Date of Award

12-2016

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Advisor

Robert J. Lad

Second Committee Member

Robert W. Meulenberg

Third Committee Member

R. Dean Astumian

Additional Committee Members

MacKenzie R. Stetzer

William J. DeSisto

Abstract

The development of high-temperature-stable electrically conductive thin films and associated microelectronic sensors will enable reduced energy usage and greenhouse gas emissions, and increased longevity of complex, expensive high-temperature machinery. This thesis discusses electrically conductive Pt1−xSix films (0.0⩽x⩽0.8), which were synthesized via electron beam (e-beam) co-evaporation and then characterized to correlate film structure and morphology with electrical conductivity. Both as-deposited films and films annealed up to 1300 °C in nominal oxygen partial pressures of 10−9−10+2 Torr (i.e., ultrahigh vacuum to ambient air) were investigated.

Single-phase films of the well-known orthorhombic-PtSi and tetragonal-Pt2Si phases were formed, as well as of the lesser-known monoclinic-Pt3Si phase, to thicknesses of 50−400 nm. When grown at elevated temperatures (⩾200 °C), Pt3Si film morphology is not columnar like that of co-evaporated Pt2Si and PtSi films, as determined by electron microscopy. Of the three platinum silicides, Pt2Si films exhibit the greatest electrical conductivity, 1.72×106 S/m (~46% the conductivity of pure Pt films), despite measurements that reveal the Pt3Si phase to have greater DOS population near Fermi level.

For Pt3Si films, the film density, thermal expansion, polymorphic transition temperature, and melt temperature were quantified using in situ high-temperature X-ray diffraction methods. Co-evaporated Pt1−xSix films exhibit morphological stability in vacuum to higher temperatures than those synthesized via traditional solid-state reaction methods.

Pt1−xSix films were air annealed up to 1300 °C and the stability of electronic and structural properties was characterized, wherein the Pt3Si composition was discovered to exhibit metallic conductivity up to 45 hours at 1000 °C. However, the mechanism for the stability of these films involves decomposition of the Pt3Si phase into a highly conductive, nanograined Pt network within an amorphous-SiO2 matrix.

Prototype surface acoustic wave (SAW) resonator devices with Pt3Si interdigitated transducers (IDTs) were fabricated using lift-off photolithography and piezoelectric langasite (LGS) substrates. Pt3Si IDTs have < 2 nm of RMS roughness with excellent adhesion, resulting in >10 dB of |S11| reflection coefficient response upon device fabrication, without use of adhesion layer or post-deposition annealing. Preliminary investigations indicate 700 °C as a suitable annealing temperature to decompose Pt3Si and stabilize the Pt/a-SiO2 nanocomposite IDT structure to enable higher-temperature operation.

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