Thomas Robert Albrecht

Frequency modulation detection using high‐Q cantilevers for enhanced force microscope sensitivity

A new frequency modulation (FM) technique has been demonstrated which enhances the sensitivity of attractive mode force microscopy by an order of magnitude or more. Increased sensitivity is made possible by operating in a moderate vacuum (<10−3 Torr), which increases the Q of the vibrating cantilever. In the FM technique, the cantilever serves as the frequency determining element of an oscillator. Force gradients acting on the cantilever cause instantaneous frequency modulation of the oscillator output, which is demodulated with a FM detector. Unlike conventional ‘‘slope detection,’’ the FM technique offers increased sensitivity through increased Q without restricting system bandwidth. Experimental comparisons of FM detection in vacuum (Q∼50 000) versus slope detection in air (Q∼100) demonstrated an improvement of more than 10 times in sensitivity for a fixed bandwidth. This improvement is evident in images of magnetic transitions on a thin‐film CoPtCr magnetic disk. In the future, the increased sensitivi...

Demonstration of thermomechanical recording at 641 Gbit/in/sup 2/

Ultrahigh storage areal densities can be achieved by using thermomechanical local-probe techniques to write, read back, and erase data in the form of nanometer-scale indentations in thin polymer films. This paper presents single-probe experimental results in which large data sets were recorded at 641 Gbit/in/sup 2/ and read back with raw bit-error rates better than 10/sup -4/. (d,k) modulation coding is used to mitigate the effect of partial erasing, occurring when subsequent indentations are spaced too closely together, and to increase the effective areal density. The physical indentation profile, the sensitivity of the probe in readback mode, and noise sources that affect data detection are also discussed. Quantitative measurements of the partial erasing effect in both the on-track and cross-track directions are reported.

Timing-based track-following servo for linear tape systems

Timing-Based Servo (TBS) is a unique servo technology developed specifically for linear tape drives. In TBS systems, recorded servo patterns consist of transitions with two different azimuthal slopes, and head position is derived from the relative timing of pulses generated by a narrow head reading the pattern. Position signals are nearly perfectly linear over multiple track widths, and highly immune to errors caused by head wear, head instability, debris, and media defects. Multitrack TBS servo patterns are written in a single pass using a novel multigap horizontal thin film servo writing head. The design of the pattern and its dimensions are optimized to provide sampling rate, noise level, and error rate suitable for the intended application. An all-digital TBS servo channel provides a speed-invariant position signal. Pattern recognition algorithms detect servo signal errors, providing a highly robust servo signal. Test results show approximately I pm linearity and 0.3 /spl mu/m noise level over a width of 400 /spl mu/m width with 18 kHz sampling rate. The TBS pattern allows flexibility for encoding additional information without affecting the position signal. By shifting transitions as little as 0.1 /spl mu/m from their nominal pattern positions, a low error rate serial bitstream can be encoded in the servo track. This technique allows tape longitudinal position to be encoded with a resolution of about 2 mm, allowing efficient and precise tape transport control based on the servo signal alone.

Low-temperature force microscope with all-fiber interferometer

Abstract A low-temperature force microscope has been demonstrated which is suitable for both repulsive and attractive mode (including magnetic) imaging. This instrument uses microfabricated cantilevers and an all-fiber interferometer for remote sensing of cantilever deflection. The all-fiber interferometer is ideal for remote sensing, since the only connection between the microscope and the outside environment is a single optical fiber. This allows all electronic components to operate at room temperature far from the mechanical portion of the microscope. The microscope mechanics are enclosed in a cylindrical vacuum chamber which is inserted into a helium storage Dewar for refrigiration. The sample holder is fitted with either a superconducting magnet capable of 200 Oe or a permanent magnet for higher fields. The instrument has been used successfully for topographic imaging and magnetic force gradient imaging at 5 and 300 K. An appendix to this paper gives practical information for constructing the all-fiber interferometer.

Load/Unload technology for disk drives

Load/Unload (L/UL) is an alternative to contact start-stop (CSS) technology which eliminates stiction and wear failure modes associated with CSS. Other benefits of L/UL include increased areal density due to smooth disk surfaces, thinner overcoats and lower head flying height; improved shock resistance due to elimination of head slap; and reduced power consumption. Several mechanical design options exist for L/UL, and tolerance analysis plays a key role in height budgeting, interdisk spacing, and disk real estate usage. To prevent stiction failures arising from unintended landing of heads on stopped disks, a reliable actuator latch and power-off retract system are employed. A bidirectional inertia latch has better reliability than conventional inertia latch designs. A low voltage drop retract rectifier is required for reliable power-off retract in drives with supply voltages of 5 V or less.

Magnetic lithography using a flexible master: A method for instantaneous magnetic recording on media surfaces with flatness imperfections

A method for instantaneous parallel recording on magnetic media using a flexible master has been developed. Magnetic lithography (qualitatively analogous to optical lithography) transfers information from a patterned magnetic mask (analog of optical photomask) to magnetic media (analog of photoresist). The mask consists of patterned soft magnetic material (FeNiCo, FeCo) on a flexible polyethylene tetraphthalate (PET) substrate. When uniformly magnetized media is brought into intimate contact with the magnetic mask, an externally applied magnetic field selectively changes the magnetic orientation in the areas not covered with the soft magnetic material. Imperfect flatness or the presence of particular contaminants can result in local loss of intimate contact between the master and media, resulting in loss of resolution of submicron features in the transferred magnetic pattern. A flexible master, held against the media via an applied pressure, offers superior compliance to imperfections, even at relatively ...

Magnetic lithography using flexible magnetic masks: applications to servowriting

In this paper, magnetic lithography using flexible magnetic masks and its application to servowriting were investigated. The mask consists of a flexible 127 /spl mu/m thick polyethylene teraphtalate (PET) plastic film patterned with 160-250 nm thick soft magnetic material (FeNiCo, FeCo) and the SEM and MFM images were also obtained in this experiment.

Laser Smoothing of the Load/Unload Tabs of Magnetic Recording Head Gimbal Assemblies

A novel technology to smooth the metal tab surfaces using a pulsed laser beam is applied to reduce the wear of the load/ unload ramps used in disk drives that employ load/unload technology. The laser pulse length, pulse energy and the pulse repetition rate are so chosen that they cause the surface layer of the load/unload tab, approximately 2-3 um deep, to melt and refreeze quickly. As the surface layer melts, the surface tension of the melt removes most of the micro roughness and a smooth surface is obtained. The reduction in the micro surface roughness is confirmed by the AFM traces and a sharp decrease in the light scattered from the tab surface. In wear tests, such tabs show a remarkable improvement in the wear of the plastic load/unload ramps, allowing 5-10 X more load/unload cycles for a given amount of ramp wear.

Advances in Force Sensing and Magnetic Force Microscopy

In this paper we discuss some of the experimental methods we use in our laboratory for force sensing and force microscopy. Our emphasis is on the detection of long range interactions, such as magnetic forces. We also introduce a simple mechanical parametric amplifier that can significantly increase the motional response of a microcantilever for small harmonic force excitations. Using the parametric amplifier, we have observed for the first time a phase dependent reduction of thermal vibrations (i.e., the squeezing of thermo‐mechanical noise).