Thermoelectric Microcoolers Research Articles

General strategy for developing thick-film micro-thermoelectric coolers from material fabrication to device integration

Micro-thermoelectric coolers are emerging as a promising solution for high-density cooling applications in confined spaces. Unlike thin-film micro-thermoelectric coolers with high cooling flux at the expense of cooling temperature difference due to very short thermoelectric legs, thick-film micro-thermoelectric coolers can achieve better comprehensive cooling performance. However, they still face significant challenges in both material preparation and device integration. Herein, we propose a design strategy which combines Bi2Te3-based thick film prepared by powder direct molding with micro-thermoelectric cooler integrated via phase-change batch transfer. Accurate thickness control and relatively high thermoelectric performance can be achieved for the thick film, and the high-density-integrated thick-film micro-thermoelectric cooler exhibits excellent performance with maximum cooling temperature difference of 40.6 K and maximum cooling flux of 56.5 W·cm−2 at room temperature. The micro-thermoelectric cooler also shows high temperature control accuracy (0.01 K) and reliability (over 30000 cooling cycles). Moreover, the device demonstrates remarkable capacity in power generation with normalized power density up to 214.0 μW · cm−2 · K−2. This study provides a general and scalable route for developing high-performance thick-film micro-thermoelectric cooler, benefiting widespread applications in thermal management of microsystems.

Substrate integrated micro-thermoelectric coolers in glass substrate for next-generation photonic packages

Substrate integrated micro-thermoelectric coolers in glass substrate for next-generation photonic packages

Design of a Novel PID Controller Based on Machine Learning Algorithm for a Micro-Thermoelectric Cooler of the Polymerase Chain Reaction Device

Design of a Novel PID Controller Based on Machine Learning Algorithm for a Micro-Thermoelectric Cooler of the Polymerase Chain Reaction Device

Silicon Microthermoelectric Coolers for Local Heat Removal in Integrated Circuit Chips

Silicon Microthermoelectric Coolers for Local Heat Removal in Integrated Circuit Chips

High Thermoelectric Performance of Non-Stoichiometric and Oriented GeTe Thin Films.

The increasing demand for micro-thermoelectric coolers and generators promotes the research on thermoelectric (TE) thin films. As a promising medium-temperature TE material, GeTe has attracted wide attention recently. However, the thermoelectric performance of thin-film GeTe remains inferior. Herein, oriented GeTe films with excessive Ge are obtained by magnetron co-sputtering technique, which can not only reduce the carrier concentration but also increase the carrier mobility, maintaining the high electrical conductivity of GeTe. Furthermore, higher structural symmetry and grain boundary scattering enhance the Seebeck coefficient of oriented GeTe films. As a result, the power factor (PF) value can reach as high as 2848 µW m-1 K-2 at room temperature and increase to 5263 µW m-1 K-2 at 600 K. Furthermore, a TE device with the Ge-rich GeTe thin film is fabricated and the maximum output power density (power per unit area) reaches 0.3W cm-2 at ΔT = 250 K. This work demonstrates that the stoichiometry and orientation modulations are effective strategies to improve the thermoelectric performance of GeTe thin films.

Doped Organic Micro‐Thermoelectric Coolers with Rapid Response Time (Adv. Electron. Mater. 12/2022)

Doped Organic Micro-Thermoelectric Coolers The operation mechanism of doped organic Peltier cooling device is illustrated. Organic semiconductors offer unique opportunities for local cooling devices due to their intrinsic mechanical flexibility, light weight and biocompatibility and could enable novel device concepts for display and healthcare applications. More details can be found in article number 2200629 by Shu-Jen Wang, Heiko Reith, Karl Leo, and co-workers.

