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Sol–gel formulations were applied to replace silicone as matrix material for phosphors in pc-LEDs. The content of organic groups was minimized in order to reduce yellowing during the operation of the elements. It was possible to evenly embed YAG:Ce particles in sol–gel binders. Further processing on LED chips resulted in operational light sources; and their performance was compared to standard silicone-based elements. Additional deposition of ALD laminates seals possible defects within the sol–gel matrix as additional protection of the phosphors and the underlying LEDs.

A large-area thermoelectric generator (TEG) utilizing a folded thin-film concept is implemented and the performance evaluated for near room temperature applications having modest temperature gradients (< 50 K). The TEGs with the area of ~0.33 m^2 are shown capable of powering a wireless sensor node of multiple sensors suitable e.g. for monitoring environmental variables in buildings. The TEGs are based on a transparent, non-toxic and abundant thermoelectric material, i.e. aluminium-doped zinc oxide (AZO), deposited on flexible substrates. After folding, both the electrical current and heat flux are in the plane of the thermoelectric thin-film. Heat leakage in the folded TEG is shown to be minimal (close to that of air), enabling sufficient temperature gradients without efficient heat sinks, contrary to the conventional TEGs having the thermal flux and electrical current perpendicular to the plane of the thermoelectric films. The long-term stability studies reveal that there are no significant changes in the electrical or thermoelectric properties of AZO over several months, while the contact resistance between AZO and silver ink is an issue exhibiting a continuous increase over time. The performance of the TEGs and technological implications in relation to a state-of-the-art thermoelectric material are further assessed via a computational study., 15 pages, 5 figures, post-peer-review, pre-copyedit version of an article published in Renewable Energy

To meet the dimensional requirements for bioelectronic medicine, new packaging solutions are needed that could enable small, light-weight and flexible implants. For protecting the implantable electronics against biofluids, recently various atomic layer deposited (ALD) coatings have been proposed with high barrier properties. Before implantation, however, the protective coating should be evaluated for any defects which could otherwise lead to leakage and device failure. In these cases, the conventional helium leak test method can no longer be used due to the millimeter size of the implant. Therefore, an in-situ sensing platform is needed that could evaluate the coating and justify the implantation of the final device. In this work, we explore the possibility of using the CMOS bulk for such a platform. Towards this aim, as a proof of concept, test chips were made in a standard 6-metal 0.18 µm CMOS process and for the connection to the bulk, a p+ diffusion was used. A group of samples was then coated with an ALD multilayer. For coating evaluation, off-chip DC current leakage and impedance measurements were carried out in saline between the CMOS bulk and a platinum reference electrode. Results were compared between non-coated and coated chips that clearly demonstrated the potential of using the bulk as a sensing platform for coating evaluations. This novel approach could pave the way towards an all integrated in-situ hermeticity test, currently missing in mm-size implants.

H2020-ICT-2014-1 ERC-CoG-2014 CapTherPV, 647596 Aluminium doped zinc oxide (AZO) films were grown by Atomic Layer Deposition (ALD) on yellow Kapton and transparent Kapton (type CS) substrates for large area flexible transparent thermoelectric applications, which performance relies on the thermoelectric properties of the transparent AZO films. Therefore, their adhesion to Kapton, environmental and bending stability were accessed. Plasma treatment on Kapton substrates improved films adhesion, reduced cracks formation, and enhanced electrical resistance stability over time, of importance for long term thermoelectric applications in external environment. While exposure to UV light intensity caused the films electrical resistance to vary, and therefore their maximum power density outputs (0.3–0.4 mW/cm3) for a constant temperature difference (∼10 °C), humidity exposure and consecutive bending up to a curvature radius above the critical one (∼18 mm) not. Testing whether the films can benefit from encapsulation revealed that this can provide extra bending stability and prevent contacts deterioration in the long term. publishersversion published

