Abstract:
A magnetic recording head system is protected against electrostatic discharge (ESD) and electrical overstress (EOS). The system includes a transducing read element and a drive circuit for connection to operate the transducing read element. A microelectromechanical switch has an input to receive an electrical control signal that selectively switches between a first state for protecting the transducing read element and a second state for operating the transducing read element.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of Provisional Application No. 60/362,508 filed Mar. 6, 2002 for “MEMS-based ESD protection of magnetic recording head” by E. Granstrom. 
     INCORPORATION BY REFERENCE 
     The aforementioned Provisional Application No. 60/362,508 is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to protection of magnetic recording heads from electrostatic discharge (ESD), and more particularly to a microelectromechanical system (MEMS) for controllably shunting a recording head away from its driving circuit and/or electrical contacts during periods of non-operation. 
     Magnetic recording heads possess an acute sensitivity to damage or failure from ESD or electrical overstress (EOS) events, both during disc drive production and after assembly of the drive. During production, it is possible to electrically disconnect the recording head from the other electronic components of the drive, thereby offering protection against damage from ESD or EOS. Alternatively, systems have been proposed in which simple mechanical clamps are added to a disc drive during production to provide a shunt from reader elements of the recording head to each other or to ground to provide ESD protection. However, both of these systems tend to add expense to production of the drive, perhaps even greater than the benefit they provide, due to the addition of separate physical elements to the recording head and the requirement to enable and disable during different stages of production and use of the drive. Furthermore, such proposed systems are temporary and need to be removed or permanently disabled prior to final assembly. 
     Improvements are needed in the art of ESD protection for magnetic recording heads, which is the subject of the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a magnetic recording head system that is protected against electrostatic discharge (ESD) and electrical overstress (EOS). The system includes a transducing read element and a drive circuit for connection to operate the transducing read element. A microelectromechanical switch has an input to receive an electrical control signal that selectively switches between a first state for protecting the transducing read element and a second state for operating the transducing read element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a typical, exemplary disc drive. 
     FIG. 2 is a perspective view of a portion of a disc drive illustrating a typical, exemplary configuration of a head interconnection circuit for electrically connecting a drive circuit to a transducing read/write head. 
     FIG. 3 is a diagram illustrating the switched ESD protection provided by the present invention. 
     FIGS. 4A and 4B are diagrams illustrating the operation of a MEMS-based ESD protection switch in accordance with the present invention. 
     FIG. 5 is a diagram schematically illustrating an ESD protection shunt in accordance with the present invention. 
     FIGS. 6A and 6B are diagrams illustrating the operation of a MEMS-based ESD protection shunt in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a perspective view of typical, exemplary disc drive  10 . Disc drive  10  includes voice coil motor (VCM)  12  arranged to rotate actuator arm  14  on a spindle around axis  16 . Head suspension  18  is connected to actuator arm  14  at head mounting block  20 . Flexure  22  is connected to an end of head suspension  18 , and carries slider  24 . Slider  24  carries a transducing head (not shown in FIG. 1) over disc  27 , for reading and/or writing data on concentric tracks  28  of disc  27 . Disc  27  rotates around axis  29 , so that windage is encountered by slider  24  to keep it aloft a small distance above the surface of disc  27 . 
     FIG. 2 is a perspective view of a portion of disc drive  10  illustrating a typical, exemplary configuration of head interconnection circuit  30  for electrically connecting drive circuit  32  to a transducing read/write head. Interconnect circuit  30  connects drive circuit  32  to read head leads  34  via conductive leads  36 , and connects drive circuit  32  to write head leads  38  via conductive leads  40 . It will be understood by those skilled in the art that other configurations of the components of disc drive  10  and interconnect  30  may also be used, and that the ESD protection scheme of the present invention has application to all such configurations. 
     While a disc drive (such as disc drive  10 ) is being produced and assembled, the transducing read head is vulnerable to damage caused by ESD. This vulnerability can be reduced by either electrically disconnecting the head from its associated drive circuitry or by providing a low resistance electrical path (shunt) in parallel to the transducer during these stages of disc drive production. The head can be protected by disconnecting one or more of the head leads or by connecting the head leads together or to ground, for example. However, during electrical testing and during operation of the disc drive, the head must be connected back to the drive circuitry and be without any shunts remaining in the circuit path. In the past, this has meant manually adding and removing a mechanical clamp or operating a mechanical switch, which adds labor costs to the process of assembling and testing a disc drive. The present invention provides a MEMS-based switch or shunt to allow the head to be selectively connected and disconnected, or alternatively shunted and deshunted, from the drive circuitry in response to an electrical control signal. 
