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We propose a new quantization method for superconducting electronic circuits involving a Josephson-junction device coupled to a linear microwave environment. The method is based on an exact impedance synthesis of the microwave environment considered as a blackbox with impedance function $Z(s)$. The synthesized circuit captures dissipative dynamics of the system with resistors coupled to the reactive part of the circuit in a nontrivial way. We quantize the circuit and compute relaxation rates following previous formalisms for lumped element circuit quantization. Up to the errors in the fit our method gives an exact description of the system and its losses.

We demonstrate enhanced relaxation and dephasing times of transmon qubits, up to ~ 60 \mu s by fabricating the interdigitated shunting capacitors using titanium nitride (TiN). Compared to lift-off aluminum deposited simultaneously with the Josephson junction, this represents as much as a six-fold improvement and provides evidence that previous planar transmon coherence times are limited by surface losses from two-level system (TLS) defects residing at or near interfaces. Concurrently, we observe an anomalous temperature dependent frequency shift of TiN resonators which is inconsistent with the predicted TLS model., Comment: 3 figures

MRAM technology offers an attractive combination of performance, density, low power, non-volatility, and write endurance. While first stand-alone MRAM products appear poised for introduction, major technology advances are also being reported. In this review, we discuss our work on a 16Mbit demonstrator chip with a 1.42 /spl mu/m/sup 2/ cell in 180 nm technology in the context of recent world wide advances in MRAM technology. These include a cell architecture that resolves the magnetic half select write disturb issue and an advanced tunnel barrier material, MgO, that promises much larger signals for MRAM read operations.

A model is presented for magnetic force microscope (MFM) images obtained with a ferromagnetic tip and a ferromagnetic sample. Results of calculations are compared to recent MFM experiments and show good agreement using known values for magnetic parameters characterizing tip and sample. The model describes a limit in resolution determined by the demagnetizing effect of tip and sample, predicts the appearance of a novel image artifact which is particularly observable in images of narrow domains of reversed magnetization, and suggests an explanation for the observed contrast between regions of opposite magnetization.

Spin torque switching is investigated in perpendicular magnetic tunnel junctions using Ta∣CoFeB∣MgO free layers and a synthetic antiferromagnet reference layer. We show that the Ta∣CoFeB interface makes a key contribution to the perpendicular anisotropy. The quasistatic phase diagram for switching under applied field and voltage is reported. Low switching voltages, Vc 50 ns=290 mV are obtained, in the range required for spin torque magnetic random access memory. Switching down to 1 ns is reported, with a rise in switching speed from increased overdrive that is eight times greater than for comparable in-plane devices, consistent with expectations from a single-domain model.

The Scanning Capacitance Microscope has been used to profile insulating, semiconducting and conducting surfaces with resolution down to 25 nanometers. In the case of semiconducting materials, it has been demonstrated that lateral dopant profiling can be achieved with 100 nanometer spatial resolution‐well beyond that which can be achieved by conventional techniques. Measurements on semiconductors indicate that the technique should be useful for device characterization. In this paper, we review the basis of Scanning Capacitance Microscopy and present some of the more recent results.

A method is presented for performing attractive‐mode force potentiometry with submillivolt accuracy and a typical spatial resolution of order 50 nm. The technique permits measurements to be made in air on specimens which may be passivated or oxidized, conducting or semiconducting, with virtually no sensitivity to oxide thickness or character. An initial demonstration is presented showing voltage measurements on a commercial operational amplifier.

Recently, high‐resolution mapping of dopant concentration has been demonstrated with the scanning capacitance microscope (SCM). Here, we demonstrate that a similar measurement can be made with the atomic force microscope using the previously demonstrated capacitive force sensing mode. By applying appropriate bias to the force tip, depletion‐induced capacitive variation is mapped over regions of varying dopant density. This method has a predicted sensitivity comparable to the SCM, and in addition allows imaging of trapped charge, as well as an independent measurement of the surface topography. Results of first‐order model calculations are presented which give estimates as to the limits in sensitivity and resolution of this method

We demonstrate that surface deformation mediated by contamination plays a major role in images of graphite obtained by a scanning tunneling microscope in air. Atomic resolution has been obtained with the surface compressed by as much as 100 \AA{}, where abnormally high atomic corrugations, up to 24 \AA{}, are observed. Calculation of the deformation profile reveals that the force necessary to deform the surface must be spread over several thousand square angstroms. The measured deformation is negligible in vacuum with a clean sample and tip, and the corrugation is 0.9 \AA{}.

