Patent Publication Number: US-2009219653-A1

Title: Head slider equipped with piezoelectric element

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priorities of prior Japanese Patent Applications No. 2008-048921 filed on Feb. 29, 2008 and No. 2008-300547 filed on Nov. 26, 2008, the entire contents of which are incorporated herein by references. 
     FIELD 
     The present invention relates to a head slider used in a hard disk drive, the hard disk drive and a method for manufacturing the head slider. 
     BACKGROUND 
     In a hard disk drive (HDD), the track pitch in a magnetic disk has been narrowed with the increase in capacity of recording data at a very high rate based on technical improvements in the magnetic disk, a magnetic head, signal processing, etc. in the HDD. In such a situation, a gap between the head slider and the magnetic disk, i.e. a floating quantity of the magnetic head relative to a front surface of the magnetic disk, has become very small. For this reason, there is a demand for control of the floating quantity with high accuracy and at a high speed. 
     As a method for adjusting the floating quantity of a magnetic head with high accuracy, there has been known a technique in which a heater is mounted in the inside of a head slider so that a floating surface of the head slider is protrudes by thermal expansion of the heater. On the other hand, there has been also known a technique in which a piezoelectric element is mounted in a head slider so that the position of a magnetic head is displaced by use of the displacement of the piezoelectric element. 
     The technique of mounting a heater in the inside of a head slider has a problem that response speed is low because the technique uses a phenomenon that the heater expands thermally. The other technique has a problem that it is difficult to manufacture head sliders with uniform response characteristics because the piezoelectric element must be stuck to a slider substrate in manufacturing. 
     SUMMARY 
     According to one aspect of the invention, a head slider includes a slider substrate, an actuator provided in an end portion of the slider substrate and equipped with a piezoelectric element, and a magnetic head disposed on a side opposite to the slider substrate with interposition of the actuator. The piezoelectric element has piezoelectric bodies polarized along a first direction connecting the slider substrate and the magnetic head. The piezoelectric element has electrodes which apply an electric field to the piezoelectric bodies along a second direction intersecting the first direction. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing a schematic structure of a hard disk drive according to Embodiment 1; 
         FIG. 2  is a view showing schematic blocks of a control circuit portion according to Embodiment 1; 
         FIGS. 3A and 3B  are views showing a magnetic head support according to Embodiment 1; 
         FIG. 4  is a perspective view showing a schematic structure of a head slider according to Embodiment 1; 
         FIG. 5  is a perspective view showing a schematic structure of an actuator according to Embodiment 1; 
         FIGS. 6A to 6I  are views showing respective manufacturing steps of the head slider according to Embodiment 1; 
         FIG. 7  is a typical view showing a displacement state of a head portion according to Embodiment 1; 
         FIG. 8  shows a result of simulation by which displacement of the actuator according to Embodiment 1 is confirmed; 
         FIG. 9  is a schematic sectional view showing a head slider according to Embodiment 2; 
         FIGS. 10A to 10E  are views showing respective manufacturing steps of the head slider according to Embodiment 2; 
         FIG. 11  is a view showing a condition used when simulation is performed for an actuator according to Embodiment 2; 
         FIG. 12  shows a result (part  1 ) of simulation by which displacement of the actuator according to Embodiment 2 is confirmed; 
         FIG. 13  shows a result (part  2 ) of simulation by which displacement of the actuator according to Embodiment 2 is confirmed; 
         FIG. 14  shows a result (part  3 ) of simulation by which displacement of the actuator according to Embodiment 2 is confirmed; 
         FIG. 15  is a schematic sectional view showing a head slider according to Embodiment 3; 
         FIGS. 16A to 16H  are views showing respective manufacturing steps of the head slider according to Embodiment 3; 
         FIG. 17  is a schematic sectional view showing a head slider according to Embodiment 4; 
         FIG. 18  is a perspective view showing a schematic structure of an actuator according to Embodiment 4; 
         FIGS. 19A to 19G  are views showing respective manufacturing steps of the head slider according to Embodiment 4; 
         FIG. 20  is a perspective view showing a schematic structure of an actuator according to Embodiment 5; and 
         FIGS. 21A to 21G  are views showing respective manufacturing steps of a head slider according to Embodiment 5. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the invention will be described below in detail with reference to the drawings. Incidentally, the embodiments are simply exemplified and the invention is not necessarily limited to the configurations shown in the embodiments. 
     Embodiment 1 
     Hard Disk Drive 
     A hard disk drive  1  shown in  FIG. 1  has a housing  2  as its exterior illustrates in  FIG. 1 . A magnetic disk  4  and a head slider  5  are provided in the inside of the housing  2 . The magnetic disk  4  is mounted on a rotary shaft  3  so that the magnetic disk  4  can rotate on the rotary shaft  3 . The head slider  5  is equipped with a magnetic head which records/reproduces information on/from the magnetic disk  4 . A suspension  6 , a carriage arm  8 , an electromagnetic actuator  9 , etc. are further provided in the inside of the housing  2 . The suspension  6  holds the head slider  5 . The carriage arm  8  moves the suspension  6  along a front surface of the magnetic disk  4  so that the suspension  6  pivots on an arm shaft  7 . The electromagnetic actuator  9  drives the carriage arm  8 . A cover (not shown) is attached to the housing  2 , so that the aforementioned constituent parts are disposed in an internal space formed by the housing  2  and the cover. 
     As shown in  FIG. 2 , the hard disk drive  1  further has a control circuit portion  10  which controls operation of the hard disk drive  1 . For example, the control circuit portion  10  is mounted on a control board (not shown) provided in the inside of the housing  2 . As shown in  FIG. 2 , the control circuit portion  10  has a CPU (Central Processing Unit)  12 , a RAM (Random Access Memory)  14 , a ROM (Read Only Memory)  15 , an I/O circuit  19 , and a bus  17  or the like. The RAM  14  temporarily stores data etc. processed by the CPU  12 . The ROM  15  stores a control program etc. The I/O circuit  19  performs input/output of a signal from/to the outside. Signals are transmitted among these circuits by the bus  17 . 
     As shown in  FIG. 2 , the slider  5  has a ceramic substrate  5   a , and a magnetic head  5   h  formed in the ceramic substrate  5   a . For example, the magnetic head  5   h  is connected to the I/O circuit  19  in the control circuit portion  10  by wires  11   a  and  11   b  so that the magnetic head  5   h  performs recording (write operation) of information on the magnetic disk  4  and reproduction (read operation) of information stored in the magnetic disk  4 . For the read or write operation, the carriage arm  8  is driven by the electromagnetic actuator  9  to move the magnetic head  5   h  to a desired track on the magnetic disk  4 . 
     —Magnetic Head Support— 
     An example of a magnetic head support according to this embodiment will be described with reference to  FIGS. 3A and 3B . Incidentally, the magnetic head support is also called HGA (Head Gimbal Assembly).  FIGS. 3A and 3B  are views showing the magnetic head support according to Embodiment 1.  FIG. 3A  is a perspective view of the magnetic head support.  FIG. 3B  is a side view of the magnetic head support (in an X direction shown in  FIG. 3A ). 
