Characteristics of Gadolinium Oxide Nanocrystal Memory with Optimized Rapid Thermal Annealing

Abstract

Gadolinium oxide nanocrystal ͑Gd 2 O 3 -NC͒ memories treated by postdeposition rapid thermal annealing were investigated. Bandgap offset performed by a crystallized Gd 2 O 3 -NC dot surrounded by amorphous Gd 2 O 3 dielectrics is successfully demonstrated and proven by the transmission electron microscopy images and electron diffraction pattern. The Gd 2 O 3 -NC memory exhibits a hysteresis memory window of 4 V and NC dot density of more than 8.5 ϫ 10 11 cm −2 . In addition, the formation of Gd 2 O 3 -NC and charge loss characteristics on annealing temperature were analyzed and optimized at 850°C. The data endurance of 10 4 program and erase cycling for a sufficient memory window ͑Ͼ2 V͒ was also observed for the Gd 2 O 3 nanocrystal memory.In order to scale down floating gate ͑FG͒ nonvolatile memory ͑NVM͒, tunnel oxide limitation for sufficient charge retention has to be overcome. 1 One way is to implement high-dielectric-constant ͑high-k͒ materials such as Al 2 O 3 thin film as the tunnel oxide for the reduction of operation voltage while satisfying the data retention and endurance. 2 The other is using a discrete charge-storage concept for thinner tunnel oxide without sacrificing nonvolatility. Isolated Si and Ge semiconductor nanocrystal ͑NC͒ memories are NVMs that have been demonstrated to have a more simplified fabrication process, better punchthrough effect, and immunity to oxide defects as compared to conventional FG NVMs. 1,3,4 To achieve the fast write/ erase and long retention time simultaneously, metal NC memories are presented to engineer the depth of the potential well at storage nodes. Heavy metals, 4-7 silicide, 8,9 nitrided-metal, 10 and metal-oxide 11,12 are NC memories used as storage nodes. Compared with the semiconductor NC memories, metal counterparts exhibit a higher density of states around the Fermi level, stronger coupling with the conduction channel, a wider range of available work functions, and smaller energy perturbation due to carrier confinement. 13 Gadolinium oxide ͑Gd 2 O 3 ͒, the rare-earth sesquioxides ͑R 2 O 3 ͒, has been reported to be candidates as gate dielectrics for silicon and compound semiconductor device applications. 14,15 They are demonstrated to exhibit three different structures such as cubic, monoclinic, and hexagonal under different growth temperatures. 16 In addition, a different energy bandgap of amorphous ͑6.3-6.4 eV͒ and crystallized ͑5.0-5.4 eV͒ Gd 2 O 3 thin films has also been discovered. 17,18 Recently, magnetic nanocrystalline Gd 2 O 3 particles embedded in silica glass have been proposed for memory applications. 19 In this work, we demonstrate that a crystallized gadolinium oxide with low bandgap acts as a charge-storage node when it is surrounded by amorphous gadolinium oxide with higher bandgap to form Gd 2 O 3 nanocrystal memories ͑Gd 2 O 3 -NC͒. This separate charge-storage structure is different from the previous research regarding NC memory devices, 4-12 and the tunnel oxide thickness is effectively increased for better charge retention. The memory...

Charge storage and data retention characteristics of forming gas-annealed Gd2O3-nanocrystal nonvolatile memory cell

“…The RTA treatment of amorphous Gd 2 O 3 film is an effective and simple method to form Gd 2 O 3 -NCs, which are used as Si-based and heterostructure GaN/AlGaN-based charge trapping devices [19,20]. It has been demonstrated that the capacitance-voltage sweep measurement yields a large memory window of the Gd 2 O 3 -NC memories.…”

Enhanced memory performance by tailoring the microstructural evolution of (ZrO2)0.6(SiO2)0.4 charge trapping layer in the nanocrystallites-based charge trap flash memory cells

“…Figure 6 illustrates the room temperature data retention characteristics of RTA treated ZrO 2 NC-based CTF memory cells before (solid symbols) and after 10 5 W/E cycles operation (open symbols). The charge loss is defined as [20]:…”

Thickness dependence of Al2O3/HfO2/Al2O3 stacked tunneling layers on gadolinium oxide nanocrystal nonvolatile memory

“…In addition, a 4-nm-thick SiO 2 film was thermally grown on a silicon wafer by furnace in O 2 ambient, which was fabricated for comparison and denoted as C. After that, an 8-nm-thick Gd 2 O 3 layer was deposited by using the RF sputtering with a 99.9% pure gadolinium (Gd) target in argon (Ar) and oxygen (O 2 ) mixed ambient at room temperature. The flow ratio of Ar to O 2 was 7:1 under a chamber pressure of 10 mtorr and an RF power of 100 W. After the Gd 2 O 3 film had been formed, the samples were subjected to rapid thermal annealing (RTA) at 900°C for 30 s in N 2 ambient to form Gd 2 O 3 -NCs [14]. A 10-nm-thick SiO 2 layer was deposited by plasma-enhanced chemical vapor deposition (PECVD) system to act as a blocking oxide.…”

“…Furthermore, the gadolinium oxide (Gd 2 O 3 ) nanocrystal, a rare earth metal oxide material, has been proposed to exhibit superior memory properties [14][15][16][17][18][19]. The Gd 2 O 3 -NCs can be formed by the crystallized Gd 2 O 3 dots with small band-gap surrounded by the amorphous Gd 2 O 3 film with large band-gap [20], which is different from the traditional NCs embedded in SiO 2 matrix [6,[11][12][13].…”