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A method of fabrication of patterned magnetic nanodots by means of laser interference lithography is presented. This method includes the use of a diluted positive photoresist, and modifcations in the etching angle and acceleration voltage of the ion beam etching process. Vertical standing waves were suppressed by using a high exposure dose (supra-exposure) instead of an antireflective coating. Field dependent magnetic force microscopy was used to measure the switching field distribution, which was found to range from 80 to 192 kA/m.

In this chapter Magnetic Force Microscopy is treated in detail. The emphasis is on high resolution and the design and realisation of MFM tips.

Heat-assisted magnetic probe recording on a CoNi/Pt multilayered film is demonstrated by delivering a current through a magnetic force microscopy tip into the recording medium, in combination with an external magnetic field. Without local heating by the probe, no bits could be written because the external field exceeds a level that demagnetizes the medium in its entirety due to local variations in the coercivity of the medium. In contrast, magnetic bits were successfully written by the heat-assisted magnetic probe recording into a saturated medium even if there was no external field, because of the demagnetization field from the surrounding of the heated area. A magnetic bit as small as 80nm in diameter was obtained by this method.

The areal bit density of magnetic disk recording has made a colossal increase over the last decades. Extrapolation leads to recording parameters not likely to be achieved without changes in the present way of storing magnetic data. One of the potential solutions is the use of patterned media, which should consist of a regular two-dimensional array of single domain dots with large uniaxial magnetic anisotropy. Such media will shift the super paramagnetic limit positively in comparison with the present thin film media.Theoretically, a bit density in the order of Tbpsi is possible. This paper will discuss the most valuable methods for preparing patterned media.

Enkele jaren geleden begon het allemaal, de fundamentele grenzen van de harde schijf kwamen in zicht. Het grootste probleem van de harde schijf de is de één kop per kant strategie. Deze strategie schaalt slecht: de hoeveelheid data die kan worden opgeslagen wordt snel groter, maar de accesstijd en datarate blijven sterk achter[1]. De oplossing: probe recording. In dit soort data opslagsystemen werken grote aantallen lees-schrijfkoppen samen om een hoge datarate te verkrijgen. Bovendien schaalt het aantal kopjes lineair met de capaciteit van het systeem[2] [3]. De ontwikkeling is in volle gang, maar wat kunnen we op dit gebied verder nog verwachten voor de toekomst?

Thin-film yoke-type magnetoresistive (MR) tape heads with eight channels have been used for scanning magnetoresistance microscopy. The NiFe read flux guides of the channels have been trimmed down from 12 /spl mu/m to widths varying between 5 /spl mu/m and 100 nm by focused ion-beam milling with Ga/sup +/ ions. The tape-bearing surface of the milled regions has been reconstructed in situ by the local deposition of Pt. Tracks with a minimum bit length of 1 /spl mu/m have been written on Co-Ni-O metal evaporated tape and Co-/spl gamma/-Fe/sub 2/O/sub 3/ particulate tape with trimmed and untrimmed write channels and have been successfully imaged with all the trimmed read channels. A linear decrease in readback voltage across the MR sensor is observed for channels possessing flux guides trimmed down to 2 /spl mu/m, in agreement with finite-element modeling of the trimmed heads. The severe attenuation in readback voltage observed for flux guides trimmed below 2 /spl mu/m is attributed to a combination of micromagnetic effects. Additionally, damage to the NiFe from Ga/sup +/ ion implantation may make a minor contribution to the loss in sensor performance. A 65% drop in readback voltage is observed for a channel possessing a flux guide that was trimmed by 98.3% to 200 nm.

The domain structure and the switching field of Co50 Ni50 /Pt multilayer dots, prepared by laser interference lithography,were micromagnetically simulated. The simulations were carried out with a three-dimensional simulation package, optimized for large-scale problems. The single-domain state is the lowest energy state for dots with a diameter below 75 nm. The switching field was computed by using suitable minimization techniques, and was used to analyze the effect of size, dot shape and edge defects.

De harde schijf gaat langzaam ten onder aan zijn eigen succes, zo beschreven we in het meinummer van Natuur & Techniek wetenschapsmagazine. De snelle capaciteitsverhoging gaat niet gepaard met een gelijke verbetering van de de leessnelheid en de toegangstijd. Twente loopt voorop in de zoektocht naar een geschikte opvolger.

Scanning magneto-resistance microscopy has been performed with thin film yoke-type magneto-resistive tape heads possessing eight channels. The read flux guides of these channels have been trimmed down from 24 μm to widths varying between 5.5 μm and 148 nm by focused ion beam milling with Ga+ ions. Tracks written on ME tape with an untrimmed write channel have been successfully imaged with all the trimmed channels. A significant attenuation (>5%) of read-back voltage across the MR sensor is only observed for channels possessing flux guides trimmed by 77% to 5.5 μm. A 52% (6 dB) drop in read-back voltage is observed for a channel possessing a flux guide trimmed by 99.4% to 148 nm.

