Abstract:
The present disclosure relates to a solid-state mass memory storage device which comprises a printed circuit assembly and a plurality of nonvolatile, high density storage devices mounted to the printed circuit assembly and electrically connected thereto. The solid-state memory device includes at least one controller mounted to the printed circuit assembly and electrically connected thereto, and a connector mounted to the printed circuit assembly and electrically connected thereto, the connector being adapted to electrically connect the solid-state mass memory storage device to a separate electronic device.

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to a solid-state mass memory storage device. More particularly, the disclosure relates to a semiconductor mass memory storage device suitable for disk drive replacement. 
     BACKGROUND OF THE INVENTION 
     As the volume of data generated by computing devices increases, the importance of memory space rises. Over the past several years, increases in demand for memory has caused a concomitant increase in the capacity of mass memory storage devices. Conventionally, these mass memory storage devices comprise rotating mass storage devices such as disk drives. Although great strides have been made in disk drive design in terms of capacity and speed, the versatility of conventional disk drives is limited. As a first matter, disk drive technology could soon reach a limit imposed by the superparamagnetic effect (SPE). As is known in the art, SPE is a physical phenomenon in which the energy that holds the magnetic spin in the atoms forming each bit becomes susceptible to ambient thermal energy and, therefore, is subject to random flipping which corrupts the data which the atoms represent. Unfortunately, the miniaturization currently popular in disk drive manufacture exacerbates the SPE problem. 
     A second limitation of disk drives relates to speed. Because disk drives require moving parts, the speed at which data can be stored on or accessed from the drive is limited by the speed with which the various mechanical parts of the drive can move. To increase this speed, manufacturers have continually increased the speeds at which the internal disks of the drives rotate. However, along with this increased angular velocity comes increased air turbulence and vibration which can cause misregistration of the disk tracks. In addition, to achieve high capacity and high speed, disk drives must be very precise in operation. Typically, disk drives comprise one or more disk platters and a plurality of read-write heads which record and retrieve data from circumferential tracks formed in the platters. The heads are normally moved with servomechanical actuator arms. In order to properly satisfy their record/write functions, the heads must be positioned in very close proximity to the platters, the separation between the heads and the platters typically measuring only fractions of microinches. This level of precision often results in a very fragile mechanism that can be easily damaged by moderate to large vibrations. Such susceptibility is particularly disadvantageous for portable computing devices which are often bumped and/or jolted through normal use. 
     In addition to fragility, disk drives further present the disadvantage of requiring relatively large amounts of power to operate. This again relates to the fact that disk drives have moving parts which require electrical power. Although not a major concern for plug-in devices such as desktop computers, this power consumption can be problematic for portable devices. 
     Yet another disadvantage of conventional disk drives is the physical space normally required to house the drives. Again, space constraints normally are not critical for desktop devices. However, space typically is at a premium in portable devices where smaller is often considered better. Due to such space limitations, portable devices typically do not enjoy the redundancy possible with stationary devices such as conventional network servers. As is known in the art, such stationary devices normally include a redundant array of inexpensive disks (RAID) which share the data stored in the disk drive. With this arrangement, a failure of a particular disk will not necessarily adversely effect the data stored by the drive in that the data normally can be reconstructed due to the redundancy of the data stored across the several disks. Typically, the desired level of redundancy, e.g. RAID 5 protection, requires a minimum of three disks. Due to the space limitations of portable devices such as notebook computers, however, normally only one such disk is provided. Accordingly, the desired redundancy typically cannot be provided for such devices. 
     From the foregoing, it can be appreciated that it would be desirable to have a high capacity, high speed, mass memory storage device which uses relatively little power, which is relatively rugged in construction, and which provides for data storage redundancy. 
     SUMMARY OF THE INVENTION 
     The present disclosure relates to a solid-state mass memory storage device. The solid-state mass memory device comprises a printed circuit assembly and a plurality of nonvolatile, high density storage devices mounted to the printed circuit assembly and electrically connected thereto. The solid-state memory device includes at least one controller mounted to the printed circuit assembly and electrically connected thereto, and a connector mounted to the printed circuit assembly and electrically connected thereto, the connector being adapted to electrically connect the solid-state mass memory storage device to a separate electronic device. 
