C-axis aligned crystalline indium-gallium-zinc oxide (CAAC-IGZO) and high-k charge trapping film for flash memory application

Abstract

C-axis aligned crystalline indium-gallium-zinc oxide (CAAC-IGZO) was obtained using tantalum (Ta) induced crystallization with appropriate post-annealing and applied as a channel of the thin film transistor (TFT) flash memory device. Atomic layer deposited Al2O3, HfO2, and Al2O3 thin films were used for the blocking layer (BL), charge trap layer (CTL) and tunneling layer (TL), respectively. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) analysis show the formation of a CAAC-IGZO layer with a (009) peak on the c-axis. Compared with a device using amorphous IGZO (a-IGZO) material as a channel, a device using CAAC-IGZO as a channel material shows improved transistor characteristics with low threshold voltage, low subthreshold swing, high field effect mobility, and high on-current to off-current ratio (ION/OFF). In the program/erase (P/E) characterization, CAAC-IGZO channel device (ΔVTH = 1.0 V) has a larger memory window than a-IGZO channel device (ΔVTH = 0.5 V). The retention and endurance characteristics of the CAAC-IGZO device were obtained up to 104 s and 103 cycles, respectively, without any noticeable degradation. It is believed that the proposed CAAC-IGZO material could be considered as an alternative to the poly-Si material having defects due to the grain-boundaries.