Pressure monitoring in various organs of the body is essential for appropriate diagnostic and therapeutic purposes. In almost all situations, monitoring is performed in a hospital setting. Technological advances not only promise to improve clinical pressure monitoring systems, but also engage toward the development of fully implantable systems in ambulatory patients. Such systems would not only provide longitudinal time monitoring to healthcare personnel, but also to the patient who could adjust their way-of-life in response to the measurements. In the past years, we have developed a new type of piezoresistive pressure sensor system. Different bench tests have demonstrated that it delivers precise and reliable pressure measurements in real-time. The potential of this system was confirmed by a continuous recording in a patient that lasted for almost a day. In the present study, we further characterized the functionality of this sensor system by conducting in vivo implantation experiments in nine female farm pigs. To get a step closer to a fully implantable system, we also adapted two different wireless communication solutions to the sensor system. The communication protocols are based on MICS (Medical Implant Communication System) and BLE (Bluetooth Low Energy) communication. As a proof-of-concept, implantation experiments in nine female pigs demonstrated the functionality of both systems, with a notable technical superiority of the BLE.

The accuracy of MEMS sensing devices can be greatly increased by controlling the operating temperature. This work is part of a project where the goal is to develop an active thermal control unit (TCU) capable of regulating a packaged MEMS device at 70°C ± 1 °C in the temperature range from -46 °C to 90 °C. To accomplish this, a thermoelectric cooler (TEC) is sandwiched between the MEMS package and a heat sink with a thermal interface material (TIM). An in-house tool has been used to calculate the optimum TEC parameters, ending up with 72 legs of 1 mm x 1 mm x 2 mm dimension (l x w x h). Simulations in COMSOL show that the TEC can reach the target temperature within the required time and power consumption. In this work we have built a full demonstrator using a thermal test chip (TTC) to represent a MEMS. Tests done in a climatic chamber show large performance discrepancies compared to the simulations. The TEC manages to keep the target temperature when the ambient temperature is below 70 °C, but does not manage when the temperature is 90 °C. This is due to the insufficient heat dissipation from the hot side of the TEC.

The accuracy of MEMS sensing devices can be greatly increased by controlling the operating temperature. This work is part of a project where the goal is to develop an active thermal control unit (TCU) capable of regulating a packaged MEMS device at 70 degrees C +/- 0.2 degrees C in the temperature range from -46 degrees C to 90 degrees C. To accomplish this, a thermoelectric cooler (TEC) is sandwiched between the MEMS package and a heat sink with a thermal interface material (TIM). An in-house tool has been used to calculate the optimum TEC parameters, ending up with 72 legs of 1 mm x 1 mm x 2 mm dimension (l x w x h). Simulations in COMSOL show that the TEC can reach the target temperature within the required time and power consumption. In this work we have built a full demonstrator using a thermal test chip (TTC) to represent a MEMS and tested various scenarios in a climate chamber. The tests confirmed to a large degree the simulations of behaviour at constant current. Two regulation algorithms were tested and optimised for of keeping the temperature as constant as possible during temperature changes. The best result kept the TTC temperature within 0.2 degrees C during temperature cycling. The power consumption during heating mode was reduced by decreasing the heat sink thermal transfer, but such a configuration would not work in cooling mode.

Thermoelectric modules can be used in waste heat harvesting, sensing, and cooling applications. Here, we report on the fabrication and performance of a four-leg module based on abundant silicide materials. While previously optimized Mg 2 Si 0.3 Sn 0.675 Bi 0.025 is used as the n -type leg, we employ a fractional factorial design based on the Taguchi methods mapping out a four-dimensional parameter space among Mn x-ε Mo ε Si 1.75−δ Ge δ higher manganese silicide compositions for the p -type material. The module is assembled using a scalable fabrication process, using a Cu metallization layer and a Pb-based soldering paste. The maximum power output density of 53 μW cm –2 is achieved at a hot-side temperature of 250 °C and a temperature difference of 100 °C. This low thermoelectric output is related to the high contact resistance between the thermoelectric materials and the metallic contacts, underlining the importance of improved metallization schemes for thermoelectric module assembly.

It is well known that the packaging of electronic devices is of paramount importance, none more so than in MEMS were fragile mechanical elements are realized. Among the different approaches, wafer to wafer bonding guarantees the advantages of the wafer scaling and provides protection of the devices during the final phase of fabrication. Direct bonding, also known as fusion bonding, is seldom implemented in MEMS fabrication due to the high surface quality required, the high temperature involved and the compulsory wet activation process. In this paper a direct bonding process for MEMS inertial sensor without the need of any wet activation step is presented.

