Dr. Jonathan S. Lindsey
Ultradense Information Storage with Hybrid Molecular/Semiconductor Chip

Department of Chemistry
North Carolina State University

The central tenet of “molecular electronics” is that molecules can serve as active elements in future computational devices. In a new approach for information storage, we are using molecules attached to an electroactive surface as the active medium wherein information is stored in the discrete oxidation states of molecules. The molecular medium mimics the function of a semiconductor capacitor such as that found in a dynamic random access memory (DRAM) cell. 2 For implementation, a hybrid architecture is composed of information-storage molecules located in the memory cells of traditional, photolithographically constructed memory chips.

The design of molecules that are suitable for incorporation in hybrid memory chips presents daunting challenges, because the molecules must first meet the criteria that are satisfied by existing semiconductor materials: (1) withstand the high temperature processing steps in the semiconductor fabrication process (400 °C), (2) operate over a large number of cycles (≥10 12), and (3) function at typical chip temperatures (~85 °C). Even if one can imagine a future, totally molecular computer, built via low-temperature processes from the “bottom up,” such molecules would still need to meet the real-world criteria of operation for >10 12 cycles under the hot conditions characteristic of high-speed, high-density chips.

The attraction of redox-active molecules for use as charge-storage elements in capacitors is that redox-active molecules afford intrinsic features that are not available with semiconductors. The features include (1) scalability to small dimensions, (2) high charge density, (3) low voltage operation, (4) long charge-retention times, (5) availability of multiple states, (6) fault tolerance, and (7) facile ability to tailor potentials, charge-retention times, number of states, and overall molecular architecture using the power of synthetic chemistry.

We have prepared over 350, primarily porphyrinic, molecules for studies of charge storage. The generic design of the information-storage molecules includes a redox-active unit and a tether for surface attachment. We have developed synthetic methods to gain access to molecules for attachment to Au, metal oxides (e.g., TiO 2 and SiO 2), and Si. Molecules have been designed and characterized that exhibit up to 8 states with a potential range of <1.8 V, charge-retention times of up to 15 minutes, stability at 400 °C, and integrity after 10 12 cycles. 3 The use of molecules that function under real-world conditions in conjunction with standard semiconductor lithography may provide an initial foothold for the beginning of a practical molecular electronics.

• The work described stems from a collaborative effort of synthetic chemists (the author’s group), physical chemists and surface scientists (Prof. David Bocian’s group at UC Riverside), electrical engineers with expertise in nanodevice design (Prof. Veena Misra’s group at NC State), and electrochemists and chip fabrication experts (Dr. Werner Kuhr’s group, formerly at UC Riverside and now at ZettaCore, Inc.).
• “Molecular Approach Toward Information Storage Based on the Redox Properties of Porphyrins in Self-Assembled Monolayers,” Roth, K. M.; Dontha, N.; Dabke, R. B.; Gryko, D. T.; Clausen, C.; Lindsey, J. S.; Bocian, D. F.; Kuhr, W. G. J. Vac. Sci. Technol. B.2000, 18, 2359–2364.
• “Molecular Memories that Survive Silicon Device Processing and Real-World Operation,” Liu, Z.; Yasseri, A. A.; Lindsey, J. S.; Bocian, D. F. Science 2003, 302, 1543–1545.

Biosketch

Location: Welcome Center at 2:30 p.m.