In this study, a numerical investigation is presented to characterize the transient behaviors of microdiffuser pumps. The motivation of the present work is to clarify the scaling and dynamic effects on the flow rectification of microdiffuser pumps. Two primary parameters, half angle (θ = 5° to 55°) and excitation frequency (f = 1 Hz to 1000 Hz), are considered. A time-dependent sinusoidal pressure with fixed pressure amplitude is applied at the inlet as the boundary condition. Different from previous investigations and despite the corresponding low Reynolds numbers, circulation is observed for all tested half angles and excitation frequencies. The persistence of the backflow helps to augment flow rectification since the vortical structures block a portion of the diffuser and prevent the through flow from decelerating. Contrary to past claims, diffusers with larger half angles show better rectification effects for 5° ⩽ θ ⩽ 35°. For θ > 35°, the net flow rate is nearly independent of the half angle. The computational results also yield that the net flow rate is independent of excitation frequency for f < 25 Hz but decreases with increased frequency for f > 25 Hz. Hence, the role of excitation frequency is classified into three different regimes by the Roshko number: frequency independent regime (Ro < 0.25), transition regime (0.25 < Ro < 2) and frequency dependent regime (Ro > 2). An essential contribution of this study is that it provides design guidelines for microdiffuser pumps, further expanding the knowledge of flow rectification properties to make more efficient use of microdiffuser pumps in various microscopic applications.
This study presents a novel CMOS-MEMS out-of-plane linear accelerometer. This capacitance-type accelerometer contains specially designed gap-closing sensing electrode arrays with on-chip fully differential sensing circuits. Moreover, the comb-finger electrodes have the characteristics of the high fill factor and sub-micron gap to increase the sensing capacitance. Thus, the sensitivity and signal-to-noise ratio can be further improved. This study has established a post-CMOS wet-etching process to realize the accelerometer with sensing electrodes of the sub-micron gap in the out-of-plane direction. The present accelerometer has been demonstrated using the standard TSMC 2P4M process plus the post-release technique. The measurement results demonstrate that the accelerometer has a sensitivity of 1.14 mV g−1, and a nonlinearity of 3.4%.
The effect of diamondlike carbon (DLC) films coated by pulsed laser deposition technique on the electron emission characteristics of Mo tips is examined. Turn-on voltage (V0) was lowered from 40 V for Mo tips to 22 V for DLC coated Mo tips and maximum anode current (IA) was increased from ∼44 μA for Mo tips to ∼2.0 mA for DLC coated Mo tips. Maximum anode current (IA) for the DLC coated Mo tips, however, decreased during operation. Raman spectroscopy and selected area diffraction (SAD) in transmission electron microscopy (TEM) revealed that the degradation of electron emission behavior can be ascribed to the conversion of sp3-bonds, characteristic for diamond, to sp2-bonds, characteristics for graphite. The transformation of the structure is assumed to be induced by the local heat from the DLC coatings.
This paper presents a novel single proof-mass tri-axis capacitive type complementary metal oxide semiconductormicroelectromechanical system accelerometer to reduce the footprint of the chip. A serpentine out-of-plane (Z-axis) spring is designed to reduce cross-axis sensitivity. The tri-axis accelerometer has been successfully implemented using the TSMC 2P4M process and in-house postprocessing. The die size of this accelerometer chip containing the MEMS structure and sensing circuits is 1.78 × 1.38 mm, a reduction of nearly 50% in chip size. Within the measurement range of 0.8 ∼ 6G, the tri-axis accelerometer sensitivities (nonlinearity) of each direction are 0.53 mV/G (2.64%) for the X-axis, 0.28 mV/G (3.15%) for the Y-axis, and 0.2 mV/G (3.36%) for the Z-axis, respectively. In addition, the cross-axis sensitivities of these three axes range from 1% to 8.3% for the same measurement range. The noise floors in each direction are 120 mG/rtHz for the X-axis, 271 mG/rtHz for the Y-axis, and 357 mG/rtHz for the Z-axis. Index Terms-Complementary metal oxide semiconductor (CMOS)-MEMS, tri-axis accelerometer. I. INTRODUCTIONS MALL SIZE, low cost, multifunction, low power consumption, and easy integration with consumer electronics are some of the primary design issues for commercial microelectromechanical system (MEMS) applications such as inertia sensors and microphones. Various approaches have been reported to meet the related design requirements. The fabrication of micromechanical components using existing IC foundries provides a promising option to realize MEMS sensors. MEMS sensors can be fabricated by means of a complementary metal oxide semiconductor (CMOS) process together with post-CMOS processing, named the CMOS-MEMS process [1].
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