Content Millipede memory Introduction. The Millipede concept. Reading and Writing data. Stored bits. Cantilever Structure. Usage Scenarios Modern disk Storage Current state of the art Future challenges Conclusion

What is millipede ?

Millipede is a non-volatile  computer memory  stored on nanoscopic pits burned into the surface of a thin polymer layer, read and written by a MEMS-based probe.

Millipede storage technology is being pursued as a potential replacement for magnetic recording in hard drives, at the same time reducing the form-factor to that of Flash media. At launch, it would probably be more expensive per-megabyte than prevailing technologies, but this disadvantage is hoped to be offset by the sheer storage capacity that Millipede technology would offer.

How it is ? Using an innovative nanotechnology,

scientists have demonstrated a data storage density of a trillion bits per square inch -- 20 times higher than the densest magnetic storage available today.

Rather than using traditional magnetic or electronic means to store data, Millipede uses thousands of nano-sharp tips to punch indentations representing individual bits into a thin plastic film.

The 'Millipede' technology is re-writeable (meaning it can be used over and over again), and may be able to store more than 3 billion bits of data in the space occupied by just one hole in a standard punch card.

Need of Millipede ? Flash memory is not expected to surpass 1-2 gigabytes of

capacity in the near term, Millipede technology could pack 10 - 15 gigabytes of data into the same tiny format, without requiring more power for device operation.

"The Millipede project could bring tremendous data capacity to mobile devices such as personal digital assistants, cellular phones, and multifunctional watches,“

Using revolutionary nanotechnology, scientists have

made it to the millionths of a millimeter range, achieving data storage densities of more than one terabit (1000 gigabit) per square inch, equivalent to storing the content of 25 DVDs on an area the size of a postage stamp.

The Millipede concept The main memory of modern computers is constructed from number

of DRAM-related devices. DRAM basically consists of a series of capacitors, which store data as the presence or absence of electrical charge. Each capacitor and its associated control circuitry, referred to as a cell, holds one bit, and bits can be read or written in large blocks at the same time.

Hard drives store data on a metal disk that is covered with a magnetic material; data is represented as local magnetization of this material.

Millipede storage attempts to combine the best features of both. Like the hard drive, millipede stores data in a "dumb" medium that is simpler and smaller than any cell used in an electronic medium.

Animated View of Millipede

Writing data Bits are written by heating

a resistor built into the cantilever to a temperature of 400 degrees Celsius.

The hot tip softens the polymer and briefly sinks into it,&

generating an indentation.

Reading Data

For reading, the resistor is operated at lower temperature, typically 300 degrees Celsius, which does not soften the polymer.

When the tip drops into an indentation, the resistor is cooled by the resulting better heat transport, and a measurable change in resistance occurs.

Overwriting Data

To over-write data, the tip makes a series of offset pits that overlap so closely their edges fill in the old pits, effectively erasing the unwanted data.

The write or overwrite cycles are limited to 1,00,000 cycles.

Stored bits

Fig. shows that more than 80 percent of the 1,024 cantilevers of an experimental setup were able to write data (12 storage areas at right).

Stored bits The close-ups (center) present 40

nm (nanometers) wide indentations at a "pitch" (distance between centers of neighboring indentations) of 120 nm (left) and 40 nm (right), pitch. 

The latter leading to areal density of ca. 400 GB per square inch. The same magnification factor has been applied to the image at the bottom, which demonstrates the potential for Terabit-per-square-inch density with 10-nm-diameter marks at a 20-nm

What is a Cantilever ?

The core components of probe storage system are a two-dimensional array of silicon probes (cantilevers) and a micro-mechanical scanner which moves the storage medium relative to the array.

For the device to perform its reading, writing and erasing functions, the cantilever tips are brought into contact with the storage medium — a thin film of a custom designed cross-linked polymer coated on a silicon substrate, which is moved in the x- and y-directions. The storage medium is positioned with nanometer-scale accuracy relative to the cantilever array.

How Cantilevers are manufactured ?

Our most recent array design consists of an array of 64 × 64 cantilevers (4096) on a 100 µm pitch.

The 6.4 × 6.4 mm² array is fabricated on a 10 × 10 mm²

silicon chip using a newly developed "transfer and join" technology that allows the direct interconnection of the cantilevers with CMOS electronics .

With this technology the cantilevers and CMOS electronics are fabricated on two separate wafers, allowing the processes used in the fabrication to be independently optimized.

Using a few additional processes steps, the cantilevers are transferred onto the CMOS wafer, using a soldering process that provides a mechanical and electrical interconnect to the CMOS wafer.

About used Cantilevers The cantilevers used in the array are of a

three-terminal design, with separate heaters for reading and writing, and a capacitive platform for electrostatic actuation of the cantilevers in the z-direction.

The cantilevers are approximately 70 µm long, with a 500-700 nm long tip integrated directly above the write heater. The apex of each tip has a radius on the scale of a few nanometers allowing data to be written at extremely high densities (greater than 1 Tb/in²).

Zoom to a section of the Millipede cantilever array as seen in an optical microscope. 

