Patent Application
20130288078
Various embodiments of the present disclosure are generally directed to a magnetic element that is capable of efficient data reading and recording from reduced form factor data storage devices. In accordance with various embodiments, a thin film deposited on a cryogenically'cooled substrate can be stress tuned during primary annealing to reduce unwanted stress anisotropy and produce near zero internal thin film stress after the primary annealing.
Data storage device product design has focused on reducing the size of data bits while increasing data access rates from a data storage media in an effort to raise data capacity, transfer rates, and reliability. With such a reduction in size, data reading and writing components can be challenged to accurately perform, especially with respect to magnetic characteristics. That is, reducing the size of data access components can affect how those components behave, which can inhibit the writing and sensing of data bits.
The deposition of thin film materials may involve build-up of mechanical stress, which can adversely affect the performance of a magnetic element. Specifically, unwanted magnetic anisotropy can be generated by intrinsic stress present in deposited magnetic thin films. The residue stress in the films can also result in film delamination and cracking, which may produce reliability concerns for the devices. Thus, there is increasing industry interest in controlling the stress experienced by both magnetic and non-magnetic thin films in order to provide data elements that have minimal residue stress with maintained magnetic properties despite post deposition annealing.
Accordingly, soft magnetic thin films, such as magnetic shields and write poles, may be deposited on a cryogenic substrate to have the stress tuned during primary annealing to reduce unwanted stress anisotropy. The ability to control the stress experienced by the deposited thin film can allow for the construction of data elements that exhibit soft magnetic characteristics despite high temperature annealing while having reduced grain sizes. Such tuned stress for magnetic shields and poles further allows for high production rates and sustained resistance to elevated operating temperatures often encountered in reduced form factor data storage devices.
Stress present in sputtered thin films can originate from structural defects within the film, such as grain boundaries, dislocations, voids, and impurities, and from the interface between the film and substrate, such as lattice mismatch and difference in thermal expansion coefficient. At very low substrate temperatures, several effects can contribute to the change of stress in thin films deposited at such low substrate temperatures. First, backscattered Ar neutrals have a higher probability to become trapped and buried into the thin film matrix due at least in part to reduced
Second, when a thin film deposited on a cryogenically cooled substrate warms to room temperature, an annealing condition is effectively experienced in which different thermal expansion of film and substrate may result in irreversible residual stress. Third, the presence of tensile stress in a deposited thin film can result in micro-voids in the thin film, which strongly depend on sputtering pressure. At high sputtering pressures, the magnitude of energetic bombardment is also reduced due to gas scattering that can produce less dense films that are more likely to develop tensile stress.
As such, there are many factors that can contribute to the overall-stress of thin films. Depositing thin films on a cryogenically cooled substrate can increase thermal stress in the thin film and provide a bigger knob to tune the stress through the adjustment of sputtering pressure and power to achieve close to zero stress in as deposited or annealed thin films, while keeping a fully dense film structure.
Turning to the drawings,
The transducing clement 100 has an actuating assembly 102 that positions a transducing head 104 over programmed data bits 106 present on a magnetic storage media 108. The storage media 108 is attached to a spindle motor 110 that rotates during use to produce an air bearing surface (ABS) 112 on which a slider portion 114 of the actuating assembly 102 flies to position a head gimbal assembly (HGA) 116, which includes the transducing head 104, over a desired portion of the media 108.
The transducing head 104 can include one or more transducing elements, such as a magnetic writer and magnetically responsive reader, which operate to program and read data from the storage media 108, respectively. In this way, controlled motion of the actuating assembly 102 induces the transducers to align with data tracks (not shown) defined on the storage media surfaces to write, read, and rewrite data.
The magnetic reading element 122, as shown, has a magnetoresistive layer 130 disposed between leading and trailing shields 132 and 134. Meanwhile, the writing element 124 has a write pole 136 and at least one return pole 138 that creates a writing circuit to impart a desired magnetic orientation to the adjacent storage media. While not limiting, some embodiments use the writing element 124 to write data perpendicularly to the adjacent data media. Such perpendicular recording can allow for more densely packed data bits, but can also increase the effect of EAW as multiple data bits can be concurrently influenced by residual magnetic flux.
