Silicon integrated circuits (ICs) are central to the next-generation miniature active neural implants, whether packaged in soft polymers for flexible bioelectronics or implanted as bare die for neural probes. These emerging applications bring the IC closer to the corrosive body environment, raising reliability concerns, particularly for chronic use. Here, we evaluate the inherent hermeticity of bare die ICs, and examine the potential of polydimethylsiloxane (PDMS), a moisture-permeable elastomer, as a standalone encapsulation material. For this aim, the electrical and material performance of ICs sourced from two foundries was evaluated through one-year accelerated in vitro and in vivo studies. ICs featured custom-designed test structures and were partially PDMS coated, creating two regions on each chip, uncoated "bare die" and "PDMS-coated". During the accelerated in vitro study, ICs were electrically biased and periodically monitored. Results revealed stable electrical performance, indicating the unaffected operation of ICs even when directly exposed to physiological fluids. Despite this, material analysis revealed IC degradation in the bare regions. PDMS-coated regions, however, revealed limited degradation, making PDMS a suitable IC encapsulant for years-long implantation. Based on the new insights, guidelines are proposed that may enhance the longevity of implantable ICs, broadening their applications in the biomedical field.

A compact electrochemical sensor module for pH detection was developed for potential integration into specialized devices used for live cell or tissue incubation, for applications in highly parallelized cell culture analysis, by incorporating Organ-on-Chip devices. This research focuses on the deposition, structural and chemical analysis, and functional characterization of different titanium-oxide layers with various compositions as potentially sensitive materials for pH sensing applications. The titanium-oxide layers were deposited using vacuum sputtering and atomic layer deposition at 100 °C and 300 °C, respectively. Transmission electron microscopy and X-ray photoelectron spectroscopy were utilized to determine the specific composition and structure of different titanium-oxide layers. These TiOx-functionalized electrodes were connected to the application-specific analog front-end chip of the low-power readout circuit for precise evaluation. The pH sensitivity of the differently modified electrodes, employing various TiOx materials, was evaluated using pH calibration solutions ranging from pH 6 to 8. Among the various deposition solutions, such as sputtering or high-temperature atomic layer deposition, the TiOx layer deposited using low-temperature atomic layer deposition proved more suitable for pH sensing applications, with a sensitivity of 54.8–56.7 mV/pH, which closely approximates the Nernstian response.

A compact pH measuring electrochemical sensor module was developed for Smart Multi-Well Plates (SMWP) applicable for highly parallelized cell culture analysis using incorporated Organ-on-Chip devices. A specific electronic architecture was designed and manufactured containing an extended gate field effect transistor as the transducer device. Electrochemical electrodes were functionalized using pH sensitive metal-oxides and applied as the gate material. The composition and the related pH sensitivity of differently deposited materials were characterized and the suitability of ALD-deposited, non-stoichiometric titanium oxide (TiOx) for sensitive pH measurement was verified showing excellent responses close to the ideal Nernstian slope (59 mV/pH).

Silicon integrated circuits (ICs) are central to the next-generation miniature active neural implants, whether packaged in soft polymers for flexible bioelectronics or implanted as bare die for neural probes. These emerging applications bring the IC closer to the corrosive body environment, raising reliability concerns, particularly for long-term clinical use. Here, we evaluated the long-term electrical and material stability of silicon-ICs from two foundries, after one-year accelerated in vitro and in vivo animal studies. The ICs featured various custom-designed test structures and were partially PDMS coated, creating two regions on each chip, uncoated “bare die” and “PDMS-coated”. During the accelerated in vitro study, ICs were electrically biased and periodically monitored. Results demonstrated stable electrical performance for at least a year, suggesting that bare die ICs can function in the body for months. Despite electrical stability, material analysis revealed chemical and electrically driven degradation of the IC passivation in the bare die regions. In contrast, PDMS-coated regions revealed no such degradation, making PDMS a highly suitable encapsulant for ICs intended for years-long implantation. Based on the new insights, guidelines are proposed that may enhance the longevity of implantable ICs, significantly broadening their applications in the biomedical field.### Competing Interest StatementThe authors have declared no competing interest.

