Micro and Nano Engineering最新文献

Microfluidic devices hold enormous potential for the development of cost-effective and faster alternatives to existing traditional methods across life science applications. Here we demonstrate the feasibility of fabricating a microfluidic device by means of photolithography comprising a single cell trap, a delay structure and a chamber defined by micropillars. This device is aimed to be used for biological applications such as replicative lifespan determination (RLS) of yeast cells, where single cell trapping, and cell counting are essential. The novelty of the present work lies on the integration of the above-mentioned microfluidic structures in a single device by means of the established method of photolithography by fine-tuning critical parameters needed to achieve the desired high aspect ratio (1:5) employing commercially available resins. The fine-tuning of the fabrication parameters in combination with appropriately selected resins allows for patterning reproducibly micron-sized features. The design of the proposed device ultimately aims at replacing the very cumbersome assays still commonly used today for RLS determination in budding yeast by a methodology that is drastically simpler and more time efficient.

Plasmonic metal nanomaterials are usually supported by rigid substrates, typically made of silicon or glass. Recently, there has been growing interest in developing soft plasmonic devices. Such devices are low weight, low cost, exhibit elevated flexibility and improved mechanical properties. Moreover, they maintain the features of conventional nano-optic structures, such as the ability to enhance the local electromagnetic field. On account of these characteristics, they show promise as efficient biosensors in biological, medical, and bio-engineering applications. Here, we demonstrate the fabrication of soft polydimethylsiloxane (PDMS) plasmonic devices. Using a combination of techniques, including electroless deposition, we patterned thin membranes of PDMS with arrays of gold nanoparticle clusters. Resulting devices show regular patterns of gold nanoparticles extending over several hundreds of microns and are moderately hydrophilic, with a contact angle of about 80°. At the nanoscale, scanning electron and atomic force microscopy of samples reveal an average particle size of ∼50 nm. The nanoscopic size of the particles, along with their random distribution in a cluster, promotes the enhancement of electromagnetic fields, evidenced by numerical simulations and experiments. Mechanical characterization and the stress-strain relationship indicate that the device has a stiffness of 2.8 MPa. In biological immunoassay tests, the device correctly identified and detected anti-human immunoglobulins G (IgG) in solution with a concentration of 25 μg/ml.

We demonstrate the fabrication of sub-100 nm T-Gate structures using a single electron beam lithography exposure and a tri-layer resist stack - PMMA/LOR/CSAR. Recent developments in modelling resist development were used to design the process, in which each resist is developed separately to optimise the resulting structure. By using a modelling approach and proximity correcting for the full resist stack, we were able to independently vary gate length (50-100 nm) and head size (250-500 nm) at the design stage and fabricate these T-Gates with high yield.

Microscope-based Laser Doppler vibrometers (LDV) are optical instruments using laser Doppler interferometry to measure the motion of vibrating structures. As laser vibrometers measure without contact, they are also widely used for the characterization of the vibrational dynamics of silicon based micro-electro-mechanical systems (MEMS). Because silicon is opaque for visible light, MEMS-devices must be prepared without encapsulation to enable vibration measurements with standard laser vibrometers. However, the encapsulation itself is a critical process step during MEMS fabrication, and the reopening of the encapsulation bears the risk of damaging the device or altering its characteristics. Due to the high refractive index of silicon, vibrometry using infrared light is compromised by the inevitable influence of interfering reflections from encapsulation and device boundaries on the measurement results.

A novel low-coherent measurement technique is presented allowing to effectively suppress spurious interferences. This way, highly accurate vibration measurements and thus reliable analysis of the device dynamics of encapsulated MEMS are possible.

Water-based bio-sourced resists are promising candidates as alternatives for deep ultraviolet (DUV) lithography by replacing current photoresists issued from petro-chemistry for microelectronics application. Chitosan films produced from seafood industry wastes enable patterning processes free of organic solvent and alkali-based developers, by substitution with water. After demonstrating high-resolution patterning at lab-scale after transfer into silica 10 mm wafer, we investigate here the industrial pre-transfer chitosan-based photoresist on the 300 mm pilot line scale at CEA-Leti for 193 nm DUV lithography.

The damage inflicted to silicon nanowires (Si NWs) during the HF vapor etch release poses a challenge to the monolithic integration of Si NWs with higher-order structures, such as microelectromechanical systems (MEMS). This paper reports the development of a stencil lithography-based protection technology that protects Si NWs during prolonged HF vapor release and enables their MEMS integration. Besides, a simplified fabrication flow for the stencil is presented offering ease of patterning of backside features on the nitride membrane. The entire process on Si NW can be performed in a resistless manner. HF vapor etch damage to the Si NWs is characterized, followed by the calibration of the proposed technology steps for Si NW protection. The stencil is fabricated and the developed technology is applied on a Si NW-based multiscale device architecture to protectively coat Si NWs in a localized manner. Protection of Si NW under a prolonged (>3 h) HF vapor etch process has been achieved. Moreover, selective removal of the protection layer around Si NW is demonstrated at the end of the process. The proposed technology also offers access to localized surface modifications on a multiscale device architecture for biological or chemical sensing applications.