In another non-limiting embodiment, the writing element 124 can include at least two return poles 138 positioned contactingly adjacent a non-magnetic spacer layer 140 and an air bearing surface (ABS) shield 142. The writing element 124 may further include a coil 144 that can be one or many individual wires and a yoke 146 that attaches to the write pole 136 and operates with the coil 144 to impart a magnetic flux that travels from the write pole 136 through conductive vias 148 to conclude at the return poles 138. It should be noted that the various aspects of the head 120 can be characterized as either uptrack or downtrack, along the Y axis, depending on the motion of the head.
As deposited, the microstructure of grains in the soft magnetic materials that develop in the magnetic shields 126 and 132 and the magnetically active structure 128, especially when deposited on a cryogenic substrate, can affect the stresses and magnetic properties, namely anisotropy, experienced by the deposited layer as it warms either through natural or artificial annealing. While artificial high temperature annealing, such temperatures above 400° C., may contrast naturally allowing deposited films to warm from cryogenic to room temperatures, the ability to tune stress in the deposited layers allows for the production of near zero stress by minimizing the development of unwanted stress anisotropy.
The presence of above room temperature artificial annealing is illustrated in
For example, line 182 shows how an 8 kW sputtering power and approximately 50 sccm air flow rate produce a near zero stress subsequent to artificial annealing, but not as deposited, as shown by line 180. The tuning of stress with flow rate can concurrently provide a predetermined film roughness. As such, adjustment of flow rate can simultaneously provide predetermined stress and surface roughness. As an example, flow rate can be kept low while substrate temperature increases to produce material properties simultaneously with near zero stress.
With the ability to tune stress for a given soft magnetic thin film based on a variety of parameters, deposition power and flow rate, thickness, substrate temperature, and annealing, stress induced anisotropy can be minimized. As such, substrate temperature provides a knob that can be manipulated, much as deposition power and flow rate, to form a soft magnetic thin film with close to zero residue stress to avoid unwanted stress-induced anisotropy that may correspond with improved reliability of the thin films.
While not required or limited to a particular manner for forming a soft magnetic thin film to be used in a data writing element,
Step 212 may further evaluate and determine how and if the thin film is to be annealed. While an annealing condition may take place as the deposited layer naturally warms from cryogenic temperatures to room temperature, step 212 may further evaluate if an above room temperature anneal would tune stresses present in the film. With the various aspects of the layer being designed in step 212, step 214 begins depositing the thin film on a cryogenic substrate, such as substrate 122 of
As the layer is being deposited in step 214, decision 216 determines if any aspect of the deposition process is to be adjusted. For example, if the deposition power and air flow rate are to be changed to provide more or less compressive stresses on the thin film. If the deposition manner started in step 214 is to be altered, step 218 conducts those alterations to further tune the stress experienced by the film. At the conclusion of the adjustment of the deposition, or in the event no adjustment is chosen in decision 216, step 220 begins to anneal the thin film with the anneal profile determined in decision 216. The annealing profile may solely involve the natural warming of the layer from cryogenic to room temperature, or include additional above room temperature annealing, such approximately 225° C. annealing for two hours.
The annealing of the thin film in step 220 can be followed by decision 222 in which the construction of additional layers is contemplated. If more layers are chosen, the routine begins anew with step 212. However, if no additional layers are to be formed, the routine 210 can terminate or transition to another aspect of manufacturing, such as assembly and packaging.
With the various decisions and steps provided by routine 210, a magnetic reading and writing element may be fabricated with a wide variety of parameters that are tuned to have a near zero stress with the reduction of unwanted stress induced anisotropy. However, the routine 210 is not limited to the process shown in
It can be appreciated that the configuration and material characteristics of the magnetic element described in the present disclosure allows for enhanced magnetic reading and programming by providing a soft magnetic thin film that has magnetic properties favorable to use in high areal density data storage devices. Moreover, the ability to tune and optimize the internal stress of various layers can allow for precise reduction of stress induced anisotropy and increase mechanical properties of the films. In addition, while the embodiments have been directed to magnetic programming, it will be appreciated that the claimed technology can readily be utilized in any number of other applications, such as data sensing and solid state data storage applications.
It is to be understood that even though numerous characteristics and advantages of various embodiments of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of various embodiments, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts within the principles of the present disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements may vary depending on the particular application without departing from the spirit and scope of the present technology.
