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In this paper, a new genre of spin-transfer torque (STT) MRAM is proposed, in which bidirectional writing is achieved using thermoelectrically controlled magnonic current as an alternative to conventional electric current. The device uses a magnetic tunnel junction (MTJ), which is adjacent to a nonmagnetic metallic and a ferrite film. This film stack is heated or cooled by a Peltier element, which creates a bidirectional magnonic pulse in the ferrite film. Conversion of magnons to spin current occurs at the ferrite-metal interface, and the resulting STT is used to achieve fast ( ~ nanosecond) precessional switching of the ferromagnetic free layer in the MTJ. Compared to the electric-current-driven STT-MRAM with perpendicular magnetic anisotropy (PMA), thermoelectric STT-MRAM reduces the overall magnetization switching energy by more than 40% for nanosecond switching, combined with a write error rate (WER) of less than 10-9 and a lifetime of ten years or higher. The combination of higher thermal activation energy, subnanosecond read/write speed, improved tunneling magnetoresistance (TMR), and tunnel barrier reliability make thermoelectric STT-MRAM a promising choice for future nonvolatile memory applications.

A new class of spin-transfer torque magnetic random access memory (STT-MRAM) is discussed, in which writing is achieved using thermally initiated magnonic current pulses as an alternative to conventional electric current pulses. The magnonic pulses are used to destabilize the magnetic free layer from its initial direction, and are followed immediately by a bipolar electric current exerting conventional spin-transfer torque on the free layer. The combination of thermal and electric currents greatly reduces switching errors, and simultaneously reduces the electric switching current density by more than an order of magnitude as compared to conventional STT-MRAM. The energy efficiency of several possible electro-thermal circuit designs have been analyzed numerically. As compared to STT-MRAM with perpendicular magnetic anisotropy, magnonic STT-MRAM reduces the overall switching energy by almost 80%. Furthermore, the lower electric current density allows the use of thicker tunnel barriers, which should result in higher tunneling magneto-resistance and improved tunnel barrier reliability. The combination of lower power, improved reliability, higher integration density, and larger read margin make magnonic STT-MRAM a promising choice for future non-volatile storage., 9 Pages, 11 Figures

Summary and Conclusions A novel MTJ freelayer wet etching process selective to the MTJ tunneling barrier has been demonstrated. The etching solution uses trifluoromethane sulfonic acid as the freelayer etchant, and a member of the family of alkanesulfonate surface active compounds, e.g. sodium 1-tetradecansulfonate, as an AlO x tunnel barrier etch inhibitor at the conclusion of freelayer etching. Open circuit potential measurements were shown to be extremely useful for monitoring the progress of freelayer wet etching and for evaluating alumina barrier etch inhibitors. Also discussed was a means of dramatically lowering lateral freelayer etching under the mask using an etch inhibitor, BTA. This was achieved by setting up a difference in surface coverage of the BTA between the field areas of the patterned wafer and the newly-patterned edges of the freelayer metal film at the base of the mask. Differences in inhibitor solution mass transport efficiencies between these two regions were sufficient to achieve such coverage differences. The effectiveness of the wet etching method was strongly dependent on the effectiveness of the preceding RIE cap layer etch. Since the wet etching method described here is selective, it can overcome non-uniformity in freelayer thickness resulting from the capping layer RIE etching process; however, any residual capping layer due to nonuniformity in RIE etching will mask, or impede, wet etching. Removal

We discuss a new measurement technique called thermal proximity sensing (TPS) and its application to the inspection of magnetic hard-disk surfaces. This method uses the magneto-resistive (MR) readback element of a hard-disk file in a novel thermally sensitive mode to actively sense the air-bearing gap spacing while the disk spins under the slider. We present model calculations that describe the origin of the thermal sensitivity and its range of applicability. By collecting height information as a function of position, we have obtained high-resolution images of disk topography with sensitivity in the subnanometer range. Initial results of the technique, obtained on a test stand, showed an exceptional imaging ability for surface features. We have also obtained useful surface structure data from in situ measurements of disk surface defects in an operating hard-disk file.

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

Through-substrate-vias (TSVs) provide conduction paths to allow for three-dimensional integration of microelectronic structures. It is also known that metallic TSVs can be used to suppress resonance modes within dielectric substrates by altering the propagation of electromagnetic waves. Numerical analyses of transmission through substrates containing metallic TSVs revealed that although resonance modes of the composite structure are shifted to higher frequencies, these frequencies are not solely dictated by the TSV periodicity. Simulations show that hybrid modes are formed through a convolution of the original substrate modes and a long-wavelength mode analogous to that found in a two-dimensional photonic crystal. An analytical formula is proposed that provides a simple relation between the intrinsic substrate mode frequencies and the long-wavelength mode that scales with the ratio of TSV radius to its periodicity.

