IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 1, NO. 1, MARCH 2002 39 The “Millipede”—Nanotechnology Entering Data Storage P. Vettiger, Fellow, IEEE, G. Cross, M. Despont, U. Drechsler, U. Dürig, B. Gotsmann, W. Häberle, M. A. Lantz, H. E. Rothuizen, R. Stutz, and G. K. Binnig Abstract—We present a new scanning-probe-based data-storage concept called the “millipede” that combines ultrahigh density, terabit capacity, small form factor, and high data rate. Ultrahigh storage density has been demonstrated by a new thermomechan- ical local-probe technique to store, read back, and erase data in very thin polymer films. With this new technique, nanometer-sized bit indentations and pitch sizes have been made by a single can- tilever/tip into thin polymer layers, resulting in a data storage densities of up to 1 Tb/in . High data rates are achieved by parallel operation of large two-dimensional (2-D) atomic force microscope (AFM) arrays that have been batch-fabricated by silicon sur- face-micromachining techniques. The very large-scale integration (VLSI) of micro/nanomechanical devices (cantilevers/tips) on a single chip leads to the largest and densest 2-D array of 32 32 (1024) AFM cantilevers with integrated write/read/erase storage functionality ever built. Time-multiplexed electronics control the functional storage cycles for parallel operation of the millipede array chip. Initial areal densities of 100–200 Gb/in have been achieved with the 32 32 array chip, which has potential for fur- ther improvements. A complete prototype system demonstrating the basic millipede functions has been built, and an integrated five-axis scanner device used in this prototype is described in detail. For millipede storage applications the polymer medium plays a crucial role. Based on a systematic study of different poly- mers with varying glass-transition temperatures, the underlying physical mechanism of bit writing has been identified, allowing the correlation of polymer properties with millipede-relevant parameters. In addition, a novel erase mechanism has been established that exploits the metastable nature of written bits. Index Terms—Atomic force microscope (AFM) array chips, mi- croscanner, millipede, nano-indentation, polymer films, scanning probe data storage, thermomechanical write/read/erase. I. INTRODUCTION I N THE 21st century, the nanometer will very likely play a role similar to the one played by the micrometer in the 20th century. The nanometer scale will presumably pervade the field of data storage. In magnetic storage today, there is no clear-cut way to achieve the nanometer scale in all three dimensions. The basis for storage in the 21st century might still be mag- netism. Within a few years, however, magnetic storage tech- nology will arrive at a stage of its exciting and successful evo- lution at which fundamental changes are likely to occur when current storage technology hits the well-known superparamag- netic limit. Several ideas have been proposed on how to over- come this limit. One such proposal involves the use of patterned Manuscript received January 25, 2002; revised February 14, 2002. The authors are with IBM Research, Zurich Research Laboratory, 8803 Rüschlikon, Switzerland (e-mail: pv@zurich.ibm.com). Publisher Item Identifier S 1536-125X(02)04585-4. magnetic media, for which the ideal write/read concept still needs to be demonstrated but the biggest challenge remains the patterning of the magnetic disk in a cost-effective way. Other proposals call for totally different media and techniques such as local probes or holographic methods. In general, if an ex- isting technology reaches its limits in the course of its evolution and new alternatives are emerging in parallel, two things usu- ally happen: First, the existing and well-established technology will be explored further and everything possible done to push its limits to take maximum advantage of the considerable in- vestments made. Then, when the possibilities for improvements have been exhausted, the technology may still survive for cer- tain niche applications, but the emerging technology will take over, opening up new perspectives and new directions. Consider, for example, the vacuum electronic tube, which was replaced by the transistor. The tube still exists for a very few applications, whereas the transistor evolved into today’s mi- croelectronics with very large-scale integration (VLSI) of mi- croprocessors and memories. Optical lithography may become another example: Although still the predominant technology, it will soon reach its fundamental limits and be replaced by a tech- nology yet unknown. Today we are witnessing in many fields the transition from structures of the micrometer scale to those of the nanometer scale, a dimension at which nature has long been building the finest devices with a high degree of local function- ality. Many of the techniques we use today are not suitable for the coming nanometer age; some will require minor or major modifications, and others will be partially or entirely replaced. It is certainly difficult to predict which techniques will fall into which category. For key areas in information-technology hard- ware, it is not yet obvious which technology and materials will be used for nanoelectronics and data storage. In any case, an emerging technology being considered as a serious candidate to replace an existing but limited technology must offer long-term perspectives. For instance, the silicon microelectronics and storage industries are huge and require correspondingly enormous investments, which makes them long-term oriented by nature. The consequence for storage is that any new technique with better areal storage density than today’s magnetic recording [1] should have long-term potential for further scaling, desirably down to the nanometer or even atomic scale. The only available tool known today that is simple and yet provides these very long-term perspectives is a nanometer-sharp tip. Such tips are now being used in every atomic force mi- croscope (AFM) and scanning tunneling microscope (STM) for imaging and structuring down to the atomic scale. The simple 1536-125X/02$17.00 © 2002 IEEE