Thermal Conductivity Of Films Research Articles

Thermal conductivity of ultrathin tetrahedral amorphous carbon films

We investigate the thermal conductivity of ultrathin tetrahedral amorphous carbon (ta-C) films on silicon, down to subnanometer thickness. For films with an initial sp3 content of 60%, the thermal conductivity reduces from 1.42to0.09W∕mK near room temperature as the thickness decreases from 18.5to∼1nm. The variation in ta-C film thickness is accompanied by changes in Young’s modulus, density, and sp3 content. The thermal resistance of the finite-thickness interface layer, which forms between ta-C and silicon, is ∼10−8m2K∕W near room temperature, thus producing a noticeable effect on thermal transport in ultrathin ta-C films.

Thermal transport in a semiconductor heterostructure measured by time-resolved x-ray diffraction

We report studies of thermal transport across the interface of a semiconductor heterostructure using x-ray diffraction to measure the time-dependent lattice expansion after ultrafast laser excitation. Femtosecond laser pulses are used to rapidly and locally heat the substrate at the buried interface of an ${\text{Al}}_{0.3}{\text{Ga}}_{0.7}\text{As}/\text{GaAs}$ heterostructure grown by molecular-beam epitaxy. High-resolution time-resolved x-ray diffraction is used to study the heating and cooling of the film and substrate independently. The data are compared with a simple model for the thermal transport incorporated into dynamical diffraction calculations allowing us to extract the room-temperature cross-plane film thermal conductivity. The value is 40% lower than that extrapolated from prior results on liquid-phase epitaxy grown samples of varying concentrations.

Influence of upper layer on measuring thermal conductivity of multilayer thin films using differential 3- ω method

We present an intrinsic error in differential 3- ω measurement method due to two-dimensional heat spreading effect in the upper layer of the target film. By measuring thermal conductivities of 300 nm PECVD-grown silicon dioxide thin films with various thicknesses of upper layers, significant heat spreading effect is observed. Also, analytical modeling regarding apparent thin film thermal conductivity is conducted for verification of experimental results. Experimental results as well as analytical results show that the measurement error tends to increase with thickness of upper layer due to two-dimensional heat spreading effect.

Size Effect on the Thermal Conductivity of Thin Metallic Films Investigated by Scanning Joule Expansion Microscopy

A technique to extract in-plane thermal conductivity of thin metallic films whose thickness is comparable to electron mean free path is described. Microscale constrictions were fabricated into gold films of thicknesses 43nm and 131nm. A sinusoidal voltage excitation across the constriction results in a local temperature rise. An existing technique known as scanning joule expansion microscopy, measures the corresponding periodic thermomechanical expansion with a 10nm resolution and determines the local temperature gradient near the constriction. A three-dimensional finite-element simulation of the frequency-domain heat transfer fits the in-plane thermal conductivity to the measured data, finding thermal conductivities of 82±7.7W∕mK for the 43nm film and 162±16.7W∕mK for the 131nm film, at a heating frequencies of 100kHz and 90kHz, respectively. These values are significantly smaller than the bulk thermal conductivity value of 318W∕mK for gold, showing the electron size effect due to the metal-dielectric interface and grain boundary scattering. The obtained values are close to the thermal conductivity values, which are derived from electrical conductivity measurements after using the Wiedemann–Franz law. Because the technique does not require suspended metal bridges, it captures true metal-dielectric interface scattering characteristics. The technique can be extended to other films that can carry current and result in Joule heating, such as doped single crystal or polycrystalline semiconductors.

Thermal conductivity of nitrogenated ultrananocrystalline diamond films on silicon

The authors report on the experimental investigation of the thermal conductivity of nitrogenated ultrananocrystalline diamond (UNCD) films on silicon. For better accuracy, the thermal conductivity was measured by using two different approaches: the 3ω method and transient “hot disk” technique. The temperature dependence of the thermal conductivity of the nitrogenated UNCD films was compared to that of undoped UNCD films and microcrystalline diamond (MCD) films on silicon. It was shown that the temperature dependence of the thermal conductivity of UNCD films, which is substantially different from that for MCD films, can be adequately described by the phonon-hopping model. The room-temperature thermal conductivity of UNCD is 8.6–16.6 W/m K and decreases with the addition of nitrogen. The obtained results shed light on the nature of thermal conduction in partially disordered nanostructured materials and can be used for estimating the thermal resistance of doped UNCD films.

