Lavinia Nistor - Academia.edu (original) (raw)

Papers by Lavinia Nistor

In this paper the memory performances of the TiN/HfO₂/Ti/TiN and TiN/Ta&lt... more In this paper the memory performances of the TiN/HfO₂/Ti/TiN and TiN/Ta₂O₅/TaOx/TiN memory stacks are compared. First, the bipolar switching parameters and the effect of the compliance current on the memory window and endurance are investigated. Then, the endurance and data retention properties are compared at a given operating current (100μA). Ta₂O₅ based memory stack exhibits a better memory window (2 decades) and data retention, while the HfO₂ one shows good endurance properties (10⁸ cycles). Finally, thanks to ab initio calculations using Density Functional Theory, the stability of the conductive filament is investigated in both HfO_x and TaO_x dielectrics.

Applied Physics Letters, Nov 15, 2021

IEEE Transactions on Magnetics, Nov 1, 2014

We demonstrated a self-aligned two-step reactive ion etching (RIE) process to pattern high densit... more We demonstrated a self-aligned two-step reactive ion etching (RIE) process to pattern high density magnetic tunnel junction (MTJ) arrays. We did the RIE for the top electrode (TE) and stop in the middle of the tunnel barrier. A nitride conformal film was coated on the device pillars as a dielectric spacer. The conformal spacer protects the tunnel barrier from shorting by redeposition and provides a mask for the bottom electrode (BE) RIE. We used this process and completed perpendicular MTJ devices with our process flow. We tested the devices by measuring magnetic field switching and spin transfer torque switching. We get tunneling magnetoresistance (TMR) up to 100%, switching current as low as 60 µA at 100 ns, switching current density J c0 as low as 2.5 × 10 6 A/cm 2 and endurance above 10 9 for devices as small as 50 nm in diameter. The results are compared with devices from a TE RIE only process, and we find minimum damage was made by the BE RIE. We also discuss the size dependence of MTJ parameters such as TMR and free layer coercive field and offset field, which is very related to the RIE process.

Applied Physics Letters, Jan 5, 2009

This letter presents a study of perpendicular magnetic anisotropy in oxide/Co/Pt structures, whic... more This letter presents a study of perpendicular magnetic anisotropy in oxide/Co/Pt structures, which could constitute the upper magnetic electrode of magnetic tunnel junctions. The growth of cobalt layers on SiO2 substrates shows that all 0.6 nm thick Co films are superparamagnetic, whereas perpendicular magnetic anisotropy is obtained for 1.5 nm films after annealing. Co layers grown on various Al and Mg oxides prepared by sputtering also exhibit perpendicular magnetic anisotropy after annealing. Combined with inverse Pt/Co(CoFeB)/oxide stackings, these structures allow preparing tunnel junctions with thicker magnetic electrodes and much better thermal stability than those based on standard Pt/Co multilayers.

ABSTRACT This work reports on advances in MRAM cells aiming at sub-nanosecond switching and for s... more ABSTRACT This work reports on advances in MRAM cells aiming at sub-nanosecond switching and for sub-20nm technology nodes. Ultrafast precessional spin-transfer switching in elliptical magnetic tunnel junction nanopillars is possible to obtain in samples integrating a perpendicular polarizer and a tunnel junction with in-plane magnetized electrodes. We show that spin transfer torque (STT) switching in less than 500ps can be achieved in these structures with corresponding write energy less than 100fJ. For high density integration and possibly sub-20nm diameter cells the use of a thermally assisted concept for perpendicular anisotropy cells, where the intrinsic heating is used to simultaneously achieve high thermal stability and low current switching.

Journal of Applied Physics, Jan 28, 2014

Perpendicular spin transfer torque magnetic random access memories with high spin torque efficien... more Perpendicular spin transfer torque magnetic random access memories with high spin torque efficiency and thermal stability for embedded applications (invited)

IEEE Transactions on Magnetics, Oct 1, 2009

Antiferromagnetic coupling between magnetic electrodes has been observed in non-epitaxial perpend... more Antiferromagnetic coupling between magnetic electrodes has been observed in non-epitaxial perpendicularly magnetized MgO tunnel junctions. This coupling becomes less negative with increasing annealing temperature up to 375 C. This can be possibly related to homogeneization of oxygen in the barrier and de-oxidation of the magnetic electrodes. However, the evolution of coupling field with both barrier and electrode thickness doesn't agree with existing coupling theories. Similar structures with in-plane magnetized electrodes exhibit classical ferromagnetic coupling.