2D materials offer excellent possibilities for high performance gas detection due to their high surface-to-volume ratio, high surface activities, tunable electronic properties and dramatic change in resistivity upon molecular adsorption. This paper demonstrates a simple field effect transistor (FET) of molybdenum disulphide (MoS2) fabricated on a hexagonal boron nitride (hBN) substrate that can detect NOx down to concentrations of 6 ppb and possibly far below at room temperature (RT) with a systematic optimization of the device design and fabrication parameters as well as the device operating conditions. The effects of the substrate, number of MoS2 layers, channel layout and biasing conditions on the response of MoS2 FETs to NOx were investigated, providing directions for maximizing the sensitivity. This work also sheds light the issues of recovery and stability and present a methodology for calibration of the sensors which is critical for repeatable and reliable measurements. (c) 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Most available fine pitch interconnects, like micro bumps and copper pillars, are not particularly compliant whereas available compliant interconnects, like plastic core solder balls, are not fine pitch. Using Ag-plated polymer spheres (MPS) in conjunction with a nano-Ag conductive ink has the potential to achieve mechanically compliant flip chip interconnects since the structural integrity is maintained by the flexible polymer core while the electrical conductivity is maintained by the Ag plated shell. Additionally, the low processing temperature means that it is relevant for systems that require low temperatures or that are very sensitive to thermomechanical stress, like MEMS sensors. Previous work has shown that a major challenge in the proposed process was the confinement of the conductive ink onto the Au pad. This workfocuses on finding an oleophobic coating that can be patterned to confine the ink on the contact pads. Two materials were tested, a fluoroacrylate additive for photoresists and a fluoropolymer that needed to be patterned separately. The latter showed superior oleophobicity and was therefore chosen. Patterning by positive and negative photoresist was tested. Using positive photoresist as a masking layer for reactive ion etching proved incompatible with the desired output. The use of negative photoresist with a lift-off technique showed potential, but needs to be optimized. Using reactive ion etching through a stencil mask showed the best results.

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Most available fine pitch interconnects, like micro bumps and copper pillars, are not particularly compliant whereas available compliant interconnects, like plastic core solder balls, are not fine pitch. Using Ag-plated polymer spheres (MPS) in conjunction with a nano-Ag conductive ink has the potential to achieve mechanically compliant flip chip interconnects since the structural integrity is maintained by the flexible polymer core while the electrical conductivity is maintained by the Ag plated shell. Additionally, the low processing temperature means that it is relevant for systems that require low temperatures or that are very sensitive to thermomechanical stress, like MEMS sensors. Previous work has shown that a major challenge in the proposed process was the confinement of the conductive ink onto the Au pad. This workfocuses on finding an oleophobic coating that can be patterned to confine the ink on the contact pads. Two materials were tested, a fluoroacrylate additive for photoresists and a fluoropolymer that needed to be patterned separately. The latter showed superior oleophobicity and was therefore chosen. Patterning by positive and negative photoresist was tested. Using positive photoresist as a masking layer for reactive ion etching proved incompatible with the desired output. The use of negative photoresist with a lift-off technique showed potential, but needs to be optimized. Using reactive ion etching through a stencil mask showed the best results.

In this work, a complementary microstructural and optical approach is used to define processing conditions favorable for the formation of deep boron-related acceptor centers that may provide a pathway for achieving an intermediate band behavior in highly B-doped 3C-SiC. The crystallinity, boron solubility and precipitation mechanisms in sublimation-grown 3C-SiC crystals implanted to 1-3 at.% B concentrations were investigated by STEM. The revealed defect formation and boron precipitation trends upon thermal treatment in the range 1100-2000°C have been cross-correlated with the optical characterization results provided by imaging PL spectroscopy. We discuss optical activity of the implanted B ions in terms of both shallow acceptors and deep D-centers, a complex formed by a boron atom and a carbon vacancy, and associate the observed spectral developments upon annealing with the strong temperature dependence of the D-center formation efficiency, which is further enhanced by the presence of implantation-induced defects.

Boron (B) has the potential for generating an intermediate band in cubic silicon carbide (3C-SiC), turning this material into a highly efficient absorber for single-junction solar cells. The formation of a delocalized band demands high concentration of the foreign element, but the precipitation behavior of B in the 3C polymorph of SiC is not well known. Here, probe-corrected scanning transmission electron microscopy and secondary-ion mass spectrometry are used to investigate precipitation mechanisms in B-implanted 3C-SiC as a function of temperature. Point-defect clustering was detected after annealing at 1273 K, while stacking faults, B-rich precipitates and dislocation networks developed in the 1573 - 1773 K range. The precipitates adopted the rhombohedral B13C2 structure and trapped B up to 1773 K. Above this temperature, higher solubility reduced precipitation and free B diffused out of the implantation layer. Dopant concentrations E19 at.cm-3 were achieved at 1873 K.

