Charge Storage in Pentacene/Polymethylmethacrylate Memory Devices

Abstract

The electrical behavior of organic metal-insulatorsemiconductor (MIS) structures incorporating a layer of selfassembled metallic nanoparticles is described. These have been based on thermally evaporated pentacene (semiconductor) and spin-coated polymethylmethacrylate (insulator). The MIS devices containing the nanoparticles exhibited significant hysteresis in their capacitance-versus-voltage and conductance-versus-voltage characteristics, which was attributed to the charging and discharging of the nanoparticles. The memory structure reported here offers a useful advance in the development of flexible organic memory structures.

Low-voltage organic memory transistors

“…The counterclockwise hysteresis after sweeping the accumulation suggests neutralization of the trapped electrons, while holes are trapped in the floating gate resulting in the clear hysteresis. Although the operating voltages of these devices are higher than the devices reported by Mabrook et al based on Au nanoparticles [5], the shift in flatband voltage is much larger.…”

“…Applications such as light emitting displays [1], organic solar cells [2] and organic thin film transistor [3] are all the focus of intense study. Organic memory devices based on bistable switching [4], charge storage in metal-insulator-semiconductor structures (MIS) [5] and organic thin film memory transistors (OTFMTs) [6] have been reported. Memory operation can be achieved by charging nanoparticles, nanowires or nanocrystals integrated into the insulating layer of the MIS structures [5,6].…”

“…Such structures can operate as memories with high speed, high density, and low cost but with high operating voltage. In our previous work [5,6] we have reported on MIS devices and transistor structures in which a monolayer of gold nanoparticles was incorporated into insulating films. Although low temperature processes were developed for these devices the high voltage required to achieve memory status prevents them from use in commercial memory devices of this type.…”

A pentacene-based organic thin film memory transistor

“…These results are consistent with our recent capacitance C versus voltage V studies of pentacene/PMMA devices, in which hysteresis in the C-V curves was attributed to the presence of nanoparticles at the semiconductor/insulator interface. 16 The counterclockwise hysteresis direction of the transfer characteristics in Fig. 2͑b͒ indicates that charging and discharging of the memory transistor take place through the pentacene surface.…”

Organic bistable devices utilizing carbon nanotubes embedded in poly(methyl methacrylate)

“…The position of the charge traps in the middle of the insulating layer is believed to enhance the performance of the OBDs in terms of stability and retention. 12 PMMA was chosen as the insulator where the charge traps were embedded due to our previous knowledge about the low leakage current in PMMA under high gate voltages in metal-insulator-semiconductor and transistor structures 13,14 Furthermore, PMMA have been used as an insulator in similar structures (embedded with charge traps) and showed stability upon the applied voltages and reliability in the confinement of carriers inside the charge traps when the voltage was turned off. 8 Moreover, in our previous work on hybrid memory devices, charging and discharging of the charge elements were through a thin layer of PMMA (40 nm).…”