Surface Acoustic Wave (SAW) technique is one of the most promising MEMS-based detection systems for gas sensing. It depends on the modulation of SAW to detect the target gases. The benefits of an acoustic wave hydrogen sensor include high sensitivity, simplicity, stability, quick response time, etc. The SAW sensor converts an input electrical signal into an acoustic wave which can be easily influenced under mass loading. The change in amplitude, phase, frequency or time-delay between the input and output electrical signals can be used to measure the presence of hydrogen. In the present work, the SAW sensor was designed and fabricated for a resonant frequency of 100 MHz on a Lithium Niobate substrate with palladium (Pd) thin film as the sensing layer. The sensor exhibited linear shift in resonant frequency as a function of hydrogen concentration.
Fabrication of Microfluidic devices have gained popularity in a wide range of application demanding fluid flow control such as Anti-microbial resistance, Integrated blood test systems, drug delivery system, protein separation, DNA extraction, in- vitro diagnostic studies, lab-on-a-chip, organ-on-a-chip, inkjet printers and other industrial sensors. Fluid flow regulation, on/off switching and sealing of fluids can be achieved by incorporating Microvalves. The shape of the microvalve plays a key role in desired actuation of the microvalves. Therefore, a detailed study of various structures of the microvalve is crucial. This work discusses about the stability and reliability of different microvalve shapes. Simulation work gives a comparative study showcasing the displacement of the microvalve thin film polymer layer on account of applied pressure on several shapes of same area. Furthermore, details of stress distribution for the same has been carried out. The analysis focusses on the circular, elliptical and capsule shapes of the microvalve. The comparative study of the simulation results revealed that the maximum stress experienced by the microvalves of circular shape is 1.1 times lower than that of elliptical shape. While, circular shape microvalve shows 1.22 times lower stress when compared to capsule shape. In addition, displacement of the circular shape microvalve is 1.33 and 1.31 times greater than elliptical and capsule shapes for the same area and applied pressure respectively. The study manifests that the circular shape microvalve performance indicate better stable actuation when compared to the rest of the shapes. Microfabrication of the same is carried out using dry film photoresist which is highly cost effective.
This article [J. Micro/Nanolith. MEMS MOEMS. , 12, (3 ), 033020 (2013)] was originally published online on 25 September 2013 with errors in the authors’ names.
The names originally appeared as Lakshminarayanan Sujatha, Murali Siddhartha Goutham, Mani Saravanan, and Varatharajan Subramani Selvakumar. The corrected names appear above.
All online versions of the article were corrected on 27 September 2013. The article appears correctly in print.
Recently, microgrippers are finding more importance in the field of tissue engineering and microassembly in semiconductor electronics. Large force and, hence, large displacement, low power, and low temperature are the essential features to be considered during the design of the microgrippers. The electrical and mechanical behaviors of electrothermally actuated silicon microgrippers are presented. The effect of increasing the flexure length and the cold arm area to improve the displacement is discussed. These microgrippers are normally of the open type, in which the arms have an initial open gap of 20 μm, and they move away from each other with the applied voltage. The displacement of each arm is observed to be 24 μm for the applied voltage of 10 V. The response time of the device is less than 5 ms, and the maximum power dissipation is 110 mW. The displacement of the microgrippers can be increased with increased flexure length and cold arm length with short extended arms. This structure also shows lower stress.
Due to the low Young's Modulus of porous silicon (PS), Si/PS composite membranes - where the silicon membrane is
converted into PS to a certain depth - deform more than silicon membranes and hence MEMS pressure sensors with
composite membranes have higher sensitivity. But the Si/PS composite membranes exhibit a smaller range of linear
response with applied pressure than silicon membranes with the linear range being less for Si/microPS as compared to
Si/macroPS composite membranes. In addition, while the composite membrane deformation saturates at high pressures
like silicon membranes, the deformation is irreversible unlike that seen with silicon membranes within reasonable limits.
With the possibility that the irreversible deformation could be due to stiction force between the collapsed pore walls at
high pressure, we investigate the effect of formation of self-assembled monolayer (SAM) antistiction coating on the
performance of Si/PS composite membranes.
Since porous silicon (PS) has a much lower Young's modulus than single crystalline silicon, Si/PS composite membranes deflect more and can be used to fabricate pressure sensors with improved sensitivity. However, PS has some drawbacks, like weaker structural stability and being more susceptible to humidity due to its large surface-to-volume ratio. We discuss the fabrication and testing of Si/PS composite membrane pressure sensors with MicroPS and MacroPS of varying porosity. For the same porosity, the composite membranes with Si/MicroPS show higher sensitivity than Si/MacroPS. The sensor output is linear and repeatable at pressures less than 1 bar. The deformation of composite membranes measured up to 10 bar showed that it saturates at high pressure and is irreversible. Composite membranes also exhibit higher offset voltage than single crystal silicon membranes, which could be attributed to the stress developed in the membrane during PS formation and subsequent processing. The composite membrane pressure sensors were packaged on TO 39 headers, and the effect of humidity and temperature variation were investigated.
Since porous silicon (PS) has a lower Young's Modulus as compared to silicon, Silicon/Porous Silicon (Si/PS)
composite membranes are expected to show higher sensitivity as compared to membranes of silicon alone. In this paper
we discuss the fabrication and testing of Si/PS composite membranes where a part of the silicon membrane depth is
converted into PS. Composite membranes with Si/ microPS and Si/ macroPS were fabricated with varying porosity and
same thickness. The composite membranes with micro PS show higher sensitivity than composite membranes with
macro PS. Formation of microporous and macroporous silicon produces stress on the membrane varying with the
porosity. The variation in compressive stress on the membrane with porosity for both micro and macro PS has been
studied by measuring the deformation of the composite membrane with a surface profiler and the stress is found to be
larger for microPS. The compressive stress results in an increase in the offset voltage by more than an order of
magnitude for composite membranes with porosity above 50% as compared to one with a single crystalline silicon one.
Though the composite membranes exhibit saturation and hysteresis at higher pressures, the response is linear and
repeatable at pressures below 1 bar making this a viable option for sensing low pressures.
Porous Silicon (PS) has many interesting and unique properties that make it a viable material in the field of MEMS. In this paper we investigate the application of PS in improving the sensitivity of bulk micromachined piezoresistive pressure sensors. A part of the silicon membrane thickness has been converted into PS by electrochemical etching in HF based electrolyte. The property of low Young's modulus of PS and its dependence on porosity have been exploited in obtaining higher sensitivity compared to pressure sensors with single crystalline silicon membranes. The sensitivity is found to increase with the porosity and thickness of PS layer and these can be easily controlled by varying the PS formation parameters.
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