The dependence of electron work function, Φ, on the thickness of Ti layers was investigated by making use of the Kelvin method under ambient conditions. Layers were produced by vacuum phase deposition and were analyzed by x-ray photoelectron spectroscopy and transmission electron microscopy. A quantum size effect was revealed finding work function to increase as the layer thickness, z, decreased below 4 nm. The extent of increase, ΔΦ, was understood in terms of a simple particle-in-a-box model arriving at the function ΔΦ=ℏ2π2/2mez2. This equation being free of any adjustable parameter, consisting only of the Planck constant and electron mass, seems to be a reasonable first approximation.

Due to their complex electro-thermal characteristics microhotplates used in environmental gas sensors require careful design to exhibit uniform temperature and low power dissipation during the expected long time operation. The layout design becomes more complex if the multiple operational parameters required by the battery operation and the driver and readout logic are considered. In this paper, we describe a simple analytical filament design procedure to determine the dimensions of the annular metal filament exhibiting uniform surface temperature without additional heat distribution layer. The presented method operates with the cumulative thermal losses towards the ambient and heat conduction via the membrane. Moreover, it handles the operation requirements like the targeted temperature in the atmospheric environment, supply voltage range, current density, filament layer thickness and its coverage ratio. The efficacy of the method is demonstrated by electrical and thermal characterisation of the manufactured devices having 150 µm diameter active area. The microheater achieves the targeted 500 °C operation temperature with 1.4–1.55 V supply. The temperature non-uniformity along the filament was measured by Spectral pyrometry and was found to decrease from ± 3.5% to ± 1% when the temperature was raised from 530 to 830 °C.

The growing interest in artificial skin-based tactile systems requires sufficiently accurate, stretchable, low-power mechanical sensors. In this study, we present a novel capacitive device and an evaluation method capable of retrieving the force vector and determining the position of the loading point on an extended area without the application of a large matrix of individual sensors. With this tool, we can simultaneously increase the extractable information from an extended surface area and reduce the complexity, thereby the power consumption of the system. Thus, an alternative path is opened toward robotic tactile sensing by using a small array of sensors but covering a relatively large receptive field. Even a single sensor can meet the requirements of specific devices—for example, in catheters—to detect tissue hardness, bending, or narrowing of the arteries or veins. Apart from the medical and robotic applications, the flexibility in processing the Flex2Rigid platform enables the mimicry of human fingers or hands with integrated sensors and driving circuits.

A reduced size thermocatalytic gas sensor was developed for the detection of methane over the 20% of the explosive concentration. The sensor chip is formed from two membranes with a 150 µm diameter heated area in their centers and covered with highly dispersed nano-sized catalyst and inert reference, respectively. The power dissipation of the chip is well below 70 mW at the 530 °C maximum operation temperature. The chip is mounted in a novel surface mounted metal-ceramic sensor package in the form-factor of SOT-89. The sensitivity of the device is 10 mV/v%, whereas the response and recovery times without the additional carbon filter over the chip are <500 ms and <2 s, respectively. The tests have shown the reliability of the new design concerning the hotplate stability and massive encapsulation, but the high degradation rate of the catalyst coupled with its modest chemical power limits the use of the sensor only in pulsed mode of operation. The optimized pulsed mode reduces the average power consumption below 2 mW.

