Molecular Memories Based on a CMOS Platform
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Molecular Memories Based on a CMOS Platform
Werner G. Kuhr, Antonio R. Gallo, Robert W. Manning, and Craig W. Rhodine Abstract Hybrid complementary metal oxide semiconductor (CMOS)/molecular memory devices are based on a dynamic random-access memory (DRAM) architecture, are fast, have high density, and exhibit low power consumption. These devices use a well-characterized charge storage mechanism to store information based on the intrinsic properties of molecules attached to a CMOS platform. The molecules are designed in a rational way to have known electrical properties and can be incorporated into CMOS devices with only minor modification of existing fabrication methods. Each memory element contains a monolayer of molecules (typically 100,000–1,000,000) to store charge; this process yields a structure that has many times the charge density of a typical DRAM capacitor, obviating the necessity for a trench or stacked capacitor geometry. The magnitude of voltage required to remove each electron is quantized (typically a few hundred millivolts per state), making it much easier to put molecules in a known state and to detect that state with low-power operation. Existing devices have charge retention times that are 1000 times that of semiconductors, and nonvolatile strategies based on simple modifications of existing systems are possible. All of these devices are ultimately scalable to molecular dimensions and will enable the production of memory products as small as state-of-the-art lithography will allow. Keywords: charge storage, complementary metal oxide semiconductors, CMOS, molecular capacitors, molecular memory, porphyrins, redox monolayers.
Introduction State-of-the-art semiconductor devices now have critical feature dimensions that are substantially less than 0.1 m.1 While many devices can be manufactured effectively at such small dimensions through the continued extension and optimization of existing process technologies, it is uncertain at what point along the path of miniaturization that such devices, which rely on the bulk properties of materials, will be unable to retain the required functional characteristics. Much work has been done in the field of molecular electronics, where investigators have attempted to mimic transistor properties in molecular systems.1 While the creation of a molecular transistor has received the dominant share of attention (and recent criticism regarding the presumed mechanism of operation),2 transistor fabrication is
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expected to scale to 10 nm dimensions, albeit with a great deal of effort.3 Indeed, the component that is most urgently in need of replacement for most semiconductor devices is the charge storage device, that is, the capacitor. All leading-edge memory devices use charge storage as the mechanism of information storage, including dynamic randomaccess memory (DRAM), flash memory (where devices rely on electron storage in the floating gate of a field-effect transistor), and 1T SRAM (one-transistor static RAM, similar in function to DRAM, but using a different s
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