Resistance Drift Research Articles

Kinetic effects of E × B sheared flow on the hydrodynamic drift instabilities

The temporal evolution of the hydrodynamic ion temperature gradient instability and resistive hydrodynamic drift instability of plasma flow with velocity shear is analytically investigated. The non-modal kinetic theory (Mikhailenko et al 2011 Phys. Plasmas 18 062103) is applied which uses the method of shearing modes (or so-called non-modal approach) as its foundation. In this theory, the velocity shear reveals as the time-dependent effect of the finite Larmor radius in the integral equation for the electrostatic potential, and resulted in the decrease with time the frequencies and the growth rates of the instabilities.

Defects in amorphous phase-change materials

Abstract

Spinel-structured Ni-free Zn0.9Cu x Mn2.1-x O4 (0.1 ≤ x ≤ 0.5) thermistors of negative temperature coefficient

Most spinel-structured materials of negative temperature coefficient (NTC) contain Ni, which have high cost. In this work, Ni-free Zn0.9Cu x Mn2.1-x O4 (0.1 ≤ x ≤ 0.5) NTC material system is developed. X-ray diffraction (XRD) spectra show that Zn0.9Cu x Mn2.1-x O\intered at 1100 °C crystallizes in a tetrahedral spinel structure, which is caused by the Jahn-Teller effect of the Mn3+ ions at the B sites. Cu2p3/2 X-ray photoelectron spectra (XPS) demonstrate that most of Cu ions located at B sites are at the valance of 2+. The resistivity of Zn0.9Cu x Mn2.1-x O4 varies from 1,340 Ω cm to 51,489 Ω cm, and B value from 3,357 K to 4,276 K. The resistivity drift after annealing at 150 °C in air for 1,000 h is less than 3 % which is stable enough for practical application.

Laser Trim Pattern Optimization for CuAlMo Thin-Film Resistors

The influence of varying laser trim patterns on the electrical performance of a novel CuAlMo thin-film resistor material is investigated. The benefits and limitations of various trim geometries are considered before two patterns, the “L” cut and serpentine cut, are selected to laser-trim resistor samples to target values of 1-10 Ω, using previously optimized laser conditions. The effect of increasing trim gain and varying trim pattern on the stability and standard deviation of the films is then systematically investigated. A two-stage trimming process is used to reduce resistance drift to <;0.1% following storage for 168 h at 125°C in air, which also allows much tighter resistance tolerances of <;±0.1% to be achieved.

Prospective study on surface-enhanced laser desorption/ionization protein fingerprinting for diagnosing gene polymorphism leading to drug resistance drift: sequential therapy with a platinum-based regimen and gefitinib for non-small cell lung cancer

背景与目的本研究组前期研究发现借助于SELDI技术可以预测吉非替尼的疗效，而且指出其蛋白质指纹图谱M/Z：8, 693±50H+丰度≤25%，可以作为吉非替尼治疗非小细胞肺癌（non-small cell lung cancer, NSCLC）患者取、舍的筛选指标，以这个指标为界定，观察含铂方案治疗失败的患者以蛋白质指纹为依据指导化疗与吉非替尼的序贯应用的方法的远期效果。方法选择TP、DP和GP方案化疗失败，且经SELDI检测M/Z（质核比）8, 693±50H+的丰度≤15%的NSCLC患者9例，口服吉非替尼250 mg，1次/d，治疗期间每2个月查患者血清SELDI指纹，以M/Z: 8, 693±50H+的丰度 > 25%作为再化疗指标，并以M/Z: 8, 693±50H+丰度≤15%为继续服用吉非替尼的指标，两者之间根据肿块变化和肿瘤标记物变化决定取舍吉非替尼治疗时间，指导吉非替尼与含铂方案的序贯治疗，观察总生存时间。结果随访至2010年12月，9例患者中位总生存期为27个月（10个月-66个月）。结论 SELDI技术通过指纹的描述，有计划地选择这些抗肿瘤药物治疗NSCLC的取、舍，可提高药物治疗的获益率和获益时间。

Stoichiometry dependence of resistance drift phenomena in amorphous GeSnTe phase-change alloys

In phase-change materials, the amorphous state resistivity increases with time following a power law ρ ∝ (t/t0)αRD. This drift in resistivity seriously hampers the potential of multilevel-storage to achieve an increased capacity in phase-change memories. This paper presents the stoichiometric dependence of drift phenomena in amorphous GeSnTe systems (a-GeSnTe) and other known phase-change alloys with the objective to identify low drift materials. The substitution of Ge by Sn results in a systematic decrease of the drift parameter from a-GeTe (αRD = 0.129) to a-Ge2Sn2Te4 (αRD = 0.053). Furthermore, with increasing Sn content a decrease in crystallization temperature, trap state density, optical band gap, and activation energy for electronic conduction is observed. In a-GeSnTe, a-GeSbTe, and a-AgInSbTe alloys as well, the drift parameter αRD correlates to the activation energy for electronic conduction. This study indicates that low drift materials are characterized by low activation energies of electronic conduction. The correlation found between drift and activation energy of electronic conduction manifests a useful criterion for material optimization.