Journal of Applied Physics, Nov 14, 2016

We measure the frequencies of spin waves in nm-thick perpendicularly magnetized FeCoB systems, an... more We measure the frequencies of spin waves in nm-thick perpendicularly magnetized FeCoB systems, and model the frequencies to deduce the exchange stiffness of this material in the ultrathin limit. For this, we embody the layers in magnetic tunnel junctions patterned into circular nanopillars of diameters ranging from 100 to 300 nm, and we use magneto-resistance to determine which rf-current frequencies are efficient in populating the spin wave modes. Micromagnetic calculations indicate that the ultrathin nature of the layer and the large wave vectors used ensure that the spin wave frequencies are predominantly determined by the exchange stiffness, such that the number of modes in a given frequency window can be used to estimate the exchange stiffness. For 1 nm layers, the experimental data are consistent with an exchange stiffness A ¼ 2062 pJ/m, which is slightly lower than its bulk counterpart. The thickness dependence of the exchange stiffness has strong implications for the numerous situations that involve ultrathin films hosting strong magnetization gradients, and the micromagnetic description thereof. Published by AIP Publishing.

IEEE Transactions on Magnetics, Jun 1, 2010

The perpendicular magnetic anisotropy (PMA) of Pt/CoFe(B)/MgO bottom electrodes and the tunnel ma... more The perpendicular magnetic anisotropy (PMA) of Pt/CoFe(B)/MgO bottom electrodes and the tunnel magnetoresistance (TMR) of CoFeB-based magnetic tunnel junctions (MTJ) have been analyzed as a function of Mg thickness for naturally oxidized barriers. Low PMA and TMR values are found for over-oxidized (small MgO thickness) and under-oxidized (large MgO thickness) barriers. When CoFe is used as bottom electrode, a strong correlation is observed between TMR and PMA variation as a function of MgO thickness with maxima in both quantities occurring for an MgO thickness around 1.2 nm. On the contrary, for CoFeB bottom electrodes, the sensitivity of PMA to MgO thickness is completely lost, as a probable consequence of boron diffusion towards the MgO interface.

Physical Review B, Jun 15, 2010

The influence of magnetic layer thickness on the interlayer coupling through a tunnel barrier is ... more The influence of magnetic layer thickness on the interlayer coupling through a tunnel barrier is investigated in Co/MgO/Co structures with perpendicular anisotropy. Despite the rather large MgO thickness, a clear antiferromagnetic coupling is observed. It oscillates with increasing magnetic layer thickness, in agreement with theories on indirect coupling through insulating spacers. Although the average interlayer coupling strength decreases with increasing annealing temperature, constant period and amplitude of these oscillations are observed for all annealing temperatures.

Applied Physics Letters, Jan 19, 2009

arXiv (Cornell University), Nov 2, 2021

arXiv (Cornell University), Sep 30, 2021

In the last decade, several works have focused on exploring the material and electrical propertie... more In the last decade, several works have focused on exploring the material and electrical properties of GeTe/Sb 2 Te 3 superlattices (SLs) in particular because of some first device implementations demonstrating interesting performances such as fast switching speed, low energy consumption, and non-volatility. However, the switching mechanism in such SL-based devices remains under debate. In this work, we investigate the prototype GeTe/Sb 2 Te 3 SLs, to analyze fundamentally their electronic and thermal properties by ab initio methods. We find that the resistive contrast is small among the different phases of GeTe/Sb 2 Te 3 because of a small electronic gap (about 0.1 eV) and a consequent semi-metallic-like behavior. At the same time the out-of-plane lattice thermal conductivity is rather small, while varying up to four times among the different phases, from 0.11 to 0.45 W/mK, intimately related to the number of Van der Waals (VdW) gaps in a unit block. Such findings confirm the importance of the thermal improvement achievable in GeTe/Sb 2 Te 3 superlattices devices, highlighting the impact of the material stacking and the role of VdW gaps on the thermal engineering of the Phase-Change Memory cell.

