Temperature-dependent Thermal Resistance Research Articles

Temperature-dependent thermal resistance of phase change memory

One of the key challenges of phase change memory (PCM) is its high power consumption during the reset operation, when the phase change material (typically Ge2Sb2Te5, i.e., GST) heats up to ∼900 K or more in order to melt. Here, we study the temperature-dependent behavior of PCM devices by probing the reset power at ambient temperatures from 80 to 400 K. We find that different device structures exhibit contrasting temperature-dependent behavior. The reset power in our confined-type PCM is nearly unchanged with ambient temperature, corresponding to a temperature-dependent thermal resistance, whereas results for mushroom-type PCM from the literature show a linear relation between power and temperature, suggesting a more constant thermal resistance. This discrepancy is ascribed to different temperature distributions and thermal properties of the dominant components of the PCM cell thermal resistance, as shown by electro-thermal modeling. In the confined cell, the thermal boundary resistance of the GST and the thermal conductivity of the bottom electrode dominate the thermal resistance, while for the mushroom cell, the GST thermal conductivity plays a greater role. These findings can help to design more power- and energy-efficient PCM devices by better focusing thermal management efforts on the key components of the device.

Mean Operating Temperature (MOT) of Commercial Roof Assembly and Its Impact on the Energy Performance

In the thermal design of low sloped roofing assemblies, two parameters are overlooked, one is the surface temperature of the roof assemblies which provides the required temperature gradient for heat flow, and the other is the mean operating temperature of the roof assembly, which has direct implications on the thermal performance of the insulation. An in situ field study was conducted in collaboration with Alberta Roofing Contractors Association (ARCA) on their headquarters building located in Calgary, to generate data on the mean operating temperature of the roof assemblies and to determine whether the thermal design of roofing assemblies using conventional methods is an accurate portrayal of in-service thermal performance. For the present study, two roof assemblies insulated with polyisocyanurate insulation, one with a white reflective roof membrane and the other with the black membrane were selected and instrumented. During the monitoring period, the mean operating temperature (MOT) of the roof assembly whether it is calculated as the average of interior and exterior ambient (MOTAIR,) or the average of surface temperatures (MOTSurface), was found to be below 24 °C (75 °F), which opposes the current roof thermal designs that are being designed using label R-value (thermal resistance) of the insulation reported at the mean temperature of 24 °C (75 °F) rather than temperature-dependent thermal resistance. The comparison of two energy transfer theoretical models, QConvention and QMOT, with the measured data indicated that the conventional approach of roof thermal design underestimates the energy performance of the roof assembly on average by 30%. The use of roof surface temperatures and the corresponding temperature-dependent thermal resistance of the insulation as in QMOT has been demonstrated to improve predictions of the energy performance. In addition the loss in thermal resistance due to blowing agent diffusion in polyisocyanurate was evaluated after two years of in situ installation.

A Study on Self-Heating and Mutual Thermal Coupling in SiGe Multi-Finger HBTs

In this paper, the self-heating and mutual thermal coupling in a state-of-the-art SiGe:C multi-finger heterojunction bipolar transistor (HBT) was investigated in static dc operation conditions. Multi-finger HBT structure was created using Sentaurus structure editor with dimensions similar to the layout of SiGe:C multi-finger HBTs in ST-Microelectronics BiCMOS55 (B55) technology (f T > 300 GHz, f max > 400 GHz) as per ST’s BiCMOS55 process design kit guidelines. Three-dimensional thermal technology computer aided design (TCAD) simulations were carried out to obtain the temperature distribution in static dc operation. The lattice temperature (T Lattice) and heat flux (F Heat) distribution inside the device were studied. The impact of back-end-of-line (BEOL) layers on static thermal behavior of the state-of-the-art SiGe:C multi finger HBTs was also investigated. The temperature dependent thermal resistance of different fingers of the trench isolated SiGe multi-finger HBT was extracted without and with back-end-of-line (BEOL) effect. An electro-thermal dc compact model of self-heating and mutual thermal coupling in multi-finger HBTs was proposed and applied to compare the modeling results with the TCAD simulation results. Very good agreement was achieved between results obtained from TCAD simulation and those obtained from compact model-based simulation.

