Patent Publication Number: US-7710691-B2

Title: Three terminal magnetic sensor having an in-stack longitudinal biasing layer structure in the collector region and a pinned layer structure in the emitter region

Description:
BACKGROUND 
     1. Field of the Technology 
     This invention relates generally to three terminal magnetic sensors (TTMs) suitable for use in magnetic heads, which includes spin valve transistors (SVTs), magnetic tunnel transistors (MTTs), or double junction structures. 
     2. Description of the Related Art 
     Magnetoresistive (MR) sensors have typically been used as read sensors in hard disk drives. An MR sensor detects magnetic field signals through the resistance changes of a read element, fabricated of a magnetic material, as a function of the strength and direction of magnetic flux being sensed by the read element. The conventional MR sensor, such as that used as a MR read head for reading data in magnetic recording disk drives, operates on the basis of the anisotropic magnetoresistive (AMR) effect of the bulk magnetic material, which is typically permalloy. A component of the read element resistance varies as the square of the cosine of the angle between the magnetization direction in the read element and the direction of sense current through the read element. Recorded data can be read from a magnetic medium, such as the disk in a disk drive, because the external field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the read element, which causes a change in resistance of the read element and a resulting change in the sensed current or voltage. 
     A three terminal magnetic sensor (TTM) of a magnetic head may comprise a spin valve transistor (SVT), for example, which is a vertical spin injection device having electrons injected over a barrier layer into a free layer. The electrons undergo spin-dependent scattering, and those that are only weakly scattered retain sufficient energy to traverse a second barrier. The current over the second barrier is referred to as the magneto-current. Conventional SVTs are constructed using a traditional three-terminal framework having an “emitter-base-collector” structure of a bipolar transistor. SVTs further include a spin valve (SV) on a metallic base region, whereby the collector current is controlled by the magnetic state of the base region using spin-dependent scattering. Although the TTM may involve an SVT where both barrier layers are Schottky barriers, the TTM may alternatively incorporate a magnetic tunnel transistor (MTT) where one of the barrier layers is a Schottky barrier and the other barrier layer is a tunnel barrier, or a double junction structure where both barrier layers are tunnel barriers. 
     Since it is advantageous to form a very thin base region for increased areal recording densities, it has been identified that the base region in the TTM will have a relatively large electrical resistance. Given an estimated trackwidth (TW) of approximately 50 nanometers (nm) for a magnetic head, for example, the electrical resistance of the base region may be much greater than 100Ω. Thus, as the sense current passes through the base region from the emitter lead to the base lead, the base region may be prone to failure or damage (e.g. it could “blow” like a fuse). Further, a relatively large resistance for the base region raises the noise floor for the TTM, such that a much larger input signal would be required for suitable operation. 
     Another important consideration is that the free layer should be longitudinally biased parallel to the sensing (or ABS) plane and parallel to the major planes of the thin film layers of the TTM, such that the free layer is magnetically stabilized. This has been typically accomplished by first and second hard bias magnetic layers which are adjacent to first and second sides of the TTM. Unfortunately, the magnetic field through the free layer between the first and second sides is not uniform since a portion of the magnetization is lost in a central region of the free layer to the shields. This is especially troublesome when the track width of the TTM may be in sub-micron dimensions. End portions of the free layer which abut the hard bias layers may be over-biased and become very magnetically stiff in their response to field signals from the moving media. The stiffened end portions can take up a large portion of the total length of the TTM and can significantly reduce the signal amplitude of the TTM. 
     Accordingly, there is a need to solve these problems so that TTMs may be suitable for use in magnetic heads and other devices. 
     SUMMARY 
     In one illustrative embodiment of the present application, a three terminal magnetic sensor (TTM) suitable for use in a magnetic head has a sensor stack structure which includes a base region, a collector region, and an emitter region. A first barrier layer separates the emitter region from the base region, and a second barrier layer separates the collector region from the base region. A plurality of terminals of the TTM include a base lead coupled to the base region, a collector lead coupled to the collector region, and an emitter lead coupled to the emitter region. Preferably, the base region consists of a free layer structure so as to have a relatively small thickness. A pinned layer structure is made part of the emitter region. An in-stack longitudinal biasing layer (LBL) structure is formed in stack with the sensor stack structure and has a magnetic moment that is parallel to a sensing plane of the TTM for magnetically biasing the free layer structure. The in-stack LBL structure is made part of the collector region which also includes a layer of semiconductor material. In one variation, the emitter region has the in-stack LBL structure and the collector region has the pinned layer structure. The TTM may comprise a spin valve transistor (SVT), a magnetic tunnel transistor (MTT), or a double junction structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages of the invention will become more apparent to those skilled in the art after considering the following detailed description in connection with the accompanying drawings. 
