Shawna M. Liff

Achieving excellent electro-optic activity and thermal stability in poled polymers through an expeditious crosslinking process

A series of highly efficient and thermally stable electro-optic (EO) polymers have been developed by poling and crosslinking in situ the blend of high glass-transition temperature (Tg) anthracene-containing polymers and acrylate-functionalized dendritic nonlinear optical (NLO) chromophores. By molecular engineering of the shape, nonlinearity, Tg, and crosslinking moieties of the chromophores and polymers, the resultant materials showed significantly enhanced EO activities (r33 values as high as 126 pm V−1 at 1310 nm) and alignment stability (up to 200 °C). Poling efficiency of these EO polymers could be improved by 35–50% by using simplified lattice hardening and poling protocols. The combined good processability, large EO activities, and high temperature stability endow these materials as promising candidates for device exploration in the CMOS-based photonics.

A low power electro-optic polymer clad Mach-Zehnder modulator for high speed optical interconnects

Electro-optic (EO) polymer cladding modulators are an option for low-power high-speed optical interconnects on a silicon platform. EO polymers have inherently high switching speeds and have shown 40 Gb/s operation in EO polymer clad ring resonator modulators (RRM). In EO polymer clad RRM, the modulator’s area is small enough to be treated as a lumped capacitor; the capacitance is sufficiently low that the modulation speed is limited by the bandwidth of the resonator. A high Q resonator is needed for low voltage operation, but this can limit the speed and/or require precise control of the resonator’s wavelength, necessitating power consuming heaters to maintain optimal performance over a large temperature range. Mach Zehnder modulators (MZM), on the other hand, are not as sensitive to temperature fluctuations, but typically are relatively long and must employ power consuming terminated travelling wave electrodes. In this paper, a novel MZM design is presented using an EO polymer clad device. In this device, the electrodes are broken into short parallel segments and the waveguide folds around them. The segments of the electrode length are designed to provide good signal integrity up to 20 GHz without termination. The electrodes are driven by a single drive voltage and provide push-pull modulation. Modulators were designed and fabricated using silicon nitride waveguides on bulk silicon wafers and were demonstrated at high speed (20 GHz). A VπL as low as 1.7 Vcm is measured on initial devices. An optimized device could provide 40 Gb/s performance at 1 V drive voltages, ~100 fF total device capacitance and less than 2 dB optical insertion loss.

Moisture-assisted failure mechanisms in underfill epoxy/silicon systems for microelectronic packaging

Synergistic effects of moisture and mechanical stress on debond kinetics of underfill epoxies used in semiconductor packaging are increasingly understood, however, the dramatic effect of increasing both temperature and humidity is not well known. We demonstrate a way to quantitatively measure the mechanical and kinetic behavior of an underfill epoxy resin containing a broad range of filler particles. With the introduction of fillers into the bisphenol-F-based resin, the fracture energy at the epoxy/Si interface is largely increased compared to the unfilled epoxy/Si interface. We characterize the cohesive and adhesive properties of each filled epoxy to the adjacent passivated silicon substrate and report on the moisture-assisted debonding kinetics in varying humidity and temperature environments, including accelerated testing conditions.

Efficient and scalable single mode waveguide coupling on silicon based substrates

One of the key challenges in Silicon based optical interconnect system remains to be the efficient coupling of optical signals from the submicron size on-chip waveguides to standard single mode (SM) fibers with low insertion loss (IL) and relaxed alignment tolerance. Large optical alignment tolerance allows optical connectors to be attached to on-chip waveguides passively using standard semiconductor pick-and-place assembly tools that have placement accuracies of 10- 15μm. To facilitate the assembly, optical fiber coupling elements need to be modular and compact. They have to also have low profile to avoid blocking air flow or mechanical interference with other elements of the package. In this paper we report the development of a two-dimensional (2D) SM optical fiber coupling architecture that consists of Si based photonic lightwave circuit (PLC) substrate and a high-density micro-lensed fiber optic connector. The system is compact, efficient and has large optical alignment tolerance. At 1300nm an insertion loss of 2.4dB and 1.5dB was measured for the PLC module and the fiber optic connector, respectively. When the PLC module and connector was aligned together, a total insertion loss of 7.8dB was demonstrated with x,y alignment tolerance of 40μm for 1dB optical loss. The SM optical coupling architecture presented here is scalable, alignment tolerant and has the potential to be manufactured in high volume. To our knowledge, such a system has not been reported in the literature so far.