Fabrication of AD/DA microfluidic converter using deep reactive ion etching of silicon and low temperature wafer bonding

The purpose of this work is to describe an original process that has been designed for the fabrication of a microfluidic converter. The fabrication is based on deep reactive ion etching of silicon and low temperature full wafer adhesive bonding. The technology development includes an improvement of the bonding process in order to produce an adaptive strength of SU-8 bond which not only ensures absence of debonding failures during the silicon deep etching procedure and the subsequent dicing procedure, but also avoids the potential SU-8 overflow leakage into channels due to the bonding step. Besides, the originality of the work is not only in the process but also in the design of the device. Common actuation method for microfluidic system is either based on closed-channel continuous-flow microfluidic (CMF) or droplet-based microfluidic (DMF). Both of them have advantages and disadvantages, and their integration on a single system is in dire need. In this paper, we briefly discuss the concept of microfluidic converter, integrating CMF with DMF, which can: (i) continuously preload reagents, (ii) independently manipulate several droplets, (iii) recombine and export samples into closed-channel continuous flow, making it ideal for interfacing to liquid-handling instruments and micro-analytical instruments.     

Two-dimensional simulation of local oxidation of silicon:calibrated viscoelastic flow analysis

Local Oxidation of Silicon (LOCOS) remains the common isolation technology for mass-production of integrated circuits. The work reported in this paper contributes to the improvement of the numerical modeling of the LOCOS process. A physical two-dimensional (2-D) modeling of the thermal oxidation of silicon has been developed based on the explicit treatment of the reaction expansion. The originality of this modeling is to propose a general solution taking into account of the silicon deformation, incorporating the viscoelastic behaviour of oxide and nitride and, particularly, giving a complete calibration of the stress-dependent parameters. The prediction capabilities are demonstrated by the calculations of oxide shapes and oxidation-induced stresses in a silicon substrate for very advanced isolation techniques     

Modeling and experimental validation of sharpening mechanism based on thermal oxidation for fabrication of ultra-sharp silicon nanotips

This paper aims at modeling the thermal oxidation of silicon pillars leading to the formation of very sharp silicon tips. The model is used to determine optimum process parameters with respect to the initial shape of the silicon pillars and the geometry of the desired tip. The modeling concept is to extend a previous approach, which predicts the oxidation mechanism of silicon cylinders versus their initial radius. The silicon pillar geometry is approximated by a superposition of silicon cylindrical structures featuring a local curvature radius. Experimental validation has been performed for several initial silicon pillar shapes, at 1000/spl deg/C and 1100/spl deg/C under dry oxidation conditions, leading to formation of very sharp silicon tips. The numerical predictions are shown to agree well with these experimental data. The motivation of this study aims at designing and fabricating a nanoelectromechanical filter device. Its vibrating part consists of a silicon nanotip, covered with a thin gold layer, the geometrical features of which affect the center frequency of the nanofilter device.     

Calibration of a two-dimensional numerical model for theoptimization of LOGOS-type isolations by response surface methodology

The models used for process simulation have to be carefully calibrated in order to insure a correct prediction of the topography and doping/stress profiles of microelectronic devices. With the current miniaturization of these devices, the requirements on the accuracy of the simulated results become greater, which puts more constraints on the calibration methodology. This is particularly the case for the silicon oxidation model, which is involved in numerous fundamental steps of an industrial process. In this paper, using response surface methodology, a viscoelastic oxidation model has been calibrated on a wide range of process conditions, which has allowed the optimization of LOCOS-type isolation structures for a 0.35-μm CMOS technology     

Techniques for mechanical strain analysis in sub-micrometer structures: TEM/CBED, micro-Raman spectroscopy, X-ray micro-diffraction and modeling

In this paper, three techniques are discussed that provide information on process-induced local mechanical stress in silicon: the convergent beam electron diffraction technique of transmission electron microscopy, X-ray micro-diffraction and micro-Raman spectroscopy. We discuss the principles of these techniques, their spatial resolution, the ease-of-use, the information that can be obtained, the required sample preparation, the measurement time, and the complementarities of these techniques. We demonstrate this for stress induced by shallow trench isolation and correlate the results to finite element analysis results.     

New Possibilities in the Dyeing of Wool

Meeting of the Scottish Region, held at Galashiels College of Technology, on 3 February 1972, Mr A. E. Edmondson in the chair The use of the auxiliary Unisol BT in the level and rapid dyeing of wool at 85–90d?C, with no adverse effect on the properties of the fibres, is described. The dyeing of wool-acrylic blends is also considered.     

Influence of the silicon nitride oxidation on the performances of NCLAD isolation

In order to study NCLAD isolation structures, a silicon nitride oxidation model has been studied and implemented in the process simulation program IMPACT-4. Comparing the models proposed by Kamins, Enomoto and Deal and Grove (DG), it appears that the DG model is the best trade-off between accuracy and easiness of implementation. The calibration against one-dimensional experimental data has been performed and reveals an excellent agreement. The use of this new modeling capability shows that the oxidation of silicon nitride cannot be neglected when optimizing a NCLAD structure. As a result, it has been possible to improve the topography of the oxidation stack of a recessed NCLAD structure in order to obtain the minimum bird's-beak punchthrough.     

Integrated 3-D Silicon Electrodes for Electrochemical Sensing in Microfluidic Environments: Application to Single-Cell Characterization

A microtechnology allowing the integration of thin metal electrodes and three dimensional highly doped bulk silicon electrodes on a hybrid PDMS/glass fluidic microchip has been developed. The fabrication involved anodic bonding of a silicon wafer onto glass substrate, deep reactive ion etching of 3-D bulk silicon electrodes, and plasma bonding of a PDMS microfluidic structure on a silicon/gold/glass substrate. The devices realized using this technology have been used for electrical impedance characterization of chemical and biological material. Microdevices with typical dimensions of hundreds of micrometers have been fabricated and tested in the determination of the conductivity of NaCl solutions. Smaller sensors, with critical dimensions under 10 m, have been achieved for single-cell characterization. Human hepatocellular liver carcinoma cells have been introduced in the microimpedance sensors. Measurements show the interfacial relaxation of the cellular membrane in the range. It is expected that other electrochemical sensors and electrokinetic actuators can benefit from this technology.     

Zipping effect on omniphobic surfaces for controlled deposition of minute amounts of fluid or colloids

When a drop sits on a highly liquid-repellent surface (super-hydrophobic or super-omniphobic) made of periodic micrometer-sized posts, its contact-line can recede with very weak mechanical retention providing that the liquid stays on top of the microsized posts. Occurring in both sliding and evaporation processes, the achievement of low-contact-angle hysteresis (low retention) is required for discrete microfluidic applications involving liquid motion or self-cleaning; however, careful examination shows that during receding, a minute amount of liquid is left on top of the posts lying at the receding edge of the drop. For the first time, the heterogeneities of these deposits along the drop-receding contact-line are underlined. Both nonvolatile liquid and particle-laden water are used to quantitatively characterize what rules the volume distribution of deposited liquid. The experiments suggest that the dynamics of the liquid de-pinning cascade is likely to select the volume left on a specific post, involving the pinch-off and detachment of a liquid bridge. In an applied prospective, this phenomenon dismisses such surfaces for self-cleaning purposes, but offers an original way to deposit controlled amounts of liquid and (bio)-particles at well-targeted locations.