Thermal conductivity of semi-insulating, p-type, and n-type GaN films on sapphire

The thermal conductivity of undoped, n-type, and p-type GaN films deposited on (0001) substrates of sapphire was measured by the 3-ω method in the temperature range between 215 and 300K. The thickness, thermal conductivity, and heat capacity of the individual layers were used to simulate the experimental value of the increment in temperature of the heater using a multilayer model. The thermal conductivity of undoped GaN film was found to be much higher than that of p-type film. Also, the thermal conductivity of n-type GaN film was slightly smaller than that of p-type film. Modeling of the temperature dependence of the thermal conductivity in the films showed that phonon-dopant and three-phonon umklapp scattering are important. Smaller thickness and hence smaller volume fraction of the film with lower dislocation density was also found to be responsible for lower thermal conductivity in n- and p-type GaN films.

Thermal Conductivity Measurement of Submicron-Thick Aluminium Oxide Thin Films by a Transient Thermo-Reflectance Technique

Thermal conductivity of submicron-thick aluminium oxide thin films prepared by middle frequency magnetron sputtering is measured using a transient thermo-reflectance technique. A three-layer model based on transmission line theory and the genetic algorithm optimization method are employed to obtain the thermal conductivity of thin films and the interfacial thermal resistance. The results show that the average thermal conductivity of 330–1000 nm aluminium oxide thin films is 3.3 Wm−1K−1 at room temperature. No significant thickness dependence is found. The uncertainty of the measurement is less than 10%.

Theoretical consideration of the parameter space for thermal conductivity measurements of thin diamond films

Thin diamond films have important technological applications in microelectronics. The advent of new methods of synthesis and a wide variety of growth morphologies require effective characterization of their thermal properties. The theoretical basis for the measurement of thin film thermal conductivity is discussed. Temperature distributions in the case of steady state and transient methods of thermal conductivity measurement are enumerated with a view to providing a quantitative basis for thermal property measurements of diamond thin films. The effect of three different substrate materials viz., glass, Si and SiC on the thermal conductivity measurement are numerically evaluated. It is shown that the presence of a substrate material does significantly alter the calculated temperature profiles, thereby indicating that a careful consideration of the experimental implementation is imperative for effective extraction of the thermophysical data. A brief discussion on thermal conductivity anisotropy is also included.

Thermoelectric Properties of YbBiPt and YBiPt Thin Films

AbstractMonolayer thin films of YbBiPt and YBiPt have been produced with 560 nm and 394 nm thick respectively in house and their thermoelectric properties were measured before and after MeV ion bombardment. The energy of the ions were selected such that the bombarding Si ions stop in the silicon substrate and deposit only electronic energy by ionization in the deposited thin film. The bombardment by 5.0 MeV Si ions at various fluences changed the homogeneity as well as reducing the internal stress in the films thus affecting the thermal, electrical and Seebeck coefficient of thin films. The stoichiometry of the thin films was determined using Rutherford Backscattering Spectrometry, the thickness has been measured using interferometry and the electrical conductivity was measured using Van der Pauw method. Thermal conductivity of the thin films was measured using an in-house built 3ω thermal conductivity measurement system. Using the measured Seebeck coefficient, thermal conductivity and electrical conductivity we calculated the figure of merit (ZT). We will report our findings of change in the measured figure of merit as a function of bombardment fluence.

Thermal Conductivity in Nanoporous Gold Films during Electron‐Phonon Nonequilibrium

The reduction of nanodevices has given recent attention to nanoporous materials due to their structure and geometry. However, the thermophysical properties of these materials are relatively unknown. In this article, an expression for thermal conductivity of nanoporous structures is derived based on the assumption that the finite size of the ligaments leads to electron‐ligament wall scattering. This expression is then used to analyze the thermal conductivity of nanoporous structures in the event of electron‐phonon nonequilibrium.

MeV Si Ions Bombardment Effects on the Properties of Nano-Layers of SiO2/SiO2+Ag

ABSTRACTWe have grown 100 periodic SiO2/SiO2+Ag multi-nano-layered systems where the SiO2+Ag layers were 7.26 nm and SiO2 buffer layer were 4 nm, total thickness is 563 nm. Using interferometer as well as in-situ thickness monitoring, we measured the thickness of the layers; using Rutherford Backscattering Spectrometry (RBS) measured the concentration and distribution of Ag in SiO2. The electrical conductivity, thermal conductivity and the Seebeck coefficient of the layered structure were measured at room temperature before and after bombardment by 5 MeV Si ions. The energy of the Si ions were chosen such that the ions are stopped in the silicon substrate and only electronic energy due to ionization is deposited in the layered structure. The electrical conductivity measured using Van der Pauw method. Thermal conductivity of the thin films was measured using an in-house built 3ω thermal conductivity measurement system. Using the measured Seebeck coefficient, thermal conductivity and electrical conductivity we calculated the figure of merit (ZT). We will report our findings of change in the figure of merit as a function of the bombardment fluence.

