Feasibility study of GaN-based MEMS capacitive microphone using finite element method

Gallium nitride (GaN) is an excellent choice of semiconductor material due to its optoelectronic, mechanical and wide bandgap properties which are highly demanded by high-power and radio-frequency (RF) electronics but also widely employed for the fabrication of Light Emitting Diode (LED). In this paper, we explored the advantage of GaN as an electromechanical material to be used in microelectromechanical systems (MEMS) microphone as a thin film membrane through a theoretical study performed using the finite element method. We consider also the anisotropy and symmetry structural of GaN to be employed as microphone membrane. In addition, we compared also its performance in terms of sensitivity, C-V measurement and pull-in voltage with several conventional membrane materials such as silicon, nickel, and silicon nitride. The result shows that GaN-based MEMS capacitive microphone has sensitivity -57 dBV/Pa which is 4% higher than silicon nitride-based microphone and resonance frequency of 19 kHz which is higher 11.3% than nickel-based microphone. Hence, this theoretical study could pave a way for GaN to be developed especially for MEMS microphone applications and boasted also by the recent advancement of GaN related fabrication. The advantages of GaN compared to other conventional semiconductor material could be useful for the development of ultrasonic MEMS microphone for utilize detection of sound beyond audible frequency range

Third-order nonlinearity with subradiance dark-state in ultra-strong excitons and surface plasmon coupling using self-antiaggregation organic dye

A strong coupling regime with dressed states is formed when a propagating surface plasmon (PSP) mode coherently exchanges energy with an ensemble of excitons at a rate faster than the system's losses. These states are superpositions of superradiance excitons and PSP modes, accompanied by remaining subradiance or 'dark' exciton states. Dark-states are ubiquitous, especially in disordered systems, and they rise in number as the number of excitons increases. Here, the ultra-strong coupling regime was experimentally observed with the coupling strength to bare energy as high as g/${E}_{exciton}\,$∼ 0.23 using a self-antiaggregation organic dye, BOBzBT2 in an Otto-SPR configuration. We show that the hybrid system of excitons in a nonlinear organic dye layer and a PSP mode can be described by employing dark-state in a theory of nonlinear third-order sum-frequency generation (TSFG). Close agreement between the theory and the experiment has been demonstrated. The study opens up a new perspective for establishing a relationship between the optical properties of a third-order nonlinear material and the extent of strong coupling

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У статті коротко описана методика проведення позакласної роботи з інформатики у початковій школі

Analysis and simulation of carriers statistic for semiconducting single wall carbon nanotube

In scaling down to 10 nm, the electron transportation is predominantly ballistic. Moreover, in most of the doped nanoscale devices, the carrier density is in the degenerate regime. In these cases the failure of Boltzmann statistic has led the research to new explanations. In this paper the authors formulate and simulate the carrier concentration in a semiconducting single wall carbon nanotube using the Fermi-Dirac distribution function. It was shown that the band structure of semiconducting single wall carbon nanotube nearby the minimum energy is parabolic and density of state is proportional to the Fermi-Dirac distribution. In the non-degenerate regime, Fermi energy is a weak logarithmic function of carrier concentration and varies linearly with temperature, but for strongly degenerate statistics, the Fermi energy is a strong function of carrier concentration and is independent of temperature

A Theoretical Study of Surface Mode Propagation with a Guiding Layer of GaN/Sapphire Hetero-Structure in Liquid Medium

Gallium Nitride (GaN) is considered as the second most popular semiconductor material in industry after silicon. This is due to its wide applications encompassing Light Emitting Diode (LED) and power electronics. In addition, its piezoelectric properties are fascinating to be explored as electromechanical material for the development of diverse microelectromechanical systems (MEMS) application. In this article, we conducted a theoretical study concerning surface mode propagation, especially Rayleigh and Sezawa mode in the layered GaN/sapphire structure with the presence of various guiding layers. It is demonstrated that the increase in thickness of guiding layer will decrease the phase velocities of surface mode depending on the material properties of the layer. In addition, the Q-factor value indicating the resonance properties of surface mode appeared to be affected with the presence of fluid domain, particularly in the Rayleigh mode. Meanwhile, the peak for Sezawa mode shows the highest Q factor and is not altered by the presence of fluid. Based on these theoretical results using the finite element method, it could contribute to the development of a GaN-based device to generate surface acoustic wave, especially in Sezawa mode which could be useful in acoustophoresis, lab on-chip and microfluidics applications

Performance reduction and discrepancies between supported and suspended 1D photonic-crystal/photonic-wire with medium extended microcavity length

We report the performance of silicon-on-insulator medium-length extended microcavity (3 to 4.5  μm long) one-dimensional photonic crystal waveguide. Quality-factor (Q-factor) values ranging from 2000 to 37,000 were observed. The waveguides/wire were fabricated using an inductively coupled plasma reactive ion etching with SF6 and C4F8 gasses. Optical transmission of the design is heavily influenced by the surface roughness of the waveguide wall. We achieved a good free spectral range control for resonance frequency separations in between 39 and 65 nm. Supported and suspended microcavity structures for the case of a medium-length extended microcavity were compared. We observed an inferior performance in terms of the optical transmission and Q-factor in the latter. We have selected 4-μm microcavity length for comparison. The suspended structure was obtained by utilizing the wet etching technique on the same device. A high Q-factor value of ∼26,000 was observed in one of the resonances excited for cladding-layer supported extended microcavity. However, the Q-factor was reduced to ∼17,000 after removing the silica cladding beneath the silicon waveguide core