Abstract:
A transducing device responsive to magnetic fields includes a writer, a reader, an actuator, and a void. The actuator is positioned proximate the writer and reader. The void is positioned between at least one of the reader and writer and a substrate of a sensing device. The void is also positioned proximate an external surface.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to a magnetic head that has controlled thermal expansion. In particular, the present invention relates to a magnetic head having an actuator and a void region. 
     Magnetic data storage and retrieval systems store and retrieve information on magnetic media. In a magnetic data storage and retrieval system, a magnetic head typically includes a writer portion for storing magnetically-encoded information on a magnetic media and a reader portion for retrieving the magnetically-encoded information from the magnetic media. To write data to the magnetic media, an electrical current is caused to flow through a conductive write coil to induce a magnetic field in a write pole. By reversing the direction of the current through the write coil, the polarity of the data written to the magnetic media is also reversed. 
     The magnetic head is supported relative to a magnetic media surface by a slider. During operation, the disc is rotated by a spindle motor which creates airflow along a storage interface surface (SIS) of the slider from a leading edge to a trailing edge of the slider. Airflow along the SIS of the slider creates a hydrodynamic lifting force so the head of the slider essentially flies above the surface of the magnetic media. The distance between the slider and the magnetic media is known as the fly height. 
     During operation of the magnetic data storage and retrieval system, the fly height is preferably small enough to allow for writing to and reading from the magnetic media with a large areal density, and great enough to prevent contact between the magnetic media and the magnetic head. Performance of the magnetic head depends primarily upon head-media spacing (HMS). High density recording preferably requires a small HMS and a low fly height. Prior to using each magnetic head, there are small variations in fly height that must be accounted for due to changing operating conditions and head-to-head variations. 
     Current magnetic head designs use an actuator to heat the transducer and reduce the HMS by controlled thermal expansion of the transducer. The actuator is typically placed close to, or even inside, the writer coil to maximize heating of the writer. For effective operation, the actuator must provide a large enough stroke when the write pole is either close to the magnetic media or only slightly recessed from the point at the storage interface surface where the writer protrudes most. In addition, the fly clearance must be measured for each magnetic head by a controlled measurable non-destructive head-media contact so that the proper algorithm for operating the actuator is used for each magnetic head. 
     In order to compensate for variations of fly height due to both head-to-head variations and changing operating conditions, the actuator provides adjustments. For applications where power supplies are limited or low power dissipation is required, actuator designs must be efficient enough to provide the needed HMS within the power requirements. These designs must actuate both the reader and the writer in order to achieve optimal efficiency. However, current designs have limited stroke and excessive power requirements due to the actuator being mechanically constrained and thermally heat sunk to the slider by the alumina basecoat. 
     Further, the differing mechanical and chemical properties of the substrate and transducer layers further affect the SIS during operation of the magnetic head. As the magnetic data storage and retrieval system is operated, the magnetic head is subjected to increasing temperatures within the magnetic data storage and retrieval system. In addition, a temperature of the magnetic head itself, or a part hereof, may be significantly higher than the temperature within the magnetic data storage and retrieval system due to heat dissipation caused by electrical currents in the magnetic head. 
     The coefficient of thermal expansion (CTE) is a measure of the change in length of a unit length of material for an incremental change in temperature. The CTE of materials used in forming the substrate is typically much smaller that the CTE of materials used in forming the metallic layers of the transducer. Due to the larger CTE of the metallic layer, those layers tend to expand a greater amount than the substrate. Thus, when the transducer is subjected to higher operating temperatures, the metallic layers tend to protrude closer to the magnetic disc than the substrate, affecting the pole tip recession (PTR) of the transducer. This change in PTR caused by temperature is referred to as the Thermal PTR (TPTR). The PTR of a particular layer is defined as the distance between the planar SIS of the substrate and the planar SIS of that layer. 
     To keep the distance between the transducer and the magnetic media constant, PTR should not change significantly with temperature. If TPTR is large, then the spacing between the transducer and the media will change significantly with temperature, thereby requiring the low-temperature fly height to be high enough to accommodate this variation at higher operating temperatures. Much of the TPTR originates from the metallic layers exposed at the SIS. It is the mismatch in the CTEs between the metallic layers of the transducer and the substrate material (which forms the SIS) that gives rise to the thermal protrusion. Thus, there is a need in the art for a magnetic head design that decouples the metallic layers of the transducer from the substrate. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, the invention is a transducing device responsive to magnetic fields and includes a writer, a reader, an actuator, and a void region. The actuator is positioned proximate the writer and reader. The void region is positioned between at least one of the reader and writer and a substrate of a sensing device. The void region is also positioned proximate an external surface. 
