Geometrical Magnetoresistance Research Articles

Geometrical Magnetoresistance as a Tool for Carrier Mobility Extraction in InGaAs MOSFETs

Geometrical Magnetoresistance as a Tool for Carrier Mobility Extraction in InGaAs MOSFETs

Universal material trends in extraordinary magnetoresistive devices

Extraordinary magnetoresistance (EMR) is a geometric magnetoresistance emerging in hybrid systems typically comprising a high-mobility material and a metal. Due to a field-dependent redistribution of electrical currents in these devices, the electrical resistance at room temperature can increase by 107% when applying a magnetic field of 5 T. Although EMR holds considerable potential for realizing sensitive, all-electronic magnetometers, this potential is largely unmet. A key challenge is that the performance of EMR devices depends very sensitively on variations in a vast parameter space where changes in the device geometry and material properties produce widely different EMR performances. The challenge of navigating in the large parameter space is further amplified by the poor understanding of the interplay between the device geometry and material properties. By systematically varying the material parameters in four key EMR geometries using diffusive transport simulations, we here elucidate this interplay with the aim of finding universal guidelines for designing EMR devices. Common to all geometries, we find that the sensitivity scales inversely with the carrier density, while the MR reaches saturation at low carrier densities. Increasing the mobility beyond 20 000 cm2 Vs−1 is required to observe strong EMR effects at 1 T with the optimal magnetoresistance observed for mobilities between 100 000–500 000 cm2 Vs−1. An interface resistance below cm2 between the constituent materials in the hybrid devices was also found to be a prerequisite for very high magnetoresistances in all geometries. By further simulating several high-mobility materials at room and cryogenic temperatures, we conclude that encapsulated graphene and InSb are amongst the most promising candidates for EMR devices showing high magnetoresistance exceeding 107% below 1 T at room temperature. This study paves the way for understanding how to realize EMR devices with record-high magnetoresistance and high sensitivity for detecting magnetic fields.

Unconventional Giant "Magnetoresistance" in Bosonic Semiconducting Diamond Nanorings.

The emergence of superconductivity in doped insulators such as cuprates and pnictides coincides with their doping-driven insulator-metal transitions. Above the critical doping threshold, a metallic state sets in at high temperatures, while superconductivity sets in at low temperatures. An unanswered question is whether the formation of Cooper pairsin a well-established metal will inevitably transform the host material into a superconductor, as manifested by a resistance drop. Here, this question is addressed by investigating the electrical transport in nanoscale rings (full loops) and half loops manufactured from heavily boron-doped diamond. It is shown that in contrast to the diamond half-loops (DHLs) exhibiting a metal-superconductor transition, the diamond nanorings (DNRs) demonstrate a sharp resistance increase up to 430% and a giant negative "magnetoresistance" below the superconducting transition temperature of the starting material. The finding of the unconventional giant negative "magnetoresistance", as distinct from existing categories of magnetoresistance, that is, the conventional giant magnetoresistancein magnetic multilayers, the colossal magnetoresistancein perovskites, and the geometric magnetoresistance in semiconductor-metal hybrids, reveals the transformation of the DNRs from metals to bosonic semiconductors upon the formation of Cooper pairs. DNRs like these could be used to manipulate Cooper pairs in superconducting quantum devices.

Mobility and quasi-ballistic charge carrier transport in graphene field-effect transistors

The optimization of graphene field-effect transistors (GFETs) for high-frequency applications requires further understanding of the physical mechanisms concerning charge carrier transport at short channel lengths. Here, we study the charge carrier transport in GFETs with gate lengths ranging from 2 μm down to 0.2 μm by applying a quasi-ballistic transport model. It is found that the carrier mobility, evaluated via the drain–source resistance model, including the geometrical magnetoresistance effect, is more than halved with decreasing the gate length in the studied range. This decrease in mobility is explained by the impact of ballistic charge carrier transport. The analysis allows for evaluation of the characteristic length, a parameter of the order of the mean-free path, which is found to be in the range of 359–374 nm. The mobility term associated with scattering mechanisms is found to be up to 4456 cm2/Vs. Transmission formalism treating the electrons as purely classical particles allows for the estimation of the probability of charge carrier transport without scattering events. It is shown that at the gate length of 2 μm, approximately 20% of the charge carriers are moving without scattering, while at the gate length of 0.2 μm, this number increases to above 60%.

