Gimbal design for hard disk drive device

[0001] This application claims the benefit of, and priority to, U.S. Provisional Application No. 63/469,321 filed on May 26, 2023, which is hereby incorporated by reference in its entirety.

[0002] The present disclosure relates to hard disk drives, and more particularly to a gimbal design as part of a suspension assembly for hard disk drives.

[0003] A hard disk drive (HDD) is a non-volatile storage device that stores digitally encoded data on one or more circular disks having magnetic surfaces. In operation, each disk spins rapidly. Data is read from and written to the disk using a read-write head that is positioned over a specific data track or location on the disk surface by a suspension assembly, which in turn is attached to the arm of the head stack assembly, which is rotated by a voice coil motor or actuator integral to the head stack assembly. Keeping the read-write head stable, and aligned with a targeted data track upon the disk surface defines the primary function of the suspension assembly during hard disk drive operation. Optimized suspension assembly design and manufacture can minimize the effects of mechanical, thermal, and other off-track disturbances which can degrade the performance of the hard disk drive. The suspension assembly includes a load beam. In operation, the actuator positions the distal end of the load beam over the desired portion of the disk (e.g., one of the circular tracks on the disk surface). A gimbal assembly (also referred to as a flexure) is mounted on the distal end of the load beam. The gimbal assembly includes components such as a slider containing the read-write head and microactuator devices (piezoelectric devices, will be named PZT from here onward) that rotate a portion of the gimbal assembly for fine positioning of the slider (as opposed to more coarse positioning of the slider by the actuator). The pressure caused by air viscosity between the slider and the spinning disk causes the slider to hover over (in close proximity to) the surface of the disk. While the load beam is relatively stirr, particularly in the lateral axis, the gimbal assembly is more flexible so that the slider can pitch and roll as it floats over the disk surface in order to maintain its operational distance immediately over the disk surface.

[0004] FIG. 1 illustrates a portion of a conventional head stack assembly 1, while FIGS. 2-3 illustrate a conventional head gimbal assembly 10 of the head stack assembly 2. The head stack assembly 2 includes a suspension assembly 3 with a load beam 4 terminating at a proximal end with a hinge 6 that is connected to a baseplate 8. A head gimbal assembly 10 is mounted on the distal end of the load beam 4. The baseplate 8 is connected to an actuator arm 12 of the head stack assembly 2, which is rotated by an integral actuator (not shown).

[0005] As best shown in FIGS. 2 and 3, head gimbal assembly 10 comprises a gimbal 14 of thin components of sheet metal (e.g., stainless steel), a circuit 16 that includes conductive traces (e.g., copper) and insulation material (e.g., polyimide), a slider 18 with the read/write head mounted on the gimbal 14 (e.g., by adhesive), and PZT actuators 22 mounted on the same side of the gimbal 14 as the slider 18. Circuit 16 extends along the load beam 4 and head gimbal assembly 10 for electrical signal communication to the read/write head of the slider 18 and to PZT actuators 22. The conductive traces of the circuit 16 are electrically insulated from the gimbal 14 by the insulation material of the circuit 16.

[0006] The gimbal 14 includes a base portion 14a and a tongue 14b, which are connected to each other by a neck portion 14c. The tongue 14b is configured to rotate about the neck portion 14c (for fine position control of the slider 18). The slider 18 is mounted on the tongue 14b. The PZT actuators 22 are mounted between the tongue 14b and the base portion 14a, for rotating the tongue 14b about the neck portion 14c when the PZT actuators 22 expand and contract in response to electrical signals provided by the circuit 16, which provides fine movement control of the slider 18 relative to the disk tracks during operation. In this example, the PZT actuators 22 are indirectly mounted on the gimbal 14, meaning that the PZT actuators 22 are mounted on the circuit 16, which is in turn mounted on the gimbal 14. Conventional thinking calls for the base portion 14a to be rigid and the tongue 14b to be more flexible, for better stroke performance. This is achieved by having the base portion 14a disposed fully under and fully supporting the bonding sites 16a of the circuit 16 to which the PZT actuators 22 are mounted, and the tongue 14b disposed only partially under and only partially supporting the bonding sites 16b of the circuit 16 to which the PZT actuators 22 are mounted.

