Current-induced Heating Research Articles

Effective Temperature of Au Nanocontacts under High Biases

The effective local temperature of gold nanocontacts under high biases has been evaluated at 77 K by studying the two-level fluctuations (TLFs) of conductance. Upon varying bias from 0.2 to 0.6 V, TLF frequency increases exponentially while the effective contact temperature remains unchanged, which indicates negligible current-induced heating in Au nanocontacts at least up to 0.6 V at 77 K, in accordance with a theoretical model proposed by Todorov et al. [Phys. Rev. Lett. 86 (2001) 3606].

Numerical Analysis for the Application of Electric Current to Silicon Semiconducting Materials

The application of electric field to silicon semiconductors materials is used to modify the melt convection mode in the Czochralski growth configuration and to control the structures at the crystal surface. Nonlinear phenomena, namely, the decrease of the stabilized applied voltage in a closed circuit with the increase of the electric current, were observed experimentally. A mathematical model for predicting the temperature of silicon crystal and the electric field in a closed circuit has been developed to study the electric current-induced Joule heating phenomena in silicon semiconductor materials. In this work, numerical simulations have been performed using the Newton method and implicit Euler time integration. It has been demonstrated that numerical analyses are in qualitative agreement with the experimental results, and it is possible to reproduce the nonlinear behavior and to simulate the transport phenomena in the application of electric current to silicon materials.

Current and temperature tuning of quantum-well lasers operating in 2.0-to 2.4-µm range

Radiation spectra of GaInAsSb/GaAlAsSb-based quantum-well diode lasers in pulsed and quasi-continuous operation modes were studied in the temperatures range from −10 to +20°C with driving currents varying from 50 to 200 mA. For currents exceeding the threshold value by no more than 30%, a single-mode lasing was usually observed. A further increase in current leads, as a rule, to the appearance of 3–5 additional long-wavelength cavity modes, which suggests the growth of gain in this spectral range due to the interaction of modes. In single-mode conditions, the lasing wavelength is red-shifted with temperature at a rate of 2–3 A/K because of the current-induced heating of the laser and the corresponding increase in the refractive index. The rate of this heating is estimated at 0.1 µs.

Interferometric study of thermal dynamics in GaAs-based quantum-cascade lasers

The thermal dynamics in quantum-cascade lasers under pulsed operation is investigated by a scanning interferometric thermal mapping technique. An infrared laser beam probes the change in the refractive index caused by current-induced heating of the working devices. The measured phase shift provides a quantitative information on the thermal characteristics with a micrometer spatial and a nanosecond time resolution. Comparing the experiments with a two-dimensional thermal model enables us to determine the anisotropic heat conductivity in the multilayered active region, found to be much lower than the one of bulk GaAs, as well as the temperature increase in the active region during pulsed operation.

Performance evaluation of WDM components based on tunable dielectric membrane technology

Wavelength division multiplexing has become a leading technology for long-haul transmission systems which operate at 1550 nm wavelength. The recent slump in the fibre optics industry has put a strong focus on the development of new flexible and tunable components, as well as cost effectiveness and reliability. Two-chip micromachined devices are very promising candidates to fulfil these demands. A tunable optical filter structure is discussed, which uses a simple bulk-micromachining process based on low-cost dielectric Bragg mirrors. The tuning is achieved by current-induced thermal heating of the membrane suspensions. This concept combines the advantages of low-cost dielectric mirror processing and the simple actuation principle by current flow to create a best-of-breed two-chip solution. The alignment process of the two-chip cavity has been simplified to the point where a simple place-and-fix strategy can be applied. Based on this concept, a tunable two-chip resonant-cavity light-emitting diode (RC-LED) is presented, which utilises the same bulk-micromachined chip. This validates that these micromachined tunable membranes can serve as basic building blocks for a wide variety of tunable components for wavelength division multiplexing systems, such as optical filters, receivers and vertical-cavity surface-emitting lasers (VCSELs).

Modelization of resistive heating of carbon nanotubes during field emission

In this paper we simulate the resistive heating of carbon nanotubes (CNT's) during field emission (FE) using the one-dimensional heat equation including radiation and conductive losses. The simulations are in relatively good agreement with our recent experiments in which we measured the heating of individual CNT's to as high as 2000 K during FE for currents ${I}_{\mathrm{FE}}$ of $\ensuremath{\approx}2 \ensuremath{\mu}\mathrm{A}.$ For low temperatures where radiation is negligible the simulations reduce to an analytic solution that provides a universal guide to estimating current-induced heating in CNT's. The effects of this heating are included in the calculations of ${I}_{\mathrm{FE}}$ as a function of voltage.

