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For the realization of advanced bio-microsystems for medical applications such as implants, fabrication processes require the usage of biocompatible materials only. Especially for the encapsulation and hermetic sealing, e. g. of microfluidic structures, a biocompatible wafer bonding process is necessary. Additionally, the ongoing integration of new and temperature sensitive materials in micro systems, such as biomolecules, requires bonding processes with low bonding temperatures only. However, when choosing the wafer bonding process, additional criteria are a high reliability, since the bonding is critical for the operation of the chip, as well as the applicability on 6” and 8” wafer level in order to fabricate a high number of devices at low costs. In order to fulfill all these requirements, we propose an adhesive bonding process, which uses Parylene C as intermediate layer. Parylene C is a thermoplastic polymer, which is ISO 10993 certified as biocompatible and biostable, chemically inert against all common acids, bases and solvents, as well as a low permeable and optical transparent. In addition and in contrast to other established bond adhesives, such as SU8, the Parylene layers are deposited by CVD, and offer a very high three dimensional conformity as well as a very high homogeneity without any pinholes. Furthermore, due to its chemical inertness, Paryleneis compatible with a variety of established microtechnologies. Previous studies prove that adhesive bonding using Parylene C is feasible. However, these works are limited to 4” wafer level and the bonding provides only low tensile strengths, e. g. 10 MPa. [1-7] Our presented Parylene based adhesive bonding technology uses a 0.5 µm to 10 µm Parylene C layer, which is deposited on 6” and 8” wafers and can be patterned optionally by an oxygen plasma without leaving residues. A subsequent thermal and adhesive bonding process at temperatures of 280°C to 300°C as well as moderate wafer contact pressures are performed to successfully bond the wafers. Within our study, different materials combinations for the bond interface, e. g. silicon - silicon, silicon - silicon dioxide, silicon – glass, silicon – silicon nitride, and silicon – aluminum were investigated. Doing so, only one wafer was coated with Parylene. Additionally, bonding processes were performed with two Parylene coated wafers, and hence, a Parylene - Parylene bond interface. Since almost all materials, established in microsystem technologies can be coated with Parylene, this enables the usage of this bonding process for a high variety of material combinations and particularly materials, which were not investigated by our study. The focus of the experiments was the investigation and optimization of a feasible parameter range in respect of the bonding time, bonding temperature, wafer contact pressure, and Parylene thickness. The characterization of the bonding process was performed using Parylene test structures of squared geometry and different width. The bonding process was analyzed by IR imaging to determine voids and defects. Afterwards the wafers were diced into chips, centering the Parylene frame. The investigation of tensile and shear strengths proved a high reliability of the bonding but also a strong dependency on the bonding parameters. The tensile strength reached up to 35 MPa was improved by a factor of 3 compared to previous studies, the shear strength reached up to 80 MPa Furthermore, the impact of thermal and mechanical shocks as well as long-time load on the tensile strength was investigated. Finally, cross-sections of the bonded chips were analyzed by SEM. The results prove that the Parylene frame structure was still intact after bonding and not flattened due to bonding. Furthermore, the hermetic properties of the Parylene bonds were investigated. Doing so, the Helium leakage rate was determined to < 1∙10-7 mbar ∙ l/s. The study was completed by the investigation of the bonding process on three dimensional structures, which refers to bonding over patterned metal but also bonding of cavities without previous pattern of the Parylene. Finally, after successfully bonding the test frames, the established bonding process was applied on a real microsystem. References: [1] M. Kurihara, et al., IEEE MEMS 2012 (Paris, France) pp 196-9 [2] Y.-C. Yen, et al., IEEE MEMS 2012 (Paris, France) pp 381-384 [3] Q. Shu, et al., International Conference on Solid-State and Integrated-Circuit Technology 2009 (Beijing, China) [4] D. P. Poenar, et al., Sens. Actuators, A 139, 2007, 162–71 [5] A. T. Ciftlik et al., J. Micromech. Microeng. 21, 2011, 35011 [6] D. Ziegler, et al., J. Microelectromech. Syst. 15 (6), 2006, 1477–82 [7] H.-S. Noh, et al., J. Microelectromech. Syst. 14, 2004, 625–31