An Electrothermal Model for Empirical Large- Signal Modeling of AlGaN/GaN HEMTs Including Self-Heating and Ambient Temperature Effects

Accurate modeling of electrothermal effects of GaN electronic devices is critical for reliability design and assessment. In this paper, an electrothermal model for large signal equivalent circuit modeling of AlGaN/GaN HEMTs including self-heating and ambient temperature effects is presented. To accurately describe the effect of ambient temperature, two separate electrothermal networks (I diss , R diss , and C diss for self-heating, and I amb , R amb , and C amb for ambient temperature effect) are used to describe drain-source current slump due to self-heating and ambient temperature effects, respectively. A temperature-dependent thermal resistance and thermal capacitance model is proposed and implemented in the electrothermal network. The extraction of the thermal parameters is fulfilled by using numerical finite-element method. Single tone on wafer load-pull measurements at two operating frequencies (3 and 14 GHz) are carried out for verification purposes. The results show that good agreements on fundamental output power, the second and third harmonics output power, and power added efficiency have been achieved between simulations and measurements over a wide range of -55 °C to 175 °C.

Heat Dissipation in Resistive Switching Devices: Comparison of Thermal Simulations and Experimental Results

The local temperature plays a key role in resistive switching devices. We have previously presented a method to experimentally evaluate the filament temperature using metal-insulator-semiconductor bipolar transistor structure. In light of the experimental results, we discuss here the various possible heat dissipation mechanisms, and compare thermal simulations with the measured temperatures. Since the applied bias dropped across a tunneling gap, heat dissipation occurs at the interfaces. The simulations are consistent with our experimental data for a filament tip diameter of ~ 1 nm. A temperature-dependent thermal resistance of the interfaces and/or bulk was introduced to obtain a fit between the simulations and measured data. Thermal resistances imposed by interfaces dominated bulk material heat transport in the simulations.

Electrical measurement of the junction temperature and thermal resistance of HBTs

A simple method is proposed to derive the junction temperature and the bias- and temperature-dependent thermal resistance of heterojunction bipolar transistors (HBTs) using a radio frequency (RF) signal. The method exploits the thermal dependence of the current gain of a transistor whose dissipated power is modified by applying an RF signal. The new method is used to derive the junction temperature and thermal resistance of a power HBT. The results are compared with state-of-the-art techniques.

Thermal Conductivity of Textured Polycrystalline CdTe

The thermal conductivity of optical-quality textured polycrystalline CdTe prepared by vapor deposition is measured in the range 80–400 K before and after deformation along the growth direction and subsequent recrystallization. At low temperatures, the thermal conductivity of polycrystalline CdTe is anisotropic relative to the growth direction, which is attributable to phonon scattering by preferentially aligned dislocations. The thermal conductivity anisotropy persists after deformation and recrystallization. The temperature-dependent thermal resistance of the CdTe lattice shows a break at 200–300 K, which is due to interaction between acoustic and optical phonons. The electrical conductivity of polycrystalline CdTe is measured from 300 to 850 K.

A mechanism for catastrophic failure of avalanche diodes

A simple computer model of the dc electrical-thermal behavior of a Schottky-barrier GaAs IMPATT diode has been modified to include the effects of temperature-dependent thermal resistance. This has made possible the computation of dc V-I characteristics for various IMPATT diode designs and parameters. Computed terminal V-I characteristics, as well as E-J characteristics for points within the depletion layer invariably have shown successive regions of increasing, then decreasing, positive differential resistance, culminating in a region of negative differential resistance. According to an analysis of differential negative resistance appearing in the literature [5], it is a natural consequence of operation in a negative resistance region for high-current filaments to form. Furthermore, a phenomenological argument is cited to justify high-current filamentation in a region of decreasing positive resistance. Experimental evidence is advanced to support the contention that IMPATT shortouts are the natural consequence of diode operation beyond a differential resistance maximum, where the resistance, although positive, is decreasing and the formation of destructive high-current filaments is inevitable.