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Exploring split-gate thin-film storage

Posted: 17 Oct 2012 ?? ?Print Version ?Bookmark and Share

Keywords:split-gate thin-film storage? NVM? ferroelectric RAM?

Another unique advantage of SG-TFS is that the individual nanocrystals are less influenced by electric fields that may originate along the edges of the bit cell. This means the edges can be brought closer together, and the electrical behavior of the array of nanocrystals is not strongly affected. In other words, the active part of the bit cell can be scaled more easily.

To summarize, the advantages of thin-film storage based nanocrystals are:

???Reliability: Charge is stored in a thin film of nanocrystals, so data is maintained even if one crystal loses charge.
???Low cost: Cell structure is simple to integrate into CMOS, and doesn't require triple poly layers, complicated polishes, multiple spacer formations, etc.
???Scalability: Cell operation doesn't depend on coupling ratios, and basic operation is maintained even as feature sizes are reduced with each generation of lithography.
???Application diversity: Able to meet a broad range of market applications

Future of flash technologies
For future technologies, beyond 40 nm, embedded flash integration will become more challenging. This is because the base logic platform is becoming more and more complex, and more sensitive to interactions between various types of IP, including non-volatile memory.

For decades the industry has been using silicon dioxide as a gate oxide material. As the industry has progressed along the Moore's law curve and transistors have decreased in size, the thickness of the silicon dioxide gate dielectric has also decreased, increasing the gate capacitance, output current, and ultimately raising device performance. Beyond 40 nm, gate oxide leakage current has increased drastically, leading to higher power consumption as well as lower device reliability.

In order to combat this effect, the silicon dioxide gate dielectric is often replaced with a high-K material, allowing increased gate capacitance (hence higher performance) without the associated leakage. Future memory solutions will thus be dealing with a new material system (high-K metal gate). In addition, the base platform is moving to different structures, such as FINFET-type structures which enable scaling of the area consumed by CMOS logic.

Integration of flash into these technologies will be aided by flash cell types which are more planar, more compatible with different materials systems, and electrically easier to scale. The SG-TFS technology developed at Freescale has several advantages in these areas.

Why is the commercialization of SG-TFS so significant? As with every area of the semiconductor industry, the arena for embedded flash products, such as microcontrollers, is very dynamic. Simple structures which can be integrated easily and scaled readily will have many advantages. Moving this technology from the drawing board, through the R&D phase and into volume production has laid the foundation for a very promising technology roadmap as we go forward.

SG-TFS is an ideal choice for future of NVM technology, offering superior reliability, with much lower cost of integration, much lower power consumption, and scalability to meet the technology and manufacturing challenges beyond 40 nm. Other commercially viable traditional flash technologies out there are in their third or fourth generation of development, with all innovations already "squeezed out" of the technology. SG-TFS, meanwhile, is already very competitive with other flash technologies in only its first generation of commercialization, and has huge untapped upside ahead of it. One may say that the future of flash technology is already here, and will outperform other types of technologies for years to come, as others are running out of steam.

About the authors
Kaivan Karimi is the Head of Portfolio Management & Business Development at Freescale's Auto, Industrial, and Multi-Market Solutions Group (AISG), and holds MSEE and EMBA degrees.

Kelly Baker is a Freescale Fellow and serves as Chief NVM Technologist in Freescale's Auto, Industrial, and Multi-Market Solutions Group (AISG).

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