Electrical Thermal Stress Research Articles

Electrical and Reliability Characterization of Ti/TiN Thin Film Resistor

The resistance, resistance versus temperature, thermal stability, electrical stress, and constant voltage reliability stress The Ti/TiN thin film resistors were studied. The results indicate that Ti/TiN thin film resistor has excellent thermal stability up to 350oC. According to the electrical measurements, Ti layer has a weaker electrical resistance than the TiN layer. Additionally, the main failure mechanism of Ti/TiN thin film resistors is thermally activated by Joule-heating effect. The thermal activation energy is determined to be 1.3 for failure of the Ti layer and 1.8 eV for failure of the TiN layer. Based on these results, Ti/TiN thin film resistors are projected to be electrically stable for ten years of operation if their temperature is kept below 311oC.

Linking ionic conductivity and piezoelectric resonance in KTiOPO4

The interplay between the ionic conductivity and the ferroelectric polarization is a key point for understanding and tuning the properties of KTiOPO${}_{4}$ (KTP) single crystals. We show here that the piezoelectric resonance undergoes a well-defined splitting at 200 K for several KTP samples exhibiting different geometries, crystalline orientations, and ferroelectric domain states. This method is a powerful way for probing the buildup of ionic space charges when the ionic conductivity stops to screen the ferroelectric polarization. We also show that it is useful to track the evolution of this space charge under several thermal and moderate electrical stresses.

Comparison of SOI and Partial-SOI LDMOSFETs Using Electrical–Thermal–Stress Coupled-Field Effect

The requirement of electrical-thermal-stress (E-T-S) modeling of semiconductor devices as indicated by ITRS2006 demands the use of finite-element analysis (FEA) for device simulation. In this paper, we perform E-T-S coupled-field simulation from the first principle by considering the stress-induced modification of the Si band structures and employ FEA software COMSOL to apply the E-T-S model on lateral double-diffused MOS field-effect transistors (LDMOSFETs) as an example. From the comparison of the electrical characteristics computed using the models with and without the mechanical stress caused by material thermal mismatch in the device structures, we found that the effect of the mechanical stress is insignificant in the forward-bias condition but it does have impact in the reverse-bias condition, namely, the reverse leakage current is higher if the mechanical stress is considered. Simulations are performed on two types of LDMOSFETs, namely, silicon-on-insulator (SOI) and partial-SOI (PSOI) LDMOSFETs, because the temperature and mechanical stress distributions are very different in these LDMOSFETs even under the same operating conditions. From the comparison of the computational results of SOI and PSOI LDMOSFETs, the results indicate that PSOI power LDMOSFET structure enables efficient heat conduction from the hot junctions and offers higher breakdown voltage.

Electrical–Thermal–Stress Coupled-Field Effect in SOI and Partial SOI Lateral Power Diode

The requirement of electrical-thermal-stress (E-T-S) modeling of semiconductor devices, as indicated by ITRS2006, demands the use of finite-element analysis (FEA) for device simulation. In this study, we perform E-T-S coupled-field simulation from the first principle by considering the stress-induced modification of the Si band structures, and employ the FEA software COMSOL to apply the E-T-S model to the study of lateral power diodes as an example. This power diode is a basic building block for power electronic devices and circuits, and as a first attempt for the ETS model application, only the steady-state characteristics of the lateral power diodes are considered. Simulations are performed on two types of diodes, namely, silicon-on-insulator (SOI) and partial SOI (PSOI) lateral power diodes because the temperature and mechanical stress distributions are very different in these diodes even under the same operating conditions. From the comparison of the computational results of SOI and PSOI diodes, the results indicate that PSOI power diode structure enables efficient heat conduction from the hot junctions and offers higher breakdown voltage. However, it has larger reverse current, higher thermomechanical stress that can lead to reliability issues.

Assessments of Low-Temperature Aging Test Method for the Dielectric Materials Immersed in Liquid Nitrogen

Among the various factors influencing the service life of the electric equipment, the performance of dielectric insulation materials has an important role to determine their whole service life. Degradation of insulating materials is fatal to insulation breakdown and finally lead to stop their operations. So the evaluation methods for the degree of degradation and aging for solid, oil and gas insulation have been developed and utilized very effectively to determine their performances. In order to determine the degradation of insulating materials immersed in extremely low temperature media such as liquid nitrogen, the abrupt temperature change from cryogenic to normal room temperature should be considered. But the assessments of low-temperature aging test method for the dielectric materials immersed in liquid nitrogen considering these conditions were not fully reported. Therefore, for the fundamental step to establish the suitable degradation test methods for cryogenic dielectric materials, we focused on the evaluation of aging test methods for dielectric materials exposed to low temperature environments considering thermal shock by cool-down and warm up test, thermal stress test and electric field stress test. In order to verify the effect of various degradation methods on cryogenic dielectric materials, Kraft, Kapton(polyimide) and Nomax type 410 sheets have been prepared and degradation experiments have been conducted. Then dielectric breakdown tests were performed. According to the test results, it was found that thermal shock degradation could be effective factor determining the degradation of cryogenic dielectric materials.