Bulletin of the American Physical Society, Mar 21, 2011

Interlayer exchange coupling (IEC) has been of great interest for spintronic community and has be... more Interlayer exchange coupling (IEC) has been of great interest for spintronic community and has been shown directly related to equilibrium spin current (ESC). Here we present a study of the influence of the electronic occupation numbers on the angular dependence of the IEC in magnetic layered nanostructures with finite thickness ferromagnetic (FM) layers. The calculations were performed within the tight-binding model using the nonequilibrium Green function technique both within perturbation theory and exact diagonalization approaches. We found that the period of IEC oscillations as a function of FM layer thickness has nonmonotonic variation with electronic states occupation numbers (Fermi level position). In the limit of 2-site model it is found that perturbation theory fails to describe correctly exchange coupling angular dependence always giving sinusoidal behavior for the ESC while the exact solution alternates between sinusoidal and strongly nonsinusoidal behavior as a number of electrons in the system is varied.

Resistive memories such as STT-MRAM, RERAM and PCRAM use many elements, alloys and compounds that... more Resistive memories such as STT-MRAM, RERAM and PCRAM use many elements, alloys and compounds that are not used in traditional semiconductor memory and even logic devices. Even newer FERAM materials based on doped HfOx, require optimizing crystal structure to get ferro-electric properties, that are not typically preferred for logic devices. For all these materials, requirements such as precise thickness in sub Angstrom values, precise composition control, surface smoothness and texture control become very critical. In addition, etching of these materials provide new challenges because halogens used in traditional RIE are in many cases too aggressive for some of these materials. The focus of this paper is on status of deposition (PVD and ALD) and etching approaches used for resistive memories. Blanket film data as well as some typical electrical behavior obtained from metalinsulator-metal (MIM) pillar structures is presented.

Physical Review B, 2017

We present a theory of the Anisotropy of Tunneling Magnetoresistance (ATMR) phenomenon in magneti... more We present a theory of the Anisotropy of Tunneling Magnetoresistance (ATMR) phenomenon in magnetic tunnel junctions (MTJ) attributed to Rashba spin-orbit interaction in the insulating barrier. ATMR represents the difference of tunnel magnetoresistance (TMR) amplitude measured with in-plane and out-of-plane magnetic configurations. It is demonstrated that within the spinpolarized free electron model, the change of conductance associated with the ATMR is exactly twice of the change of conductance measured at full saturation (i.e. in parallel configuration of magnetizations) between in-plane and out-of-plane configuration, i.e. the tunneling anisotropic magnetoresistance (TAMR). Both ATMR and TAMR are closely related to the TMR amplitude and spin-orbit constant. The predicted ATMR phenomenon is confirmed experimentally, showing a few percent values in case of the widely studied CoFeB/MgO/CoFeB based MTJ.

2018 IEEE International Memory Workshop (IMW), 2018

Resistive memories such as STT-MRAM, RERAM and PCRAM use many elements, alloys and compounds that... more Resistive memories such as STT-MRAM, RERAM and PCRAM use many elements, alloys and compounds that are not used in traditional semiconductor memory and even logic devices. Even newer FERAM materials based on doped HfOx, require optimizing crystal structure to get ferro-electric properties, that are not typically preferred for logic devices. For all these materials, requirements such as precise thickness in sub Angstrom values, precise composition control, surface smoothness and texture control become very critical. In addition, etching of these materials provide new challenges because halogens used in traditional RIE are in many cases too aggressive for some of these materials. The focus of this paper is on status of deposition (PVD and ALD) and etching approaches used for resistive memories. Blanket film data as well as some typical electrical behavior obtained from metalinsulator-metal (MIM) pillar structures is presented.

Applied Physics Letters, 2021

In the last decade, several works have focused on exploring the material and electrical propertie... more In the last decade, several works have focused on exploring the material and electrical properties of GeTe/Sb 2 Te 3 superlattices (SLs), in particular because of some first device implementations demonstrating interesting performances such as fast switching speed, low energy consumption, and non-volatility. However, the switching mechanism in such SL-based devices remains under debate. In this work, we investigate the prototype GeTe/Sb 2 Te 3 SLs to analyze fundamentally their electronic and thermal properties by ab initio methods. We find that the resistive contrast is small among the different phases of GeTe/Sb 2 Te 3 because of a small electronic gap (about 0.1 eV) and a consequent semi-metallic-like behavior. At the same time, the out-of-plane lattice thermal conductivity is rather small, while varying up to four times among the different phases, from 0.11 to 0.45 W m À1 K À1 , intimately related to the number of Van der Waals (VdW) gaps in a unit block. Such findings confirm the importance of the thermal improvement achievable in GeTe/Sb 2 Te 3 superlattices devices, highlighting the impact of the material stacking and the role of VdW gaps on the thermal engineering of the phase-change memory cell.

