Thermoreflectance System Research Articles

Research on heat transfer capability of liquid film in three-phase contact line area

• Heat transfer studies were carried out in the three-phase contact line region using the TDTR method with high spatial and temporal resolution. • The experimentally measured results of the overall heat transfer coefficient of the n-octane liquid film in the evaporating thin-film region can reach 439 kW/(m 2 ·K). • A bidirectional heat transfer model for the TDTR experiment was built during data processing. • The usability of the TDTR method in microscopic liquid film heat transfer studies is demonstrated by numerical calculation. The three-phase contact line area plays a vital role in the heat dissipation of micro-devices due to its intense heat transfer capacity. However, the scale of the three-phase contact line area is small, and experimental studies are mainly used to observe the film profile. Few experiments can characterize this area with high spatial resolution, making it a well-known challenge to make a quantitative assessment of the limit of heat transfer capacity. In this work, we use the time-domain thermoreflectance system to measure the liquid film heat transfer capacity in the contact line region. The effective thermal conductivity of the liquid film obtained from the experiment can well reflect the heat transfer capacity of the liquid film at different positions and can be used to calculate the evaporating heat flux and the overall heat transfer coefficient of the liquid film. We also established a theoretical model and performed numerical calculations compared with the experimental results. The results show that the liquid film has the most vital heat transfer capacity in the evaporating thin-film region. The overall heat transfer coefficient can reach ∼439 kW/(m 2 ·K), and the evaporating heat flux of the liquid film can reach ∼1.8 × 10 6 W/m 2 . This work provides a new idea for the experimental study of the three-phase contact line area, offers experimental support for theoretical research, and lays a foundation for revealing the heat and mass transport mechanism in the three-phase contact line area.

Picosecond transient thermoreflectance for thermal conductivity characterization

ABSTRACTWe developed a picosecond transient thermoreflectance (ps-TTR) system for thermal property characterization, using a low-repetition-rate picosecond pulsed laser (1064 nm) as the heating source and a 532 nm CW laser as the probe. Low-repetition-rate pump eliminates the complication from thermal accumulation effect. Without the need of a mechanical delay stage, this ps-TTR system can measure the thermal decay curve from 500 ps up to 1 ms. Three groups of samples are tested: bulk crystals (glass, Si, GaAs, and sapphire); MoS2 thin films (157 ~ 900 nm thickness); InGaAs random alloy and GaAs/InAs digital alloy (short period superlattices). Analysis of the thermoreflectance signals shows that this ps-TTR system is able to measure both thermal conductivity and interface conductance in nanostructures. The measured thermal conductivity values in bulk crystals, MoS2 thin films, and InGaAs random alloy are all consistent with literature values. Cross-plane thermal conductivity in MoS2 thin films does not show obvious thickness dependence. Thermal conductivities of GaAs/InAs digital alloys are smaller than InGaAs random alloy, due to the efficient scattering at interfaces. We also discuss the advantages and disadvantages of this newly developed ps-TTR system comparing with the popular time-domain thermoreflectance system.

High-throughput heterodyne thermoreflectance: Application to thermal conductivity measurements of a Fe-Si-Ge thin film alloy library.

A High-Throughput Time-Domain ThermoReflectance (HT-TDTR) technique was developed to perform fast thermal conductivity measurements with minimum user actions required. This new setup is based on a heterodyne picosecond thermoreflectance system. The use of two different laser oscillators has been proven to reduce the acquisition time by two orders of magnitude and avoid the experimental artefacts usually induced by moving the elements present in TDTR systems. An amplitude modulation associated to a lock-in detection scheme is included to maintain a high sensitivity to thermal properties. We demonstrate the capabilities of the HT-TDTR setup to perform high-throughput thermal analysis by mapping thermal conductivity and interface resistances of a ternary thin film silicide library FexSiyGe100-x-y (20<x,y<80) deposited by wedge-type multi-layer method on a 100 mm diameter sapphire wafer offering more than 300 analysis areas of different ternary alloy compositions.

Complex Refractive Index, Specific Heat Capacity, and Thermal Conductivity for Crystalline Sb–Te Alloys and ZnS–SiO2 with Various Compositions at High Temperatures

We have measured the temperature dependence of the complex refractive index, specific heat capacity, and thermal conductivity of crystalline Sb–Te alloys and ZnS–SiO2 with various compositions by using a spectroscopic ellipsometer, differential scanning calorimeter, and nanosecond pulsed light heating thermoreflectance system. The temperature range was set from room temperature to several hundred degrees Celsius. The values of these properties are useful for calculating realistic temperatures in memory devices and for designing device structures.

Thermophysical and electrical properties of Al-doped ZnO films

Thermal diffusivity of Al-doped ZnO (AZO) films with a thickness of 200 nm was quantitatively analyzed using a “rear heating/front detection type” nanosecond thermoreflectance system. AZO monolayer and Mo/AZO/Mo three-layered films were prepared on synthesized silica substrates by DC magnetron sputtering using high density ceramic ZnO–Al2O3 (Al2O3: 2.5 wt. %) and Mo metal targets. The thermal diffusivity and electrical resistivity of the deposited AZO films ranged 1.8 × 10−6 –2.4 × 10−6 m2 s−1 and 2.3 × 10−3–5.9 × 10−4 Ω cm, respectively. The thermal conductivity corresponding to the thermal diffusivity was one order of magnitude smaller than that of sintered AZO ceramics prepared from ZnO and Al2O3 powders. However, it was found to be larger than that of In2O3-based transparent conductive oxide (TCO) films with approximately the same electrical conductivity, thus implying that AZO can be considered an excellent material for diathermanous TCO circuits.

