Heike Bartsch

TU Ilmenau, Institute of Micro- and Nanotechnologies, Faculty Member

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LTCC-based Y-type thermoelectric generator with improved heat flow guide for automotive waste heat recovery

Sustainable Energy & Fuels, 2022

Thermoelectric generators (TEGs) are essential devices that convert thermal energy into electrica... more

Schlussbericht zum Projekt "Realisierung neuartiger Verbindungsverfahren zwischen selbstorganisierten, nanostrukturierten Siliciumoberflächen und adaptierten LTCC-Folien" : "Nano-SilKe

Cofiring of LTCC multilayer assemblies with integrated NTC thermistor temperature sensor layers

Ceramics International, 2021

Abstract We have studied the integration of Ni–Co–Zn–Mn spinel NTC thermistor layers into LTCC mu... more Abstract We have studied the integration of Ni–Co–Zn–Mn spinel NTC thermistor layers into LTCC multilayer modules. Sintering of the cubic spinel Ni0.5Co0.5Zn0.75Mn1.25O4 with addition of 3 wt% Bi2O3 additive at 900 °C resulted in samples with 96% density and with good electrical performance. Thermistor spinel tapes, fabricated using doctor blade tape casting, were stacked with layers of a commercially available low-k dielectric LTCC tape, and cofired at 900 °C. Free or constrained cofiring did not give crack-free multilayer samples. Thermistor layers were then integrated combining the commercial LTCC tape with a Zn titanate-based tape in one multilayer laminate, and error-free multilayer samples with a room-temperature resistivity of ρ298 = (2,9 ± 0.08) kΩcm and a thermistor constant of B = (4280 ± 200) K were obtained. This demonstrates the possibility of cofiring of functional ceramic and low-k LTCC tapes and shows the potential of NTC spinel thermistor layers as temperature sensors integrated in complex LTCC multilayer architectures.

LTCC as substrate - enabling semiconductor and packaging integration

2019 22nd European Microelectronics and Packaging Conference & Exhibition (EMPC)

Gallium nitride (GaN) is commonly used in high-power and high-frequency devices but one limiting ... more Gallium nitride (GaN) is commonly used in high-power and high-frequency devices but one limiting factor for its wide application is the availability of cost-effective substrates. The approach of “engineered substrates” is consequently followed up in this work. Low temperature cofired ceramics are used as carrier substrates in this work. The flexible material system allows the creation of a thermo-mechanically compatible base for GaN components. Sputtered aluminum nitride (AlN) layer form the buffer layer for the GaN deposition. The surface quality of these buffer layers reaches an arithmetic mean height R of 10 nm after chemical mechanical polishing and forms thus a surface quality which is adequate for thin film processing. GaN layers grown on these substrates can have both, tensile and compressive stress levels, while such grown on (100) silicon for comparison purpose show exclusively tensile stress. The growth of the GaN layer and resulting morphology is assumed to be mainly influenced by the process conditions during molecular beam epitaxy. The polycrystalline GaN layers show pronounced c-axis orientation at deposition temperatures of 700°C and 800°C. These first results encourage a further development of this new substrate architecture for integrated GaN systems.

Functionalized Three-Dimensional Multilayer Ceramic Modules

Electronics, 2021

Three-dimensional interconnect devices are still strongly related to plastic materials. Since the... more Three-dimensional interconnect devices are still strongly related to plastic materials. Since the use of these materials is limited in harsh environments, there is an application gap, which could be filled by ceramic circuit carriers. Low-temperature cofired ceramics (LTCC) offer promising solutions to fill this gap. This work provides a feasibility study, including the whole technological chain of ceramic multilayer processing. Targeting a curved multilayer substrate, fully equipped with SMD (Surface-mounted device) components, the particularities of single process steps are investigated. Two shaping methods based on quartz glass molds are compared with regard to shape fidelity and technological effort. The investigation of internal conductor lines and via connections reveals that the metallization should have a minimum width of 200 µm and the via diameter is limited to 150 µm. Further considerations focus on the possible footprint of components and use of cavities to increase the ...

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Sol gel thin films on LTCC ceramic multilayers enable their use as thin film substrates

2015 European Microelectronics Packaging Conference (EMPC), 2015

The sol gel process is an interesting method to functionalize different surfaces. It enables the ... more The sol gel process is an interesting method to functionalize different surfaces. It enables the deposition of non-metallic inorganic layers from the liquid phase. The sol is prepared from precursors, typically based on metal alkoxides. It is applied on the surface, where by dip coating, spray coating or spin coating can be used. The liquid sol flows into hollows and thus smooth the coarse ceramic. The gel-like layer contains liquid and solid portions. This layer is dehumified during the drying process and in a firing step a further densification an cross-linking is achieved. The firing temperature amounts to of 500°C and thus the sol gel can be classified as a low-temperature process, which enables cost-effective coating of layers with controlled properties. In this work two coating agents are compared: one alkoxide based on TEOS and one water based sol gel blend, filled with fused silica nanoparticles. The use of the silica nanoparticle dispersion enables layers with a thickness o...

