@article{MTMT:36229412,
	title = {Process optimization and performance evaluation of back contact integrated cooling devices for CPV cells},
	url = {https://m2.mtmt.hu/api/publication/36229412},
	author = {Rózsás, Gábor and Takács, Gábor and Plesz, Balázs and Bognár, György},
	doi = {10.1016/j.mtsust.2025.101170},
	journal-iso = {MATER TODAY SUSTAIN},
	journal = {MATERIALS TODAY SUSTAINABILITY},
	volume = {31},
	unique-id = {36229412},
	issn = {2589-2347},
	abstract = {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.},
	year = {2025},
	eissn = {2589-2347},
	orcid-numbers = {Takács, Gábor/0000-0001-8081-1169; Plesz, Balázs/0000-0002-9689-906X; Bognár, György/0000-0003-4582-3900}
}

@article{MTMT:36282899,
	title = {Validation Methodology of Wireless Brain-Computer Interface for Event-Related Potential Application},
	url = {https://m2.mtmt.hu/api/publication/36282899},
	author = {Salamon, Ádám and Takács, Gábor and Bognár, György},
	doi = {10.36244/ICJ.2025.2.1},
	journal-iso = {INFOCOMMUNICATIONS J},
	journal = {INFOCOMMUNICATIONS JOURNAL},
	volume = {17},
	unique-id = {36282899},
	issn = {2061-2079},
	abstract = {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.},
	year = {2025},
	eissn = {2061-2125},
	pages = {2-10},
	orcid-numbers = {Takács, Gábor/0000-0001-8081-1169; Bognár, György/0000-0003-4582-3900}
}

@article{MTMT:35547972,
	title = {Thermal Characterization Methodologies for Experimental Minichannel Heat Sink Designs in Printed Circuit Board Assemblies},
	url = {https://m2.mtmt.hu/api/publication/35547972},
	author = {Bognár, György and Szabó, Péter Gábor and Takács, Gábor},
	doi = {10.1016/j.csite.2024.105468},
	journal-iso = {CASE STUD THERM ENG},
	journal = {CASE STUDIES IN THERMAL ENGINEERING},
	volume = {64},
	unique-id = {35547972},
	issn = {2214-157X},
	abstract = {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.},
	year = {2024},
	eissn = {2214-157X},
	orcid-numbers = {Bognár, György/0000-0003-4582-3900; Szabó, Péter Gábor/0000-0001-7601-743X; Takács, Gábor/0000-0001-8081-1169}
}

@article{MTMT:34074342,
	title = {A novel approach for cooling chiplets in heterogeneously integrated 2.5D packages applying microchannel heatsink embedded in the interposer},
	url = {https://m2.mtmt.hu/api/publication/34074342},
	author = {Bognár, György and Takács, Gábor and Szabó, Péter Gábor},
	doi = {10.1109/TCPMT.2023.3298378},
	journal-iso = {IEEE T CPMT},
	journal = {IEEE TRANSACTIONS ON COMPONENTS PACKAGING AND MANUFACTURING TECHNOLOGY},
	volume = {13},
	unique-id = {34074342},
	issn = {2156-3950},
	year = {2023},
	eissn = {2156-3985},
	pages = {1155-1163},
	orcid-numbers = {Bognár, György/0000-0003-4582-3900; Takács, Gábor/0000-0001-8081-1169; Szabó, Péter Gábor/0000-0001-7601-743X}
}

@inproceedings{MTMT:33265628,
	title = {Optimized process for the manufacturing of integrated microchannel cooling devices in the back contact of concentrator solar cells},
	url = {https://m2.mtmt.hu/api/publication/33265628},
	author = {Rózsás, Gábor and Bognár, György and Takács, Gábor and Plesz, Balázs},
	booktitle = {2022 Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS (DTIP)},
	doi = {10.1109/DTIP56576.2022.9911724},
	unique-id = {33265628},
	abstract = {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.},
	keywords = {EFFICIENCY; COPPER; Concentration (process); cooling; Solar cells; Photoresists; Microchannels; Waste heat; Heat resistance; Microchannel; Electroplating; Fabrication Technologies; thermal management; Photoelectrochemical cells; Back contact; fabrication technology; copper electroplating; copper electroplating; CPV; CPV; cooling devices; Concentrator solar cells; Integrated micro-channel cooling; Concentrator systems; Optimized process; Record efficiencies},
	year = {2022},
	orcid-numbers = {Bognár, György/0000-0003-4582-3900; Takács, Gábor/0000-0001-8081-1169}
}