The continuous downscaling of nanoelectronics devices requires metrology solutions with sub-nanometer spatial resolution. Electrical scanning probe microscopy (E-SPM) techniques such as scanning spreading resistance microscopy have become important tools to map the electronic properties of these devices at nanometer scale using conductive diamond tips. Yet, the spatial resolution that can be achieved in an E-SPM measurement critically depends on the sharpness of the tip being used. Although much progress has already been made in optimizing the tip sharpness, cost-efficiently fabricated high-aspect-ratio diamond tips with ultra-high sharpness are still missing. Therefore, we have developed in this work a dry etching process for super sharp high-aspect-ratio conductive diamond tips, called hedgehog full diamond tips (HFDT), starting from standard low-aspect-ratio full diamond tips (FDT). The distinctive feature of our approach is the self-patterning etch step which benefits the high-volume production of such tips. The self-patterned mask is formed by nanoparticles originating from the interfacial layer deposited during the initial stage of the diamond growth, and metal particles from the surrounding metal cantilever material. In this work, we present our newly developed HFDTs and provide evidence that these tips outperform other conducting tips in terms of spatial resolution during E-SPM measurements.

In this work, we fabricate a hexagonal array of pillars where each pillar has a “micro-hoodoo” shape, i.e., a reentrant cross section. The shape of the pillars makes them more resilient towards total wetting, i.e., transition from a Cassie-Baxter non-wetting state to a Wenzel wetting state. We show the single-step fabrication of 4 × 4 mm² arrays by two-photon polymerization direct laser writing of the polydimethylsiloxane (PDMS)-derived commercial resin IP-PDMS. The use of a hydrophobic resin for rapid prototyping of reentrant structures enables the fabrication of surfaces patterns displaying superhydrophobic behavior despite the use of relatively simple structures, i.e. with a single reentrant surface. By changing the size of the micro-hoodoos and the packing density of the arrays, we map wetting behaviors ranging from the pinning of water droplets in Wenzel state to non-wetting Cassie-Baxter states. The measured contact angles follow quite well the theoretical results obtained by minimizing Gibbs free energy using the Wenzel, Cassie-Baxter and partial wetting theories. Among the tested micropatterns, five exhibited superhydrophobic properties, with a static contact angle with water as high as 158.1° ± 7.1°. This is the first demonstration of superhydrophobic surfaces produced by two-photon polymerization direct laser writing of PDMS in a single-step process.

Tactile sensing is an essential physical-electrical gateway in sensing technology. Creating such sensors is a complex challenge if the goal is to reproduce human-like sensation. Classical MEMS tactile sensor solutions in typical environmental conditions exist few types, but harsh conditions such as space technology or high-temperature range are not solved yet. One proposed material complex is the GaN/AlGaN system. In this study, we present an AlGaN/GaN MEMS force sensor for external force and load direction sensing in the mN range. The demonstrated sensor showed a sensitivity of 100 mV/N/V, which is an order of magnitude higher than the Si-based sensor with the same geometry. The sensing mechanism is based on the interface discontinuity between compound alloy layers, where two-dimensional electron gas (2DEG) is created and in which the carrier concentration can be linearly modulated by the internal crystal stress. The location of the sensing element was optimized by FEM simulation. The maximum load force of the samples varies with direction, which information allows the sensor to be used without fatigue and to obtain safety an electrical response signal under different external tensions. In addition to the advantage of this design for harsh environments, it is also possible to monolithically integrate active elements adjacent to the sensor for local acquisition and processing of the measured signal.

Through Random Telegraph Noise (RTN) analysis, valuable information can be provided about the role of defect traps in fine tuning and reading of the state of a nanoelectronic device. However, time domain analysis techniques exhibit their limitations in case where unstable RTN signals occur. These instabilities are a common issue in Multi-Level Cells (MLC) of resistive memories (ReRAM), when the tunning protocol fails to find a perfectly stable resistance state, which in turn brings fluctuations to the RTN signal especially in long time measurements and cause severe errors in the estimation of the distribution of time constants of the observed telegraphic events, i.e., capture/emission of carriers from traps. In this work, we analyze the case of the unstable filaments in silicon nitride-based ReRAM devices and propose an adaptive filter implementing a moving-average detrending method in order to flatten unstable RTN signals and increase sufficiently the accuracy of the conducted measurements. The τ_e and τ_c emission/capture time constants of the traps, respectively, are then calculated and a cross-validation through frequency domain analysis (Lorentzian fitting) was performed proving that the proposed method is accurate.