Ultrahigh Carrier Mobilities in Ferroelectric Domain Wall Corbino Cones at Room Temperature.

Recently, electrically conducting heterointerfaces between dissimilar band insulators (such as lanthanum aluminate and strontium titanate) have attracted considerable research interest. Charge transport and fundamental aspects of conduction have been thoroughly explored. Perhaps surprisingly, similar studies on conceptually much simpler conducting homointerfaces, such as domain walls, are not nearly so well developed. Addressing this disparity, magnetoresistance is herein reported in approximately conical 180° charged domain walls, in partially switched ferroelectric thin-film single-crystal lithium niobate. This system is ideal for such measurements: first, the conductivity difference between domains and domain walls is unusually large (a factor of 1013 ) and hence currents driven through the thin film, between planar top and bottom electrodes, are overwhelmingly channeled along the walls; second, when electrical contact is made to the top and bottom of the domain walls and a magnetic field is applied along their cone axes, then the test geometry mirrors that of a Corbino disk: a textbook arrangement for geometric magnetoresistance measurement. Data imply carriers with extremely high room-temperature Hall mobilities of up to ≈3700 cm2 V-1 s-1 . This is an unparalleled value for oxide interfaces (and for bulk oxides) comparable to mobilities in other systems seen at cryogenic, rather than at room, temperature.

Geometrical magnetoresistance effect and mobility in graphene field-effect transistors

Further development of graphene field-effect transistors (GFETs) for high-frequency electronics requires accurate evaluation and study of the mobility of charge carriers in a specific device. Here, we demonstrate that the mobility in the GFETs can be directly characterized and studied using the geometrical magnetoresistance (gMR) effect. The method is free from limitations of other approaches since it does not require an assumption of the constant mobility and the knowledge of the gate capacitance. Studies of a few sets of GFETs in the wide range of transverse magnetic fields indicate that the gMR effect dominates up to approximately 0.55 T. In higher fields, the physical magnetoresistance effect starts to contribute. The advantages of the gMR approach allowed us to interpret the measured dependencies of mobility on the gate voltage, i.e., carrier concentration, and identify the corresponding scattering mechanisms. In particular, the range of the fairly constant mobility is associated with the dominating Coulomb scattering. The decrease in mobility at higher carrier concentrations is associated with the contribution of the phonon scattering. Analysis shows that the gMR mobility is typically 2–3 times higher than that found via the commonly used drain resistance model. The latter underestimates the mobility since it does not take the interfacial capacitance into account.

Low-Field Mobility and High-Field Velocity of Charge Carriers in InGaAs/InP High-Electron-Mobility Transistors

Development of transistors for advanced low-noise amplifiers requires better understanding of mechanisms governing the charge carrier transport in correlation with the noise performance. In this article, we report on study of the carrier velocity in InGaAs/InP high-electron-mobility transistors (HEMTs) found via geometrical magnetoresistance in the wide range of the drain fields, up to 2 kV/cm, at a cryogenic temperature of 2 K. We observed, for the first time experimentally, the velocity peaks and found that the peak velocity and corresponding field decrease significantly with the transverse field. The low-field mobility and peak velocity are found to be up to 65 000 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.2\times 10^{{6}}$ </tex-math></inline-formula> cm/s, respectively. Extrapolations to the lower transverse fields show that the peak velocity can be as high as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.7\times 10^{{7}}$ </tex-math></inline-formula> cm/s. The corresponding intrinsic transit frequency can be up to 172 GHz at the gate length of 250 nm. We demonstrated, for the first time, that the low-field mobility and peak velocity reveal opposite dependencies on the transverse field, indicating the difference in carrier transport mechanisms dominating at low and high fields. Therefore, the peak velocity is an appropriate parameter for characterization and development of the low-noise HEMTs, complementary to the low-field mobility. Analysis indicates that the low-field carrier transport is governed by screening of the Coulomb potential of ionized impurities responsible for the carrier scattering. The velocity overshoot is associated with the electron quantization and subband formation caused by the transverse field. The results of the research clarify the ways of the further development of the HEMTs for advanced applications.

