Memory Effect in the Current-Voltage Characteristics of Diodes based on PEDOT:PSS
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I9.35.1
Memory Effect in the Current-Voltage Characteristics of Diodes Based on PEDOT:PSS Zhengchun Liu, Fengliang Xue, Yi Su* and Kody Varahramyan Institute for Micromanufacturing, Louisiana Tech University 911 Hergot Ave, Ruston, LA 71272, U.S.A. *[email protected]
ABSTRACT: Diodes were formed by intermediating a thin film of PEDOT:PSS between aluminum and heavily doped silicon. Both p-type and n-type Si substrates were used. Hysteresis loops were observed in their current-voltage (I-V) characteristics. A ‘state’ can be written by applying a voltage pulse to aluminum electrode. The state of the device can be read out from the current under a small probe voltage (0.3-0.6 V, to Al electrode). Appling +4.0 V induces a ‘low’ conductance state while applying -4.0 V switches the device back to the ‘high’ conductance state. The current difference between two states is up to 3 orders of magnitude. The space charge storage in the polymer is believed to be responsible for the memory effect. Upon positive voltage bias the charges are injected into the place near the Al/PEDOT:PSS interface. The charges are stored there and will resist subsequent charge injection, resulting in the ‘low’ conduction state. The redox reactions further reduce the conductance of the device. Negative bias can remove the stored charges and reverse the redox reactions, thus recover the device back to ‘high’ conduction state. KEY WORDS: PEDOT/PSS, memory effect, contacts
INTRODUCTION As an air-stable, solution-processable and commercially available conducting polymer, poly(ethylene dioxythiophene) doped with poly(styrene sulfonate) (PEDOT/PSS) has been widely studied for electronic applications such as diodes [1, 2], organic light emitting diodes [3], organic photovoltaic device [4], and organic thin film transistors [5]. Recently, write-once-read-many-times memory devices were realized using this polymer sandwiched between gold and ITO electrodes [6]. Replacing ITO with p-type or n-type silicon results in similar memory devices with lower switching voltage [7, 8]. Previously, we reported that the Al/PEDOT:PSS/Au devices exhibit hysteresis behavior in their electrical characteristics [9]. In this work we replaced the Au electrode with heavily doped p-type silicon and n-type silicon, respectively, in order to further understand the hysteresis phenomena. Reversible memory effects were found, suggesting the possibility of realizing erasable memory devices based on PEDOT/PSS in the future.
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EXPERIMENTAL The starting materials are heavily-doped p-type silicon (p+-Si) and heavily-doped ntype silicon (n+-Si) wafers. The resistivities are in the range of 0.01~0.001 ohm·cm. At first, the wafer surface is cleaned using acetone and isopropyl alcohol. Then the wafers are immersed in the dilute HF water solution to remove the surface native oxide. After being rinsed with deionized water and dried with nitrogen blow, the bare silicon wafers are then coated with the thin films of PEDOT/PSS (Baytron P from H.C. Starck Inc.) using spin-coating technique. The
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