Graduate Studies
Embargoed Master's Theses
First Advisor
Jeffrey Shield
Committee Members
Craig Zuhlke, Jerry Hudgins
Date of this Version
4-2025
Document Type
Thesis
Citation
A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science
Major: Mechanical Engineering and Applied Mechanics
Under the supervision of Professor Jeffrey Shield
Lincoln, Nebraska, April 2025
Abstract
As microelectronics evolve towards higher power outputs, miniaturization, and increased power density, effective thermal management is vital for stable operation. This research aims to investigate bonding dissimilar materials such as diamond (Dia), molybdenum (Mo), and a molybdenum-copper alloy (Mo85Cu15) to enhance thermal conductivity. Dia, known for its exceptional thermal conductivity, is sputter-coated with 500 nm of Mo. This layer serves both as a thermal interface and a carbide-forming interlayer to promote bonding to Dia. The second interface, between Mo and Mo85Cu15, is formed via high-temperature high pressure (HTHP) diffusion bonding, investigating both solid-state and liquid state phase mechanisms. A temperature range of 1050 °C to 1100 °C with a constant torque of 3 in-lbs. was investigated.
The influence of bonding temperature on interfacial adhesion is central in this research. Samples bonded at 1070 °C and 1085 °C demonstrated successful adhesion, with pull tests results revealing adhesion strengths of 0.99 MPa and 0.14 MPa, respectively. The results show that adhesion of the samples is highly sensitive to the bonding temperature. Post-fracture analysis conducted by Energy Dispersive X-ray Spectroscopy (EDS) showed that failure consistently occurred at the sputtered Mo and Dia interface. This observation, further supported by surface examination, identifies the sputtered Mo and the Dia interface as the weakest link in the material stack, while implying a comparatively stronger adhesion at the sputtered Mo and Mo85Cu15 interface.
This research investigates the feasibility of integrating high thermally conductive materials into microelectronics. Hybrid bonding techniques are utilized to join dissimilar materials together with the aim of enhancing the overall thermal conductivity of the sample. Findings in this work lay the building block for future research in enhancing microelectronic reliability for greater power densities required.
Advisor: Jeffrey Shield
Comments
Copyright 2025, Brooke B. Carlson. Used by permission