A major barrier for a wider use of thermoelectric devices for energy harvesting is their low efficiency, which tends lead to a high cost per converted power. The ability to use non-toxic and abundant materials has also become increasingly important in the recent years and enhanced the interest towards improving the thermoelectric properties of metal oxides. Tin-doped indium oxide (ITO) is one of the most commonly used transparent conductive oxides due to its high electrical conductivity and high transparency. However, aluminum-doped zinc oxide (AZO) provides an environmentally friendly alternative that is more abundant, has better thermoelectric properties and lower cost. In this work, we present selected results of our thermoelectric device development based on AZO aiming at flexible thin-film TEG applications. Thermodynamic modelling and performance simulations are conducted for selected designs in order to estimate the available thermal gradients, the performance of the thermoelectric elements and the power available from the thermoelectric modules consisting of various geometries and configurations [1]. In addition to the electrical properties, the heat transfer mechanisms over the modules are studied. In addition to the conventional material characterizations, the potential of the materials is also evaluated by constructing experimental test devices of the thin-films and building corresponding simulation models of the test devices. By combining the experimental and theoretical approaches through device evaluations, the optimization of the thin-film materials and device designs can be performed in parallel for constructing a large-area thermoelectric module for thermal energy harvesting applicable in various environments without elaborated heat sinks. The ultimate goal of the project is to build a distributed sensor network integrating large-area thin-film thermoelectric devices and sensors for multifunctional smart windows and flexible high impact volume applications.

Atomic layer deposition (ALD) is widely in use for depositing a variety of materials, such as metal oxides, metal nitrides and metals, in a conformal and defect-free form at low temperatures on high aspect-ratio substrates. These advantages make ALD uniquely powerful method for applications where sensitive substrate materials combine with extreme demands on coating quality and temperature/chemical resistance, such as those often seen in the medical applications.

Implantable medical devices must withstand the corrosive environment inside the human body for prolonged periods of time. Hermetic sealing of the device to protect it from the corrosive environment of human body and vice versa is a key step to enable long life time for the smart medical devices. Atomic layer deposition (ALD) is an advanced deposition technique belonging to the family of chemical vapor deposition (CVD) techniques. In ALD the substrate to be coated is exposed sequentially to precursor chemicals that react with the reactive surface sites on the substrate and form a chemically bonded adsorption layer. This growth mode of the film enables extremely conformal and uniform films to be coated on three-dimensional objects having any shape. Even the smallest, nanometer sized features on the objects can be coated with ease, making the technique extremely useful when hermetic sealing of complex shaped objects are required. The advantages of ALD over other deposition techniques makes it powerful method for applications where sensitive substrate materials combine with extreme demands on coating quality and temperature/chemical resistance, such as those often seen in the medical applications. In order to make a robust protective sealing for the medical device, the film properties must fulfill certain key criteria. First and foremost, the film material needs to be non-toxic for human cells in order to be biocompatible. Secondly, the film needs to function as an highly efficient diffusion barrier against the ions and molecules present in body fluids. In addition, the adhesion of the film with the device surface needs to be strong enough to prevent the delamination of the film. In our recent work [1] we have shown that SiO2-HfO2 coated sub-millimeter-sized microelectronic chiplets for wireless body implants can last without degradation and electronic failure in accelerated aging tests in saline at T = 87 °C for more than 180 days. This corresponds an equivalent lifetime of more than 10 years at human body equivalent temperature of 37 °C. Latest results on ALD films (deposited with Picosun® R-200 Advanced ALD reactor) for medical applications will also be discussed. Biocompatibility tests for Al2O3, TiO2, HfO2, SiO2, Ta2O5 films using the ISO standard Cytotoxicity of Medical Device (ISO 10993-5) procedure will be presented. In addition, we will show results of corrosion tests in PBS solution at elevated temperature (87 °C) for a number of ALD oxides and their nanolaminates, highlighting a stress control method that can improve the long-term delamination resistance of the coatings. Furthermore, we will show some results on the diffusion barrier properties of Al2O3, TiO2, HfO2, SiO2, Ta2O5 and their nanolaminates on different electrode materials (Al, Au, Pt, TiN) when exposed to PBS solution. [1] Conformal Hermetic Sealing of Wireless Microelectronic Implantable Chiplets by Multilayered Atomic Layer Deposition (ALD) by J. Jeong, F. Laiwalla, J. Lee, R. Ritasalo, M. Pudas, L. Larson, V. Leung, and A. Nurmikko, https://doi.org/10.1002/adfm.201806440. Acknowledgements: This work is part of the ULIMPIA project funded by PENTA under grant number PENTA-2017-Call2-16101-ULIMPIA

