Millipede small scale MEMS prototype


Millipede technology is an emerging nonvolatile secondary storage technology; MEMS-based storage exhibits several desirable properties including high performance, high storage volume density, low power consumption, low entry cost, and small form factor. Systems designers needs to make trade-offs to achieve well-balanced designs. It presents an architecture in which MEMS devices are organized into MEMS storage enclosures with online spares. These enclosures are proven to be highly reliable storage building bricks with no maintenance during their economic lifetimes. 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. It promises a data density of more than one terabit per sqinch. Millipede is a highly parallel scope probe based data storage that has a real storage densities far beyond super paramagnetic limits and data rates comparable to today's magnetic recording.


At the first glance, millipede looks like a conventional silicon chip. Mounted at the centre of the chip is a miniature two dimensional array of 1024 'v'- shaped cantilevered arms. A nano-sharp fang-like tip hangs from apex of each cantilever. The multiplex drivers allow addressing of each tip individually. Beneath the cantilever array, is a thin layer of polymer film deposited on a movable, three-axis silicon table?

A 2-D AFM cantilever array storage technique called 'millipede' is based on a mechanical parallel x/y scanning of either the entire cantilever array chip or storage medium. In addition, a feedback controlled z-approaching and level scheme brings entire cantilever array chip into contact with the storage medium. Chip approval/leveling makes use of additional integrated approaching cantilever sensors in the corners of the array chip to control the approach of the chip to storage medium. Signal from these sensors provide feedback signals to adjust the z-actuators until the contact with medium is established. Feedback loops maintain the chip leveled and in contact with the surface while x/y scanning is performed for write/read operations.

During the storage operation, the chip is raster scanned over an area called the storage field by a magnetic x/y scanner. Each cantilever/tip of the array writes and reads data only in its own storage field. This eliminates the need for lateral positioning adjustments of the tip to offset lateral position tolerances in tip fabrication. Consequently a 32 x 32 array chip will generate 32 x 32 (1024) fields on an area. The storage capacity of the system scales with areal density, cantilever pitch (storage-field size) , and the number of cantilevers in an array. A very good temperature control array chip and the medium substrate is required between read/write cycles. True parallel operation of large 2-D arrays results is very large chip size because of the space required for individual write/read wiring to each cantilever and the many I/O pads. The row/column time-multiplexing addressing scheme implemented successfully in every dynamic random access memory (DRAM) is a very elegant solution to this issue. The current millipede storage approach is based on a new thermo mechanical store write/read process in nanometer thick-polymer films. The use of polymer films for data storage results is Avery high density of storage.

Data Storage

Each probe in the cantilever array stores and reads data thermo- mechanically, handling one bit at a time. Recently, AFM thermo mechanical recording in polymer storage media has undergone extensive modifications, primarily with respect to the integration of sensors and heaters designed to enhance simplicity and to increase data rate and storage density.

Reading and Writing data

Each probe in the cantilever array stores and reads data. For reading data, the probe tip is heated and moved to data sled. If the probe is located over a pit the cantilever will push it into the hole, increasing the surface area in contact with the sled, and in turn increasing the cooling as heat leaks into the sled from the probe. Electrical resistance of the probe is a function of its temperature, rising with increasing temperature. When probe drops into a pit and cools, this is registered a drop in resistance. While reading the storage field, the tip is dragged over the entire surface and the resistance changes are constantly monitored.

To write a bit, the tip of the probe is heated above the 'glass transition temperature' of the polymer to manufacture the data sled. To write a "1", the polymer is softened, and then the tip is gently touched to it causing a dent. To erase the bit and return it to the zero state, the tip is instead pulled from the surface.

Millipede is expected to consume in range of flash memory technology and considerably below hard drives. Main advantage of the Millipede design is that it allows running at much higher speeds into the GB/s, one might expect power requirements more closely matching current hard drives.

Main features of 32 X 32 array millipede chip

  • Surface micromachining to form cantilevers at the water surface
  • All-silicon cantilevers
  • Thermal sensing
  • First and second level wiring with an insulated layer for a multiplexing row/column -

Addressing scheme

The arrays cantilevers are used for approaching and levelling of chip and storage medium is used to initially characterize the interconnected array cantilevers. Cantilever test structures are distributed over the wafer. The tip-apex height determines the force of each cantilever and influences write/read performance as well as medium and tip wear.


Current Stage

The progress of millipede technology storage product has been slower than expected. Advances in other competing storage systems have made the existing demonstrators unattractive for commercial production. Millipede technology appears to be in a race, attempting to mature quickly enough at a given technology level by newer generations of the existing technologies, when it is ready for production. Earlier millipede devices where using probes of 10 nanometres in diameter and 70 nanometres in length. When arranged in a 32 x 32 grid, the resulting 3 mm x 3 mm chip stores 500 megabits of data. IBM initially demonstrated this device in 2005 and commercially in 2007. By that point hard drives were approaching 150 Gbit/in², and have since surpassed it. Mostly recent devices demonstrated at CEBIT boosted to data storage capacity of 800 Gbit/in² using smaller pits, since the pit size can scale to about 10 nm. IBM introduced devices based on sort of density. Latest perpendicular recording hard drives feature areal densities on the order of 230 Gbit/in², and appear to top out at about 1 Tbit/in². Semiconductor-based memories offer much lower density, 10 Gbit/in² for DRAM and about 250 Mbit/in² for RAM.