Electron mobility distribution in FD-SOI MOSFETs using a NEGF-Poisson approach

Modern electronic devices consist of several semiconductor layers where each layer exhibits unique carrier transport properties that can be represented by a unique mobility characteristic. To date, the mobility spectrum analysis technique is the main approach that has been developed and applied to the analysis of conductivity mechanisms of multi-carrier semiconductor structures and devices. Currently, there are no theoretical calculations of the mobility distribution in semiconductor structures or devices and specifically in MOSFET devices. In this article, we present a theoretical study of the electron mobility distribution in planar fully-depleted silicon-on-insulator (FD-SOI) transistors employing quantum mechanical modelling. The simulation results indicate that electronic transport in the 10 nm thick Si channel layer at room-temperature is due to two distinct and well-defined electron species for channel length varying from 50 nm to 200 nm. The two electron mobility distributions provide clear evidence of sub-band modulated transport in 10-nm thick Si planar FD-SOI MOSFETs that are associated with primed and non-primed valleys of silicon. The potential of the top gate electrode has been modulated, and thus only the top channel inversion-layer electron population transport parameters have been investigated employing self-consistent non-equilibrium Green’s function (NEGF)–Poisson numerical calculations. The numerical framework presented can be used to interpret experimental results obtained by magnetic-field dependent geometrical magnetoresistance measurements and mobility spectrum analysis, and provides greater insight into electron mobility distributions in nanostructured FET devices.

Nature of the 1/f noise in graphene-direct evidence for the mobility fluctuation mechanism.

The nature of the low-frequency 1/f noise in electronic materials and devices is one of the oldest unsolved physical problems (f is the frequency). The fundamental question of the noise source-fluctuations in the mobility vs. number of charge carriers-is still debated. While there are several pieces of evidence to prove that the 1/f noise in semiconductors is due to the fluctuations in the number of the charge carriers, there is no direct evidence of the mobility fluctuations as the source of 1/f noise in any material. Herein, we measured noise in an h-BN encapsulated graphene transistor under the conditions of geometrical magnetoresistance to directly assess the mechanism of low-frequency electronic current fluctuations. It was found that the relative noise spectral density of the graphene resistance fluctuations depends non-monotonically on the magnetic field (B) with a minimum at approximately μ0B ≅ 1 (μ0 is the electron mobility). This observation proves unambiguously that mobility fluctuations are the dominant mechanism of electronic noise in high-quality graphene. Our results are important for all proposed applications of graphene in electronics and add to the fundamental understanding of the 1/f noise origin in any electronic device.

Inversion layer electron mobility distribution in fully-depleted silicon-on-insulator MOSFETs

Magnetic-field dependent geometrical magnetoresistance measurements and high-resolution mobility spectrum analysis have been employed to characterise the inversion-layer electron mobility distribution in fully-depleted silicon-on-insulator MOS transistors. The results reveal that the room-temperature electron population in the 12 nm thick Si channel layer is characterised by a broad electron mobility distribution that significantly departs from the ideal single-value discrete carrier approximation. At temperatures below 60 K, the linewidth of the distribution is shown to become significantly narrower, approaching a delta-like function at 30 K. Self-consistent Schrödinger-Poisson numerical calculations suggest that, since the total carrier population at 295 K is comprised of electrons in the ground-state level of the two subband ladders, intervalley scattering and phonon scattering will significantly influence the linewidth of the mobility distribution in the transistor channel. To the best of our knowledge, electron mobility distributions in Si-based devices have not been previously studied nor resolved in such detail.

Magnetic sensors and geometrical magnetoresistance: A review

Magnetic sensing devices are of the extremely significant kind of detectors, that are used several important and useful applications. Geometrical extraordinary magnetoresistance (EMR) is the geometrical kind of magnetoresistance associated with the non-magnetic semiconductor-metal hybrid structure and influenced by geometrical shape. As a result of Lorentz force, the current path change from metal (in absence of magnetic field) to semiconductor (under the subjection of the magnetic field) in semiconductor-metal hybrid structure is the key of EMR phenomena, i.e. once the metal is placed in a semiconductor, it works as a short circuit with the majority of applied current moving through metallic inhomogeneity and the almost whole resistance of semiconductor-metal hybrid structure drops to value smaller than that of homogeneous semiconductor in absence of magnetic field, in other hands, applying of magnetic field alters the current route to be around the metallic inhomogeneity where it works as an open circuit and the whole resistance turns into a quite high magnitude relies on the geometrical form of a device. The variables govern these phenomena are metal and semiconductor conductivity, semiconductor charge carriers mobility, and device geometry. Within this review, EMR phenomena history, variables governed it, materials, and applications of EMR devices are overviewed.

