New assembly of nanowires makes for stronger computer chips

A team of researchers in Oxford University’s Department of Materials led by Harish Bhaskaran, Professor of Applied Nanomaterials, have described a breakthrough approach to pick up single nanowires from the growth substrate and place them on virtually any platform with sub-micron accuracy. The innovative method uses novel tools, including ultra-thin filaments of polyethylene terephthalate (PET) with tapered nanoscale tips that are used to pick up individual nanowires. At this scale, adhesive van der Waals forces (tiny forces of attraction that occur between atoms and molecules) cause the nanowires to ‘jump’ into contact with the tips. The nanowires are then transferred to a transparent dome-shaped elastic stamp mounted on a glass slide. This stamp is then turned upside down and aligned with the device chip, with the nanowire printed gently onto the surface.

Deposited nanowires showed strong adhesive qualities and remained in place even when the device was immersed in liquid. The research team were also able to place nanowires on fragile substrates, such as ultra-thin 50-nanometre membranes, demonstrating the delicacy and versatility of the stamping technique. The researchers used the method to build an optomechanical sensor (an instrument that uses laser light to measure vibrations) that was 20 times more sensitive than existing nanowire-based devices.

Nanowires could enable major advancements in many different fields, from energy harvesters and sensors, to information and quantum technologies. In particular, their miniscule size could allow the development of smaller transistors and miniaturised computer chips. A major obstacle to realising their full potential has been the inability to precisely position them within devices. Most electronic device manufacturing techniques cannot tolerate the conditions needed to produce nanowires. Consequently, nanowires are usually grown on a separate substrate and then mechanically or chemically transferred to the device. In all existing nanowire transfer techniques, however, the nanowires are placed randomly onto the chip surface, which limits their application in commercial devices.

DPhil student Utku Emre Ali from the Department of Materials, who developed the technique, said that the new pick-and-place assembly process has enabled researchers to create “first-of-its-kind” devices in the nanowire realm. “We believe that it will inexpensively advance nanowire research by allowing users to incorporate nanowires with existing on-chip platforms, be it electronic or photonic, unlocking physical properties that have not been attainable so far. Furthermore, this technique could be fully automated, making full-scale fabrication of high quality nanowire-integrated chips a real possibility,” Ali said.

The full paper was published in the journal Small.

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