UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

Guest
2024-11-22 2:13
 HOME     CONFERENCES     SEARCH            LOGIN     NEW USER     IMAGES   


Conference: Bucharest University Faculty of Physics 2015 Meeting


Section: Solid State Physics and Materials Science


Title:
Ge nanocrystals embedded in HfO2 matrix for non-volatile memories


Authors:
Catalin PALADE (1,2), Adrian SLAV (1), Ana-Maria LEPADATU (1), Adrian Valentin MARALOIU (1)


Affiliation:
1) National Institute of Materials Physics

2) Faculty of Physics, University of Bucharest


E-mail
catalin.palade@infim.ro


Keywords:
Ge nanocrystals, non-volatile memory, magnetron sputtering, charge storage properties, memory window


Abstract:
The memory devices using Ge nanocrystals embedded in oxide matrices like HfO2 represents a new alternative to conventional non-volatile memory devices due to the very high value of dielectric constant (k ≈ 25) which make possible to increase the density of stored information without increasing the device size. The increased density of information is due to both a smaller equivalent oxide thickness and the presence of Ge nanocrystals embedded in HfO2. Ge nanocrystals act as charge storage nodes increasing the charge retention time of the device. For evidencing the memory properties we deposited HfO2/Ge/HfO2<.sub>/p-Si trilayer structures by using magnetron sputtering method and then we annealed them in a rapid thermal processor at different temperatures between 600 and 1000 oC for Ge nanostructuring. The MOS-like capacitors were obtained by thermal evaporation of Al contacts in an up-down configuration. The C–V characteristics were measured at different sweeping voltages and frequencies in the range 100 kHz – 1 MHz. The morphology of MOS-like capacitors was investigated by transmission electron microscopy (TEM) which shows that the nanostructures annealed at 600 oC keep the initial trilayer morphology. The presence of Ge nanoparticles embedded in crystallized HfO2 matrix has been evidenced by high angle annular dark field-scanning TEM. By increasing the annealing temperature to 800 – 1000 oC, the initial trilayer morphology disappears and the Ge nanoparticles concentration decreases. The C–V characteristics measured on the annealed samples present hysteresis, the best one being obtained for samples annealed at 600 oC which show hysteresis with memory window of 1.2 V. With the increase of annealing temperature we observe the damaging of the charge storage properties by the decrease of the memory window down to 0.2 V. The width of memory window is independent of the frequency proving that Ge nanoparticles evidenced by TEM are crystallized.


Acknowledgement:
This work was supported by the Romanian National Authority for Scientific Research through the CNCS–UEFISCDI Contract No. PN II-PT-PCCA- 9/2012.