Non-volatile memory

Details Non-volatile memory Non-volatile memory

2001-06-05

2003-11-11

Nguyen, Tan T. (Department: 2818)

Static information storage and retrieval

Systems using particular element

Semiconductive

C365S063000, C365S096000, C365S225700

Reexamination Certificate

active

06646912

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of digital memory circuits, and in particular to non-volatile memory circuits suitable for high-density, high-capacity, low cost data storage.
BACKGROUND OF THE INVENTION
Many consumer devices are now constructed to generate and/or utilize digital data in increasingly large quantities. Portable digital cameras for still and/or moving pictures, for example, generate large amounts of digital data representing images. Each digital image may require up to several megabytes (MB) of data storage, and such storage must be available in the camera. To provide for this type of data storage application, the storage memory should be relatively low in cost for sufficient capacities of around 10 MB to 1 gigabyte (GB). The storage memory should also be low in power consumption (e.g. <<1 Watt) and have relatively rugged physical characteristics to cope with the portable battery powered operating environment. For archival storage, data need only be written to the memory once. Preferably the memory should have a short access time (preferably less than one millisecond) and moderate transfer rate (e.g. 20 Mb/s). Preferably, also, the storage memory should be able to be packaged in an industry standard interface module, such as PCMCIA or Compact Flash card.
One form of storage currently used for application in portable devices such as digital cameras is Flash memory. This meets the desired mechanical robustness, power consumption, transfer, and access rate characteristics mentioned above. However, a major disadvantage is that Flash memory remains relatively expensive ($1.50-$2 per MB). Because of the price it is generally unreasonable to use Flash memory storage as an archive device, thus requiring data to be transferred from it to a secondary archival storage. Also, it becomes prohibitively expensive to include a large amount of Flash memory in an inexpensive digital camera or similar digital appliance (MP3 Player, PDA, etc.). This can make certain features unavailable in such applications, for example recording video on an inexpensive digital camera, and can impair the function of other features, for example limiting the number of pictures a digital camera can store or the number of songs which can be stored on an MP3 audio player.
Magnetic “hard disc” storage can also be used for archival storage, even in portable devices. Miniature hard disc drives are available for the PCMCIA type III form factor, offering capacities of up to 1 GB. However, such disc drives are still relatively expensive ($0.5 per MB), at least partially because of the relatively high fixed cost of the disc controller electronics. Miniature hard drives have other disadvantages when compared to Flash memory, such as lower mechanical robustness, higher power consumption (~2 to 4W), and relatively long access times (~10 mS). Hard drives also have disadvantages including rotational latency, and ‘wake-up’ time, which can be one second or more.
Removable optical storage discs can similarly be used, and offer one large advantage compared to hard disc. The removable optical media is very inexpensive, for example of the order of $0.03 per MB for Minidisc media. However in most other respects optical disc storage compares poorly with magnetic hard discs including relatively poor power consumption, mechanical robustness, bulk, and access performance.
Magnetic tape has even lower media cost than removable optical discs, however it shares other disadvantages of rotating disc storage, particularly with respect to physical bulk, and power consumption. In addition, magnetic tape has the disadvantage of serial access. This presents two additional application problems, namely very slow random access performance and restriction to uniform time compression techniques for storing video and the like.
For the specific application of photography, photographic film in the form of silver halide emulsions on plastic webs are a competing form of memory. The drawbacks of conventional film are its need for processing, limited shelf life, and physical bulk. The information storage on photographic film is inherently analogue in nature, and is quite unsuitable for directly interacting with digital processing apparatus and techniques. Furthermore, except in the case of Polaroid™ self developing photographic film, the stored information cannot be accessed immediately.
Embodiments of this invention address the problem of low cost archival storage for digital camera and other portable appliances. The requirements for this type of memory are: an industry standard interface (e.g. PCMCIA or Compact Flash), 2000 G shock tolerance, low power consumption (<<1W), short access time (<1 ms), moderate transfer rate (20 Mb/s), and sufficient capacity (10MB-1GB).
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, there is provided a data storage device comprising a cross-point memory array formed on a dielectric substrate material. The cross-point memory array comprises first and second sets of transverse electrodes separated by a storage layer including at least one semiconductor layer. The storage layer forms a non-volatile memory element at each crossing point of electrodes from the first and second sets. Each memory element can be switched between low and high impedance states, representing respective binary data states, by application of a write signal in the form of a predetermined current density through the memory element. Each memory element includes a diode junction formed in the storage layer, at least whilst in the low impedance state.
In one form of the invention the dielectric substrate is a formed from a polymeric material. In another form of the invention, the dielectric substrate is formed from a metal film, such as stainless steel, having a coating of dielectric material thereon.
The dielectric substrate may be formed, for example, from a material selected from: polyimide; polyethersulphone (PES); polyacrylate (PAR); polyetherimide (PEI); polyethylene napthalate (PEN); polyethylene terephthalate (PET); polyester terephthalate; polytetrafluoroethylene (PTFE); polycarbonate; and polyvinyl chloride (PVC);
The storage layer is preferably formed from material capable of processing at temperature lower than the processing temperature of the substrate material. In one form of the invention, the at least one semiconductor layer of the storage layer is formed from an organic semiconductor material. In embodiments of the invention, the organic semiconductor material may be selected from: copper pthalocyanine (CuPc); PTBCI (3,4,9,10-perylenetetracarbonxilic-bis-benzimidazole); PTCDA (3,4,9,10-perylenetetracarboxilic danhydride); BTQBT [(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole)]; TPD (N,N′-diphenyl-N,N′-bis(3-methylphenyl)1-1′biphenyl-4,4′-diamine); &agr;-NPD (4,4′-bis[N-(1-napthyl)-N-phenyl-amino]biphenyl); and TPP (5,10,15,20-tetraphenyl-21H,23H-porphine).
In other embodiments of the invention, the at least one semiconductor layer of the storage layer is formed from an amorphous inorganic semiconductor material, such as amorphous silicon or germanium.
The data storage device preferably includes address decoding circuitry coupled to said first and second sets of memory array electrodes, the address decoding circuitry having first and second sets of input lines for addressing the first and second sets of electrodes, respectively. Preferably the first and second sets of input lines are coupled through diode elements to selected ones of the first and second sets of memory array electrodes, respectively.
The data storage device preferably also includes at least one data sense line having diode connections to each of the first and/or second set memory array electrodes.
In a preferred form of the invention the first and second sets of memory array electrodes are formed in separate layers separated by said storage layer, wherein the first and second sets of input lines are formed in the same layers as the se

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