Nanodevices

RESEARCH

DEPARTMENTS

RESEARCH GROUPS

DESCRIPTION

The nanodevices group develops integrated sensor solutions for the biomedical, food and environment areas, as well as industrial sensing applications. In the biomedical sensor area, magnetoresistive based protein or DNA chips, and magnetoresistive cytometers (technologies previously developed at INESC MN-Lisbon), are now being tested in different clinical applications. The bioanalyte is labelled with a magnetic nanoparticle or bead, through an intervenient antibody, aptamer, complementary DNA strand, and after recognition, the signal is read in the magnetoresistive sensor array. Label-free technologies are also being developed, using direct molecular fingerprinting of compounds and molecules using microfluidics, an optical detection, starting with discrete assembly of pre-existent modules (microfluidic reactor, light source, optical spectrometer) to the full integration of components at the wafer level in collaboration with partners. The group (together with the spintronics group) is actively involved on the prototyping of tunnel magnetoresistive based sensors for industrial applications.

This project is based on a COFUND fellowship holder ( Hongyan Bi) and addresses the specific, accurate, and fast quantification through optical means of compounds within a complex matrix background.

Schematic illustration of the microfluidic sensor integrated with after-channel UV/vis spectrophotometric detection for food ingredient analysis. (b) Collected absorbance change at 266 nm of solutions containing only caffeine, and mixture of AA and caffeine before (A0) and after (A) passing through the enzyme-loaded microfluidic sensor at 5 μL/min. Arrows indicate the time when it is started to sample the solution through the microfluidic channel.

Starting project in collaboration with the Systems Engineering group, and external partners, to develop a fully integrated microspectrometer using CMOS based or a-Si:H based photodiodes, thin film multilayer band pass filters, and LEDS, into a compact format suitable for integration with control and communication hardware for a portable solution.

This project is being developed within the PhD thesis of M.Costa ( NanoFab). The goal is to incorporate magnetoresistive sensors with typical features of 100nm on the tip of AFM cantilevers, providing direct field mapping through an AFM probe.

Resonance characterization of the cantilever with a resonance frequency of ∼250 kHz. (b) Voltage output versus the external applied magnetic field response of an individualSV sensor already integrated in an AFM cantilever.

In this paper, the perpendicular magnetic anisotropy (PMA) is tailored by changing the thickness of the free layer with the objective of producing MTJ nano-pillars with smooth linear resistance dependence with both in-plane magnetic field and DC bias. We furthermore demonstrate how this linear bias dependence can be used to create a zero-threshold broadband voltage rectifier, a feature which is important for rectification in wireless charging and energy harvesting applications. By carefully balancing the amount of PMA acting in the free layer the measured RF to DC voltage conversion efficiency can be made as large as 11%.

@online{Tarequzzaman2018a,
title = {Magnetic oscillations Excited by Concurrent Spin Injection from a Tunneling Current and a Spin Hall Current},
author = { M. Tarequzzaman and T. Böhnert and M. Decker and J. D. Costa and J. Borme and B. Lacoste and E. Paz and A. S. Jenkins and S. Serrano-Guisan and C. H. Back and R. Ferreira and P. P. Freitas},
url = {https://arxiv.org/abs/1802.02224},
year = {2018},
date = {2018-01-01},
urldate = {2018-04-10},
journal = {arXiv:1802.02224 [cond-mat]},
abstract = {In this paper, a 3-terminal spin-transfer torque nano-oscillator (STNO) is studied using the concurrent spin injection of a spin-polarized tunneling current and a spin Hall current exciting the free layer into dynamic regimes beyond what is achieved by each individual mechanism. The pure spin injection is capable of inducing oscillations in the absence of charge currents effectively reducing the critical tunneling current to zero. This reduction of the critical charge currents can improve the endurance of both STNOs and non-volatile magnetic memories (MRAM) devices. It is shown that the system response can be described in terms of an injected spin current density $J_s$ which results from the contribution of both spin injection mechanisms, with the tunneling current polarization $p$ and the spin Hall angle $textbackslashtheta$ acting as key parameters determining the efficiency of each injection mechanism. The experimental data exhibits an excellent agreement with this model which can be used to quantitatively predict the critical points ($J_s = -2.26textbackslashpm 0.09 textbackslashtimes 10textasciicircum9 textbackslashhbar/e$ A/m$textasciicircum2$) and the oscillation amplitude as a function of the input currents. In addition, the fitting of the data also allows an independent confirmation of the values estimated for the spin Hall angle and tunneling current polarization as well as the extraction of the damping $textbackslashalpha = 0.01$ and non-linear damping $Q = 3.8textbackslashpm 0.3$ parameters.},
note = {arXiv: 1802.02224},
keywords = {},
pubstate = {published},
tppubtype = {online}
}

