Novel Application of Imprinting Lithography for Multi-bit Ferroelectric Memories

Abstract

This thesis is about an innovative application of nanoimprinting lithography in organic ferroelectric memories, which can achieve multi-bit data storage. Multi-bit data storage, defined here as storage of multiple bits in a single device cell, can potentially make higher density ferroelectric memory at a lower price. The idea is based on ferroelectric response with regard to ferroelectric film thickness. Two kinds of memory cells were fabricated to test the functionality and performance of the proposed concept. After optimizing the thermal nano-imprinting process to replicate periodicity micro-structure to a ferroelectric poly(vinylidene fluoride-trifluoroethylene) film, we first fabricated the ferroelectric capacitor cells with the imprinted polymer film. The fabricated cells, with sizes down to 0.0589 mm^2, showed a promising multi-bit functionality and retention property. Four different imprinting patterns were also compared, the repeating grating structure as line: 20 um / space: 10 um represented the best multi-bit performance in terms of identification of the operation voltage for different bits. A prediction of the imprinting pattern and the ferroelectric capacitor performance were given according to the results. With the same imprinting condition, we also fabricated ferroelectric field effect transistors (FeFETs). The FeFETs with periodicity pattern of line: 20 um / space: 10 um was investigated. It is observed that, the smallest imprinted cell with a gate length of 5 um and width of 5 mm only has several nano-ampere of leakage current, which is 10^5 times smaller than the ON current. Using a drain voltage of 50 mV, states can be read out easily. It is evident that the four states of the system retain distinguishable after the 10^4 second retention test.DIMESElectrical Engineering, Mathematics and Computer Scienc