     As shown in  FIGS. 3A and 3B , the magnetic head support  20  generally means a structure after a base plate  22  and the head slider  5  or the like are attached to the suspension  6 . However, the magnetic head support  20  sometimes means a state before the base plate  22  and the head slider  5  are attached to the suspension  6 , i.e. the magnetic head support  20  may mean only the suspension  6 . Further, the magnetic head support  20  sometimes means a structure after either of the base plate  22  and the head slider  5  is attached to the suspension  6 . Here, for example, the suspension  6  is a plate-like member of stainless steel 20 μm thick. The base plate  22  is joined to one end of the suspension  6  on the carriage arm  8  side while the head slider  5  is attached to the other end (tip portion  6   p ) of the suspension  6 . More specifically, for example, the head slider  5  is fixed to a gimbal  6   g  provided in the tip portion  6   p  of the suspension  6 . Incidentally, the head slider  5  is disposed in a position opposite to a front surface  4   c  of the magnetic disk. 
     As shown in  FIG. 3B , when the magnetic disk rotates in a direction of a arrow C, air flows into a gap under a floating surface  5   f  of the head slider  5  from a direction of a arrow “Air” in  FIG. 3B . The flow of air produces a buoyant force in the head slider  5 , so that the head slider  5  floats up from the front surface  4   c  of the magnetic disk  4 . 
     —Head Slider — 
       FIG. 4  is a perspective view showing a schematic structure of the head slider  5  in Embodiment 1. As shown in  FIG. 4 , an actuator  33  is disposed in an end portion of a ceramic substrate (slider substrate)  5   a . A head portion  37  having a magnetic head  5   h  formed therein is disposed on a side opposite to the ceramic substrate  5   a  with interposition of the actuator  33 . That is, the magnetic head  5   h  is located on a side opposite to the ceramic substrate  5   a  with interposition of the actuator  33 . As shown in  FIG. 4 , for example, external terminals  42   t  and  46   t  for applying a voltage to the actuator  33  are provided in the head portion  37 . For example, the ceramic substrate  5   a  is made of an AlTiC(Al 2 O 3 —TiC) material. The AlTiC material is one kind of ceramic. Specifically, the AlTiC material is a sintered material of alumina (Al 2 O 3 ) and titanium carbide (TiC). 
     An insulating layer  34  for electrically insulating the ceramic substrate  5   a  and the actuator  33  from each other is provided between the ceramic substrate  5   a  and the actuator  33 . For example, the insulating layer  34  is a film of an insulating material with a thick of 500 nm. As shown in  FIG. 4 , the insulating layer  34  is formed on an end surface of the ceramic substrate  5   a . Examples of the material allowed to be used as the insulating layer  34  include alumina (Al 2 O 3 ), and titanium oxide (TiO 2 ). When such an insulating layer  34  is provided, the ceramic substrate  5   a  can be completely insulated from electrodes of the actuator  33  to prevent electric noise on the actuator  33  side from leaking to the ceramic substrate  5   a.    
     Incidentally, the insulating layer  34  provided between the ceramic substrate  5   a  and the actuator  33  may be replaced by a conducting layer  34 D (not shown) provided in the position of the insulating layer  34  shown in  FIG. 4 . Examples of the material allowed to be used as the conducting layer  34 D are metals such as platinum (Pt), iridium (Ir), etc. Further examples of the material allowed to be used as the conducting layer  34 D are conductive nitrides such as titanium nitride (TiN), etc. and conductive oxides such as indium tin oxide (ITO), etc. In this case, a voltage supply terminal (not shown) is provided in the ceramic substrate  5   a  so that a GND potential from the control circuit portion  10  can be given to a voltage supply portion  43  via the ceramic substrate  5   a . In this case, the GND potential is grounded via the ceramic substrate  5   a  (at a position near the head slider  5 ) so that the GND potential can be stabilized easily. 
     An insulating layer  35  is provided between the actuator  33  and the head portion  37  so that the actuator  33  and the head portion  37  can be electrically insulated from each other by the insulating layer  35 . For example, the insulating layer  35  is a film of an insulating material with a thick of 500 nm. Examples of the material allowed to be used as the insulating layer  35  are alumina (Al 2 O 3 ), titanium oxide (TiO 2 ), etc. Incidentally, a portion where the actuator  33  is disposed between the insulating layer  34  and the insulating layer  35  is referred to as displacement portion  30 . The shape of the displacement portion  30  is deformed in accordance with distortion of the actuator  33 . A lower electrode  32  and the actuator  33  are provided in the displacement portion  30 . The lower electrode  32  will be described later. 
     —Actuator— 
     As shown in  FIG. 5 , for example, the actuator  33  has a piezoelectric body  41 , and two electrodes. The piezoelectric body  41  is made of a piezoelectric material. The two electrodes are a minus-side electrode  42  and a plus-side electrode  46 . As shown in  FIG. 5 , piezoelectric body layers  41   aa  to  41   dd , each of which is a part of the piezoelectric body  41 , are wedged between branch portions  45  ( 45   a  to  45   d ) of the minus-side electrode  42  and branch portions  49  ( 49   a  to  49   d ) of the plus-side electrode  46 , respectively. For example, the film thickness of each of these branch portions  45   a  to  45   d  and  49   a  to  49   d  is about 2-5 μm. 
     Here, it is preferable that the electrode pattern of the actuator  33  is formed so as to range from the floating surface  5   f  of the head slider  5  to an opposite surface thereof. When the electrode pattern of the actuator  33  is formed widely in the head slider  5  in this manner, a shear actuating force of the actuator  33  is produced on the whole area of a process surface of the head slider  5  so that the head portion  37  can move in parallel smoothly. 
     Examples of the piezoelectric material allowed to be used as the piezoelectric body  41  are ferroelectric materials such as lead zirconate titanate PZT (Pb(Zr,Ti)O 3 ), lead lanthanum zirconate titanate PLZT ((Pb,La)(Zr,Ti)O 3 ), etc. Besides these materials, potassium niobate (KNbO 3 ) can be used. Further, a substance containing PZT and Nb added to PZT can be used. 
     Examples of the material allowed to be used as the minus-side electrode  42  and the plus-side electrode  46  are conductive materials such as copper (Cu), gold (Au), platinum (Pt), iridium (Ir), etc. Among these materials, copper (Cu) and gold (Au) are particularly preferred because copper (Cu) and gold (Au) can be easily applied to plating. 
     As shown in  FIG. 5 , the minus-side electrode  42  is made up of three parts, i.e. the voltage supply portion  43 , a base portion  44  and the branch portions  45 . The voltage supply portion  43  is a portion which is supplied with, for example, a minus-side potential (0V in the control circuit portion  10 ) from the control circuit portion  10  and which is located on a side opposite to the floating surface  5   f  of the head slider  5 . The base portion  44  extends from one part of the voltage supply portion  43  toward the floating surface  5   f . The branch portions  45  ( 45   a  to  45   d ) branch from the base portion  44 . All of these branch portions  45   a  to  45   d  extend in parallel with the floating surface. That is, each branch portion  45  is a plate-like wiring pattern extending along the floating surface  5   f . Incidentally, this plate-like wiring pattern has upper and lower principle surfaces along the floating surface  5   f , and a thickness decided by the distance between of the upper and lower principle surfaces. 
