Key Invention Underlying 3-D Memory Development

The key invention underlying the technology is the introduction of a specially patterned “soft” magnetic matrix to isolate magnetic bits of information from each other[1]. Previously, it was shown that patterning of a SUL could substantially increase the strength and maintain the localization of the recording across the entire thickness [2]. For comparison, the simulated field profile across the recording media without and with a patterned SUL is shown in Figure 1. This comparison illustrates substantially improved localization of the field across the thickness when SUL is used. This is an important factor to record high-density information across the thickness. The same concept could be extended into the implementation in which the field is controlled not only by one patterned SUL on the opposite side of the media (with respect to the recording transducer) but via the use of a set of patterned soft interlayers (SIL), with each SIL separating two adjacent magnetic layers.

          
Figure 1. The recording field profiles across the media thickness for two recording systems, without (left) and with a patterned SUL, respectively.

The latter effect was developed into the concept of a patterned soft magnetic matrix. Through atomistic calculations, the patterned soft matrix is presented as a 3-D grid of magnetic images.  Each node in the matrix consists of a set of various “hard” and/or “soft” ferromagnetic materials. The magnetic “softness” of the matrix and thus the intensity of each image in the grid are controlled via a set of electric currents, as shown in Figure 2. This mechanism is used to access information inside the 3-D matrix. The parallel mechanism used to address data both during writing and reading enables an ultra-fast access time.

Figure 2.  A schematic of a 3-D matrix with three sets of address lines. Each node in the matrix consists of a set of various “hard” and/or “soft” ferromagnetic materials.

Ferromagnetic Resonance to Locally Control Media Coercivity

To further substantially increase signal-to-noise ratio, ferromagnetic resonance (FMR) could be used to access the data in the matrix. In the above matrix implementation, the ferromagnetic resonance occurs only in the region (s) of a bit cell (s) for which all three address lines conduct a non-zero electric current. Therefore at the condition of FMR, individual bits or arrays of bits could be addressed for writing and reading information. Among other advantages of using FMR are 1) relatively small currents to access information for writing and reading and 2) relatively low power consumption. It is anticipated that with this technology, 100 terabits of data could be stored in a cube with a side of approximately 1 cm. There are many ways to fabricate the nanoscale matrix for the memory and potential magnetic logic implementations. FIB and oblique vapor deposition or sputtering are among the methods explored in this study [ 3]. Another promising technology to fabricate 3D matrix is to use vertically aligned periodic arrays of carbon nanotubes (CNTs). To integrate CNT-based fabrication into the 3D memory effort, the group collaborates with the Robert Haddon group at UCR.

Future Work With CNT-based Memory Matrix

Another example of the matrix for the described memory structure could be in the form of a grid made of periodic arrays of vertically aligned carbon nanotubes (CNT), as shown in Figure 3. The use of CNT-based matrix may become the most reliable way to scale the technology down to a single-molecule level. In the current implementation, CNTs are vertically aligned. An array of ferromagnetic materials could be electro-plated or deposited via other methods inside or outside CNTs. Among many advantages, the vertically aligned CNTs with shape-defined vertical anisotropy could substantially broaden the selection of ferromagnetic and other materials that could be used. In accordance with the model above, CNT arrays could be further patterned into separate square or other shape islands of CNTs, as shown in the left schematic in Figure 3. Throughout the project, the described interdisciplinary study of practical memory applications will be further developed through various existing and new partnerships with other universities (RPI, UH, Duke) and companies (Seagate, IBM, Hitachi).

All the above described memory implementations could be substantially improved through the implementation of vertically aligned and periodically ordered CNTs. In summary, among these implementations are 1) trivial multi-level mode of 3-D memory with an array of giant magnetoresistive (GMR) or tunneling magnetoresistive sensors (TMR) or some form of ballistic sensors on top of the recording media, 2) absolute 3-D memory with a nanosensor or a set of nanosensors (CNTs themselves could be developed for ballistic sensing) in each node of a 3-D matrix, 3) 3-D memory forms with FMR-based access of information for writing and reading.  The key advantages due to the use of CNTs are:

Figure 3 . Schematics showing a 3-D bit pattern in a patterned CNT-based matrix (left) and a 3-D bit pattern in a continuous CNT-based matrix. In this implementation, CNTs are vertically aligned. A set of ferromagnetic materials could be electro-plated or deposited via other methods.

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