The present invention relates to a magnetic material, and to MEMS (micro electromechanical) devices which employ the magnetic material.
As modern technology advances, many electronic components and devices have been scaled down to the micro regime aiming for faster and more portable operation. This has given rise to the emergence of micro-electromechanical systems (MEMS) technology that made use of semiconductor manufacturing technology for the fabrication of micro- and nano-devices. In line with the trend of development, there is a need to develop cost-effective processes that can be integrated easily in batch processing. Many modern magnetic MEMS devices (such as including micro-actuators, sensors, and frictionless micro-gears) require a magnetic film which can produce a high vertical magnetic field.
It is known to use electroplating to deposit various thin magnetic films for magnetic recording purposes. In contrast to many other thin-film deposition methods such as sputtering and evaporation, electroplating offers a much faster and cost-effective method of depositing thick (˜100 um) films with easy control of process parameters for achieving specific film characteristics. In line with the rising demand for microdevices, electroplating has been actively explored in recent years as a favorable method for deposition of high aspect ratio microstructures in the fabrication of MEMS devices [1-3] since it is compatible with many other microfabrication processes.
Cobalt-based alloys with the addition of Ni, P, As, Sb, Bi, W, Cr, Mo, Pt or Cu have been electroplated as either binary or ternary material systems [4-8]. However, there are not many studies on the vertical anisotropy of material systems fabricated by electroplating. So far, material systems such as CoNiP [9], CoMnP [10], CoNiMnP [10], CoPtWP [11] and CoPt [12,13] has been an attractive candidate under development as a hard magnetic material with high vertical magnetic anisotropy. Nevertheless, these reports have been limited to magnetic film thickness of a few microns (<10 um) which might not meet the requirement of many magnetic MEMS devices. In order to generate sufficient forces for microactuation purposes, substantial material volume is necessary hence the requirement for thick films. Although electroplated CoNiMnP in the form of thick array (40 um height) [14] has been reported to exhibit high vertical anisotropy by virtue of their magnetic array geometry, material systems of much higher intrinsic properties should be utilized so as to maximize the performance of devices.
In view of the above considerations, there is a need to develop new material of sufficient vertical magnetic property by a suitable process that is capable of thick film deposition.
The present invention aims to provide a new and useful magnetic material which may be formed by electroplating.
It further aims to provide micro-devices which employ the magnetic material. Examples of micro-devices include micro-actuators, sensors, frictionless micro-gears etc.
The invention proposes that a magnetic material comprises 50-80 wt % of Cobalt (Co), 9-15 wt % of Nickel (Ni), 10-25 wt % of Rhenium (Re), 0.1 to 2.0 wt % of Phosphorus (P), and 5-10 wt % of Tungsten (W) or Platinum (Pt). The magnetic material may be formed as a layer, and it has been found that such compositions may have good vertical magnetic properties (e.g. when magnetised can provide a high magnetic field strength in the direction perpendicular to the plane of the layer). The layer preferably has a thickness of above 1 μm (and typically more than about 50 μm, though normally less than 200 μm).
In a method according to the invention, the layer of magnetic material is formed by electroplating, for example onto a microstructure suitable for fabrication of magnetic micro-devices such as actuators.
The proposed magnetic material based on Co—Ni—Re—P—W or Co—Ni—Re—P—Pt is an attractive candidate for many integrated micro-devices, since it would provide potentially high vertical magnetic performance and ease of property control by process parameters. Such devices are proposed in other expressions of the invention.
Preferred features of the invention will now be described, for the sake of illustration only, with reference to the following figures in which:
The present inventors have performed the following experiments in which layers of magnetic materials (some being embodiments of the invention) were produced by electroplating and tested.