[0007] PZT actuators 22 can be multi-layer devices of piezoelectric material. A commonly used example of piezoelectric material can be lead zirconate titanate, although other piezoelectric materials are also used and known, which expand and contract in response to electronic signals. FIG. 4 shows a cross-section of a conventional PZT actuator 22, with three layers 24, 26, 28 of piezoelectric material, although more or fewer layers can be used. PZT actuator 22 can include a first electrode 30 disposed on at least a portion of the bottom surface of the first PZT layer 24. A second electrode 32 can be disposed between at least a portion of the first PZT layer 24 and the second PZT layer 26. A third electrode 24 can be disposed between at least a portion of the second PZT layer 26 and the third PZT layer 28. Finally, a fourth electrode 36 can be disposed on at least a portion of the top surface of the third PZT layer 28. The shared lengths (i.e., overlap) of the first electrode 30 and the second electrode 32 can define the effective electrode length 38 and thus an active piezoelectric layer length of PZT layer 24. Furthermore, the shared lengths (i.e., overlap) of the third electrode 34 and the fourth electrode 36 can define the effective electrode length 40 and thus an active piezoelectric layer length of PZT layer 28. Conventional thinking calls for maximizing effective electrode lengths and active piezoelectric layer lengths 38 and 40 to maximize the expansion/contraction performance of the PZT actuator 22 in response to given electrical signals. However, it is also known to have the length L1 of the top electrode (i.e., the fourth electrode 36 in this example) be shorter than the lengths L2 of the other electrodes 30, 32, 34 for higher stroke sensitivity, even though the effective electrode length 40 is reduced, as shown in FIG. 4.

[0008] It has been discovered by the present inventors, however, that using the PZT actuator 22 of FIG. 4, with the reduced length top electrode 36, together with the head gimbal assembly of FIGS. 2-3, results in low frequency modes that have more variations for different z-heights. Specifically, FIG. 5 is a graphical representation of a resonant frequency (FRF) of the suspension assembly 3 with the multi-layer PZT 22 mounted on the gimbal 14 as shown in FIGS. 2-3. The resonant frequency (FRF) has low frequency modes around frequencies of 9000 Hz and 14000 Hz with more variations for different z-heights.

[0009] There is a need for a gimbal design that is more compatible with PZT actuators with reduced length top electrodes, that better balances stroke sensitivity and resonant frequency performance.

[0010] The aforementioned problems and needs are addressed by a head gimbal assembly that includes a gimbal having a base portion and a tongue that are joined together by a neck portion, a circuit mounted on the gimbal; a slider mounted on the tongue, and electrically connected to the circuit, a first PZT actuator having a proximal end mounted on a first bonding site of the circuit and a distal end mounted on a second bonding site of the circuit, and a second PZT actuator having a proximal end mounted on a third bonding site of the circuit and a distal end mounted on a fourth bonding site of the circuit. The first and third bonding sites do not overlap with and are not directly supported by the base portion. The second and fourth bonding sites overlap with and are directly supported by the tongue.

[0011] A suspension assembly includes a baseplate, a load beam connected to the baseplate by a hinge, a gimbal mounted to the load beam, wherein the gimbal comprises a base portion and a tongue that are joined together by a neck portion, a circuit mounted on the gimbal, a slider mounted on the tongue, and electrically connected to the circuit, a first PZT actuator having a proximal end mounted on a first bonding site of the circuit and a distal end mounted on a second bonding site of the circuit, and a second PZT actuator having a proximal end mounted on a third bonding site of the circuit and a distal end mounted on a fourth bonding site of the circuit. The first and third bonding sites do not overlap with and are not directly supported by the base portion. The second and fourth bonding sites overlap with and are directly supported by the tongue.

[0012] Other objects and features of the present disclosure will become apparent by a review of the specification, claims and appended figures.

[0022] It has been discovered that, contrary to conventional thinking, making the base portion of the gimbal less rigid, and making the gimbal's tongue more rigid, make the gimbal more compatible with short electrode PZT's. Such a gimbal can be used with the head stack assembly 2 shown in FIG. 1.

[0023] FIGS. 6 and 7 illustrate top and bottom views, respectively, of a head gimbal assembly 50 according to one example, which is compatible with the head stack assembly 2 and suspension assembly 3 discussed above (i.e., the head gimbal assembly 50 can be mounted on the load beam 4 discussed above with respect to FIG. 1). Head gimbal assembly 50 includes a gimbal 52, forming thin components of sheet metal. The gimbal 52 may be formed of stainless steel. A circuit 54 is mounted or otherwise attached to the gimbal 52, and includes conductive traces and insulation material. The conductive traces can be copper, and the insulation material can be polyimide. A slider 56 is mounted on the gimbal 52, and includes a read/write head. The slider can be mounted on the gimbal 52 by an adhesive.

[0024] The gimbal 52 includes a base portion 52a and a tongue 52b, which are joined together by a neck portion 52c. The slider 56 is mounted on the tongue 52b (either directly, or indirectly where the slider 56 is directly mounted on the circuit 54 and the circuit 54 is directly mounted on the tongue 52b, or both). The tongue 52b is configured to rotate or otherwise be displaced relative to the base portion 52a about the neck portion 52c, in order to provide relatively small movements of the slider 56 for fine position control of the slider 56 during operation. PZT actuators 58 are mounted between the tongue 52b and the base portion 52a, for rotating or otherwise displacing the tongue 52b (and the slider 56 mounted thereto) relative to the base portion 52a about the neck portion 52c when the PZT actuators 58 expand and contract in response to electrical signals provided by the circuit 54 (for providing fine positioning control of the slider 56 relative to the disk tracks during operation).

