Our study introduces a novel approach to true random number generation (TRNG) using speckle patterns generated by laser-engraved holograms on carbon fiber-reinforced polymer (CFRP) composite substrates. Unlike previous methods, our approach simplifies the process by generating the necessary image dataset from a single microscope image of the engraved hologram. We achieve a high extraction ratio of 76 %, demonstrating the effectiveness of our TRNG. Moreover, our method successfully passes rigorous statistical tests proposed by the National Institute of Standards and Technology (NIST), indicating its suitability for cryptographic and secure system applications. This work offers promising implications for enhancing security in various domains, from secure communication networks to IoT devices.

Quantification of pattern distortion in nanoimprint lithography (NIL) is required when applying it to specific applications, especially those with tight tolerances. We present a systematic study on full wafer NIL distortion using soft stamps made of different carrier foils and UV-curable polymer structure layers. These errors are evaluated by overlay patterning using NIL and optical lithography on 4-in. wafers over a distance of 80 mm. Potential causes for pattern distortion and possible correction methods are discussed in terms of stamp composition and environmental impact. Pattern distortion along axes causing dimensional change is stamp dependent, and stiffer stamps show less pattern dimensional change than the softer ones. In the best case, the minimum variation is 4 ppm (ppm), and in the worst case, 252 ppm with a softer stamp. Stamp flatness and uniform contact during imprinting are important in reducing high-order pattern distortion. A maximum dimensional variation of 32 ppm in a batch run demonstrates good pattern repeatability. Long-term dimensional stability can be affected by relative humidity, with variations on the order of 100 ppm.

Hydrogen silsesquioxane (HSQ) and Medusa are spin-on-glasses used for several applications and more specifically for electron-beam lithography. To characterize the thermal densification of these resists on silicon, the mean resist film stress was measured in situ as function of temperature up to 600 °C in a vacuum chamber by the curvature method. The curvature was evaluated from 3D profiles of uncoated and coated dies measured by full field phase shifting interferometry. Three resists were investigated: FOx-15, FOx-25 and Medusa-82. The initial resist stress at room temperature after spin coating and baking is slightly compressive and becomes highly compressive above a certain temperature dependent on the resist. This variation is mainly attributed to resists densification. FOx-15 and FOx-25 start densifying at 500 °C, and FOx-25 densifies more than FOx-15. Medusa-82 is densifying around 300 °C and has the highest compressive thermal stress but the film relaxes beyond 405 °C. In the case of FOx-15, it was found that vacuum annealing prevents densification. Finally, we evaluated the in-plane average coefficient of thermal expansion of the resists from stress measurements during cooling to room temperature. For FOx-15, a CTE equal to 1.59 ppm/K is found, while it is 1.73 ppm/K for FOx-25 and 1.38 ppm/K for Medusa-82.

In this work we investigate the release of hydrogen gas from PECVD silicon nitride thin films in the cavities of MEMS based inertial sensors. Firstly, material characterization is conducted on two types of PECVD silicon nitride thin films to study the release of hydrogen gas with analytical methods. The release of hydrogen gas from these materials in encapsulated cavities of MEMS sensors, and its influence on the cavity pressure is also investigated experimentally with the help of functional microchips of MEMS based inertial sensors. Based on our findings and reports from other works, we propose steps by which change in the cavity pressure of the investigated microchip occurs over its different fabrication processes. We suggest that hydrogen gas is released form PECVD silicon nitride thin films at high temperatures during wafer bonding, which can then diffuse in cavities at low pressure over the lifetime of the sensor.

Photovoltaic retinal implants are emerging as a promising technological solution for restoring vision for patients suffering from retinal degenerative diseases such as retinitis pigmentosa and age-related macular degeneration. These prostheses contain arrays of miniaturized solar cells converting light into electrical output signals, which subsequently are employed for local activation of the intact neuroretina via microelectrodes. Leveraging cutting-edge microfabrication techniques, photovoltaic retinal implants are compact and provide a high density of solar cell pixels. This potentially increases the resolution of the artificial vision and the field of view and lowers the threshold for stimulation of retinal neurons. The introduction of flexible substrates and the integration of 3D electrodes has greatly improved the connection with retinal neurons, optimizing the spatial resolution and potentially lowering the stimulation threshold. This review explores the latest developments in photovoltaic retinal prostheses, highlighting key aspects of their design, fabrication and performance. This field of research is still in its early stage and particular emphasis is laid on promising future research directions including miniaturization of pixels, incorporation of organic flexible semiconductors and first studies considering 3D stimulating electrode structures. Despite the significant progress made, there are still substantial challenges to overcome, such as ensuring long-term biocompatibility and validation of the novel concepts in clinical trials. Ongoing interdisciplinary research and development are essential for moving these promising technologies from the lab to real-world clinical applications, ultimately enhancing vision restoration. This review aims to provide a comprehensive overview of the current state of photovoltaic retinal implants and pinpoints critical areas for future research to further advance this transformative technology.

