Page 11 - Molecules for Charge-Based Information Storage

Molecules for Charge-Based Information Storage Lindsey and Bocian

FIGURE 11. Metal deposition on redox-active molecules attached to a surface: (A) illustration of molecule with top contact; (B) AFM image of surface
following Ag deposition; (C) profile of the surface following Ag deposition.

Raman spectroscopy, XPS, cyclic voltammetry, and current
voltage measurements (Figure 11). The studies indicate
that all of the porphyrin monolayers are robust under the
conditions of metal deposition. Neither Cu nor Ag penetrates
through the monolayer to form electrically conductive fila-
ments, whereas Au does penetrate through the porphyrin
monolayer and contacts the Si substrate.

Demonstration of Low-Power, High Charge
Density, Semiconductor/Molecular Memory
Devices FIGURE 12. Photograph of 1 Mb test chip developed by ZettaCore, Inc.
The ultimate goal of our research program was to imple- cell is equal to (or greater than) that achieved in trench/stack
ment the charge-storage molecules in hybrid semiconduc- designs. This aspect of the hybrid semiconductor/molecular
tor/molecular memory devices. This goal was achieved in a design was another key objective of our research program.
2
prototypical 1-Mb DRAM test chip design (Figure 12). The Another important feature of the hybrid semiconductor/
chip incorporates 4 256 kbit arrays of molecularSi molecular DRAM is that all of the peripheral circuits were
capacitors. The circuits on the chip were fabricated on a fabricated with conventional technology. Consequently, the
0.35 μm flow process to avoid the high costs of masks only variation in the manufacturing process is where
prepared on smaller lithography nodes. A key feature of the hybrid molecularSi structures are formed. Owing to
the chip architecture is that the capacitors are planar rather the high charge density (and consequent planar design), the
than utilizing the vertical dimension (trenches or stacks). overall fabrication process requires less than 10% of the
Despite the planar area of the capacitor, the demonstrated number of steps typically required in the fabrication of
charge-storage density in each molecular-based memory commercial DRAM chips. The process is also compatible

648 ’ ACCOUNTS OF CHEMICAL RESEARCH ’ 638–650 ’ 2011 ’ Vol. 44, No. 8