         FIG. 1  is a cross-sectional view of a disk drive which may embody a magnetic head having a three terminal magnetic sensor (TTM) comprising a spin valve transistor (SVT); 
         FIG. 2  is a top-down view of the disk drive of  FIG. 1 ; 
         FIG. 3  is an illustration for general SVT operation; 
         FIG. 4  is a perspective view of a TTM having a metal layer formed so as to reduce the base resistance; 
         FIG. 5  is a perspective view of another TTM having an alternative metal layer formed so as to reduce the base resistance; 
         FIG. 6  is a perspective view of yet another TTM having an alternative metal layer formed so as to reduce the emitter resistance; 
         FIG. 7A  is a sensor plane (or ABS) view of one embodiment of a TTM which includes a base region having a free layer structure, a pinned layer structure, and an in-stack longitudinal biasing layer (LBL) structure which magnetically biases the free layer structure; 
         FIG. 7B  is a sensor plane (or ABS) view of one variation of the embodiment of  FIG. 7A  where the layers in the base region are inverted; 
         FIG. 7C  is a sensor plane (or ABS) view of another variation of the embodiment of  FIG. 7A , where the base region has the free layer structure, the in-stack longitudinal biasing layer (LBL) structure, and a self-pinned layer structure; 
         FIG. 7D  is a sensor plane (or ABS) view of a variation of the embodiment of  FIG. 7C , where the base region has the free layer structure, the self-pinned layer structure, and the in-stack longitudinal biasing layer (LBL) structure which also has a self-pinned layer structure; 
         FIG. 8A  is a sensor plane (or ABS) view of another embodiment of a TTM, the TTM including a base region having a free layer structure and a pinned layer structure, and a collector region having an in-stack LBL structure which magnetically biases the free layer structure; 
         FIG. 8B  is a sensor plane (or ABS) view of one variation of the embodiment of  FIG. 8A , where the layers of the base region and the in-stack LBL structure are inverted such that the base region has the free layer structure and the pinned layer structure and the emitter region has the in-stack LBL structure; 
         FIG. 8C  is a sensor plane (or ABS) view of another variation of the embodiment of  FIG. 8A , where the base region has the free layer structure and a self-pinned layer structure and the collector region has the in-stack LBL structure; 
         FIG. 8D  is a sensor plane (or ABS) view of a variation of the embodiment of  FIG. 8C , where the base region has the free layer structure and the self-pinned layer structure and the collector region has the in-stack LBL structure which also includes a self-pinned layer structure; 
         FIG. 9A  is a sensor plane (or ABS) view of yet another embodiment of a TTM, the TTM including a base region having a free layer structure, an emitter region having a pinned layer structure, and a collector region having an in-stack LBL structure which magnetically biases the free layer structure; 
         FIG. 9B  is a sensor plane (or ABS) view of one variation of the embodiment of  FIG. 9A , where the base region has the free layer structure, the emitter region has the in-stack LBL structure, and the collector region has the pinned layer structure; 
         FIG. 9C  is a sensor plane (or ABS) view of another variation of the embodiment of  FIG. 9A , where the base region has the free layer structure, the emitter region has a self-pinned layer structure, and the collector region has the in-stack LBL structure; 
         FIG. 9D  is a sensor plane (or ABS) view of a variation of the embodiment of  FIG. 9C , where the base region has the free layer structure, the emitter region has the self-pinned layer structure, and the collector region has the in-stack LBL structure which also includes a self-pinned layer structure; 
         FIG. 10  is a sensor plane (or ABS) view of a final embodiment of a TTM of the double tunnel junction type which includes a base region having a free layer structure, an emitter region having a pinned layer structure, and a collector region having an in-stack LBL structure which magnetically biases the free layer structure; 
         FIG. 11  is a sensor plane (or ABS) view of an antiparallel (AP) pinned layer structure for use in the TTMs of  FIGS. 7-10 ; and 
         FIGS. 12A-21B  are illustrations of a TTM being fabricated according to a particular method, preferably in the order presented. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In one illustrative embodiment of the present application, a three terminal magnetic sensor (TTM) suitable for use in a magnetic head has a base region, a collector region, and an emitter region. A first barrier layer separates the emitter region from the base region, and a second barrier layer separates the collector region from the base region. A sensing plane is defined along sides of the base region, the collector region, and the emitter region. The base region consists of a free layer structure so as to have a relatively small thickness. A pinned layer structure is made part of the emitter region. An in-stack longitudinal biasing layer (LBL) structure which magnetically biases the free layer structure is made part of the collector region. In one variation, the emitter region has the in-stack LBL structure and the collector region has the pinned layer structure. The TTM may comprise a spin valve transistor (SVT), a magnetic tunnel transistor (MTT), or a double junction structure. 
