Marco Antonio Robert Alves

Fabrication of sharp silicon tips employing anisotropic wet etching and reactive ion etching

Abstract We developed a process to obtain sharper silicon tips by employing anisotropic etching in a KOH solution followed by SF6 plasma etch. The tips were further sharpened using the established thermal oxidation technique to decrease the cone angle and, therefore, obtain smaller curvature radii. We have analyzed the impact of such changes in geometry on a figure of merit associated with the field emission characteristics. An increase in the figure of merit by a factor of three was found in relation to the tips before sharpening.

CF4 plasma etching of materials used in microelectronics manufacturing

Amorphous hydrogenated carbon a-C:H films, deposited on silicon substrates by radio frequency plasma-enhanced chemical vapor deposition (RF PECVD), and AZw 5214 organic photoresist have been etched in a low-pressure and high frequency tetrafluoromethane (CF4) plasma. The etching of Si and SiO2 was also measured in order to determine their selectivities to a-C:H films and AZ 5214 photoresist. The etch rates were measured as a function of RF power in the range of 20‐60 W. Carbona-C:H films were found to be more etch resistant than organic AZ 5214, Si, and SiO2. AZ 5214 demonstrated a relatively high etch rate (300‐700 A ˚ /min). The best etch rate ratios of Si and SiO2 to carbon films were achieved at low RF power. Carbon films can be used as masks for deep pattern transfer to Si and SiO 2 in photolithography. q 2000 Elsevier Science Ltd. All rights reserved.

Simulation of the enhancement factor from an individual 3D hemisphere-on-post field emitter by using finite elements method.

This paper presents a 3D computational framework for evaluating electrostatic properties of a single field emitter characterized by the hemisphere-on-post geometry. Numerical simulations employed the finite elements method by using Ansys-Maxwell software. Extensive parametric simulations were focused on the threshold distance from which the emitter field enhancement factor (γ) becomes independent from the anode-substrate gap (G). This investigation allowed demonstrating that the ratio between G and the emitter height (h) is a reliable reference for a broad range of emitter dimensions; furthermore, results permitted establishing G/h ≥ 2.2 as the threshold condition for setting the anode without affecting γ.

Numerical study on performance of pyramidal and conical isotropic etched single emitters

Abstract A full three-dimensional model was implemented in order to investigate the electrical characteristics of conical and pyramidal isotropic etched emitters. The analysis was performed using the finite element method (FEM). The simulations of both emitters were modeled using a combination of tetrahedral and hexahedral elements that are capable of creating a mapped and regular mesh in the vacuum region and an irregular mesh near the surfaces of the emitter. The electric field strengths and electric potentials are computed and can be used to estimate the field enhancement factor as well as the current density using the Fowler–Nordheim (FN) theory. The FEM provides results at nodes located at discrete coordinates in space; therefore, the surface of the emitter can be generated through a function interpolating a set of scattered data points. The emission current is calculated through integration of the current density over the emitter tip surface. The influences of the device geometrical structure on its potential distribution, electric field and emission characteristics are discussed.

Measurement of optical constants of thin a-C:H films

Abstract Amorphous hydrogenated carbon films (a-C:H) are very interesting materials for optical applications. They are transparent in the near IR part of the spectrum and its refractive index and absorption coefficient may be changed with the deposition parameters. In this paper we measure the optical constants of a-C:H films, deposited by plasma enhanced chemical vapor deposition as a function of the radio frequency power. The measurements were performed by the method of Abeles in λ=633 nm and by the approximation of Lambert–Beer in the transmission measurements using a spectrophotometer. Both methods do not require the use of thick films that are difficult to deposit due to the intrinsic stress of these films. The measurements were compared with that obtained by the fringe peaks in transmission measurements of a thick film. Our results showed that it is possible, in our system, to deposit homogeneous and uniform films with any refractive index chosen between 1.8 and 2.2 at λ=633 nm .

Automotive EMC analysis using the hybrid finite element boundary integral approach

The majority of innovative trends in automotive industry today relies on electronic systems. Understanding the electromagnetic behavior of the electronic control units (ECUs) in a vehicle has become an ever increasing concern of automotive manufacturers. Computational Electromagnetic Modeling (CEM) is a cost effective approach that has being adopted by the automotive industry to address electromagnetic compatibility (EMC) problems. Automotive structures are electrically large in nature and the systems required for a complete EMC analysis can be fairly complex. For this reason, there is no single numerical technique that can be used to address all automotive EMC problems. This paper shows how the automotive standard ISO11452-2 can be solved using the hybrid Finite Element Boundary Integral (FEBI) approach. A comparative study indicates that FEBI is faster and requires less computational effort than the Finite Element Method (FEM) for this particular analysis. Recent technology advances on FEBI are also presented showing the great potential of this technique to address automotive EMC problems.

Some optical properties of amorphous hydrogenated carbon thin films prepared by rf plasma deposition using methane

Amorphous hydrogenated carbon (a-C:H) films were prepared by plasma enhanced chemical vapor deposition (PECVD) using methane. The optical properties of a-C:H films were investigated by reflectance and transmittance spectrometry in the visible and near-infrared regions. The dependence of refractive index, optical gap, and absorption coefficient are examined as a function of plasma power.

Comments on the FCC approval of finite element method for biomedical transmitters

The Federal Communications Commission (FCC) ruled on February 1st 2011 that the finite element method (FEM) is a valid technique to simulate transmitters that are placed inside, on the surface, or near the human body. This paper investigates how FEM can be employed on biomedical engineering. A complete high fidelity human body model including frequency dependent materials and complex geometries was used. Three examples are described including a magnetic resonance imaging (MRI) system, a human body on a substation environment and specific absorption rate (SAR) simulations on a human head due to a cell phone radiation. Advanced multiphysics technology coupling electromagnetic and thermal simulations are also addressed. A very good agreement between FEM simulations and measurement data was achieved for SAR calculations.

Influence of the substrate thickness and radio frequency on the deposition rate of amorphous hydrogenated carbon a-C:H films

Amorphous hydrogenated carbon a-C:H films were deposited on silicon and quartz substrates in a parallel plate reactor by radio frequency (rf) plasma-enhanced chemical vapor deposition. The deposition rates of the films have been studied in the low-frequency region of the electric field. The Si and quartz substrates of different thickness have been used. The rf and substrate thickness dependencies of the deposition rates are discussed in terms of a theory of ion bombardment.

Diffractive structures holographically recorded in amorphous hydrogenated carbon (a-C:H) films.

We propose and demonstrate the direct recording of submicrometer relief gratings in amorphous hydrogenated carbon (a -C:H) films by reactive ion etching (RIE) for use as diffractive optical components. The high refractive index of this film and its transparency in the IR make such structures promising candidates for IR-transmission diffractive optical components. The structures are holographically recorded in photoresist and then transferred to a thin aluminum layer that is used as a mask for RIE of the a -C:H films. The diffraction measurements of the structures recorded in these films demonstrated the feasibility of using the materials as diffractive optical components.