A miniaturized implantable multi-sensor system for cardiovascular monitoring of physiological parameters is presented. High accuracy pressure measurements within the vessel can be performed by a capacitive pressure sensor. Additional information about the patient, e. g., sudden movement, inclination or increased temperature can be obtained by additional sensor components such as an acceleration sensor and a temperature sensor unit. This information facilitates compensation of interferences for more accurate pressure measurements. A multi-functional ASIC enables, amongst others, sensor signal processing, power management and telemetric communication with extracorporeal electronics. Sensor chips, the multi-functional ASIC and passive components are assembled on a LTCC circuit board in which an antenna coil is integrated for telemetric energy and data transmission at a frequency of 13.56 MHz. In order to support further miniaturization, the implant shall be encapsulated with a stack of very thin and hermetic ceramics applied by ALD instead of using bulky metal housings. Further encapsulation with polymers, which can be functionalised with appropriate biomolecules, is necessary for a proper shape, a biocompatible interface to the surrounding tissue and, thereby, reduction of thrombogenicity.

Next to powders, inks, and microelectronics, many technologies that carry the attribute nano in their name are still waiting for their breakthrough and wide acceptance in engineering and industry. At least nanofabrication technologies are the subject of a vivid track in research and development in a variety of scientific fields but yet most of them are mainly invisible in everyday products. This paper aims to describe three inspiring examples of research work in the area of nanopatterning and systems integration at the micro-nano interface to motivate applications with new and unprecedented functionalities. The application examples comprise the fields of bio-inspired computing, optoelectronic sensing, and spectral imaging. First, network-based biocomputing uses biological agents in a nanopatterned fluidic channel system and opens horizons for energy-efficient solutions to complex mathematical problems. Second, nanoelectronic devices based on carbon nanotubes (CNTs) have emerged because of the outstanding mechanical, electronic, and optical properties of the CNTs. The adaptivity of nanostructures to the world of biological molecules and other nanoscopic building blocks such as quantum dots and nanoparticles enables novel, even personalized, devices and technical solutions. Third, early-on ""nano"" fame has been devoted to optical effects-the authors here discuss an advanced integrated micro-opto-mechanical system on a micromirror plate forming a Fabry-Pérot Interferometer.

t a novel miniaturized multi sensor implant for monitoring hemodynamic parameters in cardiovascular regions. Pressure measurements are performed with a highly accurate capacitive pressure sensor. An additional acceleration and temperature sensor allows compensating the impact of patient's inclination and temperature variations on the pressure measurement, respectively. A multi-functional transponder application-specific integrated circuit (ASIC) manages sensor signal processing, storage of ID, sensor calibration data, telemetric energy, and data transmission with an extracorporeal reading unit. Each component of the implant is assembled on a low temperature co-fired ceramics (LTCC) circuit board with an integrated antenna coil enabling an inductive near-field coupling at a frequency of 13.56 MHz. For a streamlined shape and reduction of thrombogenicity, the implant is encapsulated by biocompatible polymers.

Hermetic and mechanically strong glass-to-metal seals are required for many applications in technological fields such as aerospace engineering or medical engineering. While traditional glass-to-metal bonding technologies require melting of the glass, modern technologies such as anodic bonding use glass in its solid state. In this publication, a novel glass-to-metal bonding method with process temperatures around the softening point of the glass material is investigated. A glass window (silica based crown glass B270) in a titanium (grade 5) housing is manufactured by applying compressive force to the glass in a controlled low pressure argon atmosphere. Adherence of the glass-to-metal interface is determined with a universal testing machine. Hermeticity is measured directly with either pressure gain test or helium leak test. Experiments were performed in a full factorial design with 3 different process temperatures, 3 different process forces and 3 different methods for preparing the titanium surface. The results indicate that the bonding method is capable of producing hermetic seals with leak rates below 10−8 mbar l/s. Roughening of the metal surface generally improves both hermeticity and interface strength. Bonding strength can be further improved by increasing either processes temperature or, especially for rough surfaces, process force. For improving hermeticity either processes temperature or, especially for smooth surfaces, process force must be increased. The results indicate that successful bonding of glass and titanium with the new bonding method is influenced by the effects of mechanical interlocking and chemical reactions at the material interface.

