Abstract:
A storage device comprises a probe and storage cell having moveable parts that are actuatable to plural positions to represent respective different data states. The probe interacts with the moveable parts to selectively actuate the moveable parts to the plural positions.

Description:
BACKGROUND  
       [0001]     In computing systems, such as desktop computers, portable computers, personal digital assistants (PDAs), servers, and others, storage devices are used to store data and program instructions. One type of storage device is a disk-based device, such as magnetic disk drives (e.g., floppy disk drives or hard disk drives) and optical disk drives (e.g., CD or DVD drives). Such disk-based storage devices have a rotating storage medium with a relatively large storage capacity. However, disk-based storage devices offer relatively slow read-write speeds and greater space and power consumption when compared to operating speeds of other components of a computing system, such as microprocessors and other semiconductor devices.  
         [0002]     Another type of storage device is a solid state memory device, such as a dynamic random access memory (DRAM), static random access memory (SRAM), flash memory, and electrically erasable and programmable read-only memory (EEPROM). Although solid state memory devices offer relatively high read-write speeds, usually on the order of nanoseconds, they have relatively limited storage capacities.  
         [0003]     With improvements in nanotechnology (technology involving microscopic moving parts), other types of storage devices are being developed. 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, a scanning probe has a tip that is contacted to a surface of the storage medium. Storage of data in the storage medium is based on perturbations created by the tip of the probe in the surface of the storage medium. In one implementation, a perturbation is a dent or pit in the storage medium surface. The dent or pit is imprinted by heating a tip of the probe to an elevated temperature and pressing the tip against the storage medium surface.  
         [0004]     Yet another type of storage device uses micromechanical storage cells in which each storage cell includes two deflectable cantilevers that are selectively engageable with each other at two different positions to represent different data states. Electrostatic, magnetic, or heating is used to move such deflectable cantilevers to the different positions. The different positions of the cantilevers of a storage cell cause the resistance or capacitance associated with the storage cell to change to indicate respective different data states.  
         [0005]     The various types of storage devices discussed above may be associated with one or more of the following issues: low storage capacity, low access speed, relatively expensive manufacturing cost, circuit complexity, reduced reliability associated with having to heat storage elements during circuit operation, and others. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIGS. 1 and 2  are cross-sectional views of a portion of a probe-based storage device according to one embodiment.  
         [0007]      FIG. 3  shows a portion of the probe-based storage device that includes a storage medium containing storage cells, the storage device also including a plurality of probes that are scannable across the storage cells to read and write data.  
         [0008]      FIG. 4  is a cross-sectional view of a probe, according to one embodiment of the invention.  
         [0009]      FIG. 5  is a schematic diagram of a probe substrate containing an array of probes and peripheral circuitry to interact with the probes.  
         [0010]      FIG. 6  illustrates a probe substrate positioned to face the storage medium in the probe-based storage device.  
         [0011]      FIG. 7  is a cross-sectional view of a portion of a probe-based storage device according to another embodiment.  
         [0012]      FIG. 8  is a block diagram of a system that includes a computing device having a port to connect to a probe-based storage device.  
     
    
     DETAILED DESCRIPTION  
       [0013]      FIG. 1  shows an example probe-based storage device that includes a storage substrate  10  on which are arranged storage cells generally indicated as  12  ( 12 A and  12 B illustrated). Each storage cell  12  includes micromechanical structures that are manufactured according to nanotechnology techniques. A “micromechanical storage cell” refers to a storage cell that includes very small structures, with dimensions usually on the order of micrometers, nanometers, or less. The structures of a micromechanical storage cell include moveable parts that are actuatable to different positions to represent different data states.  
         [0014]     The micromechanical structures of the storage cells  12  may be formed onto the storage substrate  10 . Alternatively, the micromechanical structures may be formed from the material of the storage substrate  10 .  
