TY - JOUR AU - Rózsás, Gábor AU - Takács, Gábor AU - Plesz, Balázs AU - Bognár, György TI - Process optimization and performance evaluation of back contact integrated cooling devices for CPV cells JF - MATERIALS TODAY SUSTAINABILITY J2 - MATER TODAY SUSTAIN VL - 31 PY - 2025 PG - 14 SN - 2589-2347 DO - 10.1016/j.mtsust.2025.101170 UR - https://m2.mtmt.hu/api/publication/36229412 ID - 36229412 N1 - The research reported in this paper was supported by the K_20 grant through the project No. 135224 and 2020–1.1.2-PIACI-KFI-2021-00242 of the National Research, Development and Innovation Office (NKFIH). AB - Despite their high efficiency, concentrator solar cells have one major issue: they produce a significant amount of waste heat. This leads to excessive temperatures inside the cell, which reduces the efficiency of the electrical conversion and shortens the life of the cell. Therefore, efficient cooling solutions are needed. In this paper, a novel approach for the cooling of concentrator solar cells is proposed. Compared to the solutions found in the literature, the proposed solution incorporates microchannels into the backside metal contact layer of the solar cell. This way, there are no restrictions regarding the semiconductor material, no decrease in mechanical stability, and no thermal interface material is required. First, the appropriate channel geometry and theoretical performance were determined for a 2 × 2 cm2 solar cell using Siemens FloTherm computational fluid dynamics and an in-house analytical modelling tool written in ANSI C. The paper describes the step-by-step iterations of the design and the manufacturing process that were necessary to reach the theoretically calculated ideal performance. Hydrodynamic and thermal measurements were performed generation by generation, taking into account the results obtained from simulation results. For the latest generation, comparing the hydrodynamic properties at a flow rate of 80 cubic centimeters per minute, the difference between the simulated and the average difference of measured pressure drop values is 2.29 %. The measured data confirms that the partial thermal resistance of the microchannel-based cooling device is 0.32 K/W at a maximum applied pressure drop of 1 bar. This means that the temperature increment for a solar cell with a surface area of 4 cm2 exposed to a concentration level of 100 suns is only 11.5 K. LA - English DB - MTMT ER - TY - JOUR AU - Salamon, Ádám AU - Takács, Gábor AU - Bognár, György TI - Validation Methodology of Wireless Brain-Computer Interface for Event-Related Potential Application JF - INFOCOMMUNICATIONS JOURNAL J2 - INFOCOMMUNICATIONS J VL - 17 PY - 2025 IS - 2 SP - 2 EP - 10 PG - 9 SN - 2061-2079 DO - 10.36244/ICJ.2025.2.1 UR - https://m2.mtmt.hu/api/publication/36282899 ID - 36282899 AB - Electroencephalography (EEG) is a technique used to observe brain activity by measuring the dynamic changes of the electric field induced by neurons' activity. Brain-computer interface (BCI) systems are used in cognitive psychology examinations measuring the changes of brain activities. This paper presents a validation methodology to characterize BCI systems with wireless communication interface and the applicability on a preselected BCI system. This way, the delay, the functionality, and the frequency selectivity can be determined of the overall BCI system, taking into account the effect of the hardware, the software, and the electrodes, avoiding noise artifacts. The presented and validated BCI system proved to be successfully applied in ERP EEG measurements such as steady-state visually evoked potential, pattern-reversal visually evoked potential, and P300 event-related potential. LA - English DB - MTMT ER - TY - JOUR AU - Bognár, György AU - Szabó, Péter Gábor AU - Takács, Gábor TI - Thermal Characterization Methodologies for Experimental Minichannel Heat Sink Designs in Printed Circuit Board Assemblies JF - CASE STUDIES IN THERMAL ENGINEERING J2 - CASE STUD THERM ENG VL - 64 PY - 2024 PG - 25 SN - 2214-157X DO - 10.1016/j.csite.2024.105468 UR - https://m2.mtmt.hu/api/publication/35547972 ID - 35547972 N1 - Correspondence Address: Szabó, P.G.; Department of Electron Devices, 2 Magyar Tudósok Krt., Hungary; email: szabo.peter@vik.bme.hu Funding details: Nemzeti Kutatási Fejlesztési és Innovációs Hivatal, NKFIH Funding details: Nemzeti Kutatási, Fejlesztési és Innovaciós Alap, NKFIA Funding details: 135224 Funding text 1: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Gyorgy Bognar reports financial support was provided by National Research Development and Innovation Office. Peter G. Szabo reports financial support was provided by Pro Progressio Foundation. Gabor Takacs reports financial support was provided by Pro Progressio Foundation. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.The research reported in this paper was supported by the K_20 grant through project No. 135224 of the National Research, Development and Innovation Office (NKFIH). This research is also partly founded by TKP2021-NVA-02 project implemented with the support provided by the Ministry of Culture and Innovation of Hungary from the National Research, Development and Innovation Fund, financed under the TKP2021-NVA funding scheme. The authors wish to thank Flex Ltd. for their financial support through the ProProgressio Foundation of Budapest University of Technology and Economics for pursuing their research related to new thermal-aware technologies. Funding text 2: The research reported in this paper was supported by the K_20 grant through project No. 135224 of the National Research, Development and Innovation Office (NKFIH). AB - There has been a growing demand for novel, highly efficient, power-saving cooling solutions in recent years. In many cases, standard cooling techniques offer only limited opportunities to prevent the overheating of circuits. Such issues concern high-speed Printed Circuit Board Assemblies (PCBA) in data centers and telecommunication racks, where the flow of the cooling medium is obstructed due to the lack of space. Size limitations can also be a serious problem when cooling high-power devices because the devices consume a large space. Since the heat sink-based cooling solutions and the sophisticated IC packages only deal with one possible heat flow path, we were given the idea of enhancing the secondary heat flow path towards the Printed Circuit Board (PCB). Led by this intention, the idea of creating an embedded minichannel system inside the circuit board and circulating the cooling agent was realized. Through this method, we could decrease the board-to-ambient thermal resistance significantly. This paper presents the demonstration and feasibility study of this method. One of the main aims of this study is to demonstrate the applicability of the proposed concept in PCBAs, where the primary concerns are the low-cost manufacturability and available space. The other goal is to create an adaptation of the standard thermal characterization methodologies to deal with the specific dissipating components in the PCBA demonstrators. In the first part, the manufacturing technology is elaborated on, and its efficiency is characterized by thermal transient testing and Computational Fluid Dynamics (CFD) simulations. For these use cases, it was noted that the cumulative thermal resistance decreased by approximately 60% when a volumetric flow rate of 100 ccm was applied in the minichannels. In the second part, a more sophisticated technology demonstration is realized and characterized by adding the proposed embedded minichannel heat sink to an existing high-speed PCBA. A specific thermal transient testing was implemented specifically for this use case, and it was carried out on programmable logic devices by utilizing general-purpose programmable logic to construct the necessary measurement methods. In the future, this feature can be used in different logic circuit designs where it is not possible to determine the junction temperature directly. LA - English DB - MTMT ER - TY - JOUR AU - Bognár, György AU - Takács, Gábor AU - Szabó, Péter Gábor TI - A novel approach for cooling chiplets in heterogeneously integrated 2.5D packages applying microchannel heatsink embedded in the interposer JF - IEEE TRANSACTIONS ON COMPONENTS PACKAGING AND MANUFACTURING TECHNOLOGY J2 - IEEE T CPMT VL - 13 PY - 2023 IS - 8 SP - 1155 EP - 1163 PG - 10 SN - 2156-3950 DO - 10.1109/TCPMT.2023.3298378 UR - https://m2.mtmt.hu/api/publication/34074342 ID - 34074342 LA - English DB - MTMT ER - TY - CHAP AU - Rózsás, Gábor AU - Bognár, György AU - Takács, Gábor AU - Plesz, Balázs ED - IEEE, , TI - Optimized process for the manufacturing of integrated microchannel cooling devices in the back contact of concentrator solar cells T2 - 2022 Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS (DTIP) PB - Institute of Electrical and Electronics Engineers (IEEE) CY - Piscataway (NJ) SN - 9781665491679 PY - 2022 PG - 5 DO - 10.1109/DTIP56576.2022.9911724 UR - https://m2.mtmt.hu/api/publication/33265628 ID - 33265628 N1 - Conference code: 183490 Export Date: 24 November 2022 Funding details: Nemzeti Kutatási Fejlesztési és Innovációs Hivatal, NKFIH, 135224 Funding text 1: ACKNOWLEDGMENT The Authors would like to thank Adél Tóth-Blum for the assistance in sample processing and Péter Lajos Neumann for preparing the SEM images. The research presented in this paper was fully supported by the K_20 grant of the National Research, Development and Innovation Office (NKFIH) through the project No. 135224. AB - The record efficiencies of the most modern photovoltaic cells currently reach above 45%, which are achieved by concentrator systems (CPV). However, despite better device efficiencies, CPVs have a major drawback: The high amount of waste heat caused by the high power density and the photovoltaic conversion losses. Extracting the heat is an important issue, as the efficiency of the device is