     The following description is the best embodiment presently contemplated for carrying out the present invention. This description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. 
       FIG. 1  is a simplified block diagram of a conventional magnetic recording disk drive for use with a three terminal magnetic sensor (TTM) of a magnetic head.  FIG. 2  is a top view of the disk drive of  FIG. 1  with the cover removed. Referring first to  FIG. 1 , there is illustrated in a sectional view a schematic of a conventional disk drive of the type using a TTM. The disk drive comprises a base  510  to which are secured a disk drive motor  512  and an actuator  514 , and a cover  511 . Base  510  and cover  511  provide a substantially sealed housing for the disk drive. Typically, there is a gasket  513  located between base  510  and cover  511  and a small breather port (not shown) for equalizing pressure between the interior of the disk drive and the outside environment. A magnetic recording disk  516  is connected to drive motor  512  by means of a hub  518  to which it is attached for rotation by drive motor  512 . A thin lubricant film  550  is maintained on the surface of disk  516 . A read/write head or transducer  525  is formed on the trailing end of a carrier, such as an air-bearing slider  520 . Transducer  525  is a read/write head comprising an inductive write head portion and a read head portion. Slider  520  is connected to actuator  514  by means of a rigid arm  522  and a suspension  524 . Suspension  524  provides a biasing force which urges slider  520  onto the surface of the recording disk  516 . During operation of the disk drive, drive motor  512  rotates disk  516  at a constant speed, and actuator  514 , which is typically a linear or rotary voice coil motor (VCM), moves slider  520  generally radially across the surface of disk  516  so that read/write head  525  may access different data tracks on disk  516 . 
       FIG. 2  illustrates in better detail suspension  524  which provides a force to slider  520  to urge it toward disk  516 . Suspension  524  may be a conventional type of suspension, such as the well-known Watrous suspension, as described in U.S. Pat. No. 4,167,765. This type of suspension also provides a gimbaled attachment of the slider which allows the slider to pitch and roll as it rides on the air bearing surface. The data detected from disk  516  by transducer  525  is processed into a data readback signal by signal amplification and processing circuitry in an integrated circuit chip  515  located on arm  522 . The signals from transducer  525  travel via a flex cable  517  to chip  515 , which sends its output signals to the disk drive electronics (not shown) via cable  519 . 
       FIG. 3  illustrates TTM operation associated with a spin valve transistor (SVT)  300  which has a semiconductor emitter region  302 , a semiconductor collector region  304 , and a base region  306  which contains a spin valve (SV). The semiconductors and magnetic materials used in SVT  300  may include an n-type silicon (Si) material for emitter  302  and collector  304 , and a Ni 80 Fe 20 /Au/Co spin valve for the region  306 . Energy barriers, also referred to as Schottky barriers, are formed at the junctions between the metal base  306  and the semiconductors. It is desirable to obtain a high quality energy barrier at these junctions with good rectifying behavior. Therefore, thin layers of materials (e.g. platinum and gold) are oftentimes used at the emitter  302  and collector  304 , respectively. Moreover, these thin layers separate the magnetic layers from the semiconductor materials. 
