Experimental Observation of Non-Volatile Charge Injection and Molecular Redox in Fullerenes C 60 and C 70 in an EEPROM-T
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Experimental Observation of Non-Volatile Charge Injection and Molecular Redox in Fullerenes C60 and C70 in an EEPROM-Type Device Udayan Ganguly1, Chungho Lee2 and Edwin C. Kan2 Department of Materials Science and Engineering, 2School of Electrical and Computer Engineering, Cornell University
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ABSTRACT Molecular interface with CMOS is an area indispensable to the enhancement of our understanding of the nano-scale world. We report the integration of fullerenes in CMOS gate stack and demonstrate a functional molecular interface by effecting molecular redox operations through non-volatile charge injection in an EEPROM-type device. The gate stack of the MOS capacitor consists of a tunneling thermal oxide. A sub-monolayer of fullerenes is deposited. Then the control oxide is deposited and finally the gate metal is patterned. Charge injection occurs at a specific potential of the fullerene molecules with respect to the conduction band of Si at the Si/SiO2 interface, independent of the concentration of the fullerene sub-monolayer. This strongly indicates molecular redox in solid state that is electrostatically controllable. Such molecular interfaces can be used to enhance the spatial sensitivity of chemical sensors like the CνMOS to be able to interface with macromolecular systems. INTRODUCTION A challenge in nanotechnology is to be able to build interfaces from the macro-world to communicate with the nano-scale world. Molecular interfaces with CMOS, is an area that proposes to use the silicon platform to electronically address molecules. Molecules of carbon, like fullerenes and nanotubes have aroused a great deal of scientific curiosity. Carbon molecules are known for their chemical stability and can be found in myriad forms from spheres to nanotubes. They exhibit a wide range of electronic properties which can be further modified by using the rich chemistry of carbon. Carbon nanotubes have been used in a wide range of electrical sensing application as well as a logic and memory elements [1]. In the present paper, we report our ability to control the charge state of a carbon molecule embedded in the dielectric of a CMOS gate stack. From a technological point of view, such interfaces can have a tremendous impact. Carbon nanotubes, chemically similar to fullerenes, used as a floating gate as in a CνMOS [2], whose charge is controlled by a CMOS interface, can act as a electrical probe with nanometric spatial resolution. Charge injection of this precise nature constrained by chemistry can also pave way for multi-level charge storage and high density memory. EXPERIMENTAL SET-UP A MOS capacitor is the ideal set-up to measure charge injection as a function of injection voltage. The structure of the device has been shown elsewhere [3]. Briefly, the device consists of a silicon doped p-type to 2×1017 cm-3 density. After making a standard
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LOCOS isolation as described elsewhere [3], a 2.3 - 2.7 nm dry thermal oxide is grown on the active area. The fullerenes C60 and C70 are evaporated thermally to a few angstroms
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