         [0015]     In the example implementation shown in  FIG. 1 , each storage cell  12  includes a pair of deflectable structures. In the storage cell  12 A, a first deflectable structure includes a deflectable member  14 A that is attached at a first end to a support member  16 A. In the illustrated example, the deflectable member  14 A is integrally attached to the support member  16 A. In a different embodiment, the members  14 A and  16 A are separate elements that are bonded or otherwise attached together. The second deflectable structure of the storage cell  12 A includes a deflectable member  14 B having a first end attached to a support member  16 B. Each deflectable member  14  can be moved in response to an applied force. The movement can involve one or both of the following: (1) deflecting movement of the deflectable member  14  with respect to the support member  16 ; and (2) deflecting movement of the support member  16  with respect to the base provided by the storage substrate  10 .  
         [0016]     The second ends (referred to as “contact ends”  18 A,  18 B) of respective deflectable members  14 A,  14 B are engaged to each other, with the contact end  18 A of the deflectable member  14 A overlapping the contact end  18 B of the deflectable member  14 B. In a first position, the contact end  18 A of the deflectable member  14 A sits over the contact end  18 B of the deflectable member  14 B to represent a first state of a data bit that is stored by the storage cell  12 A.  
         [0017]     Storage cell  12 B stores a data bit that has a second state, which is represented by the deflectable structures of the storage cell  12 B being at a second position. The first deflectable structure of the storage cell  12 B includes a deflectable member  14 C attached to a support member  16 C. The second deflectable structure of the storage cell  12 B includes a deflectable member  14 D attached to a support member  16 D. The contact ends  18 C and  18 D of the deflectable members  14 C and  14 D, respectively, also overlap, with the contact end  18 C located under the contact end  18 D. This relative position of the first deflectable member  14 C with respect to the second deflectable member  14 D corresponds to the second position of the storage cell  12 B.  
         [0018]     In one implementation, the first state of the data stored in the storage cell  12 A corresponds to a logical “0,” while the second state of the data stored in the storage cell  12 B corresponds to a logical “1.” Alternatively, the first state of the storage cell  12 A is a logical “1” while the second state of the storage cell  12 B is a logical “0.” 
         [0019]     In other implementations, instead of storage cells each with a pair of deflectable structures, other storage cells can include other types of moveable micromechanical parts. The moveable parts in these other storage cells are also actuatable to different positions to represent different data states.  
         [0020]     The substrate  10  can be formed of any type of material that is relatively cost-efficient to produce, such as silicon, polymer, or another material. The support members  16  and deflectable members  14  making up the storage cells  12  can also be formed of any one of number of different types of materials. A desired characteristic of the materials that make up the support members  16  and deflectable members  14  is that the materials be sufficiently strong to withstand repeated deflections of deflectable members  14  and/or the support members  16  without breakage. For example, the members  14  and  16  can be formed of a metal, silicon, polysilicon, and so forth. Alternatively, the various members noted above can be formed from the material of the storage substrate  10 .  
         [0021]     In accordance with some embodiments of the invention, to write to and read from the storage cells  12 , a probe  20  is employed. The probe  20  includes a cantilever  22  and a tip  24  that is attached to and extends outwardly from the cantilever  22 . In the arrangement shown in  FIG. 1 , the probe  20  is provided above the storage cell  12 , so that the tip  24  depends from a lower surface of the cantilever  22 . In an alternative embodiment, the arrangement of the storage cells  12  to the probe  20  is reversed, such that the tip  24  points upwardly towards the storage cells  12 . The cantilever  22  and tip  24  can be formed of any of a number of materials, such as metal, silicon, and others.  
         [0022]     To write data to the storage cell  12 A, a downward force is applied by the probe  20  such that the tip  24  presses downwardly on the deflectable member  14 A. In response to an applied downward force of greater than a predetermined amount, the deflectable member  14 A is pushed underneath the deflectable member  14 B, as shown in  FIG. 2 . This position causes the storage cell  12 A to change states, such that a different state of data is represented by the storage cell  12 A in  FIG. 2 . Similarly, to write to the storage cell  12 B to change its state, a downward force is applied to the deflectable member  14 D to push the deflectable member  14 D below the deflectable member  14 C. In this manner, the storage cells  12 A and  12 B are writeable to store either a logical “0” or logical “1.” 
         [0023]     Once the deflectable members of a storage cell are actuated by the probe tip  24  to a given position, the deflectable members are mechanically latched at that position. The mechanical latching of the deflectable members provides for non-volatile or stable storage of a data bit such that the state of each storage cell can be maintained even though power is removed from the storage device. At a later time, the state of the storage cell can be changed by actuating the deflectable members of the storage cell to a different position.  