Laser-Induced Abnormal Cryogenic Magnetoresistance Effect in a Corbino Disk

The geometric magnetoresistance effect in semiconductors has remained a heated discussion for many years. However, there are few reports on laser-triggered geometric magnetoresistance in traditional structures. In this work, we use a laser to change the carrier concentration to obtain a large magnetoresistance (212.6%) under a low magnetic field (1 T) at 150 K in a Corbino disk with $\mathrm{Co}$-$\mathrm{Ag}$ films. One unanticipated finding is that the large positive magnetoresistance does not change monotonously with temperature, which is different from previous research. Theoretical calculation reveals that the interaction among a photogenerated carrier, bending of the current path, and magnetic nanoparticles in low temperature improves the magnetoresistance in a Corbino disk. These findings reveal an important strategy for creating laser-trigged nanoscale magnetoresistance devices, while presenting a wide range of possibilities for exploring the dependence of photogenerated carriers on temperature under magnetic field.

On the angular dependence of InP high electron mobility transistors for cryogenic low noise amplifiers in a magnetic field

The InGaAs-InAlAs-InP high electron mobility transistor (InP HEMT) is the preferred active device used in a cryogenic low noise amplifier (LNA) for sensitive detection of microwave signals. We have investigated the angular dependence of the InP HEMT when oriented in a magnetic field at 2 K ambient temperature up to 14 T. A sharp angular dependence as a function of the magnetic field was measured for the output current of the InP HEMT. This was accurately described by a geometrical magnetoresistance expression for all angles and magnetic field strengths. Key device parameters such as transconductance and on-resistance were significantly affected at small angles and magnetic fields. The strong angular dependence of the InP HEMT output current in a magnetic field has important implications for the alignment of cryogenic LNAs in microwave detection experiments involving magnetic fields.

Exchange bias and large room temperature magnetoresistance in ion beam-synthesized Co nanoparticles in SiO2

Magnetic nanogranular materials have shown promising magnetic and electron transport properties, offering key advantages for a range of applications from spintronics components to magnetic field sensors. In this paper, the properties of Co nanoparticles synthesized using low-energy ion implantation and electron beam annealing (EBA) on SiO2 were investigated. EBA leads to the growth of crystalline face-centred cubic Co nanoparticles from small nanoparticles within a Co-rich region in the near surface. The as-implanted and EBA samples are ferromagnetic with Curie temperatures above 300 K. The saturated magnetic moment per implanted Co atom was measured to be as high as 4.25 ± 0.5 μB. The moment per Co atom decreases and approaches that of bulk Co with increased EBA time. This suggests that there may be a ferromagnetic Co1-xSixOy phase that has not been previously reported. An exchange bias is observed and proposed to arise from a thin antiferromagnetic CoO layer surrounding the Co nanoparticles. We find a room temperature magnetoresistance as high as 22.8% at 8 T with linear behaviour above ~ 3 T. The linear magnetoresistance is likely to be due to a geometric magnetoresistance that is observed in inhomogeneous nanomaterials containing metallic nanoparticles in a semiconducting matrix. Thus, EBA leads to Co nanoparticles that are expected to be electronically spin polarized but there is no evidence for spin-dependent tunnelling. These unique characteristics could provide the base for novel devices.

Extremely Large Magnetoresistance at Low Magnetic Field by Coupling the Nonlinear Transport Effect and the Anomalous Hall Effect.

The anomalous Hall effect of a magnetic material is coupled to the nonlinear transport effect of a semiconductor material in a simple structure to achieve a large geometric magnetoresistance (MR) based on a diode-assisted mechanism. An extremely large MR (>10(4) %) at low magnetic fields (1 mT) is observed at room temperature. This MR device shows potential for use as a logic gate for the four basic Boolean logic operations.

