Thirty-Day-Long Data Retention in Ferroelectric-Gate Field-Effect Transistors with HfO₂ Buffer Layers

Abstract

Metal–ferroelectric–insulator–semiconductor (MFIS) diodes and p-channel MFIS field-effect transistors (FETs) were fabricated and their electrical properties were characterized. These MFIS structures were formed using HfO 2 as an insulating buffer layer, and SrBi 2 Ta 2 O 9 (SBT) and (Bi,La) 4 Ti 3 O 12 (BLT) as ferroelectric films. HfO 2 buffer layers of about 8 nm physical thickness were deposited by ultrahigh-vacuum (UHV) electron-beam evaporation, then ferroelectric films of about 400 nm thickness were deposited by sol–gel spin coating. The fabricated p-channel MFIS-FETs with the SBT/HfO 2 gate structure exhibited a drain current on/off ratio larger than 10 3 even after 30 days had elapsed. It was also found that the degradation of ferroelectricity was not pronounced even after applying 2.2×10 11 bipolar pulses.