         [0024]     In the implementation discussed above, actual contact is made between the probe tip  24  and a deflectable member  14  of a storage cell  12  to perform a write. In an alternative embodiment, instead of contact to provide the force necessary to move the deflectable member  14 , an electrostatic force can be generated by the probe tip  24  to move the deflectable member  14 . In this implementation, the deflectable members  14  are formed of an electrically conductive material such that they can be tied to a reference voltage, such as ground or some elevated voltage. To create electrostatic force, a different voltage is applied to the tip  24  or to some other structure of the probe  20 . The difference in voltage between the probe  20  and the deflectable member  14  generates the electrostatic force to move the deflectable member  14 .  
         [0025]     In alternative embodiments, other techniques can be used to cause movement of the deflectable member  14 . For example, the probe  20  can be formed of a magnetic material to generate a magnetic force to move the deflectable members  14 . In yet another implementation, the tip  24  of the probe  20  is heatable to an elevated temperature to heat moveable structures in a storage cell  14  to cause movement by thermal expansion and contraction.  
         [0026]     To read data, the probe  20  is scanned along a given direction, such as the direction represented by the arrow  26  in  FIGS. 1 and 2 . In one example, it is assumed that the storage cells  12 A and  12 B are at the states represented by  FIG. 1 , and the probe  20  is scanned in direction  26 . As the tip  24  is dragged across the upper surfaces of the deflectable members  14 A and  14 B of the storage cell  12 A, the tip  24  will drop relatively abruptly when it transitions from the upper surface of the deflectable member  14 A to the upper surface of the deflectable member  14 B. This downward transition causes a sudden downward deflection of the cantilever  22  of the probe  20 .  
         [0027]     As the probe  20  continues to scan along direction  26 , it crosses the upper surface of the deflectable member  14 C in the storage cell  12 B. The probe tip  24  then engages an abrupt upward transition from the upper surface of the deflectable member  14 C to the upper surface of the deflectable member  14 D. This upward transition causes an abrupt upward deflection of the cantilever  22  of the probe  20 . The abrupt deflections are detected by circuitry attached to the probe  20  as well as by remote circuitry of the storage device, as further discussed below.  
         [0028]      FIG. 3  shows an array of storage cells  12  and multiple probes  20 . In the arrangement of  FIG. 3 , the multiple probes  20  are capable of concurrently accessing multiple storage cells  12  in a given row of the storage array for improved access speeds. Each probe  20  is also capable of being scanned along a column of storage cells  12  in the array.  
         [0029]      FIG. 4  is a cross-sectional view of a probe  20  according to one embodiment. The cantilever  22  of the probe  20  is attached to but is deflectable with respect to a base member  104 . A piezoresistive element  100  is formed as a layer over the upper surface of the cantilever  22 . Piezoresistivity refers to resistance changes of a material when stress is applied to the material. The piezoresistive element  100  is in turn electrically connected to an electrical conductor  102  that extends from the probe  20  to remote detection circuitry for detecting one of two states of data stored in a given storage cell  12 . Deflection of the cantilever  22  caused by surface features of the storage cells  12  changes the resistance of the piezoresistive element  100 , which is measured by the remote detection circuitry. The downward and upward deflections of the cantilever  22  as the probe tip  24  engages the abrupt transitions between deflectable members of a storage cell causes abrupt changes in the resistance of the piezoresistive element  100  that can be detected to indicate whether a logical “0” or a logical “1” is indicated.  
         [0030]      FIG. 5  illustrates a probe substrate  50 , which includes an array of probes  20  formed in the substrate  50 . Peripheral circuitry  52  and  54  are provided on the peripheral sides of the probe substrate  50 . For example, peripheral circuitry  52  and  54  can drive X and Y select lines to select bits of the storage array to read from or write to. A row of probes  20  may be activated by the select lines to read from or write to storage cells that the probes are in contact with. Alternatively, a single one of the probes is activated to read from or write to a storage cell. The peripheral circuitry  52  and  54  include sensing devices and decoders to detect analog signals from the probes  20  and to convert the analog signals to the digital representation of a logical “0” or a logical “1.” The sensing devices include devices to sense the changes in resistivity of the piezoresistive element  100  ( FIG. 4 ) of each probe  20 . The decoders detect how the resistance changes, with resistance change in one direction indicating a first data state (e.g., logical “0”), while resistance change in a different direction representing a second data state (e.g., logical “1”).  