A novel mechanism for thermal management at the cold side of a pulsed two-stage thermoelectric micro-cooler with different PCM heat sink shapes

A new mechanism for thermal management at the cold side of a pulsed two-stage thermoelectric micro-cooler (Two-stage μTEC) is presented. The Two-stage μTEC operates under different electric current values at each stage and uses a phase change material (PCM) in different heat sink shapes for temperature control in the cold junction. A geometric factor γ is defined for designing an optimal heat sink based on reducing the cross-sectional area of the second stage thermoelements. The aim is to save the amount of PCM used and keep the cold side temperature (Tc) constant for as long as possible. This thermoelectric device is proposed to treat skin diseases and is suitable for use in cryomassage. A one-dimensional numerical model is considered in the system’s heat transfer, and cooling by natural convection on the hot side is considered. PCM is used as a cooling substance because it can absorb large amounts of latent heat at a nearly constant temperature. The influence of the electric current pulse and the γ geometric relationship on the micro-cooler are analyzed to determine the optimum operating values that allow a constant temperature of 243 K to be reached in the cold junction. The temperature of the cold side is kept constant by using different electric currents in each stage for the geometric factor γ=4 during Δtpulse=95.7s. On the other hand, the optimization of the heat sink, the geometric factor

Active thermal management of hotspot under thermal shock based on micro-thermoelectric cooer and bi-objective optimization

The highly non-uniform transient power density in modern semiconductor device leads to thermal shocks with high temperature and temperature variation, which causes performance and reliability challenges. This study established a three-dimensional numerical model to investigate the potential of micro-thermoelectric cooler to mitigate the adverse effect of fluctuating hotspot caused by thermal shock. This study also proposed to assess the chip reliability under thermal shock considering both the influences of peak temperature and temperature variation, and a lumped reliability enhancement factor was defined. Furthermore, the operating scheme of micro-thermoelectric cooler to mitigate the adverse effect of thermal shock was investigated. Results show that the micro-thermoelectric cooler can effectively restrain temperature fluctuation of chip undergoing thermal shock. It also found that keeping the micro-thermoelectric cooler working all the time is not necessarily good considering both the influences of peak temperature and temperature variation. The reliability analysis shows that the lumped reliability enhancement factor is greater than 1 as long as the micro-thermoelectric cooler provides cooling capacity for frequency rising to high. However, for frequency reducing to mild, it is beneficial to turn on the micro-thermoelectric cooler when the ratio of influence weight coefficien is larger than 1, otherwise it is better to turn off the micro-thermoelectric cooler. After the micro-thermoelectric cooler was optimized, the critical ratio of influence weight coefficien could be decreased, indicating a wider practicability of the micro-thermoelectric cooler. Meanwhile, the reliability of chip could be further enhanced. For the case of the ratio of influence weight coefficien equaling to 1, when the thermoelectric element thickness increases from 7.5 μm to 30 μm, the maximum lumped reliability enhancement factor of frequency rising to high and frequency reducing to mild could be respectively improved from 1.9 to 5.4, and 1 to 1.9.

Investigation of a novel separately-configured micro-thermoelectric cooler to enabling extend application scope

Owing to the physical restriction of the buildings and willingness of seeking a higher temperature difference, the hot and cold sides of a thermoelectric module often require a separation treatment, whilst the soft wire or wireless connections between the hot and cold sides can be implemented. This paper investigated a novel separated micro-thermoelectric cooler (micro-TEC) configuration for cooling, which splits the hot and cold sides of the micro-TECs for a distance, with the copper connecting wire in between. A dedicated mathematic numerical simulation for the micro-TEC was carried out. The results show that for a traditional micro-TEC, the maximum coefficient of power (COP) of the micro-TEC is 1.1923 which occurs at the current of 50 mA and temperature difference of 20 K. For the novel separated micro-TEC with connecting wires, the maximum COPs at the wire lengths of 25 μm, 50 μm, 100 μm, 200 μm are 0.9258, 0.9226, 0.9162 and 0.9035 respectively, during which current of 50 mA and temperature difference of 20 K are applied. Although the maximum COP of the micro-TEC is reduced by about 0.2, the distance between the cold and hot sides has a significant increase. Under the condition of current of 50 mA and temperature difference of 20 K, the cooling capacity of the micro-TEC with connecting wire length of 0 μm, 25 μm, 50 μm, 100 μm and 200 μm are 0.0023943 W, 0.0021351 W, 0.0021292 W, 0.0021173 W and 0.0020937 W respectively. Thus, the reduction of the cooling capacity caused by connecting wire is less than that of the COP loss. Further, the maximum COPs of the micro-TEC under the wire length ratio of 4:1, 3:2, 1:1, 2:3 and 1:4 are 0.87924, 0.8953, 0.9035, 0.91186 and 0.92922, during which current is 50 mA and temperature difference is 20 K. The cooling capacity of the micro-TEC under the length ratio of 4:1, 3:2, 1:1, 2:3 and 1:4 are 0.0020319 W, 0.0020729 W, 0.0020937 W, 0.0021148 W and 0.0021577 W respectively, during which the current of 50 mA and temperature difference of 20 K are implemented.