Residual stress-loaded titanium–nickel shape-memory alloy thin-film micro-actuators

Residual stress in titanium–nickel thin films has been exploited as a force load for thin-film shape-memory alloy micro-actuators, thus eliminating the need for providing ‘external’ force load for device training and operation. Thermal cycling during device operation is accomplished using electrical current-induced Joule's heating for temperature ramp-up and thermal conduction/convection-induced cooling for temperature ramp-down. In response to thermal cycling, hysteresis loops in both the displacement and electrical resistance of the micro-actuator have been observed—thus demonstrating the existence of shape-memory effect in the micro-actuators. Elimination of manual training of individual devices makes it possible to operate large arrays of shape-memory alloy micro-actuators realizable using micro-fabrication techniques.

What initiates the explosion of a current-carrying conductor?

It is shown that the explosion of a conductor heated by a high-power current pulse is initiated by the nuclei of liquid phase that appear in the layer of a supersaturated vapor surrounding the liquid current-carrying core. The instant of electric explosion and the expansion velocity predicted by this scenario are confirmed by the experimental and computational data on current-induced heating of a tungsten conductor.

Rapid crystallization of silicon films using pulsed current-induced joule heating

Crystallization of silicon films formed on glass substrates was achieved by rapid-joule heating of Cr strips adjacently formed via 200-nm-thick SiO 2 intermediate layers. 3-μs-pulsed voltages applied to the Cr strips caused a high joule heating intensity about 1×10 6 W/ cm 2 . Transmission electron microscopy measurements confirmed a crystalline grain size of 50–100 nm. 1-μm-long crystalline grain growth was observed just beneath of the edge of Cr strips. The activation of phosphorus atoms according to crystallization was also achieved.

Crystallization of silicon thin films by current-induced joule heating

Electrical-current-induced joule heating was applied to the crystallization of silicon films formed on glass substrates. Electrical energy accumulated at a capacitance was applied to the silicon films. Coincident irradiation with 30-ns-pulsed laser melted films partially reduced their resistance. Complete melting of 42 μs and solidification duration of 28 μs were observed in the case of heating at a capacitance of 2 μF The analysis of electrical conductivity reveled a density of defect states of 1.3×1012 cm−2 at grain boundaries. The formation of 15-μm crystalline grains was observed. The preferential crystalline orientation was (110).

AlGaAs hot-electron optical modulator

We propose and analyze a promising surface-normal optical modulator for use in optical interconnects. The device is based on n-AlGaAs materials, operating with red light, and is therefore fully compatible with silicon photodetectors. The operation principle is based on current-induced electron heating, with redistribution of carriers between conduction band valleys playing a significant part. Calculations predict efficient absorption modulation with operating voltages <1 V and switching times of units of picoseconds.

Impact of in-plane anisotropic strain on the polarization behavior of vertical-cavity surface-emitting lasers

We experimentally demonstrate that the presence of switching between two fundamental modes with orthogonal linear polarization in vertical-cavity surface-emitting lasers and the current at which this phenomenon occurs depend on both the magnitude and the orientation of an externally induced in-plane anisotropic strain. We interpret this behavior by considering the anisotropy in gain and in refractive index, both induced by the in-plane strain, and by accounting for a redshift of the two gain curves as a result of current-induced heating.

Large crystalline grain growth using current-induced Joule heating

Electrical-current-induced Joule heating was applied to crystallization of 60-nm-thick amorphous silicon films formed on glass substrates. 3-μs-pulsed voltages were applied to silicon films connected with a capacitance in parallel. Coincident irradiation with 28-ns-pulsed excimer laser melted films partially and reduced its resistance. Complete melting for 12 μs and a low cooling rate at 1.1×108 K/s were achieved by Joule heating from electrical energy accumulated in the capacitance at 0.22 μF. For 7.4×1017 cm-3 phosphorus-doped films, analysis of temperature change in the electrical conductivity gave that the density of defect states localized at grain boundaries was 1.5×1012 cm-2. Formation of 3.5-μm-long crystalline grains was observed by transmission electron micrograph. Preferential crystalline orientation was (110).

Field-Emission-Induced Luminescence from Carbon Nanotubes

We report on the observation of luminescence during electron field emission on singlewall and multiwall carbon nanotubes. Spectra acquired at different emitted currents, as well as the dependence of the luminescence intensity with the current, show that the light emission is not due to blackbody radiation or to current-induced heating. In fact, our results suggest that the light emission is caused by electron transitions between different electronic levels participating in the field emission.