Thermal and Electrical Investigation on LTCC Gas Sensor Substrates

International Journal of Information and Electronics Engineering, 2016

Metal Oxide (MOx) semiconductor gas sensors typically operate at temperatures of few hundred Cels... more Metal Oxide (MOx) semiconductor gas sensors typically operate at temperatures of few hundred Celsius degrees and consume hundreds of miliwatts of power. It is therefore, essential, to investigate the heat flux and power consumption in MOx sensors, especially designed for applications in battery-powered devices. The work presents the thermal and electrical investigations on LTCC substrates (Low Temperature Cofired Ceramic) as a base material for gas sensors. A novel shape of substrates with reduced heat capacity is showed. The sensor temperature was modulated with a pulsed heater voltage, therefore decreasing the average power consumption.

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Low temperature epitaxial deposition of GaN on LTCC substrates

2017 IEEE 5th Workshop on Wide Bandgap Power Devices and Applications (WiPDA), 2017

Technological results about low temperature epitaxial deposition of GaN layers on LTCC substrates... more Technological results about low temperature epitaxial deposition of GaN layers on LTCC substrates are reported. Epitaxial growths of GaN layers have been performed on commercially available LTCC substrates at 540 °C. Pre-growth preparations of the LTCC substrates has been carried out by aluminum oxide buffering layers on the LTCC surface. Further depositions have been performed in an epitaxial reactor using metal organic chemical vapor deposition (MOCVD) techniques with trimethylgallium (TMGa) and either RF or DC nitrogen plasma for different samples in a remote exposure configuration. The traditional precursor flow in MOCVD has been modified to separately introduce each precursor to the chamber, allowing increased lateral migration of adatoms and reduced vapour parasitics. The grown layers have been characterized by XRD, SEM, EDX, CTEM and HRTEM measurements. GaN (0002) XRD measurements show FWHM of 0.22° for peak position at 34.86° as the variations around these values for differe...

LTCC-Based Multi-Electrode Arrays for 3 D in Vitro Cell Cultures

Current technologies to monitor neuronal cultures in vitro are based on 2-dimensional (2D) multi-... more Current technologies to monitor neuronal cultures in vitro are based on 2-dimensional (2D) multi-electrode arrays and cell cultures. The complexity of actual high-level neurobiological systems requires 3-dimensional (3D) cultures and 3D electrode arrays to improve our understanding of such systems. The realization calls for smart multilayer and packaging technology. Our approach uses low-temperature cofired ceramics (LTCC) for the design of a 3-dimensional multi-electrode array (3D MEA). An LTCC multilayer board with gold electrodes forms the basis of the system. The layout of the 3D MEA is designed to fit into widely used measurement adapters for 2D signal recordings, enabling data processing identical to that of established chips. Design and manufacturing of the new 3D device as a basic tool for the investigation of 3D cell cultures are described. Features of thick-film gold electrodes are characterized by means of microscopic and spectroscopic tools complemented with complex impe...

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System for automated cell cultivation and analysis

Phase Transformation and Characterization of 3D Reactive Microstructures in Nanoscale Al/Ni Multilayers

Applied Sciences

Reactive multilayer systems represent an innovative approach for potential usage in chip joining ... more Reactive multilayer systems represent an innovative approach for potential usage in chip joining applications. As there are several factors governing the energy release rate and the stored chemical energy, the impact of the morphology and the microstructure on the reaction behavior is of great interest. In the current work, 3D reactive microstructures with nanoscale Al/Ni multilayers were produced by alternating deposition of pure Ni and Al films onto nanostructured Si substrates by magnetron sputtering. In order to elucidate the influence of this 3D morphology on the phase transformation process, the microstructure and the morphology of this system were characterized and compared with a flat reactive multilayer system on a flat Si wafer. The characterization of both systems was carried out before and after a rapid thermal annealing treatment by using scanning and transmission electron microscopy of the cross sections, selected area diffraction analysis, and differential scanning ca...