Finite Element Analysis of Miniature Thermoelectric Cooler for the Thermal Management of Si-Based Photonic Integrated Circuits

Today’s electronic and photonic devices are facing a bottleneck in removing and managing the excess heat flux due to its progressive miniaturization and integration density. Generation of high heat flux during device operation has become a major challenge and makes the Si-based photonic integrated circuits (PIC) less efficient to function at the desired temperature. Hence, it is essential to remove/ manage the heat flux to maintain efficient and reliable operation of the device. The state-of-art solution to control device temperature involves macro thermoelectric coolers (TEC), which are inefficient in meeting the thermal management requirement for photonic integrated circuits (PIC). Thermal management of these optoelectronic chips using a micro-thermoelectric coolers (µTECs) can be a better proposition, as it can be integrated directly on the photonic chip by removing the large macro-TECs, which will allow precise control of the thermal load [1]. µTECs integrated with optoelectronic devices (lasers, modulators, etc.) can handle large heat flux, with fast response time and can provide high device performance with reduced cost [2].In this work, a comprehensive study focusing on the cooling performance of the µTECs for a photonic package is performed by finite element method (FEM) using COMSOL Multiphysics software. All the simulations and design optimizations have been done following the microfabrication constraints along with the realistic heat flux scenarios. In order to enable the full potential of silicon-based photonic devices, we considered Si as the substrate. The effect of parameters such as load current, the thickness and shape of the thermoelectric pillars, thickness of the interconnect material and number of thermoelectric pillars on device cooling performance are optimized. It is known that bismuth-telluride (Bi-Te) based thermoelectric materials currently have the highest cooling performance near room temperature. For design optimization, first, a single uni-pair is considered and thermoelectric properties of electrodeposited CuTe and BiSbTe are selected as the n- and p-type thermoelectric materials [3, 4]. Also, the effect of substrate, which significantly influences the heat flow between the µTEC and atmosphere is studied. The results indicate that with increasing the leg height, first ΔT increases and later decreases due to joule heating while the coefficient of performance (COP) decreases. A range of load current (I) between 5 to 450 mA is applied and a maximum temperature difference of around 35 K is achieved at 250 mA. In summary, µTEC can be better choice as opposed to macro-TEC in terms of energy efficiency with the benefit of using less toxic materials, which may pave the way of future highly integrated optoelectronic circuits. Acknowledgments This work received funding from the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 825114 (SmartVista). This publication has emanated from research supported in part by a research grant from Science Foundation Ireland (SFI) and is co-funded under the European Regional Development Fund under Grant Number 15/IA/3160, 12/RC/2276 and 13/RC/2077 References R. Enright, S. Lei, K. Nolan, I. Mathews, A. Shen, G. Levaufre, R. Frizzell, G. H. Duan and D. Hernon, Bell Labs Technical Journal, 19, 31 (2014). S. Corbett, D. Gautam, S. Lal, K. Yu, N. Balla, G. Cunningham, K. M. Razeeb, R. Enright and D. McCloskey, ACS Applied Materials & Interfaces, 13, 1773 (2021). S. Lal, K. M. Razeeb and D. Gautam, ACS Applied Energy Materials, 3, 3262 (2020). S. Lal, D. Gautam and K. M. Razeeb, APL Materials, 7, 031102 (2019). Figure 1