A method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. In this work, field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2-7 V with a duration of 500 ns were applied to a CoNi/Pt multilayered film. Different types of Ir/Pt and W STM tips were used in the experiment. The results show that thermally recorded magnetic marks are formed with a nearly uniform mark size of 170 nm when the pulse voltage is above a threshold voltage. The threshold voltage depends on the material work function of the tip, with W having a threshold voltage about 1 V lower than Pt. The emission area of our tip-sample system derived from an analytic expression for field emission current is approximately equal to the mark size, and is largely independent of pulse voltage. This emission area is large compared to lateral heat diffusion in the film. Thus higher applied voltages lead to higher peak temperatures in the model of the write process, but the mark diameter remains relatively unchanged.

The transfer functions of tips with various sharpened tip ends were calculated and the resolution of these tips was estimated by considering the resolution limit due to thermal noise at room temperature. The tip having an ellipsoidal tip end (ellipsoidal tip) is found to be a suitable candidate for high-resolution magnetic force microscopy. Sharpening of the flat tip end makes zero signal frequencies disappear for tips with ellipticities larger than tan45/spl deg/. The sensitivity shows a maximum around an ellipticity of tan80/spl deg/. The ellipsoidal tip shows a much smaller tip thickness dependence compared to the tip having a flat tip end because only the tip end mainly contributes to signals in case of the ellipsoidal tip.

In single-pole heads with a pole tip cross section trimmed down to 1003200 nm by focused ion beam, the remanence of the head becomes nonzero if the pole length is too high. Large-scale three-dimensional micromagnetic simulations are performed to understand this effect, and to calculate the critical length of the pole as a function of the pole tip cross section.

We present our results on the development of magnetic sensors for application in magnetic probe recording. Successful writing experiments on a magnetic medium with perpendicular anisotropy show that magnetic domains of 130 nm can be reversed in a heat-assisted process. For reading purposes we propose a magnetoresistive sensor. The optimization of the shape of the sensor was performed using micromagnetic simulations with the requirement that the sensor has to be capable of both read and write operations. At this stage, the experimental realization of the sensor was carried out at a wafer-base level. The fabrication technique consists of a combination of optical lithography and focused ion beam etching.

Enkele jaren geleden begon het allemaal, de fundamentele grenzen van de harde schijf kwamen in zicht. Het grootste probleem van de harde schijf de is de één kop per kant strategie. Deze strategie schaalt slecht: de hoeveelheid data die kan worden opgeslagen wordt snel groter, maar de accesstijd en datarate blijven sterk achter[1]. De oplossing: probe recording. In dit soort data opslagsystemen werken grote aantallen lees-schrijfkoppen samen om een hoge datarate te verkrijgen. Bovendien schaalt het aantal kopjes lineair met de capaciteit van het systeem[2] [3]. De ontwikkeling is in volle gang, maar wat kunnen we op dit gebied verder nog verwachten voor de toekomst?

Magnetic force microscopy (MFM) is a scanning probe technique that is used to generate a high–resolution image of stray fields above a magnetic thin film, with very little sample preparation. This makes the MFM the instrument of choice for the analysis of bit patterns in hard disks. The tremendous increase in data density of magnetic storage systems has pushed the bit size down into the nanometer range, close to the maximum resolution of current MFM’s. This resolution, which is currently limited by the geometry of the magnetic tip, has to be improved, or the hard disk research community will loose a very powerful imaging technique. In this thesis a new probe for magnetic microscopy and recording, called the CantiClever, is presented. This probe is designed to address the issue of the tip geometry of conventional MFM tips. The new probe also allows for integration of other sensors besides an MFM tip with relative ease due to its planar fabrication process.

Magnetic force microscopy (MFM) is a scanning probe technique that is used to generate a high–resolution image of stray fields above a magnetic thin film, with very little sample preparation. This makes the MFM the instrument of choice for the analysis of bit patterns in hard disks. The tremendous increase in data density of magnetic storage systems has pushed the bit size down into the nanometer range, close to the maximum resolution of current MFM’s. This resolution, which is currently limited by the geometry of the magnetic tip, has to be improved, or the hard disk research community will loose a very powerful imaging technique. In this thesis a new probe for magnetic microscopy and recording, called the CantiClever, is presented. This probe is designed to address the issue of the tip geometry of conventional MFM tips. The new probe also allows for integration of other sensors besides an MFM tip with relative ease due to its planar fabrication process.

We describe the design rationale for a hardware tamper resistant secure storage system based on probe storage with a patterned magnetic medium. This medium supports normal read/write operations by magnetising individual dots perpendicular to the media plane. We report on an experiment to show that in principle the medium also supports a separate class of read/write-once operations by allowing individual dots in the media to be destroyed irreversibly by precise local heating. Security stems from the fact that bulk-erase is not possible.