Statistical Analyses of Turbulent Particle and Momentum Fluxes in a Cylindrical Magnetized Plasma

A nonlinear simulation of resistive drift wave turbulence in a cylindrical plasma is carried out. Long time evolution of turbulence with formation of a zonal flow is obtained for more than 1000 times of the typical drift wave period, which is sufficient for statistical analyses. Dynamical particle and momentum balance for the formation of the mean reveals that the radial turbulent fluxes are dominant contributors for the evolution of fluctuations. The particle flux is found to precede the momentum flux for 0.4 times of the typical drift wave period with large temporal variance. The analyses of the time series data of 3-D fields give the understanding of the dynamical structural formation mechanism. c

Some results on the germanium telluride density of states

Germanium telluride (GeTe) is one of the most studied phase change materials. Surprisingly, only little is known about the distribution of states (DOS) in its band gap. In this paper we investigate both experimentally and theoretically the amorphous GeTe DOS and we propose a model for this DOS as well as orders of magnitude of some of the transport parameters of this material. The DOS we propose is subsequently compared to those suggested to explain the threshold switching and the resistance drift phenomena.

On the density of states of germanium telluride

Germanium telluride (GeTe) is one of the most studied phase change materials. Surprisingly, only little is known about the density of states (DOS) in its band gap. In this paper, the DOS of amorphous GeTe films is investigated both experimentally and theoretically. We propose a model for this DOS as well as estimates of some of the transport parameters of this material. Thin films of amorphous GeTe have been deposited by sputtering. Their dark and photoconductivity have been measured as a function of temperature. By means of the modulated photocurrent technique their DOS was probed, while their absorption was investigated by photothermal deflection spectroscopy at room temperature. Numerical calculations were employed to reproduce the experimental results with a proper set of transport parameters and choice of DOS. These data constitute a good basis for further study on the influence of the DOS on the aging of the sample resistance (“resistance drift”).

Preparation and characterization of Cu and Zn modified nickel manganite NTC powders and thick film thermistors

Abstract A simple ball milling/thermal treatment procedure was applied to obtain fine thermistor powders. Three different powder compositions were analyzed–Cu 0.2 Ni 0.5 Zn 1.0 Mn 1.3 O 4 , Cu 0.25 Ni 0.5 Zn 1.0 Mn 1.25 O 4 and Cu 0.4 Ni 0.5 Mn 2.1 O 4 . XRD analysis showed that all three powder compositions had a cubic spinel structure. Correlation between the sintering temperature, structure and resulting electrical properties was analyzed on bulk samples. Thick film pastes were composed and segmented thick film thermistors were screen printed on alumina, dried and fired. SEM analysis revealed a typical dendrite structure with small grains and a developed surface area. Thick film sheet resistance was measured on a test matrix and the resistance decreased with increasing Cu content. The temperature dependence of sample resistance was measured in a climatic chamber enabling calculation of the material constant and activation energy. Aging of the obtained segmented thermistors was analyzed and the resistivity drift was 0.23% for the Cu 0.2 Ni 0.5 Zn 1.0 Mn 1.3 O 4 NTC thick film thermistor confirming greater stability of thermistors containing Zn and Cu that in combination with the determined good thermistor characteristics make them good candidates for temperature and heat loss sensor applications.