     FIG. 3 is a diagram illustrating an ESD protection switch provided by the present invention. Leads  36   a  and  36   b  connect read head  34  to drive circuit  32  (FIG.  2 ), and leads  40   a  and  40   b  connected write head  38  to drive circuit  32  (FIG.  2 ). A controllable ESD protection switch is controlled by input control signals on leads  50   a  and  50   b , and is operable to disconnect read head  34  from its associated drive circuit by creating interrupt  52  in lead  36   a . It should be understood by those skilled in the art that the depiction of interrupt  52  in FIG. 3 is schematic in nature, and is a simplified illustration of an actual implementation of the controllable switch. 
     FIGS. 4A and 4B are diagrams illustrating the operation of exemplary MEMS-based ESD protection switch  60  in accordance with an embodiment of the present invention. Control signals are carried on leads  50   a  and  50   b  to cause structure  62  to either separate from structure  64  (FIG. 4A) or to contact structure  64  (FIG.  4 B). In the separated position (FIG.  4 A), structure  62  is separated from structure  66 , leaving lead  36   a  separated at interruption  52 . In the contacted position, structure  62  contacts structure  66  so that lead  36   a  provides a continuous conductive path for the read head to be connected its associated drive circuit. 
     Exemplary switch  60  is configured as a MEMS, constructed according to MEMS fabrication techniques generally known in the art of an appropriate MEMS material. As such, switch  60  is capable of being formed with extremely small size and high resolution, controllable by an electrical signal in order to achieve mechanical movement. In an exemplary embodiment, structures  62  and  64  are separated in an unenergized (passive) state, and actuated to contact one another in an energized (active) state. Other configurations of a MEMS-based switch may also be employed within the scope of the present invention. 
     FIG. 5 is a diagram schematically illustrating ESD protection shunt  70  in accordance with the present invention. Leads  36   a  and  36   b  connect read head  34  to drive circuit  32  (FIG.  2 ), and leads  40   a  and  40   b  connected write head  38  to drive circuit  32  (FIG.  2 ). Controllable ESD protection shunt  70  is controlled by input control signals (not shown in FIG. 5 for the sake of simplicity), and is operable to connect leads  36   a  and  36   b  together in order to isolate read head  34  from drive circuit  32  (FIG. 2) for protection from ESD. It should be understood by those skilled in the art that the depiction of shunt  70  in FIG. 5 is schematic in nature, and is a simplified illustration of an actual implementation of the controllable shunt. 
     FIGS. 6A and 6B are diagrams illustrating the operation of exemplary MEMS-based ESD protection shunt  70  in accordance with an embodiment of the present invention. Lead  36   b  is connected to conductive structure  72 , and lead  36   a  is connected to conductive structure  74 . In an operative (non-ESD protected) state, shown in FIG. 6A, leads  36   a  and  36   b  are not connected together. This allows signals to be passed along leads  36   a  and  36   b  between the read head and drive circuitry in a normal manner for operation of the disc drive. In a shunted (ESD protected) state, shown in FIG. 6B, leads  36   a  and  36   b  are connected together through mated conductive structures  72  and  74 . This prevents signals from being passed along leads  36   a  and  36   b  between the read head and drive circuitry, effectively disconnecting the read head from the drive circuitry and providing protection against damage caused by ESD. 
     Exemplary shunt  70  is configured as a MEMS, constructed according to MEMS fabrication techniques generally known in the art of an appropriate MEMS material. As such, shunt  70  is capable of being formed with extremely small size and high resolution, controllable by an electrical signal in order to achieve mechanical movement. In an exemplary embodiment, structures  72  and  74  are connected together in an unenergized (passive) state, and actuated to pull apart from one another in an energized (active) state. Also, it is contemplated in an alternative embodiment that shunt  70  may connect one of leads  36   a  and  36   b  to ground or another fixed potential rather than to one another in order to provide ESD protection. Other configurations of a MEMS-based shunt may also be employed within the scope of the present invention. 
     In another embodiment, a large bleed resistor is connected between. read head  34  and ground, in addition to shunt  70 , offering further ESD protection. The bleed resistor equalizes the potentials between read head  34  and any connected circuit element (such as a testing tool, for example) so that ESD events are prevented. When it is desired for read head  34  to operate, a MEMS-based structure is actuated to contact the appropriate reader leads  36   a  and  36   b  to provide the necessary low resistance signal path. 
     The present invention provides a MEMS-based switching mechanism for selectively disconnecting a read head from its associated drive circuitry or shunting the read head&#39;s leads to each other or to a fixed potential in response to an input control signal. The disconnection or shunting of the read head provides protection against ESD, which is particularly desirable during the production and assembly stages of disc drive manufacture. The MEMS-based design allows the ESD protection device to be implemented in the disc drive as a permanent part, controllable by an electrical signal, rather than requiring manual removal from the disc drive once assembly is complete. The MEMS configuration of the present invention is particularly beneficial for disc drives employing a MEMS microactuator in order to improve the achievable resolution of head positioning. In such a disc drive, the MEMS-based ESD protection of the present invention can be readily incorporated into the design of the microactuator, without adding significant expense. 
     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.