     In one embodiment, the printed circuit assembly has a form factor equivalent to a conventional disk drive and the at least one controller includes control electronics and firmware which emulate a disk drive such that the device in which said solid-state mass memory storage device will interpret and treat the solid-state mass memory storage device as a disk drive. With such an arrangement, the solid-state mass memory device can be used as a disk drive replacement. 
     In another embodiment, the high density storage devices are removably mounted in storage device sockets formed in said printed circuit assembly in a redundant array. 
    
    
     The features and advantages of the invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. 
     FIG. 1 is a perspective view of a mass memory storage device constructed in accordance with the principles of the present invention. 
     FIG. 2 is a perspective view of an alternative mass memory storage device constructed in accordance with the principles of the present invention 
     FIG. 3 is a schematic view of the architecture of the mass memory storage device shown in FIG.  1 . 
     FIGS. 4A-4C are various views of an high density storage device which can be used with the mass memory storage devices shown in FIGS. 1 and 2. 
     FIG. 5 is a schematic view illustrating field emitters reading from storage areas of the high density storage device shown in FIGS. 4A-4C. 
     FIG. 6 is a schematic view illustrating a storage medium of the high density storage device shown in FIGS. 4-5. 
     FIG. 7 is a perspective view illustrating a first alternative high density storage device which can be used with the mass memory storage devices shown in FIGS. 1 and 2. 
     FIG. 8 is a perspective detail view illustrating the construction of the first alternative high density storage device shown in FIG.  7 . 
     FIG. 9 is a perspective view illustrating a second alternative high density storage device which can be used with the mass memory storage devices shown in FIGS. 1 and 2. 
     FIG. 10 is a perspective detail view illustrating the construction of the second alternative high density storage device shown in FIG.  9 . 
    
    
     DETAILED DESCRIPTION 
     Referring now in more detail to the drawings, in which like numerals indicate corresponding parts throughout the several views, FIG. 1 illustrates a mass memory storage device  10  constructed in accordance with the principles of the present invention. As shown in this figure, the mass memory storage device  10  can generally comprise a printed circuit assembly (PCA)  12 . Connected to the PCA  12  is a plurality of high density storage devices  14  which are described in greater detail below. Preferably, however, each of the high density storage devices  14  comprises a non-volatile semiconductor device which is resistant to wearout. Normally, each of the high density storage devices  14  is disposed within a storage device socket  15  formed within the PCA  12  such that each individual high density storage device  14  can be removed and replaced, if necessary. Further connected to the PCA  12  is one or more controllers  16 . As illustrated in FIG. 1, each controller  16  typically comprises a semiconductor chip which can be electrically connected to the PCA with a plurality of connectors  18 . By way of example, the controller  16  can comprise an integrated circuit including a read only memory (ROM) for storing control instructions, a microprocessor for executing these instructions, and a random access memory (RAM) for temporary storage of information. As will be appreciated from the description that follows, the controller  16  can also comprise other circuitry and software with which the controller  16  interfaces with the storage devices  14  and the device  10  host (e.g., personal computer) to ensure a predetermined level of storage redundancy. Also connected to the PCA  12  is a connector  20  which, as indicated in FIG. 1, can be attached to the PCA  12  at one of its ends. 
