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An Introduction to MEMs Engineering - Nadim Maluf and Kirt Williams Part 3

Tham khảo tài liệu 'an introduction to mems engineering - nadim maluf and kirt williams part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 20 Materials for MEMS Thin Metal Films The choice of a thin metal film depends greatly on the nature of the final application. Thin metal films are normally deposited either by sputtering evaporation or chemical vapor deposition gold nickel and Permalloy NixFey and a few other metals can also be electroplated. Table 2.3 lists some metals and conducting compounds used as thin films along with their resistivities resistivity varies with deposition conditions and is usually higher for thin films than for bulk material . For basic electrical interconnections aluminum usually with a few percent silicon and perhaps copper is most common and is relatively easy to deposit by sputtering but its operation is limited to noncorrosive environments and to temperatures below 300 C. For higher temperatures and harsher environments gold titanium and tungsten are substitutes. Aluminum tends to anneal over time and with temperature causing changes in its intrinsic stresses. As a result it is typically located away from stress- or strain-sensing elements. Aluminum is a good light reflector in the visible and gold excels in the infrared. Platinum and palladium are two very stable materials for electrochemistry though their fabrication entails some added complexity. Gold platinum and iridium are good choices for microelectrodes used in electrochemistry and in sensing biopotentials. Silver is also useful in electrochemistry. Chromium titanium and titanium-tungsten are frequently used as very thin 5-20 nm adhesion layers for metals that have poor adhesion to silicon silicon dioxide and silicon nitride. Metal bilayers consisting of an adhesion layer e.g. chromium and an Table 2.3 List of Selected Metals That Can Be Deposited As Thin Films Up to a Few ttm in Thickness with Corresponding Electrical Resistivities and Typical Areas of Application Metal pMA cml Typical Areas of Application Ag 1.58 Electrochemistry Al 2.7 Electrical interconnects optical reflection in the