Nanoporous silicon nitride membranes fabricated from porous nanocrystalline silicon templates

Abstract

The extraordinary permeability and manufacturability of ultrathin silicon-based membranes are enabling devices with improved performance and smaller sizes in such important areas as molecular filtration and sensing, cell culture, electroosmotic pumping, and hemodialysis. Because of the robust chemical and mechanical properties of silicon nitride (SiN), several laboratories have developed techniques for patterning nanopores in SiN using reactive ion etching (RIE) through a template structure. These methods however, have failed to produce pores small enough for ultrafiltration (<100 nm) in SiN and involve templates that are prone to microporous defects. Here we present a facile, wafer-scale method to produce nanoporous silicon nitride (NPN) membranes using porous nanocrystalline silicon (pnc-Si) as a self-assembling, defect free, RIE masking layer. By modifying the mask layer morphology and the RIE etch conditions, the pore sizes of NPN can be adjusted between 40 nm and 80 nm with porosities reaching 40%. The resulting NPN membranes exhibit higher burst pressures than pnc-Si membranes while having 5× greater permeability. NPN membranes also demonstrate the capacity for high resolution separations (<10 nm) seen previously with pnc-Si membranes. We further demonstrate that human endothelial cells can be grown on NPN membranes, verifying the biocompatibility of NPN and demonstrating the potential of this material for cell culture applications.

Modification of Nanoporous Silicon Nitride with Stable and Functional Organic Monolayers

“…Affinity encoded, surface-grafted peptides or other organic molecules could improve the specificity of membranes used in sensors of biological or hazardous molecules. We recently introduced ultrathin nanoporous silicon nitride (NPN) 10 as a more mechanically robust, more chemically stable, and lower-cost alternative to the original nanomembrane material made from pure silicon. 11 Our objective in this work is to develop a general strategy for the coating of NPN with stable organic molecules that add functionality without diminishing the benefits of high permeability and size selectivity of the nanomembranes.…”

DNA Translocations through Nanopores under Nanoscale Preconfinement

“…This essentially creates an architecture comprising two pores in series. NPN is a recently developed highly porous nanomembrane technology with tunable pore sizes (20 – 80 nm) and porosities (1–40%) 29 . The gap between the nanofilter and SiN membranes is achieved through the lithographic patterning of a hexagonal grid of 1 µm diameter holes in a 200-nm thick SiO 2 layer deposited on top of SiN.…”

Protein Separation and Hemocompatibility of Nitride Membranes in Microfluidic Filtration Systems

“…The ultrathin NPN membranes are fabricated in silicon chips via a transfer etch process [4]. The pore pattern is formed into a hard mask on the surface of a silicon wafer by rapid thermal annealing of a stack of materials whose properties, along with the anneal parameters, control the pore size and density [12].…”

“…Our group has developed nanoporous silicon nitride (NPN) membranes for inclusion in a small format HD device. These membranes, which were first described by our group four years ago [4], are 100 to 1000 times thinner than conventional HD membranes and are therefore orders-of-magnitude more efficient for dialysis [5]. In fact, given the molecular thickness of these membranes (~15 nm to ~75 nm) and their appreciable porosity (~15%), NPN membranes operate near the maximum permeability that is achievable for a nanoporous membrane [5–10].…”