Investigations on irreversible- and reversible-type gas sensing for ZnO and Mg0.5Zn0.5Fe2O4 chemi-resistive sensors

Semiconducting metal oxides are attractive material candidates for combustible gas sensors. Little or marginal base resistance drift of these metal oxide sensors is desirable during repeated response and recovery cycles. However, due to the partial recovery, often a significant drift in base resistance is observed. The gas sensing is termed irreversible when there is a partial recovery of base resistance, whereas for reversible sensing the base resistance is fully recovered. For reducing gas (hydrogen and carbon monoxide) sensing we have reported reversible and irreversible resistance transients for magnesium zinc ferrite and zinc oxide sensing elements, respectively. For a wide range of gas concentrations and operating temperatures, the response transients for these sensing elements are modelled using the Langmuir–Hinshelwood reaction mechanism. It is revealed that for irreversible-type sensing, the response time is reduced with the increase in test gas concentration. On the other hand, for reversible-type sensing, the response time is found to be independent of the gas concentration. Based on the estimation of pore size, pore size distribution and specific surface area of the calcined powder together with the analyses of the surface morphology of the sensing elements we have argued that due to the porous morphology of the magnesium zinc ferrite sensing element the oxidized product can easily desorb from the sensor during recovery. Therefore, irrespective of the test gas concentration, the base resistance of the magnesium zinc ferrite sensor recovers fully during the recovery process.

The influence of resistance drift on measurements of the activation energy of conduction for phase-change material in random access memory line cells

Temporal drift of the amorphous resistance in phase-change random access memory (PRAM) is a temperature accelerated process. Increasing the temperature will speed up the drift process which is shown to affect measurements of the activation energy of conduction (Ea, slope of log(R) versus 1/kT). Doped SbTe phase change (PRAM) line cells were brought to the amorphous state and were subjected to annealing experiments. First, it is shown that when the temperature is increased by a fixed rate, the resistance does not follow a unique function of temperature but depends on the heating rate. This can be attributed to resistance drift taking place during the ramp. Upon cooling, the drift process freezes and only then physically relevant, i.e., time independent, values for Ea can be obtained, because of the absence of additional drift. The observed increase in resistance as a function of annealing history (for various frozen-in drift levels) is modeled and well-reproduced using a trap limited band transport model. The model explains these observations by an increase of the temperature dependent band gap by about 47 meV due to drift at 418 K.

Improving reliability of non-volatile memory technologies through circuit level techniques and error control coding

Non-volatile resistive memories, such as phase-change RAM (PRAM) and spin transfer torque RAM (STT-RAM), have emerged as promising candidates because of their fast read access, high storage density, and very low standby power. Unfortunately, in scaled technologies, high storage density comes at a price of lower reliability. In this article, we first study in detail the causes of errors for PRAM and STT-RAM. We see that while for multi-level cell (MLC) PRAM, the errors are due to resistance drift, in STT-RAM they are due to process variations and variations in the device geometry. We develop error models to capture these effects and propose techniques based on tuning of circuit level parameters to mitigate some of these errors. Unfortunately for reliable memory operation, only circuit-level techniques are not sufficient and so we propose error control coding (ECC) techniques that can be used on top of circuit-level techniques. We show that for STT-RAM, a combination of voltage boosting and write pulse width adjustment at the circuit-level followed by a BCH-based ECC scheme can reduce the block failure rate (BFR) to 10–8. For MLC-PRAM, a combination of threshold resistance tuning and BCH-based product code ECC scheme can achieve the same target BFR of 10–8. The product code scheme is flexible; it allows migration to a stronger code to guarantee the same target BFR when the raw bit error rate increases with increase in the number of programming cycles.

Implication of molecular orientation on charge transport and gas sensing characteristics of cobalt–phthalocyanine thin films

Charge transport and gas sensing characteristics of cobalt phthalocyanine films deposited along (ATB) and perpendicular (PTB) to the natural twin boundaries of (001) LaAlO3 substrate have been investigated. The charge carrier mobility of ATB films (∼5cm2V−1s−1) is five orders of magnitude higher compared to that of PTB films (∼7×10−5cm2V−1s−1), suggesting that twin boundaries acts like a template for ordering of molecules. The ATB films on exposure to ammonia showed a reversible increase of resistance, with fast response and recovery. In contrast PTB films showed same sensitivity, but exhibits base resistance drift along with sluggish response.

Size-Dependent Drift of Resistance Due to Surface Defect Relaxation in Conductive-Bridge Memory

Conductive-bridge random access memory (CBRAM) devices have shown low-power programming, fast switching, and good device scalability. In particular, the large resistance window and good control of the conductive filament (CF) size may allow for efficient multilevel-cell (MLC) operation. Toward this aim, the structural stability of the CF must be demonstrated. This letter addresses the stability of the set states in CBRAM. We evidence a size-dependent drift of the CF resistance, which is interpreted by surface relaxation due to defect rearrangement. An analytical model is developed, describing the size-dependent drift in terms of partial and full depletion of the CF by the surface defect.