@inproceedings{MTMT:33698124,
	title = {Thermal modelling of embedded microscale channel structures realized in heterogeneous packaging},
	url = {https://m2.mtmt.hu/api/publication/33698124},
	author = {Bognár, György and Takács, Gábor and Szabó, Péter Gábor},
	booktitle = {Proceedings of the 28th International Workshop on THERMal INvestigation of ICs and Systems (THERMINIC'22)},
	doi = {10.1109/THERMINIC57263.2022.9950627},
	unique-id = {33698124},
	abstract = {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.},
	keywords = {THERMODYNAMICS; Engineering, Electrical & Electronic; heterogeneous packaging; embedded cooling},
	year = {2022},
	pages = {1-4},
	orcid-numbers = {Bognár, György/0000-0003-4582-3900; Takács, Gábor/0000-0001-8081-1169; Szabó, Péter Gábor/0000-0001-7601-743X}
}

@article{MTMT:32111868,
	title = {Integrated cooling solution for concentrator photovoltaic cells},
	url = {https://m2.mtmt.hu/api/publication/32111868},
	author = {Rózsás, Gábor and Bognár, György and Takács, Gábor and Plesz, Balázs},
	doi = {10.1556/606.2020.00172},
	journal-iso = {POLLACK PERIODICA},
	journal = {POLLACK PERIODICA: AN INTERNATIONAL JOURNAL FOR ENGINEERING AND INFORMATION SCIENCES},
	volume = {16},
	unique-id = {32111868},
	issn = {1788-1994},
	abstract = {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.},
	year = {2021},
	eissn = {1788-3911},
	pages = {110-116},
	orcid-numbers = {Bognár, György/0000-0003-4582-3900; Takács, Gábor/0000-0001-8081-1169}
}

@article{MTMT:31028059,
	title = {Integrated Thermal Management in System-on-Package Devices},
	url = {https://m2.mtmt.hu/api/publication/31028059},
	author = {Bognár, György and Takács, Gábor and Szabó, Péter Gábor and Rózsás, Gábor and Pohl, László and Plesz, Balázs},
	doi = {10.3311/PPee.14986},
	journal-iso = {PERIOD POLYTECH ELECTR ENG COMP SCI},
	journal = {PERIODICA POLYTECHNICA-ELECTRICAL ENGINEERING AND COMPUTER SCIENCE},
	volume = {64},
	unique-id = {31028059},
	issn = {2064-5260},
	abstract = {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.},
	year = {2020},
	eissn = {2064-5279},
	pages = {200-210},
	orcid-numbers = {Bognár, György/0000-0003-4582-3900; Takács, Gábor/0000-0001-8081-1169; Szabó, Péter Gábor/0000-0001-7601-743X; Pohl, László/0000-0003-2390-1381}
}

@inproceedings{MTMT:31776803,
	title = {Process and Measurement of Electroplated Back-Contact Integrated Microchannel Cooling Devices for CPV Cells},
	url = {https://m2.mtmt.hu/api/publication/31776803},
	author = {Rózsás, Gábor and Bognár, György and Takács, Gábor and Szabó, Péter Gábor and Plesz, Balázs},
	booktitle = {Proceedings of the 26th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC)},
	doi = {10.1109/THERMINIC49743.2020.9420517},
	unique-id = {31776803},
	abstract = {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.},
	year = {2020},
	orcid-numbers = {Bognár, György/0000-0003-4582-3900; Takács, Gábor/0000-0001-8081-1169; Szabó, Péter Gábor/0000-0001-7601-743X}
}

@inproceedings{MTMT:31059190,
	title = {Improved process for the manufacturing of back contact integrated cooling channels for concentrator solar cells},
	url = {https://m2.mtmt.hu/api/publication/31059190},
	author = {Rózsás, Gábor and Bognár, György and Takács, Gábor and Plesz, Balázs},
	booktitle = {2019 Symposium on Design, Test, Integration & Packaging of MEMS and MOEMS (DTIP)},
	doi = {10.1109/DTIP.2019.8752813},
	unique-id = {31059190},
	abstract = {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.},
	keywords = {Electroplating; metallization; concentrator solar cell; microcooler},
	year = {2019},
	orcid-numbers = {Bognár, György/0000-0003-4582-3900; Takács, Gábor/0000-0001-8081-1169}
}