Tamás Kárpáti

Synthesis, electronic properties and electropolymerisation of EDOT-capped σ3-phospholes

EDOT-capped sigma3-phosphole self-rigidifies due to an unprecedented P-O interaction and can be electropolymerised affording functionalizable polymers.

Self-consistent real three-dimensional simulation of vertical-cavity surface-emitting lasers

A self-consistently coupled three-dimensional dynamical model is presented for the first time, to our knowledge, to simulate noncircular vertical-cavity surface-emitting lasers. The electric, thermal, and optical processes are formulated using finite-volume-method discretization adopted on a unified mesh consisting of prism elements. Steady-state and dynamical calculations are shown for specially designed structures. An efficient numerical treatment enables one to perform large-scale calculations on single computers.

Real three-dimensional optical simulation of non-circular VCSEL structures with finite volume method

This work presents a real three-dimensional (3D) solution of the scalar Helmholtz-equation for VCSELs with finite volume method (FVM). The advantage of this formulation is that the order and structure of the system matrix can be reduced compared to vectorial finite element approach, and thus the feasible problem size can be significantly increased. Moreover, the combination with three-dimensional current flow and thermal analysis can be realized with the same discretization without extra numerical efforts. Results show the calculated fundamental mode profile on a sample VCSEL with square oxide aperture.

Optical simulation of vertical-cavity surface-emitting lasers with noncylindrical oxide confinement

Vertical-cavity surface-emitting lasers (VCSELs) have a high potential in telecommunication applications. We have developed two extensions of the weighted index method (WIM): the empirical effective-radius method (ER-WIM) and the hybrid analytical-numerical method. The ER-WIM defines two effective radii for a noncircular aperture. The two models proposed here aim to simplify the problem to a physically acceptable level. They are still reliable but computationally more feasible because they are significantly faster than a full-3D FEM and never require large computer resources.

Real three-dimensional dynamical VCSEL simulation with spatially distributed noise sources

A self-consistently coupled three-dimensional dynamical model is presented for non-circular vertical-cavity surface-emitting lasers. The electric, thermal and optical processes are simulated using the finite volume method formulation adopted on a unified mesh consisting prism elements. Spatially distributed noise sources are incorporated into the quantum-well dynamics providing relative intensity noise spectrum.

Reliable aluminum contact formation by electrostatic bonding

The paper presents a detailed study of a reliable method developed for aluminum fusion wafer bonding assisted by the electrostatic force evolving during the anodic bonding process. The IC-compatible procedure described allows the parallel formation of electrical and mechanical contacts, facilitating a reliable packaging of electromechanical systems with backside electrical contacts. This fusion bonding method supports the fabrication of complex microelectromechanical systems (MEMS) and micro-opto-electromechanical systems (MOEMS) structures with enhanced temperature stability, which is crucial in mechanical sensor applications such as pressure or force sensors. Due to the applied electrical potential of −1000 V the Al metal layers are compressed by electrostatic force, and at the bonding temperature of 450 °C intermetallic diffusion causes aluminum ions to migrate between metal layers.

Numerical optimization of single-mode photonic crystal VCSELs

The lattice constant of a single-defect photonic crystal vertical-cavity surface-emitting laser (PhC-VCSEL) is numerically optimized to achieve the highest single-mode power in the fundamental mode. The simulated results are compared to measured device characteristics, and the different factors influencing the single-mode behavior are analyzed.

Real three-dimensional spatio-temporal VCSEL simulation

We present a real three-dimensional (3D) dynamically combined model for the first time, realized with finite volume method on a flexible, triangle-based mesh. The simulation consists of a current flow, a heat flow and optical mode solvers, coupled to each other self-consistently in the quantum well laser dynamics. The transport of free carriers across the mirrors satisfies the Laplace-equation, where heterojunctions are modeled with increased resistivity in the axial direction.

Microplasma chamber for molecular emission spectroscopy

In this work the fabrication, functional characterisation and analytical application of a micromachined plasma reactor based on Dielectric-Barrier Discharge (DBD) is presented. The microplasma reactor was manufactured by the combination of conventional micromachining technology and microchannel structuring methods to form coplanar electrode system in compact glass reactor chamber. The functional parameters of the miniaturized DBD micro plasma generator were determined during the device was applied as atmospheric pressure gas plasma source. The molecular composition in the micro plasma chamber was monitored by optical spectrometer, and the analytical applicability of the source was demonstrated by detection molecular emission spectra of test gases and vapours. For studying feasibility in analytical applications CO2 and organic solvent vapour were injected and the change in detected molecular emission spectra were analysed qualitatively.

Flexible packaging for tyre integrated shear force sensor

Wireless Si 3D force sensor made by MEMS technology was integrated and tested on the sidewall of a tyre using flexible rubber repair patch (patent pending) in order to monitor the deformation of the rotating tyre in automotive applications. Finite element simulation was used to determine the optimal positioning of the sensor structure. Power supply and wireless communication is based on inductive coupling. Static characterization on a measurement pad and preliminary real life-testing has been carried out.