Effects of parallel electron dynamics on plasma blob transport

The 3D effects on sheath connected plasma blobs that result from parallel electron dynamics are studied by allowing for the variation of blob density and potential along the magnetic field line and using collisional Ohm’s law to model the parallel current density. The parallel current density from linear sheath theory, typically used in the 2D model, is implemented as parallel boundary conditions. This model includes electrostatic 3D effects, such as resistive drift waves and blob spinning, while retaining all of the fundamental 2D physics of sheath connected plasma blobs. If the growth time of unstable drift waves is comparable to the 2D advection time scale of the blob, then the blob’s density gradient will be depleted resulting in a much more diffusive blob with little radial motion. Furthermore, blob profiles that are initially varying along the field line drive the potential to a Boltzmann relation that spins the blob and thereby acts as an addition sink of the 2D potential. Basic dimensionless parameters are presented to estimate the relative importance of these two 3D effects. The deviation of blob dynamics from that predicted by 2D theory in the appropriate limits of these parameters is demonstrated by a direct comparison of 2D and 3D seeded blob simulations.

Effect of Drift Waves on Plasma Blob Dynamics

Most of the work to date on plasma blobs found in the edge region of magnetic confinement devices is limited to 2D theory and simulations which ignore the variation of blob parameters along the magnetic field line. However, if the 2D convective rate of blobs is on the order of the growth rate of unstable drift waves, then drift wave turbulence can drastically alter the dynamics of blobs from that predicted by 2D theory. The density gradients in the drift plane that characterize the blob are mostly depleted during the nonlinear stage of drift waves resulting in a much more diffuse blob with a greatly reduced radial velocity. Sheath connected plasma blobs driven by effective gravity forces are considered in this Letter and it is found that the effects of resistive drift waves occur at earlier stages in the 2D motion for smaller blobs and in systems with a smaller effective gravity force. These conclusions are supported numerically by a direct comparison of 2D and 3D seeded blob simulations.

Disorder enhancement due to structural relaxation in amorphous Ge2Sb2Te5

This work investigates the atomic structural relaxation accounting for the resistance drift of the amorphous phase of the Ge2Sb2Te5 (α-GST) chalcogenide alloy. A joint electrical and optical characterization over time on both the phase change memory cell in the reset state and the as-deposited amorphous GST film has been performed to elucidate the origin of the drift phenomenon. We highlight that the drift mechanism is ascribed to the removal of residual resonant-like bonding in the amorphous network, lowering the electronic component of the dielectric constant (ɛ∞) and leading to a progressive loosing of any medium-range order.

A swelling-based chemiresistor for a biogenic odour

Escherichia coli bacteria release 1-decanol as a byproduct of their metabolism. We demonstrate the detection of 1-decanol odour at a partial pressure in the order 100ppb by the resistance change of a swelling-based sensor, consisting of Langmuir–Schäfer deposited Au core/organic ligand shell nanoparticle films. This is an exceptionally low limit of detection for swelling-based sensors, and relies firstly, in the careful matching of the CSNPs ligands to the targeted odour, and secondly, in the very low volatility of this odour. Sensor response can be substantially increased further when films are cooled below the freezing point of 1-decanol. We observe unexpected quantitative behaviour of our sensors: response is only weakly dependent on the odour's partial pressure, and scales differently with temperature than the response of other Au-CSNP odours to more volatile odours. This may be related to their unusually strong thermal resistance drift, the difficulties in delivering very low partial pressure odour atmospheres, and the proximity to the analyte's freezing point.

Impact of resonant magnetic perturbations on nonlinearly driven modes in drift-wave turbulence

In this work, we study the effects of resonant magnetic perturbations (RMPs) on turbulence, flows, and confinement in the framework of resistive drift wave turbulence. We extend the Hasegawa-Wakatani model to include RMP fields. The effect of the RMPs is to induce a linear coupling between the zonal electric field and the zonal density gradient, which drives the system to a state of electron radial force balance for large δBrB0. Both the vorticity flux (Reynolds stress) and particle flux are modulated. We derive an extended predator prey model which couples zonal potential and density dynamics to the evolution of turbulence intensity. This model has both turbulence drive and RMP amplitude as control parameters and predicts a novel type of transport bifurcation in the presence of RMPs. We find states that are similar to the ZF-dominated state of the standard predator-prey model, but for which the power threshold is now a function of the RMP strength. For small RMP amplitude, the energy of zonal flows decreases and the turbulence energy increases with δBrB0, corresponding to a damping of zonal flows.