Temperature Dependence Of Material Parameters Research Articles

A 3D thermal simulation tool for integrated devices-Atar

This paper presents a novel three-dimensional (3D) thermal simulation tool for semiconductor integrated devices. The simulator is used to automatically generate an accurate 3D physical model of the device to be simulated from layout information. The simulator produces an appropriate mesh of the device based on a rectangular block structure. The mesh is automatically created such that a fine mesh is produced around heat generation regions, but a moderate number of blocks are used for the entire device. This paper first confirms that the simulator produces an accurate solution to the nonlinear differential equation describing the heat flow. Then model generation from three example technologies (silicon trench, GaAs mesa structures, silicon on insulator) is presented. The potential of the simulator to quickly and easily explore the effect of layout and process variations is illustrated, with the simulation of a two-transistor GaAs power cell as a large example. The program incorporates a transient solver based on a transmission line matrix (TLM) implementation using a physical extraction of a resistance and capacitance network. The formulation allows for temperature dependent material parameters and a nonuniform time stepping. An example of a full transient solution of heat flow in a realistic Si trench device is presented.

On the dynamics of laser-induced etching of tungsten–SiO 2-composites

Cw laser-induced heating of W–SiO 2-layer composites in a WF 6-atmosphere results in a locally well defined removal of W from the SiO 2 substrate. High-resolution etching is possible due to the nonlinearity of the reaction kinetics. The etching process has been simulated using a three-dimensional numerical model, which takes into account the time-dependent evolution of the etch front and the corresponding temperature distribution. All temperature dependent material parameters and time-dependent absorption characteristics have been included in the calculations. The results obtained from the model have been compared with experimental investigations.

溶融ＹＢａ２Ｃｕ３Ｏｙの交流磁化応答における微弱直流磁場印加効果

We studied, both theoretically and experimentally, the ac magnetic response of type-II superconductors superimposed on a weak Hdc field. Theoretical simulations were made within the construct of the Kim-Anderson critical-state model, where the critical current density Jc is assumed to be given by Jc=k/(Bo+|Bi|). k and Bo are temperature-dependent material parameters, and Bi is the local flux density in the sample. We also measured complex susceptibilities Xn=X′n-iX″n (n=1, 2, 3, 5, 7) of a melt-processed YBa2Cu3Oy specimen and analyzed the observed Xn by applying the magnetization equations derived from the Kim-Anderson model. We found that the experimental results were qualitatively well reproduced. Present results indicate that, for a specimen of which Jc sensitively varies with Bi, the effect of a weak Hdc should be explicitly taken into consideration for studies of the ac magnetization.

Local damage of HT-materials by laser irradiation in the SEM

By using a pulsed Nd:YAG laser the high temperature materials zirconium oxide, fine grain graphite and silicon nitride were rapidly irradiated (heating thermal shock) and their damage behavior was investigated. The laser beam parameters at sample surface were detected by a laser beam analyzing system and correlated with the local damage mechanisms of the materials as erosion, crack formation and solid-solid phase transformation. For the investigations image analysis, localized x-ray analysis, and the ion beam slope cutting technique were applied. The temperature field in the material was simulated by using temperature dependent material parameters for different laser beam parameters. The results illustrate both the strong influence of the temporal and spatial laser energy profile and the materials properties to the material damage.

Adaptive finite element methods for continuum damage modeling

The paper presents an application of adaptive finite element methods to the modeling of low-cycle continuum damage and life prediction of high-temperature components. The major objective is to provide automated and accurate modeling of damaged zones through adaptive mesh refinement and adaptive time-stepping methods. The damage modeling methodology is implemented in a usual way by embedding damage evolution in the transient nonlinear solution of elasto-viscoplastic deformation problems. This nonlinear boundary-value problem is discretized by adaptive finite element methods. The automated h-adaptive mesh refinements are driven by error indicators, based on selected principal variables in the problem (stresses, nonelastic strains, damage, etc.). In the time domain, adaptive time-stepping is used, combined with a predictor-corrector time marching algorithm. The time step selection is controlled by required time accuracy. In order to take into account strong temperature dependency of material parameters, the nonlinear structural solution is coupled with thermal analyses (one-way coupling). Several test examples illustrate the importance and benefits of adaptive mesh refinements in accurate prediction of damage levels and failure time.

Analysis of Thermal Ratchetting Strain of a Cylinder Subjected to a Temperature Front Moving Cyclically in the Axial Direction.

This paper is concerned with thermal ratchetting of a cylinder subjected to a temperature front moving cyclically in the axial direction. The thermal ratchetting strain yielded before shaking down is analyzed by approximating the deformation profile of the cylinder trilinearly and by assuming Masing's rule of cyclic plasticity. An analytical expression for the thermal ratchetting strain is thus derived in the case of a power-law type stress versus strain relation with no temperature dependence of material parameters. The resulting expression is verified by comparing its prediction with results of finite element analysis and experiments on 316 FR steel.