High-resolution mobility spectrum analysis of magnetoresistance in fully-depleted silicon-on-insulator MOSFETs

Multi-carrier transport in planar fully-depleted silicon-on-insulator (FD-SOI) MOSFETs has been investigated employing magnetic-field dependent geometrical magnetoresistance measurements and high-resolution mobility spectrum analysis. The results indicate that electronic transport in the 10nm thick Si channel layer is due to two distinct and well-defined electron species. Although self-consistent Schrödinger–Poisson numerical calculations indicate significant localization of the total electron population near the back and front interfaces, the results of mobility spectrum analysis suggest that the mobility distributions associated with these spatially localized populations are strongly coupled through carrier scattering processes, and do not have independent and distinguishable mobility distributions. The two detected electron mobility distributions are thus evidence of sub-band modulated transport in 10-nm thick Si planar FD-SOI MOSFETs. The mobility maximum of the dominant carrier was found to occur under gate bias conditions that result in a minimum perpendicular effective electric field.

Mobility Investigations on Strained 30-nm High-&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$k$ &lt;/tex-math&gt;&lt;/inline-formula&gt; Metal Gate MOSFETs by Geometrical Magnetoresistance Effect

In this paper, we present mobility investigations of strained nMOS and pMOS short-channel transistors with dimensions down to 30-nm gate length. Using the geometrical magnetoresistance (MR) effect, carrier mobility of electrons and holes in the inversion channel of a recent state-of-the-art CMOS technology is presented from linear to saturation operation conditions. The MR effect allows for a more direct access to the carrier mobility compared with the conventional current/voltage and capacitance/voltage mobility derivation methods, in which series resistance, inversion charge density, and effective channel length are necessary to extract the mobility values of the short-channel devices. In another way, the MR effect can help to disentangle the performance gain of the strained state-of-the art devices to changes in channel mobility or device connection, e.g., series resistance effects.

Geometrical Magnetoresistance in Multi-Gate FDSOI Structures

Mobility characterization is very challenging on SOI multi-gate transistors where several channels coexist and interact [1-3]. Among all mobility determination procedures, only the geometrical magnetoresistance yields accurate values free of any assumption (channel length, oxide and film thickness, doping, strain, etc). Magnetoresistance is a direct consequence of carrier deflection by a magnetic field. When carriers do not follow the shortest path from source to drain, the channel resistance increases. The relation between the resistances obtained when the magnetic field is present or not yields: RB = R0 ( 1 + μMR 2 B2 ) The carrier deviation by the Lorentz force is shown in Fig. 1a. The deviation is modulated by the device geometry. If the transistor is long and narrow (W/L < 1) the Hall field opposes to the Lorentz force and the magnetoresistance is weak. However, when the sample is wide and short (W/L >> 1) the Hall field is short-circuited by the end contacts and the Lorentz force is not compensated. Hence, carriers are deviated and the magnetoresistance is maximum. Fig. 2 illustrates the simulated electron mobility against the aspect ratio (W/L) for several magnetic field orientations. The magnetoresistance is much higher for normal magnetic fields (and W/L > 5) than for transversal fields as fully documented by experimental data [4]. On the other hand, in double-gate FinFETs (Fig. 1b), the magnetoresistance is high even in narrow samples (W ~ L). This surprising result was explained by the lateral gate action which cancels the Hall voltage so preventing the compensation of the Lorentz force and resulting in the magnetoresistance [4]. TCAD numerical simulations [5] were carried out to clarify the carrier deflection and magnetoresistance mobility in FinFETs. The impact of the device architecture, thicknesses, gate biasing scheme, and magnetic field orientation is documented and explained.

Geometrical Magnetoresistance in Multi-Gate FDSOI Structures

The geometrical magnetoresistance in advanced planar and 3D multi-gate FDSOI transistors is addressed. The strong dependence of the magnetoresistance mobility on the device architecture, size and magnetic field orientation is analyzed and discussed with the help of numerical simulations.

Experimental and Theoretical Investigation of Magnetoresistance From Linear Regime to Saturation in 14-nm FD-SOI MOS Devices

The feasibility of geometric magnetoresistance (MR) measurement from linear to saturation operation regime is demonstrated in ultrathin body and BOX fully depleted silicon-on-insulator devices from 14-nm technology node. Besides, we propose a new physical compact model for MOSFET drain current under high field transport, which reproduces experimental MR mobility from linear to saturation operation region and serves as the basis for a new extraction method of carrier saturation velocity. A benchmarking with state-of-the-art saturation velocity extraction methodologies is also conducted. Our saturation velocity results indicate that, for this technology, nonstationary transport prevails as manifested by an overshoot velocity behavior, still far from the ballistic limit.