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Cost-Effective Sensor for Flow Monitoring in Biologic Microreactors

IEEE Sensors Journal

Continuous nutrient supply of cell cultures in perfused bioreactors requires reliable flow monito... more Continuous nutrient supply of cell cultures in perfused bioreactors requires reliable flow monitoring. This work presents an approach for the flow rate measurement based on low temperature ceramic technology, which allows the direct integration of temperature sensors in the center of fluid channels. Thick film thermistors detect the flow rate in two different operation modes: the calorimetric addresses flow rates from <inline-formula> <tex-math notation="LaTeX">$20~\mu \text{l}$ </tex-math></inline-formula>/min to <inline-formula> <tex-math notation="LaTeX">$80~\mu \text{l}$ </tex-math></inline-formula>/min and the time of flight flow such as up to 1.5 ml/min. The design takes advantage of highly sensitive thermistors with negative temperature coefficient, and optimized heat exchange due to the direct thermal contact between fluid and temperature probe. In addition to calorimetric evaluation, the temperature course as a function of time is used to detect the time of flight. This allows the tracking of the flow rate independent from the thermistor’s temperature characteristic using the temperature maximum as marker. Cross-correlation applied to this temperature problem significantly improves the detection accuracy for the time of flight. Based on temperature and flow measurement data, it was proven that a fit function could replicate the flow rate as a function of the difference in time of flight between two thermistor positions with a deviation less than 4 %. The evaluation of time of flight data can extend the operation range of the sensor by two orders of magnitude. Applying this signal processing, the same method can be applied even for low flow rates, with a measurement range from <inline-formula> <tex-math notation="LaTeX">$30~\mu \text{l}$ </tex-math></inline-formula>/min to <inline-formula> <tex-math notation="LaTeX">$1500~\mu \text{l}$ </tex-math></inline-formula>/min.

Ni‐Cu‐Zn ferrites with high Curie temperature for multilayer inductors with increased operating temperatures

International Journal of Applied Ceramic Technology

Multilayer ferrite inductors for the use at high temperatures

Microelectronics International

Purpose This paper aims to investigate the usability of the nickel copper zinc ferrite with the c... more Purpose This paper aims to investigate the usability of the nickel copper zinc ferrite with the composition Ni0.4Cu0.2Zn0.4Fe1.98O3.99 for the realization of high-temperature multilayer coils as discrete components and integrated, buried function units in low temperature cofired ceramics (LTCC). Design/methodology/approach LTCC tapes were cast and test components were produced as multilayer coils and as embedded coils in a dielectric tape. Different metallization pastes are compared. The properties of the components were measured at room temperature and higher temperature up to 250°C. The results are compared with simulation data. Findings The silver palladium paste revealed the highest inductance values within the study. The measured characteristics over a frequency range from 1 MHz to 100 MHz agree qualitatively with the measurements obtained from toroidal test samples. The inductance increases with increasing temperature and this influence is lower than 10%. The characteristic of...

PEDOT coating applied on thick film gold electrodes for increased miniaturization capability

Progress in Organic Coatings

Abstract Cost-effective thick film manufacturing offers a wide material portfolio for sensor solu... more Abstract Cost-effective thick film manufacturing offers a wide material portfolio for sensor solutions. Low Temperature Cofired Ceramic (LTCC) technology as thick film based multilayer manufacturing process enables the design of complex fluid reactors used in versatile application scenarios. The technology meets the requirements for the design of 3-dimensional electrode arrays, which are essential for impedance monitoring in 3D cell cultures. Since the miniaturization of gold electrodes is limited, electrode functionalization is necessary for achieving high spatial resolution in sensor arrays. Coating of thick film gold electrodes with electropolymerized poly-3,4-ethylenedioxythiophene can significantly decrease the impedance. This work optimizes the coating process applying design of experiments. Electrode topography, chemical composition and electrochemical properties of coated and uncoated electrodes are compared and scaling effects are discussed based on fit parameters obtained from impedance spectroscopy. In addition to a reduction of impedance by two orders of magnitude, poly-3,4-ethylenedioxythiophene coating induces a reduction of size effects and a significant decrease of the variation. The scaling-down capability of electrodes achieves herewith dimensions of several tens of μm. The results evince an approach for sensor array integration with high spatial resolution providing increased measurement certainty for impedance monitoring in ceramic fluid systems and 3-dimensional bioreactors.

