S.A. Rishton

Microstructured magnetic tunnel junctions (invited)

We have used a simple self-aligned process to fabricate magnetic tunnel junctions down to submicron sizes. Optical and electron-beam lithographies were used to cover a range of areas spanning five orders of magnitude. The bottom magnetic electrodes (Co or permalloy) in our junctions were exchange biased by an antiferromagnetic layer (MnFe). The top electrodes were made of soft magnetic materials (Co or permalloy). We have consistently obtained large magnetoresistance ratios (15%–22%) at room temperature and in fields of a few tens of Oe. The shape of the field response of the magnetoresistance was varied from smooth to highly hysteretic by adjusting the shape anisotropy of one junction electrode.

Scanning capacitance microscopy on a 25 nm scale

A near‐field capacitance microscope has been demonstrated on a 25 nm scale. A resonant circuit provides the means for sensing the capacitance variations between a sub‐100‐nm tip and surface with a sensitivity of 1×10−19 F in a 1 kHz bandwidth. Feedback control is used to scan the tip at constant gap across a sample, providing a means of noncontact surface profiling. Images of conducting and nonconducting structures are presented.

Hysteresis in lithographic arrays of permalloy particles: Experiment and theory (invited)

We have investigated the effects of particle size and aspect ratio on the hysteresis in controlled arrays of small magnetic particles. The arrays of permalloy particles were fabricated via electron‐beam lithography. Each array consists of ∼ 106 identical, uniformly spaced particles. Hysteresis loops measured with an alternating‐gradient magnetometer for particles ∼5–0.1 μm are presented. We find an increase in the coercive force as the particle width decreases below 0.3 μm due to a change in the switching mechanism from domain‐wall nucleation and wall motion to vortex nucleation and vortex motion. A novel angular dependence of the loops is described in detail. Results from ab initio micromagnetic calculations on isolated rectangular Permalloy particles are compared, where applicable, with the measurements. We find excellent qualitative and, in selected cases, quantitative agreement between the experiments and calculations.

Shape-anisotropy-controlled magnetoresistive response in magnetic tunnel junctions

We show that shape anisotropy can be used to control the response characteristics of magnetic tunnel junctions. By varying the junction shape, the resistance versus field curve was made to vary from a nonhysteretic linear curve with a high-field sensitivity (0.3%/Oe) to a hysteretic response curve with high squareness.

Optical data storage read out at 256 Gbits/in.2

A new form of read out for high density read-only memory is presented whereby a data density of 400 bits/μm2, corresponding to 256 Gbits/in.2, can be accessed at data rates in the tens of MHz range. The technique is based on detecting the modulation in light scattering from a sharp scattering object due to the dipole-dipole coupling between the probe and surface being scanned using a sensitive homodyne interferometer. Theoretical considerations indicate that data densities in the 100 Tbits/in.2 range could be accessed at data rates of 100 MHz using this technology.

High-performance Si/SiGe n-type modulation-doped transistors

Enhancement-mode Si/SiGe n-type modulation-doped transistors with a 0.5- mu m-length T-gate have been fabricated. Peak transconductances of 390 mS/mm at room temperature and 520 mS/mm at 77 K have been achieved. These high values are attributable to a combination of the high quality of the material used, having a room temperature mobility of 2600 cm/sup 2//V-s at an electron sheet concentration of 1.5*10/sup 12/ cm/sup 2/, and an optimized layer design that minimizes the parasitic series resistance and the gate-to-channel distance.<<ETX>>

Electron beam technology-SEM to microcolumn

As a continued effort to improve the performance of low energy scanning electron probe systems for application in microscopy, lithography, metrology, etc., miniaturized electron beam columns, approximately 3 mm in length, demonstrating a probe size of 10 nm with a beam current of >=1 nA at 1 keV, have been successfully developed. This paper presents current status, future directions and potential applications of these microcolumns.

Nanoscale replication for scanning probe data storage

Recently, there have been significant advances in demonstrating the possible application of scanning probe techniques for high density data storage. While many obstacles have yet to be overcome, one of the more promising applications of such devices is for very high density read‐only disk drives. Such an application requires the means to pattern and replicate nanometer scale features over macroscopic dimensions. We have developed a technique for both mastering and replicating data patterns for use in such a device at a density 100 times that of current read‐only disks. The process consists of using electron beam lithography to write data features as small as 50 nm and a photopolymerization process to faithfully replicate the written marks.

Experimental high performance sub-0.1 /spl mu/m channel nMOSFET's

Very high performance sub-0.1 /spl mu/m channel nMOSFETs are fabricated with 35 /spl Aring/ gate oxide and shallow source-drain extensions. An 8.8-ps/stage delay at V/sub dd/=1.5 V is recorded from a 0.08 /spl mu/m channel nMOS ring oscillator at 85 K. The room temperature delay is 11.3 ps/stage. These are the fastest switching speeds reported to date for any silicon devices at these temperatures. Cutoff frequencies (f/sub T/) of a 0.08 /spl mu/m channel device are 93 GHz at 300 K, and 119 GHz at 85 K, respectively. Record saturation transconductances, 740 mS/mm at 300 K and 1040 mS/mm at 85 K, are obtained from a 0.05 /spl mu/m channel device. Good subthreshold characteristics are achieved for 0.09 /spl mu/m channel devices with a source-drain halo process.<<ETX>>

Magnetic tunnel junctions fabricated at tenth-micron dimensions by electron beam lithography

Abstract Magnetic tunnel junctions consisting of permalloy and cobalt thin film electrodes, separated by a thin aluminum oxide tunnel barrier, have been fabricated by e-beam lithography at dimensions down to 120 nanometers. The devices are fabricated by sputter deposition and ion milling. They exhibit magnetoresistances of up to 22% at room temperature. Evidence of individual domain switching is observed. The smaller junctions have resistances in the kilohm range, which are easily measured, leading to the possibility of sensing and microelectronic applications.