Microelectromechanical system microhotplates for reliability testing of thin films and nanowires

Abstract

Microelectromechanical system microhotplates fabricated using silicon-on-insulator wafers were designed and fabricated for accelerated lifetime testing of thin films and nanowires. Thin films of Cr∕Ru∕Au, Cr∕Ru, and Ru were examined as well as nanowires of Ru and RuOx. Rapid thermal cycling at a 1kHz pulse frequency was employed for testing the thin films. Nanowires were characterized using 1kHz and 500Hz pulse frequencies. A 40nm layer of sputtered Au deposited on 12nm of sputtered Ru and 8nm of sputtered Cr displayed a sheet resistance of 1.18Ω∕◻ and a lifetime of 267h before failure when cycled with a peak temperature of 692K. Ru thin films with a thickness of 12nm displayed a sheet resistance of 51Ω∕◻ and a lifetime of 10h under the same conditions. Sputtered Ru and RuOx nanowires with thicknesses of 15 and 32nm, respectively, displayed resistivities of 72×10−8 and 320×10−8Ωm. It was found that the cycling frequency did not influence the nanowire lifetimes in air or in N2. Ru nanowires tested in N2 displayed lifetimes of 450min followed by Ru nanowires tested in air with lifetimes of 340min and finally by RuOx nanowires tested in air with lifetimes of 45min. This latter behavior is attributed to a higher surface diffusion in RuOx compared to Ru. An activation energy of 0.29eV was observed for failure of Ru nanowires tested in air conditions. Biased percolating behavior with critical exponents ranging from 0.5 to 0.7 was found to describe the electrical behavior for all the nanowires.