Recent Progress of Ferroelectric-Gate Field-Effect Transistors and Applications to Nonvolatile Logic and FeNAND Flash Memory

Abstract

We have investigated ferroelectric-gate field-effect transistors (FeFETs) with Pt/SrBi2Ta2O9/(HfO2)x(Al2O3)1−x (Hf-Al-O) and Pt/SrBi2Ta2O9/HfO2 gate stacks. The fabricated FeFETs have excellent data retention characteristics: The drain current ratio between the on- and off-states of a FeFET was more than 2 × 106 after 12 days, and the decreasing rate of this ratio was so small that the extrapolated drain current ratio after 10 years is larger than 1 × 105. A fabricated self-aligned gate Pt/SrBi2Ta2O9/Hf-Al-O/Si FET revealed a sufficiently large drain current ratio of 2.4 × 105 after 33.5 day, which is 6.5 × 104 after 10 years by extrapolation. The developed FeFETs also revealed stable retention characteristics at an elevated temperature up to 120 °C and had small transistor threshold voltage (Vth) distribution. The Vth can be adjusted by controlling channel impurity densities for both n-channel and p-channel FeFETs. These performances are now suitable to integrated circuit application with nonvolatile functions. Fundamental properties for the applications to ferroelectric-CMOS nonvolatile logic-circuits and to ferroelectric-NAND flash memories are demonstrated.

Atomic Layer Deposition and Properties of HfO2-Al2O3 Nanolaminates

“…12 HfO 2 -Al 2 O 3 mixtures have been studied as buffer layers in Pt/SrBi 2 Ta 2 O 9 /(HfO 2 ) x (Al 2 O 3 ) 1−x ferroelectric RAM cells. 13 Al 2 O 3 /HfO 2 /Al 2 O 3 trilayer structures have exhibited promising switching resistance memory behavior. 14 Properties of HfO 2 -Al 2 O 3 nanolaminates, as well as mixtures, have also been investigated in more general terms such as chemical and phase composition, though mainly intended for MIM or CMOS based DRAM applications, 2,15 or as non-volatile resistive switching memory (memristor) materials.…”

0.5V Bit-Line-Voltage Self-Boost-Programming in Ferroelectric-NAND Flash Memory

“…Reliable electrical characteristics of the Pt/SBT/HAO/Si FeFETs as nonvolatile memory transistors were already shown such as long retention at temperatures up to 120°C, high pulse endurance, small threshold-voltage (V th ) distribution [5][6][7][8][9][10]. Downsizing of the Pt/SBT/HAO/Si FeFETs has been intensively studied and also now in progress [11,12].…”

Diffraction studies for stoichiometry effects in BaTiO3 grown by molecular beam epitaxy on Ge(001)

“…40 Summarizing, from our studies, the stoichiometry of the BTO-sample also provides a route to control its tetragonality, optimizing it for a given device application. 34,41 Figure 2. However, compared to sample A, the SAED pattern for sample B shows more diffraction spots.…”