Patent Application
20060212978
The present document describes read apparatus for reading from a storage medium, of the type wherein the storage medium is mechanically transported across the read apparatus.
Storage devices wherein a storage medium moves relative to read apparatus, where the read apparatus detects data recorded as differences in mechanical, magnetic, optical, or electrical properties of local areas of the media, currently enjoy a huge market. Such devices include optical and magnetic disk and tape drives as are commonly used in computers. These devices typically incorporate read and write apparatus, media, and apparatus for moving the media relative to the read and write apparatus.
In this market, market forces are strong incentives to reduce the bit area, the surface area of media that is allocated for each bit of data stored on the media
Storage devices are being developed using nanotechnology to realize. ultra-small bit areas. One such storage device is based on atomic force microscopy (AFM), in which one, or more microscopic scanning probes are used to read and write to a storage medium.
Typically, scanning probes have sharply pointed tips having tip diameter less than forty (40) nanometers diameter, and in recent implementations about ten nanometers, that contact the storage medium. Storage of data in the storage medium is based on perturbations in the surface of the storage medium detectable by the probes. For example, a perturbation may be a microscopic pit in the storage medium surface, with a pit representing a logical “1,” and the lack of a pit representing a logical “0.”
Previously disclosed techniques for detecting pits in storage media as the media is transported across read apparatus include apparatus that measures heat flow from the read apparatus to the media, and piezoresistive devices that measure variations in position of a part of the read apparatus induced by dents in the media passing by.
It is known that other perturbations useful for data storage include variations in storage medium composition or crystalline phase, filled or empty electronic states, magnetic domain structures or polarization states, chemical bonds in the medium, or atoms moved to or removed from the medium.
This invention provides an apparatus and method for reading bit values using a probe on a cantilever.
In particular, and by way of example only, according to an embodiment, provided is a microprobe for sensing data encoded on a media as a pattern of pits in an insulating layer disposed on a semiconductor layer having a first doping, the microprobe including: at least one cantilever having a first conductive arm and a second conductive arm; a contactor formed of a semiconductor material having a second doping, the contactor coupled to the first conductive arm and the second conductive arm of the cantilever, the contactor having a sharp point for sensing the pattern of pits.
Before proceeding with the detailed description, it is to be appreciated that the present teaching is by way of example, not by limitation. The concepts herein are not limited to use or application with a specific apparatus and method for reading data from a storage medium. Thus, although the instrumentalities described herein are for the convenience of explanation, shown and described with respect to exemplary embodiments, it will be appreciated that the principles herein may be equally applied in other types of data storage devices.
In the following description, the term “data” is understood and appreciated to be represented in various ways depending upon context. Generally speaking, the data at issue is primarily binary in nature, represented as logic “0” and logic “1”. However, it will be appreciated that the binary states in practice may be represented by relatively different voltages, currents, resistances or the like that may be measured or sensed, and it may be a matter of design choice whether a particular practical manifestation of data within a data storage media represents a “0” or a “1” or other memory state designation.
With reference to
A read device incorporates a microprobe 109 to sense the openings 108 in the insulating film 106. The microprobe 109 incorporates V-shaped cantilever 110 as a springy support for a contactor 112 located near the angle of the V. The cantilever 110 has a first conductive arm 214 and a second conductive arm 216 (
Contactor 112 (
Tips of the contactors 112 are sharpened to an effective tip diameter of less than forty (40) nanometers, and preferably between about ten (10) and twenty (20) nanometers diameter. Contactors 112 are sharpened through anisotropic etching.
When it is desired to read data from the data storage media, the contactor 112 is allowed to contact the surface of the media, while the media undergoes motion relative to the contactor 112. The cantilever arms 214, 216 are slightly flexed by forces applied to the contactor 112.
In an embodiment, the media has the form of a rotating disk, and the microprobe 109 array is stationary. In an alternative embodiment, the microprobe 109 moves relative to a stationary media. In yet another embodiment, the media has the form of a disk rotating under the microprobe array, which in turn has the ability to move radially with respect to the disk.
Where insulating film 106 is present on the media surface, the contactor 112 rides upon the insulating film 106 as media 100 and microprobe 109 move. Where a pit or opening 108 is present, the springy cantilever arms 214, 216 straighten slightly such that contactor 112 dips into the pit 108 to contact the semiconductor layer 104.
