The capillary filling speed of water in nanochannels with a rectangular cross section and a height on the order of 100nm has been measured over a length of 1cm. The measured position of the meniscus as a function of time qualitatively follows the Washburn model. Quantitatively, however, there is a lower than expected filling speed, which we attribute to the electro-viscous effect. For demineralized water in equilibrium with air the elevation of the apparent viscosity amounts up to 24±11% in the smallest channels (53nm height). When using a 0.1M NaCl (aq) solution the elevation of the apparent viscosity is significantly reduced.

We have developed a procedure for accurate fabrication of silicon-based nanochannels down to a few nanometer channel height, based on the use of a thin thermal silicon oxide spacer layer. Nanochannels with a predictable and carefully measured height between 5 and 50nm were successfully fabricated and filled with de-ionized water. For all channel heights the filling kinetics behaves according to the classical Washburn law for capillary filling, with a small correction for a loss of liquid at the moving front at a constant rate and a smaller than expected Washburn coefficient (up to a factor of 1.6 smaller for water in 5nm channels).

This paper discusses the modeling, design and realization of micromachined Coriolis mass flow sensors. A lumped element model is used to analyze and predict the sensor performance. The model is used to design a sensor for a flow range of 0-1.2 g h −1 with a maximum pressure drop of 1 bar. The sensor was realized using semi-circular channels just beneath the surface of a silicon wafer. The channels have thin silicon nitride walls to minimize the channel mass with respect to the mass of the moving fluid. Special comb-shaped electrodes are integrated on the channels for capacitive readout of the extremely small Coriolis displacements. The comb-shaped electrode design eliminates the need for multiple metal layers and sacrificial layer etching methods. Furthermore, it prevents squeezed film damping due to a thin layer of air between the capacitor electrodes. As a result, the sensor operates at atmospheric pressure with a quality factor in the order of 40 and does not require vacuum packaging like other micro Coriolis flow sensors. Measurement results using water, ethanol, white gas and argon are presented, showing that the sensor measures true mass flow. The measurement error is currently in the order of 1% of the full scale of 1.2 g h −1 .

In this paper a method is proposed to fabricate channels for fluidic applications with a depth in the nanometer range. Channels with smooth and straight sidewalls are constructed with the help of micromachining technology by etching shallow trenches into 110 silicon using native oxide as a mask material and OPD resist developer as the etchant. Sub-50 nm deep fluidic channels are formed after bonding the nanopatterned wafers with silicon or borofloat-glass wafers. The nanofabrication process is significantly simplified by using native oxide as the main mask material. The etch depth of the nanochannels is limited by the thickness of the native oxide layer, and by the selectivity of the oxide/silicon etch rate (estimated to be at least 250 for 110 silicon at room temperature).

We have realized a micromachined micro Coriolis mass flow sensor consisting of a silicon nitride resonant tube of 40 µm diameter and 1.2 µm wall thickness. Actuation of the sensor in resonance mode is achieved by Lorentz forces. First measurements with both gas and liquid flow have demonstrated a resolution in the order of 10 milligram per hour. The sensor can simultaneously be used as a density sensor.