Characterization of gas transport through micromachined submicron channels in silicon

Abstract

Gas transport through narrow channels etched in a silicon surface is characterized by mass-spectrometric measurements. The channel structures consist of 33 parallel 100 nm deep and 5 cm long channels, i.e. with a L d ratio of 500,000. which appears to be among the largest experimental ratios reported on so far. Some unexpected findings regarding for example diffusion time lag and its dependence on molecular mass and absolute pressure are reported. Furthermore, the possibility to study wall induced reactions is demonstrated by the water formation reaction on channel walls modified with a thin layer of platinum. The observations are discussed in relation to models for Knudsen flow through narrow capillaries. The main purpose is, however, to point out the special features of micromachined channels for the study of gas transport and chemical reactions controlled by the properties of the channel walls.