     A TTM operates when current is introduced between emitter region  302  and base region  306 , denoted as I E  in  FIG. 3 . This occurs when electrons are injected over the energy barrier and into base region  306  by biasing the emitter such that the electrons are traveling perpendicular to the layers of the spin valve. Because the electrons are injected over the energy barrier, they enter base region  306  as non-equilibrium hot electrons, whereby the hot-electron energy is typically in the range of 0.5 and 1.0 eV depending upon the selection of the metal/semiconductor combination. The energy and momentum distribution of the hot electrons change as the electrons move through base region  306  and are subjected to inelastic and elastic scattering. As such, electrons are prevented from entering collector region  304  if their energy is insufficient to overcome the energy barrier at the collector side. Moreover, the hot-electron momentum must match with the available states in the collector semiconductor to allow for the electrons to enter collector region  304 . The collector current I C , which indicates the fraction of electrons collected in collector region  304 , is dependent upon the scattering in base region  306  which is spin-dependent when base region  306  contains magnetic materials. Furthermore, an external applied magnetic field controls the total scattering rate which may, for example, change the relative magnetic alignment of the two ferromagnetic layers of the spin valve. The magnetocurrent (MC), which is the magnetic response of the TTM, can be represented by the change in collector current normalized to the minimum value as provided by the following formula: MC=[I P   C −I AP   C ]/I AP   C  where P and AP indicate the parallel and antiparallel state of the spin valve, respectively. 
     In  FIG. 4 , a three terminal magnetic sensor (TTM)  400  of the spin valve transistor (SVT) type is shown. Although described as incorporating an SVT (where both barrier layers are Schottky barriers), the TTM may alternatively incorporate a magnetic tunnel transistor (MTT) (where one of the barrier layers is a Schottky barrier and the other barrier layer is a tunnel barrier), or a double junction structure (where both barrier layers are tunnel barriers). TTM  400  of  FIG. 4  has a base region  15 , a collector region  20  which is adjacent base region  15 , an emitter region  5 , and a barrier region  10  which separates emitter region  5  from base region  15 . As described in relation to  FIG. 3 , collector region  20  may be a semiconductor substrate made of silicon (Si). Base region  15  preferably includes at least one soft ferromagnetic (FM) material, such as nickel-iron (NiFe), cobalt-iron (CoFe), or cobalt (Co), as well as a very thin metal (e.g. gold) which is sandwiched in between the FM materials. Barrier layer  10  is a non-magnetic insulating material, preferably made of aluminum-oxide, which is generally less than 10 Angstroms (Å) in thickness. 
     As indicated in  FIG. 4 , a trackwidth W T  of the magnetic head is defined by the dimension of emitter region  5 , base region  15 , and collector region  20  along the y-axis, while a stripe height H S  of the magnetic head is defined by the dimension of emitter region  5  along the x-axis. A sensing plane  1020  of TTM  400  is defined along sides of base region  15 , collector region  20 , and emitter region  5 . This sensing plane  1020  is at an air bearing surface (ABS) when TTM  400  is embodied in a magnetic head. A non-magnetic insulator layer  1012  is offset behind sensing plane  1020  and adjacent collector region  20  and base region  15 . Insulator layer  1012  may be, for example, an oxide materials such as alumina. An emitter lead  35 , which may be embodied as a ferromagnetic (FM) shield for TTM  400 , is positioned in contact with emitter region  5  at sensing plane  1020 . Emitter lead  35  serves as the electrical connection for emitter region  5  to an external lead (not visible in  FIG. 4 ). A base lead  36  is positioned in contact with base region  15  behind sensing plane  1020 . Base lead  36  and a collector lead (not visible in  FIG. 4 ) are preferably not formed along sensing plane  1020 . Note that additional or alternative leads may be formed in the TTM, which has at least three leads. 