     On the other hand, the plus-side electrode  46  is made up of three parts, i.e. a voltage supply portion  47 , a base portion  48  and the branch portions  49 , similarly to the minus-side electrode  42 . The voltage supply portion  47  is a portion which is supplied with, for example, a plus-side potential from the control circuit portion  10  and which is located on a side opposite to the floating surface  5   f  of the head slider  5 . The base portion  48  extends from one part of the voltage supply portion  47  toward the floating surface  5   f . The branch portions  49  ( 49   a  to  49   d ) branch from the base portion  48 . All of these branch portions  49   a  to  49   d  extend in parallel with the floating surface  5   f . That is, each branch portion  49  is a plate-like wiring pattern extending in parallel with the floating surface  5   f.    
     The external terminals  42   t  and  46   t  shown in  FIG. 4  are connected to the voltage supply portions  43  and  47 , respectively, so that the potentials from the control circuit portion  10  are supplied to the voltage supply portions  43  and  47  through the external terminals  42   t  and  46   t , respectively. The potentials from the control circuit portion  10  are given to the external terminals  42   t  and  46   t  via the wires  11   a  and  11   b , respectively. 
     The branch portions  45   a  to  45   d  of the minus-side electrode  42  and the branch portions  49   a  to  49   d  of the plus-side electrode  46  are disposed alternately as shown in  FIG. 5 . The branch portions  45   a  to  45   d  and  49   a  to  49   d  and the piezoelectric body films  41   aa  to  41   dd  wedged between the branch portions  45   a  to  45   d  and  49   a  to  49   d  form piezoelectric elements  33   aa  to  33   dd , respectively. That is, the actuator  33  has a structure in which the piezoelectric elements  33   aa  to  33   dd  are laminated continuously. Although Embodiment 1 shows an example of a structure in which seven piezoelectric elements  33   aa  to  33   dd  are laminated, the invention is effective if at least one piezoelectric element is provided. For example, each of the piezoelectric body films  41   aa  to  41   dd  is 2-5 μm thick and 3-4 μm wide in a W 33  direction. Incidentally, the width of W 33  in  FIG. 5  is, for example, 5 μm. Since each of the piezoelectric elements  33   aa  to  33   dd  has a constant distortion force, a larger displacement quantity can be expected to be obtained as the number of piezoelectric elements increases until the number of piezoelectric elements reaches a predetermined value (upper limit). 
     Adjacent ones of the piezoelectric body films  41   aa  to  41   dd  are polarized in directions opposite to each other (see  FIG. 7 ). Specifically, the piezoelectric body films  41   aa ,  41   bb ,  41   cc  and  41   dd  are polarized in a direction from the ceramic substrate  5   a  toward the head portion  37 . The piezoelectric body films  41   ab ,  41   bc  and  41   cd  are polarized in a direction from the head portion  37  toward the ceramic substrate  5   a . That is, each piezoelectric body film is polarized along a direction (first direction) which connects the ceramic substrate  5   a  and the head portion  37 . 
     When voltages are applied to these electrodes (the branch portions  45  and the branch portions  49 ), electric fields which are directed to the piezoelectric body in opposite directions are produced alternately in the piezoelectric body films  41   aa  to  41   dd  because the branch portions  45  and the branch portions  49  are disposed alternately. For example, an electric field in a direction from the surface opposite to the floating surface  5   f  toward the floating surface  5   f  is applied to each of the piezoelectric body films  41   aa ,  41   bb ,  41   cc  and  41   dd  whereas an electric field in a direction from the floating surface  5   f  toward the surface opposite to the floating surface  5   f  is applied to each of the piezoelectric body films  41   ab ,  41   bc  and  41   cd . That is, the electric fields are applied to the respective piezoelectric body films along a second direction which intersects the first direction. 
     When such electric fields are applied, all the piezoelectric elements  33   aa  to  33   dd  are distorted in the same direction. Distortion of the piezoelectric elements  33   aa  to  33   dd  on this occasion is d15 shear strain. It is preferable that the second direction is perpendicular to the first direction in order to make the applied electric fields act on the piezoelectric body films more effectively to obtain distortion in such a direction. In addition, it is preferable that the second direction is perpendicular to the floating surface  5   f  of the head slider  5 . 
     As described above, in accordance with Embodiment 1, the piezoelectric elements  33   aa  to  33   dd  can be distorted by d15 shear strain in a direction perpendicular to the direction from the ceramic substrate  5   a  toward the magnetic head  5   h  (head portion  37 ), i.e. in a direction of changing the floating quantity of the magnetic head  5   h . Incidentally, d15 shear strain is larger in piezoelectric constant than d31 strain or d33 strain. In addition, because d15 shear strain depends on the aspect ratio, d15 shear strain can provide a large displacement quantity in the direction of changing the floating quantity of the magnetic head  5   h  when the aspect ratio is made high. 
     —Head Slider Manufacturing Process— 
     A process for manufacturing the head slider  5  in Embodiment 1 will be described below with reference to  FIGS. 6A to 6I . 
     &lt;Step  1 &gt; 
     In this step, as shown in  FIG. 6A , an insulating material film  54  is first formed on one surface of an AlTiC(Al 2 O 3 —TiC) substrate  51 . 
     Specifically, for example, a wafer-shaped AlTiC substrate  51  is prepared. This AlTiC substrate  51  will be provided as a ceramic substrate  5   a  (slider substrate) of a head slider  5  after completion of the whole manufacturing process. Then, for example, alumina (Al 2 O 3 ) or titanium oxide (TiO 2 ) is deposited on a front surface of the AlTiC substrate  51  by sputtering to thereby form an insulating material film  54  with a thick of about 500 nm. This insulating material film  54  will be provided as an insulating film  34  after completion of the whole manufacturing process. 
     Incidentally, for formation of a conducting layer  34 D in place of the insulating layer  34 , for example, platinum (Pt) or iridium (Ir) is deposited on the front surface of the AlTiC substrate  51  by sputtering to thereby form a conducting material film (not shown) with a thick of about 500 nm. 
     &lt;Step  2 &gt; 
     Then, as shown in  FIG. 6B , a lower electrode layer  52  is formed on the insulating material film  54  (or the conducting material film  54 D). The lower electrode layer  52  is a layer for forming the lower electrode  32  and is formed above the AlTiC substrate  51 . 
     Specifically, platinum (Pt) or iridium (Ir) is deposited on a front surface of the insulating material film  54  by sputtering or vacuum vapor deposition to thereby form a lower electrode layer  52  with a thick of about 200 nm. Incidentally, a conductive nitride such as titanium nitride (TiN) or a conductive oxide such as indium tin oxide (ITO) may be used as the material of the lower electrode layer  52 . 
     &lt;Step  3 &gt; 
     Then, a piezoelectric body layer  50  containing a piezoelectric material as a main material or made of a piezoelectric material is formed on the lower electrode layer  52  as shown in  FIG. 6C . This piezoelectric body layer  50  is a layer for forming a piezoelectric body  41 . 
