The Hewlett-Packard Company has developed a maskless method of patterning a carbon nanotube layer on a substrate with a laser beam. The laser beam is directed onto the surface of a carbon nanotube layered on a substrate. Relative movement between the laser beam and the first surface is caused, thereby forming at least one cavity feature on the substrate layered with a thin film of carbon nanotubes.
In U.S. Patent Application 20090311489, HP inventors Lynn Sheehan (Barndarrig, IE), Kevin Dooley (Blessington, IE) and Rory Jordan (Dublin, IE) detail a system and method for direct write patterning of carbon nanotube thin films for flexible, transparent, electronics applications using laser ablation. The system provides for large area, high resolution, patterning of carbon nanotube films. The patterning method is more efficient than other methods, such as photolithographic processes, since the patterning may be accomplished in one process step as opposed to multi-step photolithographic processes
The carbon nanotube film to be patterned is first produced by filtering a fixed quantity of the dispersion through a nitrocellulose membrane. After the film is set, the surfactant is removed via solvent washing. The membrane containing the nanotube film is then transferred to a substrate, and dried for 2 hours at 90.degree. C. The membrane is removed by dissolving the membrane in a suitable solvent, such as acetone. A number of solvent baths may be performed to ensure that the membrane is totally removed. This process results in a carbon nanotube film on a substrate, which can then be patterned into desired features. The thickness of the nanotube film can be controlled by changing the concentration of tubes in the solution.
The laser is an 11 W diode pumped solid state pulsed ultraviolet (UV) laser operating at 60 kHz. The laser generates UV laser light with a wavelength of less than 400 nm, and the wavelength is tied to energies that are equal to or higher than the bond energy of the material to be patterned The interaction between the carbon nanotube layer in substrate and the pulsed UV radiation results in the dissociation of certain chemical bonds in the carbon nanotube molecules, fragmenting it into smaller units. Above a specific threshold energy, carbon nanotube fragments are ablated from the surface of substrate. The amount of material that is ablated increases with increasing laser power.
A computer that contains pattern information also includes laser power control information, which defines the laser power that is to be used at the various points in the pattern followed by the laser beam. Based on the stored pattern information, a controller is configured to cause system to scan the laser beam over the substrate in any desired pattern, and form cavity features (e.g., channels or microchannels) in the substratein a single process step by modifying the laser power above and below the ablation threshold while scanning the laser beam across the substrate. The laser patterning performed by the Hewlett-Packard system provides a reduction in process steps, compared to conventional photolithographic processes, as it provides for the patterning of features in carbon nanotube films without the need for photo-masks and the associated develop processes.
Since their discovery in 1991, carbon nanotubes (CNTs) have attracted considerable attention from researchers because of their unique electrical, mechanical, and thermal properties. The remarkable electrical properties of carbon nanotubes make them ideal candidates for applications such as sensors, interconnects, transistors, and flat panel displays. These properties provide an opportunity to develop high performance flexible, transparent electrodes for use in various products. However, for successful implementation into products such as flexible electronics, it is desirable to have methods to deposit and pattern carbon nanotubes over large areas, at high resolution, and with processing temperatures that are compatible with plastics. In order to take advantage of the potential electrical and optical properties of carbon nanotubes, manufacturers will have to be able to pattern the materials into common electronic circuitry forms.
Inkjet printing of carbon nanotubes directly onto a substrate in a desired pattern has been previously proposed. However, such a process has the disadvantages of ink formulation for the carbon nanotubes, resolution limitations, and insufficient attachment to the substrates. Patterning techniques based on substrate and carbon nanotube chemistry interactions have also been previously proposed. This process has the disadvantages of very complicated chemical science, inconsistent results for pattern fill, and the need to pattern the attach chemical prior to attaching the carbon nanotubes.
Photolithographic processes have also been proposed. Such processes have the disadvantage of requiring several photolithographic and plasma etch steps to complete the desired pattern. Another proposal is to use laser trimming of carbon nanotubes using a copper mask system. This laser trimming method can produce patterns of carbon nanotubes defined by the copper grid mask. This method has the disadvantages that only patterns defined by the copper grid can be produced, and the laser exposure needs to be uniform over the area being patterned.
Hewlett-Packard inventors believe their use of laser patterning overcomes the limitations of the above processes.
Inkjet printing of carbon nanotubes directly onto a substrate in a desired pattern has been previously proposed. However, such a process has the disadvantages of ink formulation for the carbon nanotubes, resolution limitations, and insufficient attachment to the substrates. Patterning techniques based on substrate and carbon nanotube chemistry interactions have also been previously proposed. This process has the disadvantages of very complicated chemical science, inconsistent results for pattern fill, and the need to pattern the attach chemical prior to attaching the carbon nanotubes.
Photolithographic processes have also been proposed. Such processes have the disadvantage of requiring several photolithographic and plasma etch steps to complete the desired pattern. Another proposal is to use laser trimming of carbon nanotubes using a copper mask system. This laser trimming method can produce patterns of carbon nanotubes defined by the copper grid mask. This method has the disadvantages that only patterns defined by the copper grid can be produced, and the laser exposure needs to be uniform over the area being patterned.
Hewlett-Packard inventors believe their use of laser patterning overcomes the limitations of the above processes.