Thermal conductivity of titanium dioxide films grown by metal-organic chemical vapor deposition

We studied the effect of the microstructures on the thermal conductivity of the titanium dioxide (TiO 2) films. TiO 2 films were grown by MOCVD, their morphologies were observed using a scanning electron microscope (SEM). The chemical composition was determined through Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA) measurements. The thermal conductivity of the in-plane direction was measured using an alternating current calorimetric method (laser-heating Angstrom method) in the temperature range of 300 to 470 K. The authors fabricated a TiO 2 film with extremely low thermal conductivity (~ 0.5 Wm − 1 K − 1 ), in which a feather-like texture is regularly arranged in the direction perpendicular to the heat flow. The origins of the extremely low thermal conductivity were studied from a microstructural viewpoint.

Application of scanning thermal microscopy for thermal conductivity measurements on meso-porous silicon thin films

A scanning thermal microscope (SThM) in the dc regime was used to study the thermal conductivity of homogeneous in-depth meso-porous silicon in the form of thin films on a monocrystalline silicon substrate. Measurements for different film porosities (30–80%) and thicknesses (100 nm–8 µm) were performed in order to estimate the influence of both layer porosity and thickness on the thermal conductivity values of porous silicon (PS). An analytical model predicting the SThM measurement in the case of ultra-thin monolayered samples was used to calibrate the technique, to analyse experimental data and to determine the thermal conductivity of meso-porous layers. Effective thermal conductivity of meso-PS films was found to decrease when the porosity increases. The effective thermal conductivities measured for thick porous layers (several µm) are in good accordance with those measured by micro-Raman-spectroscopy on bulk meso-PS samples. For submicrometric thicknesses (<1 µm), the effective thermal conductivity of layers decreases significantly with decreasing layer thickness due to the increased sensitivity of measurements to the thermal resistance of the film/substrate interface. An intrinsic thermal conductivity of PS was calculated independently of the film thickness and the values of interfacial thermal resistances were thus estimated. From the apparatus point of view, the results obtained show that the depth being sensed is of the order of a few micrometres for insulating materials and depends on the thermal conductivity of the films.

Two-detector measurement system of pulse photothermal radiometry for the investigation of the thermal properties of thin films

Pulsed photothermal radiometry, a method developed in previous work for thin film thermal effusivity measurements, is now further developed for the determination of thin film thermal conductivity and volumetric specific heat. The present setup consists of a nanosecond laser source and two infrared (IR) detectors for temperature response measurement. The two detectors have different sizes and frequency bandwidths enabling accurate measurement of the surface temperature both in very short (ns) and long (μs) times after the laser pulse. This enables measurement of the apparent effusivity of both the thin film and substrate. The position in time of the transition region between the film and substrate effusivity is essential for recalculation of the thermal conductivity and volumetric specific heat from the measured thermal effusivity. The presented experimental system was applied to the investigation of the thermal properties of TiO2 and Si-B-C-N thin films. The different thermal conductivity of the TiO2 films correlates well with their different phase structures. The Si-B-C-N films show a slightly different thermal conductivity and specific heat capacity for different atomic compositions.

Modelling for the thermal characterization of solid materials by dc scanning thermal microscopy

The thermal investigation of matter by use of a very localized heat source, scanning thermal microscopy (SThM), permits materials to be probed at the level of very small subsurface volumes. Therefore, the technique appears to be a promising method to study the thermal properties of thin films of submicrometric thickness. In order to estimate this possibility, we propose a new prediction modelling of the measurement with a SThM based on a hot anemometer wire probe used in a dc regime. From this modelling, a study of the sensitivity of measurement to various parameters operating in the thermal interaction between the probe and a mono-layered sample is presented. It gives new data allowing a better understanding of measurements. A new method to calibrate the technique for thermal conductivity measurement with more accuracy is deduced from this study. New data about the different physical mechanisms governing the probe–sample thermal interaction are given. The proposed approach also supplies a method for the determination of the depth resolution of a thermal probe. This last parameter is essential in the framework of thin film study with a given probe. Its dependence on sample thermal conductivity and thermal coupling area are discussed. Our results specify the possibilities of the technique and should contribute to a more accurate determination of thin film thermal conductivity in its dc regime.

