08-17-2017, 12:07 AM
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ABSTRACT
"Millipede" is a new (AFM)-based data storage concept that has a potentially ultrahigh density, terabit capacity, small form factor, and high data rate. Its potential for ultrahigh storage density has been demonstrated by a new thermomechanical local-probe technique to store and read back data in very thin polymer films. With this new technique, 3040-nm-sized bit indentations of similar pitch size have been made by a single cantilever/tip in a thin (50-nm) polymethylmethacrylate (PMMA) layer, resulting in a data storage density of 400500 Gb/in.2
High data rates are achieved by parallel operation of large two-dimensional (2D) AFM arrays that have been batch-fabricated by silicon surface-nMcromachining techniques. The very large scale integration (VLSI) of micro/nanomechanical devices (cantilevers/tips) on a single chip leads to the largest and densest 2D array of 32 x 32 (1024) AFM cantilevers with integrated write/read storage functionality ever built. Initial areal densities of 100200 Gb/in.2 have been achieved with the 32 x 32 array chip, which has potential for further improvements.
In addition to data storage in polymers or other media, and not excluding magnetics, we envision areas in nanoscale science and technology such as lithography, high-speed/large-scale imaging, molecular and atomic manipulation, and many others in which Millipede may open up new perspectives and opportunities.
INTRODUCTION
In 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. Within a few years, however, magnetic storage technology will arrive at a stage of its exciting and successful evolution at which fundamental changes are likely to occur when current storage technology hits the superparamagnetic limit.
In any case, an emerging technology being considered as a serious candidate to replace an existing but the technology must offer long-term perspectives. 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 used in every atomic force microscope (AFM) and scanning tunneling microscope (STM) for imaging and structuring down to the atomic scale.
The objectives of our research activities within the Micro- and Nanomechanics Project at the IBM Zurich Research Laboratory are to explore highly parallel AFM data storage with areal storage densities far beyond the expected superparamagnetic limit (60100 Gb/in.2) and data rates comparable to those of today's magnetic recording. The "Millipede" concept presented here is a new approach for storing data at high speed and with an ultrahigh density. Our current effort is focused on demonstrating the Millipede concept with areal densities up to 500 Gb/in.2 and parallel operation of very large 2D (32 x 32) AFM cantilever arrays with integrated tips and write/read storage functionality.
MILLIPEDE CONCEPT
"Millipede" is based on a mechanical parallel x/y scanning of either the entire cantilever array chip or the storage medium. In addition, a feedback-controlled z-approaching and -leveling scheme brings the entire cantilever array chip into contact with the storage medium. This tip, medium contact is maintained and controlled while x/y scanning is performed for write/read. It is important to note that the Millipede approach is not based on individual z-feedback for each cantilever; rather, it uses a feedback control for the entire chip, which greatly simplifies the system. However, this requires stringent control and uniformity of tip height and cantilever bending. Chip approach and leveling make use of four integrated approaching cantilever sensors in the corners of the array chip to control the approach of the chip to the storage medium. Signals from three sensors (the fourth being a spare) provide feedback signals to adjust three magnetic z-actuators until the three approaching sensors are in contact with the medium. The three sensors with the individual feedback loop maintain the chip leveled and in contact with the surface while x/y scanning is performed for write/read operations. The system is thus leveled in a manner similar to an antivibration air table. This basic concept of the entire chip approach/leveling has been tested and demonstrated for the first time by parallel imaging with a 5 * 5 array chip. These parallel imaging results have shown that all 25 cantilever tips have approached the substrate within less than 1 um of z-activation. This promising result has led us to believe that chips with a tip-apex height control of less than 500 nm are feasible. This stringent requirement for tip-apex uniformity over the entire chip is a consequence of the uniform force needed to minimize or eliminate tip and medium wear due to large force variations resulting from large tip-height nonuniformities.
High data rates are achieved by parallel operation of large two-dimensional (2D) AFM arrays that have been batch-fabricated by silicon surface-nMcromachining techniques. The very large scale integration (VLSI) of micro/nanomechanical devices (cantilevers/tips) on a single chip leads to the largest and densest 2D array of 32 x 32 (1024) AFM cantilevers with integrated write/read storage functionality ever built. Initial areal densities of 100200 Gb/in.2 have been achieved with the 32 x 32 array chip, which has potential for further improvements.
In addition to data storage in polymers or other media, and not excluding magnetics, we envision areas in nanoscale science and technology such as lithography, high-speed/large-scale imaging, molecular and atomic manipulation, and many others in which Millipede may open up new perspectives and opportunities.
INTRODUCTION
In 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. Within a few years, however, magnetic storage technology will arrive at a stage of its exciting and successful evolution at which fundamental changes are likely to occur when current storage technology hits the superparamagnetic limit.
In any case, an emerging technology being considered as a serious candidate to replace an existing but the technology must offer long-term perspectives. 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 used in every atomic force microscope (AFM) and scanning tunneling microscope (STM) for imaging and structuring down to the atomic scale.
The objectives of our research activities within the Micro- and Nanomechanics Project at the IBM Zurich Research Laboratory are to explore highly parallel AFM data storage with areal storage densities far beyond the expected superparamagnetic limit (60100 Gb/in.2) and data rates comparable to those of today's magnetic recording. The "Millipede" concept presented here is a new approach for storing data at high speed and with an ultrahigh density. Our current effort is focused on demonstrating the Millipede concept with areal densities up to 500 Gb/in.2 and parallel operation of very large 2D (32 x 32) AFM cantilever arrays with integrated tips and write/read storage functionality.
MILLIPEDE CONCEPT
"Millipede" is based on a mechanical parallel x/y scanning of either the entire cantilever array chip or the storage medium. In addition, a feedback-controlled z-approaching and -leveling scheme brings the entire cantilever array chip into contact with the storage medium. This tip, medium contact is maintained and controlled while x/y scanning is performed for write/read. It is important to note that the Millipede approach is not based on individual z-feedback for each cantilever; rather, it uses a feedback control for the entire chip, which greatly simplifies the system. However, this requires stringent control and uniformity of tip height and cantilever bending. Chip approach and leveling make use of four integrated approaching cantilever sensors in the corners of the array chip to control the approach of the chip to the storage medium. Signals from three sensors (the fourth being a spare) provide feedback signals to adjust three magnetic z-actuators until the three approaching sensors are in contact with the medium. The three sensors with the individual feedback loop maintain the chip leveled and in contact with the surface while x/y scanning is performed for write/read operations. The system is thus leveled in a manner similar to an antivibration air table. This basic concept of the entire chip approach/leveling has been tested and demonstrated for the first time by parallel imaging with a 5 * 5 array chip. These parallel imaging results have shown that all 25 cantilever tips have approached the substrate within less than 1 um of z-activation. This promising result has led us to believe that chips with a tip-apex height control of less than 500 nm are feasible. This stringent requirement for tip-apex uniformity over the entire chip is a consequence of the uniform force needed to minimize or eliminate tip and medium wear due to large force variations resulting from large tip-height nonuniformities.