Molecular Memory

Data Storage









Already some time ago was created a prototype system memory, is used as a cell protein molecules, called bacteriorhodopsin. He has a purple color, absorbs light and is present in the membrane of a microorganism, called halobacterium halobium. This microorganism was found in salt marshes, where temperatures can reach +150 ° C. When the level of oxygen in the environment are so low that it is impossible for energy use breath (oxidation), he uses the protein for photosynthesis.

Bakteriorodopsin was chosen because fototsikl (sequence of structural changes that molecule is undergoing in response to light) makes this an ideal logical molecule memory element type "&" or a type of switch from one state to another (trigger). As studies have shown, bR-state (logical "0") and Q-state (logical "1") are intermediate states of molecules and can remain stable for many years. This property, in particular providing the surprising stability of protein, and was purchased by an evolutionary struggle for survival in harsh conditions in salt marshes.

Another important feature bakteriorodopsin is that these two states are noticeably different absorption spectra. This makes it easy to define the current state of molecules using laser tuned to the appropriate frequency. The data stored in a memory, may persist about five years.

It was built a prototype system memory, which stores data in bakteriorodopsin three dimensional matrix. This matrix is a cuvette (transparent receptacle), completed poliakrid gel, which is available in protein. Cuvette has long h1h2 size of 1 inch. Protein, which is in the bR-state, fixed in space, with polymerization gel. Cuvette surround battery lasers and detector matrix built based device that uses the principle of charge injection (CID - Charge Injection Device), which serve to record and read data.

When recording data for the transfer of molecules in the Q-condition first to use yellow "pages" laser. Spatial light modulator (SLM), which, as previously mentioned, is an LCD-matrix, creating a mask in the way of a beam, leading to a strong (instituted) plane in the material inside the cuvettes. This energy intensive plane is a page of data, which may include an array of size 4096 h4096 cells.

To return the state of the rest of protein in the red recordable laser, disposable at right angles towards yellow. The second SLM also managed matrix of binary data, and thus creates a beam in the way of appropriate mask, so the exposure will be only certain point of the page. Molecules move in these places in Q-state and will represent binary unit. The rest of the page will return to its original bR-state and will represent binary zeros. To read data, it is necessary again to use laser pages, which translates to read the Q-state. This is done to ensure that in the future through differences in the absorption spectra to identify the binary zeros and ones. In two milliseconds after this page irradiated red low intensity laser radiation. Low intensity needed to warn the transition molecules in the Q-state. Molecules of a binary zero, absorb red light, a unit of binary - do not react to it. This creates a "chess" pattern of light and dark spots on the LCD-matrix, which reads a page of digital information.

To erase data is a short pulse of blue laser to recover molecules of Q-state in the original bR-state. Blue light does not have to go from laser - can erase all cuvette using ordinary ultraviolet lamps. To ensure the integrity of data when applied selectively erasing cache of several pages of related pages. When read-write transactions to protect against failures, with a common code test parity. Page data can be read without destroying up to 5000 times. Each page counter and tracked, and if the 1024 reading, the page "refreshes" (regenerated) with the help of a new operation record.

The total operation time of the reading or writing is about 10 ms. By analogy with the system holographic memory device carries out a parallel access to the read-write cycle, which allows count on the overall speed to 10 Mbps. It is assumed that if merge eight bit storage cells in the byte with a parallel access, we can reach speeds of 80 Mbps, but this method requires appropriate scheme-Tech realization of the memory subsystem. The proposed system is close to the speed of semiwire memory. Theoretically cuvette containing the protein can accommodate about one terabita data. Restrictions on capacity linked, mostly with the problems of lens systems and quality protein.

Such molecular memory "first generation" already has certain advantages compared with traditional semiwire memory. First, it was based on a protein produced in large quantities and at a low price, which contribute to the achievement of genetic engineering. Secondly, the system can operate in a wider range of temperatures than the current semiconducting memory. "Thirdly, such a nonvolatile memory. Finally, cuvettes with data can be long and safely stored.

The next step in the development of molecular memory was study the properties of individual molecules that could be in a position bistabilnom and managed not optically and electrically.

For the first time the idea of using DNA molecules as the memory was provided for in article L. Adlemana (L. Adleman) in the journal Science in 1994. Used the fact that the nature of DNA molecules such that their interaction provides the possibility of four different phases of a sequence of molecules. Like this type of molecule RNA and proteins (proteins) that can create such structures can also be used for this purpose.

Information processing in molecular scale assumed in several ways, but only Adleman identified ways of building on the basis of its general purpose computer, based on the theory of universal computing. He determined that some combination of biological molecules naturally possess "combinatorial complexity", which is the basis of life itself. Indeed, a scientist just looking for one of the ways to address the problem of computational complexity of the tasks NP-completeness and drew attention to the molecular structures that allow for parallel computing ( "massive parallelism"). As it turned out later, molecular structure can solve much larger range of tasks, such as creating effective memory devices.

Memory type of RAM, a key component of the system memory of computers, which allows users to store and manage data may be based on a molecule "catenane", which consists of two rings of atoms interacting electrochemically. The electrical impulse removes an electron from the molecule and makes one ring of atoms rotate by some angle on the second (the situation "included"). In return the state of the electron pair of rings is restored (the "off"). Such change can be made an unlimited number of times. Electrochemical nature of the change in the volatile molecules defines built based on them as static or dynamic memory. Previous experiments on the molecules, called rotaxane, showed only a single opportunity to change the state of the memory cells. The effect, appropriate action fuse, allows for the creation of memory, suitable for read-only (ROM).

Currently, chemists are working with more than half of different types of molecular switches, each with its own unique characteristics, superior properties "catenane".

Specialists company ZettaCore placed four organic molecules substances, known as porphyrins, and served in a number of small voltage across the chain. This effect causes molecules to lose electrons, which leads to a change in their electrochemical state. The state of molecules, it reads as the absence or presence of bits of information (unit or zero).

Unlike the existing volatile memory cells, which are to store only one bit of information requires six transistors, here each cell can hold three bits.

In the first phase of research molecules needed to be placed separately from each other, but then the scientists succeeded in synthesizing the structure of self (self-assembly) type of oil films, with a thickness of a few atoms. Particularly important was the transition from chaotic orientation of molecules in solution to their self in a thin film.

Experimentally it was shown that "themselves" monolayer molecules between electrodes possesses characteristics of memory devices (DRAM) in a room temperature. The device had trouble during the year, with the memory preserved without the need for regeneration charge more than 15 minutes (a typical silicon memory cell to regenerate a charge of about a thousand times per second).

One of the many problems of nanoelectronics is the process of streamlining the structures of molecules. The representative of the firm MITRE (USA) Alex Wissner-Gross invented the method in 1998, he called scaling or nanometricheskim NanoPGM. It is to create a structure "nanopaltsev" (nanofingers), which, with a few nanometers in size, could form ordered arrays in this sense molecules to create nanoelectronics devices.

Another challenge of building devices on the molecular basis of memory is to create a network of wires, the supply electrical impulses to each individual molecule. To this end, to be used so-called nanotubes.