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.

Smart tags for fast moving consumer goods are among the products predicted to be part of the Internet of Everything. The tags must be extremely low cost, be fabricated in huge volumes, and have a quality accepted by the end user. Screening tests have been performed to evaluate technologies for hybrid integration of smart tags. An anisotropic conductive adhesive (ACP) was compared with use of a low temperature solder and critical factors limiting the quality of each technology were identified. The motivation for the research was to avoid over-engineering of the quality of the joints where this would correlate with too high costs. For the system with an ACP, the matrix material was identified as the critical factor whereas for the soldered system, the quality of the backplane appeared more critical than the soldered joints themselves. Draft specifications that were considered in this work were not met for the system with ACP whereas they were easily met for all tested soldered systems.

A very compact and rugged 2.5-D integrated data logger has been built and tested. The data logger is capable of measuring accelerations exceeding 70 000 g. Microcontroller and flash memory as bare dies have been mounted onto a silicon interposer with through silicon vias using anisotropic conductive film and Au stud bump bonding. A microelectromechanical system accelerometer is mounted onto the interposer, using a robust customized flip-chip mounting approach. The interposer is mounted into a 16-pin leadless chip carrier package using isotropic conductive adhesive, where the conductive part is made of metallized polymer spheres. The ceramic package was mounted onto an application printed circuit board (PCB) with filters, power management, and an interface contact, using soldered plastic core solder balls (PCSBs). The diameter of the data logger is less than 9 mm, and the height is approximately 5 mm. The data logger fits within 12.7-mm (0.50 cal.) projectile, and acceleration measurements have been performed during firing, flight, and recovery. The measured accelerations have been verified by comparing the calculated projectile muzzle velocities with Doppler radar measurements.

Abstract Electrochromic displays are among the key components of smart tags and their performance, defined by the color switch time, is directly linked to the level of humidity inside the displays. A time-efficient procedure, based on the use of a gravimetric moisture analyzer, was implemented, where the water content in a display could be related to the temperature and relative humidity of the manufacturing environment. The electrical performance of the displays was evaluated by measuring current as a function of time during voltage pulses of 4 s as these measurements quantified the time needed for color switch (should be < 1 s). The electrical performance was also measured as a function of the temperature and relative humidity of the manufacturing environment. By varying the temperature and the relative humidity systematically and measuring water content and display performance, a correlation between water content, switch time and manufacturing environment could be established and a safe range for manufacturing conditions could be found.

Low cost and miniaturized solutions for assembly of optical microelectromechanical systems (MOEMS) are critical for increased exploitation of optical sensors and devices in consumer applications. Examples of applications based on optical sensors and devices already near or on the market are auto-focus lenses and pico-projectors for mobile phones, physiology measurement units for wearables, and high bandwidth free-space optical communication links for our homes. In addition, extensive use of photonic integrated circuits is predicted to be mandatory in order to answer to the future needs for high data transfer rates in data centers. However, the main limitation for several of these applications is the complexity, the related cost of assembly, and the unknown reliability of several lower cost assembly solutions; polymer-based solutions are e.g. prone to fail particularly fast in humid and warm conditions. In this work, a part of a European project called Lab4MEMS II, we study the feasibility of reducing the footprint, complexity and cost of assembly of silicon micro-machined mirrors directly to organic printed circuit boards, without jeopardizing the reliability of the system. We demonstrate flip-chip assembly using novel isotropic conductive adhesives (ICAs) with a particularly low content of silver that earlier indicated stable behaviour during exposure to hygrothermal aging [1]. The new solution removes the earlier needed space around the component for wire bonds, and the assembly is simplified as electrical and mechanical joints are formed in a single step. Dummy mirrors were designed with two different pad layouts that were either optimized for a large pitch (the pads are distributed evenly around the active area) or for mechanical compliance (the pads are concentrated into three groups that are oriented in a triangle). There are 12 pads in total for each design. The outer dimension of the dies is 7 x 7 mm and the diameter of the region reserved for an active area is 5 mm. The dummy samples represent mirrors that are controllable through the inclusion of a 2 Âμm lead zirconate titanate (PZT) piezo-electrical thin film. The PZT film and the bottom (Ti/Pt) and top (TiW/Au) electrode layers are included in the dummy samples for a good representation of the actual surfaces to be bonded, both their materials and their topography. A 100 nm layer of alumina was deposited for passivation. The passivation layer was opened in the contact holes by wet etching. The layout includes both Kelvin structures and daisy chains. A commercially available and widely used ICA, Epotek H20E, was selected as a reference material for two novel ICAs, Mosaic A and Mosaic B. The Epotek material contains solid Ag particles whereas the Mosaic materials contain metal coated polymer spheres with a diameter of 10 Âμm and a Ag layer coating of 140 nm. The ICAs were stencil printed onto boards having ENIG surface finish. The dummy mirror dies were flipped and aligned, and bonded by applying a tool pressure corresponding to 9 MPa as calculated based on the nominal contact hole areas. Curing was performed for one or two hours at 150 °C, depending on the recommendations from the material providers. A total of 14 boards, with 6 dummy mirrors bonded onto each, were assembled for characterization and reliability testing. The assemblies are presently measured electrically in-situ as they are exposed to hygrothermal aging. The humidity level is 85% RH in all tests, whereas the temperature is either 65, 75 or 85 °C to enable recording of lifetime distribution curves at three different temperature loads. No failures have occurred yet, illustrating already the high potential of this assembly solution, but all samples will be run to failure. Curve fitting will be used to identify distribution functions to enable lifetime predictions, but the failures will be analysed using cross-sectioning, light microscopy and scanning electron microscopy, to identify failure modes and thereby verify the correctness of accelerated testing.