Current heating in polymer light emitting diodes

We present an investigation of current-induced heating in polymer light emitting diodes. Using short electrical pulse measurements, we were able to quantify the temperature rise in the active region. We consider that heating effects play a major role in limiting the maximum efficiency of devices and in initiating degradation mechanisms. Heating and heat sinking are also discussed in the context of electrically pumped polymer lasers.

Surface etching of 1T-TaS2 with UHV-STM

Surface etching of the layered compound 1T-TaS2 with a STM tip was observed in an ultrahigh vacuum where the true vacuum tunneling gap was achieved. The etching did not always progress in a layer-by-layer manner, but etch-pits often had the depths of multiples of the unit layer. The etching rate on a clean surface was much slower than that on a surface once exposed to the ambient air, which showed a rough and irregular nano-scale morphology, implying that the surface of 1T-TaS2 is chemically degraded by the water vapor in air. On a clean surface, the STM etching started from the defect-like sites seen on the STM image, which possibly reflect the substrate impurities located on the Ta planes or van der Waals gaps, and progressed preferably in the scanning direction. The etching rate tended to increase with the bias voltage, regardless of its sign. This suggests that the electrostatic attractive force between tip atoms and surface atoms and/or the current-induced local heating contribute significantly to the STM etching of 1T-TaS2 in ultrahigh vacuum.

Dispersive self-Q-switching in self-pulsating DFB lasers

Self-pulsations reproducibly achieved in newly developed lasers with two distributed feedback sections and with an additional phase tuning section are investigated. The existence of the dispersive self-Q-switching mechanism for generating the high-frequency self-pulsations is verified experimentally for the first time. This effect is clearly distinguished from other possible self-pulsation mechanisms by detecting the single-mode type of the self-pulsation and the operation of one section near the transparency current density using it as a reflector with dispersive feedback. The operating conditions for generating this self-pulsation type are analyzed. It is revealed that the required critical detuning of the Bragg wavelengths of the two DFB sections is achieved by a combination of electronic wavelength tuning and current-induced heating. The previous reproducibility problems of self-pulsations in two-section DFB lasers operated at, in principle, suited current conditions are discussed, and the essential role of an electrical phase-control section for achieving reproducible device properties is pointed out. Furthermore, it is demonstrated that phase tuning can be used for extending the self-pulsation regime and for optimizing the frequency stability of the self-pulsation. Improved performance of the devices applied as optical clocks thus can be expected.

Thermal simulation of thin-film interconnect failure caused by high current pulses

We have performed a quantitative analysis of the time-dependent temperature distributions in response to a high current pulse for very large scale integrated (VLSI) metallization structures, especially for those used in field-programmable gate array (FPGA) devices with voltage programmable links (VPL's). Simulation results are presented as pulse width versus maximum allowed current density through Al interconnects and as visualizations of the transient temperature distributions. The adiabatic approximation for modeling the current-induced heating is found to be valid only for an extremely short pulse duration ( >

Short-time failure of metal interconnect caused by current pulses

It is pointed out that voltage programmable link (VPL) technologies impose a new criterion on the reliability of metal interconnect. Lines of metallization must support the full programming current, which can be many times larger than the signal level current, for very short periods of time. For a sufficiently short high-current pulse, the wire, encapsulated in oxide, will not reach thermal equilibrium and the current-induced heating can be modeled as being adiabatic. Energy conservation predicts a relationship between maximum current density that can be carried by a wire before it fuses, and the pulse duration time, J/sup 2/t=10/sup 8/ A/sup 2/-s/cm/sup 4/. This relationship is based on a temperature rise in the metal line at failure of theta /sub f/*=300 degrees C. The time required for the metal to reach thermal equilibrium at a given current density is shown to be proportional to the square of the oxide thickness. These predictions are experimentally verified with layered AlSi/Ti metallization on thermal oxide on silicon substrates. >

Study of phonon-injection-induced destruction of superconductivity in tin films

We have investigated the phenomenon of the destruction of superconductivity in thin film strips of tin by injecting direct currents through a transverse normal metal (silver) strip in direct contact with the superconducting strip. We observe that the critical current of the superconducting tin strip decreases continuously (in some cases with an intermediate jump discontinuity) with increasing injection current. From a careful consideration of various possible mechanisms, such as current-induced depairing, simple heating, and nonequilibrium superconductivity, we infer that the experimental observations could be mostly due to steady-state nonequilibrium phenomena associated with heat pumping from various locally heated regions.