 About Microscanner Movement of the storage medium relative to the cantilever array is

achieved using a silicon-based x/y microscanner. The scanner consists of a 6.8 × 6.8 mm² scan table, which carries the

polymer medium, and a pair of electromagnetic actuators. Both the scan table and the actuators are supported by silicon springs that are 10–12 µm wide and approximately 400 µm thick. The scan table, spring system, and actuator frames are fabricated on a silicon wafer using a deep trench etching process.

The scanner chip is mounted on a silicon base plate, which acts as the mechanical ground of the system and provides a clearance of approximately 20 µm between its top surface and the bottom surface of the moving parts of the scanner.

The scan table can be displaced approximately 120 µm in two orthogonal directions (x and y) using the two electromagnetic actuators. Each actuator consists of a pair of permanent magnets mounted in a silicon frame, with a miniature coil mounted between them on the base plate.

The actuator motion is coupled to the scan table using a pivot and a mass-balancing scheme, which makes the system robust against external vibrations and shock.

A Microscanner.

Position sensing Positioning information for the closed-loop operation of

the scanner is provided by two pairs of thermal position sensors. These sensors are fabricated on the cantilever-array chip and positioned directly above the scan table. The sensors consist of thermally isolated, resistive strip heaters made of moderately doped silicon. Each sensor is positioned above an edge of the scan table and heated by applying a current. A fraction of this heat is conducted through the ambient air into the scan table, which acts as a heat sink. Displacement of the scan table gives rise to a change in the efficiency of this cooling mechanism, resulting in a change in the temperature of the heater and thus a change in its electrical resistance. These sensors provide an effectively linear position signal over the entire 120 µm range of the scanner, with a resolution of less than 2 nm in a 10 kHz bandwidth.

Position Sensor Fig.1

Position Sensor Fig.2

Recording technology In addition to exploring novel methods for writing,

reading and erasing data in thermomechanical probe recording, research is pursued in the areas of coding, signal processing and read channel design. In this context, it has been determined that a limiting factor in the areal density that can potentially be reached in thermomechanical probe storage is the intrinsic nonlinear interaction between closely packed indentations.

Upon this realization, the storage capacity can be increased by applying (d, k)-constrained codes, similar to the ones used in optical disc recording. The d-constraint in particular is instrumental in limiting the interference between successive indentations as well as in increasing the effective areal density of the storage device.

Recording

Continuous advancements on probe-tip fabrication, storage medium design, and improvements on the writing process and on the read channel design has lead to the repeated realization of storage of large amounts of data at densities higher than 1.0 Tb/in² and reliable retrieval of the data at raw error rates better than 1E-4. At these error-rate levels, conventional error-correcting codes (ECC) can successfully correct all errors, & there will be no loss of user data.

       Scanned image of bits recorded and retrieved at an areal density of 1.008 Tb/in², the error rate was less than 1E-4.

Signal recorded at the output of the discrete component AFE while scanning a line of bits at

1.008 Tb/in².

Usage Scenarios

Micro Drives Millipede systems can be used for micro

drives, which will feature very small form factor, enabling use in small footprint devices like watches, mobile phones and personal media systems, and at the same time provide high capacity. The very high data density of millipede systems makes them a very good candidate to be put to this use.

High-capacity hard drives The Millipede system provides high data

density, low seek times, low power consumption and, probably, high reliability. These features make them candidates for building high capacity hard drives, with storage capacity in the range of terabytes. Although the data density of a Millipede is high, the capacity of an individual device is expected to be relatively low -- on the order of single gigabytes.

Modern disk Storage IBM 350 The IBM 350 was part of

the IBM RAMAC 305, the computer that introduced disk storage technology to the world. IBM introduced the IBM 350 storage unit on September, 1956 before unveiling the entire RAMAC 305 computer nine days later on September. RAMAC stood for "Random Access Method of Accounting and Control."

Modern disk Storage

IBM 353 The IBM 353 used

on the IBM 7030, was similar to the IBM 1302, but with a faster transfer rate. It had a capacity of 2,097,152 (221) 72-bit words (64 data bits and 8 ECC bits) and transferred 125,000 words per second.

Modern disk Storage IBM 2310 The IBM 2310

Removable Cartridge Drive was introduced with the IBM 1130 in 1965. It could store 512,000 words (1,024,000 bytes) on an IBM 2315 cartridge. A single 14-inch (360 mm) oxide-coated aluminum disk spun in a plastic shell with openings for the read/write arm and two heads

Current state of the art

The progress of millipede storage to a commercially useful product has been slower than expected. Huge advances in other competing storage systems, notably Flash and hard drives, has made the existing demonstrators unattractive for commercial production.

Millipede appears to be in a race, attempting to mature quickly enough at a given technology level that it has not been surpassed by newer generations of the existing technologies by the time it is ready for production.

Current state of the art

The earliest generation millipede devices used probes 10 nanometers in diameter and 70 nanometers in length, producing pits about 40 nm in diameter on fields 92 µm x 92 µm. Arranged in a 32 x 32 grid, the resulting 3 mm x 3 mm chip stores 500 megabits of data or 62.5 MB, resulting in an areal density, the number of bits per square inch, on the order of 200 Gbit/in². IBM initially demonstrated this device in 2003, planning to introduce it commercially in 2005. By that point hard drives were approaching 150 Gbit/in², and have since surpassed it.

Conclusion

Today there are no known emerging markets for nanotechnology where high density storage devices.

The HDD industry meating