L. S. Lee

Charge trapping characteristics of atomic-layer-deposited HfO2 films with Al2O3 as a blocking oxide for high-density non-volatile memory device applications

Charge trapping characteristics of high-relative permittivity (high-?) HfO2 films with Al2O3 as a blocking oxide in p-Si/SiO2/HfO2/Al2O3/metal memory structures have been investigated. All high-? films have been grown by atomic layer deposition. A transmission electron microscope image shows that the HfO2 film is polycrystalline, while the Al2O3 film is partially crystalline after a high temperature annealing treatment at 1000 ?C for 10 s in N2 ambient. A well-behaved counter-clockwise capacitance?voltage hysteresis has been observed for all memory capacitors. A large memory window of ~7.4 V and a high charge trapping density of ~1.1 ? 1013 cm?2 have been observed for high-? HfO2 charge trapping memory capacitors. The memory window and charge trapping density can be increased with increasing thickness of the HfO2 film. The charge loss can be decreased using a thick trapping layer or thick tunnelling oxide. A high work function metal gate electrode shows low charge loss and large memory window after 10 years of retention. High-? HfO2 memory devices with high-? Al2O3 as a blocking oxide and a high work function metal gate can be used in future high-density non-volatile memory device applications.

Band offsets and charge storage characteristics of atomic layer deposited high-k HfO2∕TiO2 multilayers

The band offsets and charge storage characteristics of atomic layer deposited high-k HfO2∕TiO2 multilayers with ten periods in p-Si∕SiO2∕(HfO2∕TiO2)∕Al2O3 structure have been investigated. The thickness of high-k HfO2 or TiO2 film is ∼0.5nm for each layer, before and after annealing treatment of 900°C for 1min in N2 ambient. High-resolution transmission electron microscopy, x-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy measurements on high-k HfO2∕TiO2 multilayers confirm the layer-by-layer structure after annealing treatment, suggesting the HfO2∕TiO2 multilayer quantum wells. The valence band offsets of HfO2 and TiO2 films are found to be ∼3.1 and ∼1.5eV, respectively. The conduction band offsets are found to be ∼1.7eV for HfO2 films and ∼0.9eV for TiO2 films. The high-k HfO2∕TiO2 multilayers in p-Si∕SiO2∕(HfO2∕TiO2)∕Al2O3/aluminum memory capacitor show a large capacitance-voltage hysteresis memory window of ∼5V at gate voltage of ±5V, due to the charge storage in multilayer...

Charge storage characteristics of atomic layer deposited RuOx nanocrystals

The charge storage characteristics of atomic layer deposited RuOx nanocrystals embedded in high-k HfO2∕Al2O3 films in a metal/Al2O3∕RuOx∕HfO2∕SiO2∕n-Si structure have been investigated. The size and density of RuOx nanocrystals have been measured using transmission electron microscopy. The RuOx nanocrystals show a density of ∼1×1012∕cm2 and a diameter of 5–8nm. A large hysteresis memory window of ∼13.3V at a gate voltage of 9V has been observed for RuOx nanocrystal memory capacitors. A hysteresis memory window of 0.7V has also been observed under a small sweeping gate voltage of 1V. A promising memory window of RuOx nanocrystals has been observed as compared with those of pure HfO2 and Al2O3 charge trapping layers, due to charge storage in the RuOx metal nanocrystals. The RuOx nanocrystal memory capacitor has similar leakage current with the pure HfO2 and Al2O3 charge trapping layers. The RuOx memory capacitor has a large breakdown voltage of ∼13.8V.

Physical and electrical characteristics of atomic layer deposited TiN nanocrystal memory capacitors

The physical and electrical characteristics of atomic layer deposited TiN nanocrystals embedded in high-k Al2O3 films in a metal/Al2O3∕[TiN∕Al2O3]∕SiO2∕p-Si structure have been investigated. High-resolution transmission electron microscopy and x-ray photoelectron spectroscopy show the formation of tiny TiN nanocrystals embedded in Al2O3 films after subsequent annealing treatment. The TiN nanocrystals with a high density of >1×1012∕cm2 and a small size of <3nm have been observed. A large hysteresis memory window of ∼4.3V at small sweeping gate voltage of 3V has been observed as compared with a pure Al2O3 charge trapping layer, due to highly charge confinement in the TiN metal nanocrystals. The hysteresis memory window of 1.4V has also been observed under an extremely small sweeping gate voltage of 1V. A large memory window of ∼3.9V is observed after 10years of retention. A maximum hysteresis memory window is limited by both of the nanocrystal density and leakage current at a high temperature annealing trea...