Modeling and analysis of the influence of Thomson effect on micro-thermoelectric coolers considering interfacial and size effects

Micro-thermoelectric coolers have great potential in the thermal management of highly integrated electronic devices, especially the local cooling. This paper develops a numerical model to explore the influence of Thomson effect on the cooling performance of micro-thermoelectric coolers, capturing interfacial and size effects. The presented model is validated with a commercial micro-thermoelectric cooler. And, analyses are carried out with respect to micro-thermoelectric coolers of different sizes, under different temperatures and cooling loads. The results indicate that a positive Thomson coefficient can improve the cooling capacity, and higher current and thickness correspond to greater impact of Thomson effect. In addition, the decrease of minimum cooling temperature caused by Thomson effect is even more obvious under higher cooling load. The results also show that the influence of Thomson effect on the maximum cooling temperature difference gradually becomes weaker as the cross area to thickness ratio increases. For heat fluxes of 100 W/cm2 and 200 W/cm2, the minimum cooling temperature can be respectively reduced by 2.1 K and 4.1 K, considering Thomson effect. In addition, for the thickness of 10 μm, the increment of maximum cooling temperature difference gradually declines from 2.2 K to 1.1K as the cross area to thickness ratio increases.

Publisher Correction: Integrated microthermoelectric coolers with rapid response time and high device reliability

In the version of this Article originally published, in the Methods section ‘Analytical calculation and FEM simulation’ the first equation was incorrect and has now been replaced. In addition, in the section ‘Conclusions’, the packing density mistakenly read ‘5,000 leg pairs per cm2’ and has now been corrected to read ‘5,500 leg pairs per cm2’.

Modeling of high power light-emitting diode package integrated with micro-thermoelectric cooler under various interfacial and size effects

Thermoelectric cooler has been widely used in the thermal management of various electronic devices. However, the application of micro-thermoelectric cooler to high power light-emitting diode still needs to be further explored at present. This paper aims to establish a model of high power light-emitting diode package integrated with micro-thermoelectric cooler and explore the performance of this system under various interfacial and size effects. An experiment is conducted to validate the model. Five types of the micro-thermoelectric coolers are designed and integrated to the light-emitting diode package to reduce the localized junction temperature of the light-emitting diode chip. The influence of interfacial effects, thermoelectric element size, and driving power of micro-thermoelectric cooler on the system-level thermal and optical performance is discussed. Results indicate that the micro-thermoelectric cooler with 6 × 6 thermoelectric elements shows the best cooling performance for the driving power of micro-thermoelectric cooler lower than 0.85 W. For thermoelectric cooler with 6 × 6 thermoelectric elements, a minimum chip junction of 95.9 °C, which is 12.3 °C lower than that of the light-emitting diode without micro-thermoelectric cooler, can be achieved. This characteristic can increase the luminous efficacy and lifetime by 12.3% and 50%, respectively. It also found that the electrical boundary resistance plays a more dominant role, compared with the thermal boundary resistance. However, the thermal contact resistance exhibits greater adverse impact than the electrical contact resistance. In addition, a total performance improvement proportion of 25.5% can still be achieved, although the micro-thermoelectric cooler consumes power energy by 22.5% at the driving power of 0.87 W.

Integrated microthermoelectric coolers with rapid response time and high device reliability

Microthermoelectric modules are of potential use in fields such as energy harvesting, thermal management, thermal imaging and high-spatial-resolution temperature sensing. In particular, microthermoelectric coolers (µ-TECs)—in which the application of an electric current cools the device—can be used to manage heat locally in microelectronic circuits. However, a cost-effective µ-TEC device that is compatible with the modern semiconductor fabrication industry has not yet been developed. Furthermore, the device performance of µ-TECs in terms of transient responses, cycling reliability and cooling stability has not been adequately assessed. Here we report the fabrication of µ-TECs that offer a rapid response time of 1 ms, reliability of up to 10 million cycles and a cooling stability of more than 1 month at constant electric current. The high cooling reliability and stability of our µ-TEC module can be attributed to a design of free-standing top contacts between the thermoelectric legs and metallic bridges, which reduces the thermomechanical stress in the devices. A free-standing top contact design reduces the thermomechanical stress in microthermoelectric coolers, resulting in improved reliability and cooling stability.