     Specifically, a piezoelectric material is deposited on a front surface of the lower electrode layer  52  by sputtering to thereby form a piezoelectric body layer  50  about 5 μm thick. Besides sputtering, for example, sol-gel processing, pulsed laser vapor deposition, metal organic chemical vapor deposition (MOCVD) or aerosol deposition may be used on this occasion. Examples of the piezoelectric material allowed to be used here are ferroelectric materials such as lead zirconate titanate PZT (Pb(Zr,Ti)O 3 ), lead lanthanum zirconate titanate PLZT ((Pb,La)(Zr,Ti)O 3 ), etc. Besides these ferroelectric materials, potassium niobate (KNbO 3 ) may be used. Further, a substance containing PZT and Nb added to PZT may be used. When Nb is added to PZT in this manner, the Curie temperature of PZT can be increased to prevent the polarized state of PZT from changing in heat treatment such as anneal after a polarization process. Incidentally, heat treatment at about 300° C. is generally performed as annealing in a post process for forming the magnetic head  5   h . It is preferable that the Curie temperature is set at 300° C. or higher so that the polarized state can be kept even when the piezoelectric body layer  50  is heated by such heat treatment. 
     &lt;Step  4 &gt; 
     Then, as shown in  FIG. 6D , a polarizing process is applied to the whole of the piezoelectric body layer  50 . 
     Specifically, for example, aluminum (Al) is first deposited on a front surface of the piezoelectric body layer  50  by sputtering or vacuum vapor deposition to thereby form an upper electrode layer  58   a  with a thick of about 200 nm. On this occasion, the upper electrode layer  58   a  is formed on the whole surface of the piezoelectric body layer  50 . 
     Then, a voltage is applied between the lower electrode layer  52  and the upper electrode layer  58   a . For example, 0V is applied to the lower electrode layer  52  while a voltage of 100V is applied to the upper electrode layer  58   a . When an electric field is applied to the whole film in this manner, directions of polarization of the piezoelectric material in the piezoelectric body layer  50  are made parallel with one direction. Incidentally, the direction of polarization on this occasion is a direction from the lower electrode layer  52  toward the upper electrode layer  58   a , i.e. a direction from the AlTiC substrate  51  toward the head portion  37 . 
     Finally, the upper electrode layer  58   a  is removed by wet etching using phosphoric acid (H 3 PO 4 ). 
     &lt;Step  5 &gt; 
     Then, as shown in  FIG. 6E , a polarizing process for polarization in a direction opposite to the direction in the previous step is applied to part of the piezoelectric body layer  50 . 
     Specifically, a striped resist pattern  58 R is formed on the front surface of the piezoelectric body layer  50 . For example, as shown in  FIG. 6E , the resist pattern  58 R is a striped pattern with a line width of 5 μm and a line interval of 3 μm. Incidentally, the region where the resist pattern  58 R is formed corresponds to a region other than the region where the piezoelectric body films  41   ab ,  41   bc  and  41   cd  will be formed. 
     Then, an aluminum film is formed again. Specifically, aluminum is deposited on the front surface of the piezoelectric body film  50  with the resist pattern  58 R by sputtering or vacuum vapor deposition. Then, the resist pattern  58 R is removed and local electrodes  58 , for example, about 200 nm-thick electrodes are formed by lift-off. On this occasion, as shown in  FIG. 6E , the local electrodes  58  are formed on the striped region with a line width of 3 μm and a line interval of 5 μm. 
     Then, 0V is applied to the lower electrode layer  52  while a voltage of minus 100V is applied to the local electrodes  58 . When an electric field is applied in this manner, the region where the local electrodes  58  are formed, i.e. the region where the piezoelectric body films  41   ab ,  41   bc  and  41   cd  will be formed is polarized in a direction from the local electrodes  58  toward the lower electrode layer  52 , i.e. in a direction from the head portion  37  toward the AlTiC substrate  51  (ceramic substrate  5   a ). In this manner, directions of polarization of adjacent ones of the piezoelectric body films formed in the piezoelectric body layer  50  are made substantially parallel to each other and reversed alternately. 
     Finally, the local electrodes  58  are removed by wet etching using phosphoric acid (H 3 PO 4 ). 
     &lt;Step  6 &gt; 
     Then, as shown in  FIG. 6F , a resist pattern  53  is formed. 
     Specifically, a resist film  53   a  (not shown) is formed on the whole of the front surface of the piezoelectric body layer  50  and patterned by photolithography into such a form that only the region where the piezoelectric body films  41   aa  to  41   dd  will be formed is left. Incidentally, this patterning is performed by an ultraviolet light exposure device such as an i-beam exposure device, an exposure device using a krypton fluoride (KrF) or argon fluoride (ArF) laser as a light source, or an electron beam (EB) exposure device. In this manner, for example, a striped resist pattern  53  having a pattern width of 3 μm and an interval of 1 μm between adjacent stripes of the resist pattern is formed. Incidentally, the length of the resist pattern  53  in the longitudinal direction (the inward direction into the drawing) is, for example, about 500 μm. 
     &lt;Step  7 &gt; 
     Then, as shown in  FIG. 6G , grooves  57  in which electrodes (branch portions  45   a  to  45   d  and branch portions  49   a  to  49   d ) will be formed are formed in the piezoelectric body layer  50 . 
     Specifically, grooves  57  are formed in the piezoelectric body layer  50  masked with the resist pattern  53  by dry etching using fluorine (CF 4 , SF 6 ) gas, chlorine (Cl 2 ) gas or argon (Ar) gas. For example, each groove  57  is 1 μm wide, 500 μm long (in the inward direction into the drawing) and 3 μm deep. For example, the grooves  57  are arranged at intervals of 2 μm. 
     &lt;Step  8 &gt; 
     Then, as shown in  FIG. 6H , after the resist pattern  53  is removed, branch layers  59  and  60  which will serve as electrodes (branch portions  45   a  to  45   d  and branch portions  49   a  to  49   d ) are formed in the grooves  57 . 
     Specifically, a film of copper (Cu) or gold (Au) with a thick of 100 nm is first formed by sputtering. Then, while this film is used as a seed layer, field plating with copper (Cu) or gold (Au) is performed so that the grooves  57  are filled with copper (Cu) or gold (Au). Then, chemical mechanical polishing (CMP) is performed. Thus, branch layers  59  and  60  are formed in the grooves  57 . 
     &lt;Step  9 &gt; 
     Then, as shown in  FIG. 6I , an insulating material film  65  and a head layer  67  are formed on the piezoelectric body layer  50  having the branch layers  59  and  60  formed therein. 
     Specifically, for example, alumina (Al 2 O 3 ) or titanium oxide (TiO 2 ) is deposited on the piezoelectric body layer  50  with the branch layers  59  and  60  by sputtering to thereby form an insulating material film  65  with a thick of about 500 nm. This insulating material film  65  will serve as an insulating layer after completion of the whole manufacturing process. 
     Then, external terminals  42   t  and  46   t  are formed on the insulating material film  65 . Specifically, after a resist pattern is first formed on the insulating material film  65 , openings (not shown) for the aforementioned via pattern are formed in part of the insulating material film  65  by dry etching using chlorine (Cl 2 ) gas or argon (Ar) gas. Then, the openings are filled with a conducting material by sputtering to thereby form the via pattern (not shown). Further, the same via pattern is also formed in the head portion  37  so as to be connected to the via pattern formed in the insulating material film  65 . Thus, the external terminals  42   t  and  46   t  are formed. 
     Then, a head layer  67  for forming a head portion  37  is formed on the insulating material film  65 . The head layer  67  includes a magnetic head  5   h  which has a shield layer, a read element, a write element, etc. 