The increased attention for sintered silver as die attach attracts also interest in its reliability assessment. Since the porous joint material shows rate-dependent behaviour at elevated temperature, its visco-plastic behaviour needs to be quantified. Though tensile tests are frequently used for that task is still a challenge to manufacture homogeneous specimens large enough to be safely handled and tensile tested. In this paper the we have presented a comprehensive technology for manufacturing sintered silver specimen for micro bending test. The sample length is about 10 mm but can still be tested with nanoindenter equipment. These specimens were bent at 25 °C at different strain rates. The corresponding stress-strain curves were obtained with transformation functions computed by a FE model. Tensile specimens of sintered silver were manufactured and tensile tested at 25, 100 and 175 °C for investigation of rate dependency and relaxation behaviour. For 25 °C no rate dependency was observed. At 100 °C and 175 °C significant reduction of tensile strength and increase of tensile strain was observed at smaller strain rates. The creep was caused by thermal activation of inner surface diffusion.

In this paper, we present the design, modeling, fabrication and initial wafer level characterization of Capacitive Micromachined Ultrasound Transducers (CMUTs) with target operating frequencies suitable for medical imaging and therapy. Using finite element analysis, a multilayer stack of thin film materials for the hexagonal shaped cell membrane was studied. An optimized stack in terms of membrane stress and cell size was selected for device fabrication based on a wafer bonding approach. The modelling, fabrication and characterization are treated within this paper.

Cu sintering is one of the emerging technologies in the field of micro- and power electronics where operating temperatures higher than 150°C are required. At these temperatures, solder joints reach their limits due to high homologous temperatures. Hence, Cu sintered joints can serve as a substitute for these soft solder joints, being advantageous also with respect to thermo-dynamic stability, fatigue resistance, electrical conductance and cost. This paper addresses failure analysis of sintered (neck-based) All-Cu electrical interconnects (NEI) along with soldered SnAg3.5 and transient liquid phase bonded (TLPB) specimens which form an SnCu intermetallic (IMC) and are used in a homogenous Si-Si flip chip assembly for fine pitch interconnects. The SnAg3.5 solder serves as a benchmark for the NEIs and the TLPB joints. All the flip chip specimens were free of underfill material. The test samples were assembled on spring steel substrates using a Silicone-based adhesive for a low stress bond and then put under isothermal accelerated fatigue tests using 4-point bending at low-homologous temperatures (R.T.). The reliability investigation involves monitoring of electrical resistance as a failure indicator for interconnect fatigue. A failure criterion at 20% increase in resistance is defined to establish a correlation between the experimental failure times and resistance. The fatigue behaviour of the joints was also studied using Finite Elements analysis (FEA). The focus of the modelling was towards the behaviour of the critical joint. Cross-sections were prepared and analysed using optical microscopy and SEM to investigate the failure mode and mechanism.

A necessary coating for so called double layer isolation for electronic boards in space applications is presented within this paper. A Parylene F layer with a certain thickness shall realize the second electrical isolation according to the double isolation requirements of the research project. Parylene encapsulation and isolation is one approach to improve the performance and functionalities of electronic and micro systems. By using such kind of innovative and outstanding materials new application fields will be explored, requiring new materials with advanced properties.

Mask less fabricated 3D interconnects may have a big potential in future microelectronic applications by enhancing freedom of device design or power- and footprint saving capabilities along with performance improvements. Within this paper research activities are reported about evaluation of Aerosol Jet Printing (AJP) for feasibility of fabricating non-planar nano particle based electrical chip interconnects on a 3D-integrated System in a Package (SiP) including MEMS that is capable to wake up integrated electronics from power down mode using piezoelectric MEMS components. 3D-stacked multi-chip modules with a footprint of 9 mm x 10 mm are functional connected by AJP after single chips are mounted to printed circuit board (PCB) using underfiller adhesives. AJP, morphology of printed paths, and electrical resistances are investigated. Several challenging factors like printed line width, printed layer thickness, focus limiting standoff height of printhead, thermo-mechanical properties of printed interconnects along with SiP layout were identified and discussed during process development.

