A buried vertical filter for micro and nanoparticle filtration

This paper presents a silicon micromachined filter concept suitable for separating micro- and nanoparticles. The filter is orientated vertically and buried beneath a silicon nitride surface layer. The vertically positioned structure accommodates highly uniform pores and allows for efficient use of die area while the buried aspect makes it possible for additional features to be integrated directly above the filter and its microchannels. The filter consists of a porous wall that is structurally defined inside the silicon substrate and is released, together with the microchannels, by isotropically etching the surrounding silicon. Fluidic experiments have confirmed the filtration functionality of fabricated devices using operating pressures up to 700 kPa. The proposed concept also offers the possibility to have built-in cleansing of the cake layer formed on the porous wall, by reversing the fluid flow.