     Finally, the wafer-shaped AlTiC substrate  5  having the head layer  67  formed therein thus is cut/separated into individual head sliders  5  by a dicing saw. The head sliders  5  are completed by the aforementioned manufacturing method. Incidentally, each separated head slider  5  is joined to the gimbal  6   g  of the suspension  6 , for example, by an adhesive agent. 
       FIG. 7  is a typical view showing a displacement state of the actuator in this embodiment. As shown in  FIG. 7 , when electric potentials are given to the electrodes (the minus-side electrode  42  and the plus-side electrode  46 ), the head portion  37  moves by a quantity Xd in a direction of an arrow. 
       FIG. 8  shows a result of simulation by which displacement of the actuator in the embodiment is confirmed. As shown in  FIG. 8 , a structure in which electrodes and a piezoelectric body were disposed on an AlTiC substrate was used as a subject of the simulation. As a result of application of a voltage 15V between the electrodes in the structure, it was confirmed that an MX point in the structure was displaced by 6.21 nm in the Xd direction. Incidentally, in  FIG. 8 , X is a zero point where displacement is zero, and MX is a maximum point where displacement is the largest. Here, copper was used as each electrode and a bulk of a PZT (52/48) composition was used as the piezoelectric body. 
     Embodiment 2 
     Embodiment 2 will be described below with reference to  FIGS. 9 to 14 . 
       FIG. 9  is a schematic sectional view of the head slider and the actuator  33 . As shown in an enlarged view in  FIG. 9 , Embodiment 2 shows an example in which each of electrode portions (the branch portions  45   a  to  45   d  and the branch portions  49   a  to  49   d ) includes a low Young&#39;s modulus portion YL low in Young&#39;s modulus of elasticity, and a conductor coating portion MD with which a front surface of the low Young&#39;s modulus portion YL is coated. A material higher in Young&#39;s modulus of elasticity than the low Young&#39;s modulus portion YL is used as the material of the conductor coating portion MD. That is, each electrode portion has a surface portion (high Young&#39;s modulus portion) made of a conducting material, and an inner portion (low Young&#39;s modulus portion) lower in Young&#39;s modulus of elasticity than the conducting material. 
     When the rigidity of the electrode portions per se is high, deformation of the piezoelectric elements  33   aa  to  33   dd  is disturbed by the rigidity of the electrode portions even if a distortion force is produced by the piezoelectric elements  33   aa  to  33   dd . Therefore, in Embodiment 2, configuration is made so that the electrodes for activating the piezoelectric elements are provided only in the surface to reduce the rigidity of the electrode portions per se. When the configuration is made thus, the piezoelectric elements  33   aa  to  33   dd  can be displaced easily. Incidentally, the low Young&#39;s modulus portion YL needs heat resistance against a head formation process which will be performed later, in addition to the low Young&#39;s modulus of elasticity. 
     The low Young&#39;s modulus portion YL may be a conductive material or may be an insulative material. Specific examples of the material forming the low Young&#39;s modulus portion YL are polyimide heat-resistant resins, aramid heat-resistant resins, and porous inorganic materials such as porous silica, foam metal, etc. 
     On the other hand, examples of the material allowed to be used as the conductor coating portion MD which is the high Young&#39;s modulus portion are metals such as copper (Cu), nickel (Ni), aluminum (Al), platinum (Pt) and gold (Au), and alloys of these metals. Besides these materials, conductive ceramics such as iridium oxide (IrO 2 ) and strontium ruthenate (SrRuO 3 ) can be used. 
     —Manufacturing Process— 
     The manufacturing process is as shown in  FIGS. 10A  to  10 E. 
     The initial process (specifically the steps  1  to  7  in Embodiment 1) is performed in the same manner as Embodiment 1 and description thereof will be omitted. The process after the step  7  in Embodiment 1 will be described below.  FIG. 10A  is a view showing the step  7  in Embodiment 1 (a view after the resist pattern  53  is removed from  FIG. 6G ). That is,  FIG. 10A  is a view showing a state after the grooves  57  for forming the electrode portions (the branch portions  45   a  to  45   d  and the branch portions  49   a  to  49   d ) are formed in the piezoelectric body layer  50 . 
     &lt;Step  18 &gt; 
     Then, as shown in  FIG. 10B , an MD thin film  69  for forming a conductor coating portion MD is formed on front surfaces of the grooves  57  by sputtering, vacuum vapor deposition, chemical vapor deposition (CVD), etc. On this occasion, the MD thin film  69  is formed so thinly that recesses are formed in positions of the MD thin film  69  corresponding to the grooves  57  after the formation of the MD thin film  69 . Then, as shown in  FIG. 10C , the recesses after the formation of the MD thin film  69  are filled with a low Young&#39;s modulus material  68  for forming a low Young&#39;s modulus portion YL. Incidentally, the filling is performed by spin coating or dip coating. Then, a CMP process is performed. Thus, branch portions ( 45   a  to  45   d  and  49   a  to  49   d ) for forming electrodes are formed ( FIG. 10D ). 
     &lt;Step  19 &gt; 
     Then, in step  19 , an insulating material film  65  and a head layer  67  are formed on the piezoelectric body layer  50  having these branch portions ( 45   a  to  45   d  and  49   a  to  49   d ) formed therein. That is, the insulating material film  65  and the head layer  67  are formed on the displacement portion  30 . The insulating material film  65  and the head layer  67  are formed in the same manner as in Embodiment 1. The head slider  5  is completed by the aforementioned manufacturing method ( FIG. 10E ). 
       FIG. 11  is a view showing a condition used for displacement simulation of the actuator  33  in another embodiment. That is, the condition was set so that each of the electrodes (branch layers  59  and  60 ) formed in a piezoelectric body layer  150  was made of an MD thin layer  169  and a low Young&#39;s modulus material  168 . Here, the piezoelectric body layer  150  is a layer corresponding to the piezoelectric body layer  50 . In addition, the branch layers  59  and  60  are layers corresponding to the branch portions ( 45   a  to  45   d  and  49   a  to  49   d ). 
     A condition corresponding to the insulating layer  35  was set so that a 0.5 μm-thick insulating layer  135  made of silicon oxide was formed on the front surface of the piezoelectric body layer  150  with the branch layers  59  and  60  formed therein. As shown in  FIG. 11 , each of the branch layers  59  and  60  was formed to have a size with a width of 1.5 μm and a depth of 3.0 μm and to have a taper angle set at 10°. Further, the distance between adjacent electrodes was set at 2.0 μm. When the taper angle is added to each of the electrodes (the branch layers  59  and  60 ) in this manner, a uniform thin film can be formed in each of the groove portions formed in the piezoelectric body layer  150 . When the taper angle is about 10°, there is little influence on the displacement quantity. As shown in Table 1, a condition was set so that copper (Cu) with a Young&#39;s modulus of 129 GPa was used as the material of the MD thin film  169 . 
       FIG. 12  shows a result of simulation in the case where copper (Cu) with a Young&#39;s modulus of 129 GPa was used as the low Young&#39;s modulus material  168 .  FIG. 13  shows a result of simulation in the case where polyimide (PI) with a Young&#39;s modulus of 4 GPa was used as the low Young&#39;s modulus material  168 .  FIG. 14  shows a result of simulation in the case where the portions of the low Young&#39;s modulus material  168  were replaced by hollows. 