     As identified in the foregoing, the mass memory storage device  10  is well-suited for replacing conventional disk drives in various computing devices. Accordingly, the mass memory storage device  10  typically has a form factor suitable for replacement of a disk drive such that the device  10  can be housed in the space in which the disk drive was housed previous to removal. By way of example, the mass memory storage device  10  can have a 3.5 inch, 2.5 inch, 1.8 inch, or 1.0 inch form factor. Although these particular sizes are currently considered standard and therefore desirable, it will be understood by persons having ordinary skill in the art that the mass memory storage device  10  could be sized and configured to replace substantially any disk drive. Additionally, the mass memory storage device  10  can be customized to fit in other specific applications such as handheld computing devices and mobile telephones. In such applications, the device  10  can be designed to fit in industry standard sizes (e.g., standard memory card formats as indicated in FIG.  2 ). FIG. 2 illustrates a mass memory storage device  10 ′ in exploded view. As with the storage device  10 , the storage device  10 ′ includes a printed circuit assembly  12 ′, a plurality of high density storage devices  14 , and a connector  20 ′. Furthermore, the device comprises an internal frame  28  and outer plates  30  which enclose the device  10 ′. 
     With reference to FIG. 3, illustrated is an example architecture of the mass memory storage device  10 . As indicated in this figure, each of the high density storage devices  14  is connected to a memory bus  22  which is formed within the PCA  12  (FIG.  1 ). As is further indicated in FIG. 3, the controller(s)  16  can comprise control electronics  24  and firmware  26 . Although the mass memory storage device  10  of the present invention is suitable for placement in new computing devices, the mass memory storage device  10  is particularly well-suited for replacement of disk drives in existing devices. To serve this end, therefore, the control electronics  24  and firmware  26  stored within the controller(s)  16  can emulate the disk drive that the storage device  10  is designed to replace such that the computing device would interpret and treat the mass memory storage device  10  as the preexisting disk drive. In such an arrangement, the computing device can be manufactured with a disk drive which can later be replaced with the mass memory storage device  10  of the present invention as an upgrade. Normally, all commands and/or data processed by the mass memory storage device  10  pass through the controller(s)  16 . 
     Normally a plurality of high density storage devices  14  are connected to the PCA  12  in an array. With such an arrangement, the mass memory storage device  10  can provide for redundant storage of data similar to RAID protection. Accordingly, just as in RAID arrangements, a defective device, such as a single high density storage device  14 , can be removed from its socket  15  and replaced with a properly functioning high density storage device  14  such that the data previously stored by the defective high density storage device  14  can be reconstructed in the conventional manner. By way of example, a high degree of redundancy is provided such as a level of redundancy equivalent to RAID 5 protection can be achieved, although it will be understood that other levels of protection can be provided. Accordingly, the mass memory storage device  10  of the present invention can be used to provide the level of storage redundancy previously available only from a plurality of disks in a limited amount of space. Therefore, such redundancy can be provided to portable computing devices such as notebook computers. 
     In addition to the storage redundancy available with the mass memory storage device  10 , several other advantages over conventional disk drives exist. For instance, in that the mass memory storage device  10  does not comprise large moving parts, it can be used to restore and retrieve data much more quickly than with conventional disk drives. Furthermore, substantially reduced power consumption and greater resistance to physical damage is provided. Accordingly, the mass memory storage device  10  is particularly well-suited for use in portable devices which operate under battery power and which are transported from place to place. Moreover, the mass memory storage device  10  of the present invention can provide a substantially larger capacity of data storage than can conventional disk drives. As the following discussion elucidates, this increased capacity is made possible due to the high density storage devices  14 . 
     FIGS. 4-6 illustrate a preferred embodiment of an high density storage device  14  suitable for implementation with the mass memory storage device  10  of the present invention which uses atomic resolution storage (ARS). The storage device  14  shown in these figures is disclosed and described in detail in U.S. Pat. No. 5,557,596, which is hereby incorporated by reference into the present disclosure. FIG. 4A shows a side cross-sectional view of one such high density storage device  14 . As indicated in this figure, the storage device  14  includes a number of field emitters  102 , a storage medium  106  having a number of storage areas  108 , and a micromover  110  which scans the storage medium  106  with respect to the field emitters  102  or vice versa. In a preferred embodiment, each storage area  108  is responsible for storing one bit of information. Typically, the field emitters  102  are point-emitters having very sharp tips, each tip having a radius of curvature of approximately one nanometer to hundreds of nanometers. During operation, a predetermined potential difference is applied between a field emitter  102  and a corresponding gate such as a circular gate  103  which surrounds it. Due to the sharp tip of the emitter  102 , an electron beam current is extracted from the emitter  102  towards the storage area  108 . Depending upon the distance between the emitters  102  and the storage medium  106 , the type of emitters  102 , and the spot size (e.g., bit size) required, electron optics may be useful in focusing the electron beams. Voltage may also be applied to the storage medium  106  to either accelerate or decelerate the field&#39;s emitted electrons or to aid in focusing the field emitted electrons. In a preferred embodiment, a casing  120  maintains the storage medium  106  in a partial vacuum, such as at least 10 5  torr. 