[0025] The circuit 54, slider 56 and PZT actuators 58 are all mounted on the same side (i.e., a first side) of the gimbal 52, which has the advantage of a simpler manufacturing process since the gimbal 52 need not be flipped over during manufacturing before welding the gimbal 52 onto the load beam 4. In this example, the PZT actuators 58 are indirectly mounted on the gimbal 52, meaning that the PZT actuators 58 are mounted on the circuit 54, which is in turn mounted on the gimbal 52. Circuit 54 extends along and is mounted on the gimbal 52, for conveying electrical signals from the read/write head of the slider 56, and conveying electrical signals to the PZT actuators 58 for fine positioning control of the slider 56. Therefore, the circuit 54 is electrically connected to the electrodes of the PZT actuators 58 (for providing signals that cause the PZT actuators to expand and contract) and to the slider 56 (for conveying signals to and from the slider 56 to conduct operations such a reading and writing).

[0026] The present inventors have discovered that making the base portion 52a less rigid, and the tongue 52b more rigid, provides better resonant frequency performance. This is achieved by providing cut-outs 60 in the base portion 52a, so that no portion of the base portion 52 is disposed under the bonding sites 54a of the circuit 54 to which the proximal ends of the PZT actuators 58 are mounted. Specifically, bonding sites 54a are those portions of circuit 54 to which the proximal ends of the PZT actuators 58 are mounted. No portion of the bonding sites 54a overlap with (and directly supported by) base portion 52a (due to cut-outs 60). Instead, the cut-outs 60 result in the bonding sites 54a being laterally adjacent to but spaced apart from the base portion 52a, resulting in the bonding sites 54a having no overlap with, and not directly supported by, the base portion 52a. The bonding sites 54a are only indirectly supported by base portion 52a due to base portion 52a overlapping with and directly supporting other portions of the circuit 54 which are not the bonding sites 54a. FIG. 8 is an exploded view of the head gimbal assembly 50, separately showing the gimbal 52, the insulation 62 of circuit 54, the conductive traces 64 of circuit 54, the PZT actuators 58 and the slider 56.

[0027] With this configuration, where the bonding sites 54a are adjacent to but spaced apart from the base portion 52a, because the circuit 54 is more flexible than the gimbal base portion 52a, there is less rigidity between the proximal ends of the PZT actuators 58 and the gimbal base portion 52a, compared to if the gimbal base portion 52a extended underneath and directly supported the bonding sites 54a. This flexibility is achieved by having a portion of the circuit (which is not the bonding sites 54a) overlap with and be directly supported by the base portion of the gimbal. Further, the tongue 52b is disposed under and directly supports the bonding sites 54b of the circuit 54 to which the distal ends of PZT actuators 58 are mounted. Specifically, bonding sites 54b are those portions of circuit 54 to which the distal ends of the PZT actuators 58 are mounted. Bonding sites 54b overlap with and are directly supported by tongue 52b. With this configuration, there is more rigidity between the distal ends of the PZT actuators 58 and the gimbal tongue 52b, compared to if the gimbal tongue 52b did not extend underneath and directly support the bonding sites 54b.

[0028] The combination of less rigidity between the PZT actuators 58 and the gimbal base portion 52a, and more rigidity between the PZT actuators 58 and the gimbal tongue 52b, reduces or eliminates the low frequency modes around frequencies of 9000 Hz and 140000 Hz. While the reduced rigidity between the PZT actuators 58 and the gimbal base portion 52a may reduce the level of stroke and therefore stroke performance, increased stroke performance can be achieved to offset this reduction by using the PZT configuration of FIG. 4, namely, a PZT actuator configuration with a reduced upper electrode length. FIG. 9 is a graphical representation of a resonant frequency (FRF) of the suspension assembly with multi-layer PZTs 58, having the electrode configuration of FIG. 4, mounted on the gimbal 52, as shown in FIGS. 6-8. The resonant frequency (FRF) has much cleaner low frequency modes around frequencies of 9000 Hz and 14000 Hz.

[0029] It is to be understood that the present disclosure is not limited to the example(s) described above and illustrated herein, but encompasses any and all variations falling within the scope of any claims. For example, references to the present invention, embodiments or examples herein are not intended to limit the scope of any claim or claim term, but instead merely make reference to one or more features that may be covered by one or more of the claims. Materials, processes and numerical examples described above are exemplary only, and should not be deemed to limit the claims.