HfZrO2 Based Ferroelectric-gated IGZO Thin Film Transistor Memory

초록

Recently, numerous studies have been conducted on HfO2-based ferroelectric materials for memory device applications because of its excellent ferroelectricity at a few nanometers thickness, complete compatibility with complementary metal-oxide-semiconductor (CMOS) process, and adjustable polarization (Pr)/coercive field (Ec) by doping concentration, annealing conditions, and capping layer. Ferroelectric materials have two stable polarization states that can be switched by electrical field direction. Depending on the polarization status in the ferroelectric layer, multiple memory states can be achieved. Among a number of memory devices using ferroelectricity, ferroelectric-gated thin film transistors (FeTFTs) have received much attention for memory-in-pixel applications because they can reduce the power consumption and enhance the performance during display operations. In this study, amorphous IGZO (a-IGZO) FeTFT was fabricated by using a HfZrO2 (HZO) thin film as the gate dielectric and a-IGZO as a channel material. To implement large-area and low-temperature processes, all the films including HZO ferroelectric layer and a-IGZO were deposited using RF sputtering to avoid high thermal budget of chemical vapor deposition. As a result, a large memory window of 2V and stable memory operations were obtained despite the device was fabricated only using the low-temperature processes less than 400 ℃.