Thermal Diffusivities of Tris(8-hydroxyquinoline)aluminum and N,N'-Di(1-naphthyl)-N,N'-diphenylbenzidine Thin Films with Sub-Hundred Nanometer Thicknesses

The thermal diffusivities of tris(8-hydroxyquinoline)aluminum (Alq3) and N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (α-NPD) films have been characterized quantitatively using a “rear heating/front detection-type” nanosecond thermoreflectance system. Alq3 or α-NPD films sandwiched by Al films, Al/(Alq3 or α-NPD)/Al three-layered films, were prepared by vacuum evaporation. Al acted as a reflective layer for pulse lasers in the thermoreflectance system. The nominal thicknesses of Alq3 and α-NPD layers varied roughly from 30 to 100 nm. The thermal diffusivities of Alq3 and α-NPD films were found to be (1.4–1.7)×10-7 and 1.4×10-7 m2 s-1, respectively.

Thermoelectric Properties of Bi2Te3-Based Thin Films with Fine Grains Fabricated by Pulsed Laser Deposition

Bi2Te3-based thin films were fabricated on quartz glass substrates by the pulsed laser deposition (PLD) method. By adjustment of the substrate temperature, films with c-axis orientation to the surface of the substrates were grown, and their in-plane electric resistivity and Seebeck coefficient were comparable with those of the bulk material. In contrast, their cross-plane thermal conductivity (evaluated using a thermoreflectance system with nanosecond pulsed laser heating) was comparatively much lower, possibly due to the grain size being as small as 40 nm (estimated based on X-ray diffraction measurement). The dimensionless figure of merit, ZT, for in-plane direction of n-type Bi2Te3 thin films was estimated based on the measurement results.

Effect of electrical properties on thermal diffusivity of amorphous indium zinc oxide films

Thermal diffusivity of amorphous transparent conductive films, indium zinc oxide (IZO) films, with a thickness of 200nm has been analyzed quantitatively using a newly developed nanosecond thermoreflectance system. IZO films sandwiched by molybdenum (Mo) films were prepared on fused silica substrate by dc magnetron sputtering using an oxide ceramic IZO target (89.3wt% In2O3 and 10.7wt% ZnO). The resistivity, carrier density, and Hall mobility of the IZO films ranged from 4.2×10−4to22.7Ωcm, from 2.6×1016to4.2×1020cm−3, and from 10to51cm2∕Vs, respectively. The thermoreflectance signals were analyzed based on an analytical solution of the one dimensional heat flow across the three-layered film (Mo/IZO/Mo) system. The thermal diffusivity of the IZO films was (0.6–1.3)×10−6m2∕s, depending on the electrical resistivity. The thermal conductivity carried by free electrons was estimated using the Wiedemann-Franz law. The phonon contribution to the heat transfer in IZO films with various resistivities was found to be almost constant (λph=1.85W∕mK), which was about half of the one for polycrystalline indium tin oxide films.

Quantitative thermal imaging of GaInAsSb/AlGaAsSb laser diodes by thermoreflectance

The performances of laser diodes operating in continuous wave regime, in terms of lifetime, output power and emission wavelength, are strongly limited by internal Joule heating. Using a CCD-based thermoreflectance system, we have obtained thermal images of laser diodes operating at various biases. Separate calibration procedures have been implemented to obtain quantitative temperatures on the gold-covered ridge waveguides and on the emission facets, thus providing a complete picture of the surface temperature of the device. The continuity of the obtained temperatures is a strong indication of the consistency of the measurements. Even in quasi-static regime, temperature inhomogeneities have been detected, which might lower the permanent damage threshold of the devices.

Thermal transport properties of gold-covered thin-film silicon dioxide

Due to continued miniaturization, the performance and reliability of electronic devices composed of multiple thin layers of material are highly dependent on effective thermal management. Since the thermal properties of thin films, such as SiO/sub 2/, can vary considerably from bulk values, the determination of those properties (as well as the interface resistance between SiO/sub 2/ and adjacent layers) is critical for the purposes of design. In this work, a transient thermo-reflectance system has been employed to measure the thermal characteristics of thin-film SiO/sub 2/ layers. Results show that for layers of SiO/sub 2/ in the range of 100-1000 /spl Aring/, the intrinsic thermal conductivity (TC) is independent of thickness and smaller than the traditionally reported value of bulk silicon dioxide (1.4 W/m-K). The intrinsic value was measured to be around 90% (1.27 W/m-k) and 75% (1.05 W/m-k) of the latter bulk value for thermally grown (TG) and ion beam sputtered (IBS) oxides, respectively. The thermal interface resistances of TG and IBS SiO/sub 2/ films were measured at 1.68 /spl times/ 10/sup -8/ m/sup 2/-K/W and 2.58 /spl times/ 10/sup -8/ m/sup 2/-K/W, respectively. If a chromium film of around 100 /spl Aring/ is deposited between the gold and SiO/sub 2/ layers, the interface thermal resistance improves to 0.78 /spl times/ 10/sup -8/ m/sup 2/-K/W for TG films and 1.15 /spl times/ 10/sup -8/ m/sup 2/-K/W for IBS films. Thus, the effective thermal resistance of SiO/sub 2/ thin-films (i.e., with interface effects) is up to one order of magnitude smaller than the values reported for bulk SiO/sub 2/.