     In  FIG. 12 , the maximum displacement quantity point MX was displaced by 6.21 nm. In  FIG. 13 , the maximum displacement quantity point MX was displaced by 6.36 nm. In  FIG. 14 , the maximum displacement quantity point MX was displaced by 6.38 nm. As described above, it is apparent that the displacement quantity increases as the material used as the low Young&#39;s modulus material  168  is softened. 
     Although the displacement quantity in  FIG. 14  is the largest, the strength of the head slider  5  is weakened by the hollow portions when the structure shown in  FIG. 14  is used. Therefore, from the viewpoint of practical use, the structure shown in  FIG. 13  is preferred. As described above, it is apparent that when a low Young&#39;s modulus material is used in part of each electrode, a larger displacement quantity can be ensured compared with the case where a high Young&#39;s modulus material is used in the whole of each electrode. 
     Embodiment 3 
     Embodiment 3 will be described below with reference to  FIG. 15  and  FIGS. 16A to 16H . 
       FIG. 15  is a schematic sectional view showing a head slider  5  in Embodiment 3. As shown in an enlarged view in  FIG. 15 , in Embodiment 3, an insulating underlying layer  70  is formed between electrode portions  45  and a lower electrode  32 . Although  FIG. 9  shows an example in which each of the electrode portions (the branch portions  45   a  to  45   d  and the branch portions  49   a  to  49   d ) has a low Young&#39;s modulus portion YL and a conductor coating portion MD,  FIG. 15  shows an example in which each electrode portion is provided as a single layer made of a conductive material for convenience&#39;s sake. Incidentally, each electrode portion in Embodiment 3 may be formed to have a low Young&#39;s modulus portion YL and a conductor coating portion MD, similarly to each electrode portion shown in  FIG. 9  (i.e. Embodiment 2). 
     A process of forming grooves in the piezoelectric body layer  50  is generally performed by dry etching as described in Embodiment 1. In the dry etching process, etching time is generally controlled to adjust the depth of each groove. Accordingly, the depth of the groove as a result of the process is affected by the state (forming state) of the piezoelectric body film  50  or the condition for the dry etching process. As described above, it is not easy to equalize the depths of the grooves accurately when the depths of the grooves are intended to be controlled by the etching time. As a result, there is a problem that the actuator characteristic cannot be stabilized because of wide variation (in groove depth) according to each lot. When the grooves are too deep, the distance between adjacent ones of the electrode portions (the branch portions  45   a  to  45   d  and the branch portions  49   a  to  49   d ) and the lower electrode  32  is reduced so that insulation performance between the electrode portions and the lower electrode  32  is lowered. 
     A underlying layer having a material composition different from that of the piezoelectric body layer  50  is formed between the electrode portions and the lower electrode  32 . When such a underlying layer is provided, plasma emission spectrochemical analysis can be applied during dry etching so that variation in groove depth can be suppressed. 
     —Manufacturing Process— 
     A manufacturing process in Embodiment 3 is shown in  FIGS. 16A to 16H . When the manufacturing process is performed in the same manner as the manufacturing method shown in Embodiment 1 (or Embodiment 2), description of the manufacturing process will be omitted. 
     Since the initial process (specifically the steps  1  and  2  in Embodiment 1) is formed in the same manner as in Embodiment 1, description of the initial process will be omitted. Step  3  and steps following the step  3  in Embodiment 1 will be described below. 
     &lt;Step  23 &gt; 
       FIG. 16A  is a view of a step following the step  2  of Embodiment 1. In this step, as shown in  FIG. 16A , an insulating underlying layer  70  is formed on the lower electrode layer  52  and then a piezoelectric body layer  50  is formed on the insulating underlying layer  70 . The insulating underlying layer  70  is formed of a material having a composition different from that of the piezoelectric body layer  50 . For example, BaTiO 3  is used as the material of the insulating underlying layer  70  while PZT is used as the material of the piezoelectric body layer  50 . Specifically, for example, a 1 μm-thick insulating underlying layer  70  of BaTiO 3  is first formed by sputtering. Successively, a 4 μm-thick piezoelectric body layer  50  of PZT is formed on the insulating underlying layer  70  also by sputtering. Here, it is preferable that the formation of the piezoelectric body layer  50  is continued from the formation of the insulating underlying layer  70  while the insulating underlying layer  70  is not exposed to the outside air. 
     &lt;Step  24 &gt; 
     Then, as shown in  FIG. 16B , a resist pattern  73  (a resist pattern  73  as a mask for forming grooves) is formed on a surface of the piezoelectric body layer  50 . For example, the resist pattern  73  is formed in the same manner as the resist pattern  53  in the step  6  of Embodiment 1. 
     &lt;Step  25 &gt; 
     Then, as shown in  FIG. 16C , grooves  77  are formed in the piezoelectric body layer  50 . The grooves  77  are formed in the same manner as the grooves  57  in Embodiment 1. Incidentally, in this step, the following well-known plasma emission spectrochemical analysis is performed in order to improve accuracy in forming grooves. First, etching is performed while the emission spectrum of etching plasma is monitored by a detector. The etching is terminated when emission due to barium (Ba) is detected by the detector. For example, a wavelength dispersion type detector made by Otsuka Electronics Co., Ltd. can be used as the detector. The wavelength dispersion type detector expresses the intensity of light with a specific wavelength in a spectrum. When, for example, a wavelength of (Ba) etc. is selected and the specific wavelength is fixed to the selected wavelength, the point of completion of etching can be detected by the detector. Successively, after the surface of the piezoelectric body layer  50  processed by oxygen ashing is cleaned, annealing is performed in an oxygen atmosphere. By the annealing in an oxygen atmosphere, damage given to the surface of the piezoelectric body layer  50  by plasma can be recovered. 
     Since the insulating underlying layer  70  is not present between the electrode portions (the branch portions  45   a  to  45   d  and the branch portions  49   a  to  49   d ), the material for forming the insulating underlying layer  70  need not be a piezoelectric material if the material is an insulating material. It is however preferable that the insulating underlying layer  70  is a layer (piezoelectric body) made of a piezoelectric material because a leakage of an electric field from the electrode portions acts on the insulating underlying layer  70 . It is further preferable that the insulating underlying layer  70  has the same crystal structure as that of the piezoelectric body layer  50  because the insulating underlying layer  70  is generally formed so as to be in contact with the piezoelectric body layer  50 . It is further preferable that the insulating underlying layer  70  has a grating constant close to that of the piezoelectric body layer  50  in addition to the same crystal structure as that of the piezoelectric body layer  50 . 
     When, for example, the aforementioned PZT is used as the material of the piezoelectric body layer  50 , it is preferable that perovskite type oxide which has the same crystal structure as that of PZT is used as the material of the insulating underlying layer  70 . Materials as candidates for the piezoelectric body layer  50  and the insulating underlying layer  70  and their grating constants will be listed below. 