In this paper the memory performances of the TiN/HfO₂/Ti/TiN and TiN/Ta&lt... more In this paper the memory performances of the TiN/HfO₂/Ti/TiN and TiN/Ta₂O₅/TaOx/TiN memory stacks are compared. First, the bipolar switching parameters and the effect of the compliance current on the memory window and endurance are investigated. Then, the endurance and data retention properties are compared at a given operating current (100μA). Ta₂O₅ based memory stack exhibits a better memory window (2 decades) and data retention, while the HfO₂ one shows good endurance properties (10⁸ cycles). Finally, thanks to ab initio calculations using Density Functional Theory, the stability of the conductive filament is investigated in both HfO_x and TaO_x dielectrics.

Applied Physics Letters, Nov 15, 2021

IEEE Transactions on Magnetics, Nov 1, 2014

We demonstrated a self-aligned two-step reactive ion etching (RIE) process to pattern high densit... more We demonstrated a self-aligned two-step reactive ion etching (RIE) process to pattern high density magnetic tunnel junction (MTJ) arrays. We did the RIE for the top electrode (TE) and stop in the middle of the tunnel barrier. A nitride conformal film was coated on the device pillars as a dielectric spacer. The conformal spacer protects the tunnel barrier from shorting by redeposition and provides a mask for the bottom electrode (BE) RIE. We used this process and completed perpendicular MTJ devices with our process flow. We tested the devices by measuring magnetic field switching and spin transfer torque switching. We get tunneling magnetoresistance (TMR) up to 100%, switching current as low as 60 µA at 100 ns, switching current density J c0 as low as 2.5 × 10 6 A/cm 2 and endurance above 10 9 for devices as small as 50 nm in diameter. The results are compared with devices from a TE RIE only process, and we find minimum damage was made by the BE RIE. We also discuss the size dependence of MTJ parameters such as TMR and free layer coercive field and offset field, which is very related to the RIE process.

Applied Physics Letters, Jan 5, 2009

This letter presents a study of perpendicular magnetic anisotropy in oxide/Co/Pt structures, whic... more This letter presents a study of perpendicular magnetic anisotropy in oxide/Co/Pt structures, which could constitute the upper magnetic electrode of magnetic tunnel junctions. The growth of cobalt layers on SiO2 substrates shows that all 0.6 nm thick Co films are superparamagnetic, whereas perpendicular magnetic anisotropy is obtained for 1.5 nm films after annealing. Co layers grown on various Al and Mg oxides prepared by sputtering also exhibit perpendicular magnetic anisotropy after annealing. Combined with inverse Pt/Co(CoFeB)/oxide stackings, these structures allow preparing tunnel junctions with thicker magnetic electrodes and much better thermal stability than those based on standard Pt/Co multilayers.

ABSTRACT This work reports on advances in MRAM cells aiming at sub-nanosecond switching and for s... more ABSTRACT This work reports on advances in MRAM cells aiming at sub-nanosecond switching and for sub-20nm technology nodes. Ultrafast precessional spin-transfer switching in elliptical magnetic tunnel junction nanopillars is possible to obtain in samples integrating a perpendicular polarizer and a tunnel junction with in-plane magnetized electrodes. We show that spin transfer torque (STT) switching in less than 500ps can be achieved in these structures with corresponding write energy less than 100fJ. For high density integration and possibly sub-20nm diameter cells the use of a thermally assisted concept for perpendicular anisotropy cells, where the intrinsic heating is used to simultaneously achieve high thermal stability and low current switching.

Journal of Applied Physics, Jan 28, 2014

Perpendicular spin transfer torque magnetic random access memories with high spin torque efficien... more Perpendicular spin transfer torque magnetic random access memories with high spin torque efficiency and thermal stability for embedded applications (invited)

IEEE Transactions on Magnetics, Oct 1, 2009

Antiferromagnetic coupling between magnetic electrodes has been observed in non-epitaxial perpend... more Antiferromagnetic coupling between magnetic electrodes has been observed in non-epitaxial perpendicularly magnetized MgO tunnel junctions. This coupling becomes less negative with increasing annealing temperature up to 375 C. This can be possibly related to homogeneization of oxygen in the barrier and de-oxidation of the magnetic electrodes. However, the evolution of coupling field with both barrier and electrode thickness doesn't agree with existing coupling theories. Similar structures with in-plane magnetized electrodes exhibit classical ferromagnetic coupling.

