Heike Bartsch

Microforming process for embossing of LTCC tapes

Embossing of low-temperature cofired ceramics (LTCC) enables the fine patterning of these multilayer materials in the green state and thus allows the fabrication of smart ceramic microsystems even for moderate quantities or prototypes. To understand the embossing process, mechanical properties such as the viscoelastic modulus, yield strain and densification are investigated for commercially available LTCC tapes. The forming and shrinkage behaviour are compared for large cavities as well as for fine patterns. The results are discussed and a comprehensive explanation of the forming mechanism is worked out. Relevant material properties are identified and the microforming of different tapes is explained under consideration of their mechanical properties. This paper therefore gives an essential guide to understanding the main forming influences and failures for LTCC tapes.

LTCC based bioreactors for cell cultivation

LTCC multilayers offer a wide range of structural options and flexibility of connections not available in standard thin film technology. Therefore they are considered as material base for cell culture reactors. The integration of microfluidic handling systems and features for optical and electrical capturing of indicators for cell culture growth offers the platform for an open system concept. The present paper assesses different approaches for the creation of microfluidic channels in LTCC multilayers. Basic functions required for the fluid management in bioreactors include temperature and flow control. Both features can be realized with integrated heaters and temperature sensors in LTCC multilayers. Technological conditions for the integration of such elements into bioreactors are analysed. The temperature regulation for the system makes use of NTC thermistor sensors which serve as real value input for the control of the heater. It allows the adjustment of the fluid temperature with an accuracy of 0.2 K. The tempered fluid flows through the cell culture chamber. Inside of this chamber a thick film electrode array monitors the impedance as an indicator for the growth process of 3-dimensional cell cultures. At the system output a flow sensor is arranged to monitor the continual flow. For this purpose a calorimetric sensor is implemented, and its crucial design parameters are discussed. Thus, the work presented gives an overview on the current status of LTCC based fluid management for cell culture reactors, which provides a promising base for the automation of cell culture processes.

Deposition of thick zinc oxide films with a high resistivity

ZnO is a well known piezoelectric material. Unfortunately, it is not easy to deposit thin films onto silicon with a high resistivity by using common deposition technologies. The use of such films is therefore strictly limited to high frequency applications. The goal of our work was to find out a new deposition technology that allows the deposition of ZnO films with a high resistivity. Furthermore we were looking for the deposition of film thicknesses in a range up to 20 micrometers for SAW-sensor and microactuator applications. The deposition of the ZnO films was carried out in a programmable RF-magnetron-sputtering-system. We sputtered from a pure zinc target with a variable gas composition that consists of argon and oxygen. We worked in an alternating mode to achieve a high resistivity of the films. After a deposition cycle at a sample temperature of about 30 degrees C with a ramp shaped power the silicon- samples were cooled during the following cycle in the gas atmosphere. The deposition rate we measured was dependent from the gas composition and the applied power in a range between 1,5 micrometers /h and 2,2 micrometers /h. We deposited films of a thickness of 20 micrometers . Between two sputtered aluminium electrodes the films had a resistivity in a range between 2*1010(Omega) cm and 2*1011(Omega) cm. The stress of the films could be influenced by the composition of the gases. The measured minimum stresses of the films were in a range of about 180 MPa. The films were also characterized by means of XRD- measurments. We found a weak < 101 > orientation of the layers perpendicular to the surface.

Properties of high-k materials embedded in low temperature cofired ceramics

Buried capacitors in low temperature cofired ceramics (LTCC) enable increased package density, shorter interconnects and reduced assembly time.

Engineering of III-Nitride Semiconductors on Low Temperature Co-fired Ceramics

This work presents results in the field of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fired Ceramics has been used, as a non-crystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these fields of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using different buffer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes.

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

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. PEDOT:PSS layer, titanium oxynitride and laminin coatings are deposited on LTCC gold electrodes using different 2D and 3D MEA chip designs. Their impedance characteristics are compared and discussed. Titanium oxynitride layers emerged as suitable functionalization. Small 86-µm-electrodes have a serial resistance Rs of 32 kOhm and serial capacitance Cs of 4.1 pF at 1 kHz. Thick film gold electrodes with such coatings are thus qualified for signal recording in 3-dimensional in vitro cell cultures.

LTCC Based Multi-Electrode Arrays for In-Vitro Cell Culture

Neurobiological concepts based on state-of-the art technology have so far lacked the complexity of actual high-level neurobiological systems. Two key advances are needed to improve our understanding of such systems: in vitro 3D-neuronal cell culture and 3D MEA systems for measuring such 3D-cultures. These requirements call for smart multilayer and packaging technology. The material Green Tape TM from DuPont Nemours is chosen for the presented works, because its compatibility and those of available metallisation with cell cultures is already proven. An LTCC multilayer circuit with gold electrodes is the base of the 3D MEA. The layout of the 3D MEA is designed to fit the MEA2100-System for in vitro recording from Multi Channel Systems and enable thus a comparable data processing to established 2D MEAs Slots. The surface topography of the thick film electrodes and the surface state is investigated with laser scanning microscopy, SEM, XPS and measurements of the wetting angle of contact. The impedance of the ...

Embedded Ceramic Capacitors in LTCC

The integration of passive elements in ceramic interconnect devices promises higher package densities and reliability. LTCC compatible high-k dielectrics are commercially available with k-values up to 250. Barium titanate dielectrics stand out for their high permittivity even at low sintering temperatures. This fact allows the co-firing with common metallization and commercially available tapes. In this study we investigate the co-firing of barium titanate LTCC tapes with commercially available standard tapes. Pressure assisted sintering and constraint sintering is used for the manufacturing of buried capacitors. Crucial process parameters are worked out using a statistical set up according to Taguchi. High k-values up to 2300 are obtained for embedded dielectric tape patches. Beside of the capacitor properties the process constancy is observed.

Design and fabrication of gas tight optical windows in LTCC

Beside the possibilities low temperature co-fired ceramics (LTCC) offer for electric devices they also enable the fabrication of micro fluidic elements like channels and embedded cavities. Hence, LTCC facilitate the realization of complex and integrated micro fluidic systems. Examples can be applied in many areas like micro fuel cells and reaction chambers for synthesis of chemical compounds. However, for many applications it is necessary to have an optically transparent interface to the surroundings. The integration of optical windows in LTCC opens up a wide field of new and innovative applications such as the observation of chemiluminescent reactions. These chemical reactions emit electromagnetic radiation and thus offer a method for noninvasive detection. The optical windows consist of thin glasses (≤ 500 μm) bonded by thermocompression onto a LTCC substrate. As the bonding agent, a low temperature sealing glass paste was used. Borosilicate glasses and fused silica as well as silicon were successfully ...

Measurement of nitrogen monoxide levels in gas flows with a micro total analytical system based on LTCC

The measurement of nitrogen monoxide (NO) concentration levels is a vital aspect of environmental analysis and the so called CHNS analysis. The chemiluminescent reaction with ozone in the gas phase is a well-established method for the measurement of atmospheric concentration levels in the range from 4 ppb up to 100 ppm. In this contribution we present the design of a so called micro total analytical system (μTAS) for NO measurements designed in ceramic. Low temperature co-fired ceramics (LTCC) have proven to be the ideal technology, since they offer high chemical and thermal stability as well as high degree of freedom of design. The article gives an overview of the design process with emphasis on manufacture of the components and technological challenges regarding life-time.