Bulk-Micromachined Test Structure for Fast and Reliable Determination of the Lateral Thermal Conductivity of Thin Films

A novel bulk-micromachined test structure is presented for the fast and reliable determination of the lateral thermal conductivity of thin films. The device is composed of a heater resistor and thermocouples that are fabricated in polysilicon (poly-Si), and the associated processing and DC measurement procedures are straightforward. The validity of the method is supported by numerical simulations and verified by experimental determination of the lateral thermal conductivity of aluminum (Al), aluminum nitride (AlN), p-doped poly-Si, and silicon nitride (SiN) thin films. For Al, an average value of 217 W m-1 K-1 was found for 1-mum thick layers. For the other layers, a number of thicknesses were studied, and the increase of thermal conductivity with thickness was effectively detected: for AlN, values from 7 to 11.5 W m-1 K-1 were found, and for p-doped poly-Si, values went from 21 to 46 W m-1 K-1 for thicknesses from 0.15 to 1 mum. For SiN, a value of 1.8 was extracted for layers thicker than 0.5 mum.

Application of the three omega method for the thermal conductivity measurement of polyaniline

The three omega method has proven to provide accurate and reliable measurements of thermal conductivity of thin films and other materials. However, if the films are soft and conductive, conventional methodologies to prepare samples for the measurement technique are challenging and often unachievable. Various modifications to the sample preparation to employ this technique for soft conducting films are reported in this paper including the use of shadow masks for metal heater deposition and a process for preparation of low temperature insulating films required between film and heater. In this work, thick (∼5μm) and ultrathin (∼110nm) films of polyaniline as well as a thin (∼300nm) film of low temperature plasma enhanced chemical vapor deposited SiO2 as a function of temperature were measured. Though not considered a soft material, the silicon dioxide film was utilized for comparison with previous data. Results indicate that the SiO2 film exhibits a thermal conductivity slightly lower than others’ data [S. M. Lee and D. G. Cahill, J. Appl. Phys. 81, 2590 (1997); H. Yan et al., Chem. Lett. 2000, 392; H. Yan et al., Anal. Calorim. 69, 881 (2002); J. E. de Albuquerque et al., Rev. Sci. Instrum. 74, 306 (2003)], which is likely due to the low temperature processing conditions that results in additional disorder in the film. The polyaniline films exhibit an increase in thermal conductivity with temperature, which is largely due to increasing heat capacity. The thick film thermal conductivity is many times the value corresponding to the thin film, which is likely due to significant phonon boundary scattering present in the ultrathin film.

Calibration of the Thermal Conductivity of Thin Films in Phase-Change Optical-Recording Stacks

We describe two different methods of calibrating the thermal conductivity of thin films in phase change optical recording stacks, the melt threshold method and the transmission electron microscope (TEM) picture based method. Both methods use numerical modeling to approximate the thermal conductivities of some commonly used materials in phase change recording. The aim of our study is to find a consistent set of values for the thermal conductivities, such that temperatures in different recording stacks at different velocities are correctly predicted. Both methods were found to give consistent results. The relationships between thermal conductivity, the type of interface, and the thickness of the thin film were also investigated. A good match between simulated results and experimental results was demonstrated.

Thermomechanical properties of thin organosilicate glass films treated with ultraviolet-assisted cure

Ultraviolet (UV)-assisted cure has recently been reported as an efficient method to enhance the mechanical properties of organosilicate glasses (OSG) at the expense of only minor film densification. In this work we show that, depending on the OSG material, the effect of UV-cure on fracture and thermal conductivity properties can vary to a large extent even though the same extent of stiffness enhancement is obtained. When the increase of elastic modulus is mostly due to the rearrangement of the silica matrix into more stable silica bonds, the film cohesion strength and thermal conductivity are also improved. Conversely, these properties remain unaffected when the dominant UV-cure mechanism is the increase of matrix connectivity. In the latter case, film adhesion is enhanced. The dominant UV-cure mechanism depends on the initial degree of cross-linking and on the mobility of the OSG matrix.

Determination of Thermal Conductivity of Amorphous Silicon Thin Films via Non-Contacting Optical Probing

The thermal conductivity of amorphous silicon (a-Si) thin films is determined by using the non-intrusive, in-situ optical transmission measurement. The thermal conductivity of a-Si is a key parameter in understanding the mechanism of the recrystallization of polysilicon (p-Si) during the laser annealing process to fabricate the thin film transistors with uniform characteristics which are used as switches in the active matrix liquid crystal displays. Since it is well known that the physical properties are dependent on the process parameters of the thin film deposition process, the thermal conductivity should be measured. The temperature dependence of the film complex refractive index is determined by spectroscopic ellipsometry. A nanosecond KrF excimer laser at the wavelength of 248 nm is used to raise the temperature of the thin films without melting of the thin film. In-situ transmission signal is obtained during the heating process. The acquired transmission signal is fitted with predictions obtained by coupling conductive heat transfer with multi-layer thin film optics in the optical transmission measurement.