In this paper, a 3-terminal spin-transfer torque nano-oscillator (STNO) is studied using the concurrent spin injection of a spin-polarized tunneling current and a spin Hall current exciting the free layer into dynamic regimes beyond what is achieved by each individual mechanism. The pure spin injection is capable of inducing oscillations in the absence of charge currents effectively reducing the critical tunneling current to zero. This reduction of the critical charge currents can improve the endurance of both STNOs and non-volatile magnetic memories (MRAM) devices. It is shown that the system response can be described in terms of an injected spin current density $J_s$ which results from the contribution of both spin injection mechanisms, with the tunneling current polarization $p$ and the spin Hall angle $textbackslashtheta$ acting as key parameters determining the efficiency of each injection mechanism. The experimental data exhibits an excellent agreement with this model which can be used to quantitatively predict the critical points ($J_s = -2.26textbackslashpm 0.09 textbackslashtimes 10textasciicircum9 textbackslashhbar/e$ A/m$textasciicircum2$) and the oscillation amplitude as a function of the input currents. In addition, the fitting of the data also allows an independent confirmation of the values estimated for the spin Hall angle and tunneling current polarization as well as the extraction of the damping $textbackslashalpha = 0.01$ and non-linear damping $Q = 3.8textbackslashpm 0.3$ parameters.

@patent{Ferreira2018,
title = {Magnetoresistive sensor},
author = { Ricardo Ferreira and Elvira Paz},
url = {https://patents.google.com/patent/US20180180686A1/en},
year = {2018},
date = {2018-01-01},
urldate = {2018-08-03},
number = {US20180180686A1},
abstract = {A magnetoresistive sensor is provided. The magnetoresistive sensor comprises a magnetic sensing layer, a magnetic reference layer, and a tunnel barrier layer between the magnetic sensing layer and the magnetic reference layer. The magnetoresistive sensor also comprises a sensing exchange layer having a layer of anti-ferromagnetic material. The sensing exchange layer is exchange coupled with the magnetic sensing layer. Also, the magnetoresistive sensor still further comprises a reference exchange layer having a layer of anti-ferromagnetic material. The reference exchange layer is exchange coupled with the magnetic reference layer. Moreover, the magnetoresistive sensor is configured such that in the absence of an external magnetic field, an exchange bias pinning the reference layer lies along a reference direction, an exchange bias pinning the sensing layer lies along a first direction that is orthogonal to the reference direction, and a magnetic anisotropy of the sensing layer is parallel to the first direction.},
keywords = {},
pubstate = {published},
tppubtype = {patent}
}

A magnetoresistive sensor is provided. The magnetoresistive sensor comprises a magnetic sensing layer, a magnetic reference layer, and a tunnel barrier layer between the magnetic sensing layer and the magnetic reference layer. The magnetoresistive sensor also comprises a sensing exchange layer having a layer of anti-ferromagnetic material. The sensing exchange layer is exchange coupled with the magnetic sensing layer. Also, the magnetoresistive sensor still further comprises a reference exchange layer having a layer of anti-ferromagnetic material. The reference exchange layer is exchange coupled with the magnetic reference layer. Moreover, the magnetoresistive sensor is configured such that in the absence of an external magnetic field, an exchange bias pinning the reference layer lies along a reference direction, an exchange bias pinning the sensing layer lies along a first direction that is orthogonal to the reference direction, and a magnetic anisotropy of the sensing layer is parallel to the first direction.

