| Self-assembly techniques that allow the controlled growth of nanometer-scale organic molecular films present new opportunities to develop electronic devices with dimensions much smaller than those of current technologies. In this thesis we address several of the challenges to realizing this goal, and demonstrate a molecular-scale programmable-resistance memory device.; Although technologically attractive, field-effect transistors (FETs) with a self-assembled organic channel are difficult to realize due to the poor gate-channel coupling. We have used electrostatic modeling to determine guidelines that allow the maximum gate modulation of the channel potential in these devices.; Molecular-scale devices with integrated metal wiring are desirable for practical application. However, this typically requires the vacuum deposition of metal electrodes, which can damage the thin organic layer. We developed several approaches to fabricate two-terminal molecular-scale devices with vacuum-deposited metal electrodes and minimal defects in the organic layer. To demonstrate these device structures, we used films consisting of 1 to 12 self-assembled layers of 11-mercaptoundecanoic acid (MUA). The device structures that we developed included two large-area planar structures as well as a minimal-area structure that utilizes an insulating film to limit the device area to the edge of a metal layer. These structures allowed the first study of the mechanism of conduction in MUA films, which was characterized as Richardson-Schottky emission.; Finally, we found that these devices could be operated as a programmable memory by applying voltage pulses to increase or decrease the conductivity over a range of 103. The conductivity of the stored state could be read non-destructively with low-voltage pulses. Devices had remarkably large conductance (in the low-resistance state) of up to 106 S/cm2 at 1 V, programmed states remained stable for many months, and devices were functional for more than 104 programming cycles. The likely mechanism for the programmable resistance was the formation and destruction of conducting paths due to metal injected into the MUA film. We discuss their practical application and show that because of their high conductance these devices are uniquely promising among organic memories for use in dense, high-speed memory arrays, where large conductance is required to minimize resistance-capacitance delays. |