significantly reduced if its operational temperature rises. Therefore, especially at higher concentrations, the usage of active cooling methods is unavoidable. Efficient cooling requires the conduction of large quantities of internally generated heat with the achievable minimal thermal resistance. Thus, these applications need new cooling solutions, like microscale integrated cooling devices. This paper presents an effective solution for cooling a 20 x 20 mm concentrator photovoltaic cell. In our concept, the microscale channels are integrated into the back surface metallization, formed by electroplating copper around a photoresist channel pattern. This approach has the advantage of having no restrictions regarding the solar cell material and technology. In this paper the description of an improved technological process for forming the microchannels is presented that is capable to avoid the previously experienced channel collapse and reduce the probability of channel cross-section shrinkage, thus achieving lower hydrodynamical resistance and better cooling performance. © 2022 IEEE. LA - English DB - MTMT ER - TY - CHAP AU - Bognár, György AU - Takács, Gábor AU - Szabó, Péter Gábor TI - Thermal modelling of embedded microscale channel structures realized in heterogeneous packaging T2 - Proceedings of the 28th International Workshop on THERMal INvestigation of ICs and Systems (THERMINIC'22) PB - Institute of Electrical and Electronics Engineers (IEEE) CY - Dublin SN - 9781665492294 PY - 2022 SP - 1 EP - 4 PG - 4 DO - 10.1109/THERMINIC57263.2022.9950627 UR - https://m2.mtmt.hu/api/publication/33698124 ID - 33698124 N1 - Funding Agency and Grant Number: K_20 grant of the National Research, Development and Innovation Office (NKFIH) [135224] Funding text: The research presented in this paper was fully supported by the K_20 grant of the National Research, Development and Innovation Office (NKFIH) through the project No. 135224. AB - With the continuous scale down and integration, more and more sophisticated packaging technologies are being developed to overcome the technology barriers in order to increase efficiency and computational power. However, with new packaging technologies, the same thermal-related problems still occur, but novel concepts can be examined to increase the heat transfer efficiency. In our paper, we present an idea to enhance the heat transfer in heterogeneous packages by integrating microscale channels into the silicon interposer, using them as a fluid cooling vehicles. As an introduction to the concept, a test vehicle is modelled in a CFD simulation tool to investigate the heat transfer efficiency under different fluid flow rates. In addition, a comparison is also made with a conventional heat sink cooling assembly. LA - English DB - MTMT ER - TY - JOUR AU - Rózsás, Gábor AU - Bognár, György AU - Takács, Gábor AU - Plesz, Balázs TI - Integrated cooling solution for concentrator photovoltaic cells JF - POLLACK PERIODICA: AN INTERNATIONAL JOURNAL FOR ENGINEERING AND INFORMATION SCIENCES J2 - POLLACK PERIODICA VL - 16 PY - 2021 IS - 2 SP - 110 EP - 116 PG - 7 SN - 1788-1994 DO - 10.1556/606.2020.00172 UR - https://m2.mtmt.hu/api/publication/32111868 ID - 32111868 N1 - Cited By :1 Export Date: 28 September 2022 Correspondence Address: Rozsas, G.; Department of Electron Devices, Magyar tudósok körutja 2, Hungary; email: rozsas.gabor@vik.bme.hu AB - The efficiency of the most modern photovoltaic cells currently reaches 40–45%, which is achieved by concentrator systems. However, despite better device efficiencies concentrator photovoltaic cells have major drawback, namely the high amount of waste heat, which requires new cooling solutions. This paper gives a short overview of the current cooling techniques and proposes a novel microchannel cooling solution for concentrator photovoltaic cells. In the concept, the microscale channels are integrated into the backside metallization of the PV device. The paper gives a description of the technological process that can be used to produce microchannels on the back of solar cells and shows the optimization of the channels to achieve optimal cooling performance. LA - English DB - MTMT ER - TY - JOUR AU - Bognár, György AU - Takács, Gábor AU - Szabó, Péter Gábor AU - Rózsás, Gábor AU - Pohl, László AU - Plesz, Balázs TI - Integrated Thermal Management in System-on-Package Devices JF - PERIODICA POLYTECHNICA-ELECTRICAL ENGINEERING AND COMPUTER SCIENCE J2 - PERIOD POLYTECH ELECTR ENG COMP SCI VL - 64 PY - 2020 IS - 2 SP - 200 EP - 210 PG - 11 SN - 2064-5260 DO - 10.3311/PPee.14986 UR - https://m2.mtmt.hu/api/publication/31028059 ID - 31028059 N1 - Export Date: 28 September 2022 Correspondence Address: Bognár, G.; Department of Electron Devices, P.O.B. 91, Hungary; email: bognar@eet.bme.h AB - Thanks to the System-on-Package technology (SoP) the integration of different elements into a single package was enabled. However, from the thermal point of view the heat removal path