This paper focuses on the impact of annealing on the current conduction and trap states of metal-insulator-metal capacitors with CeO2/La2O3 dielectrics. Capacitance-frequency measurements identify two main trap levels (T1 and T2), characterized by an activation energy of 0.2 and 0.3 eV, respectively, and by a time constant of 1 ms and 20 μs at room temperature. The current conduction is found to be ruled by a Poole-Frenkel effect and space charge limited current under positive and negative bias, respectively. Selective annealing of CeO2 and La2O3 layers clarifies the nature of the aforementioned traps. Although providing no change in the activation energy, an additional annealing of the CeO2 and La2O3 layer is found to significantly change the trap amplitude of T1 and T2, respectively. The corresponding change of the current conduction in the region where trap assisted mechanisms play a major role is discussed.This paper focuses on the impact of annealing on the current conduction and trap states of metal-insulator-metal capacitors with CeO2/La2O3 dielectrics. Capacitance-frequency measurements identify two main trap levels (T1 and T2), characterized by an activation energy of 0.2 and 0.3 eV, respectively, and by a time constant of 1 ms and 20 μs at room temperature. The current conduction is found to be ruled by a Poole-Frenkel effect and space charge limited current under positive and negative bias, respectively. Selective annealing of CeO2 and La2O3 layers clarifies the nature of the aforementioned traps. Although providing no change in the activation energy, an additional annealing of the CeO2 and La2O3 layer is found to significantly change the trap amplitude of T1 and T2, respectively. The corresponding change of the current conduction in the region where trap assisted mechanisms play a major role is discussed.

In this work, dispersion strengthening of copper by diamonds is explored. In particular, the influence of 50- and 250-nm diamonds at contents of 3 and 6 vol. pct on the mechanical and thermal properties of pulsed electric current sintered (PECS) Cu composites is studied. The composite powders were prepared by mechanical alloying in argon atmosphere using a high-energy vibratory ball mill. The PECS compacts prepared had high density (>97 pct of T.D.) with quite evenly distributed diamonds. The effectiveness of dispersoids in increasing the microhardness was more pronounced at a smaller particle size and larger volume fraction, explained by Hall-Petch and Orowan strengthening models. The microhardness of Cu with 6 and 3 vol. pct nanodiamonds and pure sm-Cu (submicron-sized Cu) was 1.77, 1.46, and 1.02 GPa, respectively. In annealing experiments at 623 K to 873 K (350 °C to 600 °C), the composites with 6 vol. pct dispersoids retained their hardness better than those with less dispersoids or sm-Cu. The coefficient of thermal expansion was lowered when diamonds were added, being the lowest at about 14 * 10-6 K-1 between 473 K and 573 K (200 °C and 300 °C). Good bonding between the copper and diamond was qualitatively demonstrated by nanoindentation. In conclusion, high-quality Cu-diamond composites can be produced by PECS with improved strength and better thermal stability than for sm-Cu.

