Ink Delivery by Noncontact Methods

The development of methods enabling to deliver liquid on a surface without any contact has attracted a lot of attention. The main advantage of these methods is their compatibility with any type of substrates, especially those with irregular surfaces that are difficult to pattern in direct contact. Nevertheless, the downscaling of these techniques is a challenging issue. In the following, we briefly review several strategies that have been pursued to produce and deliver ink droplets. 

Inkjet printing is also quite promising for the deposition of biological compounds since it preserves their functionality and is used for the fabrication of functional bioarrays7 Another application of this noncontact deposition method is the functionalization of fragile structures such as cantilever-based biosensors.  

Despite its potential, inkjet printing cannot accommodate a drastic downscaling. The constraints mainly come from the surface tension, which increases the pressure gradients required to form droplets, and viscous dissipation, which dramatically decreases liquid flows at small scale. As a consequence, the direct printing of features much smaller than 10 qm is rather unlikely. 

In-plane emitters with aperture width as small as 20 nm were also designed using micromachining techniques and can be compatible with parallelization, although these silicon-based sources have not yet been used for surface patterning. 

E-jet printing techniques are thus very attractive to pattern surfaces with liquids at submicron scale. Nevertheless, the use of high voltages (typically 1,000 V) requires a complicated setup. The alignment on predefined structures, which is a strong requirement in order to combine with other lithographic techniques, is also a challenging issue with noncontact methods and may limit their application. 

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