     Left Side: Material Name/Right Side: Grating Constant (unit: nm) 
     (1) Candidate for Piezoelectric Body Layer  50   
     PZT: Pb(Zr,Ti)O 3 /0.401 
     (2) Candidates for Insulating Underlying Layer  70   
     PLZT: (Pb,La)(Zr,Ti)O 3 /0.408 
     PMNT: Pb(Mg,Nb,Ti)O 3 /0.401 
     BaTiO 3 /0.399 
     BST: (Ba,Sr)TiO 3 /0.399-0.39 
     When the piezoelectric body film  50  is made of PZT, the Zr/Ti ratio in the insulating underlying layer  70  may be changed. It is however preferable that the insulating underlying layer  70  has any element not contained in PZT so that the insulating underlying layer  70  can be detected easily by plasma emission spectrochemical analysis. In addition, it is preferable that the insulating underlying layer  70  is slower in etching speed than the piezoelectric body layer  50 . Moreover, when BaTiO 3  or BST is used as the material of the insulating underlying layer  70  while the piezoelectric body layer  50  is made of PZT, the difference in etching speed between the insulating underlying layer  70  and the piezoelectric body layer  50  can be increased to improve processing accuracy. That is, use of the aforementioned materials (in combination to increase the difference in etching speed) as the materials for forming the piezoelectric body layer  50  and the insulating underlying layer  70  is preferred to use of the same Pb oxide material as the materials for forming the piezoelectric body layer  50  and the insulating underlying layer  70 . 
     It is preferable that the dielectric constant of the insulating underlying layer  70  is higher than that of the piezoelectric body layer  50 . This is because the electric field applied to the piezoelectric body layer  50  is more intense than the electric field applied to the insulating underlying layer  70  during the step of polarizing the piezoelectric body layer  50 . Therefore, when the piezoelectric body layer  50  is made of PZT, for example, PMNT, BaTiO 3 , BST, etc. can be used as the material allowed to be used for the insulating underlying layer  70  to make the dielectric constant of the insulating underlying layer  70  higher than that of PZT. 
     &lt;Step  26 &gt; 
     Then, as shown in  FIG. 16D , a film of a resin material (not shown) is formed on the piezoelectric body layer  50  having the grooves  77  formed therein, so that a resin layer  71  is formed. The resin layer  71  plays a role of a sacrificial layer which will be removed finally. In the step of forming the resin material film, the resin material film is formed, for example, by spin coating so that at least the inside of each groove  77  is filled with the resin material. Then, a surface of the formed resin material film is cut, for example, by a CMP method until at least an upper surface of the piezoelectric body layer  50  is exposed. Thus, the resin layer  71  made of the resin material is formed in the inside of each groove  77  in the piezoelectric body layer  50 . As a result, the surfaces of the piezoelectric body layer  50  and the resin layer  71  are smoothened continuously. 
     &lt;Step  27 &gt; 
     Then, as shown in  FIG. 16E , local electrodes  78  are formed on the smoothened surface of the piezoelectric body layer  50 . For example, the local electrodes  78  are formed of the same material and in the same manner as the local electrodes  58  in the step  5  of Embodiment 1. Then, the piezoelectric body layer  50  is polarized by applying an electric field between the lower electrode layer  52  and each local electrode  78 . In Embodiment 3, first, every other local electrode  78  is selected from the local electrodes  78  and a polarizing process is applied to regions of the piezoelectric body layer  50  corresponding to the selected local electrodes  78 . Then, the remaining local electrodes  78  are selected and a polarizing process in a direction reverse to the previous polarizing process is applied to regions of the piezoelectric body layer  50  corresponding to the selected local electrodes  78 . 
     &lt;Step  27 &gt; 
     Then, as shown in  FIG. 16F  and  FIG. 16G , electrode portions (branch portions  85   a  to  85   d  and branch portions  89   a  to  89   d ) are formed in the portions of the grooves  77 . Specifically, the resin layer  71  remaining in the inside of each groove  77  is first removed by etching (not shown). Then, as shown in  FIG. 16F , a conductive material layer  72  is formed on the piezoelectric body layer  50  from which the resin layer  71  has been removed. The conductive material layer  72  is formed as follows. First, a film of copper (Cu) or gold (Au) with a thick of about 100 nm is formed by sputtering. Then, while this film is used as a seed layer, field plating with copper (Cu) or gold (Au) is performed so that the grooves  77  are filled with copper (Cu) or gold (Au). 
     Then, as shown in  FIG. 16G , a front surface of the conductive material layer  72  is polished, for example, by a CMP method. On this occasion, the local electrodes  78  are also polished so that the upper surface of the piezoelectric body layer  50  is exposed. When the local electrodes  78  are polished (ground) in this manner until the upper surface of the piezoelectric body layer  50  is exposed, an electrode portion made of the conductive material are formed in the inside of each groove  77  in the piezoelectric body layer  50 . That is, the branch portions  85   a  to  85   d  (branch portions  85 ) made of the conductive material and the branch portions  89   a  to  89   d  (branch portions  89 ) made of the conductive material are formed in the inside of the grooves  77  of the piezoelectric body layer  50 . Incidentally, the surface of the piezoelectric body layer  50  and the surfaces of the electrode portions are smoothened continuously because of polishing by the CMP method. 
     The material and formation method of the branch portions  85  and  89  can be made here in the same manner as those of the branch portions  45  and  49  in the step  8  of Embodiment 1. In this manner, the respective branch portions  85  and  89  can be electrically insulated from one another. 
     &lt;Step  28 &gt; 
     Then, as shown in  FIG. 16H , an insulating material film  65  and a head layer  67  are formed. The insulating material film  65  and the head layer  67  can be formed, for example, in the same manner as in the step  9  of Embodiment 1. 
     The depth accuracy of the electrode portions in the actuator  33  produced by the aforementioned method was ±0.1 μm. On the contrary, in the related-art method, that is, when the processing time for etching was controlled to adjust the depth of each groove, the depth accuracy of the electrode portions was ±0.5 μm. As described above, processing accuracy was improved greatly by the method according to Embodiment 3. When a underlying layer having a material composition different from that of the piezoelectric body layer  50  is provided between the electrode portions and the lower electrode  32  and plasma emission spectrochemical analysis is applied as described above, a point of time of completion of etching can be detected accurately. 
     Embodiment 4 
     Embodiment 4 will be described below with reference to  FIGS. 17 and 18 . 
       FIG. 17  is a schematic sectional view of a head slider according to Embodiment 4. As shown in  FIG. 17 , each electrode is configured so that two conductor coating portions MD′ are disposed on opposite sides of a low Young&#39;s modulus portion YL′, that is, a low Young&#39;s modulus portion YL′ is wedged between two conductor coating portions MD′. An electrode MD 1  which is one of the conductor coating portions MD′ (the two conductor coating portions MD′ provided on the opposite sides of the low Young&#39;s modulus portion YL′) is electrically insulated from the other conductor coating portion MD 2 . An electric potential different from that applied to the conductor coating portion MD 2  is applied to the conductor coating portion MD 1 . 
       FIG. 18  is a perspective view showing a schematic structure of an actuator  33  in Embodiment 4. As shown in  FIG. 18 , for example, each of branch portions  45   a  and  45   b  has two electrodes one of which is connected to a minus-side electrode  42  while the other is connected to a plus-side electrode  46 . 
     Similarly, each of branch portions  49   a  and  49   b  has two electrodes one of which is connected to the minus-side electrode  42  while the other is connected to the plus-side electrode  46 . Piezoelectric body films  41   aa ,  41   ab  and  41   bb  etc. are disposed between these branch portions. 
     —Manufacturing Process— 
     The manufacturing process in Embodiment 4 is shown in  FIGS. 19A to 19G . When the manufacturing process in Embodiment 4 is performed in the same manner as the manufacturing method shown in Embodiment 1 (or Embodiment 2 and Embodiment 3), description thereof will be omitted. 
