Reliability of nc-ZnO Embedded ZrHfO High- k Nonvolatile Memory Devices Stressed at High Temperatures
- PDF / 251,673 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 89 Downloads / 196 Views
1160-H02-01
Reliability of nc-ZnO Embedded ZrHfO High-k Nonvolatile Memory Devices Stressed at High Temperatures Chia-Han Yang1, 2, Yue Kuo1, Chen-Han Lin1 and Way Kuo3 1
Thin Film Nano & Microelectronics Research Laboratory, Texas A&M University, College Station, TX 77843-3122, U.S.A. 2 Department of Industrial and Information Engineering, University of Tennessee, Knoxville, TN 37996, U.S.A. 3 City University of Hong Kong, Hong Kong
ABSTRACT The nanocrystalline ZnO embedded Zr-doped HfO2 high-k dielectric has been made into MOS capacitors for nonvolatile memory studies. The device shows a large charge storage density, a large memory window, and a long charge retention time. In this paper, authors investigated the temperature effect on the reliability of this kind of device in the range of 25°C to 175°C. In addition to the trap-assisted conduction, the memory window and the breakdown strength decreased with the increase of the temperature. The high-k film’s conductivity increased and the nc-ZnO’s charge retention capability decreased with the increase of temperature. The ncZnO retained the trapped charges even after the high-k film broke down and eventually lost the charges at a higher voltage. The difference between these two voltages decreased with the increase of the temperature. INTRODUCTION The evolution of the MOSFET technology has been driven by the aggressive shrinkage of the device size and at the same time, to improve the performance and to increase the circuit density. However, when the thickness of the gate SiO2 is reduced from 3.5nm to 1.5nm, the leakage current at a gate bias of 1V increases drastically from 10-12 A to 10 A due to quantummechanical tunneling [1]. Currently, there are many researches on replacing SiO2 with a high dielectric constant (high-k) material, such as Si3N4, HfSixOy, HfO2, and ZrO2, in order to achieve a low leakage current with improved reliability [2]. High-k dielectrics are also required for the nanosize nonvolatile memory (NVM) devices [1]. The conventional poly-Si floating-gate structure, which includes a continuous poly-Si thin film in the SiO2 gate dielectric layer to retain charges, is prone to lose all charges when a single leakage path is formed. When the continuous poly-Si layer is replaced with discrete nanodots, the above problem can be eliminated because one leaky path in the tunnel oxide can only drain charges stored in a few nanodots [3]. When the SiO2 tunnel dielectric layer is replaced with a high-k film, the leakage paths are difficult to form because the larger physical thickness. Due to the low band offset between the high-k film material and silicon (Si), this kind of memory device requires a low operating power. Therefore, the nanocrystals embedded high-k structure can potentially replace the conventional poly-Si floating-gate structure in high-density NVMs [3-5]. The Zr-doped HfO2 (ZrHfO) high-k film has many superior material and electrical properties than the undoped HfO2 film in areas such as the high crystallization temperature, the large effective
Data Loading...