SUMMARY We review the principle of differential imaging and its application to scanning tunnelling microscopy (STM). It is shown that placing a lateral dither on an STM tip at high frequency provides the means for transfering topographic information to a frequency range where noise is small. Differential STM imaging on graphite and gold is demonstrated. A simple relation between the differential image and the conventional topographic image is described.

We have shown for the first time, in previous studies, that the force microscope fitted with a magnetic tip could be used to image magnetic domains in TbFe thin films. In this report we show that the information provided by the magnetic force microscope can also include a measurement of the component of magnetization in the sample which is parallel to the surface. Measurements were taken with a magnetized tip tilted at 45° with respect to the surface normal. In a first experiment, we imaged 1μm diameter domains thermomagnetically written in a TbFe thin film. In a second measurement, we imaged a series of alternating domains in a thin film Co-alloy disc which was decorated with small magnetized particles, allowing unambiguous identification of the domain boundaries. In both cases we interpret the asymmetric portion of the images to the in-plane component of the sample magnetization.

Images of the (0001) surface of graphite observed in the scanning-tunneling microscope (STM) show a strong asymmetry in the tunneling current between neighboring carbon atoms in the hexagonal ring. The magnitude of this asymmetry is seen to be almost independent of the polarity and to decrease slightly with increasing amplitude of the bais voltage for voltages below 1 V. A theory is developed that explains this anomaly as a purely electronic effect, arising from the symmetry of the states scanned by the STM, which dominates over the topography of graphite. The predicted trends for the bias-voltage dependence of the asymmetry are confirmed experimentally.

Noise stemming from mechanical vibration, electronic noise, or low frequency (1/f power spectrum) inherent in the tunneling process, often limits the resolution, speed, or range of application of scanning tunneling microscopy (STM). We demonstrate a technique for minimizing the effect of these noise sources on the STM image. In our method, the tunneling tip is vibrated parallel to the sample surface at a frequency f0, above that of the feedback response frequency. Two signals are obtained simultaneously: the conventional topography, and a differential image corresponding to the amplitude of current modulation at f0. The resultant ac signal can be simply related to the normal STM topographic image, with significant improvement in the signal‐to‐noise ratio.

Clusters of Au and Ag deposited on the surface of highly oriented pyrolitic graphite have been imaged in air using a scanning tunneling microscope. An image is shown of a 350‐A silver cluster obtained in the constant‐current (topographic) mode. In the variable‐current mode, clusters of 6–20 atoms have been observed with atomic resolution. The motion and growth of clusters on the support are observed.

A simple walker is described that is suitable as the coarse positioner in a scanning tunneling microscope. The walker is fabricated from a single piece of piezoelectric ceramic and has feet coated with thin metal and insulating films. The walker can move in either of two orthogonal, horizontal directions on an insulated, metallized quartz substrate in steps that can be varied from 25 to 400 nm.

We present data which show that the magnetic force microscope is capable of detecting the component of the magnetic field parallel to the surface of a sample under study. Images of bits in a Co‐alloy thin‐film disk and of laser‐written bits in a TbFe film were taken with a magnetized tip tilted at 45° with respect to the surface normal. In both cases the asymmetric part of the image of a domain is interpreted in terms of gradients in the in‐plane component of the magnetic field. The bits written in the Co‐alloy disk were decorated with small magnetized particles, allowing identification of the domain boundaries and the asymmetric component of the force microscope image due to in‐plane magnetization.

We have shown for the first time, in previous studies, that the force microscope fitted with a magnetic tip could be used to image magnetic domains in TbFe thin films. In this report we show that the information provided by the magnetic force microscope can also include a measurement of the component of magnetization in the sample which is parallel to the surface. Measurements were taken with a magnetized tip tilted at 45° with respect to the surface normal. In a first experiment, we imaged 1μm diameter domains thermomagnetically written in a TbFe thin film. In a second measurement, we imaged a series of alternating domains in a thin film Co-alloy disc which was decorated with small magnetized particles, allowing unambiguous identification of the domain boundaries. In both cases we interpret the asymmetric portion of the images to the in-plane component of the sample magnetization.