Dynamic magnetic information storage or retrieval – Head mounting – For adjusting head position
Reexamination Certificate
2000-06-28
2002-10-29
Heinz, A. J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head mounting
For adjusting head position
Reexamination Certificate
active
06473274
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in part to improvements in methods and apparatuses for dynamic information storage or retrieval, and more particularly to improvements in methods and circuitry for positioning a transducer for writing or detecting data written onto a spinning data disk, and still more particularly to improvements in microactuator structures and methods. for making same. This invention also relates in part to improvements in components used in microelectromechanical systems and methods for making same.
2. Relevant Background
Mass data storage devices include well known hard disk drives that have one or more spinning magnetic disks or platters onto which data is recorded for storage and subsequent retrieval. Hard disk drives may be used in many applications, including personal computers, set top boxes, video and television applications, audio applications, or some mix thereof. Many applications are still being developed. Applications for hard disk drives are increasing in number, and are expected to further increase in the future. Mass data storage devices may also include optical disks in which the optical properties of a spinning disk are locally varied to provide a reflectivity gradient that can be detected by a laser transducer head, or the like. Optical disks may be used, for example, to contain data, music, or other information.
In the construction of mass data storage devices, a data transducer, or head, is generally carried by an arm that is selectively radially positionable by a servo motor. Recently, micromotors, or microactuators, have been investigated to provide better, or more accurate, position control of the head.
In one design, a piezoelectric “I-beam” element has the actuator mounted on an arm or suspension element. The actuator may be co-located with the head on the end of a suspension to provide a fine positioning capability to the head. However, the piezoelectric element suffers several disadvantages. For example, voltages on the order of 30 volts are required for suitable operation. Such high voltages are undesirable in most hard disk drive applications. Also, the range of movement that can be achieved is on the order of only ±1 &mgr;m. This may be enough with sufficiently high disk rotation velocities, but it is generally seen as a limitation of this system.
In another design, a microactuators that has been investigated has a microactuator element co-located with the head on the end of the arm. The microactuator may be rectangular in shape, with a platform portion to which the head is attached, and a frame portion to which the platform is tethered. The platform and frame are designed to allow the platform to freely move in only one direction in response to a current applied to associated coils. The movement of the platform causes fine radial movement of the head, for example, on the order of ±5 &mgr;m, in an axis normal to the length of the arm.
Through the provision of fine head positioning, such as by the microactuators of the type described, the track density can be packed closer together since the head position can be more accurately controlled. Thus, the higher precision of head positioning can lead to a higher number of tracks per inch that can be created on the disk. Also, the speed of the motor can be increased, and the quality of the bearings can be decreased, since the head can be more accurately positioned.
From a three-dimensional perspective, when multiple disks are used with corresponding multiple heads, the ability to provide fine position control to individual heads of the stack of heads and disks enables each head to be individually positioned to tracks within its position control range. This is in contrast to structures that are required to track along the same paths as each of the other heads. This adds great flexibility and functionality to the drive that would not otherwise be available. Among other things, this would provide an ability to write to the disks with parallel data streams, greatly increasing its speed.
In the construction of microactuators in the past, one process that was used began with a silicon wafer about 24 mils thick. For example, a cross-section side view of a portion
10
of a microactuator is shown in FIG.
1
. As can be seen, a nickel-iron structure
12
is formed on a silicon wafer substrate
14
, on both sides of a gap
16
. The gap
16
shown is the gap separating the tethered wafer structure
18
and the surrounding arm structure
20
.
A dielectric material
22
is built up adjacent to the nickel-iron material
12
, and copper coils
24
and connection wiring
26
surround a portion of the nickel-iron structure
12
, encapsulated by the dielectric
22
. The various structures are built up in layers by photolithographic, material deposition, lapping, and other. known processes. These layers of dielectric, copper, and nickel-iron were built up on the wafer to form a sandwich of materials. The nickel-iron provided a necessary magnetic material, and the copper formed the coils to which a positioning current may be applied. Then the silicon wafer was lapped, sawed, or ground off to produce a microactuator which had a thickness on the order of about 100 &mgr;m. Once this was done, however, due to the significantly differences of thermal coefficients of expansion of the various materials, the extremely thin resulting part was extremely vulnerable to warping or buckling. The various parts. also tend to delaminate from the remaining wafer substrate, and made the production yield extremely small.
Limited capability of either molding or a photographic process, which is utilized to construct the high aspect ratio (height-to-width) layers of metal and dielectric material, are also important problems. The thickness of these material layers is a primary factor in generating the required amount of magnetic force in the micromotor, or microactuator. This force, in turn, drives the amount of travel of the platform in the motor. Large travel is a key market desire.
What is needed, therefore, is a microactuator structure and method for constructing it that results in a device that is not as susceptible to the stresses caused by the differences in the thermal coefficients of expansions of the various required materials.
Additionally, recent interest has been devoted to microelectromechanical systems (MEMS), for many varied applications, such as accelerometers, mirror positioning, and the like. In many MEMS control devices, a platform is suspended by a hinge or tether in a window in a larger yoke or base. However, the substrates upon which such structures are constructed are generally very thin, on the order of a few to a few hundred microns. Consequently, they suffer the same distortion problems as described above with respect to the mass data storage device positioning arms.
SUMMARY OF THE INVENTION
In light of the above, therefore, it is an object of the invention to provide a microactuator or micromotor device that is less susceptible to distortion or warping, due to differences in thermal expansion of the various parts used to realize the structure.
It is another object of the invention to provide improved methods for manufacturing microactuator or micromotor devices, for use, for example, in mass data storage devices or microelectromechanical systems.
Thus, according to one aspect of the invention, a method for making a micromotor or microactuator is presented such that a symmetrical build up of material is allowed, thus reducing mechanical stress. More particularly, one layer of circuits is built on each side of the structure, thereby eliminating the need to stack complex patterns. Stacking one complex pattern on top of a similar pattern is difficult, because the surface, which is the base for subsequent layers, is not flat. The photolithography process that forms these patterns is note very forgiving to non-flat surfaces. Avoiding the stacked layers also allows thicker conductors to be considered for each circuit. Thicker circuits increase current
Heaton Mark W.
Lin Tsen-Hwang
Maimone Peter J.
Wachtler Kurt P.
Brady W. James
Heinz A. J.
Swayze, Jr. W. Daniel
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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