To increase the yield of the wafer-level Cu-Cu thermo-compression bonding method, certain surface pre-treatment methods for Cu are studied which can be exposed to the atmosphere before bonding. To inhibit re-oxidation under atmospheric conditions, the reduced pure Cu surface is treated by H2/Ar plasma, NH3 plasma and thiol solution, respectively, and is covered by Cu hydride, Cu nitride and a self-assembled monolayer (SAM) accordingly. A pair of the treated wafers is then bonded by the thermo-compression bonding method, and evaluated by the tensile test. Results show that the bond strengths of the wafers treated by NH3 plasma and SAM are not sufficient due to the remaining surface protection layers such as Cu nitride and SAMs resulting from the pre-treatment. In contrast, the H2/Ar plasma–treated wafer showed the same strength as the one with formic acid vapor treatment, even when exposed to the atmosphere for 30 min. In the thermal desorption spectroscopy (TDS) measurement of the H2/Ar plasma–treated Cu sample, the total number of the detected H2 was 3.1 times more than the citric acid–treated one. Results of the TDS measurement indicate that the modified Cu surface is terminated by chemisorbed hydrogen atoms, which leads to high bonding strength.

This paper describes selected technologies for the 3D integration of MEMS devices. This comprises a Via Last approach for the formation of MEMS TSVs and a Cu based thermo-compression bonding method for the realization of small 3D-WLP devices. Moreover, the Aerosol Jet technique is discussed as method for the final assembly by means of printing conducting lines over 3D topography.

Heat dissipation from 3D chip stacks can cause large thermal gradients due to the accumulation of dissipated heat and thermal interfaces from each integrated die. To reduce the overall thermal resistance and thereby the thermal gradients, this publication will provide an overview of several studies on the formation of sequential thermal underfills that result in percolation and quasi-areal thermal contacts between the filler particles in the composite material. The quasi-areal contacts are formed from nanoparticles self-assembled by capillary bridging, so-called necks. Thermal conductivities of up to 2.5 W/m-K and 2.8 W/m-K were demonstrated experimentally for the percolating and the neck-based underfills, respectively. This is a substantial improvement with respect to a state-of-the-art capillary thermal underfill (0.7 W/m-K).

Following the recent trend of miniaturization of MEMS and the approach to improve the comfort of medical implants for patients by reducing their size the polymer Parylene is a promising candidate for encapsulation issues. Parylene combines a number of excellent properties like biocompatibility / biostability, chemical inertness, transparency and low water permeability. Within the presented work the deposition characteristics and properties like conformity, permeability of water vapor, etc. are examined.

This paper addresses both, the thermal and the thermo-mechanical performance of percolating thermal underfill applied flip-chip packages. We present a thermal test platform in flip-chip package design allowing the thermal conductivity of any underfill to be measured at package scale. We give details about design technology and current fabrication status. We benchmarked the thermal performance of the platform with percolated thermal underfill against the capillary thermal underfill case. In a layout with peripheral solder bumps the performance benefit related to heat dissipation of an overall system with percolating thermal underfill can be over 50% for liquid cooling and over 25% for enforced convection. The improvement for natural convection, typical in mobile environment, is 5% in the best considered case. We also present a study of the thermo-mechanical performance of the flip chip test platform during thermo-shock cycling by the aid of finite element (FE) tools at the critical regions of interest. We benchmarked the percolating thermal underfill against capillary mechanical underfill and capillary thermal underfill. For that investigation we used an effective material merging a visco-elastic polymer and a visco-plastic solder for saving computation time. In the percolating thermal underfill applied package, we've found slightly higher risk of delamination at the die | underfill interface but very low fillet loads compared to conventional underfill. The risk of solder fatigue is significantly lower and the risk of die cracking is 25% higher for percolating than for the capillary underfills.

Eutectic aluminum–germanium wafer bonding was used to fabricate (AlGaIn)N thin-film light-emitting diodes (LEDs). Wafer bonding was carried out on 2″ wafer level at a bond temperature of 470 °C using patterned Al bond pads on the GaN-on-sapphire LED epiwafer and plain Ge substrates. The microstructure of the joint formation was characterized via cross-section analysis using scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX). Scanning acoustic microscopy was used to investigate the bond interface. The shear strength was determined to be 1–2 kN/cm2. The formation of a liquid Al–Ge phase is evident from cross-section analysis and optical microscopy. During solidification, Al and Ge are separated into distinct phases again, which is revealed by EDX. The obtained bond is not free of micro-voids, yet it is mechanically stable and suited for the fabrication of thin-film LEDs by removing the sapphire substrate via laser lift-off, which is also demonstrated.

