Thin-film Thermoelectric Modules Research Articles

Development, experimental and simulated performance of copper iodide (γ-CuI) uni-track thin film thermoelectric modules

In this article, we investigate the performance of 950 nm thick p-type γ-CuI uni-track thin film thermoelectric modules. A model was first developed to optimize a module’s geometry, focusing on the length and the number of the γ-CuI tracks. Based on the maximum power achieved and the open circuit voltage (above 225 mV), the simulation optimized module consists of three tracks of γ-CuI, each with a length of 13 mm. Using these simulation results, modules were elaborated through solid iodination process of Cu thin tracks. These γ-CuI tracks were then connected with Pt electrodes. After characterizing the structure and electrical properties of the γ-CuI material, the module’s performance was measured at various applied temperatures in a free gradient mode. The results were in agreement with the simulation. Experimental and simulated performances highlight the significant impact of contact resistance as the temperature increases limiting module performances. A maximum power of 61nW was achieved at an applied temperature of 190 °C. This suggests that higher values could be attained through optimized contacts, with the goal of enabling some commercial applications for easily manufactured modules. Due to the optoelectrical properties of γ-CuI, this even paves the way for the development of new transparent thermoelectric generators.

Mitigation of Power Factor Degradation in Bi2Te3 Thin Films

For thin-film thermoelectric modules with electrodes deposited on the sides of the thermoelectric material, the diffusion of atoms from the electrode affects the module’s performance. Long-term aging is crucial when the module is for practical applications. In this study, Bi2Te3 thin films with a highly preferred orientation were fabricated by a co-sputtering deposition method. Cu was used as the electrode because of its high electrical conductivity; it migrates through the Bi2Te3 film via surface and grain boundary diffusion. The diffusing Cu segregates at grain boundaries and forms a Cu2–xTe intermetallic compound on the sample surface. Contact resistivity at the interface between the Cu electrode and Bi2Te3 thin films substantially increases with aging time. Long-term aging unavoidably degrades the power factor (PF) of the pristine Bi2Te3 since n-type Bi2Te3 converts into p-type by the formation of antisite defects. The study shows that the diffusing Cu from the electrodes of the Cu/Bi2Te3/Cu module significantly mitigates the degradation of the PF after long-term aging.

Fabrication and Performance Analysis of AZO and MCCO as Thin Film-Thermoelectric Generator Materials

The purpose of this research was to determine the performance of AZO and MCCO materials as constituents of the thin film-thermoelectric generator module. The method used for fabrication is DC Magnetron Sputtering. The electrode material used is Ag and the substrate used is SiO2 glass. The arrangement of the thin film used for the fabrication of the thermoelectric module is P-N-P-N-P-N-P-N-P-N (5 couples of p-n junctions). Based on the test results, the thickness of the thin film type N is 74.72 nm and type P is 90.34 nm. At the highest test temperature (300 oC), the AZO Seebeck coefficient value is -108 µV/K while the MCCO Seebeck coefficient value is 350 µV/K, and the AZO electrical resistivity value is 0.07 Ω.m while the MCCO electrical resistivity value is 0.36 Ω.m. The highest temperature difference given in the test of the AZO and MCCO thin film thermoelectric module is 1.538 °C and the thermoelectric module can produce a voltage of 1,842 ± 0.047 mV, a Seebeck coefficient of 4 µV/K, and an efficiency of 0.44%. Based on this research, it can be concluded that the performance of AZO and MCCO thin film-thermoelectric modules will have better performance at temperatures around 300 - 350 °C.

