Design strategies for improvement in nonvolatile memory characteristics of metal-ferroelectric-metal-insulator-semiconductor capacitors using ferroelectric Hf0.5Zr0.5O2 thin films

摘要

The effects of top electrode and thickness control of ferroelectric HfxZr1-xO2 (HZO) film on the memory device characteristics were investigated for metal-ferroelectric-metal-insulator-semiconductor (MFMIS) capacitors. It was suggested from capacitance-voltage analysis for the MFM and MFMIS capacitors that the Al top electrode increased leakage current components and caused memory retention degradation owing to the formation of intermediate transistion layer at interfaces with HZO. Alternatively, the choice of Pt top electrode was appropriate to guarantee sound device operations without any reaction at interfaces. When the HZO thickness increased from 20 to 30 nm, the maximum memory window supported by ferroelectric field-effect increased from 2.6 to 3.1 V at an area ratio (MIS:MFM) of 60. Load-line and operating-point analysis show that polarization loops close to more saturated polarizations can be exploited for the memory operations of MFMIS capacitors using thicker HZO films. As a result, for the MFMIS capactior using 30 nm-thick HZO, the capacitance loss at on-state was only 8.7% after a lapse of retention time for 10(4) s. Choice of top electrode and control of HZO thickness were found to be important design parameters for highly-functional ferroelectric transistors using MFMIS gate-stack structures.