A novel bending machine has been designed and tested. It enables flexible electronics to be subjected to repeated bending with constant radius and tension. In-situ electrical characterization can give accurate analysis of lifetime distributions if sufficiently many samples are ran to failure, allowing reliability prediction models to be developed. Four sets of test samples with different combinations of substrate, routing, interconnect technology and components were examined. A poor level of reliability was observed when using anisotropic conductive paste to form interconnects, whereas a significantly higher level of reliability was observed when using a bismuth-tin solder paste. The assembly of larger components resulted in shortened time to failure, whereas increasing the bending radius prolonged the observed lifetimes.

An experiment was designed using optimal design of experiments to identify the most relevant parameters in an assembly step for a smart tag; the soldering of 0402 resistors to a polyimide backplane. The parameter window was set to reflect natural variations in production, and parameter variations were investigated to ascertain whether these variations could lead to unacceptable values of electrical resistance or shear-strength of the soldered joints. All tests were performed before and after exposure to hygrothermal aging, i.e. exposure to 85 °C in combination with 85 % RH, and/or cyclic bending. All test results gave values well within the predefined failure criteria. It could therefore be concluded that all of the tested combinations of parameters spanning the tested process window can be considered as safe variations for the assembly of 0402 resistors in the production of the smart tags. The parameters that influenced the electrical resistance and shear-strength of these assemblies were identified.

Abstract An anisotropic conductive film (ACF) can be utilized to simultaneously form mechanical bonds and electrical connections during flip-chip assembly. The electrical connection is created by trapping randomly dispersed metallized polymer spheres (MPS) in the ACF that are deformed during the bonding process. This work postulates that the reliability of interconnects formed with ACF depends on the degree to which the MPS are deformed. Silicon samples with fine-pitch electrical test structures were flip-chip assembled using an ACF and measured in-situ during environmental testing. Interconnects with MPS deformation below 60% proved more stable than interconnects with higher deformation during exposure to 85% relative humidity at 20 °C, 45 °C, 60 °C and 85 °C, as postulated. On the other hand, the stability of the interconnects did not show a dependence on MPS deformation during exposure to thermal shock cycling (TSC) (−55 °C / +125 °C, 7 s transit time, 700 cycles). The results suggest that deformation of MPS is a central factor with respect to reliability of ACF-bonded fine-pitch samples exposed to humid conditions, but the results also indicate that other failure mechanisms are more important for samples exposed to thermally unstable conditions.

Sublimation-grown 3C-SiC crystals were implanted with B ions at elevated temperature (400 °C) using multiple energies (100 to 575 keV) with a total dose of 1.3×10 17 atoms/cm 2 in order to form intermediate band (IB) in 3C-SiC. The samples were then annealed at 1400 °C for 60 min. An anomalous area in the center was observed in the PL emission pattern. The SIMS analysis indicated that the B concentration was the same both within and outside the anomalous area. The buried boron box-like concentration profile can reach ~3×10 21 cm -3 in the plateau region. In the anomalous area a broad emission band (possible IB) emerges at around ~1.7-1.8 eV, which may be associated with B-precipitates having a sufficiently high density.