One of the most dangerous threats to everyday life and industrial activity is the possible explosion of earth gas, which can occur in various conditions, but usually occurs due to an excess of explosive gases in an enclosed environment. In order to protect people at their home and workplace, several types of gas sensors have been developed. Nevertheless, one of the most useful devices for explosive and combustive gases detection is the catalytic gas sensor. This type of sensors has shown a good performance in detecting of flammable gases with concentration close to the lower explosion limit (LEL). In order to meet the growing need for portable devices further evolution of these gas sensors is required to make them smaller and reduce the power consumption. To achieve this goal it is essential to reduce the 120 to 150 mW power dissipation of the Pt-coil based sensors (pellistors). Low Power Thermocatalytic Sensors manufactured with SOI (silicon on insulator) technology can be functional at temperatures below 600 ℃ with the power consumption in a range of 20–50 mW. The current aim of researches is the elaboration of novel sensor processing and development of nanostructured catalyst layer which is stable and effective at high temperatures and compatible with microelectronic silicon MEMS technology.

Micro-catalytic gas sensors are essential devices for detection of combustive gases up to lower explosion limit (LEL). Micro-catalytic gas sensors capable to detect hydrocarbons below 50 mW power consumption at 550 degrees C operation temperature were developed by using a novel gas sensing material technique. Experiments were aiming at deposition of controlled volume and structure of the catalyst. Constant current method in a Wheatstone-bridge configuration was applied in functional tests of developed Al2O3 catalysts. (C) 2019 Elsevier Ltd. All rights reserved.

Introduction Catalytic gas sensors are essential devices for detection of combustive gases near lower explosion limit (LEL). As the minimum power dissipation of Pt coil based sensors (pellistors) are 120 - 150 mW [1] intensive research is devoted to reduce it to be better compatible with portable devices while preserving sensitivity and stability. The reported microheater structures can operate up to 600 oC at a cost of 20-50 mW power consumption [2]. Nowadays the research activity is focused on development of stablenanostructured catalyst layer effective at low temperature, whereas compatible with MEMS thick film technology. Gas Sensitive Catalytic Materials The approach of fabrication gas sensitive material for coil and silicon membrane sensors is different. In first case the catalyst is bulky and forms bead or cylinder with diameter 400-500µm. In MEMS structures the catalyst is deposited on a microhotplate with a characteristic diameter of 100µm, de facto forming 2D surface. In the present work nanodespersed Al2O3 and ZrO2 ceramic carriers were prepared as presented on figs.5 and 6, respectively. Each material was divided into two equal parts - an active catalytic layer from one part and a comparative element from the second part were made exhibiting equal surface area. .In order to impregnate the catalyst support with the catalyst metal, salts of palladium chloride (PdCl2) and platinum acid (H2PtCl6) were used. Having annealed at high temperature metal clusters were formed in the catalyst support. Finally the active and reference materials were mixed with an organic binder to make the paste suitable for drop-coating deposition to MEMS silicone microheater. SOI Based MEMS Microheater Uniform and reproducible crystalline Si filaments were formed from SOI (silicon on insulator) wafers, because the buried oxide provides uniform thickness of the device layer and guarantees identical geometry. Cantilevers are suspended on stress compensated SiO2-Si3N4 membrane to increase their mechanical stability and eliminate their bending out of the original plane (fig. 1-4). Thereby the reduced stress provides longer lifetime. The higher resistivity of device silicon ensures higher filament resistance at the same temperature compared to its thin film metal reference, therefore the cross section of the current routes should be increased to achieve the sufficient resistance. A plausible advantage of the single crystalline filament material and the design is the minimized degradation effect of electromigration, thereby the lifetime of the heater is expected to achieve 6000-8000 hours. Moreover, the heated area of filament can be completely covered with catalyst or passive material, similarly to the coil-type filament devices.The opened side chip design facilitates catalyst deposition. Results and Conclusions Significant issues arise when the design of thermocatalytic sensors are transferred from the volumetric to the microplanar approach. First of all, the catalytic gas-sensitive layer must provide chemical activities:3∙10-6÷10-5mW/μm3. The solution of the problem is to choose classical materials alreadybeen used for many years in coil types pellistors - catalysts of platinum group metals on Al2O3 or ZrO2 ceramic carriers. The stability and behavior of these materials at high working temperatures has been already tested over tens of years in real working conditions (mains, gas line pipes, leakage alarm systems and etc.). The decrease in the quantity of the catalytic material deposited on the microheater leads to insufficient catalytic activity of the sensor as a whole. An increase in the operating temperature can correct the situation, but it is limited by the long-term stability of the microheater and the transformation of the crystallographic phase of the ceramic catalyst carrier. The critical temperature is around 550 °C. The Pt-Pd mixed-catalysts can be applied in the microplanar structure if uniform hotplate temperature is provided and the active and the reference sensing layers are deposited such as to minimize imbalance between the two elements. Acknowledgement This research was sponsored by the Sponsored by the National Research, Development and Innovation Office Foundation, Hungary, funding No. 2017-2.3.4-TeT-RU-2017-00006, and the Ministry of Science and Higher Education of the Russian Federation founding with unique identifier RFMEFI58718X0053. References [1] Karpova, E., Mironov, S., Suchkov, A., Karelin, A., Karpov, E.E., Karpov, E.F. Increase of catalytic sensors stability (2014) Sensors and Actuators, B: Chemical, 197, pp. 358-363. [2] Bíró, F., Dücső, C., Radnóczi, G.Z., Baji, Z., Takács, M., Bársony, I. ALD nano-catalyst for micro-calorimetric detection of hydrocarbons (2017) Sensors and Actuators, B: Chemical, 247, pp. 617-625. Figure 1