Firstly, circular glass substrates (12 mm diameter) were sputtered with a seed layer of either Cr(20 nm)/Au(200 nm) or Cr(20 nm)/Cu(200 nm) before electro-deposition using a rotating disk electroplating system. The sputtered Au or Cu layer was found to have (111) crystal orientation that is beneficial for the enhancement of vertical magnetic properties of a film to be subsequently deposited. The sputtered substrates were ultrasonically cleaned using trichloroethylene and ethanol. A conducting silver paste was applied onto the back-side and side-wall of the glass substrates at two opposite points so that an electrode of the electroplating system is connected electrically to the copper seed layer on the substrates. Before plating, the surface of copper seed layer was activated using sulphuric acid. The substrates were fixed to a cathode of a known electroplating system via a holder covering the rim of substrates. Platinum wire was used as the anode for the electroplating system. An Ag/AgCl reference electrode was used as the reference electrode which was connected to the plating solution via a salt bridge. The exposed area for plating was over a central circular area of 10 mm diameter. Electrochemical deposition was carried out at room temperature (about 20° C.) by an electrical circuit which applies a suitable current density (in the range of 10 to 30 mA/cm2) between the anode and cathode via a galvanostat (a device which provides a constant current).
For different ones of the substrates, different electroplating bath compositions were selected, in the range of compositions given in Table 1. CoNiReP represents a material system consisting of Co, Ni, Re and P while CoNiReP/Mn, CoNiReP/Mo, CoNiReP/W and CoNiReP/Pt denote CoNiReP doped with Mn, Mo, W and Pt respectively. The pH of each bath solutions was adjusted using sulphuric acid and sodium hydroxide to the range of 2.0 to 5.0 before plating. For good uniformity and reproducibility, electro-deposition was carried out under agitation at a rotation speed of 500 rpm.
Subsequently, the magnetic performance of the films produced was assessed by a vibrating sample magnetometry (VSM). It was found that the film composition was very much dependent on process parameters, such as concentration of the bath solutions, and plating conditions such as pH and current density. As a result, the magnetic properties of film, which are very dependent on film composition, were very sensitive to the above parameters. In this study, the interdependency between magnetic properties and process parameters for the Co—Ni—Re—P material system is investigated.
Being a multi-component system, it is important to elucidate the effect of bath composition and concentration on the deposited film. By separately studying the effect of each individual component on the performance of the film, an optimized plating bath solution can be known.
With the Ni/Co mole ratio kept at 1.0, total concentration of Ni and Co ions is then varied to study their effect on the performance of film as shown in
The effect of P concentration is manifested in
M-H hysteresis loop of optimized CoNiReP as measured by VSM is shown in
After process optimisation of the Co—Ni—Re—P system, doping effects of Mn, Mo, Pt and W is investigated.
As shown in
A first such device is shown in
Application of a current to the coil 2 causes the coil 2 to interact with a permanent magnetic field generated by the magnetic elements 9, and causes in-plane motion to the strip 5, and in this embodiment, the strip 5 is caused to move horizontally shown by the arrow X. When the aperture 7 on the strip is aligned with the pin-hole 3 on the substrate 1, light passes through the device 100 and vice versa. The micro-shutter may be used as an optical switch or spatial light modulator.
Another application example is shown in
Having fully described the present invention, it can be appreciated that the proposed magnetic material based on Co—Ni—Re—P—W or Co—Ni—Re—P—Pt is an attractive candidate for many integrated micro-devices, since it would provide potentially high vertical magnetic performance and ease of property control by process parameters. Further, its application can be easily extended to patterned electrodeposition and hence it offers great advantages over post-deposition etching of films especially when small structure with vertical sidewall and high aspect ratio are essential.
The described embodiments and experiments should not be construed as limitative. For example, although the experiments describe conducting the electrochemical deposition at about 20° C., other temperatures are also envisaged, but preferably below 30° C. Also, although the described embodiment describes the magnetic material having a suitable proportion (wt %) of either W or Pt, it is envisaged that the magnetic material can include a combination of these materials with suitable wt % of each material.
Further, the embodiments describe a micro-shutter and micro-motors as application examples, but it would be apparent that the present invention is also useful to be included in other micro-devices such as sensors, frictionless micro-gears etc.
Number | Date | Country | Kind |
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200403719-8 | Jun 2004 | SG | national |
This is a division of application Ser. No. 11/168,698, filed Jun. 27, 2005, now U.S. Patent No. 7,435,485, which is entitled to the priority filing date of Singapore application 200403719-8 filed on Jun. 29, 2004, the entirety of which is incorporated herein by reference.
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Number | Date | Country | |
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20090065366 A1 | Mar 2009 | US |
Number | Date | Country | |
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Parent | 11168698 | Jun 2005 | US |
Child | 12200991 | US |