Magnetic tunnel junction (MTJ) micropillars were fabricated with integrated thermometers and a heater line (HL) for thermovoltage measurements. This novel thermometer configuration enabled a direct measurement of ? T across the MTJ micropillar. The MTJ devices were patterned from a CoFeB/MgO/CoFeB stack, with a 1.2?nm to 1.6?nm MgO wedge across the wafer, resulting in resistance area products in the range of 0.7 k? · µ m 2 ??<?? R ??×?? A ??<??55 k? · µ m 2 . This allowed the measurement of thermoelectric properties as a function of the tunnel barrier thickness. The thermometers showed a homogeneous heating behavior for all devices across the wafer. Combining the in-stack temperature measurements and finite element simulations the thermal profile across the MTJ structure and the thermopower were estimated with a noticeable improvement of the measurement accuracy. The studied MTJ structures showed tunneling magnetoresistance (TMR) ratios up to 125%, and tunneling magnetothermopower (TMTP) up to 35%.

It was recently shown that the presence of thermal gradients in magnetic nano-devices influences the magnetization state and dynamics in several ways, as for example by the generation of spin currents, spin waves, spin transfer torque, etc..

@article{Martins2017,
title = {Optimization of the buffer surface of CoFeB/MgO/CoFeB-based magnetic tunnel junctions by ion beam milling},
author = {L. Martins and J. Ventura and R. Ferreira and P.P. Freitas},
url = {http://www.sciencedirect.com/science/article/pii/S0169433217304750},
doi = {https://doi.org/10.1016/j.apsusc.2017.02.112},
issn = {0169-4332},
year = {2017},
date = {2017-01-01},
journal = {Applied Surface Science},
volume = {424},
pages = {58 - 62},
abstract = {Due to their high tunnel magnetoresistance (TMR) ratios at room temperature, magnetic tunnel junctions (MTJs) with a crystalline MgO insulating barrier and CoFeB ferromagnetic (FM) layers are the best candidates for novel magnetic memory applications. To overcome impedance matching problems in electronic circuits, the MgO barrier must have an ultra-low thickness (∼1nm). Therefore, it is mandatory to optimize the MTJ fabrication process, in order to prevent relevant defects in the MgO barrier that could affect the magnetic and electrical MTJ properties. Here, a smoothing process aiming to decrease the roughness of the buffer surface before the deposition of the full MTJ stack is proposed. An ion beam milling process was used to etch the surface of an MTJ buffer structure with a Ru top layer. The morphologic results prove an effective decrease of the Ru surface roughness with the etching time. The electrical and magnetic results obtained for MTJs with smoothed buffer structures show a direct influence of the buffer roughness and coupling field on the improvement of the TMR ratio.},
note = {7th International Conference on Advanced Nanomaterials, 2nd International Conference on Graphene Technology, 1st International Conference on Spintronics Materials},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

Due to their high tunnel magnetoresistance (TMR) ratios at room temperature, magnetic tunnel junctions (MTJs) with a crystalline MgO insulating barrier and CoFeB ferromagnetic (FM) layers are the best candidates for novel magnetic memory applications. To overcome impedance matching problems in electronic circuits, the MgO barrier must have an ultra-low thickness (∼1nm). Therefore, it is mandatory to optimize the MTJ fabrication process, in order to prevent relevant defects in the MgO barrier that could affect the magnetic and electrical MTJ properties. Here, a smoothing process aiming to decrease the roughness of the buffer surface before the deposition of the full MTJ stack is proposed. An ion beam milling process was used to etch the surface of an MTJ buffer structure with a Ru top layer. The morphologic results prove an effective decrease of the Ru surface roughness with the etching time. The electrical and magnetic results obtained for MTJs with smoothed buffer structures show a direct influence of the buffer roughness and coupling field on the improvement of the TMR ratio.