     Since the initial process (specifically, the steps  1  to  7  in Embodiment 1) is formed in the same manner as in Embodiment 1, description of the initial process will be omitted. Step  7  and the steps following step  7  in Embodiment 1 will be described below.  FIG. 19A  is a view showing step  7  in Embodiment 1 (a view after the resist pattern  53  is removed from  FIG. 6G ). That is,  FIG. 19A  shows the state that grooves  57  for forming electrode portions (the branch portions  45   a  to  45   d  and the branch portions  49   a  to  49   d ) are formed in the piezoelectric body layer  50 . Incidentally, at this stage, the piezoelectric body layer  50  has been polarized. As shown in  FIG. 19A , the directions of polarization are made the same to be one direction, differently from other embodiments. 
     &lt;Step  38 &gt; 
     Then, as shown in  FIG. 19B , an MD thin film  69  for forming conductor coating portions MD is formed on surfaces of the grooves  57  by sputtering, vacuum vapor deposition, CVD, etc. On this occasion, the MD thin film  69  is formed so thinly that recesses are formed in positions corresponding to the grooves  57  in the MD thin film  69  after formation of the MD thin film  69 . 
     &lt;Step  39 &gt; 
     Then, as shown in  FIG. 19C , a resist pattern  78  is formed on the MD thin film  69 . Specifically, a photoresist material is first applied on the whole area of a front surface of the MD thin film  69  so that the inner walls of the recesses corresponding to the grooves  57  are also coated with the photoresist material. Then, as shown in  FIG. 19B , the photoresist material is partially removed from the centers (bottoms) of the recesses by exposure and development to thereby form a resist pattern  78 . 
     &lt;Step  40 &gt; 
     Then, as shown in  FIG. 19D , the MD thin film  69  is partially removed with use of the resist pattern  78  as a mask. Specifically, dry etching using argon (Ar) gas etc. is performed on the substrate having the resist pattern  78  formed therein. The MD thin film  69  is removed from the centers (i.e. portions where the photoresist material has been removed in the step  39 ) of the recesses by the dry etching process. 
     &lt;Step  41 &gt; 
     Then, as shown in  FIG. 19E , the resist pattern  78  is removed from the substrate processed by the step  40 . 
     &lt;Step  42 &gt; 
     Then, as shown in  FIG. 19F , an insulating material layer  71  is formed on the substrate after the resist pattern  78  is removed from the substrate. The formation of the insulating material layer  71  is performed in such a manner that the substrate is filled with an insulating material by spin coating or dip coating. Incidentally, a heat-resistant resin such as a polyimide resin or an aramid resin or a porous inorganic material such as porous silica or foam metal can be used as the insulating material. 
     &lt;Step  43 &gt; 
     Then, as shown in  FIG. 19G , a CMP process is performed so that branch portions ( 45   a  to  45   d  and  49   a  to  49   d ) for forming electrodes are formed. 
     &lt;Step  44 &gt; 
     Then, an insulating material film  65  and a head layer  67  are formed on the piezoelectric body layer  50  having the branch portions ( 45   a  to  45   d  and  49   a  to  49   d ) formed therein. That is, the insulating layer  35  and the head portion  37  are formed on the displacement portion  30 . The insulating material film  65  and the head layer  67  are formed in the same manner as in Embodiment 1. The head slider  5  is completed by the aforementioned manufacturing method. 
     Embodiment 5 
     Further, Embodiment 5 will be described with reference to  FIG. 20  and  FIGS. 21A to 21G . 
       FIG. 20  is a perspective view showing a schematic structure of an actuator  33  in Embodiment 5. As shown in  FIG. 20 , for example, a sensor  90  for measuring displacement of the actuator  33  is provided between an electrode  42  and an electrode  46 . Specifically, as shown in  FIG. 20 , the sensor  90  is formed, for example, in a layer the same in level as the insulating layer  35  provided on the actuator  33 . Opposite ends of the sensor  90  are electrically connected to electrodes  82  and  86  respectively. The electrodes  82  and  86  are provided on the electrode  42  side and the electrode  46  side, respectively. A groove portion  92  which is internally hollow is provided in the center of the sensor. 
     The sensor  90  is made of a piezoelectric material having a large piezoresistance effect. That is, for example, p-type silicon doped with boron (B) or aluminum (Al) or n-type silicon doped with phosphorus (P) or arsenic (As) can be used as the piezoelectric material of the sensor  90 . Beside these materials, semiconductor such as SiGe, conductive oxide such as LaSrMnO 3  or carbon nanotube can be used as the piezoelectric material. 
     —Manufacturing Process— 
     A manufacturing process in Embodiment 5 is shown in  FIGS. 21A to 21G . When the manufacturing process in Embodiment 5 is performed in the same manner as the manufacturing method shown in Embodiment 1 (or Embodiments 2 to 4), description thereof will be omitted. 
     Since the initial process (specifically the steps  1  to  7  in Embodiment 1) is formed in the same manner as in Embodiment 1, description of the initial process will be omitted. Step  7  and the steps following step  7  in Embodiment 1 will be described below.  FIG. 21A  is a view showing step  7  in Embodiment 1 (a view corresponding to  FIG. 6G  of Embodiment 1). That is,  FIG. 21A  shows the state where grooves  57  for forming electrode portions (the branch portions  45   a  to  45   d  and the branch portions  49   a  to  49   d ) are formed in the piezoelectric body layer  50 . Grooves  107  for forming a groove portion  92  and electrodes  82  and  86  are formed adjacently to the grooves  57  for forming the electrode portions. Incidentally, at this stage, regions of the piezoelectric body layer  50  where the electrode portions will be formed are polarized. 
     &lt;Step  48 &gt; 
     Then, as shown in  FIG. 21B , a resist pattern  53  is removed. 
     &lt;Step  49 &gt; 
     Then, as shown in  FIG. 21C , a resist pattern (not shown) is formed on all regions except the groove  107  in the center. Then, SiO 2  is deposited in the groove  107  in the center by sputtering to thereby form a sacrificial layer  102 . 
     &lt;Step  50 &gt; 
     Then, as shown in  FIG. 21D , all the grooves except the groove with the sacrificial layer  102  formed therein are filled with a conducting material. Branch layers  59  and  60  for forming electrodes are formed of the conducting material. 
     &lt;Step  51 &gt; 
     Then, as shown in  FIG. 21E , a sensor  90  is formed on the sacrificial layer  102 . A sacrificial layer  108  is formed on the sensor  90  so that the sensor  90  is covered with the sacrificial layer  108 . The sacrificial layer  108  is formed by deposition of SiO 2  by sputtering. 
     &lt;Step  52 &gt; 
     Then, as shown in  FIG. 21F , an insulating material film  65  is formed in a layer the same in level as the sacrificial layer  108 . Then, a head layer  67  is formed on the insulating material film  65 . 
     &lt;Step  53 &gt; 
     Then, as shown in  FIG. 21G , the sacrificial layer  102  and the sacrificial layer  108  are dissolved and removed by wet etching. Because a gap is formed around the sensor  90  in this manner, the displacement quantity of the actuator  33  can be measured accurately when the actuator  33  is displaced. Incidentally, the step of removing the sacrificial layers is performed after the substrate is separated into individual head sliders  5 . 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.