     The TTM allows hot electrons emitted from emitter region  5  to travel through to base region  15  to reach collector region  20 , which collects the magnetocurrent (i.e. collects the electrons). In operation, the device acts as a hot spin electron filter whereby barrier region  10  between emitter region  5  and base region  15  operates to selectively allow the hot electrons to pass on through to base region  15  and then on through collector region  20 . When TTM  400  is not functioning, the device is in a known quiescent state. In this case, the magnetization of the free layer which comprises all or part of base region  15  is parallel to the ABS plane. The direction of this magnetization depends on the direction of the magnetic field produced by a pinned layer (not visible) formed adjacent the free layer. The scattering of electrons within the free layer is dependent upon the orientation of the magnetization within the free layer. For example, if the magnetization is pointing in the parallel direction relative to the pinned layer (i.e. parallel to the ABS plane), then the electrons are not scattered as much as compared to the case where the free layer is antiparallel relative to the pinned layer. The performance of the device may be different depending upon the relative configuration of emitter region  5 , the free layer, and the hard bias layer. 
     Since it is advantageous to form a very thin base region  15  (e.g. between about 20-200 Å) for increased areal recording densities, base region  15  will have a relatively large electrical resistance if nothing is done to reduce it. With the trackwidth (TW) of the magnetic head being defined at between about 10 and 100 nanometers (nm) (e.g. approximately 50 nm), the electrical resistance of base region  15  may be much greater than 100Ω. Thus, as the sense current passes through base region  15  from emitter lead  35  to base lead  36 , base region  15  may be vulnerable to damage or failure (e.g. it could “blow” like a fuse). A relatively large resistance of base region  15  also raises the noise floor for the TTM  400  such that a much larger input signal for TTM  400  would be required for suitable operation. 
     Accordingly, a metal layer  1050  is formed in TTM  400  so as to be offset from sensing plane  1020  and in-plane and in contact with magnetic materials of base region  15 . In  FIG. 4 , metal layer  1050  is formed in contact with insulator layer  1012  but not in contact with base lead  36 . This metal layer  1050  is thicker than any other metal film which may be formed within base region  15  itself; metal layer  1050  is preferably formed to a thickness of between 50-500% (at least 50%) of the total thickness of base region  15 . For example, metal layer  1050  may be formed to a thickness of between about 100-1000 Å. Note that metal layer  1050  stops where insulator layer  1012  ends; it does not extend over collector region  20 . If a metal were formed over a collector via  22  where collector region  20  meets base region  15 , it would cause a short between the two leads. As an alternative to or in combination with metal layer  1050 , TTM  400  of  FIG. 4  also shows that a metal layer  1050  may be formed adjacent and between (in contact with) insulator layer  1012  and base lead  36 . In addition, an alternative TTM  500  of  FIG. 5  shows that metal layer  1050  may be alternatively formed along a top surface of base region  15  and in contact with base lead, not formed in contact with insulator layer  1012 , and otherwise being the same as that shown and described in relation to  FIG. 4 . 
     Such metal layers of  FIGS. 4 and 5  reduce the electrical resistance of base region  15 , which is advantageous as it serves to reduce signal noise in TTM  400  by lowering the noise floor. Preferably, metal layer  1050  has an electrical resistivity of less than 10 μΩ-centimeter (cm). For example, metal layer  1050  may be made of copper (Cu), gold (Au), ruthenium (Ru), alloys and/or combinations thereof. Copper has an approximate electrical resistivity of 2 μΩ-cm, gold has an approximate electrical resistivity of 5 μΩ-cm, and ruthenium has an approximate electrical resistivity of 7 μΩ-cm. In comparison, base region  15  alone with magnetic materials (e.g. ferromagnetic (FM) materials such as nickel-iron (NiFe) and cobalt-iron (CoFe) may have an electrical resistivity of between about 18-40 μΩ-cm. On the other hand, the electrical resistivity of combined materials for base region  15  and metal layer  1050  may be between about 2-18 μΩ-cm. As a result, the combined layer may have a combined electrical resistance of between about 5-100 Ω. 
     As an alternative to or in combination with the metal layers of  FIG. 4  or  5 , a TTM  600  of  FIG. 6  shows that a metal layer  1054  may be formed in plane and in contact with magnetic materials of emitter region  5 . This TTM  600  of  FIG. 6  has a different construction than that shown and described in relation to  FIGS. 4 and 5 . Comparing the embodiment of  FIG. 6  with that of  FIG. 4 , emitter region  5  extends much further behind sensing plane  1020 . Emitter lead  35  of  FIG. 6  is located where the previous base lead in  FIG. 4  was formed and base lead  36  of  FIG. 6  is located where the previous metal layer in  FIG. 4  was formed. Again, this metal layer  1054  is formed in plane and in contact with magnetic materials of emitter region  5 . Metal layer  1054  is also formed in contact with emitter lead  35 . This metal layer  1054  is offset from sensing plane  1020  and does not make contact with collector region  20 . Otherwise metal layer  1054  of  FIG. 6  may be the same or similar to that described in relation to  FIG. 4 , where it reduces the electrical resistance of emitter region  5  with the same or similar results. 
