{"id":1579,"date":"2010-07-12T10:46:04","date_gmt":"2010-07-12T14:46:04","guid":{"rendered":"https:\/\/wpmu2.mit.local\/?p=1579"},"modified":"2010-07-12T15:14:54","modified_gmt":"2010-07-12T19:14:54","slug":"metallic-and-other-glasses-for-mems","status":"publish","type":"post","link":"https:\/\/wpmu2.mit.local\/metallic-and-other-glasses-for-mems\/","title":{"rendered":"Metallic and Other Glasses for MEMS"},"content":{"rendered":"

Chalcogenide glasses are widely used as \u201cphase change materials\u201d for optical data storage media in rewrit\u00adable compact discs (CD\u00b1RW) and rewritable digital video disks (DVD\u00b1RW, DVD-RAM). Recently, they have also shown high potential for use in phase-change random ac\u00adcess memories (PC-RAMs or PRAMs), which might replace flash memories in the future. In these applications, information storage is accomplished by reversible amorphization and crystallization.\u00a0 Metallic glasses have also recently generated interest because of their having a combination of high elastic moduli and fracture strengths.\u00a0 They have been used, for example, as torsional springs in micro-mirror arrays.\u00a0 In both types of applications, the mechanical properties of films in the glassy state are important in determining their functionality and reliability.\u00a0 Of particular interest is the stability in the glassy state and stress changes associated with crystallization, both of which can be studied through measurements of cantilever displacements associated with crystallization.<\/p>\n

In prior work we have shown that the stress change associated with crystallization of chalcogenides depends strongly on the thickness of films, and on whether or not the films are capped with materials with high stiffness (Figure 1).\u00a0 This large dependence is the result of inelastic accommodation of a component of the large volume change (~6%). The yield stress of the glasses is strongly thickness- and encapsulation-dependent [1<\/a>]<\/sup> [2<\/a>]<\/sup>.<\/p>\n

In more recent studies we have focused on metallic glasses, both for applications as memory media and as mechanical components in MEMS devices.\u00a0 We have used combinatorial deposition on cantilever arrays to characterize the volume change on crystallization in the binary Cu-Zr [3<\/a>]<\/sup> and ternary Cu-Zr-Al systems [4<\/a>]<\/sup>.\u00a0 We found significant and complex dependences of the volume\/stress change on composition (Figure 2).\u00a0 These variations were also found to correlate with the ease with which these alloys of specific compositions could be deposited or quenched into the glassy state.\u00a0 We are now measuring the compositional dependence of the elastic modulus, thermal expansion coefficient, and hardness of as-deposited and annealed metallic glasses.<\/p>\n

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\"Figure<\/a> <\/dt>\n
Figure 1: Crystallization-induced stress in Ge2<\/sub>Sb2<\/sub>Te5<\/sub> (GST) layers for different GST-to-SiN cantilever thickness ratios, hGST<\/sub>\/hSiN<\/sub><\/em>. Tensile stress is defined to be positive. The filled squares are data points for samples with ZnS\u2013SiO2<\/sub> capping and underlayers [2<\/a>]<\/sup>. <\/dd>\n<\/dl>\n
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\"Figure<\/a> <\/dt>\n
Figure 2: Density changes associated with crystallization as a function of the position of nine die with cantilever arrays in a sputtering system with three separate Al, Cu, and Zr sources. Compositions vary over ranges of about 10% (see [4<\/a>]<\/sup>). <\/dd>\n<\/dl>\n



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\r\nReferences
  1. J.A. Kalb, Q. Guo, X. Zhang, Y. Li, C. Sow, and C.V. Thompson, \u201cPhase-Change Materials in Optically Triggered Microactuators,\u201d\u00a0J. of Microelectromechanical Systems<\/em> 17, 1094 (2008) [↩<\/a>]<\/li>
  2. Q. Guo, M. Li, Y. Li, L. Shi, T.C.C., J.A. Kalb, and C.V. Thompson, \u201cCrystallization-induced stress in thin phase change films of different thicknesses,\u201d Appl. Phys. Lett.,<\/em> 93, 221907 (2008). [↩<\/a>] [↩<\/a>]<\/li>
  3. Y. Li, Q. Guo, J.A. Kalb, and C.V. Thompson, Matching Glass-Forming Ability with the Density of the Amorphous Phase,\u201d Science <\/em>322, 1816 (2008). [↩<\/a>]<\/li>
  4. Q. Guo, J. H. Noh, P. K. Liaw, P. D. Rack, Y. Li, C. V. Thompson, \u201c<\/sup>Density change upon crystallization in amorphous Zr-Cu-Al thin films,\u201d Acta Materialia<\/em> 58<\/strong>, 3633 (2010). [↩<\/a>] [↩<\/a>]<\/li><\/ol><\/div>","protected":false},"excerpt":{"rendered":"

    Chalcogenide glasses are widely used as \u201cphase change materials\u201d for optical data storage media in rewrit\u00adable compact discs (CD\u00b1RW) and…<\/p>\n<\/div>","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[29],"tags":[69,4167],"_links":{"self":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/1579"}],"collection":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/comments?post=1579"}],"version-history":[{"count":12,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/1579\/revisions"}],"predecessor-version":[{"id":1770,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/1579\/revisions\/1770"}],"wp:attachment":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/media?parent=1579"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/categories?post=1579"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/tags?post=1579"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}