Unitary Micro-Flexure Structure and Method of Making Same

This invention relates to a unitary micro-flexure structure, and to a method of making the same. A preferred embodiment of the invention is described herein in a setting wherein the invention finds particular applicability, and namely in the setting of an electromagnetic read/write structure for the reading and writing of magnetic images on and with respect to a relatively moving magnetic recording medium, such as a disk or drum. Thus, and in the setting of this read/write application, the invention relates to a unique, unitary, elongate, integrated read/write head/flexure/conductor cantilever structure of extremely small size, which structure includes an elongate flexure body with a stretch which is specially formed, as by ablation (laser and/or reactive-ion and/or chemical etching) and in certain modifications progressively diminished in cross section, e.g., tapered, in the direction from the body's mounting end toward its free end.

The structure of this invention, in the read/write setting expressed above, offers, in certain applications, decided improvements in dynamic mechanical performance over generically similar structures which are disclosed in four of my prior-filed U.S. Patents Applications: Ser. Nos. 07/441,716, filed Nov. 27, 1989, for "INTEGRATED MAGNETIC READ/WRITE HEAD/FLEXURE/CONDUCTOR STRUCTURE", 07/632,958, filed Dec. 21, 1990, for "METHOD OF MAKING INTEGRATED MAGNETIC READ/WRITE HEAD/FLEXURE/CONDUCTOR STRUCTURE" (as amended), 07/710,561, filed Jun. 5, 1991, for "INTEGRATED MAGNETIC READ/WRITE HEAD/FLEXURE/CONDUCTOR STRUCTURE", and 07/710,891, filed Jun. 11, 1991 for "INTEGRATED MAGNETIC READ/WRITE HEAD/FLEXURE/CONDUCTOR STRUCTURE". Much of the important background of the invention disclosed and claimed herein, as well as a fully detailed description of read/write-application internal electromagnetic structure, and of preferred fabrication methodology, are found in those prior-filed applications, and accordingly, and in order to avoid unnecessary, detailed repetition herein, the entire contents of these four referenced patent applications are hereby incorporated by reference.

In the structure disclosed in these earlier application documents, an elongate flexure body is illustrated which has a substantially uniform cross-sectional area, and lateral dimension, along nearly all of its length, extending between its mounting end and its free, magnetic-"head-carrying" end. Such construction has been proven to offer wide, successful applicability in many read/write systems applications, for all of the special reasons expressed in the earlier-filed, referenced patent applications.

Described and set forth, inter alia, in these earlier documents is a unique manufacturing technique wherein, in certain instances, etchable walls, or stripes, that are "laid down" during the explained thin-film deposition and patterning processes, are used to define the lateral boundaries (dimensions) of the final structures. In all instances, an ablation process(es) is (are) employed to give final lateral boundary definition to the final structures.

Further explaining, in addition to the special technique of using etchable walls or stripes to aid in defining the lateral boundaries of final micro-flexure body structures, we also recognize that, as just mentioned, other ablation, or etch-like, processes are usable and may be employed where desired.

For example, discussed herein specifically are two other ablation/etching-type approaches to the formation of flexure bodies - one of which employs a focused, high-power-density laser beam, and the other of which employs a reactive-ion etch using a plasma. All of the etching techniques employable in the practice of the invention take place in a non-mechanical, ablating fashion, and can be viewed or thought of as involving the fluid-entrainment removal of material to provide the final desired topographical outline for a wide variety of flexure bodies. Such unique fabrication methodology has led us to recognize how readily it lends itself to simple and easily controlled fabrication of micro-flexure structures with bodies having not only uniform cross-sectional dimensions, but also with graduated and changing cross-sectional areas and lateral dimensions along their lengths. Both simple and complex shapes are easily attained. Micro-flexure bodies can thus be uniquely designed to offer, readily, a wide variety of desired mechanical spring characteristics, resonance characteristics, dynamic-reaction characteristics, etc., to suit different specific systems applications.