This work analyses the role of phase changes in TiO2/Pt/TiO2 layer stacks for micro-heater application regarding their stability and reliable operation. The polycrystalline Pt layer wrapped in a TiO2 adhesion layer underwent a continuous recrystallisation in a self-heating operation causing a drift in the resistance (R) versus temperature (T) performance. Simultaneously, the TiO2 adhesion layer also deteriorates at high temperature by phase changes from amorphous to anatase and rutile crystallite formation, which not only influences the Pt diffusion in different migration phenomena, but also reduces the cross section of the Pt heater wire. Thorough scanning electron microscopy, energy dispersive spectroscopy, cross-sectional transmission electron microscopy (XTEM) and electron beam diffraction analysis of the structures operated at increasing temperature revealed the elemental structural processes leading to the instabilities and the accelerated degradation, resulting in rapid breakdown of the heater wire. Owing to stability and reliability criteria, the conditions for safe operation of these layer structures could be determined.

Smart laparoscope device was developed and integrated into the ROBIN HEART surgery robot system. Miniaturised silicon based force sensors were developed and integrated into laparoscope tweezers for the special applications. Different sensors were applied to detect tactile information at the tip of the laparoscope and to measure the clamping force between the tweezers. Preliminary tests were accomplished to evaluate the force and tactile signals of the integrated sensors during interventions. Tactile measurements were implemented on artificial and real animal tissues to prove the applicability of the device for biomechanical screening during Minimal Invasive Surgery.

3D force sensors were developed to further integration in laparoscopic heads of surgery robots. The Si sensors operate with piezoresistive transduction principle by measuring the stress induced signals of the symmetrically arranged four piezoresistors in a deforming membrane. As the chip size has to be reduced to a few mm(2), the conventional anisotropic alkaline etching technique was replaced by deep reactive ion etching (DRIE) for membrane formation. Moreover, DRIE enables to form any geometry of the membrane and offers the formation of monolith force transfer rod protruding over the chip surface. This rod increases shear sensitivity of the structure, thereby plays crucial role in tactile sensing. The technology applies SOI (silicon on insulator) wafers of appropriate device layer thickness, which provide highly uniform membranes and reproducibility of the process.According to the medical and functional requirements the sensors must be covered by biocompatible and sterilisable elastic polymers. As the elastomer drastically effect on the performance of the device, the proposed sensor structures were modelled by coupled finite element simulation to determine the appropriate geometric parameters meet the functional requirements. Sensors were covered with spherically shaped PDMS (polydimethylsiloxane) polymer and the effect of the elastic coating was also studied in terms of sensitivity and response time. Finally, the design of the laparoscopic head with the integrated 3D MEMS force sensors is also demonstrated.

