Aicha Elshabini-Riad

Thermal interaction of semiconductor devices on copper-clad ceramic substrates

The temperature rise due to the spacing between two heat dissipating devices mounted on metallized or copper-clad ceramic substrates is presented. The thickness of the copper layer, the thermal conductivity of the substrate material, and the thermal resistance of the heat sink system are considered. Results for parameters typically found in power hybrid applications are presented in nondimensional form. The results indicate that increasing the thickness of the copper metallization requires that the devices be placed farther apart to prevent thermal interaction. An increase in the copper layer thickness can significantly decrease the device temperatures on alumina, but may increase temperatures on high thermal conductivity ceramic substrates such as beryllia (BeO). The results also demonstrate that the external heat sink thermal resistance can cause significant heat flow spreading and increased temperatures in the substrate. As the external resistance increases, the spacing required to prevent thermal interaction also increases. >

Characterization of Titanium Etching in Cl2 / N 2 Plasmas

The effects of etch time, nitrogen and chlorine gas flows, radio frequency power, pressure, and temperature on the etch rate of sputtered titanium films in chlorine-nitrogen plasmas were investigated in this work. The radio frequency power was found to have the greatest effect on the etch rate, followed by the reaction pressure. The increase in Ti etch rate with radio frequency power can be attributed to increased ionization of the gases and increase in ion and eiectron energies in the plasma. The increase in pressure led to a decline in the etch rate, probably due to loss of chlorine through recombination reactions. It was observed that the etch rate increased with increase in chlorine for gas flows below 100 sccm. Addition of nitrogen increased the etch rate to a flow of 10 sccm due to generation of free chlorine radicals, but led to a decrease in etch rate for nitrogen flows beyond 25 sccm due to dilution effect. There was only slight dependence of etch rate on the temperature within the range of this investigation.

Investigation of injection mechanisms for InGaAs/InP double heterostructure bipolar transistors

Abstract A more complete model for InP/InGaAs Double Heterojunction Bipolar Transistors (DHBT) is obtained in this paper by physically analyzing the transport process of the main current components. The potential distribution of the energy barrier constitutes a fundamental analytical concept and is employed for applying the diffusion, the thermionic emission, and the tunneling theories in investigating the injection mechanisms at the e − b heterojunction interface. The diffusion transport is considered first for electron injection from the emitter into the base. The thermionic emission is applied properly at the point of maximum potential energy as one of the boundary conditions at that interface. A suitable energy level is selected with respect to which the energy barrier expression is expanded for the calculation of the tunneling probability. The first “spike” at the conduction band discontinuity is described as the potential energy for the injected electrons to obtain kinetic energy to move into the base region with a substantially high velocity. The electron blocking action of the second “spike” at the b − c junction is also analyzed by considering the transport velocity with which electrons are swept out of that boundary. Based on the material parameters recently reported for both InP and InGaAs, computations of the current components are carried out to provide β characteristics in good agreement with the reported experimental results.

Microelectronics and electronic packaging education and research at Virginia Tech

Instruction and research at Virginia Tech, in the area of Microelectronics and Electronic Packaging, center around a core group of students and faculty in the Microelectronics Laboratory. This group offers courses in microelectronics with a strong emphasis on multichip module design and fabrication, interconnects, and electronic packaging, and include an introductory course in microelectronics as well as several graduate courses in electronic packaging, electronic devices, and microwave circuit design and fabrication. This paper outlines these instructional and research efforts as well as the capabilities of the Microelectronics laboratory. In addition, the courses structure and recent efforts to expand the microelectronics education to include integrated circuit fabrication, as well as advances in power electronic packaging will be discussed in this paper.

Comprehensive evaluation of ITO thick films produced under optimum annealing conditions

Abstract Indium-tin-oxide (ITO) is a transparent semiconductor that can be formed so that it exhibits a very low resistivity. The applications of this material include solar cells, photodetectors, and transparent contacts for devices such as flat panel displays, and touch sensitive cathode ray tube screens. The authors have investigated the role of both vacuum and reducing atmosphere (N 2 + H 2 ) annealing on the properties of thick film ITO. Both vacuum annealing and forming gas (N 2 + H 2 ) annealing result in films with significantly lower resistivity than unannealed films. Samples with sheet resistances of 150 Ω/square have been produced. These values are the lowest reported to date for ITO thick films. Optical characterization including transmission and reflectivity have been conducted, as well as examination of the conductivity as a function of temperature.

Time domain modeling of a microwave Schottky diode

Time domain technique is introduced to demonstrate an efficient way of modeling microwave devices with non-linearity. A microwave Schottky diode, represented by a lumped model, is used in this paper to illustrate the time domain technique. A fast transition pulse is applied to the diode under zero-bias and forward-bias conditions. Reflected signals are measured using the time domain reflectometry (TDR) technique. Based on time domain analysis of the diode model as well as wave propagation on a transmission line, a set of differential equations are solved numerically and iteratively using the measured incident pulse as an enforced excitation. The lumped element values are extracted by comparing the simulated and the measured waveforms. The non-linearity of the diode are modeled accurately and efficiently using this technique. The method used demonstrates the advantages of time domain techniques over the conventional frequency domain technique in modeling nonlinear devices.

Etch characteristics of Ti in Cl2/N2 and TiN in Cl2/N2/BCl3 plasmas by response surface methodology

The etch characteristics of titanium (Ti) film in Cl2/N2 plasmas and titanium nitride (TiN) film in Cl2/N2/BCl3 plasmas are examined by design of experiment using central composite-face centered type design and modeled by response surface methodology (RSM). The Ti and TiN etch experiments are carried out in a Lam Research Rainbow 4600 single wafer parallel plate metal etcher. For the Ti etch process, the effects of variation of the process parameters such as Cl2, N2 gas flow, RF power and reaction pressure on output responses, etch rate and etch uniformity, are investigated. For TiN etch process, BCl3 gas flow is added as a factor in addition to the factors listed above. A statistical analysis software package, JMP, is used to design experiment and analyze the results. The factors are normalized with respect to center point for the design and analysis of the experiment in order to compare the relative significance of the model terms. Using the etch rate and uniformity data obtained from the experiment, a quadratic model is developed for etch rate and uniformity for each rate and uniformity data obtained from the experiment, a quadratic model is developed for etch rate and uniformity for each of the films. From the coefficients of the models thus developed, it is easy to determine the relative influence of the first and second order effects of factors, and two factor interactions on the etch rate and uniformity response. Contour plots, which are helpful in determining the optimum process window, are generated for both etch rate and uniformity factors. Addition of nitrogen is found to decrease the etch rate due to dilution effect. The reaction pressure decreases the etch rate probably due to loss of energies of radicals, ions and electrons. Increasing of all the factors except nitrogen flow lead to better etch uniformity. Increase in nitrogen flow is causing poor uniformity probably due to dilution of etchant species leading to across-the-wafer nonuniformity.

Analytical model for leakage current in InGaAsP avalanche photodiodes

Abstract A complete expression for the dark current in InGaAsP/InP avalanche photodetectors is successfully derived by taking into account the diffusion process, the thermal generation process, the tunneling process, and the multiplication process. The expression is computed in order to achieve the I – V reverse characteristics of the device with consideration of the effect of epitaxial layer width, uniform doping concentration, and a doping profile in the active region on the dark current value. Analysis of the computed results indicates that a large tunneling current component appears over the range of 0.75 V B to V B , thereby limiting the effective performance of the device. A trade-off exists among the requirements of a high gain, a low dark current value, a fast response, and a good signal-to-noise power ratio.