Shane O'Brien

Inverse scattering approach to multiwavelength Fabry-Pérot laser design

A class of multiwavelength Fabry-Perot lasers is introduced where the spectrum is tailored through a non-periodic patterning of the cavity effective index. The cavity geometry is obtained using an inverse scattering approach and can be designed such that the spacing of discrete Fabry-Perot lasing modes is limited only by the bandwidth of the inverted gain medium. A specific two-color semiconductor laser with a mode spacing in the THz regime is designed, and measurements are presented demonstrating the simultaneous oscillation of the two wavelengths. The extension of the Fabry-Perot laser concept described presents significant new possibilities in laser cavity design.

Capacitance and

This paper presents a method for measuring the complex permittivity of a dielectric material on a dielectric/metal stack without etching the dielectric layer. A series of circular capacitor test structures were designed and fabricated. For the first time, the unwanted capacitance Cp, which is formed by the oxide layer between the bottom metal layer and the silicon substrate, was defined and systematically investigated. The technique is shown to be suitable for characterization of a lead magnesium niobate-lead titanate (PMNT) material on the complex cross sections involved in the development of a novel high-k material. An extremely high- k of 1115 (high capacitance density of 26 fF/μm2) for a PMNT metal-insulator-metal (MIM) capacitor was achieved. In addition, low leakage current density of 2 × 10-10 A/cm2 and low loss tangent were also obtained. These results clearly showed that the PMNT MIM capacitors are very promising for both decoupling and more general RF and mixed-signal applications until the year 2020, according to the International Technology Roadmap for Semiconductors (ITRS).

S

High-performance metal-insulator-metal (MIM) capacitors using novel Pb(Mg_0.33Nb_0.67)_0.65Ti_0.35O₃ (PMNT) thin films were fabricated and investigated. The dielectric properties of the PMNT capacitors were characterized at both dc and radio frequencies. A significant high-κ of 1115 (high capacitance density of 26 fF/μm²) for a PMNT MIM capacitor has been achieved. In addition, small leakage current density of 2 × 10^-10 A/cm² and low loss tangent of 0.0188 are also obtained. The results indicate that high-κ PMNT is a promising candidate material for high-performance MIM capacitors.

-Parameter Techniques for Dielectric Characterization With Application to High-

A diol-based sol-gel method was used to prepare UV sensitive precursor solutions in the processing of modified lead titanate ferroelectric thin films. Films were deposited by spin-coating onto platinized Si-based substrates. A <111> preferential orientation was promoted by appropriated choice of the substrate and multiple deposition and crystallization steps. Processing under UV radiation was carried out in a novel RTP equipment including an arrangement of high intensity UV excimer lamps. To obtain the desired ferroelectric perovskite structure, moderate temperatures and times were required, with respect to those of the processing without UV irradiation. XRD measurements were carried out to determine the degree of orientation of the films. Ferroelectric characterization was made to investigate the optimum poling conditions of the films. Piezoelectric coefficients, e 31 and d 33 , were determined in order to evaluate the feasibility of the use of the films in piezoelectric sensors.

k

A Pb(Mg0.33Nb0.67)0.65Ti0.35O3 material system was synthesized by the sol-gel method; thin films were deposited via the spin-coating technique, and processed using the rapid thermal annealing. Effects of preparation parameters, such as annealing temperature and atmosphere, on the phase composition, microstructure and electrical properties were identified. Morphologically uniform and crack-free films were obtained. Among the obtained films, the highest k value was found to be 1425 for the 380 nm thick film that was annealed at 750 °C in O2 indicating the suitability of this material system for ultrahigh-value capacitor applications.

PMNT Thin-Film Layers

We propose a method to combine a number of discrete-mode lasers to construct a complex network with a nontrivial topology. The topological properties of this network are only encoded in the selection of the active modes for each laser, while the optical fibre coupling between the lasers is trivial. In a very simplified model of this network, we establish the stability of the fixed point with all lasing modes switched on.

High-Performance MIM Capacitors Using Novel PMNT Thin Films

A method which combines polymer particle assembly, chemical infiltration and etching with an aerosol assisted deposition process is described for the fabrication of 3D inverse opal (IO) structures with sub-micron periodicity and precision. This procedure not only overcomes limitations associated with slow, expensive micro-fabrication methods but also permits the tuning of refractive index contrast via the direct incorporation of photonically-active, preformed, tailored silicon nanostructures. It is demonstrated that this approach can be used to modify the photonic band gap (PBG) by effectively depositing/patterning optically active silicon nanocrystals (ncSi) onto the pore walls of a 3D inverse opal structure. This simple, yet effective method for preparing functional complex 3D structures has the potential to be used generically to fabricate a variety of functional porous 3D structures that could find application not only in new or improved photonic crystal (PC) devices but also in areas such as catalysis, separation, fuel cells technology, microelectronics and optoelectronics.

Ca and La-Modified Lead Titanate Sol-Gel Thin Films by UV-Assisted Processing for Piezoelectric Sensors

This paper presents the systematic investigation by electrical characterization of PMNT (lead magnesium niobate - lead titanate, Pb(Mg_0.33Nb_0.67)_0.65Ti_0.35O₃) thin-films with different fabrication parameters. The PMNT thin-films are processed under different conditions including annealing at various temperatures. Capacitance-voltage (C-V), current-voltage (I-V), capacitance-frequency (C-F), dissipation factor-frequency (D-F) and complex impedance-frequency (Z-F) measurements are presented.

Sol-gel-derived lead-magnesium-niobium titanate thin films for ultrahigh-value capacitor applications

A proposal for an all-optical memory based on a bistability of single-mode states in a dual-mode diode laser with time-delayed optical feedback is presented. The system is modeled using a multimode extension of the Lang-Kobayashi equations with injected optical pulses. We uncover the bifurcation structure by deriving analytical expressions for the boundaries of the bistable region and demonstrate how the delay time in the external cavity determines an optimal pulse duration for efficient switching of the memory element. We also show the relevant role played by gain saturation and by the dual-mode solutions of the Lang-Kobayashi equations for the existence of the bistable regions. Our results demonstrate that feedback-induced bistability can lead to significant performance improvements when compared to memory elements based on the injection locking bistability in dual-mode devices.

Complex networks based on discrete-mode lasers

To enhance the light extraction efficiency of a resonant cavity light-emitting diode (RCLED), a soft embossing technique was developed to fabricate a 2-D grating on the RCLED output surface. The optimal 2-D grating parameter was designed by a rigorous coupled wave analysis code. By embossing the 2-D grating on the output of a commercial RCLED, a 49% light extraction enhancement was achieved using a novel high refractive index (n = 2) TiO2 sol-gel and a 24% enhancement using a UV curable polymer with lower refractive index (n = 1.56). The overall emission pattern was also modified making the patterned RCLED potentially easier to couple into a fiber.