Charge-Trapping-Type Flash Memory Device With Stacked High-

Operating properties of charge-trapping-type Flash memory devices with single or stacked structures on trapping layer are investigated in this letter. Improved operation and reliability characteristics can be achieved by adapting the stacked high-k films as charge-trapping layer due to the modification in the trap density and the energy level of traps, the mechanism of electron/hole transmission, and the suitable band offset. Moreover, with a small bandgap of second film in the stacked trapping layer, operating characteristics of devices are further enhanced.

k

Satisfactory operation and reliability characteristics of SONOS-type flash devices are achieved by an optimal Hf/Al content in HfAlO charge-trapping layer. Results indicate that operation performance can be improved by a suitable band offset of HfAlO charge-trapping layer. High-speed operation can be realized by adopting CHEI programming and F-N erasing for NOR flash applications.

Charge-Trapping Layer

Operation properties of polysilicon-oxide-nitride-oxide-silicon-type Flash device with HfAlO charge-trapping layer having various Al contents were investigated in this letter. Satisfactory performance in terms of operation speed, retention, and program/erase endurance of the Flash device is achieved with the optimal Al content of 18%-28% in the HfAlO trapping layer. In addition, high-speed operation can be attained with the combination of channel-hot-electron-injection programming and band-to-band hot hole erasing for NOR architecture applications.

Novel SONOS-Type Nonvolatile Memory Device with Suitable Band Offset in HfAlO Charge-Trapping Layer

The memory characteristics of atomic-layer-deposited high-K HfAlO nanocrystals in a p-Si/SiO 2 /CHfO 2 /Al 2 O 3 ]/Al 2 O 3 /platinum structure have been investigated. After the annealing treatment, the high-K HfAlO nanocrystals with a small diameter of 5 X 10 11 cm 2 have been observed by high-resolution transmission electron microscopy. A large hysteresis memory window of ∼ 10.4 V has been obtained. The high-K HfAlO nanocrystal memory capacitor with a small capacitance equivalent thickness of ∼ 8.5 ± 0.5 nm shows a small leakage current density of ∼ 22 μA cm 2 at a gate voltage of -16 V. A large memory window of ∼8 V has also been observed after 10 5 s of retention, due to the charge confinement in the high-K HfAlO multilayer nanocrystals.

Novel SONOS-Type Nonvolatile Memory Device With Optimal Al Doping in HfAlO Charge-Trapping Layer

Charge-trapping type flash memory devices with various integrations of metal gates having different work functions and blocking oxides were investigated in this work. Improved erasing speed together with acceptable reliability characteristics can be achieved by the integration of high work-function metal gate and high-k blocking oxide due to an efficient suppression of electron back tunneling through the blocking oxide during erasing operation for the MoN sample. Specifically, the high work-function value of MoN metal gate can be kept only by integrating with the Al2O3 blocking oxide because it can suppress the formation of molybdenum-silicide. Moreover, high-speed erasing can also be demonstrated by combining the MoN metal gate with an HfAlO charge trapping layer when band-to-band hot hole erasing method is adopted.

Memory Characteristics of Atomic-Layer-Deposited High- κ HfAlO Nanocrystal Capacitors

Memory characteristics of TiN metal nanocrystals embedded by high-κ Al2O3 films have been investigated. The TiN (0.5 nm)/Al2O3 (1 nm) multilayers with high-κ Al2O3 film as a blocking oxide on SiO2/p-Si substrates have been deposited by Atomic Layer Deposition (ALD). After subsequent annealing treatment (>900°C), tiny TiN nanocrystals with a diameter of ∼3 nm have been formed. The size and density of TiN nanocrystals have been measured by High-Resolution Transmission Electron Microscopy (HRTEM). The densities of TiN nanocrystals are found to be ∼1.6 × 1012/cm² at 950°C for 2 min and ∼5.3 × 1012/cm² at 900° for 2 min in N2 (90%) + O2 (10%) annealing ambient. X-ray Photoelectron Spectroscopy (XPS) shows the Ti-N bonds, suggesting that the TiN nanocrystals embedded in high-κ Al2O3 films can be formed. A high programming speed of threshold voltage shift (ΔVt) ∼6.7 V @ 0.1 ms can be observed for the TiN nanocrystal memory devices. The erasing speed of ΔVt ∼6.7 V @ 20 ms is slow, due to low work function poly-Si gate electrode. The charge loss of the TiN nanocrystal memory devices is ∼14% at 20°C and ∼17% at 85°C, which is better result as compared with the best published data in the literatures. A good programming speed, endurance and retention characteristics have been observed, due to small metal nano-dot, high density and deep level charge trapping as well as strong charge confinement in the TiN nanocrystals. The memory device performance can be improved with increasing the density of TiN nanocrystals. The TiN nanocrystal flash memory devices can be useful in future nanoscale high-performance applications.