Flexible thermoelectric module based on zinc oxide thin film grown via SILAR

In this work, we used the low temperature solution growth Successive Ionic Layer Adsorption and Reaction (SILAR) for a deposition of the nanostructured undoped and indium doped (ZnO and ZnO:In) thin films on flexible polyimide (PI) substrates for their use as cheap non-toxic thermoelectric materials in the flexible thermoelectric modules of planar type to power up portable and wearable electronics and miniature devices. The use of a zincate solution in the SILAR method allows to obtain ZnO:In film, which after post-growth annealing at 300 °C has low resistivity ρ ≈ 0.02 Ω m, and high Seebeck coefficient −147 μV/K and thermoelectric power factor ~1 μW K−2 m−1 at near-room temperatures. As evidence of the operability of the manufactured films as the basis of the TE device, we have designed and tested experimental lightweight thin-film thermoelectric module. This TE module is able to produce specific output power 0.8 μW/m2 at ΔT = 50 K.

Wearable and flexible thin film thermoelectric module for multi-scale energy harvesting

Developing a thermoelectric generator(TEG) with shape conformable geometry for sustaining low-thermal impedance and large temperature gradient (ΔT) is fundamental for wearable and multi-scale energy harvesting applications. Here we demonstrate a flexible architectural design, with efficient thin film thermoelectric generator as a solution for this problem. This approach not only decreases the thermal impedance but also multiplies the temperature gradient, thereby increasing the power conversion efficiency (PCE) as comparable to bulk TEG. Intact thin films of Tin telluride (p-type) and Lead Telluride (n-type) are deposited on flexible substrate through physical vapor deposition and a thermoelectric module possessing a maximum output power density of 8.4 mW/cm2 is fabricated. We have demonstrated the performance of p-SnTe/n-PbTe based TEG as a flexible wearable power source for electronic gadgets, as a thermal touch sensor for real-time switching and temperature monitoring for exoskeleton applications.

Transfer of P-type to N-type Thermoelectric Properties of Ag-Sb-Te Thin Film Through Temperature Annealing and Its Electrical Power Generation

Ag-Sb-Te (AST) thin film was successfully fabricated on a flexible polyimide substrate by using DC magnetron sputtering from the AgSbTe (AST) target. As-deposited samples were annealed at temperatures between 300 and 450°C under vacuum for 30 min. Then, uni-leg AST thin film thermoelectric modules of five elements were fabricated. Thermal annealing induced a change of thermoelectric characteristic of the thin film from p-type material (300–350°C) to n-type material (400–450°C) through the change in structures (amorphous to crystalline, atomic composition ratio and surface roughness, etc.). The highest power factor was 0.97 mW m−1 K−2 and 0.065 mW m−1 K−2 for p-type and n-type, respectively. The maximum power generation of the uni-leg AST thin film thermoelectric module was approximately 0.88 nW for p-type and 0.54 nW for n-type, with a temperature difference of around 20 K.

Superlattice-based thin-film thermoelectric modules with high cooling fluxes.

In present-day high-performance electronic components, the generated heat loads result in unacceptably high junction temperatures and reduced component lifetimes. Thermoelectric modules can, in principle, enhance heat removal and reduce the temperatures of such electronic devices. However, state-of-the-art bulk thermoelectric modules have a maximum cooling flux qmax of only about 10 W cm−2, while state-of-the art commercial thin-film modules have a qmax <100 W cm−2. Such flux values are insufficient for thermal management of modern high-power devices. Here we show that cooling fluxes of 258 W cm−2 can be achieved in thin-film Bi2Te3-based superlattice thermoelectric modules. These devices utilize a p-type Sb2Te3/Bi2Te3 superlattice and n-type δ-doped Bi2Te3−xSex, both of which are grown heteroepitaxially using metalorganic chemical vapour deposition. We anticipate that the demonstration of these high-cooling-flux modules will have far-reaching impacts in diverse applications, such as advanced computer processors, radio-frequency power devices, quantum cascade lasers and DNA micro-arrays.