LEDs have narrow radiation bandwidth which should be broadened for use them in near infrared spectroscopy. The well-known methods are not satisfactory for this purpose. We modified the output spectrum of the GaInAsP/InP LED chip by introducing wavelength converter layers into a normal LED structure outside from p-n junction. LEDs with luminescent layers made by us have spatially and spectrally stable structure, negligible current and temperature dependence. We made LEDs with two luminescent layer with new improved wavelength converter system which has further advantages and good efficiency. (C) 2017 Elsevier Ltd. All rights reserved.

Explosion alarm in atmospheric condition requires detection of hydrocarbons at the level of volume percent concentration range. This is best achieved by the combustion type detection, contrary to the available sensitive conductive type sensors, which would be driven to saturation by concentration close to LEL. Therefore, for catalytic gas sensing a micro-heater system was prepared with an integrated thin film porous Anodic Aluminium Oxide (porous AAO) on the heated area which offers simultaneously large surface support material and better thermal control. Uniformly distributed Pt catalyst was selectively deposited in the porous AAO by atomic layer deposition (ALD). The device was tested and characterized by detection of methane and propane concentrations between 20 and 100% of their Lower Explosion Limit (LEL), and provided readings of > 30 mV for 20% LEL (> 5 vol%) of both methane and propane. The combination of porous alumina with ALD deposited Pt exhibited catalytic activity for both gases. As the temperature of the micro-heater is limited to ca. 700 degrees C, during methane detection the sensor can be operated in the reaction kinetic controlled regime, whereas for propane measurement the temperature range of the ideal mass transport control can be set. The sensitivity loss was analysed in terms of possible ways for optimization. (C) 2017 Elsevier B.V. All rights reserved.

WO3 nano-structured layers on top of micro-hotplates were formed by sol–gel deposition technique and electrochemical anodic etching of thin tungsten layers. Both types of gas sensing layers were activated by drop coated Pt nano-particles and alternatively, by atomic layer deposited (ALD) Pt. Due to the limited number of ALD cycles the Pt layer is not a contiguous but composed of uniformly distributed nano-particles of 2–3 nm size. Devices were characterized by their responses for exposure of H2S and NH3. Investigation of sensitivity, selectivity and device dynamics revealed that the ALD sensitized, electrochemically formed porous WO3 layer is suitable for quick detection of H2S.

Broad spectrum InGaAsP/InP light emitting heterostructures were grown by low temperature liquid phase epitaxy (LPE). The structure of the LED wafers was investigated by optical transmission measurements, and the layer thicknesses were also measured by electron microscopy. Two quaternary light emitting layers of different composition were built in one device structure in order to broaden the usable wavelength range of the emission spectrum. One of the layers is electrically, whereas the other is optically excited as a result of internal absorption and re-emission of the LED light. As a result of this absorption and re-emission process the modified LED chips have substantially broader emission spectra and higher radiance than the conventional surface emitting multi-wavelength NIR LED structures. The two emission peaks of the spectrum were designed for matching the first and second harmonic wavelength of the fundamental absorption band of C-H bonds. The internal quantum efficiency of the wavelength conversion in this type of LEDs is nearly 100%.

Various deposition techniques were tested to form Pt catalyst on nano-structured materials characterized by 50-200 nm dimensions. Different layer structures applied in gas sensing were sensitized by Pt sputtering and droplet deposition of Pt nano-particles formed from H2[PtCl6] solutions. Besides, atomic layer deposition (ALD) of Pt was also investigated. The layers to be coated were disordered piles of WO3 nano-rods and sol-gel deposited WO3 nano-crystals as well as electrochemically formed alumina with high aspect ratio perpendicular pores. Distribution of Pt particles inside these layers was analyzed by scanning (SEM) and transmission electron microscopy (TEM). Demonstration of functionality is also provided.