We describe the design rationale for a hardware tamper resistant secure storage system based on probe storage with a patterned magnetic medium. This medium supports normal read/write operations by magnetising individual dots perpendicular to the media plane. We report on an experiment to show that in principle the medium also supports a separate class of read/write-once operations by allowing individual dots in the media to be destroyed irreversibly by precise local heating. Security stems from the fact that bulk-erase is not possible.

Summary form only given. With the current rate of increase in areal density of magnetic recording systems, todays resolution of MFM needs to be improved in order to remain useful as a measurement tool. The resolution of MFM is amongst others determined by the geometry of the magnetic tip, which for commercial probes consists of a thin magnetic coating deposited on a pyramidal Si AFM tip. Analysis of the imaging process shows that the shape of these tips is not ideal. For higher resolution, the tip must be shaped as an elongated bar with a flat front end. In this contribution we present a completely new MFM cantilever, the CantiClever, which is not derived from traditional AFM probes but optimized for MFM. Our design incorporates the cantilever and the magnetic tip in a single manufacturing process with the use of silicon micromachining techniques, allowing for batch fabrication of the probes. We realise the ideal tip shape by deposition of the magnetic material (Co) on the side of a free hanging silicon nitride layer.

The design for a new type of non-volatile mass storage memory is discussed. This new design, based on scanning probe techniques, combines the low volume and power consumption of the FlashRAM, with the high capacity of the hard disk. The small form factor of the device makes it an excellent candidate for mass storage in handheld embedded systems. Its hierarchical architecture allows us to make a trade-off between data-rate, access time and power consumption. The power consumption scales linearly with the desired data-rate, and is expected to be lower than what can be achieved with competing technologies.

The design for a new type of non-volatile mass storage memory is discussed. This new design, based on scanning probe techniques, combines the low volume and power consumption of the FlashRAM, with the high capacity of the hard disk. The small form factor of the device makes it an excellent candidate for mass storage in handheld embedded systems. Its hierarchical architecture allows us to make a trade-off between data-rate, access time and power consumption. The power consumption scales linearly with the desired data-rate, and is expected to be lower than what can be achieved with competing technologies.

The design for a new type of non-volatile mass storage memory is discussed. This new design, based on scanning probe techniques, combines the low volume and power consumption of the FlashRAM, with the high capacity of the hard disk. The small form factor of the device makes it an excellent candidate for mass storage in handheld embedded systems. Its hierarchical architecture allows us to make a trade-off between data-rate, access time and power consumption. The power consumption scales linearly with the desired data-rate, and is expected to be lower than what can be achieved with competing technologies.

The design for a new type of non-volatile mass storage memory is discussed. This new design, based on scanning probe techniques, combines the low volume and power consumption of the FlashRAM, with the high capacity of the hard disk. The small form factor of the device makes it an excellent candidate for mass storage in handheld embedded systems. Its hierarchical architecture allows us to make a trade-off between data-rate, access time and power consumption. The power consumption scales linearly with the desired data-rate, and is expected to be lower than what can be achieved with competing technologies.

In this paper, a new design of dedicated magnetic force microscope (MFM) cantilever is presented. In this design, the cantilever and the magnetic tip are realized in an integrated manufacturing process. The use of silicon micromachining techniques enables batch fabrication of several hundred cantilevers on a single Si wafer. The magnetic tip is prepared by deposition of magnetic material on a free standing silicon nitride layer. The width and thickness of the magnetic tip are defined by the thickness of the silicon nitride layer and the magnetic layer respectively. The length of the tip is lithographically defined. This enables us to realize very thin, high aspect ratio magnetic tips with excellent control over the tip dimensions.

The areal bit density of magnetic disk recording has increased since 1990 60% per year and even in the last years 100%. Extrapolation of these rates leads to recording parameters not likely to be achieved without changes in the present way of storing hard disk data. One of the possible solutions is the development of so-called patterned magnetic media. Such media will also shift the superparamagnetic limit positively in comparison with the present thin film media. Theoretically, a bit density in the order of Tbits/in 2 may be possible by using this so-called discrete magnetic recording scheme. The patterned structures presented in this paper consist of a regular two-dimensional array of single domain dots with large uniaxial magnetic anisotropy and have been prepared from CoNi/Pt multilayers with strong intergranular exchange coupling and large perpendicular magnetic anisotropy. For the preparation of the patterned media, a patterning process based on Laser Interference Lithography method (LIL) and Ion Beam Etching has been developed. This technology provides the possibility to pattern 2-D arrays of submicron dots smaller than the critical size for the transition from multi to single domain. The smallest prepared dot sizes are 60 nm with a center-to-center dot spacing of 200 nm and thickness of 30 nm. The magnetic characterization of these dots showed that they are single domain with reasonable coercivity and good thermal stability. Micromagnetic simulations show that the single domain state is the lowest energy state for dots with a diameter below 75nm, which confirms the experimental observations.