Microcontact-Enhanced Thermoelectric Cooling of Ultrahigh Heat Flux Hotspots

The dissipated power of insulated gate bipolar transistor and high electron mobility transistor amplifiers is typically nonuniform, resulting in areas of elevated temperature, or hotspots, which can have very large heat fluxes, on the order of 1000 W/cm2. While various bulk cooling systems are being researched to remove large amounts of heat, they uniformly reduce the chip temperature, leaving the temperature nonuniformity. Therefore, advanced hotspot cooling techniques, which provide localized cooling, are also required to unlock the full potential of cutting edge power devices. Thermoelectric coolers have previously been demonstrated as an effective method of producing on-demand cooling for the removal of localized hotspots. However, the heat flux of the hotspots that can be cooled is limited by the maximum cooling flux of thermoelectric devices. This paper demonstrates the thermal and reliability performance of a microcontact-enhanced thermoelectric cooling configuration, which uses a contact structure etched directly out of the electronic substrate to concentrate the cooling produced by a commercially available thermoelectric module. The 22 K of cooling, resulting in a hotspot temperature rise of <6 K for a heat flux of 2.5 kW/cm2, was experimentally demonstrated using a Laird HV37 thin-film thermoelectric module with a maximum device level cooling flux of 66 W/cm2. A numerical model was created, and it is predicted that when the chip and microcontact geometry is optimized, hotspots with heat fluxes in excess of 3 kW/cm2 can be cooled by nearly 40 K, reducing the hotspot temperature rise to 0 K.

Расчет тонкопленочного термоэлектрического модуля, изготавливаемого методом импульсного лазерного осаждения

Расчет тонкопленочного термоэлектрического модуля, изготавливаемого методом импульсного лазерного осаждения

Non-contact method for characterization of small size thermoelectric modules.

Conventional techniques for characterization of thermoelectric performance require bringing measurement equipment into direct contact with the thermoelectric device, which is increasingly error prone as device size decreases. Therefore, the novel work presented here describes a non-contact technique, capable of accurately measuring the maximum ΔT and maximum heat pumping of mini to micro sized thin film thermoelectric coolers. The non-contact characterization method eliminates the measurement errors associated with using thermocouples and traditional heat flux sensors to test small samples and large heat fluxes. Using the non-contact approach, an infrared camera, rather than thermocouples, measures the temperature of the hot and cold sides of the device to determine the device ΔT and a laser is used to heat to the cold side of the thermoelectric module to characterize its heat pumping capacity. As a demonstration of the general applicability of the non-contact characterization technique, testing of a thin film thermoelectric module is presented and the results agree well with those published in the literature.

The Effects of the Size and the Doping Concentration on the Power Factor of n-type Lead Telluride Nanocrystals for Thermoelectric Energy Conversion

For the first time, we demonstrate a successful synthesis of colloidal n-type lead telluride nanocrystals doped with iodine. By tuning the reaction time and iodine concentration in the precursor solution, nanocrystals with different sizes and doping concentrations are synthesized. The Seebeck coefficient and electrical conductivity of the nanocrystals are measured on nanocrystal thin films fabricated by dip-coating glass substrates in the nanocrystals solution. Investigations on the influence of size and doping concentration on the electrical properties have been performed. The results show that the size of the nanocrystals significantly influences the electrical conductivity but not the Seebeck coefficient of nanocrystal films, while higher doping concentration leads to lower Seebeck coefficient but higher electrical conductivity in the nanocrystal films. Proof-of-concept thin-film thermoelectric modules are also fabricated using both p-type and n-type PbTe nanocrystals for the conversion of thermal energy into electrical energy.

Prospects of Thin-Film Thermoelectric Devices for Hot-Spot Cooling and On-Chip Energy Harvesting

Advances in thin-film thermoelectric (TE) materials have created opportunities for using TE devices in high heat flux applications such as hot-spot (H-S) cooling and on-chip energy harvesting. In this paper, we compare the performance of TE modules integrated directly on the silicon die with those that are attached to the heat spreader of the chip package. We make use of the Bi2Te3/Sb2Te3 super lattice material to explore tradeoffs between the two integration options for H-S cooling and energy-harvesting applications. Package level finite element simulations show that on-chip energy harvesting can yield up to 30 mW of power from an H-S with a heat flux of 200 W/cm2, or the same H-S can be cooled as much as 19°C in the cooling mode. In addition, the TE module integrated on the die is shown to have a disadvantage due to the higher thermal resistance from the hot side of the module to the ambient.

