Johannes Bernardus Charles Engelen

Thermally induced switching field distribution of a single CoPt dot in a large array

Magnetic dot arrays with perpendicular magnetic anisotropy were fabricated by patterning Co(80)Pt(20)-alloy continuous films by means of laser interference lithography. As commonly seen in large dot arrays, there is a large difference in the switching field between dots. Here we investigate the origin of this large switching field distribution, by using the anomalous Hall effect (AHE). The high sensitivity of the AHE permits us to measure the magnetic reversal of individual dots in an array of 80 dots with a diameter of 180 nm. By taking 1000 hysteresis loops we reveal the thermally induced switching field distribution SFD(T) of individual dots inside the array. The SFD(T) of the first and last switching dots were fitted to an Arrhenius model, and a clear difference in switching volume and magnetic anisotropy was observed between dots switching at low and high fields.

A single-mask thermal displacement sensor in MEMS

This work presents a MEMS displacement sensor based on the conductive heat transfer of a resistively heated silicon structure towards an actuated stage parallel to the structure. This differential sensor can be easily incorporated into a silicon-on-insulator-based process, and fabricated within the same mask as electrostatic actuators and flexure-based stages. We discuss a lumped capacitance model to optimize the sensor sensitivity as a function of the doping concentration, the operating temperature, the heater length and width. We demonstrate various sensor designs. The typical sensor resolution is 2 nm within a bandwidth of 25 Hz at a full scale range of 110 μm.

Optimized comb-drive finger shape for shock-resistant actuation

This work presents the analytical solution, finite-element analysis, realization and measurement of comb drives with finger shapes optimized for shock-resistant actuation. The available force for actuating an external load determines how large shock forces can be compensated for. The optimized finger shape provides much more available force than the standard straight finger shape, especially at large displacements. A graphical method is presented to determine whether stable voltage control is possible for a given available force curve. An analytical expression is presented for the finger shape that provides a constant large available force over the actuation range. The new finger shape is asymmetric, and the unit-cell width is equal to the unit-cell width of standard straight fingers that are commonly used, and can be used in all applications where a large force is required. Because the unit-cell width is not increased, straight fingers can be replaced by the new finger shape without changing the rest of the design. It is especially suited for shock-resistant positioning and for applications where a constant force is desired.

Improved performance of large stroke comb-drive actuators by using a stepped finger shape

In this work we describe an electrostatic mass-balanced planar x/y-scanner, using an optimized comb finger shape, designed for parallel-probe storage applications. We show a new stepped comb finger shape design, that has superior force/displacement characteristics leading to a larger stroke at the same voltage and a larger available force compared to straight or tapered shapes.

Optimized comb drive finger shape for shock-resistant actuation

This work presents the analytical solution, realization and measurement of a comb drive with finger shapes optimized for shock-resistant actuation. The available force for actuating an external load determines how large shock forces can be compensated for. An analytical expression is presented for the finger shape that provides a constant large available force over the actuation range. The finger shape is asymmetric, resulting in a 20% smaller unit cell width compared to a symmetric shape. This finger shape provides 4 times more available force than the standard straight finger shape.

Optimization of comb-drive actuators : nanopositioners for probe-based data storage and musical MEMS

The era of infinite storage seems near. To reach it, data storage capabilities need nto grow, and new storage technologies must be developed.This thesis studies one naspect of one of the emergent storage technologies: optimizing electrostatic combdrive nactuation for a parallel probe-based data storage system. nIt is no longer possible to store all created information. New storage technologies nmust be developed as current commercial technologies reach their fundamental nlimits. One promising technology is parallel probe-based data storage, using a nnanometre-scale probe to write data on a moving platform. The working principle nis very similar to that of a record player applied in parallel on the nano scale. In norder to access all bits on the storage medium, a nano-positioner, or scanner, is nused to move the storage medium relative to the read-out probes. nSeveral nano-positioner designs for probe data storage are found in the literature. nIt is not clear which actuator type (electromagnetic, electrostatic, or piezoelectric) nis most suited for probe data storage. We replaced the electrodynamic nactuators by comb-drives in the scanner prototype by IBM, to enable a direct comparison. ne comb-drive’s areal efficiency is low, due to a relatively low electrostatic nforce. e comb-drive finger profile is optimized for probe data storage, for an nincreased shock resistance. ne suitability of electromagnetic and electrostatic actuation is, among others, determined by their energy consumption.Three (partly) hypothetical scanner designs nusing electrodynamic, electromagnetic and electrostatic comb-drive actuators nare described. Their performance is approximately equal, however electrostatic ncomb-drive actuation requires an order of magnitude less energy. Equations are npresented for further investigations into the performance and energy consumption nof the different actuation types for different file-system use cases. nWe succeeded in making music with MEMS structures, and named our microinstrument n‘the micronium’. Due to fabrication inaccuracies, the instrument is outof- ntune and requires tuning. Besides teaching students about MEMS technology in na fun way, the micronium succeeded in presenting MEMS technology to a broad naudience.

Listening to MEMS: An acoustic vibrometer

A new way to characterize vibrating MEMS devices is presented. Using an acoustic particle velocity sensor the coupled sound field is measured, which is a measure for the movement of the MEMS device. We present several possible applications of this measurement method. It can be used as a read-out system for a mass flow sensor, and for characterization of in- and out-of-plane movements of MEMS devices. The method is an interesting alternative to laser scanning vibrometry due to its small size and low complexity; furthermore, it allows the user to ‘listen’ directly to MEMS devices.

A non-skiving tape head with sub-ambient air pressure cavities

A small head-medium spacing is crucial for achieving high linear densities in magnetic tape recording. Traditional contoured (cylindrical) tape heads have been superseded by flat-profile tape heads with sharp skiving edges to remove the natural air bearing that forms between tape and a contoured head, to reduce the head-tape spacing [1]. This means that tape is in contact with the head surface and that the spacing is determined predominantly by the tape surface roughness. To further reduce the head-medium spacing, the tape surface roughness needs to be reduced, which however results in increased head-medium friction. High friction is problematic for tape durability, for reliable operation of the data channel, and for accurate track-follow control. Although friction is lower for smaller tape wrap angles, reducing the wrap angle in a skiving configuration is not desirable because it results in an unacceptable increase in head-medium spacing. Furthermore, recent research has shown that a substantial amount of the friction originates at the skiving edges of the head. In this work, we present a new tape head design which allows dispensing with the skiving edges to reduce friction, while simultaneously maintaining tape-head contact above the read/write transducers.

Technologies for magnetic tape recording at 100Gb/in 2 and beyond

Magnetic tape systems provide high reliability storage at a low total cost of ownership and are well suited for the long term storage of less frequently accessed data. The current explosive growth rate of digital data is driving demand for cost effective storage technologies and has resulted in a renaissance in applications for tape systems. Current state of the art tape systems operate with areal densities up to ~6 Gb/in2 and provide cartridge capacities up to 10TB. The future success of tape systems depends on continued areal density and capacity scaling to maintain or increase the current cost advantage of tape over competing technologies. In this work we describe a set of technologies that enable the scaling of tape recording to areal densities of 100 Gb/in2 and beyond.