Clearly as important as uniform dimensionality, among different, desired, cantilever flexure bodies usable, for example in a read/write setting, is a body which exhibits a graduated, or tapered, lateral configuration, and accordingly a graduated cross-sectional area progressing, generally, from larger adjacent the mounting end toward smaller adjacent the read/write, head-carrying end. Given the etchable wall/stripe and laser and reactive-ion fabrication technologies expressed herein and in the above-referenced prior documents as available manufacturing technology, an infinite variety of graduated/tapered configurations are easily and inexpensively possible.

Accordingly, the present invention proposes several unique, different generic forms of a flexure body, including tapered bodies, in a structure of the type generally outlined above, with some of these bodies including, and some not including, mass-reducing and dynamic-performance-differentiating, through-body void spaces. The special kinds of different performance enhancements which are achievable through such graduated topographics will be discussed in detail in the descriptions presented below.

Plainly among the important advantages offered and attained by the present invention are that flexure topography can be controlled with infinite variety, and that the same can be fabricated in a fashion which allows for very closely controlled fine-tuning of mechanical performance specifications. Similarly significant is that all of this can be achieved with great manufacturing simplicity, and in particular, with a manufacturing approach which does not require expensive, tricky, and potentially low-yield-producing and damaging machining operations.

These and other important objects and advantages that are offered by the present invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.

FIG. 1 is a working-side plan view of a micro-flexure structure (this figure being employed to depict three modifications) constructed in accordance with the present invention - such structure being intended for magnetic read/write applications, and thus including integrated read/write head and related electrical structure.

FIG. 2 is a side elevation taken from the upper side of FIG. 1.

FIG. 3 is an enlarged, longitudinal, lateral cross section of a fragment of the structure of FIGS. 1 and 2, illustrating integration therein of a probe-type head, and of an electrical coil and conductive traces connecting therewith, all of the latter being formed within the embedding, elongate, dielectric flexure body of the microflexure structure.

FIG. 4 is a working-side plan view of an alternative, curvilinearly configured embodiment of a micro-flexure structure (two more modifications being depicted here) constructed in accordance with the present invention.

FIG. 5 is a side elevation taken from the upper side of FIG. 4.

Turning now the drawings, and referring first of all to FIGS. 1-3, inclusive, indicated generally at 20 is a micro-flexure structure, herein illustrated as a read/write head/flexure/conductor structure, which is constructed in accordance with the present invention. Structure 20 in this, and in all other embodiments disclosed herein, has an overall mass which is less than about 3.0-milligrams. As has been indicated above in the description of the drawing figures, FIG. 1 is employed herein to illustrate, alternatively, three different modifications of one outline-type (rectilinear) embodiment of the invention. The fragmentary dash-triple-dot lines indicate a generally orthogonal rectilinear micro-flexure structure like the structure which is illustrated in the above-reference patent applications. The solid lines in this figure illustrate a solid-body, tapered modification. And, the fragmentary region shown in dash-double-dot lines is to be read, as will be explained shortly, to illustrate a tapered modification with a through-the-body void space.

With respect to the first-mentioned modification, shown in dash-triple-dot lines fragmentarily, the reader is referred to the referenced patent applications for a topographic, full representation of this "uniform-dimensionality" micro-flexure structure. Continuing, therefore, with what else is shown in these figures, as can be seen in FIG. 1, and referring to the "solid line" modification, structure 20, relative to its longitudinal axis 20a, is uniformly and symmetrically tapered in a rectilinear fashion in the stretch which extends between its mounting end 20b and its free, "head-carrying" end 20c.

Structure 20, in the form now being described as being illustrative, has an overall cantilever length A of about 10.2-millimeters, a width B, adjacent mounting end 20b, of about 1.0-millimeters, a width C, adjacent free end 20c, of about 0.5-millimeters, and a thickness D, throughout most of its length, of about 40-micrometers.

