Electrical & Computer Engineering
Mechanical Limitations of Materials for Steel Foil Based Flexible Electronics
This work investigates mechanical limitations of thin film materials on steel foil substrates for flexible electronic applications. A three layer structure consisting of 100 μm thick stainless steel foil as the substrate, followed by 1 μm thick spin-on-glass passivation layer and 0.3 μm thick patterned aluminum interconnect layer on top with varying widths between 10- 35 μm. A collapsing radius test method was adopted for the bending experiment and an elliptical curve fit was used to facilitate the strain measurement. The failure strain of aluminum interconnect layer was detected by monitoring the continuity of the test circuit during the experiment. The corresponding results reveal that the passivation layer cracked at a tensile strain of 0.46% and delaminated at a compressive strain of 0.68%. The metal interconnect layer ruptured at a tensile strain of 1.26% and delaminated from the substrate at a compressive strain of 1.22% due to the delamination of the passivation layer underneath. The steel foil substrate was plastically deformed at the relative small strain of 0.13%. The flexibility of steel foil based electronics can be effectively improved by using thinner foil substrates.
Rapid Convective Deposition Of Microsphere Monolayers For Fabrication Of Microlens Arrays
Micron-sized microspheres were deposited into thin films via rapid convective deposition using a similar method to that studied by Prevo and Velev, Langmuir, 2003. By varying deposition rate and contact angle, the optimal operating ranges in which 2D closed-pack of silica existed were obtained. Using a confocal laser scanning microscope, dynamic self-assembly of colloidal particles under capillary force during solvent evaporation was revealed. The resulting microstructure is controlled by varying the macroscale parameters and interaction between substrate and colloidal particles played an important role in formation of ordered crystalline arrays. Using the same technique, stacked layers of 1 micron silica monolayer on top of 1.1 micron polystyrene monolayers and subsequent melting of the polystyrene to partially wet the silica microspheres were deposited on GaN layer. This process was implemented on the top p-GaN layer of InGaN quantum wells light emitting diode (LEDs) device structure, resulting in the formation of a microlens array for enhancing its light extraction efficiency. This approach led to ~230% increase of the LEDs output power.
Design of unidirectional subwavelength slit coupler for THz surface plasmons
In this paper, we demonstrate a unidirectional subwavelength slit coupler at THz frequencies by using two-dimensional finite difference time domain (FDTD) modeling. The near-field light emitted from the narrow slit serves as a subwavelength-scaled excitation source. By placing a particular grating structure on one side of the slit, the light could be guided in only one direction. This unidirectional subwavelength slit coupler is amenable to incorporation into optical integrated circuits at THz frequencies.