Investigation on the origin of the memory effect in metal/organic semiconductor/metal structures

Abstract

We report on the resistive switching effect in metal/organic semiconductor/metal structures and present a general explanation of the switching mechanism in these devices. The J-V characteristics of metal/tris(8- hydroxyquinolinato)aluminum (Alq3)/metal devices will be discussed and it will be further shown that these sustain only a limited number of switching cycles. Besides Alq3, we also investigate other organic semiconductor materials and obtain a bistable behavior, which is independent of the organic material but dependent on the current injection conditions of the interface between the organic material and the metal top electrode. Further, we investigate the material independent switching effect using impedance spectroscopy and can disclose a transition from capacitive to resistive behavior at switching voltages. We propose that the switching in metal/organic semiconductor/metal structures is caused by the growth and rupture of resistive filaments in the organic semiconductor.

Metal nanoparticle mediated space charge and its optical control in an organic hole-only device

“…The resistance values for the high-resistance state (HRS) and the low-resistance state (LRS) are calculated from the curve linear best-fit (dashed lines); R LRS $ 2:8 Â10 5 X and R HRS $ 4:9Â10 2 X. Sebastian et al reported on a conceptually identical device (ITO/a-NPD/Al). 29 Accordantly, the impedance spectroscopy analysis reveals the filamentary nature of the switching.…”

“…28,29 The layer of a-NPD had the same nominal thickness (120 nm) as the previous devices. No metal NPs were intentionally introduced within the a-NPD film.…”

Nonvolatile memory and opto-electrical characteristics of organic memory devices with zinc oxide nanoparticles embedded in the tris(8-hydroxyquinolinato)aluminum light-emitting layer

“…Therefore, with the rapid develop-52 ment of organic memory technology, a lot of effort has been made 53 to improve organic memory device structures and to understand 54 their operating mechanisms. 55 A number of device structures of the nonvolatile organic memory 56 have been manufactured and extensively explored, such as a single-57 layer structure consisting of only one type of organic material [5,6], a 58 tri-layer structure in which nano-traps for charge carriers are sand- 59 wiched between two organic layers [7,8], and a spin-cast blend of 60 polymer and nano-traps in which nano-traps are randomly dis- 61 persed in the polymer layer [9][10][11][12][13][14][15][16]. Because the charges stored 62 inside the nano-traps can efficiently change the conductivity of 63 the organic layer, finding appropriate materials to produce the 64 nano-traps has been the major issue in the tri-layer or hybrid com-65 posite structures of the organic memory.…”

3D imaging of filaments in organic resistive memory devices

“…A complete overview on materials and architectures can be found in recent reviews [12,13]. RS mechanism in OMDs has been attributed to very different phenomena, based on charge injection/trapping mechanisms [14][15][16][17], or the formation of conductive filaments (CFs) [18][19][20][21][22][23][24]. Filaments were argued to be based on metallic [25], or carbon rich [26] dendritic paths.…”