The nonisothermal viscoplastic behavior of a titanium-matrix composite

The thermomechanical fatigue (TMF) response of a unidirectional SCS-6/Timetal 21S composite is determined using the unified inelastic-strain model of Bodner and Partom for the matrix response. The Bodner-Partom model captures the strain-rate sensitivity and time-dependent behavior of Timetal 21S for a wide range of temperatures (25–815°C) and strain rates (10 −3-10 −7s −1). For nonisothermal conditions, special terms are added to the inelastic-strain-rate expressions that account for changes in the temperature-dependent material parameters with changing temperatures. This viscoplastic model is implemented into the finite element package ADINA through user-defined subroutines. The unidirectional composite is represented by a concentric cylinder geometry formulated from axisymmetric elements. Numerical simulations predict an increase in residual stresses as the cooling rate from consolidation is increased. The composite response under in- and out-of-phase TMF loading compares well with experimental measurements. Compared to out-of-phase TMF, in-phase TMF shows considerably more ratchetting. For in-phase TMF, both the response and fatigue lives are more sensitive to variations in fiber-volume fraction than the out-of-phase case. The numerical model is consistent with the experimental observations in that the fibers control the in-phase TMF behavior, while the matrix controls the out-of-phase TMF behavior.

Analysis of Infrared Photoacoustic Wave Form Detected by Piezoelectric Transducer

Voltage wave forms induced by CO2 laser irradiation in a PLZT transducer attached to p-Ge and glass samples were studied and compared with simulated ones taking account of temperature dependent material parameters. Spikes or jumps apparently due to a pyroelectric component appear in the longitudinal configurations along with an enhanced rear edge due to temperature dependent parameters; while wave forms are closer to the temperature wave form in the transverse configuration and when PLZT itself is irradiated. Resonant excitation of the bending mode is confirmed in glass plates.

Pulsed laser heating of silicon: The coupling of optical absorption and thermal conduction during irradiation

Transient laser annealing of semiconductors is examined extensively and the rise in lattice temperature specifically attained in silicon under the influence of a high-power laser beam irradiation is characterized analytically over a wide range of laser wavelengths, intensities, and durations. For the case of silicon, with increasing lattice temperature the optical absorption coefficient is drastically enhanced, while the thermal conductivity is considerably reduced. These two temperature-dependent material parameters are, therefore, strongly coupled during the laser beam irradiation, and the effects of this coupling on the ensuing lattice-temperature rise are examined comprehensively. Specifically, the threshold pulse energy for the onset of surface melting is analytically calculated as a function of both material parameters and operating laser beam characteristics.

Temperature Characterization of Pulsed Laser Annealing of Semiconductors

ABSTRACTThe dynamic characteristics of lattice temperature, T attained in Si under the influence of a high power laser beam irradiation are examined analytically over a wide range of laser wavelengths, pulse intensities and durations. The strongly temperature-dependent material parameters, such as optical absorption coefficient α(T) and thermal diffusivity D(T) are incorporated in heat diffusion equation, and their nonlinear coupling effect on the ensuing temperature in laser-processed semiconductors are examined. Specifically, the threshold pulse energy for surface melting is characterized as a function of both material and annealing laser beam parameters. This analytic description of pulsed laser heating of semiconductors should provide considerable insight into the transient heating phenomena and localized material modifications.

Cryogenic stability of composite conductors taking into account transient heat transfer

To predict stability behaviour of various conductors under different cooling conditions, a computer program was developed to solve the one-dimensional heat diffusion equation along the conductor using temperature dependent material parameters. Transient heat transfer is included basing on results of earlier heat transfer measurements. To check the validity of these calculations experiments were performed using a copper stabilized multifilamentary NbTi-superconductor under pool boiling conditions. The normal transition was initiated by an ohmic heater. The minimum energy needed to induce quenching as well as the propagation velocity of the normal zone are then compared with numerical results and show good agreement.

Modeling thermal fire resistance

Computer-aided procedures have been developed to allow architects and engineers with no previous computer knowledge to predict the theoretical fire ratings of different layers of fireproofing materials. The device which permits such a theoretical evaluation is a computer model known as FIRE (Fire Intensity-Resistance Evaluation). Using this procedure a engineer can choose up to three different layers of material to be evaluated under various fire intensities. The layers which can contain water or different transformation products can be considered to be in intimate contact or separated by an air gap. The various layers can be considered to be attached to a heat sink which represents the mass of various structural members of different sizes. A directory of fifty materials is available for evaluation under fire exposures of different intensities and durations. Correlations are now being carried out with existing fire tests to insure the best fit for the different temperature-dependent material parameters that are required.