DESCRIPTION

The nanodevices group develops integrated sensor solutions for the biomedical, food and environment areas, as well as industrial sensing applications. In the biomedical sensor area, magnetoresistive based protein or DNA chips, and magnetoresistive cytometers (technologies previously developed at INESC MN-Lisbon), are now being tested in different clinical applications. The bioanalyte is labelled with a magnetic nanoparticle or bead, through an intervenient antibody, aptamer, complementary DNA strand, and after recognition, the signal is read in the magnetoresistive sensor array. Label-free technologies are also being developed, using direct molecular fingerprinting of compounds and molecules using microfluidics, an optical detection, starting with discrete assembly of pre-existent modules (microfluidic reactor, light source, optical spectrometer) to the full integration of components at the wafer level in collaboration with partners. The group (together with the spintronics group) is actively involved on the prototyping of tunnel magnetoresistive based sensors for industrial applications.

This project is based on a COFUND fellowship holder ( Hongyan Bi) and addresses the specific, accurate, and fast quantification through optical means of compounds within a complex matrix background.

Schematic illustration of the microfluidic sensor integrated with after-channel UV/vis spectrophotometric detection for food ingredient analysis. (b) Collected absorbance change at 266 nm of solutions containing only caffeine, and mixture of AA and caffeine before (A0) and after (A) passing through the enzyme-loaded microfluidic sensor at 5 μL/min. Arrows indicate the time when it is started to sample the solution through the microfluidic channel.

Starting project in collaboration with the Systems Engineering group, and external partners, to develop a fully integrated microspectrometer using CMOS based or a-Si:H based photodiodes, thin film multilayer band pass filters, and LEDS, into a compact format suitable for integration with control and communication hardware for a portable solution.

This project is being developed within the PhD thesis of M.Costa ( NanoFab). The goal is to incorporate magnetoresistive sensors with typical features of 100nm on the tip of AFM cantilevers, providing direct field mapping through an AFM probe.

Resonance characterization of the cantilever with a resonance frequency of ∼250 kHz. (b) Voltage output versus the external applied magnetic field response of an individualSV sensor already integrated in an AFM cantilever.

In this paper, the perpendicular magnetic anisotropy (PMA) is tailored by changing the thickness of the free layer with the objective of producing MTJ nano-pillars with smooth linear resistance dependence with both in-plane magnetic field and DC bias. We furthermore demonstrate how this linear bias dependence can be used to create a zero-threshold broadband voltage rectifier, a feature which is important for rectification in wireless charging and energy harvesting applications. By carefully balancing the amount of PMA acting in the free layer the measured RF to DC voltage conversion efficiency can be made as large as 11%.

@online{Tarequzzaman2018a,
title = {Magnetic oscillations Excited by Concurrent Spin Injection from a Tunneling Current and a Spin Hall Current},
author = { M. Tarequzzaman and T. Böhnert and M. Decker and J. D. Costa and J. Borme and B. Lacoste and E. Paz and A. S. Jenkins and S. Serrano-Guisan and C. H. Back and R. Ferreira and P. P. Freitas},
url = {https://arxiv.org/abs/1802.02224},
year = {2018},
date = {2018-01-01},
urldate = {2018-04-10},
journal = {arXiv:1802.02224 [cond-mat]},
abstract = {In this paper, a 3-terminal spin-transfer torque nano-oscillator (STNO) is studied using the concurrent spin injection of a spin-polarized tunneling current and a spin Hall current exciting the free layer into dynamic regimes beyond what is achieved by each individual mechanism. The pure spin injection is capable of inducing oscillations in the absence of charge currents effectively reducing the critical tunneling current to zero. This reduction of the critical charge currents can improve the endurance of both STNOs and non-volatile magnetic memories (MRAM) devices. It is shown that the system response can be described in terms of an injected spin current density $J_s$ which results from the contribution of both spin injection mechanisms, with the tunneling current polarization $p$ and the spin Hall angle $textbackslashtheta$ acting as key parameters determining the efficiency of each injection mechanism. The experimental data exhibits an excellent agreement with this model which can be used to quantitatively predict the critical points ($J_s = -2.26textbackslashpm 0.09 textbackslashtimes 10textasciicircum9 textbackslashhbar/e$ A/m$textasciicircum2$) and the oscillation amplitude as a function of the input currents. In addition, the fitting of the data also allows an independent confirmation of the values estimated for the spin Hall angle and tunneling current polarization as well as the extraction of the damping $textbackslashalpha = 0.01$ and non-linear damping $Q = 3.8textbackslashpm 0.3$ parameters.},
note = {arXiv: 1802.02224},
keywords = {},
pubstate = {published},
tppubtype = {online}
}

