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/SrBi₂Ta ₂O₉(SBT)/HfO₂/Si and Pt/(Bi,La) ₄Ti₃O₁₂(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 μm, 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 10⁵ 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.