This study explores the development and characterization of plasma etching for sub-micron features using a nonlinear evolution of parameter in a three-step cyclic Bosch process. Comparing this nonlinear approach with traditional linear parameter evolution, we aimed to address issues such as bowing at the top of the features and narrowing at the bottom. Constant parameter etching produced tapered profiles, undercutting, and non-uniform scallops due to particle deflection. Linear parameter evolution partially mitigated these problems by balancing etch and deposition cycles and gradually increasing radio frequency power, achieving high selectivity to the photoresist. One nonlinear exponential evolution method resulted in a higher etch rate but caused slight damage to the top-side wall, while the etch depth was reduced. The other nonlinear method balanced the etch and deposition steps more effectively, achieving a comparable etch rate and selectivity to the linear method. Further optimization of this second method led to improved vertical profiles and controlled scallops, achieving greater depth, smoother sidewalls, and higher etch rates. This optimized technique successfully fabricated high aspect ratio periodic sub-micron structures with excellent uniformity across the wafer, demonstrating its potential for achieving even higher aspect ratios with thicker masks.

In this paper we describe and fully characterize a novel vibration harvester intended to harness energy from the vibration of a wind turbine (WT), to potentially supply power to sensing nodes oriented to structural health monitoring (SHM). The harvester is based on electromagnetic conversion (EM) and can work with vibrations of ultra-low frequencies in any direction of a plane. The harvester bases on a first prototype already disclosed by the authors, but in this paper, we develop an accurate model parameterized by a combination of physical parameters and others related to the geometry of the device. The model allows predicting not only the power generation capabilities, but also the kinematic behaviour of the harvester. Model parameters are estimated by an identification procedure and validated experimentally. Last, the harvester is tested in real conditions on a wind turbine.

In this study, we report a novel approach for separating microspheres or cells on microstructured surfaces. These structures consist of μ-structured hydrogel coatings fabricated by photolithography on the bottoms of standard plastic microplate wells. The process is based on the deposition and subsequent irradiation of copolymers containing a hydrophilic main component and benzophenone moieties that can react with C, H groups during UV exposure through a photomask, a process known as “C,H insertion crosslinking” (CHic). The photolithographic process is used to generate an egg-box-like topography of the coating. Gravity, Brownian motion, and physical surface interactions drive particles or cells pipetted onto the surfaces to distinct locations on this topography so that after a short time these locations contain only one single particles or cells. We show that the presented technique enables the separation of thousands of objects as different as polymer microparticles or biological cells by simply adding a suspension to the coated wells of the microplate and wait for a short time (a few minutes). This strategy is quite general and not specific to a certain type of cell or microparticle and thus allow effortless separation of particles or cells.

Electron beam lithography (EBL) is pivotal for micro- and nanoscale fabrication, offering sub-micron precision. This study explores the utilization of the Novolac-based negative resist AR-N 7520 for EBL and its potential as an etch mask for reactive ion etching (RIE) of silicon. Recent comparisons of negative EBL resists have revealed promising results for AR-N 7520 in terms of resolution and adaptability with other lithography techniques. In this article, we conduct an exploration of patterning of AR-N 7520 (new) for EBL, addressing key parameters in achieving optimal patterning fidelity. Furthermore, we investigate its compatibility with RIE processes, aiming to provide insights into its effectiveness as an etch mask for creating sub-micron silicon structures. Experimental results show that optimal e-beam dose with 100 kV exposure is 300–350 μC/cm2. Selectivity of around 9:1 can be achieved by optimizing etching parameters for a continuous etch and higher than 14:1 for a cyclic etch process.