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This work presents design, fabrication and optimization of methanol concentration and flow channel cross-sectional geometry for enhanced power output in passive micro-direct methanol fuel cells. Passive micro-direct methanol fuel cells are fabricated with flow channels in silicon having both rectangular and trapezoidal cross-sectional geometry for flow of methanol at anode and air at cathode using microelectromechanical systems (MEMS) fabrication technique. The experiments are conducted at 25 °C by feeding methanol with a flow rate of 25 μl min −1 and supply of air at cathode by air-breathing method. Results show a peak in open circuit voltage and power density at 7 M methanol concentration for passive micro-direct methanol fuel cells having both rectangular and trapezoidal cross-sectional geometry. A study of influence of silicon flow channel cross-sectional geometry on passive micro-direct methanol fuel cell performance shows for the first time that the flow channels with trapezoidal cross-section enhance the power density (6.64 mW cm −2 ) nearly by a factor of two compared to that of flow channels with rectangular cross-section (3.9 mW cm −2 ) at 7 M methanol concentration.We believe that, though our results of significant enhancement of power density with trapezoidal fuel flow channels are obtained with micro-direct methanol fuel cells as a platform, they should also be applicable to other proton exchange membrane fuel cells with ethanol or humidified hydrogen as fuel.

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Low frequency piezoelectric P(VDF-TrFE) micro-cantilever vibration sensors have been developed for the first time with a novel MEMS process. Design and simulation of microcantilevers were carried out using COMSOL Multiphysics based on finite element method. Frequencies and device dimensions were determined based on simulation results. The design was implemented on 〈110〉 Si wafer using a specially developed bulk micromachining process. Micro-cantilevers were fabricated with 2.5 μm thick P(VDF-TrFE) co-polymer film deposited by spin coating technique; electrodes for power output were formed by sequential thermal evaporation of Cr-Au thin films. The two critical process steps used for the suspension of P(VDF-TrFE) micro-cantilevers are: (1) bulk micromachining of silicon from the backside using anisotropic wet etchant TMAH to define the micro-cantilever suspension regions, and (2) CHF 3 /O 2 based plasma etching of SiO 2 from backside for the final release of P(VDF-TrFE) micro-cantilevers. These devices were operated in longitudinal mode with Cr-Au interdigitated electrodes on P(VDF-TrFE) micro-cantilevers for power extraction. The experimental results obtained with laser Doppler vibrometer for micro-cantilevers with 1000 μm length, 300 μm width and 2.5 μm thickness showed resonant frequency 477.03 Hz and power output 187.4 pW for tip displacement 312.5 μm which are closely in agreement with the simulated values 453.65 Hz and 189 pW for tip displacement 310 μm, respectively. The volume power density of this P(VDF-TrFE) unimorph micro-cantilever is 249.92 nW mm −3 , which is found to be better compared with other polymer piezoelectric cantilevers.

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