Static information storage and retrieval – Systems using particular element – Molecular or atomic
Reexamination Certificate
2000-01-14
2001-04-03
Nelms, David (Department: 2818)
Static information storage and retrieval
Systems using particular element
Molecular or atomic
C365S106000, C365S153000, C365S173000
Reexamination Certificate
active
06212093
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to memory devices. In particular, this invention provides an electronic memory device capable of storing information in extremely high density.
BACKGROUND OF THE INVENTION
Basic functions of a computer include information processing and storage. In typical computer systems, these arithmetic, logic, and memory operations are performed by devices that are capable of reversibly switching between two states often referred to as “0” and “1”. In most cases, such switching devices are fabricated from semiconducting devices that perform these various functions and are capable of switching between two states at a very high speed using minimum amounts of electrical energy. Thus, for example, transistors and transistor variants perform the basic switching and storage functions in computers.
Because of the huge data storage requirements of modern computers, a new, compact, low-cost, very high capacity, high speed memory configuration is needed. To reach this objective, molecular electronic switches, wires, microsensors for chemical analysis, and opto-electronic components for use in optical computing have been pursued. The principal advantages of using molecules in these applications are high component density (upwards of 10
18
bits per square centimeter), increased response speeds, and high energy efficiency.
A variety of approaches have been proposed for molecular-based memory devices. While these approaches generally employ molecular architectures that can be switched between two different states, all of the approaches described to date have intrinsic limitations making their uses in computational devices difficult or impractical.
For example, such approaches to the production of molecular memories have involved photochromic dyes, electrochromic dyes, redox dyes, and molecular machines all have fundamental limitations that have precluded their application as viable memory elements. These molecular architectures are typically limited by reading/writing constraints. Furthermore, even in cases where the effective molecular bistability is obtained, the requirement for photochemical reading restricts the device architecture to a 2-dimensional thin film. The achievable memory density of such a film is unlikely to exceed 10
10
bits/cm
2
. Such limitations greatly diminish the appeal of these devices as viable molecular memory elements.
SUMMARY OF THE INVENTION
This invention provides novel high density memory devices that are electrically addressable, permitting effective reading and writing, that provide a high memory density (e.g., 10
15
bits/cm
3
), that provide a high degree of fault tolerance, and that are amenable to efficient chemical synthesis and chip fabrication.
In a preferred embodiment, this invention provides an apparatus for storing data (e.g., a “storage cell”). The storage cell includes a fixed electrode electrically coupled to a “storage medium” comprising a sandwich coordination compound having a plurality of different and distinguishable oxidation states where data is stored in the (preferably non-neutral) oxidation states by the addition or withdrawal of one or more electrons from said storage medium via the electrically coupled electrode.
Particular examples of sandwich coordination compounds that may be used to carry out the present invention have the Formula I (for double-decker sandwich compounds) or Formula II (for triple-decker sandwich compounds):
wherein:
M
1
and M
2
(when present) are metals independently selected from the group consisting of metals of the lanthanide series (Ln=La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, as well as Y, Zr, Hf, and Bi, and in the actinide series Th and U (radioactive elements such as Pm are generally less preferred);
L
1
, L
2
and L
3
(when present) are independently selected ligands (e.g., porphyrinic macrocycles); and
Q
1
, Q
2
and Q
3
may be present or absent and when present are independently selected linkers (the linker preferably including a protected or unprotected reactive group such as thio, seleno or telluro group). Preferably, at least one of Q
1
, Q
2
, and Q
3
is present.
In preferred storage cells, the storage medium stores data at a density of at least one bit, and preferably at a density of at least 2 bits. Thus, preferred storage media have at least 2, and preferably at least 4, 8 or 10 or more different and distinguishable oxidation states. In particularly preferred embodiments, the bits are all stored in non-neutral oxidation states. In a most preferred embodiment, the different and distinguishable oxidation states of the storage medium can be set by a voltage difference no greater than about 5 volts, more preferably no greater than about 2 volts and most preferably no greater than about 1 volt.
The storage medium is electrically coupled to the electrode(s) by any of a number of convenient methods including, but not limited to, covalent linkage (direct or through a linker), ionic linkage, non-ionic “bonding”, simple juxtaposition/apposition of the storage medium to the electrode(s), or simple proximity to the electrode(s) such that electron tunneling between the medium and the electrode(s) can occur. The storage medium can contain or be juxtaposed to or layered with one or more dielectric material(s). Preferred dielectric materials are imbedded with counterions (e.g. Nafion® fluoropolymer). The storage cells of this invention are fully amenable to encapsulation (or other packaging) and can be provided in a number of forms including, but not limited to, an integrated circuit or as a component of an integrated circuit, a non-encapsulated “chip”, etc. In some embodiments, the storage medium is electronically coupled to a second electrode that is a reference electrode. In certain preferred embodiments, the storage medium is present in a single plane in the device. The apparatus of this invention can include the storage medium present at a multiplicity of storage locations, and in certain configurations, each storage location and associated electrode(s) forms a separate storage cell. The storage medium may be present on a single plane in the device (in a two dimensional or sheet-like device) or on multiple planes in the device (in a three-dimensional device). Virtually any number (e.g., 16, 32, 64, 128, 512, 1024, 4096, etc.) of storage locations and storage cells can be provided in the device. Each storage location can be addressed by a single electrode or by two or more electrodes. In other embodiments, a single electrode can address multiple storage locations and/or multiple storage cells.
In preferred embodiments, one or more of the electrode(s) is connected to a voltage source (e.g. output of an integrated circuit, power supply, potentiostat, microprocessor (CPU), etc.) that can provide a voltage/signal for writing, reading, or refreshing the storage cell(s). One or more of the electrode(s) is preferably connected to a device (e.g., a voltammetric device, an amperometric device, a potentiometric device, etc.) to read the oxidation state of said storage medium. In particularly preferred embodiments, the device is a sinusoidal voltammeter. Various signal processing methods can be provided to facilitate readout in the time domain or in the frequency domain. Thus, in some embodiments, the readout device provides a Fourier transform (or other frequency analysis) of the output signal from said electrode. In certain preferred embodiments, the device refreshes the oxidation state of said storage medium after reading said oxidation state.
Particularly preferred methods and/or devices of this invention utilize a “fixed” electrode. Thus, in one embodiment, methods and/or devices in which the electrode(s) are moveable (e.g. one or more electrodes is a “recording head”, the tip of a scanning tunneling microscope (STM), the tip of an atomic force microscope (AFM), or other forms in which the electrode is movable with respect to the storage medium) are excluded. Similarly in certain embodiments, methods and/or devices and/or storage media, in which
Myers Bigel & Sibley & Sajovec
Nelms David
North Carolina State University
Yoha Connie C.
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