M.F. da Silva

Combined spectral and histogram analysis for fast ADC testing

The integral nonlinearity (INL) of analog-to-digital converters (ADCs) can be described by a behavioral error model expressed as one-dimensional image in the code domain. This image consists of low and high code frequency components which allow describing the ADC performance with a small number of parameters. This paper presents new methods for low code frequency and high code frequency testing. The identification of the low code frequency components is performed by multiharmonic sine fitting in the time domain. The high code frequency components are estimated in the statistical domain by a narrow band histogram test using a triangular stimulus signal. The performance of the proposed method is assessed for various ADC devices.

Crystallization and mechanical behaviour of bulk Zr-Ti-Ni-Cu-Be metallic glasses

Abstract Bulk amorphous samples of Zr-Ti-Ni-Cu-Be alloy have been prepared with the aim of studying the amorphous-to-crystalline transformation in different conditions. The crystallization process has been studied by means of differential scanning calorimetry. The transformation is accomplished in several stages, the extent of which depends on either the heating rate or the annealing temperature. A phase separation in the amorphous matrix or the formation of crystals of extremely small size probably occurs in the first stage; with further annealing a hexagonal nanocrystalline phase is produced; finally the remaining amorphous part of the alloy transforms to a tetragonal phase. The rate of crystallization is strongly influenced by the atmosphere employed during thermal treatments, and a high resistance to crystallization was observed in vacuum. Rutherford back-scattering spectroscopy analysis showed an increase in 0 content after annealing. The hardness of amorphous and partially crystallized samples has a...

Lattice location and annealing behavior of Mn implanted GaN

Abstract Gallium nitride (GaN) is a direct wide-band-gap semiconductor material, which can be used to produce blue-light-emitting diodes and lasers, high-temperature and high-power devices. While manganese (Mn) represents a potential acceptor in GaN, Mn-doped GaN may form an interesting diluted magnetic semiconductor. In this study, GaN was implanted at room temperature using 180 keV Mn+ ions to fluences ranging from 5×1015 to 3×1016 cm−2. Subsequent annealing was performed in a flowing N2 ambient, at 1050 °C for 12 min. The damage buildup and removal, as well as the lattice site location of Mn in GaN was studied by using Rutherford backscattering/channeling combined with particle induced X-ray emission. The angular scans around the 〈0 0 0 1〉 and 〈1 0 1 1〉 axial directions indicate that Mn mainly occupies substitutional Ga sites. During the thermal treatment, no significant redistribution of the implanted Mn ions was found.

Amorphization of GaN by ion implantation

Abstract The ion-beam-induced amorphization of GaN was studied by using 180 keV Ar+ and Ca+ implantation at −150°C and room temperature, respectively. The structure of the GaN films before and after implantation was characterized by Rutherford backscattering/channeling and X-ray diffraction. Lattice expansion due to ion implantation was found, and excessive lattice expansion results in local collapse of the GaN lattice into amorphous clusters. Accumulation of these amorphous zones should be the mechanism of amorphization. The critical energy deposited into nuclear processes is determined to be 90 eV/atom, or 8×10 21 keV / cm 3 , above which amorphization and below which dynamical crystallization dominates. This high value indicates that GaN is extremely resistant to amorphization compared to other semiconductors.

Diffusion and microstructures induced by excimer laser irradiation in Ge-Sb thin film bilayers

Abstract Nanosecond laser pulses are used to irradiate Ge-Sb thin bilayer films. Time-resolved reflectivity measurements are used to follow kinetically the laser-induced process. Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM) are used to perform depth profile and microstructure analyses. Diffusion of the elements is observed upon irradiation. It occurs within the liquid phase and is interfacially initiated. The calculated diffusion coefficients follow an Arrhenius-like law as a function of the laser energy density. Amorphous phases together with some crystalline segregation are observed.

Oxygen gettering by hafnium implanted in beryllium: A 〈0001〉 Hf‐O dumbbell?

The interaction of hafnium implanted into beryllium single crystals with diffusing oxygen was studied using hyperfine interaction and Rutherford backscattering channeling techniques. It was observed that oxygen is trapped at hafnium in a well defined lattice position. The formation of a 〈0001〉 Hf‐O mixed dumbbell in the tetrahedral interstitial cage of the beryllium lattice is suggested to explain the experimental results.

Incorporation of tungsten in lithium niobate by diffusion

Abstract The incorporation of W in lithium niobate (LiNbO3) by diffusion was studied using RBS/channeling. Tungsten was deposited onto LiNbO3 single crystals at 1000 °C under vacuum, resulting in a W rich layer with a peak concentration of 7 at.%. To decrease the damage introduced by the deposition process the samples were annealed at 1000 °C in flowing wet oxygen causing the W to diffuse rapidly towards the bulk. The lattice location measurements show that a large fraction of the W was incorporated on Nb sites, in contrast to other dopants introduced by diffusion, which occupy Li sites.

Modification and characterization of Al surfaces implanted with Cr ions

Abstract High fluence Cr + implantations into polycrystalline aluminium samples were performed under different conditions of fluence and temperature. Rutherford backscattering spectrometry (RBS) was used to determine Cr distribution profiles, while the formation of Al–Cr intermetallic compounds was investigated by grazing incidence X-ray diffraction (GIXRD). Clear evidence for the direct formation of the intermetallic compounds Al 86 Cr 14 and Al 13 Cr 2 during ion implantation is presented. The influence of implantation temperature and fluence on the formation of these Al–Cr intermetallic compounds was also investigated. The stability of such intermetallic compounds was studied by means of annealing treatments, and it was found that the Al 86 Cr 14 phase forms first and is then transformed into Al 13 Cr 2 by a proper thermal annealing.

Fast ADC testing by spectral and histogram analysis

The integral nonlinearity (INL) of analog to digital converters (ADCs) can be described by a behavioral error model expressed as one dimensional image in the code domain. This image consists of low and high code frequency components which allow describing the ADC performance with a small number of parameters. This paper presents new methods for low code frequency and high code frequency testing. The identification of the low code frequency components is performed by multi-harmonic sine fitting in the time domain. The high code frequency components are estimated in the statistical domain by a narrow band histogram test using a triangular stimulus signal. The performance of the proposed method is assessed for various ADC devices.

Least-squares fitting algorithms applied to periodic signals

A new generation of multipurpose measurement equipment is transforming the role of computers in instrumentation. The new features involve mixed devices, as analog-to-digital and digital-to-analog converters, and digital signal processing techniques, able to substitute typical discrete instruments like multimeters, analyzers, etc. Signal-processing applications frequently use least-squares sine-fitting algorithms. Periodic signals may be interpreted as a sum of sine waves with multiple frequencies, the Fourier series. This paper proposes a new algorithm which is able to fit a multi-harmonic acquired signal determining the amplitude and phase of all harmonics. Simulation and experimental results are presented.