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0Raman study of phase transitions in thin films of hafnium oxide
M. Martyshov1, D. Zhigunov2, A. Pavlikov1*
1-Faculty ofPhysics, M.V. Lomonosov Moscow State University, Moscow, Russia 2- Skolkovo Institute of Science and Technology, Moscow, Russia
* pavlikovav@my. msu.ru
Hafnium dioxide (HfO2) is a good dielectric with a wide bandgap and a high dielectric constant. It is used as a replacement for silicon dioxide as an insulating layer in thin film capacitors and in the gates of field effect transistors. Transistor-based memories no longer meet modern needs due to problems with their scalability and power consumption. One of the main candidates that can replace it is resistive random access memory (RRAM) [1]. It is a non-volatile type of memory that stands out due to its simple two-pin design, high potential scalability and speed of operation.
In this work, thin films of hafnium oxide were obtained, which were subsequently annealed in a furnace in an air atmosphere. To study the optical properties of the films, Raman spectra were measured, which provide information about the crystal structure of the samples under investigation. The spectra were measured using a Horiba HR-800 micro-Raman spectrometer. A helium-neon laser with a wavelength of 633 nm was used for excitation. 10x, 50x and 100x objectives were applied to focus the laser beam.
Comparing our experimental data on Raman scattering with the literature, we can conclude that the pristine sample does not have pronounced peaks and is initially in the amorphous phase. At a temperature of 400°C, lines characteristic of the crystalline monoclinic phase begin to appear in the sample, the shape of which reaches sharpness already at 500°C and does not change significantly with the next increase in the annealing temperature. The spectra contain a photoluminescent background, and the width of the lines that appeared at temperatures of 500°C and 600°C indicates the nanosize of the crystallites. Based on these data, it can be assumed that nanocrystals with a monoclinic structure are formed in the sample already at a temperature of about 500°C.
The research was carried out with the support of the grant from the Russian Science Foundation no. 23-19-00268, https://rscf.ru/project/23-19-00268/.
[1] E. Linn, Resistive Switching (John Wiley & Sons), Chapter 2, (2016).