Perfect contact is not required, since tunneling conduction occurs when the insulating film 106 is sufficiently thin and contactor 112 is sufficiently close to semiconductor layer 104. When the tip of the contactor 112 contacts the semiconductor layer 104, an effective diode junction is formed.
As illustrated in
The microprobe structure has an equivalent circuit comprising resistors 420, 422, representing parasitic electrical resistance of the cantilever arms 214, 216 as well as resistance of the semiconductor contactor 112. The equivalent circuit also has diode 424, switch 426, and diode resistor 428.
When the microprobe's 109 contactor 112 rides on full-thickness insulating film 106, switch 426 is open and current does not flow in diode 424, leaving voltage at the microprobe at the biased level. In at least one embodiment, this biased level is representative of logical 1.
When the microprobe's 109 contactor 112 approaches sufficiently close to, or comes in contact with, the semiconductor layer 104 of the media; switch 426 of this model closes and current flow in diode 424, diode resistor 428 and switch 426 reduces voltage at the microprobe sufficiently that amplifier 430 can detect a voltage drop. In at least one embodiment, this dropped voltage is representative of logical 0.
The sequence of bias-level voltages and dropped voltages are used to reconstruct a data stream representing the stored data. For example, user data such as “28088” may be represented in binary form as “110110110111000” by a series of appropriately spaced smooth spaces and openings 108 in insulating film 106.
Other methods of sensing current flow in diode 424 may be used. In one alternative embodiment, the sense amplifier is located in the semiconducting substrate of the media instead of in the microprobe array.
In an embodiment of the read apparatus 500 illustrated in the top view of
Each microprobe 109 has associated sensing electronics 506 for generating a data stream according to a pattern of pits on the disk. In this embodiment, with multiple microprobes in an array, selection electronics 507 selects one or more data streams from amplifiers 230 of the array for further processing.
In a particular embodiment of the read apparatus 500, there are eight rows of microprobes 109, where cantilevers occur every forty-five (45) microns in each row. The microprobes of the rows are interdigitated such that the array has an effective track spacing of under six microns;
The cantilevers 502 are fabricated on the lower surface of a silicon wafer 510, which has been etched back to free all but an attachment portion of the cantilevers 502 and to allow the cantilevers 502 to flex. On the remaining portion of the silicon wafer 510 are sensing circuitry 506, including bias resistors and amplifiers, associated with each cantilever 502 and microprobe 504.
The method of reading data is summarized in
Insulating film 106 is initially smooth (i.e., does not contain openings 108). The data values initially present in data storage media 100 are all the same, and for example are conventionally recognized as logical “1”. The creation of an opening 108 therefore represents a logical “0”. In alternative embodiments, this relationship may be reversed such that the initial data values are recognized as logical “0” and the creation of an opening 108 is recognized as logical “1”.
Writing of data onto the media can be done in several ways. In an embodiment, write switches 434 associated with selected microprobes 109 turn on at selected points during relative motion of media 100 and microprobes 109 such that the contactor 112 heats momentarily, due to current flow in the contactor resistance modeled by resistors 420, 422 of the equivalent circuit of
By electronically controlling which microprobes heat at which times, a pattern of pits 108 may be generated on the media In an alternative embodiment writing is done optically, by burning away insulating film 106 where pits are desired.
In another alternative embodiment, writing the media is performed through a method similar to that of stamping DVD's. A master is generated by selectively burning a pattern of pits into a surface of a master with an electron beam. The master is then electroplated with nickel to create a negative punch having raised portions corresponding to a desired pattern of pits. The negative punch may, but need not, be replicated through an intermediate positive to a secondary negative punch.
Blank media 100, having a smooth insulating film 106, is heated, the negative punch is then pressed into the insulating film 106, displacing portions of the film 106 to leave pits 108. The negative punch is then removed from the media 100 leaving a pattern of pits 108. The pattern of pits 108 contains data corresponding to data encoded in the pattern of pits burned into the master by the electron beam.
An alternative embodiment having an array with four rows of interdigitated microprobes is illustrated in
While the microprobe and associated read circuitry has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes may be made in the above methods, systems and structures without departing from the scope hereof. It should thus be noted that the matter contained in the above description and/or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method, system and structure, which, as a matter of language, might be said to fall therebetween.