The particular dimensions just presented above are representative of values that have been found to work particularly well in many circumstances requiring what is the key offering of the present invention--namely, special attention to enhancing certain features of mechanical performance, such as those expressed earlier. These illustrative values lie within preferred ranges of values which are set forth immediately below:

A. 5-12.7-millimeters

B. 0.25-1.27-millimeters

C. 0.13-0.76-millimeters

D. 15-64-micrometers

As can be seen especially in FIG. 3, the micro-flexure read/write structure now being described is formed with a probe-type head for perpendicular recording, with this head including a main pole 22, a yoke 24, a back-gap stud 26, and a flux-return yoke 28. These components, referred to collectively as read/write pole structure, are magnetically coupled to form a low-reluctance path, terminating in a high-reluctance gap 30 between main pole 22 and the end of flux-return yoke 28. Further details of the construction and operation of the magnetic components just described, in relation to a magnetic recording medium, are found in several of the disclosures of the prior-filed patent applications mentioned earlier.

Digressing momentarily from the structure illustrated herein, it is not at all necessary that, in a magnetic read/write application, a probe-type head be incorporated in the structure 20. More specifically, and as is plainly expressed in material elaborated in the referenced prior-filed applications, other kinds of read/write heads for specific use in conjunction with other-than-perpendicular kinds of recording may readily be used. One should recognize, of course, that other types of magnetic head structures could be employed, such as cross-field structures, like what is disclosed in U.S. Pat. No. 4,751,598, and magneto-resistive structures, such as disclosed in U.S. Pat. No. 4,878,140.

Continuing with FIGS. 1, 2 and 3, inductively coupled to yoke 24 in structure 20 is electrical structure including an electrically conductive helix coil 32, the ends of which coil connect through lead conductors, such as conductor 34, to suitable connective bonding pads (not shown) formed adjacent the mounting end of structure 20.

The magnetic read/write pole structure, and the electrical coil and conductor structure (means), just generally described, are formed preferably in the manner set forth in detail in the referenced prior-application material as structure embedded within an elongate, dielectric flexure body which is made herein of a suitable metal oxide, such as, for example, aluminum oxide. Alternatively, recognized, usable flexure-body materials include silicon dioxide, diamond-like carbon, as well as others.

The modification suggested by dash-double-dot lines which appear on flexure body 36 in FIG. 1 is one wherein this body is formed with a through-the-body void space which both lightens the mass of the overall structure, and offers some slightly different mechanical dynamic/spring/resonance, etc., characteristics. A fragment of such a void space is shown generally at 38, and this fragment (were it fully shown in FIG. 1) represents a void space that has generally the same kind of appearance as the void space which appears in nearly complete solid-perimetraloutline form in the structural embodiment illustrated in FIG. 4. Referring to, and thus borrowing, letter designators for void-space dimensions that appear in FIG. 4, and relating these to corresponding measurements for void space 38, space 38 has a lateral dimension H, adjacent the mounting end of structure 20, of about 0.5-millimeters, a lateral width I, located toward its terminus roughly midway between opposite ends of structure 20, of about 0.13-millimeters, and an overall length G of about 7.6-millimeters.

By employing this trapezoidal flexure in a disk drive application, the mechanical, dynamic, and resonant characteristics of the flexure beam can be modified and optimized to achieve a given set of disk drive design/performance parameters. When compared to a rectangular shaped flexure, a trapezoidal flexure beam having a free-end width equal to the width of rectangular beam (where the free-end is located at the narrowest end of the trapezoidal beam) has a dramatically increased lateral resonant frequency, a slightly increased vertical resonant frequency, and a moderately decreased torsional resonant frequency. These resonance improvements are achieved at the expense of a slight flexure beam mass increase, but the advantage gained by improving the lateral resonant frequency, which is the mode that first limits the performance of flexure beams used in disk drive applications, far outweighs the tradeoffs required.

