The high spatial resolution of the atomic force microscope (AFM) has motivated recent efforts to apply the technique to high-density data storage. However, little attention has been given to satisfying the other necessary attributes required of any new data storage technology. Using a system based on reading topographic data features on a rotating disk with a high-frequency piezoresistive cantilever, we address several of these issues. A timing-based control method for data tracking is demonstrated and shown to maintain the radial tip position to within a standard deviation of 31 nm. While maintaining the tip position under both load and tracking control with a disk velocity of 3 cm/s, 200 nm diameter marks are read continuously for over 145 h without any significant change in signal amplitude. This represents a tip travel distance of 16 km, and each bit was read over 500 000 times.One of the potential applications of atomic force microscope (AFM)-based techniques is high-density data storage. Current magnetic disk drives have an areal data density of approximately 300 Mbit/cm 2 and are increasing in areal density at a 60% compound annual growth rate. However, such growth is not expected to continue unbounded, as the magnetic grains in current magnetic storage media may become thermally unstable at an areal density of around 6 Gbit/cm 2 . In imaging applications, the AFM has demonstrated atomicscale resolution, and thus one can imagine reading data at densities as high as 10 14 bit/cm 2 . Various high-density AFM-based writing techniques have been demonstrated [1-6], as well as methods for mass replicating read-only plastic disks containing 50 nm marks [7,8], with data densities of 10-15 Gbit/cm 2 . While much attention has been given to achieving high data density, significantly less attention has been paid to other aspects of the technology, such as high data rates, servo bandwidth (load and tracking), reliability and long data retention times, which would be required of any new technology. We present here results in addressing several of these areas, namely load and tracking control and tip/media wear, for AFM-based data storage using a rotating disk.
ExperimentWhile AFM imaging applications typically use an x-y raster scan mode, for high-speed data storage it may be advantageous to use a rotating disk. To store a reasonable amount of data, 1 Gbyte, using 100 nm bits (10 Gbit/cm 2 ), a 10 mm diameter disk is required. Such an area is much greater than that accessible by the usual piezoelectric tube scanners used for AFM imaging. In addition, the reading of 100 nm bits at magnetic disk drive data rates of over 10 Mbit/s with a single AFM cantilever would require a relative tip-to-media velocity of over 1 m/s. This is much faster than typical AFM scan rates, but is easily achieved using spinning disk drive technology. Therefore we have chosen to mount the data disk on a spinning air-bearing motor.To control the load and radial position of the AFM tip above the disk, the lever is mounted on a voice-coil type actu...