Catalytic Synthesis and Characterization of Biodegradable ...

Chapter 1
the device is switched to a low resistance near –4.5 V as the threshold voltage. The low
resistance state is maintained during the reverse sweep of the voltage from –5 to +1.4 V. The
low-resistance or ON state was observed for repeated sweeps, regardless of the sweep
direction. When a bias of –1.5 V was applied, the device sharply switched to the
high-resistance or OFF state again. In the hysteretic curve, the ON–OFF ratio amounted to
four orders of magnitude. The retention cycles of the ON and OFF states under open-circuit
conditions persisted for more than 10 4 times. Furthermore, each state survived for a month
after the corresponding once-time-only pulse as well as consecutive pulses.
The charge injection at the radical polymer/electrode interface and transport in the bulk of
the radical polymer layer are dominated by the Schottky barrier and the Poole–Frenkel
mechanism. In the ON state, charges are trapped at the radical polymer/PVDF interfaces, and
induce accumulation of the opposite charge at the radical polymer/electrode interfaces and
reduction the Schottky barriers, allowing charges to transfer across the radical
polymer/electrode interfaces even at low voltages. 192 The SOMO levels of the p-type PTMA
and the n-type PGSt are near 5.4 and 4.7 eV, respectively.
Figure 1.6.5 p-type and n-type radical polymer-based memory architecture, and charge injection,
transporting, and trapping configuration.
The p-type layer accepts holes, and electrons are injected into the n-type layer. The
injected holes and electrons are transported by the hopping mechanism, and are stored at the
radical polymer/PVDF interfaces. Under open-circuit conditions, the trapped holes and
electrons were nonvolatile due to charge trapping at the radical polymer/PVDF interfaces and
to blocking of the charge transfer in the polymer layers having sufficient resistances. The
asymmetric configuration of the electrodes with the different work functions allows
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