     In another aspect, the invention is a magnetic head including a transducer, a substrate positioned adjacent the transducer, an actuator, and at least one void region. The actuator is positioned proximate the reader. The void region is positioned between the transducer and the substrate and proximate a first external surface of the transducer. 
     In another aspect, the invention is a transducer positioned adjacent a substrate. The transducer includes a plurality of metallic layers, an actuator, and a void region. The void region is positioned between at least one of the plurality of metallic layers and the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a sectional view of a first embodiment of a magnetic head having a void region prior to heating. 
         FIG. 1B  is a sectional view of the first embodiment of the magnetic head after heating with a localized actuator. 
         FIG. 2  is a sectional view of a second embodiment of the magnetic head having a void region. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A and 1B  are sectional views of magnetic head  10  before and after heating, respectively, and will be discussed in conjunction with one another. Magnetic head generally includes transducer  12 , substrate  14 , and void region  16 . Void region  16  is positioned between transducer  12  and substrate  14  proximate an external surface of transducer  12  and serves to mechanically decouple transducer  12  from substrate  14 . The external surface is the surface of transducer  12  that is the first contact point between magnetic head  10  and media M. In some embodiments, the external surface of transducer  12  is a storage interface surface (SIS) or an air-bearing surface (ABS) of transducer  12  relative to media M. 
     Transducer  12  of magnetic head  10  generally includes basecoat  18 , reader  20 , writer  22 , and actuator  24 . Basecoat  18  is formed on substrate  14  and reader  20  and writer  22  is deposited on basecoat  18 . Writer  22  generally includes return pole  26 , write pole  28 , write pole tip  30  located at an end of write pole  28  at the ABS, yoke  32 , back via  34 , write coil  36  (shown as write coil turns  36 A,  36 B,  36 C,  36 D,  36 E, and  36 F), and insulator  38 . Although magnetic head  10  is shown having one return pole  26 , writer  22  may have two return poles or no return pole without departing from the intended scope of the invention. 
     Return pole  26  and write pole  28  extend from the ABS and are connected to each other distal from the ABS at back via  34 . Yoke  32  is formed on write pole  28  but does not extend the full length of write pole  28 . Insulator  38  separates return pole  26 , write pole  28 , and write coil  36  from each other. Return pole  26  and yoke  32  are formed from metallic ferromagnetic materials. Preferably, each of these components is formed from an alloy composed primarily of Fe, Ni, and/or Co, which typically has a large CTE. 
     As shown in  FIGS. 1A and 1B , write coil  36  has coil turns  36 A,  36 B,  36 C,  36 D,  36 E, and  36 F. Write coil turns  36 A,  36 B,  36 C,  36 D,  36 E, and  36 F wrap around write pole  28  such that the flow of electrical current through conductive write coil  36  generates a magnetic flux at write pole tip  28 . In one configuration, write coil  36  may be wrapped in the following order:  36 A to  36 D to  36 B to  36 E to  36 C to  36 F. Although  FIGS. 1A and 1B  show write coil  36  wrapped in a helical configuration, other configurations can be used without departing from the scope of the intended invention. Each individual coil turn  36 A,  36 B,  36 C,  36 D,  36 E, and  36 F is separated from one another and from return pole  26  and write pole  28  by insulator  38 . Write coil  36  is generally formed from an electrically-conductive metal, such as Cu, Au, or Ag. Most commonly used is Cu, which has a CTE in the range of about 16.0×10 −6 /° C. to 18.0×10 −6 /° C. 
     Insulator  38  surrounds write coil  36  and is preferably formed from a dielectric material with high thermal conductivity to facilitate the removal of heat from write coil  36  via return pole  26  and write pole  28 . Insulator  38  is preferably formed from Al 2 O 3  or a photoresist. 
     Actuator  24  is positioned between write pole  28  and write coil turns  36 D,  36 E, and  36 F and acts as a localized heat source for transducer  12 . While actuator  24  heats both reader  20  and writer  22 , actuator  24  primarily heats writer  22  to reduce the head-media spacing (HMS) by controlled thermal expansion of transducer  12 . As previously mentioned, actuator  24  is typically positioned close to, or even inside, write coil  36  to maximize heating of writer  22 . 
