Oct 28, 2008
Nanoindenter passes memory test
Scanning probe-based data storage is back in the news as IBM researchers turn their attention to the thermo-mechanical indentation of polymer media at high patterning densities and fast transfer rates.
Results published in the journal Nanotechnology suggest that there could be more mileage in polymer systems than experts first thought and nanotechweb.org interviews Urs Dürig of IBM's Zurich Research Laboratory, Switzerland, to find out more.
What are the attractions of polymer probe technology compared with other data storage schemes?
Polymer probe technology offers the potential of extremely high storage density, up to 4 Tb/inch2. The basic principle of hot-embossing the information in the form of indents is conceptually simple and lends itself well to a highly parallel MEMS implementation. In this way, we address several critical issues. The data rate can be boosted by two to three orders of magnitude by operating a corresponding number of indenters in parallel. Small size also means low power consumption, which is critical in particular for portable applications. Small size also means robustness of the device against shock and vibration. Finally, small size also means fast positioning, which translates to worst case seek/access times in the order 1 ms in comparison with 10 ms for hard disk drives.
What are the biggest hurdles when it comes to ramping up the performance of the device?
Some of the more difficult challenges are the accurate control, on the scale of nanometres, of the scanning motion at 10–30 mm/s velocity, which is three to four orders of magnitude faster than in a typical scanning probe microscope, and the taming of the cantilever response. The cantilever has to absorb the vertical motion of the tip well above the resonance frequency of the fundamental mode, giving rise to the excitation of higher-order flexure modes. To alleviate these problems we intend to use smaller cantilevers with accordingly faster response characteristics in the future. Moreover, the positioning accuracy of MEMS nanoposititioners has been and will be further improved by incorporating sophisticated feedback control schemes and optimizing the mechanical design.
How robust are the tips? Did you experience any problems with breakage?
We performed extensive reliability studies with particular regard to tip endurance. We never observed catastrophic breakage of tips, which might come as a bit of a surprise given the small size of the indenter. This results because nanoscale wear is quite different from wear on the macrosopic scale. We have developed a technique for wear mitigation during read-back and have demonstrated sliding for more than 750 m – the equivalent of the readback of ~1011 symbols , with no detectable wear of the tip apex. After this test, we were able to write and read-back data with this tip at a density of 1 Tb/in2. Moreover, we have demonstrated that more than 108 indents could be written at 1 Tb/in2 density with a single tip.
What are the likely applications? For example, is this something that would fit into a laptop, or is the technology more suited to archiving and offsite data storage?
Originally, the scanning probe data-storage project, internally dubbed "millipede project" targeted mobile applications such as SD (secure digital) form factor storage devices. Typically a probe-storage-based SD device would hold several tens of gigabytes of data and would feature a user data rate of 10 MB/s. To demonstrate the technical viability of the concept, we have completed a fully functional prototype system consisting of all relevant building blocks, including a form-factor MEMS array and nanopositioner, a CMOS analog front-end circuit, servo and tracking, error correction coding and data formatting (see A Pantazi et al. 2008 IBM J. Res. Develop. 52 493).
Although the probe-storage technology has the potential for scaling the areal density and hence the cost per gigabyte, flash memory has made tremendous progress over the past few years achieving a remarkable price drop of approximately two orders of magnitude since 2000. As a result, the economic advantage of mobile probe storage has eroded, making it difficult to justify the risk associated with the development of an entirely new technology. On the other hand, the high data density that can be achieved with probe storage makes it an attractive option for high-capacity data repositories. To further explore the potential of probe-storage technology in this area, we are participating in a European FP6 program, ProTem, which investigates how probe storage could be used in the archival storage domain.
Back in the lab, what are the next steps for you and your colleagues?
Given the imperative for a high data rate in archival storage systems, we would like to further increase the data rate by a factor of three in the near term. To this end, we have developed new, extremely fast cantilevers and a scanning system that should allow us to achieve scan speeds of 50 mm/s.
The researchers presented their work in Nanotechnology.
About the author
James Tyrrell is editor of nanotechweb.org.