In this paper, a 3-terminal spin-transfer torque nano-oscillator (STNO) is studied using the concurrent spin injection of a spin-polarized tunneling current and a spin Hall current exciting the free layer into dynamic regimes beyond what is achieved by each individual mechanism. The pure spin injection is capable of inducing oscillations in the absence of charge currents effectively reducing the critical tunneling current to zero. This reduction of the critical charge currents can improve the endurance of both STNOs and non-volatile magnetic memories (MRAM) devices. It is shown that the system response can be described in terms of an injected spin current density $J_s$ which results from the contribution of both spin injection mechanisms, with the tunneling current polarization $p$ and the spin Hall angle $textbackslashtheta$ acting as key parameters determining the efficiency of each injection mechanism. The experimental data exhibits an excellent agreement with this model which can be used to quantitatively predict the critical points ($J_s = -2.26textbackslashpm 0.09 textbackslashtimes 10textasciicircum9 textbackslashhbar/e$ A/m$textasciicircum2$) and the oscillation amplitude as a function of the input currents. In addition, the fitting of the data also allows an independent confirmation of the values estimated for the spin Hall angle and tunneling current polarization as well as the extraction of the damping $textbackslashalpha = 0.01$ and non-linear damping $Q = 3.8textbackslashpm 0.3$ parameters.

@patent{Ferreira2018,
title = {Magnetoresistive sensor},
author = { Ricardo Ferreira and Elvira Paz},
url = {https://patents.google.com/patent/US20180180686A1/en},
year = {2018},
date = {2018-01-01},
urldate = {2018-08-03},
number = {US20180180686A1},
abstract = {A magnetoresistive sensor is provided. The magnetoresistive sensor comprises a magnetic sensing layer, a magnetic reference layer, and a tunnel barrier layer between the magnetic sensing layer and the magnetic reference layer. The magnetoresistive sensor also comprises a sensing exchange layer having a layer of anti-ferromagnetic material. The sensing exchange layer is exchange coupled with the magnetic sensing layer. Also, the magnetoresistive sensor still further comprises a reference exchange layer having a layer of anti-ferromagnetic material. The reference exchange layer is exchange coupled with the magnetic reference layer. Moreover, the magnetoresistive sensor is configured such that in the absence of an external magnetic field, an exchange bias pinning the reference layer lies along a reference direction, an exchange bias pinning the sensing layer lies along a first direction that is orthogonal to the reference direction, and a magnetic anisotropy of the sensing layer is parallel to the first direction.},
keywords = {},
pubstate = {published},
tppubtype = {patent}
}

A magnetoresistive sensor is provided. The magnetoresistive sensor comprises a magnetic sensing layer, a magnetic reference layer, and a tunnel barrier layer between the magnetic sensing layer and the magnetic reference layer. The magnetoresistive sensor also comprises a sensing exchange layer having a layer of anti-ferromagnetic material. The sensing exchange layer is exchange coupled with the magnetic sensing layer. Also, the magnetoresistive sensor still further comprises a reference exchange layer having a layer of anti-ferromagnetic material. The reference exchange layer is exchange coupled with the magnetic reference layer. Moreover, the magnetoresistive sensor is configured such that in the absence of an external magnetic field, an exchange bias pinning the reference layer lies along a reference direction, an exchange bias pinning the sensing layer lies along a first direction that is orthogonal to the reference direction, and a magnetic anisotropy of the sensing layer is parallel to the first direction.