Surface properties and biocompatibility of thick film materials used in ceramic bioreactors

Materialia

Low temperature cofired ceramics (LTCC) have conquered a niche segment in biological microelectro... more Low temperature cofired ceramics (LTCC) have conquered a niche segment in biological microelectromechanical systems (BioMEMS) during the last two decades. Since 3-dimensional assembly and rapid prototyping capability are outstanding features of the technology, bioreactors with complex geometry can easily be produced. Particularly needed functions are working electrodes, e.g. for impedance measurements and reference electrodes consisting in platinum or silver-silver chloride. Although the distinct grainy surface of thick film materials influences the double layer properties, data describing the bioelectronic interface and biocompatibility of common thick film materials are rarely published up to now. This works aims to fill this gap by studying the surface properties, composition, electrochemical properties and biocompatibility of commercially available thick film materials. It was found that thick film gold is suitable as electrode material in direct cell contact since an appropriate proliferation of the cell culture was observed. Poly(3,4-ethylenedioxythiophene) coating decreases the absolute value of the zeta potential of thick film gold from 16.55 V to 11.78 mV without any change in vitality of the cells. Thick film platinum layers have a porous structure entailing an enlargement of the effective surface by a factor of 21.6 and can be used as reference instead of silver/silver chloride, which was identified to be incompatible with cell culture. The investigations show that some commercially available cost-effective thick film materials are compatible with cell culture and the here presented data give an orientation for the use of the same in LTCC bioreactors.

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Magnetron Sputtered AlN Layers on LTCC Multilayer and Silicon Substrates

Coatings

This work compares the deposition of aluminum nitride by magnetron sputtering on silicon to multi... more This work compares the deposition of aluminum nitride by magnetron sputtering on silicon to multilayer ceramic substrates. The variation of sputter parameters in a wide range following a fractional factorial experimental design generates diverse crystallographic properties of the layers. Crystal growth, composition, and stress are distinguished because of substrate morphology and thermal conditions. The best c-axis orientation of aluminum nitride emerges on ceramic substrates at a heater temperature of 150 °C and sputter power of 400 W. Layers deposited on ceramic show stronger c-axis texture than those deposited on silicon due to higher surface temperature. The nucleation differs significantly dependent on the substrate. It is demonstrated that a ceramic substrate material with an adapted coefficient of thermal expansion to aluminum nitride allows reducing the layer stress considerably, independent on process temperature. Layers sputtered on silicon partly peeled off, while they ad...

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PEDOT Coated Thick Film Electrodes for In Situ Detection of Cell Adhesion in Cell Cultures

Biosensors

Low temperature cofired ceramics (LTCC) provide a technology for the 3-dimensional integration of... more Low temperature cofired ceramics (LTCC) provide a technology for the 3-dimensional integration of sensor arrays into bioreactors covering dimensions of several hundred micrometers. Since optical control in such assemblies is not possible, the in situ detection of cell adhesion on impedance electrodes with high spatial resolution would deliver crucial information. A current limitation is the increasing impedance of microelectrodes with decreasing diameter. This study evaluates the suitability of thick film gold electrodes, pristine and coated with electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT), for the detection of cell adhesion on the electrode surface. The impedance as criterion for cell attachment is measured with a recording system for electroactive cells with the aim of improving usability. Two cell cultures with different adhesion characteristic are used for adhesion assessment on planar test chips. The impedance increase measured on individual PEDOT coated electro...

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Influence of Nanoscaled Surface Modification on the Reaction of Al/Ni Multilayers

Sputtered reactive multilayers applied as a heat source in electronic joining processes are an em... more Sputtered reactive multilayers applied as a heat source in electronic joining processes are an emerging technology. It promises low-stress assembly of components while improving the thermal contact and thus thermal resistance. The use of nanostructures can significantly enhance the adhesion and reliability of joints between different materials. This work presents a phenomenological proof of the hypothesis. Reactive multilayers of nickel and aluminum directly deposited on nanostructured surfaces of silicon wafers and reference samples with flat surface are compared. The investigation of the self-propagating reaction shows a clear influence of the layer thickness, dependent on the multilayer thickness and nanostructure morphology. Rapid thermal annealing results in the formation of Al1.1Ni0.9 phase. The necessary annealing temperature is much higher than this applied for nanofoils, sputtered multilayer or particles. The nanostructured interface seems to hinder the full transformation ...

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Functionalized Thick Film Impedance Sensors for Use in In Vitro Cell Culture

Biosensors, Jan 5, 2018

Multi-electrode arrays find application in electrophysiological recordings. The quality of the ca... more Multi-electrode arrays find application in electrophysiological recordings. The quality of the captured signals depends on the interfacial contact between electrogenic cells and the electronic system. Therefore, it requires reliable low-impedance electrodes. Low-temperature cofired ceramic technology offers a suitable platform for rapid prototyping of biological reactors and can provide both stable fluid supply and integrated bio-hardware interfaces for recordings in electrogenic cell cultures. The 3D assembly of thick film gold electrodes in in vitro bio-reactors has been demonstrated for neuronal recordings. However, especially when dimensions become small, their performance varies strongly. This work investigates the influence of different coatings on thick film gold electrodes with regard to their influence on impedance behavior. PSS layer, titanium oxynitride and laminin coatings are deposited on LTCC gold electrodes using different 2D and 3D MEA chip designs. Their impedance c...

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