Journal of Applied Physics, Nov 14, 2016

We measure the frequencies of spin waves in nm-thick perpendicularly magnetized FeCoB systems, an... more We measure the frequencies of spin waves in nm-thick perpendicularly magnetized FeCoB systems, and model the frequencies to deduce the exchange stiffness of this material in the ultrathin limit. For this, we embody the layers in magnetic tunnel junctions patterned into circular nanopillars of diameters ranging from 100 to 300 nm, and we use magneto-resistance to determine which rf-current frequencies are efficient in populating the spin wave modes. Micromagnetic calculations indicate that the ultrathin nature of the layer and the large wave vectors used ensure that the spin wave frequencies are predominantly determined by the exchange stiffness, such that the number of modes in a given frequency window can be used to estimate the exchange stiffness. For 1 nm layers, the experimental data are consistent with an exchange stiffness A ¼ 2062 pJ/m, which is slightly lower than its bulk counterpart. The thickness dependence of the exchange stiffness has strong implications for the numerous situations that involve ultrathin films hosting strong magnetization gradients, and the micromagnetic description thereof. Published by AIP Publishing.

IEEE Transactions on Magnetics, Jun 1, 2010

The perpendicular magnetic anisotropy (PMA) of Pt/CoFe(B)/MgO bottom electrodes and the tunnel ma... more The perpendicular magnetic anisotropy (PMA) of Pt/CoFe(B)/MgO bottom electrodes and the tunnel magnetoresistance (TMR) of CoFeB-based magnetic tunnel junctions (MTJ) have been analyzed as a function of Mg thickness for naturally oxidized barriers. Low PMA and TMR values are found for over-oxidized (small MgO thickness) and under-oxidized (large MgO thickness) barriers. When CoFe is used as bottom electrode, a strong correlation is observed between TMR and PMA variation as a function of MgO thickness with maxima in both quantities occurring for an MgO thickness around 1.2 nm. On the contrary, for CoFeB bottom electrodes, the sensitivity of PMA to MgO thickness is completely lost, as a probable consequence of boron diffusion towards the MgO interface.

Physical Review B, Jun 15, 2010

The influence of magnetic layer thickness on the interlayer coupling through a tunnel barrier is ... more The influence of magnetic layer thickness on the interlayer coupling through a tunnel barrier is investigated in Co/MgO/Co structures with perpendicular anisotropy. Despite the rather large MgO thickness, a clear antiferromagnetic coupling is observed. It oscillates with increasing magnetic layer thickness, in agreement with theories on indirect coupling through insulating spacers. Although the average interlayer coupling strength decreases with increasing annealing temperature, constant period and amplitude of these oscillations are observed for all annealing temperatures.

Applied Physics Letters, Jan 19, 2009

arXiv (Cornell University), Nov 2, 2021

arXiv (Cornell University), Sep 30, 2021

In the last decade, several works have focused on exploring the material and electrical propertie... more In the last decade, several works have focused on exploring the material and electrical properties of GeTe/Sb 2 Te 3 superlattices (SLs) in particular because of some first device implementations demonstrating interesting performances such as fast switching speed, low energy consumption, and non-volatility. However, the switching mechanism in such SL-based devices remains under debate. In this work, we investigate the prototype GeTe/Sb 2 Te 3 SLs, to analyze fundamentally their electronic and thermal properties by ab initio methods. We find that the resistive contrast is small among the different phases of GeTe/Sb 2 Te 3 because of a small electronic gap (about 0.1 eV) and a consequent semi-metallic-like behavior. At the same time the out-of-plane lattice thermal conductivity is rather small, while varying up to four times among the different phases, from 0.11 to 0.45 W/mK, intimately related to the number of Van der Waals (VdW) gaps in a unit block. Such findings confirm the importance of the thermal improvement achievable in GeTe/Sb 2 Te 3 superlattices devices, highlighting the impact of the material stacking and the role of VdW gaps on the thermal engineering of the Phase-Change Memory cell.