Ongoing Developments

  1. Millipede technology is operating large 2D AFM arrays for thermo mechanical data storage in thin polymer media. In doing so, it has demonstrated key milestones of the Millipede storage concept.
  2. Well-controlled processing techniques are developing to fabricate array chips with good yield and uniformity. This VLSINEMS chip has the potential to open up new perspectives in applications such as scanning probe techniques.
  3. Millipede technology is not limited to storage applications, these is applied to other storage medium, including magnetic ones, making Millipede a possible universal parallel write/read head for future storage systems.
  4. Besides storage, other Millipede applications can be envisioned for large-area, high-speed imaging and high-throughput nanoscalelithography, as well as for atomic and molecular manipulation and modifications.
  5. The smoothness of the reflowed medium allowed multiple rewriting of the same storage field. This erasing process does not allow bit-level erasing; it will erase larger storage areas. However, in most applications single-bit erasing is not required anyway, because files or records are usually erased as a whole. These erasing and multiple rewriting processes, as well as bit-stability investigations.
  6. Overall system reliability, including bit stability, tip and medium wear, erasing/rewriting.

Future Work

  1. MEMS storage enclosures without repairs exhibit unconventional no exponential lifetime distributions.
  2. Storage systems would exhibit reliability characteristics quite different from those of disks, whose lifetimes are typically regarded as exponential.
  3. Deciding upon a particular architecture, it is also necessary to understand the cost trade-offs between system maintenance and investment on spare devices.
  4. The performance of MEMS caching disk is sensitive to various degrees, segment size and workload characteristics.
  5. However, we can identify streaming workloads at the controller level and bypass MEMS to minimize its impact on system performance. Techniques that can automatically identify workloads characteristics are desirable.


Conventional data storages, such as disk drives and CD/DVD's are based on system that sense changes in magnetic fields or light to perform the read/write/store/erase functions. Millipede is unique both in form and the way it performs data storage tasks; it is based on a chip mounted, mechanical system that sense a physical change in a storage media. The millipede's technology is actually closer to, although on an atomic scale, the archaic punched card than the more recent magnetic media. Using millipede, the IBM scientists have demonstrated a data storage density of a trillion bits per square inch -20 times higher than the densest magnetic storage available today. Millipede is dense enough to store the equivalent of 25 DVD's on the surface of the size of a postage stamp. This technology mat boost the storage capacity of handheld devices - personal digital assistants (PDAs) and cell phones - often criticized for low storage capabilities.


The researchers admit that technology is a number of years away from being ready for practical application. As a retype, millipede has proven the design concept works. However, several challenges remain that must be prior to market the storage devices commercially. The multimedia design team listed concerns about overall system reliability, bit stability, tip and medium wear, limits of data rate, CMOS integration, and optimization of the multiplexing scheme, array chip tracking and data versus power consumption tradeoffs. Other questions are, whether millipede has overcome the write slow/read fast problem of flash technology and how stable millipede data is at various temperatures. All are significant valid concerns that must be addressed prior to full-scale production.


There is not a single step in fabrication that needs to be invented. Millipede would be relative inexpensive to manufacture because chips can be made using IBM's existing manufacturing equipments and techniques.


  • Storage capacity - 1 terabit per square inch Equal to 25 DVD
  • 25 billion texts in a stamp sized surface
  • Enable 10Gb of storage in cell phones
  • Uses atomic force probes
  • Data reads & writes in the storage field
  • Access time is small
  • Data rate is 1Gb/s
  • Needs less power about 100mw
  • DRAM 10 Gb/ Sq inch
  • Flash Drive 25 Gb/ Sq inch
  • Hard Drive 250 Gb/ Sq inch


  • Inexpensive
  • Unique
  • Rewritable
  • Simple and Compact
  • High data rate
  • Lower power consumption
  • Small form factor
  • Ultra high storage density
  • Terabit capacity


  • Nan scale lithography
  • Large area microscopic imaging
  • Atomic and molecular manipulation
  • Small form factor storage system (Nan drive)
  • Terabit drive
  • High capacity hard drives
  • Mobile devices like PDA's, cellular phones and multifunctional watches
  • Other market target includes applications where weight, form factor and ultra high density are important considerations (aircraft, spacecraft, electric cars etc.)


Micro Drives

Millipede systems are used in micro drives for small form factor using in small footprint devices like watches, mobile phones and personal media systems to provide high capacity. High data density millipede systems make them a very good candidate to put in use.

High-capacity hard drives

The Millipede system provides high data density, low seek times, low power consumption and, probably, high reliability. These makes millipede 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. Thus replacing hard drives probably requires economically collecting around 100 Millipede devices into a single enclosure.


Today, there are no emerging markets for nano technology's ultra high density storage devices. Millipede is meeting/exceeding current customer demand for storage capacity. It is likely that demand for small factor components will increase in the near future. The desire for smallest, lighter laptop computers and hand held electronic devices is an obvious potential market for new chips. It is reasonable to expect that millipede technology storage devices could overtake the market and become disruptive within the next decade. The high areal storage density and form factor make millipede very attractive as a potential future storage technology in mobile applications, offering terabit capacity and low power consumption.


  1. IBM Millipede 2008: Bachelor of Information Technology (2008), Retrieved 19 July, 2008, from college- seminars Web site: REPORT.html . In-text citation: Cochin institute of Technology (2008).
  2. Millipede 2009: Undergraduate student information (2009), Retrieved 13 April, 2009, from Scribe Web site: In-text citation: Texas A&M University (2009).

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