Organic electrical bistable devices and rewritable memory cells

Abstract

Electrical bistability is a phenomenon in which a device exhibits two states of different conductivities, at the same applied voltage. We report an organic electrical bistable device (OBD) comprising of a thin metal layer embedded within the organic material, as the active medium [L. P. Ma, J. Liu, and Y. Yang, US Patent Pending, (2001)]. The performance of this device makes it attractive for memory-cell type of applications. The two states of the OBD differ in their conductivity by several orders in magnitude and show remarkable stability, i.e., once the device reaches either state, it tends to remain in that state for a prolonged period of time. More importantly, the high and low conductivity states of an OBD can be precisely controlled by the application of a positive voltage pulse (to write) or a negative voltage pulse (to erase), respectively. One million writing-erasing cycles for the OBD have been tested in ambient conditions without significant device degradation. These discoveries pave the way for newer applications, such as low-cost, large-area, flexible, high-density, electrically addressable data storage devices.

Electrical memory devices based on inorganic/organic nanocomposites

“…Ma et al first demonstrated that resistive switching could be achieved by depositing a layer of aluminum nanoparticles between two organic layers. 3 Because the depositions of the nanoparticles and the organic layer are independently controlled, the distribution of nanoparticles can be very well controlled in these devices. Figure 1 shows a typical structure for such devices.…”

“…Obviously, for practical applications, a high switching speed (o100 ns) is necessary to meet the requirement of ultra-high-density information storage. Ma et al 3 reported that a hybrid memory cell could exhibit a switching speed as fast as 10 ns.…”

“…9 Semiconducting materials, for example, MoO 3 and so on, 10 with suitable energy band levels can also be used in place of the metal particles. However, as shown by the vast differences in the electrical characteristics of the devices fabricated in different laboratories, 3,[6][7][8] the reproducibility of the device depends very much on the vacuum chamber and deposition conditions. Therefore, a more repeatable fabrication process is required for the large-scale manufacture of such devices.…”

“…The device area is defined by the overlap between the top and the bottom electrodes; therefore, a very high memory density can be easily achieved by using cross-bar arrays. [1][2][3][4][5] The organic material used can consist of small organic molecules or polymers. Small organic molecules have low molecular weight and can be deposited under high vacuum without decomposition by using thermal evaporation.…”

Multi-layer stackable polymer memory devices

“…Polymer memory devices show fast switching speed and non-volatile characteristics (Ma et al 2002;Ouyang et al 2004;Scott & Bozano 2007), and are therefore ideal candidates to replace existing memory technologies. However, in order for polymer memory to achieve commercial success, there are a few hurdles that need to be overcome.…”