This paper reports the influence of applied sintering process – pulsed electric current sintering (PECS) and hot isostatic pressing (HIP) – on the microstructure and mechanical properties of Cu–Cu 2 O composites. In PECS fine-grained structure was obtained while in HIPing the grain growth was more noticeable, mostly due to the longer process time. The studies also showed that Cu 2 O-phase distributed in Cu-matrix increased microhardness; at a fixed grains size Cu–Cu 2 O structure had higher hardness than Cu so that 20% higher microhardness was obtained when Cu 2 O was doubled from 19.1 to 37.2 vol%. At best, 99.1% density with 690 nm grain size and 1.35 GPa hardness were achieved by PECS whereas by HIP the same density with 1860 nm grain size gave 1.02 GPa hardness. The grain growth and the effect of second phase clustering on the grain growth were evaluated experimentally.

In this paper pulsed electric current sintering (PECS) is applied for submicron-sized copper (sm-Cu) based composite-powders aiming to produce MMC’s with higher strength and better temperature stability than reference sm-Cu. Incorporation of cuprite (Cu2O), alumina (Al2O3), titaniumdiboride (TiB2) and nano- and submicronsized diamonds (ND’s and SMD’s) improved noticeably the room temperature mechanical properties and the high-temperature stability of copper the effects becoming more noticeable with smaller dispersion size and higher amount of reinforcement. The hardness increment was at highest, when using ND’s or Al2O3. E.g., the microhardness for the reference sm-Cu sample and Cu with 3 vol.% ND’s, 6 vol.% ND’s and 2.5 vol.% Al2O3 were 1.02, 1.43, 1.77 and 1.58 GPa, respectively. Similar trend was noted also in the case of thermal stability and CTE. The study shows that Cu-ND, Cu-SMD and Cu-Cu2O are suitable for use at moderate temperatures around 623 - 673 K, whereas Cu-Al2O3 and Cu-TiB2 are suitable above 1023 K. In conclusion, PECS is suitable method to produce high quality Cu-composites having superior thermal and mechanical properties compared to those of sm-Cu.

In this work, the influences of the microstructure on the mechanical and thermal properties of pulsed electric currentsintered (PECS) Cu-Al2O3 composites are investigated. The process parameters were optimized for four different grades ofcomposite powders to obtain dense samples (98-99.6%T.D.). Higher hardness and better thermal stability were attained tothe samples compacted from commercial internally oxidized (IO) powders than to the compacts made from the chemicallysynthesised experimental powders. This difference was attributed to the distribution and size of Al2O3-particles in the twotypes of composites. The CTE values of all the compacts were between 17 and 20 x 10-6K-1 (370-770 K). The results showthat PECS can be used to produce dense high quality Cu-Al2O3 composites.

This paper describes the microstructures and nanomechanical properties of copper consolidated of oxidized submicron-sized Cu-powder (average particle size 410 nm) by spark plasma sintering (SPS). Good compact density, small grain size (460 nm) and microhardness of 1.24 GPa were achieved at 873 K in 6 min with 100 MPa, Cu2O-content being close to 20%. At higher sintering temperature, the grain size increased leading to decrease in hardness. The HIPed compact that was made for reference contained lower Cu2O and had lower density and larger grain size. It was concluded that the SPS process was superior to HIP consolidation in terms of microhardness and microstructure of the final material. Furthermore, the presence of Cu2O seemed not to have a marked effect on the SPS consolidation process, i.e. the obtained densities of the SPS samples were of 99.7% of theoretical density at the best.

The WC-8Co powder, crushed and milled from recycled hard metals, was compacted with the pulsed electric current sintering method. The smallest particles were of the size about 0.4 µm and agglomerates 1-7 µm. Effect of the sintering temperature and heating rate were studied. Hard metal was sintered to a density of 98.3% at 1613 K within 3.5 min under 16 MPa pressure. Density and hardness were highest for the slowest heating regime, 98.1% and HV1 1981 kg/mm 2 , respectively. Heating speed 100 K/min was used for fabrication of fully densed samples, sintered under pressure of 100 MPa, at 1593 K in 3 min.