in modern packaging technologies (FCBGA) goes through several layers of thermal interface material (TIM) that together with the package material create a relatively high thermal resistance which may lead to elevated chip temperature which causes functional error or other malfunctions. In our concept, we overcome this problem by creating integrated microfluidic channel based heat sink structures that can be used for cooling the high heat dissipation semiconductor devices (e.g.: processors, high power transistor or concentrated solar cells). These microchannel cooling assemblies can be integrated into the backside of the substrate of the semiconductor devices or into the system assemblies in SoP technology. In addition to the realization of the novel CMOS compatible microscale cooling device we have developed precise and valid measurement methodology, simulation cases studies and a unique compact model that can be added to numerical simulators as an external node. In this paper the achievements of a larger research are summarized as it required the cooperation of several experts in their fields to fulfil the goal of creating a state-of-the-art demonstrator. LA - English DB - MTMT ER - TY - CHAP AU - Rózsás, Gábor AU - Bognár, György AU - Takács, Gábor AU - Szabó, Péter Gábor AU - Plesz, Balázs TI - Process and Measurement of Electroplated Back-Contact Integrated Microchannel Cooling Devices for CPV Cells T2 - Proceedings of the 26th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC) PB - Institute of Electrical and Electronics Engineers (IEEE) CY - Piscataway (NJ) SN - 9781728176437 T3 - International Workshop on Thermal Investigations of ICs and Systems, ISSN 2474-1515 PY - 2020 PG - 6 DO - 10.1109/THERMINIC49743.2020.9420517 UR - https://m2.mtmt.hu/api/publication/31776803 ID - 31776803 N1 - Export Date: 9 June 2022 Correspondence Address: Rozsas, G.; Budapest University of Technology and Economics, Hungary; email: rozsas@eet.bme.hu AB - Concentrator photovoltaics (CPV) is one of the promising solutions in the fields of green energy production. Their main advantage is that the concentration of incident light significantly increases their efficiency compared to traditional photovoltaics. Unfortunately, light concentration also increases the temperature, which has a negative effect on the efficiency so, the cooling of CPVs is an essential issue to fully utilize their potentials. The idea presented by our team is to use microchannels integrated into the backside metallization of the PV-devices. The proposed process is based on an evaporated titanium and copper seed layer followed by selective copper electroplating around a photoresist microchannel pattern. After removing the photoresist microchannels remain in the grown copper that also serves as the back contact of the solar cell. In this paper we present several improvements of the process to avoid the formation of photoresist residues and clogging that were identified as the main reason of unsatisfactory cooling performance in previous implementations. Cooling performance of the manufactured device was confirmed by hydrodynamic and thermal characterization procedures and compared to simulation results of the same device layout. LA - English DB - MTMT ER - TY - CHAP AU - Rózsás, Gábor AU - Bognár, György AU - Takács, Gábor AU - Plesz, Balázs ED - Juillard, J ED - Lefeuvre, E ED - Smith, S ED - Schneider, P ED - Nouet, P ED - Mita, Y ED - Mailly, F ED - Pressecq, F TI - Improved process for the manufacturing of back contact integrated cooling channels for concentrator solar cells T2 - 2019 Symposium on Design, Test, Integration & Packaging of MEMS and MOEMS (DTIP) PB - Institute of Electrical and Electronics Engineers (IEEE) CY - New York, New York SN - 9781728132860 PY - 2019 PG - 5 DO - 10.1109/DTIP.2019.8752813 UR - https://m2.mtmt.hu/api/publication/31059190 ID - 31059190 AB - Cooling of CPV devices is one of the essential issues to enable the full exploitation of the advantages of light concentration. To address the problem of cooling CPV devices this research work proposes an improved method for the processing of back metallization integrated microcoolers for photovoltaic devices. The back metallization integrated microcooler has the advantage of not being applicable for a wide variety of semiconductor solar cell and not requiring any TIM material. The proposed process is based on the evaporation of a titanium and copper dual layer with subsequent photoresist patterning and electroplating of copper around the photoresist pattern to form the cooling microchannels in the back metallization. The improvement of the process is the introduction of an intermediate seed layer that is deposited after thickness of the electroplated copper has reached the photoresist thickness. This additional seed layer will increase process speed since closing of the channels will not depend on the lateral growth of the electroplated copper any more. LA - English DB - MTMT ER -