     In the embodiment shown in FIG. 4A, each field emitter  102  is associated with a corresponding storage area  108 . As the micromover  110  scans the medium  106  to different locations, each emitter  102  is positioned above different storage areas. With the micromover  110 , an array of field emitters  102  can scan over the storage medium  106 . The field emitters  102  are responsible for reading and writing information on the storage areas  108  by means of the electron beams they produce. Thus, the field emitters  102  suitable for the present invention are preferably of the type that produce electron beams which are narrow enough to achieve the desired bit density of the storage medium  106 , and which provide the power density of the beam current needed for reaching from and writing to the medium  106 . A variety of methods are known in the art which are suitable for making such field emitters  102 . 
     In a preferred embodiment, there can be a two-dimensional array of emitters  102 , such as 100 by 100 emitters with an emitter pitch of 15 micrometers in both the X and Y directions. Each emitter  102  may access bits in tens of thousands to hundreds of millions of storage areas  108 . For example, the emitters  102  can scan over the storage medium  106  (which has a two-dimensional array of storage areas  108 ) with a periodicity of approximately 1 to 100 manometers between any two storage areas  108  and the range of the micromover is 15 micrometers. In addition, each of the emitters  102  may be addressed simultaneously or in a multiplexed manner. Such a parallel accessing scheme significantly reduces access time and increases data rate of the storage device  14 . 
     FIG. 4B shows a top view of the storage device  14  and illustrates a two-dimensional array of storage areas  108  and a two-dimensional array of emitters  102 . To reduce the number of external circuits, the storage medium  106  can be separated into rows, such as row  140 , where each row contains a number of storage areas  108  such that each emitter  102  is responsible for a number of rows. However, in such an embodiment, each emitter  102  need not be responsible for entire length of the rows. Instead, the emitter  102  can be responsible for the storage areas  108  within rows  140  through  142 , and within the columns  144  through  146 . All rows of storage areas accessed by one emitter  102  typically are connected to one external circuit, for example, rows  140  through  142 . To address a storage area  108 , the emitter  102  responsible for that storage area  108  is activated and is displaced with the micromover  110  to that storage area  108 . 
     A preferred micromover  110  can be made in a variety of ways as long as the micromover  110  has sufficient range and resolution to position the field emitters  102  over the storage areas  108 . As a conceptual example, the micromover  110  can be fabricated by a standard semiconductor microfabrication process to scan the medium  106  in the X and Y directions with respect to the casing  120 . 
     FIG. 4C shows a top view of the cross-section A—A of FIG.  4 A and illustrates the storage medium  106  being held by two sets of thin-walled microfabricated beams  112 - 118 . The faces of the first set of thin-walled beams are in the X-Z plane, such as  112  and  114 . This set of beams may be flexed in the X direction allowing the medium  106  to move in the X direction with respect to the casing  120 . The faces of the second set of thin-walled beams are in the X-Z plane, such as  116  and  118 . This set of beams allows the medium to move in the Y direction with respect to the casing  120 . The storage medium  106  is held by the first set of beams  112 ,  114 , which is connected to a frame  122 . The frame is held by the second set of beams  116 ,  118 , which is connected to the casing  120 . The field emitters  102  scan over the storage medium  106 , or the storage medium  106  scans over the field emitters  102 , in the X-Y directions by electrostatic, electromagnetic, or piezoelectric means known in the art. 