In contact recording disk drive applications, the higher flexure structure mass can be tolerated so long as the "effective mass" of the head and flexure combination is less than about 1.5-milligrams, beyond which point it is believed that the effective mass or inertia of the head/flexure combination would create an unacceptable risk of catastrophic wear when the head operated in contact with a high speed rotating rigid disk. The "effective mass" of a head and flexure combination is the equivalent free mass that would accelerate at the same rate as the head structure when subjected to a given net inertial force in a direction perpendicular to the disk surface. When a net force is applied to the head structure in a direction perpendicular to surface of the disk, the resultant acceleration of the head is determined not only by the actual mass of the head structure, but also by the mass of a portion of the flexure beam, which necessarily moves along with the head. The effective mass of typical head/flexure combinations can be approximated by adding one-fourth to one-third of the mass of the flexure structure to the mass of the head structure, and in present air-bearing "micro-slider" heads (also referred to as "seventy-percent slider"), the effective mass is about 26.5-milligrams. In contrast, the effective mass of the head/flexure combination employed in a preferred embodiment of the present invention is only about 1.0-milligrams (1/3 .times.3-milligrams mass for the trapezoidal flexure beam--in this embodiment, the head structure adds only trivial mass contributions), which is below the threshold at which the risk of catastrophic wear or head crash arising from head/disk contact becomes a significant limiting factor on component reliability.

When used within a servo loop, head/flexure components having higher resonant frequencies permit the servo electronics to be designed utilizing a higher bandwidth, which allows faster and more accurate positioning. Additionally, the higher bandwidth servo provides a stiffer servo response, which allows a disk drive utilizing such a servo to respond faster to externally applied disturbances, such as shock and vibration. In addition to faster access capability, the increased accuracy of the high bandwidth servo, coupled with the stiff mechanical components, permits higher track densities to be achieved.

Although vertical stiffness is increased somewhat through the use of trapezoidal flexure design, an excessive increases in vertical stiffness arising from the trapezoidal configuration can easily be offset by utilizing the versatile flexure fabrication technique disclosed herein. For example, the free end of the trapezoidal flexure could be narrowed or the entire beam could be made thinner in order to reduce the vertical stiffness, while still maintaining a high resonant frequency in the lateral mode. These techniques would also lower the effective mass of the head structure. Alternatively, the trapezoidal flexure structure may employ a void space in order to control the vertical stiffness of the flexure without compromising the lateral stiffness. The void space would also reduce the effective mass of the head/flexure structure. The vertical stiffness of the flexure must be carefully controlled because if the vertical stiffness is too high, the head/flexure structure will be overly sensitive to small changes in the height of the disk surface. Conversely, a low vertical stiffness may provide an insufficient force to maintain a uniform contact between the head and disk during operation.

Turning attention now to FIGS. 4 and 5, these figures show at 40 an additional embodiment of a read/write head/flexure/conductor structure, with structure 40 being substantially the same in all respects (two modifications being illustrated by these figures) as what is shown in FIGS. 1-3, inclusive, with the exception that the tapering outline of the integrated flexure body, from its mounting end toward its free end, is characterized by curvilinearity, and more particularly, by the slight concave curvilinearity clearly apparent in FIG. 4. Solid lines in the center of structure 40 illustrate a through-the-body void space--fragmented at one end (the right end) to illustrate a body structure without such a void space.

Building on the teachings set forth in the discussion on the trapezoidal flexure beams, a curvilinear design can be fabricated which further optimizes the resonant, mechanical, and dynamic characteristics of a flexure beam. Computer aided design and simulation tools can be used to provide curvilinear flexure beam shapes that optimize lateral resonance while minimizing increases in mass and vertical stiffness. Designs can include optimized solid curvilinear flexure beams, as well as curvilinear beams having void spaces as shown in FIG. 4. Due to the novel flexure beam fabrication technique disclosed herein, these shapes can be made with a minimum increase in manufacturing complexity over rectangular and trapezoidal shapes.