The role of Ca traces in the passivation of silicon dioxide dielectrics for electron transport in pentacene organic field effect transistors

Recently, n-type transport in organic field effect transistors (OFETs) incorporating pentacene on a silicon dioxide (SiO2) dielectric has been demonstrated by Ahles et al. [Appl. Phys. Lett. 85, 4499 (2004)]. The electron transport was made possible by modifying the dielectric/semiconductor interface using traces of Ca. While the facilitation of electron current in pentacene remained unclear at that point, an interface near filling of electron trap states in the transistor channel or on the SiO2 dielectric could be suggested as a possible explanation. In the following the influence of the Ca interlayer on the n-type transport in pentacene based OFETs will be correlated with an x-ray photoelectron spectroscopy analysis of the SiO2/Ca interface, in dependence of the Ca layer thickness. It is demonstrated that for low thicknesses an oxidized Ca insulator is formed on the SiO2 dielectric, allowing for the observed pentacene electron transport. The formation of the oxide is suggested to compensate available electron traps, in the form of hydroxyl groups on the SiO2 surface, thus reducing the trap density and isolating remaining interface traps from the transistor channel. Furthermore, it is substantiated for an increased Ca layer thickness, that metallic Ca remains in the oxidized Ca interlayer. This leads to a substantial degradation of the OFET charge carrier transport properties. It is found that up to a Ca layer thickness of ∼12 Å, the metallic Ca fraction in the oxidized Ca layer can be effectively reduced by thermal or cyclic electrical stress, leading to a permanent improvement in the n-type OFET transport properties.

Device level electrical-thermal-stress coupled-field modeling

The requirement of electrical-thermal-stress (ETS) modelling of semiconductor devices demands the use of finite element analysis (FEA) for device simulation. In this work, we employ a new finite element analysis software, FEMLAB for the ETS simulation of power diode, a basic building blocking for power electronic devices, and the static electrical and recovery transient characteristics of power diode are considered. The E-T model of the power diode is compared with the results from Medici, and the T-S model of the power diode is compared with the results from ANSYS. Good agreements are observed from both comparisons. The S-E model of power diode is computed using the deformation potential theory, and we demonstrate that the electron and hole mobilities of (0 1 0) biaxial compressive stressed power diode are modified by the stress due to energy splitting. The strain-induced changes of bandgap and effective mobilities cause a reduction in the diode drive current by about 5% at the maximum along [0 0 1] direction.

Some considerations when using a microwave oven as a laboratory research tool

Microwave ovens can be used in laboratories for the rapid heating of material – either to dry them completely or to subject a workpiece to sudden thermal stress or electric field stress. Determinations of the moisture content levels in soil or leaf tissue samples, for example, can be made within tens of seconds rather than hours. It is often assumed that placing a load within a microwave oven will result in it being heated evenly as well as quickly, but this is not always the case. This paper describes how a microwave oven works and illustrates how the heating effect within a workpiece can vary. The size and shape of a sample as well as its physical properties determine the power absorption. Equal volumes of water in different shaped containers attain different final temperatures and a tall, cylindrical water load is shown to have different temperatures at different levels. Most microwave ovens do not have a true, variable power capability, but rely on an on/off timing ratio to vary mean power. If this is not appreciated, then erroneous conclusions might be drawn from a set of experiments involving different power levels. Changes in mains supply voltage can affect the amount of energy dissipated in a load. This may introduce variations in results if experiments are conducted over a period of several hours. Experiments are described which illustrate these effects and some criteria and working practices are suggested to improve the consistency and reliability of results when using a microwave oven as a research tool.

Thermal simulation and characterisation of the reliability of THz Schottky diodes

Pulsed stress reliability investigations have been carried out for Pt GaAs Schottky diodes. A thermal characterisation of the devices is performed using a numerical, coupled electrical thermal SPICE simulator. Different degradation mechanisms have been identified investigated. A comparison between thermal stress and electrical stress shows an influence of the operating current density and the anode diameter on the device degradation. Analytical calculations, simulation results, and results from the Wunsch-Bell model have been compared.