Bulletin of the American Physical Society, Mar 21, 2011

Interlayer exchange coupling (IEC) has been of great interest for spintronic community and has be... more Interlayer exchange coupling (IEC) has been of great interest for spintronic community and has been shown directly related to equilibrium spin current (ESC). Here we present a study of the influence of the electronic occupation numbers on the angular dependence of the IEC in magnetic layered nanostructures with finite thickness ferromagnetic (FM) layers. The calculations were performed within the tight-binding model using the nonequilibrium Green function technique both within perturbation theory and exact diagonalization approaches. We found that the period of IEC oscillations as a function of FM layer thickness has nonmonotonic variation with electronic states occupation numbers (Fermi level position). In the limit of 2-site model it is found that perturbation theory fails to describe correctly exchange coupling angular dependence always giving sinusoidal behavior for the ESC while the exact solution alternates between sinusoidal and strongly nonsinusoidal behavior as a number of electrons in the system is varied.

Resistive memories such as STT-MRAM, RERAM and PCRAM use many elements, alloys and compounds that... more Resistive memories such as STT-MRAM, RERAM and PCRAM use many elements, alloys and compounds that are not used in traditional semiconductor memory and even logic devices. Even newer FERAM materials based on doped HfOx, require optimizing crystal structure to get ferro-electric properties, that are not typically preferred for logic devices. For all these materials, requirements such as precise thickness in sub Angstrom values, precise composition control, surface smoothness and texture control become very critical. In addition, etching of these materials provide new challenges because halogens used in traditional RIE are in many cases too aggressive for some of these materials. The focus of this paper is on status of deposition (PVD and ALD) and etching approaches used for resistive memories. Blanket film data as well as some typical electrical behavior obtained from metalinsulator-metal (MIM) pillar structures is presented.

Physical Review B, 2017

We present a theory of the Anisotropy of Tunneling Magnetoresistance (ATMR) phenomenon in magneti... more We present a theory of the Anisotropy of Tunneling Magnetoresistance (ATMR) phenomenon in magnetic tunnel junctions (MTJ) attributed to Rashba spin-orbit interaction in the insulating barrier. ATMR represents the difference of tunnel magnetoresistance (TMR) amplitude measured with in-plane and out-of-plane magnetic configurations. It is demonstrated that within the spinpolarized free electron model, the change of conductance associated with the ATMR is exactly twice of the change of conductance measured at full saturation (i.e. in parallel configuration of magnetizations) between in-plane and out-of-plane configuration, i.e. the tunneling anisotropic magnetoresistance (TAMR). Both ATMR and TAMR are closely related to the TMR amplitude and spin-orbit constant. The predicted ATMR phenomenon is confirmed experimentally, showing a few percent values in case of the widely studied CoFeB/MgO/CoFeB based MTJ.

2018 IEEE International Memory Workshop (IMW), 2018

Resistive memories such as STT-MRAM, RERAM and PCRAM use many elements, alloys and compounds that... more Resistive memories such as STT-MRAM, RERAM and PCRAM use many elements, alloys and compounds that are not used in traditional semiconductor memory and even logic devices. Even newer FERAM materials based on doped HfOx, require optimizing crystal structure to get ferro-electric properties, that are not typically preferred for logic devices. For all these materials, requirements such as precise thickness in sub Angstrom values, precise composition control, surface smoothness and texture control become very critical. In addition, etching of these materials provide new challenges because halogens used in traditional RIE are in many cases too aggressive for some of these materials. The focus of this paper is on status of deposition (PVD and ALD) and etching approaches used for resistive memories. Blanket film data as well as some typical electrical behavior obtained from metalinsulator-metal (MIM) pillar structures is presented.

Applied Physics Letters, 2021

In the last decade, several works have focused on exploring the material and electrical propertie... more In the last decade, several works have focused on exploring the material and electrical properties of GeTe/Sb 2 Te 3 superlattices (SLs), in particular because of some first device implementations demonstrating interesting performances such as fast switching speed, low energy consumption, and non-volatility. However, the switching mechanism in such SL-based devices remains under debate. In this work, we investigate the prototype GeTe/Sb 2 Te 3 SLs to analyze fundamentally their electronic and thermal properties by ab initio methods. We find that the resistive contrast is small among the different phases of GeTe/Sb 2 Te 3 because of a small electronic gap (about 0.1 eV) and a consequent semi-metallic-like behavior. At the same time, the out-of-plane lattice thermal conductivity is rather small, while varying up to four times among the different phases, from 0.11 to 0.45 W m À1 K À1 , intimately related to the number of Van der Waals (VdW) gaps in a unit block. Such findings confirm the importance of the thermal improvement achievable in GeTe/Sb 2 Te 3 superlattices devices, highlighting the impact of the material stacking and the role of VdW gaps on the thermal engineering of the phase-change memory cell.