The effect of Cr buffer layer thickness on voltage generation of thin-film thermoelectric modules

The effect of Cr buffer layer thickness on the open-circuit voltage generated by thin-film thermoelectric modules of Bi0.5Sb1.5Te3 (p-type) and Bi2Te2.7Se0.3 (n-type) materials was investigated. A Cr buffer layer, whose thickness generally needs to be optimized to improve adhesion depending on the substrate surface condition, such as roughness, was deposited between thermoelectric thin films and glass substrates. When the Cr buffer layer was 1 nm thick, the Seebeck coefficients and electrical conductivity of 1 µm thermoelectric thin films with the buffer layers were approximately equal to those of the thermoelectric films without the buffer layers. When the thickness of the Cr buffer layer was 1 µm, the same as the thermoelectric films, the Seebeck coefficients of the bilayer films were reduced by an electrical current flowing inside the Cr buffer layer and the generation of Cr2Te3. The open-circuit voltage of the thin-film thermoelectric modules decreased with an increase in the thickness of the Cr buffer layer, which was primarily induced by the electrical current flow. The reduction caused by the Cr2Te3 generation was less than 10% of the total voltage generation of the modules without the Cr buffer layers. The voltage generation of thin-film thermoelectric modules could be controlled by the Cr buffer layer thickness.

Thermal–Photovoltaic Hybrid Solar Generator Using Thin-Film Thermoelectric Modules

We fabricated thin-film thermoelectric modules for thermal–photovoltaic hybrid solar generator. Bi0.5Sb1.5Te3 (p-type) and Bi2Te2.7Se0.3 (n-type) thermoelectric thin films were deposited by radio-frequency magnetron sputtering method and patterned to form plane-type thermoelectric modules using lift-off technique. The hybrid module consisted of the thin-film thermoelectric module, a photovoltaic module, a hot mirror, and a near-infrared (NIR) focusing lens. NIR light, which does not contribute to photovoltaic conversion, was separated from solar light using the hot mirror. When the NIR light was focused onto the hot side of the thermoelectric module by the lens, the open voltage generated by the thin-film thermoelectric generator was 78 mV. The total open voltage of the thermal–photovoltaic hybrid generator increased by 1.3% compared to that of the photovoltaic module alone.

Thermal–Photovoltaic Hybrid Solar Generator Using Thin-Film Thermoelectric Modules

We fabricated thin-film thermoelectric modules for thermal–photovoltaic hybrid solar generator. Bi0.5Sb1.5Te3 (p-type) and Bi2Te2.7Se0.3 (n-type) thermoelectric thin films were deposited by radio-frequency magnetron sputtering method and patterned to form plane-type thermoelectric modules using lift-off technique. The hybrid module consisted of the thin-film thermoelectric module, a photovoltaic module, a hot mirror, and a near-infrared (NIR) focusing lens. NIR light, which does not contribute to photovoltaic conversion, was separated from solar light using the hot mirror. When the NIR light was focused onto the hot side of the thermoelectric module by the lens, the open voltage generated by the thin-film thermoelectric generator was 78 mV. The total open voltage of the thermal–photovoltaic hybrid generator increased by 1.3% compared to that of the photovoltaic module alone.

