Method for fabricating a permanent magnetic structure in a substrate

Information

  • Patent Grant
  • 6553651
  • Patent Number
    6,553,651
  • Date Filed
    Monday, March 12, 2001
    23 years ago
  • Date Issued
    Tuesday, April 29, 2003
    21 years ago
Abstract
A method for fabricating a permanent magnetic structure in a substrate, the method comprises the steps of providing a substrate with at least one cavity; providing magnetic particles dispersed with a bonding material for forming a bonding compound; filling the cavities with the bonding compound; and curing the compound to form the permanent magnetic structure in the substrate.
Description




FIELD OF THE INVENTION




The invention relates generally to the field of magnetization and, more particularly, to substrates having cavities which contain a magnetized compound.




BACKGROUND OF THE INVENTION




Advances in micro-systems technology have spawned the rapid development of a variety of devices for both research and commercial use. These devices include accelerometers, light modulators, micro-fluidic devices, micro-motors, molecular filters and various actuators and sensors. To date, the majority of MEMS actuators have been electro-statically driven. There are at least two reasons for this. First, electrostatic activation is compatible with standard microelectronic fabrication methods. Secondly, the electrostatic force scales relatively well at the micro-domain. Specifically, if the electric field is kept constant, the electrostatic force scales as L


2


, where L is the characteristic dimension of the device. Thus, if the size of the device is decreased by ten, the electrostatic force decreases by a factor of one hundred.




The implementation of magnetically actuated MEMS devices is much less developed then the electrostatic case. One reason for this is that the magnetic force for current driven devices scales as L


4


when the current density is kept constant. This is two orders of magnitude weaker than the electrostatic case. This disadvantage can be overcome if permanent magnets are used. Specifically, if all the linear dimensions of a permanent magnet are reduced, the field strength at all the re-scaled observation points remains constant (assuming that the magnetization is constant). Moreover, there is no power consumption. However, few if any methods exist for producing integrated permanent magnet structures for use in MEMS devices.




Therefore, a need exists for a practical method for fabricating permanent magnet structures on the order of 10 to 100s of microns on a substrate for use as a field source in a MEMS device. More specifically, there exists a need for such a method that can be adapted for the batch processing in which tens to hundreds of devices can be simultaneous fabricated on a single silicon wafer.




SUMMARY OF THE INVENTION




A method for fabricating a permanent magnetic structure in a substrate, the method comprises the steps of: (a) providing a substrate with at least one cavity; (b) providing magnetic particles dispersed with a bonding material for forming a bonding compound; (d) filling the cavities with the bonding compound; and (e) curing the compound to form the permanent magnetic structure in the substrate.











BRIEF DESCRIPTION OF THE DRAWINGS




The above and objects, features and advantages of the present invention will become apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical features that are common to the figures, and wherein:





FIG. 1

is a perspective of a substrate with micromachined recesses,





FIG. 2

is a view of a magnetic particle that is to be embedded in a the recesses in the substrate;





FIG. 3

is a view of a collection of magnetic particles filled in a recess in a substrate;





FIG. 4

shows an apparatus for producing ultrasound energy for application to the substrate with the deposited magnetic particles, and





FIG. 5

shows a process for magnetizing the magnetic particles once they are embedded.











DETAILED DESCRIPTION OF THE INVENTION




Referring to

FIG. 1

, there is shown a perspective view of a silicon substrate


10


having a plurality of recesses


12


,


14


,


16


that may range from 10 to 100′ of microns. The recess may have a variety of shapes, for example a cross-shape


14


, arcuate


16


, linear


12


and the like.




Referring to

FIG. 2

, there is shown a view of a magnetic particle


18


for filling the cavities, as described in detail hereinbelow. The magnetic particle


18


is preferable ferric oxide (Fe


2


O


3


), and the particle size is preferably from 1 to 5 microns. The magnetic particle


18


, preferably Hc of 315 Oe (approximately 40% ferrite) doped with Co is mixed with bonding compound for forming a magnetizable-bonding magnetic compound


22


that adheres to the cavities


12


,


14


,


16


of the substrate


10


when placed therein.




In this regard and referring to

FIG. 3

, there is shown the magnetizable-bonding compound


22


placed in the cavity


12


of the silicon wafer


10


. For clarity of illustration, only one of the cavities is shown although there are a plurality of cavities. Referring to

FIG. 4

, there is shown an ultrasound apparatus


24


having a transducer


26


and a power supply


28


which, when energized, causes the transducer


26


to apply ultrasound energy to the substrate


10


having the deposited compound


22


. This causes the compound


22


to be compactly placed in the cavity


12


. After the compound


22


are packaged into the cavity


12


, the compound is fused in the wafer cavities preferably at 200 degrees C. for 0.5 to 1 seconds depending on the size of the cavity.




Referring to

FIG. 5

, there is shown the magnetizing process of the imbedded compound


22


. A permanent magnet


30


is used to polarize the particles


18


of the compound


22


in a pre-determined preferred orientation. Alternatively, magnetic heads or electromagnetic coils could used be also. The magnetic field could be applied before or after the fusing of the compound


22


.




Therefore, the invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention.




PARTS LIST






10


substrate






12


linear recess






14


cross-shape recess






16


arcuate recess






18


magnetic particle






20


cobalt (Co)






22


magnetizable-bonding compound






24


ultrasound apparatus






26


transducer






28


power supply






30


permanent magnet



Claims
  • 1. A method for fabricating a permanent magnetic structure in a substrate, the method comprising the steps of:(a) providing a substrate with at least one cavity substantially between 10 to 100 microns; (b) providing magnetic particles dispersed with a bonding material for forming a bonding compound; (c) filling the cavities with the bonding compound; (d) compacting the bonding compound for creating a higher density bonding compound; and (e) curing the compound to form the permanent magnetic structure in the substrate.
  • 2. The method as in claim 1 further comprising the step of magnetizing the cured compound.
  • 3. The method as in claim 1, wherein step (b) includes providing bonded magnetic particles with Hc of 315 Oe doped with Co.
  • 4. The method as in claim 1, wherein step (c) includes curing the compound at substantially 200 degrees C.
  • 5. The method as in claim 4, wherein step (c) includes curing the compound at substantially 0.5 to 1 second.
  • 6. The method as in claim 1, wherein step (a) includes providing either an arcuate-shaped cavity, an cross-shaped cavity, or a linear-shaped cavity.
  • 7. The method as in claim 6 further comprising providing a plurality of cavities each of which may be arcuate-shaped, cross-shaped, or linear-shaped.
US Referenced Citations (1)
Number Name Date Kind
5243752 Moore et al. Sep 1993 A