Impact of HfO2 buffer layers on data retention characteristics of ferroelectric-gate field-effect transistors

Electrical properties of the p-channel metal-ferroelectric-insulator-silicon field-effect transistors (MFISFETs) using Pt/SrBi2Ta2O9(SBT)/HfO2/Si and Pt/(Bi,La)(4)Ti3O12(BLT)/HfO2/Si gate structures were investigated. Sol-gel-derived 400-nm-thick SBT and BLT films were deposited on an HfO2 film of approximately 10 nm in thickness. The channel width and channel length of the fabricated MFISFETs were 50 and 5 mum, respectively. The significant drain current on/off ratios were retained for over 10 days at room temperature. The fabricated MFISFETs using a Pt/SBT/HfO2/Si gate structure exhibited a drain current on/off ratio of about 10(5) even after 15.9 days had elapsed. It was also found in the fabricated MFISFETs that a write pulse width as short as 20 ns was enough for obtaining the significant drain current on/off ratio. It is concluded from these results that HfO2 is one of the best buffer layer materials for realizing MFISFETs with long data retention and high operation speed. (C) 2004 American Institute of Physics.