In this paper, a new design of dedicated magnetic force microscope (MFM) cantilever is presented. In this design, the cantilever and the magnetic tip are realized in an integrated manufacturing process. The use of silicon micromachining techniques enables batch fabrication of several hundred cantilevers on a single Si wafer. The magnetic tip is prepared by deposition of magnetic material on a free standing silicon nitride layer. The width and thickness of the magnetic tip are defined by the thickness of the silicon nitride layer and the magnetic layer respectively. The length of the tip is lithographically defined. This enables us to realize very thin, high aspect ratio magnetic tips with excellent control over the tip dimensions.

De harde schijf maakt sinds zijn uitvinding een stormachtige ontwikkeling door. Jaarlijks verdubbelt de opslagcapaciteit. Deze halsoverkopsnelheid brengt de fundamentele grenzen aan de ontwikkeling snel dichterbij. In twee artikelen exploreert Natuur & Techniek de technologische uitdagingen. Deze maand deel 1: de grenzen aan de groei.

The areal bit density of magnetic disk recording has increased since 1990 60% per year and even in the last years 100%. Extrapolation of these rates leads to recording parameters not likely to be achieved without changes in the present way of storing hard disk data. One of the possible solutions is the development of so-called patterned magnetic media. Such media will also shift the superparamagnetic limit positively in comparison with the present thin film media. Theoretically, a bit density in the order of Tbits/in 2 may be possible by using this so-called discrete magnetic recording scheme. The patterned structures presented in this paper consist of a regular two-dimensional array of single domain dots with large uniaxial magnetic anisotropy and have been prepared from CoNi/Pt multilayers with strong intergranular exchange coupling and large perpendicular magnetic anisotropy. For the preparation of the patterned media, a patterning process based on Laser Interference Lithography method (LIL) and Ion Beam Etching has been developed. This technology provides the possibility to pattern 2-D arrays of submicron dots smaller than the critical size for the transition from multi to single domain. The smallest prepared dot sizes are 60 nm with a center-to-center dot spacing of 200 nm and thickness of 30 nm. The magnetic characterization of these dots showed that they are single domain with reasonable coercivity and good thermal stability. Micromagnetic simulations show that the single domain state is the lowest energy state for dots with a diameter below 75nm, which confirms the experimental observations.

This article describes an approach for implementing a complete computer system (CPU, RAM, I/O, and nonvolatile mass memory) on a single integrated-circuit substrate (a chip)—hence, the name “single-chip computer.” The approach presented combines advances in the field of microelectromechanical systems (MEMS) and micromagnetics with traditional low-cost very-large-scale integrated circuit style parallel lithographic manufacturing. The primary barrier to the creation of a computer on a chip is the incorporation of a high-capacity [many gigabytes (GB)] re-writable nonvolatile memory (in today’s terminology, a disk drive) into an integrated circuit (IC) manufacturing process. This article presents the following design example: a MEMS-based magnetic memory that can store over 2 GB of data in 2 cm2 of die area and whose fabrication is compatible with a standard IC manufacturing process.

Large scale 3D micromagnetic simulations are performed on single pole read heads with pole tip cross sections of 45345 and 1003200 nm. It is shown that tips with these dimensions have a much higher output than predicted by an analytical theory using the reciprocity theorem. The larger of these tips still behaves in a relatively soft manner and has an output waveform shape very close to the one predicted by the analytical model. The response of the small tip however is hysteretic.

Reversed single magnetic bits of 130nm in diameter were successfully written in a CoNi/Pt multilayered film by means of magnetic probe recording. A weak exchange coupled layer deposited onto a stronger exchange coupled layer effectively induces a local magnetic reversal, which results in the formation of small and stable magnetic bits.

The authors propose a concept n mass data storage system architecture, in which thousands of read/write heads,storage robots or StoBots move independently over a large,.flat storage medium.This concept,which has not been previously proposed,offers new degrees of freedom in data storage systems design, which could lead to a superior performance over conventional systems such as hard disks and tape.The impact of different file system architectures on the access time and data-rate of the StoBot drive is investigated.

The micromagnetic properties of a soft underlayer in perpendicular media are studied. It is shown that stray fields from a recording layer can substantially modify magnetic properties of soft underlayer material. The degree of modification is determined by the characteristic bit size in the recording layer and by the soft underlayer material magnetic characteristics. It is found that there exists a thin layer within a soft underlayer with reduced permeability. The effects of the presence of such a reduced permeability region within a soft underlayer on both reading and writing processes are discussed.