All of the embodiments of the micro-flexure structure of the invention are formed utilizing a unique methodology wherein a metal oxide is patterned using thin film techniques and deposited on a suitable substrate structure to have a predefined general outline and topography. The substrate is prepared preferably with an etchable layer, and in certain instances, with a pair of commonly etchable lateral-dimension-boundary-defining walls/stripes which can be removed selectively by an ablation process, such as laser or chemical etching, or reactive-ion etching, or a combination thereof, to effect final lateral side definition for a unit, and to free the unit from the substrate. The etchable layer and walls/stripes and ablation processes allow for infinite choice in the outline shape of a micro-flexure.

The above-incorporated patent applications describe in some detail how embodiments of the micro-flexure structure of the invention can be formed utilizing a commonly, chemically etchable substrate coating, or layer, and a pattern of walls/stripes that define the lateral topographical outlines of the various structures. In addition, and as was mentioned earlier, other ablation, etch-type processes can be used effectively to define the topographic outlines of structures like those described, and a pair of such additional techniques are now discussed.

A laser approach to precision formation of microflexure body structures involves preparation on a host substrate, through deposition and patterning steps like those expressed in the referenced patent applications, of what might be thought of as a generally continuous layer of dielectric flexure body-forming material, such as the several materials mentioned hereinabove, with appropriate read/write pole, etc. structures formed in an integrated fashion within this material and distributed throughout over the substrate at predetermined locations. This having been done, a focused laser beam of high power density (for example in the range of about 10.sup.2 to about 10.sup.6 watts/cm.sup.2) and short pulse duration (on the order of nanoseconds) from a Q-switched Nd:YAG, Nd:Glass or excimer laser is used to effect vaporization etching. Successfully used, for example, has been a pulsed laser beam with a wavelength of 266-nanometers and a power density of 7.times.10.sup.4 watts/cm.sup.2. Either the beam spot from the laser, or the substrate with deposited material (mounted on a translation stage), is moved to create, via relative motion, the desired etch pattern to remove material, and thus to create the final topographical outline shapes for flexure bodies via a maskless etching process.

Preferably, the requisite laser operating parameters, and the relative motion of the beam and of the deposit-carrying host substrate (the workpiece), are computer controlled. The output from the Nd:YAG or Nd:Glass laser may be frequency doubled, tripled or quadrupled to obtain the required output from the visible to the ultraviolet region of the electromagnetic spectrum, if necessary. Preferably, also the beam spot size is controlled by an automated aperture.

Alternatively, a mask stencil may be used to define the desired pattern shape, recognizing that this latter method may require additional deposition steps.

The ability of a laser beam thus to etch and ablate deposited material to form micro-flexure structures according to this invention depends upon the coupling which exists between the light and the material to be etched (i.e. optimum laser operating parameters may vary depending upon the absorptive capacity of the to-be-etched material). Frequencies in the ultraviolet range appear to be the most effective for defining accurate etch activity in aluminum oxide films of the thickness contemplated.

Thus, a computer-controlled laser etch process can be used effectively to define the shapes, boundaries, etc. of integrated, unitary head/flexure/conductor structures, and the like. Because of the fact that relative movement of the laser beam spot can be predictably repeatable and precisely guided under computer control, economical fabrication of small structures, having a wide variety of pre-selected shapes optimized for different ultimate operating environments, can easily be accomplished.

For flexure bodies which are formed of diamond-like carbon, an anisotropic etch, ablation process, such as a reactive-ion (plasma)-etch-through-a-mask process, can be used as an alternative to either a chemical etch or a laser etch process. Because such a reactive plasma etch process is largely anisotropic, the lateral side wall definitions of individual etched components can be quite precise and uniform.

With either a laser etch or a reactive-ion etch process employed, finally prepared components can be released from the associated underlying support substrate material in substantially the same manner described earlier - namely by way of chemical etching of an etchable intermediate layer.

Therefore, there is thus proposed by the present invention, a microflexure structure, and an ablation/etching methodology of making the same, which offer a very high degree of precision, infinitely variable control over the topology, and therefore the various performance characteristics, of a micro-flexure structure.