Microfabricated fluid dynamic bearing
View Patent ↗A fluid dynamic bearing formed by a microelectromechanical systems (MEMS) wafer-level batch-fabrication process is provided. The process results in a high performance and high reliability fluid dynamic bearing having features including higher bearing lifetime at high RPM, improved bearing stiffness, durability and thrust/restoring forces capabilities. The present invention is especially useful with small form factor disc drive memory devices having constraints in motor height, such as a 2.5 inch disc drive, requiring high performance including high rotational speed and large areal density. A sacrificial layer is utilized in the process to simultaneously form symmetrical facing surfaces of relatively rotatable components. The facing surfaces define, therebetween, a desired feature, such as a journal bearing, a thrust bearing, a fluid channel, a fluid reservoir, a capillary seal, pressure generating grooves, and other profile geometries. Such geometry control allows for design freedom in obtaining a desired bearing performance and stiffness.
1. A method comprising:
forming a stationary component;
forming a rotatable component positioned for relative rotation about the stationary component;
forming a sacrificial layer between the stationary component and the rotatable component; and
removing the sacrificial layer, wherein said removing comprises:
simultaneously forming symmetrical facing surfaces of the stationary component and the rotatable component, and
defining between the symmetrical facing surfaces at least one of a gap, a journal bearing, a thrust bearing, a fluid channel, a fluid reservoir, a capillary seal, a grooved pumping seal, and a pressure generating groove.
2. The method as in claim 1 , wherein the forming and the removing the sacrificial layer comprises patterning silicon dioxide, and subsequently removing the silicon dioxide from between the symmetrical facing surfaces.
3. The method as in claim 1 , wherein the forming and the removing the sacrificial layer comprises:
growing a first silicon dioxide layer on a silicon substrate;
etching the silicon substrate using an inductively coupled plasma etch and using the first silicon dioxide layer as a mask to establish a desired shape of the silicon substrate;
stripping the first silicon dioxide layer from the silicon substrate and conformally growing a sacrificial silicon dioxide layer on the silicon substrate;
depositing a conformal polysilicon layer over the sacrificial silicon dioxide layer and patterning a photoresist on the conformal polysilicon layer;
selectively etching the conformal polysilicon layer to define a groove and converting the conformal polysilicon layer to a second silicon dioxide layer;
depositing a chrome copper seed layer over the sacrificial silicon dioxide layer and the second silicon dioxide layer and electroplating the chrome copper seed layer; and
ion milling a portion of the chrome copper seed layer and removing the sacrificial silicon dioxide layer situated between the silicon substrate and the chrome copper seed layer, wherein the area defined by the removed sacrificial silicon dioxide layer defines the symmetrical facing surfaces.
4. The method as in claim 3 , further comprising filling fluid into the area defined by the removal of the sacrificial silicon dioxide layer via a fluid fill hole, wherein the fluid fill hole is formed by the ion milling a portion of the chrome copper seed layer.
5. The method as in claim 1 , wherein microelectromechanical systems (MEMS) wafer-level batch-fabrication techniques form the sacrificial layer.
6. The method as in claim 1 , wherein the stationary component and the rotatable component are utilized with a small form factor motor for a disc drive data storage device, wherein the stationary component and the rotatable component have a diameter of less than 5 millimeters.
7. The method as in claim 1 , wherein the facing surfaces are formed with an axial or a radial asymmetry tolerance of less than 1 micron.
8. The method as in claim 1 , wherein the stationary component comprises a shaft and a stator and the rotatable component comprises a sleeve and a magnet, wherein further the shaft is established with a diameter of less than 0.6 mm and a length of less than 0.8 mm.
9. The method as in claim 1 , further comprising integrating electrical, mechanical, or magnetic layers with the stationary component and the rotatable component.
10. An apparatus comprising:
a stationary component;
a rotatable component positioned for relative rotation about the stationary component; and
symmetrical facing surfaces of the stationary component and the rotatable component, wherein
the facing surfaces are formed by removing a sacrificial layer between the stationary component and the rotatable component,
the facing surfaces define, therebetween, at least one of a journal bearing, a thrust bearing, a fluid channel, a fluid reservoir, a capillary seal, a grooved pumping seal, and a pressure generating groove, and
the facing surfaces maintain an axial or a radial asymmetry tolerance of less than 1 micron.
11. The apparatus as in claim 10 , further comprising:
two facing bi-spherical bearing surfaces formed by the microfabrication process, wherein the two facing bi-spherical bearing surfaces are stationary relative to one another and define a gap therebetween, and
a diverging capillary seal radially outboard from and fluidly connected to the gap.
12. The apparatus as in claim 11 , further comprising an asymmetrical sealing system, wherein
the capillary seal is defined between the bi-spherical bearing surface and a facing surface of the stationary component, wherein the capillary seal comprises a diameter smaller than a diameter of the diverging capillary seal,
the diverging capillary seal is situated within a fluid channel defined by the stationary component; and
the diverging capillary seal is fluidly connected to and opposes the capillary seal.
13. The apparatus as in claim 10 , further comprising a fluid fill hole defined by the stationary component or the rotatable component, wherein the fluid fill hole is formed by ion milling a portion of one of the stationary component and the rotatable component.
14. The apparatus as in claim 10 , wherein the sacrificial layer is formed by microelectromechanical systems (MEMS) wafer-level batch-fabrication.
15. The apparatus as in claim 10 , wherein the stationary component and the rotatable component are utilized with a small form factor motor for a disc drive data storage device, wherein the stationary component and the rotatable component have a diameter of less than 5 millimeters.
16. The apparatus as in claim 10 , wherein the stationary component and the rotatable component are used with a 2.5 inch disc drive.
17. The apparatus as in claim 10 , wherein one of the symmetrical facing surfaces is formed, at least partially, in the shape of a cone or sphere.
18. The apparatus as in claim 10 , wherein the grooves are shaped as a sinusoidal, a spiral, a chevron, or a herringbone pattern.
19. The apparatus as in claim 10 , wherein the stationary component comprises a shaft and a stator and the rotatable component comprises a sleeve and a magnet, wherein the shaft is established with a diameter of less than 0.6 mm and a length of less than 0.8 mm.
20. The apparatus as in claim 10 , further comprising a data storage disc attached to the rotatable component and an actuator supporting a head proximate to the data storage disc for communicating with the data storage disc.