Thin-Film Thermoelectric Modules for Power Generation Using Focused Solar Light

We demonstrated the fabrication of thin-film thermoelectric generators and evaluated their generation properties using solar light as a thermal source. Thin-film elements of Bi0.5Sb1.5Te3 (p-type) and Bi2Te2.7Se0.3 (n-type), which were patterned using the lift-off technique, were deposited on glass substrates using radiofrequency magnetron sputtering. After annealing at 300°C, the average Seebeck coefficients of p- and n-type films were 150 μV/K and −104 μV/K, respectively, at 50°C to 75°C. A cylindrical lens was used to focus solar light to a line shape onto the hot side of the thin-film thermoelectric module with 15 p–n junctions. The minimum width of line-shaped solar light was 0.8 mm with solar concentration of 12.5 suns. We studied the properties of thermoelectric modules with different-sized p–n junctions on the hot side, and obtained maximum open voltage and power values of 140 mV and 0.7 μW, respectively, for a module with 0.5-mm p–n junctions. The conversion efficiency was 8.75 × 10−4%, which was approximately equal to the value estimated by the finite-element method.

Implementation of Single-Wire Communication Protocol for 3D IC Thermal Management Systems using a Thin Film Thermoelectric Cooler

We propose and implement a single-wire communication protocol for thermal management systems using thin film thermoelectric modules for 3D IC cooling. The proposed single-wire communication protocol connects the temperature sensors, located near hot spots, to measure the local temperature of the chip. A unique ID number identifying the location of each hot spot is assigned to each temperature sensor. The prototype chip was fabricated by a 0.13 ㎛ CMOS MPW process, and the operation of the chip is verified.

Large external ΔT and cooling power densities in thin-film Bi2Te3-superlattice thermoelectric cooling devices

Experimental I-V-Tc-ΔT data of thin-film superlattice thermoelectric modules is used to determine the internal ΔT, cross-plane Seebeck coefficient, effective thermal interface resistance, device ZT, and Qmax. We demonstrate 55K of external cooling at 300K (Tcmin=244.8K), with an estimated heat pumping capacity of 128W∕cm2. The average ZT300 for the best superlattice devices is 0.75, compared to 0.66 for a bulk BixSb2−xTe3∕Bi2SexTe3−x device. Our model indicates a significantly higher internal ΔT occurs across the active thermoelectric element, which was verified using buried thermocouples.

Thermal Stability of p-type Bi2Te3/Sb2Te3 and n-type Bi2Te3/Bi2Te2-xSex Thermoelectric Superlattice Thin Film Devices

ABSTRACTThermolectric devices have been constructed using Bi2Te3/Sb2Te3 and Bi2Te3/Bi2Te2-xSex superlattice thin films. Since these devices are intended for use in systems that will operate at elevated temperatures over their lifetime as in many power conversion applications, thermal stability of the thermoelectric figure of merit is an important consideration. The ZTe of p-type and n-type superlattice thin film elements was evaluated at specific intervals during exposure to elevated temperatures of 150°C for up to 60 hrs. Results indicate that the figure of merit for p- and n-type superlattice films is not compromised over time when exposed to these operating temperatures. In fact, both p- and n-type superlattice thin film ZTe remains very constant or improves slightly when subjected to continuous exposure to elevated temperatures. Evaluation of these thin film thermoelements is reported and implications of these results are considered for thin film thermoelectric modules.

An analysis for geometrical effects on the cooling performance of (Bi, Sb)2Te3/Bi2(Te, Se)3-based thin film thermoelectric modules

Geometrical effects on the cooling performance of the thin film thermoelectric (TFTE) modules were investigated by varying the film thickness and the number of p/n couples of the (Bi, Sb)2Te3/Bi2(Te, Se)3-based system which were fabricated by the flash evaporation technique. Maximum temperature difference (δTmax, maximum cooling) and optimum input current (Iopt) increased with film thickness for a fixed number of couples. For the case of given thickness, however, Iopt decreased with the number of couples, maintaining almost constant δTmax. The measured values for the cooling characteristics were compared with the results obtained through computer simulation work by the finite difference method (FDM). The thinner the film and the larger the number of p/n couples of the modules, the larger was the deviation between the experimental and the simulated values.