Thursday, May 03, 2007

SmartTip 's NanoProbe Fountain Pen - a Dip Pen Nanolithography Tool

SmartTip is an unusually innovative spinoff of the Netherlands' University of Twente's division of Transducer Science and Technology (formerly called MicMec), which has done prodigious amounts of R&D in micromachining of all kinds of microsensors and actuators, including the more conventional mems structures like pressure sensors and accelerometers and other more novel devices.

I enjoyed reading dissertations from Twente's institute, as invariably the research was fascinating, and often novel, and always well characterized. I learned of Twente's efforts when I was at IC Sensors, and Hal Jerman and Steve Terry had a couple of the interesting dissertations around the offices, which made for fascinating reading. Plus on staff there was an engineer Dedrick DeBruin, who came from Twente if I am not mistaken...

So recently it seems after SmartTip's few earlier efforts at mildly novel nanoprobe developments for SPM / AFM (notably the Canticlever for magnetics MFM and related devices), SmartTip is fielding an inking type scanned nanoprobe, derived from a standard atomic force microscope cantilever. The firm is calling the devices Fountain Pens and is going into a beta type customer sampling to learn of the application subtleties before attempting to field a product on a larger scale.

While there is little reference to Dip Pen Nanolithography at SmartTip's page, close examination of the mechanism used, seems like this is what it may very well be doing (ie using DPN(tm) 's described ink transfer methods), although not with dipping to preload the tip for wicked type inking from a solid tip nib. It is a curious connection...

The Smart Tip [aka DPN(tm)] Fountain Pen devices have taken a more common low stress silicon nitride AFM cantilever and incorporated an inking well in the body of the otherwise solid pyrex glass chip, drilled 1-2 holes in the pyrex and incorporated some recesses in the glass using the otherwise normal anodic bond side glass etch, and then added a fluid channel in the cantilever arm(s), plus an inlet coupling the cantilever fluidic channel to the pyrex glass region's ink well, and a tiny etched outlet from the far end of the fluidic channel just near the back of the pyramidal molded silicon nitride AFM tip.

[ed - postscript MAY 24th 2007 - this picture linked above, hints at the potential for IP in useful systems integration of continuous feed microfluidics, beyond the mere static reservoir shown in the hole drilled in the glass existing chip's design.

A systems level integration for near continuous feed, would embody an external larger reservoir, linked to the chip level reservoir which might include tubing, a demountable compression seal at the top of the drilled glass substrate chip and various combinations of external / internal valving, sensors for flow and level / volume remaining, and even integrated electrochemical sensors.

This basic device platform also might permit /enable microvalve fluidic chemistry switching either remotely with longer cycle time / dead volume or more closely coupled fluidic switching closer to the cantilever or a multi microvalve manifold microfabricated on or near the cantilever, even best near the tip to reduce the dead volume of chemistry switching from multiple microvalves - Mark Wendman]

Interesting structure, but possibly not novel enough? Granted this seems to be the 1st commercially fielded AFM cantilever that incorporates and integral microfluidic channel(s) in the cantilever arm, but it still seems to be a device using Dip Pen Nanolithography methods, as DPN(tm) if I am not mistaken, is described more generally as what transpires at a solid Tip apex to wick a meniscus of fluid to the scanned surface just as an ink nib does conventionally.

Also DPN(tm) is not restricted to applications that require dipping per se to provide the ink supply, but I might be mistaken, even if the name DPN(tm) implies dipping, the actual technology might not stipulate this with restrictions of DPN(tm) to dipped supply of "inks".

In short, DPN(tm) likely includes cases in which the fluidic supply to the tip is integrated into the cantilever, and specifically with cases of cantilever incorporates a microfluidic channel.

There seems to be a novel configuration enabled by the integrated inkwell and fluidics channel - where on this web page at Twente is described that the MFP probe enables AFM-based electrochemical conductor deposition by connecting the metal electrode on top of the probe chip (anode) and the sample substrate where conductor deposition is intended (cathode) to a bias power supply. The electrical circuit is formed using the electrolyte solution in the cantilever microchannels. The deposition is voltage regulated since well performing currents for this method are very tiny.

Regrettably they as yet have not acheived electrodeposit linewidths much smaller than 250nm, which I suspect might be due to the substrate spreading resistance, or the gap between the hole at the end of the microfluidics channel being further away from the tip apex. It could also be possible that the electrical biases and writing speeds need further optimization?

I like the structures, even if the ideas might not be as novel with respect to technology as Twente's MicMec / SmartTip might otherwise hope for.

In the Beta Field testing, I'd guess that 3 critical aspects of the device's features are implicitly being evaluated - 1] the fluid channel of the cantilever(lever stiffness and fluidics flow for various sample fluid viscosities), 2] the diameter of the fluid channel opening, in proximity to the tip (just behind the tip ) and 3] the desired sharpness of the tip...

Additionally one might ask if the reflected spot quality from the lever backside AFM laser reflection is in any way affected by the fluidics channel. This largely will be determined by how the fluidics channel fabrication was integrated into the cantilever process ( ie how flat the resulting reflecting surface is so that laser spot quality is not excessively degraded).

Fascinating stuff ...

note - DPN(tm) is a trademark of NanoInk inc.
Dip Pen NanoLithography is also a trademark of NanoInk, but has been used in academic contexts before trademarking


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