An effective method of evaluating the device-level thermophysical properties and performance of micro-thermoelectric coolers

Despite the success of achieving thermoelectric materials with high figure of merit, precisely evaluating the performance of micro-thermoelectric coolers remains challenging at the microdevice level because of various interfacial effects and device construction. This study develops a method for the effective evaluation of the device-level thermophysical properties capturing various interfacial and size effects, and establishes a three-dimensional numerical model to evaluate the cooling performance of micro-thermoelectric coolers. The model is validated by the reported experimental data. The impact of interaction between boundary and size effects is captured in the investigation of Seebeck coefficient, thermal conductivity and electricity resistivity of the thermoelectric materials at the device-level. Contact resistances are also considered in analyzing the cooling performance. Results indicate that the device-level figure of merit decreases by 5–18.1% with decreased thermoelectric element thickness from 20 μm to 5 μm. The boundary effects considerably weaken the cooling performance of the microdevice, and a higher heat flux corresponds to a greater impact of boundary effects. Cooling temperature increases by 6.1 K due to the boundary effects when heat flux is 300 W/cm2, while the temperature difference decreases by 17.1%. Finally, the three-dimensional numerical model is performed to evaluate the cooling performance and optimal working condition of the micro-thermoelectric cooler. At heat flux of 300 W/cm2 and 200 W/cm2, the minimum cold side temperatures of 310.7 K and 287.3 K are predicted to be achieved at 11 μm/20 mA (Hte/I), 15 μm/16 mA, respectively.

Performance of Segmented Thermoelectric Cooler Micro-Elements with Different Geometric Shapes and Temperature-Dependent Properties.

In this work, the influences of the Thomson effect and the geometry of the p-type segmented leg on the performance of a segmented thermoelectric microcooler (STEMC) were examined. The effects of geometry and the material configuration of the p-type segmented leg on the cooling power () and coefficient of performance () were investigated. The influence of the cross-sectional area ratio of the two joined segments on the device performance was also evaluated. We analyzed a one-dimensional p-type segmented leg model composed of two different semiconductor materials, and . Considering the three most common p-type leg geometries, we studied both single-material systems (using the same material for both segments) and segmented systems (using different materials for each segment). The , and temperature profile were evaluated for each of the modeled geometric configurations under a fixed temperature gradient of T = 30 K. The performances of the STEMC were evaluated using two models, namely the constant-properties material (CPM) and temperature-dependent properties material (TDPM) models, considering the thermal conductivity (), electrical conductivity () and Seebeck coefficient (). We considered the influence of the Thomson effect on and using the TDPM model. The results revealed the optimal material configurations for use in each segment of the p-type leg. According to the proposed geometric models, the optimal leg geometry and electrical current for maximum performance were determined. After consideration of the Thomson effect, the STEMC system was found to deliver a maximum cooling power that was higher than that of the single-material system. The results showed that the inverse system (where the material with a higher Seebeck coefficient is used for the first segment) delivered a higher performance than the direct system, with improvements in the and of and , respectively. Finally, analysis of the relationship between the areas of the STEMC segments demonstrated that increasing the cross-sectional area in the second segment led to improvements in the and of and , respectively.

Analysis of a Hybrid Thermoelectric Microcooler: Thomson Heat and Geometric Optimization

