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 Â 10 11 bipolar pulses.

Ferroelectric Gate on AlGaN/GaN Heterostructures

“…Takahashi et al [2005], and Aizawa et al [2004] have used HfO 2 as a inter-diffusion barrier layer for silicon semiconductor substrates before the deposition of the ferroelectric gates SrBi 2 Ta 2 O 9 and (BiLa) 4 Ti 3 O 12 . The initial idea standing behind the development of the HfO 2 deposition process was also to use it as a buffer layer for limiting the diffusion between the ferroelectric, PZT, and AlGaN layers.…”

“…Lu et al [2006], Chien et al [2003] and Takahashi et al [2005] attempted to deposit HfO 2 by various methods such as atomic vapor deposition, AVD, electron beam evaporation and laser molecular beam epitaxy, LMBE. The important point is that the deposition temperature was always higher than 400…”

“…This left the two parameters of RF power and the oxygen gas flow rate as variables to optimise the deposition process. The post-deposition annealing steps performed by Chien et al [2003] and Takahashi et al [2005] are most likely too volatile, since it was learned when depositing CSD PZT that the 2DEG is extremely sensitive to the final step of high temperature annealing in oxygen.…”

“…As mentioned in section 2.5.1, HfO 2 was successfully used as a buffer layer for SBT/HfO 2 /Si and BLT/HfO 2 /Si FeFETs by Takahashi et al [2005], and Aizawa et al [2004]. The HfO 2 was annealed in oxygen at 800…”

“…For the ferroelectric films of 130 nm and 250 nm, P(VDF/TrFE) has almost all of its spontaneous polarisation active to modulate the 2DEG, however, PZT has only enough bound charge available to only partially deplete the 2DEG. In section 2.5.1 the results from the papers of Aizawa et al [2004] and Takahashi et al [2005] were introduced. They integrated two different ferroelectric thin films, of thickness 400 nm, onto silicon with a HfO 2 buffer layer.…”