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)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.