Improvement of the Charge Retention of a Non-Volatile Memory by a Bandgap-Engineered Charge Trap Layer
Ziyang Cui, Dongxu Xin, Taeyong Kim, Ji‐Won Choi, Jaewoong Cho, Junsin Yi
Abstract
In recent years, research based on HfO 2 as a charge trap memory has become increasingly popular. This material, with its advantages of moderate dielectric constant, good interface thermal stability and high charge trap density, is currently gaining in prominence in the next generation of nonvolatile memory devices. In this study, memory devices based on a-IGZO thin-film transistor (TFT) with HfO 2 /Al 2 O 3 /HfO 2 charge trap layer (CTL) were fabricated using atomic layer deposition. The effect of the Al 2 O 3 layer thickness (1, 2, and 3 nm) in the CTL on memory performance was studied. The results show that the device with a 2-nm Al 2 O 3 layer in the CTL has a 2.47 V memory window for 12 V programming voltage. The use of the HfO 2 /Al 2 O 3 /HfO 2 structure as a CTL lowered the concentration of electrons near the tunnel layer and the loss of trapped electrons. At room temperature, the memory window is expected to decrease by 0.61 V after 10 years. The large storage window (2.47 V) and good charge retention (75.6% in 10 years) of the device under low-voltage conditions are highly advantageous. The charge retention of the HfO 2 /Al 2 O 3 /HfO 2 trap layer affords a feasible method for fabricating memory devices based on a-IGZO TFT.