Magnetic tunnel junction (MTJ) micropillars were fabricated with integrated thermometers and a heater line (HL) for thermovoltage measurements. This novel thermometer configuration enabled a direct measurement of ? T across the MTJ micropillar. The MTJ devices were patterned from a CoFeB/MgO/CoFeB stack, with a 1.2?nm to 1.6?nm MgO wedge across the wafer, resulting in resistance area products in the range of 0.7 k? · µ m 2 ??<?? R ??×?? A ??<??55 k? · µ m 2 . This allowed the measurement of thermoelectric properties as a function of the tunnel barrier thickness. The thermometers showed a homogeneous heating behavior for all devices across the wafer. Combining the in-stack temperature measurements and finite element simulations the thermal profile across the MTJ structure and the thermopower were estimated with a noticeable improvement of the measurement accuracy. The studied MTJ structures showed tunneling magnetoresistance (TMR) ratios up to 125%, and tunneling magnetothermopower (TMTP) up to 35%.

It was recently shown that the presence of thermal gradients in magnetic nano-devices influences the magnetization state and dynamics in several ways, as for example by the generation of spin currents, spin waves, spin transfer torque, etc..

@article{Martins2017,
title = {Optimization of the buffer surface of CoFeB/MgO/CoFeB-based magnetic tunnel junctions by ion beam milling},
author = {L. Martins and J. Ventura and R. Ferreira and P.P. Freitas},
url = {http://www.sciencedirect.com/science/article/pii/S0169433217304750},
doi = {https://doi.org/10.1016/j.apsusc.2017.02.112},
issn = {0169-4332},
year = {2017},
date = {2017-01-01},
journal = {Applied Surface Science},
volume = {424},
pages = {58 - 62},
abstract = {Due to their high tunnel magnetoresistance (TMR) ratios at room temperature, magnetic tunnel junctions (MTJs) with a crystalline MgO insulating barrier and CoFeB ferromagnetic (FM) layers are the best candidates for novel magnetic memory applications. To overcome impedance matching problems in electronic circuits, the MgO barrier must have an ultra-low thickness (∼1nm). Therefore, it is mandatory to optimize the MTJ fabrication process, in order to prevent relevant defects in the MgO barrier that could affect the magnetic and electrical MTJ properties. Here, a smoothing process aiming to decrease the roughness of the buffer surface before the deposition of the full MTJ stack is proposed. An ion beam milling process was used to etch the surface of an MTJ buffer structure with a Ru top layer. The morphologic results prove an effective decrease of the Ru surface roughness with the etching time. The electrical and magnetic results obtained for MTJs with smoothed buffer structures show a direct influence of the buffer roughness and coupling field on the improvement of the TMR ratio.},
note = {7th International Conference on Advanced Nanomaterials, 2nd International Conference on Graphene Technology, 1st International Conference on Spintronics Materials},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

Due to their high tunnel magnetoresistance (TMR) ratios at room temperature, magnetic tunnel junctions (MTJs) with a crystalline MgO insulating barrier and CoFeB ferromagnetic (FM) layers are the best candidates for novel magnetic memory applications. To overcome impedance matching problems in electronic circuits, the MgO barrier must have an ultra-low thickness (∼1nm). Therefore, it is mandatory to optimize the MTJ fabrication process, in order to prevent relevant defects in the MgO barrier that could affect the magnetic and electrical MTJ properties. Here, a smoothing process aiming to decrease the roughness of the buffer surface before the deposition of the full MTJ stack is proposed. An ion beam milling process was used to etch the surface of an MTJ buffer structure with a Ru top layer. The morphologic results prove an effective decrease of the Ru surface roughness with the etching time. The electrical and magnetic results obtained for MTJs with smoothed buffer structures show a direct influence of the buffer roughness and coupling field on the improvement of the TMR ratio.