     In use, writing is accomplished by temporarily increasing the power density of the electron beam current to modify the surface state of the storage area  108 . Reading, on the other hand, is accomplished by observing the effect of the storage area  108  on the electron beams, or the effect of the electron beams on the storage area  108 . Reading is typically accomplished by collecting the secondary and/or backscattered electrons when an electron beam with a lower power density is applied to the storage medium  106 . During reading, the power density of the electron beam is kept low enough so that no further writing occurs. One preferred embodiment of the storage medium  106  is a material whose structural state can be changed from crystalline to an amorphous by electron beams. The amorphous state has a different SEEC and BEC than the crystalline state. This leads to a different number of secondary and backscattered electrons emitted from the storage area  108 . By measuring the number of secondary and backscattered electrons, the state of the storage area  108  can be determined. To change from the amorphous to the crystalline state, the beam power density can be increased and then slowly decreased. This increase/decrease heats up the amorphous area and then slowly cools it so that the area has time to anneal into its crystalline state. To change from the crystalline to amorphous state, the beam power density is increased to a high level and then rapidly. An example of one such type of material is germanium telluride (GeTe) and ternary alloys based on GeTe. 
     FIG. 5 schematically illustrates the field of emitters  102  reading from the storage medium  106 . In this figure, the state of one storage area  150  has been altered, while the state of another storage area  108  has not. When electrons bombard a storage area  108 , both the secondary electrons and backscattered electrons will be collected by the electron collectors, such as  152 . An area that has been modified will produce a different number of secondary electrons and backscattered electrons, as compared to an area that has not been modified. The difference may be greater or lesser depending upon the type of material and the type of modification made. By monitoring the magnitude of the signal current collected by the electron collectors  152 , the state of and, in turn, the bit stored in the storage area can be identified. 
     FIG. 6 illustrates a diode approach for construction of the storage device  14 . In this approach, the storage medium  106  is based on a diode structure  200 , which can be a PN junction, a schottky, barrier or any other type of electronic valve. Although FIG. 6 illustrates a particular external circuit  202 , it will be appreciated that this circuit is provided for purposes of example only. The basic idea is to store bits by locally altering the surface of a diode in such a way that collection efficiency for minority carriers generated by the altered region is different from that of an unaltered region. The collection efficiency for minority carriers is defined as the fraction of minority carriers generated by the instant electrons which are swept across the diode junction  204  when it is biased by an external circuit  202  to cause a signal current  206  to flow in the external circuit  202 . In use, the field emitters  102  emit narrow beams of electrons onto the surface of the diode  200 . The incident electrons excite electron-hole pairs near the surface of the diode  200 . Because the diode  200  is reverse-biased by an external circuit  202 , the minority carriers that are generated by the incident electrons are swept toward the diode junction  204 . Electrons that reach the PN junction  204  are then swept across the junction  204 . Accordingly, minority carriers that do not recombine with majority carriers before reaching the junction are swept across the junction, causing a current flow in the external circuit  202 . 
     Writing onto the diode  200  is accomplished by increasing the power density of the electron beam enough to locally alter the physical properties of the diode  200 . This alteration will affect the number of minority carriers swept across the junction  204  when the same area is radiated with a lower power density read electron beam. For instance, the recombination rate in a written area  250  could be increased relative to an unwritten area  108  so that the minority carriers generated in the written area  250  have an increased probability of recombining with minority carriers before they have a chance to reach and cross the junction  204 . Hence, a smaller current flows in the external circuit  202  when the read electron beam is incident upon a written area  250  than when it is incident upon an unwritten area  208 . Conversely, it is also possible to start with a diode structure having a high recombination rate and to write bits by locally reducing the recombination rate. The magnitude of the current resulting from the minority carriers depends upon the state of the storage area  106  and the current continues the output signal  206  to indicate the bit stored. 
