فیزیک دستگاه حافظههای فروالکتریکی پلیمری
سخنران: دکتر کمال اسدی
سه شنبه ۱۷ شهریور۹۴
Ferroelectric polymers are well-suited candidates for applications that require a non-volatile memory. The ferroelectric polarization is employed to store binary information. The basic memory element is a ferroelectric capacitor. Its study is pivotal in understanding of the device physics of the ferroelectric memories.
The readout operation of the ferroelectric capacitors however is destructive, which complicates its integration in large arrays. Therefore majority of present research is focused on the development of ferroelectric memories based on resistive switching. In this contribution we provide an overview of polymeric ferroelectric field-effect transistors and diodes.
Ferroelectric field-effect transistors (FeFET) have a non-destructive read-out and low power consumption. The polarization of the ferroelectric gate insulator does/does not (On/Off) induce an accumulation layer in the semiconducting channel. Here we present an analytical model that describes the charge transport. Key ingredients are an empirical expression for the ferroelectric polarization with a density dependent hopping charge transport in organic semiconductors. We show that a good agreement between experimental and calculated current can be obtained using parameters that are directly linked to the physical properties of the comprising materials. The method is generic; any other analytical model for the polarization or for the charge transport can be easily implemented.
FeFETs have a three terminal layout that can potentially complicate their integration into a memory array. Ferroelectric diodes alleviate this problem. Blending semiconducting and ferroelectric polymers yields a phase separated system in which the ferroelectric phase enables information storage and the semiconductor phase allows for non-destructively readout. Excellent current rectification with high on/off current ratios has been demonstrated. The operation of the ferroelectric diodes is based on the modulation of the injection barrier. We have developed a morphology relevant device model and show that the origin of the resistive switching is the stray field of the polarized ferroelectric phase. We show that the current voltage characteristics of the diode can quantitatively be reproduced. We predict an ultimate memory density of the order of 1 Gb/cm۲ for a polymeric ferroelectric diode array.