigue loading for the structure indicate that nanoindentation response could be possibly used to indicate the damage level of microstructures for future reliability evaluations.
INTRODUCTION Reliability and longevity of microelectronics and microelectromechanical system (MEMS) devices for corrosive environment applications, such as devices for oceanic signal transductions and those for oil well sensing, are traditionally major concerns of device performance evaluation [1, 2]. The metallic circuits are in general vulnerable under the attack of corrosive agents such as salty water or toxic gases. As a result, a barrier layer is required for enhancing the anti-corrosion capability [3]. The deposition temperature of barrier material should be sufficiently low to avoid damaging the already patterned metallic wires. Recently, due to their nature of low temperature deposition, atomic layer deposited (ALD) dielectric films have become potential barrier materials for the above applications. For example, in our preliminary study, under a 90qC salty water environment, the resistance of aluminum wire without ALD alumina protection increased from 0.3 k ȍ to overflow in just two hours. On the other hand, for wires under the protection of 200 nm ALD alumina, the resistance was 0.3 k ȍ and remained essentially unchanged. In addition, the structural integrity of those films is also significantly different. As shown in Figure 1, the unprotected aluminum wires exhibit significant corrosion. However, microscopically, the stress induced by power On/Off during operation due to the thermo-mechanical properties mismatch could effectively damage the interface and cause fatigue delamination. The damaged ALD films could n
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