From thermodynamic to phenomenological multi-stress models for insulating materials without or with evidence of threshold (XLPE cables)

In this paper, the relationships between phenomenological and thermodynamic models used for characterization of insulating materials aged under multiple thermal-electrical stresses are derived. Phenomenological models fitting life lines for insulating materials that show or do not show a tendency to threshold are considered and compared with appropriate thermodynamic models. The thermodynamic models account for the electrical field action with an activation-energy-lowering factor that differs for threshold and non-threshold materials. The dependence of this factor on applied stresses is thoroughly explained. The models are applied to results of life tests performed on XLPE cables. The comparison shows very good agreement of test data with the threshold model when a suitable temperature-dependence of model parameters is assumed.

Aging phenomenology and modeling

The authors review aging phenomenology and life modeling; illustrate different approaches, showing their advantages and applicability limits; and raise problems relevant to practical applications of models and evaluation of material endurance. They present the fundamentals of phenomenological aging theory and life modeling and give electrical and combined-stress life data for different materials. Electrical, thermal and multistress life models valid for insulating materials and systems, showing either linear or curvilinear behavior are presented. Particular attention is given to threshold-life models under combined thermal-electrical stresses. General aging equations for single and multiple stresses are presented, and the life surface for combined thermal-electrical stresses is introduced. Generalization to N-stress life and aging models is discussed. Statistical processing of data and determination of model parameters are mentioned, and graphical methods for material characterization are proposed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electrical life threshold models for solid insulating materials subjected to electrical and multiple stresses. I. Investigation and comparison of life models

In the paper, life models, are collected valid for solid insulating materials subjected to electrical and multiple thermal-electrical stresses whose life lines show a tendency to reach an electrical threshold. Their fit is investigated with reference to several sets of data derived from accelerated life tests performed on different insulating materials (XLPE, composite Nomex-Mylar-Nomex, epoxy bisphenolic resin, polyimide). In particular, two phenomenological life models, characterized by four parameters and based on exponential and inverse-power relationships, are compared with three-parameter life models taken from the literature and derived considering different aging and breakdown mechanisms. Discussion of the ability of these models to provide significant parameters for insulation endurance evaluation and electrical system design closes the paper.

Probabilistic models for life prediction of insulating materials

A general approach to the investigation of generalized cumulative damage functions that are able to describe the endurance of insulating materials subjected to electrical stress and temperature is developed. In particular, probabilistic life models for insulating materials showing life lines for multiple thermal-electrical stresses which tend towards electrical thresholds are proposed and compared on the basis of materials and systems, i.e. flat specimens of epoxy resin and composite Nomex-Mylar-Nomex, XLPE cable models. The models are obtained starting from the two-parameter Weibull distribution of times to failure, and explaining scale and shape parameters so that time-to-failure percentiles fit life curves showing upward curvature and tendency to infinite life. Having verified the validity of these cumulative damage functions over a wide range of electrical and thermal stresses, and having derived the stress dependence of the model parameters, complete characterization of the multistress endurance as well as estimation of electrical threshold at selected temperatures, including service stresses, is obtained.

A probabilistic life model for insulating materials showing electrical thresholds

A probabilistic life model for insulating materials showing lifelines for combined thermal-electrical stresses which tend towards electrical thresholds is proposed. The model is obtained by starting from the two-parameter Weibull distribution of times to failure, and explaining scale and shape parameters so that time-to-failure percentiles agree with life curves showing an upward curvature and a tendency to infinite life. The parameters of the probabilistic life model are explained as a function of stresses, thus providing a complete characterization of the combined-stress endurance and, hence, estimation of electrical threshold at each selected temperature, including service stresses. The validity of the model is verified by means of experimental results from a test cycle carried out on XLPE (cross-linked polyethylene)-insulated cable models.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Progressively-censored aging tests on XLPE-insulated cable models

The problem of evaluating the time-to-failure percentiles in progressively-censored tests on solid insulating materials is addressed. Statistical methods to estimate the parameters of the Weibull distribution (and their confidence limits) are examined on the basis of the results of aging with combined thermal-electrical stresses carried out on XLPE insulated cable models. These tests are performed at the same stresses on samples more than 1 m long and subjected to progressive censoring of aging times, or on short specimens about 20 cm long and subjected to complete, or singly-censored, life tests. This procedure allows the effectiveness of progressively-censored tests in estimating life percentiles to be verified, and the accuracy of the methods to be compared. >