     FIGS. 7 and 8 illustrate a first alternative construction of the high density storage devices  14  shown in FIG.  1 . In particular, illustrated is a magnetic random access memory (MRAM) device  14 ′. As indicated in FIG. 7, the MRAM device  14 ′ is a solid-state memory storage device which generally comprises a plurality of cells  300  which serve as magnetic domains and a plurality of conductor bars  302  and  304 . Typically, the bars  302 ,  304  are arranged in first and second parallel planes  306  and  308  with the bars  302  of the first plane  306  aligned perpendicularly to the bars  304  of the second plane  308 . Accordingly, the bars  302 ,  304  form intersection points  310 . As is further indicated in FIG. 7, one cell  300  is disposed intermediate the two planes  306 ,  308  at each intersection point  310  formed by the bars  304 ,  308 . Therefore, as shown in the detail view of FIG. 8, one cell  300  is sandwiched between a first bar  302  and a second bar  304  at the two bars′ intersection point  306 . As indicated in FIG. 8, each cell  300  comprises a pinned magnetic layer  312  (i.e., a layer which is permanently magnetized in a predetermined direction), a relatively thin dielectric layer  314 , and a free magnetic sense layer  316  (i.e., a layer whose magnetization direction can be selectively changed). By way of example, the bars  302 ,  304  and their associated cells can be formed on one or more substrates to create an integrated device. 
     In use, writing is accomplished by passing current, i, through the conductor bars  302 ,  304  to create magnetic fields H x  and H y  which produce resultant vector addition magnetic forces, M, at the intersection points  310 . These magnetic forces are sufficient to selectively cause the magnetic orientation of the sense layers  316  to either coincide with the magnetic direction of the pinned magnetic layer  312  or to oppose it. Detection of the written state of the sense layer&#39;s magnetism can then be accomplished by determining the differential resistance in the tunneling magneto-resistive junction between the two conductor bars  302 ,  304  through the sense layer  316 , the dielectric layer  314 , and the pinned layer  312  depending upon the pinned layer&#39;s magnetic orientation. 
     FIGS. 9 and 10 illustrate a second alternative construction of the high density storage devices  14  shown in FIG.  1 . In this alternative, the storage device  14 ″ is a stylus storage device which comprises a storage medium  400  composed of a polymeric material and a 2-D stylus array chip  402 . The 2-D stylus array chip  402  comprises a plurality of styluses  404 , each having a sharp tip  406  (e.g., radius of curvature of approximately 20 nm) which rests upon the smooth surface of the storage medium. In use, writing is accomplished by passing a current through the stylus  404  to briefly heat the tip  406  to a high temperature (e.g., 400° C.). The heated tip  406  causes the surface of the medium  400  to melt, forming an indentation  408 . When a series of indentations  408  are formed, the dips and flats can be treated as 0&#39;s and 1&#39;s. To read this information, the stylus tip  406  is heated to a temperature below the melting point of the polymeric material (e.g., 350° C.). When the stylus  404  drops into an indentation  408  formed in the medium  400 , the heat from the tip  406  of the stylus  404  dissipates. This temperature drop can then be detected by monitoring the electrical resistance of the stylus  404 . 
     Although specific embodiments of the high density storage devices  14  have been provided herein, it will be appreciated that these embodiments are provided by way of example only. Most preferably, however, the storage device  14  used will have high capacity, be nonvolitile, and resistant to read/write wearout. Irrespective of the particular form of the high density storage device  14  used, several advantages can be obtained through use of the mass memory storage device  10  described herein. First, the storage device described in this disclosure is less susceptible to SPE as compared to conventional disk drives. Second, the storage device can read and write with greater speed than conventional disk drives in that the moving parts of the device are of such low mass. Furthermore, because of this low mass, the presently disclosed storage device normally is more robust than conventional disk drives and typically requires less power to operate. Moreover, the herein described storage device usually can be manufactured smaller than conventional disk drives and therefore a desirable amount of storage redundancy can be obtained, even where space is limited. 
     While particular embodiments of the invention have been disclosed in detail in the foregoing description and drawings for purposes of example, it will be understood by those skilled in the art that variations and modifications thereof can be made without departing from the spirit and scope of the invention as set forth in the following claims.