         [0031]     As further shown in  FIG. 6 , the probe substrate  50  is placed over the storage medium with the probe substrate  50  facing the surface of the storage medium on which the storage cells  12  ( FIG. 3 ) are formed. The probe substrate  50  is positioned over the storage substrate  10  so that the probe tips  24  ( FIG. 3 ) point downwardly. In an alternative arrangement, the storage substrate  10  is positioned over the probe substrate  50  so that the probe tips point upwardly. In other arrangements, the probe substrate  50  and the storage substrate  10  can be positioned laterally or diagonally.  
         [0032]     The storage substrate  10 , in the example of  FIG. 6 , is coupled to an actuator  60  that is designed to move the storage substrate  10  in both X and Y directions such that the probes  20  can be placed over desired storage cells. Data sensed by the probes  20  is provided to buffers  62 , which store output data for retrieval by an external device. The buffers  62  may also contain write data to be written to storage cells in the storage substrate.  
         [0033]     Alternatively, the actuator  60  is operatively coupled to move the probe substrate  50 , or to move both the probe substrate  50  and the storage substrate  10 . The actuator  60  is also able to move the storage substrate  10  and/or the probe substrate  50  in the Z direction, which is generally perpendicular to both the X and Y directions.  
         [0034]      FIG. 7  shows a portion of a probe-based storage device according to another embodiment.  FIG. 7  shows a storage cell  200 A and a storage cell  200 B formed on the surface of the storage substrate  10 . The storage cell  200 A includes a first deflectable structure having a deflectable member  202 A that is attached to a support member  206 A. The contact end of the deflectable member  202 A provides a stepped end portion  204 A for engagement to a contact end  208 B of a second deflectable member  202 B that is attached to a second support member  206 B. The stepped end portion  204 A has a generally vertical segment  210 A and a generally horizontal segment  212 A, with the vertical segment  210 A connecting the horizontal segment  212 A to the deflectable member  202 A. Alternatively, instead of the generally right-angled transitions in the end portion  204 A, a more curved or slanted configuration can be provided. Effectively, the end portion  204 A has a protrusion that is raised and that protrudes outwardly with respect to the deflectable member  202 A.  
         [0035]     In the storage cell  200 A, the contact end  208 B of the deflectable member  202 B is positioned underneath the stepped end portion  204 A of the deflectable member  202 A to represent a first data state. The storage cell  200 B shown in  FIG. 7  stores a second data state. The storage cell  200 B includes a first deflectable structure having a deflectable member  202 C attached to a support member  206 C. The end of the deflectable member  202 C provides a stepped end portion  204 C. The storage cell  200 B includes a second deflectable structure that has a deflectable member  202 D attached to support member  206 D. The contact end  208 D of the deflectable member  202 D sits over the stepped end portion  204 C of the deflectable member  202 C to represent the second data state.  
         [0036]     The probe-based storage device can be packaged for use in computing systems. For example, as shown in  FIG. 8 , a probe-based storage device  300  as discussed above is attached or connected to an I/O (input/output) port  302  of a computing device  304 . The I/O port  302  can be a USB port, a parallel port, or any other type of I/O port. Inside the computing device  304 , the I/O port  302  is connected to an I/O interface  306 , which in turn is coupled to a bus  308 . The bus  308  is coupled to a processor  310  and memory  312 , as well as to mass storage  314 . Other components may be included in the computing device  304 . The arrangement of the computing device  304  is provided as an example, and is not intended to limit the scope of the invention. In another embodiment, instead of being connected to an I/O port of the computing system  304 , the probe-based storage device can be mounted onto a main circuit board of the computing device  304 .  
         [0037]     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details. While the invention has been disclosed with respect to a number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover such modifications and variations as fall within the true spirit and scope of the invention.