The current feed capability of typical flip chip electrical interconnects is constrained by the solder alloy, as it is more susceptible to electromigration than the copper used for the pads and wires. Hence, interconnects formed by copper only mitigate the electromigration risk and/or allow to increase the current limit of the all-copper interconnect. In this work, two methods to form all-copper flip chip interconnects at an annealing temperature of 250 °C are presented. The interconnects in the contact region between Cu pillars and Cu pads with a pitch down to 150 µm are formed by Cu nanoparticle self-assembly and sintering. In the first method, the entire gap between a Cu pillar chip and a substrate was filled with a Cu nano-suspension. The formation of capillary bridges during the evaporation of the dispersant directed the self-assembly of the nanoparticles towards the contact region between Cu pillars and Cu pad. In the second method, the Cu pillar chip was dipped into a film of the Cu nano-suspension, followed by a transfer, placement and release with a die bonder onto pads on a substrate. The annealing of the Cu nanoparticles is performed in both cases in a reducing formic acid atmosphere. The first method was more susceptible to the formation of shorts between pillars, whereas the second method resulted in electrical functional chip to substrate assemblies. Interconnects with a mean electrical resistance of 26 ± 3 mΩ and a shear strength ranging from 4.6 to 12.3 MPa were achieved. The sintered Cu nanoparticles bridged gaps up to 10 µm between copper pillars and pads, demonstrating the potential to apply the joint also on non-planar substrates. Nevertheless, imperfections such as voids and cracks are still present in the joints and need further process development, to improve the quality and process robustness further.

This paper covers a detailed preliminary study to micro bending tests used to obtain the mechanical properties of nanoparticles as used in advanced electrical or thermal joints. A method for direct, easy, fast and highly accurate transformation of an experimental force-displacement-curve into the corresponding σ-e-curve is presented. That gives access to the elastic and plastic properties of the material. No additional profiling measurements are necessary. The authors focus on the theoretical background of both, the bending test itself as well as the transformation. Both is discussed in detail by utilizing the results of a finite elements model which simulates a micro bending test.

Heat dissipation in 3D chip stacks suffers from multiple thermal interfaces. The effective thermal resistance of the bond-line between individual dies, with the electrical interconnects can be minimized by the introduction of thermal conductive underfills. Up to now, only sequentially formed underfills result in true percolation and hence, thermal conductivities of more than 1 W/m-K. In this study, we report on various aspects to consider during the formation of percolating thermal underfills, by centrifugal filling of micron-sized particles and the subsequent backfilling of an epoxy by capillary action. Particle assemblies within silicon-glass cavities were investigated for mono and poly-dispersed spherical and facetted particles with characteristic dimension in the range of 15 µm to 50 µm. Clogging of particles between silicon pillars could be mitigated at low particle fluxes dispensed by the hour glass principle. Particle shadowing behind the silicon pillars could be eliminated by ultrasonic agitation. Finally, close to crystalline phases could be identified for the mono-dispersed particles, compared to a random packing for the poly-dispersed particles. The effective pore diameter of the particle beds was experimentally derived from a backfilling experiment with viscosity standards. A normalized pore diameter of 0.15, 0.17 to 0.20 and 0.11 was observed for mono and poly-dispersed spherical and facetted particles, respectively. The backfill dynamics can be predicted with those values and the Washburn equation. Cavities filled with particles down to 30 µm diameter could be filled completely with the available low viscosity epoxy system. Finally, we report on the re-arrangement of filler particles due to capillary action and viscous drag, during the backfilling process. Defects are minimal for fluids of low surface tension and high viscosity. Hence, only 1 area-% of defects were observed from the infiltration of epoxies.

Solid Liquid Inter-Diffusion (SLID) bonding using the systems Cu/Ga and Au/In have been investigated regarding the bonding parameters and their influence on shear strength. Especially temperature dependence and composition of interface have been focused on.

3D integration technologies show increasing importance for high volume applications while realizing the smallest system dimensions at least. Therefore vertical interconnect and wafer bonding technologies were optimized and adapted to reach a high yield using quite narrow contact areas and bond frames. These technologies must enable mechanical stable bonding with high degree of strength, hermeticity, and an electrical connection from all layers of the stack to the next level.

