KEYWORDS: Silicon, Etching, Semiconducting wafers, Photomasks, Wet etching, Deep reactive ion etching, Optical components, System on a chip, Reflectors, Dry etching
Development of silicon-based passive optical components such as reflectors, waveguides, and beam splitters coupled with active elements such as light emitters and detectors enable miniaturisation of a low-cost system-on-a-chip sensing device. In this work, we investigate methods to fabricate passive silicon elements on a chip. We use a combination of wet and dry etching techniques to realise angled and vertical sidewalls normal to the surface of a silicon wafer, respectively. For wet etching, we used Triton-X, a surfactant, added to an alkaline solution TMAH as the etchant. This allows perfect 45° inclined sidewalls to be fabricated. Dry etching using DRIE is to be performed on the reverse-side of the same wafer to realize through-hole vias with straight vertical sidewalls. A final Au metal layer can then be coated onto the sidewalls to realize reflective surfaces. Photolithography masks used in the wet and dry etch processes were designed and fabricated. By careful alignment of these masks using a mask aligner, we can fabricate a combination of inclined and vertical sidewalls to build optical reflectors and beam splitters with complex geometries. When integrated with active Si-optical devices, a fully integrated micro-optical system-on-a-chip can be realised.
KEYWORDS: Tissues, In vitro testing, Microfluidics, Silicon, Systems modeling, In vivo imaging, Semiconducting wafers, Natural surfaces, Microfabrication, Interfaces
In recent years there has been growing interest in micro engineered in-vitro models of tissues and organs. These models are designed to mimic the in-vivo like physiological conditions with a goal to study human physiology in an organ-specific context or to develop in-vitro disease models. One of the challenges in the development of these models is the formation of barrier tissues in which the permeability is controlled locally by the tissues cultured at the interface. In-vitro models of barrier tissues are typically created by generating a monolayer of cells grown on thin porous membranes. This paper reports a robust preparation method for free standing porous cyclic olefin copolymer (COC) membranes. We also demonstrate that gelatin coated membranes facilitate formation of highly confluent monolayer of HUVECs. Membranes with thickness in the range of 2-3 um incorporating micro pores with diameter approximately 20 um were fabricated and integrated with microfluidic channels. The performance of the device was demonstrated with a model system mimicking the endothelial barrier in bone marrow sinusoids.
The paper investigates conditions for depositing perovskite-oriented strontium-doped lead zirconate titanate (PSZT) thin films using RF magnetron sputtering. PSZT is a material that can exhibit high piezoelectric and ferroelectric properties. The deposition was conducted using an 8/65/35 PSZT sputtering target. The effects of sputtering conditions and the deposition rates for films sputtered onto several surfaces (including gold and platinum coated substrates) were studied. Combinations of in-situ heating during sputtering and post-deposition Rapid Thermal Annealing (RTA) were performed and resulting phases determined. RTA was carried out in argon to observe their effects. The sputtered films were analyzed by Scanning Electron Microscopy (SEM), X-ray Diffractometry (XRD), and X-Ray Photoelectron
Spectroscopy (XPS). Results show dramatic differences in the grain structure of the deposited films on the different surfaces. The stoichiometry of the sputtered films is demonstrated using XPS. In the case of gold and platinum coated substrates, sputtering was also carried out for different durations, to establish the growth rate of the film, and to observe the variation in grain size with sputtering duration. The deposited thin films were resistant to most chemical wet etchants and were Ion Beam Etched (IBE) at 19 nm/min.
In this paper, the design of a thin film thermoelectric microcooler module is examined. The module consists of n-type bismuth telluride and p-type antimony telluride thermoelectric materials. The commercial software CFD-ACE+ is used to implement and analyse the model. A two-dimensional coupled electrical and thermal synthesis was performed. The influence of the thickness of the thermoelectric materials on the change in temperature has been investigated. The thickness of the thermoelements was varied between 0.5 and 20 μm. The device performance in terms of change in temperature with and without a load has been studied. The optimal thickness for the thermoelements was found to be 2μm. At 30mA, a temperature difference of 3K below ambient was obtained.
A layered Surface Acoustic Wave (SAW) hydrogen gas sensor, based on a delay line structure with 64 finger pairs on input and output port, is fabricated on 64° Y-cut, X-propagating LiNbO3 substrate. A guiding layer of ZnO is used to increase the sensitivity of the structure. A WO3 selective layer is employed to H2 gas sensing applications at different operating temperatures between room temperature and 300°C. In this paper, the fabrication process of WO3/ZnO/64° YX LiNbO3 sensor is described and the sensor’s response features are analyzed. The improvement of the response with the addition of a gold catalytic layer on the sensor surface is also investigated.
A comparison between the performance of conductometric and layered surface acoustic wave (SAW) hydrogen sensors is presented. Both sensor structures employ an R.F. magnetron sputtered tungsten trioxide (WO3) thin film as a selective layer for hydrogen (H2) sensing applications. The conductometric device is based on an alumina substrate, while the layered SAW device structure is fabricated on a 36° Y-cut, X-propagating LiTaO3 substrate with a zinc oxide (ZnO) guiding layer. The sensors were investigated for different operational temperatures and various concentrations of H2 in synthetic air.
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