We have developed the ability to electrically characterize submicron magnetic tunnel junctions using a conducting atomic force microscope (CAFM). This technique can be applied after only a short processing route, thereby saving time and resources, and reducing the potential for damaging the junctions. The CAFM can be used to measure hysteresis loops, magnetoresistance, resistance–area product, switching astroids, current–voltage curves, and breakdown voltage of tunnel junctions. In this letter, we outline the sample requirements, detail the CAFM processing route, describe tip preparation, and report examples of data we have obtained with this technique over the last two years.

We report data from 4-kbit spin torque MRAM arrays using tunnel junctions (TJs) with magnetization perpendicular to the wafer plane. We show for the first time the switching distribution of perpendicular spin torque junctions. The percentage switching voltage width, σ(V c )/ = 4.4%, is sufficient to yield a 64 Mb chip. Furthermore we report switching probability curves down to error probabilities of 5×10−9 per pulse which do not show the anomalous switching seen in previous studies of in-plane magnetized bits.

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.

In this paper, we have demonstrated a new technique to detect and image defects on a disk surface using product data heads.

In this paper we describe improved methods of fabrication for an oxide channel field effect transistor (OxFET) similar in architecture to a conventional FET. We demonstrate that a substrate treatment consisting of a low power oxygen ashing followed by annealing yields a strontium (A-site) terminated surface in single-crystal strontium titanate (STO). This surface termination of the substrate results in pulsed laser deposited cuprate-channel films of improved quality.

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.

In this paper we describe the fabrication of oxide based devices similar in architecture to a conventional FET with source, drain, and gate electrodes and a channel. This distinctive characteristic of our device is the use of a channel material capable of undergoing a field-induced Mott insulator-metal transition at room temperature. Lithographic techniques developed for oxide materials have been combined with pulsed laser deposition of perovskite materials onto single-crystal strontium titanate (STO) substrates to fabricate these devices. Materials chosen for the Mott transition channel include La2CuO4 (LCO) and YBCO, p-type; and Nd2CuO4, n-type.

The atomic force microscope (AFM) has the potential for profiling on a nanometer scale. However, for the AFM to be useful as a reliable and accurate metrology tool, the atomic force sensor used (i.e., cantilever and sensor tip) should be highly reproducible in the fabrication process and the tip shape used should be known with high accuracy. Moreover, for profiling and critical dimension measurement of device trenches with submicron openings and trench depth of 1 μm or more, nanometer‐scale tip shapes with high aspect ratio will be required. In order to meet the above requirement, a novel high‐resolution direct electron‐beam deposition process has been developed in which a sharp tip is grown onto an existing Si cantilever structure. In the example to be discussed, sharp tips have been grown directly on the integrated tip of a micromachined Si cantilever by decomposition of a dimethyl‐gold organometallic complex. The direct e‐beam deposition process provides a unique capability for the controllable fabrica...

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

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.

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.

We describe a refined technique for magnetic force microscopy (MFM) which makes possible magnetic imaging with 25 nm resolution. Previous MFM work has relied on a servo system which used the amplitude of the response of an electropolished iron wire cantilever tip to an applied, near‐resonance excitation to maintain a constant force gradient between tip and sample. The present results have been obtained with a redesigned instrument which uses a fast lock‐in detector to servo on the phase, as opposed to the amplitude of the tip response. With these changes and the use of sharp electrochemically etched Ni tips, it is possible to servo stably on the very weak force gradients encountered in MFM, within 20 nm of the sample surface, and thus obtain 25 nm resolution.

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 demonstrate the usefulness and high sensitivity of the atomic force microscope (AFM) for imaging surface dielectric properties and for potentiometry through the detection of electrostatic forces. The attractive force with an applied voltage between tip and sample is generally much larger than the van der Waals force. On the other hand, electric forces as small as 10 -10 N have been measured, corresponding to a capacitance of 10 -19 farad. The sensitivity of our AFM should ultimately allow us to detect capacitances as low as 8 x 10 -22 farad. We have used this technique to detect the presence of dielectric material over Si, and have made measure-ments of the voltage over a p-n junction with sub-micron spatial resolution.