       FIG. 7A  is a sensing plane (or ABS) view of one embodiment of a three terminal magnetic sensor (TTM)  700   a  of the present application. TTM  700   a  of  FIG. 7A  has the general structure and functionality as described above in relation to the drawings, with or without having the metal layer for reduced lead resistance. As shown in  FIG. 7A , TTM  700   a  has an emitter region  702 , a base region  704 , and a collector region  706 . A first barrier layer  708  is located between emitter region  702  and base region  704 , and a second barrier layer  726  is located between collector region  706  and base region  704 . First barrier layer  708  may be a Schottky barrier (electrically conductive material) or a tunnel barrier (insulator material). Similarly, second barrier layer  726  may be a Schottky barrier (electrically conductive material) or a tunnel barrier (insulator material). Emitter region  702  has one or more emitter layers  728  which may be or include a silicon layer or a ferromagnetic (FM) layer such as nickel-iron. Collector region  706  has one or more collector layers  730  which may be or include a silicon layer or an FM layer such as nickel-iron. 
     In this embodiment, base region  704  includes a free layer structure  714 , a pinned layer structure  712 , an antiferromagnetic (AFM) pinning layer  718 , a first non-magnetic spacer layer  720 , an in-stack longitudinal biasing layer (LBL) structure  716 , and a second non-magnetic spacer layer  726 . Pinned layer structure  712  is adjacent first non-magnetic spacer layer  720 , which is in turn adjacent free layer structure  714 . An FM pinned layer of pinned layer structure  712  is magnetically pinned by exchange-coupling with AFM pinning layer  718 . AFM pinning layer  718  is located between and adjacent pinned layer structure  712  and first barrier layer  708 . The pinning field generated by AFM pinning layer  718  should be greater than demagnetizing fields to ensure that the magnetization direction of the FM pinned layer remains fixed during application of external fields (e.g. fields from bits recorded on the disk). The magnetization of free layer structure  714  is not fixed and is free to rotate in response to the field from the information recorded on the magnetic medium (i.e. the signal field). 
     Pinned layer structure  712  may be a single FM layer or, alternatively, a multi-layer structure. In particular, pinned layer structure  712  may be an antiparallel (AP) pinned layer structure as shown in  FIG. 11 . In  FIG. 11 , an AP pinned layer structure  1100  includes a first AP pinned layer  1102 , a second AP pinned layer  1104 , and an AP coupling layer  1106  formed between first and second AP pinned layers  1102  and  1104 . First AP pinned layer  1102 , for example, may be the layer that is exchange-coupled to and pinned by the AFM pinning layer  718 . By strong antiparallel coupling between the first and second AP pinned layers  1102  and  1104 , the magnetic moment of second AP pinned layer  1104  is made antiparallel to the magnetic moment of first AP pinned layer  1102 . 
     In-stack LBL structure  716  is located adjacent and between free layer structure  714  and second barrier layer  726 . Being formed “in-stack” with the sensor layers, LBL structure  716  is formed within the central region of the sensor but not within side regions thereof. LBL structure  716  includes a pinned layer structure  722 , an AFM pinning layer  724 , and a non-magnetic spacer layer  726 . AFM pinning layer  724  of LBL structure  716  is located between and adjacent pinned layer structure  722  and second barrier layer  710 . FM pinned layer  712  is magnetically pinned by exchange-coupling with an AFM pinning layer  718 . In particular, AFM pinning layer  724  pins a magnetic moment of pinned layer structure  722  parallel to the ABS and parallel to the planes of the sensor layers as indicated. Spacer layer  726  causes pinned layer structure  722  and free layer structure  714  to be physically separated but in close proximity to each other. Because of pinned layer structure  722 , the magnetic moment of free layer structure  714  is magnetically stabilized parallel to the ABS and parallel to the major planes of the sensor as indicated by the dashed arrows. This biasing is uniform from the sides of free layer structure  714  so that the biasing does not cause a limitation on narrow track width sensors. Pinned layer structure  722  may be a single FM layer or alternatively a multi-layer structure, and may include an AP pinned structure as previously shown and described in relation to  FIG. 11 . Spacer layer  726  may be chosen to provide either weakly ferromagnetic coupling or AP-coupling between pinned layer structure  722  and free layer structure  714 . 