Within this paper we will describe the investigations of biocompatibility testing of certain materials used for MEMS packaging and MEMS fabrication. Next to these typical semiconductor materials also nano patterned surfaces were evaluated regarding their influence to cell growth and their potential for implantable devices. Both topics were necessarily expected to be relevant for in-vivo patient monitoring applications.

By the incorporation of miniaturised systems within medical devices new functionalities can be achieved and implantable devices profit from a significant increase of functionality. The paper provides information about nowadays and future technical opportunities and focuses on the benefit micro systems can provide to implantable devices and the patients therefore.

This paper presents the simulated static and dynamic properties of a micro capacitive transducer by using commercial FEM software - ANSYS. Evaluation of the stress distribution in the stretched membrane of the transducer indicates that the location of the access holes plays an important role for reliable device fabrication and operation. Acoustic simulation shows that the pressure variation in the radiation field of a piston source can be explicitly demonstrated. Experiment results validate the effectiveness of FEM simulation as a useful tool for the design of MEMS devices and rough estimation of their properties.

In this study we successfully bonded silicon wafer substrates with metal based thermocompression technology. This technology has the advantage of inherent possibility of hermetic sealing and electrical contact. We used three different kinds of metals: gold, copper and aluminum. We will show the hermeticity, bonding strength and reliability of the different processes and compare the results.

Successful commercialization of MEMS products extremely depends on cost factors. Especially the role of integration technologies like packaging at different levels, combining MEMS with integrated circuits, and to realize 3-dimensional packaged devices is more important than ever. Bonding technologies at wafer level are key factors for 3-d integration, realizing the mechanical bond and fulfilling certain requirements like strength, hermeticity, and reliability as well as the electrical interconnection of the different functional components. From a great variety of bonding techniques eutectic bonding has got a special importance today because both hermetically sealed packages and electrical interconnects could be performed within one bonding process. Furthermore, there are some advantages such as low processing temperature, low resulting stress, and high bonding strength. These properties are mainly investigated up today. Since the early 90-ies eutectic wafer bonding is known from very large scale integration (VLSI) and is used very often in industry. Even before that time eutectic bond processes were already used in the field of chip bonding. Within this paper the development and investigation of at least two eutectic bonding technologies will be described and characterized. Although the mechanical and micro structural properties of the bond will be shown, the realization and test of electrical interconnects is focused very clearly. With an integration of certain test structures the bonding strength, the electrical properties, and the hermeticity of eutectic bonds could be measured and evaluated. At least it will be concluded with an outlook for the feasibility of eutectic bonding in 3-d integrated smart micro systems.

Microsystems that are used for medical application mostly consist of temperature sensible components. Therefore the temperatures during the fabrication process must be limited. This paper deals with the fabrication of reactive nanostructures that have the capability to be used as local heat source and thus can be used for processes during the fabrication of temperature sensible systems. Hereby, heat is produced during a self propagating exothermal reaction of two different materials that are present in a multilayered system of horizontal or vertical arranged material films in nanoscale dimensions. In this paper the principle of the self propagating reaction of those reactive systems as well as their fabrication is shown.

In this paper, wafer-to-wafer AuSi eutectic bonding was investigated and evaluated with various sets of experimental parameters. Single crystalline Si and amorphous Si were bonded with different dimension Au layers and observed by optical measurements. Material composition, adhesion layer, electrical insulation, bonding parameters, and surface pre-treatments were discussed and have improved bonding performance. Bond strength determined by micro-chevron-test and shear test was evaluated as well as hermeticity. High bond yield was achieved with 4 inch and 6 inch wafer stacks.

Customer demands for devices with new increasingly complex functionalities, higher quality, lower cost, long-term reliability and usability both for investment and consumer goods constitute new technological challenges [EPoSS, the European Technology Platform on Smart Systems Integration (http://www.smart-systems-integration.org)]. The key factor for successful products will be system integration, miniaturisation and last but not least transdisciplinary technology approaches. Bridging the gap between the nanometre scale and the customer’s macro-world will affect a multitude of technologies, materials and processes and their combination.

Two groups of microbeams with different top electrode patterns are designed as PZT on-chip actuating and sensing devices. The results of hamonic analysis reveal that such microbeams present high Qs (>500 in air) in certain ranges of frequency, which provides the design basis for various applications.