In order to improve the operation speed of phase change memory (PCM), superlattice-like Ge2Sb2Te5/Sb (SLL GST/Sb) thin films were prepared in a sputtering method to explore the suitability as an active material for PCM application. Compared with GST, SLL GST/Sb thin film has a lower crystallization temperature, crystallization activation energy, thermal conductivity, and smaller crystalline grain size. A faster SET/RESET switching speed (10 ns) and a lower operation power consumption (the energy for RESET operation 9.1 × 10−13 J) are obtained. In addition, GST/Sb shows a good endurance of 8.3 × 104 cycles.
Compared with pure Sb, N-doped Sb material was proved to be a promising candidate for the phase change memory (PCM) use because of its higher crystallization temperature (∼250 °C), larger crystallization activation energy (3.53 eV), and better data retention ability (166 °C for 10 years). N-doping also broadened the band gap and refined grain size. The reversible resistance transition could be achieved by an electric pulse as short as 8 ns for the PCM cell based on N-doped Sb material. A lower operation power consumption (the energy for RESET operation 2.2 × 10−12 J) was obtained. In addition, N-doped Sb material showed a good endurance of 1.8 × 105 cycles.
The transition process of a pure Sb thin film from amorphous to crystalline is ultrafast but thermally unstable. We fabricated Er doped Sb thin films by magnetron sputtering for the first time. By measuring the in situ film resistance vs. temperature, it was found that the crystallization temperature increased from 105 °C to 208 °C with increasing Er content, resulting in a significant improvement in the thermal stability. The phase transition speed was investigated using picosecond laser pulses, showing an ultrafast speed of ∼2 ns. SEM, EDS and XRD analyses also demonstrated the existence of Er and the improvement in the thermal stability by increasing Er-doping. The enhanced thermal stability through Er doping onto Sb thin films was attributed to the formation of Sb-Er bonds in doped films measured by XPS. The main outcomes of this work enable a prediction that the Er doped Sb thin films are well suited for data storage applications.
ExperimentalErbium doped Sb thin films of Er x Sb 1−x (0.002 ≤ x ≤ 0.018) were deposited on SiO 2 /Si (100) wafers by co-sputtering of Er and Sb targets at room temperature using magnetron sputtering. The purity of the Sb and Er targets was 99.999%. The base pressure in the deposition chamber was 2 × 10 −4 Pa. Sputtering was performed under an Ar gas pressure of 0.3 Pa, a flow of 30 SCCM, and a power of 30 W. The thin film
We investigate the sensitivity of phase estimation in a Mach–Zehnder interferometer with photon-subtracted two-mode squeezed vacuum states. Our results show that, for given initial squeezing parameter, both symmetric and asymmetric photon subtractions can further improve the quantum Cramér–Rao bound (i.e., the ultimate phase sensitivity), especially for single-mode photon subtraction. On the other hand, the quantum Cramér–Rao bound can be reached by parity detection for symmetric photon-subtracted two-mode squeezed vacuum states at particular values of the phase shift, but it is not valid for asymmetric photon-subtracted two-mode squeezed vacuum states. In addition, compared with the two-mode squeezed vacuum state, the phase sensitivity via parity detection with asymmetric photon-subtracted two-mode squeezed vacuum states will be getting worse. Thus, parity detection may not always be the optimal detection scheme for nonclassical states of light when they are considered as the interferometer states.
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