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New method to self-assemble block copolymers will pave way for ultra-high density memory devices |
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In the past 2-3 decades, researchers have been able to increasingly shrink the size of devices and the size of the patterns to make electronic data storage devices.
A striking development in the field of polymer self-assembly could possibly spell wonders for electronic data storage and microelectronics industry alike.
At a time where demands for ultra-capacity data storage are on a high, a step-change innovation and easy-to-implement technique has developed by American scientists at University of California, Berkeley, and the University of Massachusetts, Amherst. The new process relies on cutting commercially sapphire crystal at an angle and then heating it to a particular temperature. As a result, the atoms of cut crystal rearrange themselves in a series of parallel ridges resembling a saw tooth topography on a microscopic scale. On such a highly patterned surface, scientists allowed to self-assemble block copolymer thin films into highly ordered, precise, ultra-dense nanoscopic cylinders erecting from crystal�s surface. With this technique, the researchers achieved defect-free arrays of nanoscopic microdomains (of block copolymers) each as small 3 nanometers in length, translating into densities of 10 terabits per square inch (One terabit is equal to 1 trillion bits, or 125 gigabytes).
It does not depend upon the time-consuming and cumbersome nano-lithographic processes widely used in semiconductor industry. The researchers indicate that this new �bottom-up� approach of creating highly dense, orderly patterns on 1 sq. inch area will make the process more rapid and less troublesome as opposed to electron beam lithography. The microscope images of the new approach reveal that each microdomains appear as hexagonally packed dots with arrangements readily directed by the parallel ridges of sapphire crystal.
In currently available data storage devices, the bits (microdomains) are tiny non-uniform sized magnetic areas spread across the substrate. Researchers have earlier tried to exploit the self-assembly characteristic of block copolymers to be used in semiconductor manufacturing. However, a major obstacle has been the break-down in order of microdomains as the span of area increases. As a result, the individual domains cannot be read or written to, rendering them useless as a form of data storage. To solve the size constraint, the team layered a film of block copolymers onto the surface of a commercially available sapphire crystal. When the crystal is cut at an angle - a common procedure known as a miscut - and heated to 1,300 to 1,500 degrees Centigrade for 24 hours, its surface reorganizes into a highly ordered pattern of sawtooth ridges that can then be used to guide the self-assembly of the block polymers.
The new method revealed dots, only 3 nanometers in size and each equidistant from the other, are spaced at a density of 10 terabits/sq. inch. Researchers indicate that the density achievable with this new technology could one day enable the contents of 250 DVDs to fit onto a surface the size of a quarter. While other teams are engaged to solve the size barrier of self-assembled block copolymers, the new project shows immense potential since it is cost effective, easy-to-implement and quick. In addition, the new method is environmentally friendly as compared to optical lithographic techniques which employ lot of toxic chemicals and acids. UC Berkeley and UMass Amherst have filed a joint patent on this technology.
Nevertheless, the size of the ultra-dense block copolymer array depends not only on the size of the sapphire crystals but also on the temperature at which the crystal is heated. The angle and depth of the sawtooth ridges can be affected by changing the temperature at which the crystal is heated. In addition, some researchers strongly believe the formation of 10 terabit/square inch block copolymer array is but a small stride in developing ultra-density multi-terabytes memory storage systems. Additional areas to delve deeper include efficient methods to read and write the densely packed nanoscopic elements. On the other hand, the 10-terabit array of block copolymers formed in a single step on oriented one square inch sapphire crystal opens up a multitude of promise. The polymer which sits at center of every single dot (or bit) can be removed by treating the thin film copolymer coating with a solvent, leaving a nano-sieve for use as a template for a number of applications. Obvious applications of the technique include fields like data storage, nanowires or any highly precise nanoscopic structures for use in electronic devices. More so, the new method is also slated to help develop highly efficient solar cells in future.
In another research, a team from the University of Wisconsin-Madison and Hitachi Global Storage Technologies has reported a way to improve the quality and resolution of patterned templates such as those used to manufacture hard drives and other data storage devices. When added to lithographically patterned surfaces, specially designed materials called block copolymers self-assemble into structures, shown in the upper right panel, with improved quality and resolution over the original patterns. These structures can be used to make templates with nanoscale elements like the silicon pillars shown in the bottom panel, which may be useful for manufacturing higher capacity hard disk drives. The team demonstrated a patterning technology that may revolutionize the field, offering performance improvements over existing methods even while reducing the time and cost of manufacturing. The method builds on existing approaches by combining the lithography techniques traditionally used to pattern microelectronics with novel self-assembling materials called block copolymers. When added to a lithographically patterned surface, the copolymers' long molecular chains spontaneously assemble into the designated arrangements. Information is encoded in the molecules that results in getting certain size and spacing of features with certain desirable properties. Thermodynamic driving forces make the structures more uniform in size and higher density than that from traditional materials. The block copolymers pattern the resulting array down to the molecular level, offering a precision unattainable by traditional lithography-based methods alone and even correcting irregularities in the underlying chemical pattern. Such nanoscale control also allows the researchers to create higher-resolution arrays capable of holding more information than those produced today. Also, the self-assembling block copolymers only need one-fourth as much patterning information as traditional materials to form the desired molecular architecture, making the process more efficient. The large potential gains in density offered by patterned media make it one of the most promising new technologies on the horizon for future hard disk drives. In its current form, this method is very well-suited for designing hard drives and other data-storage devices, which need uniformly, patterned templates � exactly the types of arrangements the block copolymers form most readily. With additional advances, the approach may also be useful for designing more complex patterns such as microchips. |
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