In this work, we analyze the thermodynamics and geometric optimization of thermoelectric elements in a hybrid two-stage thermoelectric micro cooler (TEMC). We propose a novel procedure to improve the performance of the micro cooler based on optimum geometric parameters, cross sectional area (A) and length (L), of the semiconductor elements. Our analysis takes into account the Thomson effect to show its role on the performance of the system. We obtain dimensionless temperature spatial distributions, coefficient of performance ( C O P ) and cooling power ( Q c ) in terms of the electric current for different values of the geometric ratio ω = A / L . In our analysis we consider two cases: (a) the same materials in both stages (homogeneous system); and (b) different materials in each stage (hybrid system). We introduce the geometric parameter, W = ω 1 / ω 2 , to optimize the micro device considering the geometric parameters of both stages, w 1 and w 2 . Our results show the optimal configuration of materials that must be used in each stage. The Thomson effect leads to a slight improvement on the performance of the micro cooler. We determine the optimal electrical current to obtain the best performance of the TEMC. Geometric parameters have been optimized and results show that the hybrid system reaches a maximum cooling power 15.9 % greater than the one-stage system (with the same electric current I = 0.49 A), and 11% greater than a homogeneous system, when ω = 0.78 . The optimization of the ratio in the number of thermocouples in each stage shows that ( C O P ) and ( Q c ) increase as the number of thermocouples in the second stage increase too, but with W = 0.94 . We show that when two materials with different performances are placed in each stage, the optimal configuration of materials in the stages of the system must be determined to obtain a better performance of the hybrid two-stage TEMC system. These results are important because we offer a novel procedure to optimize a thermoelectric micro cooler considering the geometry of materials at a micro level.

Thermoelectric Micro-Refrigerator Based on Bismuth/Antimony Telluride

Thermoelectric micro-coolers based on bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) are important in many practical applications thanks to their compactness and fluid-free circulation. In this paper, we studied thermoelectric properties of bismuth/antimony telluride (Bi/SbTe) thin films prepared by the thermal co-evaporation method, which yielded among the best thermoelectric quality. Different co-evaporation conditions such as deposition flux ratio of materials and substrate temperature during deposition were investigated to optimize the thermoelectric figure␣of merit of these materials. Micron-size refrigerators were designed and fabricated using standard lithography and etching technique. A three-layer structure was introduced, including a p-type layer, an n-type layer and an aluminum layer. Next to the main cooler, a pair of smaller Bi/SbTe junctions was used as a thermocouple to directly measure electron temperature of the main device. Etching properties of the thermoelectric materials were investigated and optimized to support the fabrication process of the micro-refrigerator. We discuss our results and address possible applications.

Fabrication and Modeling of Integrated Micro-Thermoelectric Cooler by Template-Assisted Electrochemical Deposition

In this work, we report on the structured electrochemical deposition of smooth and compact 12 μm thick films of Bi2(TexSe1-x)3 and (BixSb1-x)2Te3 thermoelectric compounds. Furthermore, these materials are used as p and n-type semiconductors to fabricate a highly compact micro-thermoelectric cooler with cross-sections of the single legs and gaps between the legs in the order of 20 × 100 μm² and 8 μm, respectively. The whole process has been developed with the aim of integrating the cooling device directly on a photoelectronic integrated circuit (PIC). The complex structure of the PICs including different structure heights makes the implementation of mechanical polishing or bonding processes difficult. The electrodeposition of the materials in such small structures comes together with an edge effect that is translated in an extremely fast and dendritic growth. Direct ultrasonication of the electrolyte during the depositions has shown best results completely overcoming the edge effect, thus allowing to produce well defined structures with high spatial resolution. Moreover, this study is complemented by the analysis of the cooling performance by finite element simulations using experimental thermoelectric properties measured on continuous films.

An analytical solution for the hyperbolic unsteady thermal behaviour of micro-thermoelectric coolers with a suddenly time-dependent heat generation

The ultrafast thermal behaviour of a micro thermoelectric cooler under the hyperbolic heat conduction model is analysed. An important step forward is taken in that the instantaneous application of the electric current is modelled by means of the Heaviside function. Two terms of internal heat generation derive from this model: the former is time-independent, whereas the latter is time-dependent through Dirac’s delta function. A modified Separation of Variables method is used to solve analytically the governing equations. Also, the initial linear problem is split up into three sub-problems through the principle of superposition. In order to eliminate the numerical oscillations in the temperature profiles at early times in correspondence of the wave fronts, the semi-infinite hyperbolic body model is considered. The performance (COP) of the device is evaluated and then compared with that derived from the parabolic case. An increase of about 27% is observed at early times.