     Void region  16  is formed between transducer  12  and substrate  14  and includes hinge  40  that acts as a lever. Void region  16  is formed by locally removing material between transducer  12  and substrate  14  and serves to locally decouple transducer  12  from substrate  14 . Enough material is removed from between transducer  12  and substrate  14  to compensate for thermal protrusion of transducer  12  when heated by actuator  24 . In one embodiment, void region  16  has a thickness of between approximately 1 micron and approximately 5 microns. By forming void region  16  between transducer  12  and substrate  14 , the region of decoupling is localized to the area of transducer  12  to allow a structurally sound connection of reader  20  and writer  22  to substrate  14 . In one embodiment, after the material has been removed, a vacuum or a gas, such as air, replaces the volume of material that is now void region  16 . 
     Void region  16  is formed by first building a sacrificial layer into basecoat  18  of transducer  12 . A capping layer is formed over transducer  12  for subsequent generation of the structure of transducer  12 . A via may be milled in the capping layer to allow the sacrificial layer to be removed through either acid etching bath or gaseous etch immediately after the capping layer is formed or at a later time, for example, after transducer  12  is built. If an acid etch is used, the sacrificial layer may be copper or some other metal that is dissolved by common chemicals that do not attack basecoat  18  or substrate  14 . A possible gaseous etch process can use silicon as the sacrificial layer and XeF 2  as the etchant. The resulting basecoat configuration has a lever arm about substrate  14  that allows less constrained actuation. In this embodiment, actuation is provided by using actuator  24  to cause thermal expansion of the sacrificial layer. 
     The position of void region  16  produces hinge  40  that allows free movement of transducer  12  to produce a decrease in the HMS. The external surface, or SIS, is still solid for proper air-bearing pressurization. The low stiffness of transducer  12 , provided by hinge  40 , allows actuator  24  and transducer  12  to move more freely than if surrounded by a solid basecoat. For a given actuator power, this results in an increased actuator stroke. The lever arm design does not depend on the actuator design or type and can be incorporated with existing transducer designs. For example, actuator  24  may be, but is not limited to: a thermal actuator, a piezoelectric actuator, or a magnetostrictive actuator. 
     Void region  16  will have significantly lower thermal conductivity than alumina basecoat  18 , decreasing thermal coupling between actuator  24  and substrate  14 . The placement of void region  16  can thus be used for thermal management of magnetic head  10  to reduce temperature increases where needed when using a heat-based actuation method. For example, void region  16  can be used to reduce temperature increases near sensitive areas of transducer  12 , such as reader  20 . 
       FIG. 2  shows a sectional view of a second embodiment of magnetic head  100  having void region  102 . Magnetic head  100  generally includes transducer  12 , substrate  14 , void region  102 , and actuator  104 . Transducer  12  of the first embodiment of magnetic head  10  and the second embodiment of magnetic head  100  are the same except that actuator  104  of magnetic head  100  is positioned behind transducer  12 , rather than adjacent or internal to transducer  12 , as shown and described in the first embodiment of magnetic head  10 . Void region  102  of magnetic head  100  functions similarly to void region  16  of magnetic head  10  except that void region  102  extends further back through magnetic head  100  than void region  16  of magnetic head  10  in order to account for the heat generated from actuator  104 . Actuator  104  can thus be positioned further away from the external surface, or the SIS, and still achieve substantially the same stroke as when actuator  104  is positioned within transducer  12 . 
     The maximum achievable stroke of a magnetic head is limited by the highest temperature that reader  20  can withstand without being damaged. Because reader  20  and writer  22  are typically positioned in close proximity to one another, when the actuator is located proximate writer  22 , this causes a significant increase in the temperature proximate reader  20  as well. By positioning actuator  104  behind both reader  20  and writer  22 , the high temperature region emitted from actuator  104  is removed from reader  20 , enabling actuator  104  to operate at a higher temperature. This in turn increases the maximum stroke capability of magnetic head  100 . 
     The magnetic head of the present invention comprises a void region for locally decoupling a transducer of a magnetic head from a substrate of the magnetic head proximate the air-bearing surface to control thermal protrusion. An actuator for actuating the transducer is positioned either within or behind the transducer. The void region is formed between the transducer and the substrate and mechanically decouples the reader and writer from the substrate. The void region is positioned proximate the air-bearing surface and creates a lever arm or hinge. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.