     Note that AFM pinning layer  724  of LBL structure  716  should preferably magnetically pin at a different temperature than AFM pinning layer  718 . The reason is so that, during TTM fabrication, the pinning achieved for AFM pinning layer  724  will not be adversely affected by the subsequent pinning process utilized for AFM pinning layer  718 . As is known, the pinning of AFM pinning layers is typically achieved by heating the AFM materials to a predetermined temperature and applying a magnetic field at the same time. Preferably, to obtain the difference in pinning temperatures, AFM pinning layer  724  is made of a different material than that of AFM pinning layer  718 . For example, AFM pinning layer  718  may be made of platinum-manganese (PtMn) and AFM pinning layer  724  may be made of iridium-manganese (IrMn). A similar result may be achieved by utilizing the same materials for AFM pinning layers  718  and  724  with different thicknesses. More generally, the choice of any AFM material and its thickness may vary. The AFM layers may be the same material or alternatively have the same thickness. Preferably, the AFM layers are made of different materials and have different thicknesses. 
     Exemplary thicknesses and materials of TTM  700   a  are indicated in  FIG. 7A . In-stack longitudinal bias layer structure  716  has AFM pinning layer  724  made of platinum-manganese (PtMn) with a thickness of about 150 Angstroms, pinned layer  724  made of cobalt-iron (CoFe) with a thickness of about 20 Angstroms, and spacer layer  726  made of tantalum (Ta) with a thickness of about 20 Angstroms. AFM pinning layer  718  is made of iridium-manganese (IrMn) with a thickness of about 80 Angstroms, pinned layer  712  made of cobalt-iron (CoFe) with a thickness of about 20 Angstroms, and spacer layer  720  made of copper (Cu) with a thickness of about 20 Angstroms. Free layer structure  714  is made of nickel-iron (NiFe) with a thickness of about 40 Angstroms. 
     Preferably, there is a predetermined relationship established between the magnetic thickness of the pinned layer structure  722  of LBL structure  716  and the magnetic thickness of free layer structure  714 . Preferably, the magnetic thickness of pinned layer structure  722  is made to be substantially the same as the magnetic thickness of free layer structure  714 . However, the magnetic thickness of the pin layer may be between 50-500% of the thickness of the free layer. 
     One variation of the TTM  700   a  of  FIG. 7A  is a TTM  700   b  shown in  FIG. 7B . TTM  700   b  of  FIG. 7B  is the same as TTM  700   a  of  FIG. 7A  except that the layers in base region  704  are inverted as shown. Another variation of the TTM  700   a  of  FIG. 7A  is a TTM  700   c  shown in  FIG. 7C . TTM  700   c  of  FIG. 7C  is the same as TTM  700   a  of FIG.  7 A except that base region  704   c  includes a self-pinned layer structure  712   c  as the pinned layer structure. For TTM  700   c , the AFM pinning layer  718  of the TTM  700   a  of  FIG. 7A  is not needed for pinning purposes. A sensor of the self-pinned type relies on magnetostriction of the self-pinned structure and the ABS stress for a self-pinning effect. The AFM pinning layer, which is typically as thick as 150 Angstroms, is no longer necessary for pinning purposes so that a thinner sensor can be made. TTM  700   d  of  FIG. 7D  is another structural variation where LBL structure  716   d  also has a self-pinned layer structure  722   d . Note that the self-pinned layer structure  722   d  of  FIG. 7D  may include one or multiple layers of materials. In this variation, structure  712   c  may or may not be self-pinned. 
       FIG. 8A  is a sensing plane (or ABS) view of another embodiment of a TTM  800   a  of the present application. TTM  800   a  of  FIG. 8A  has the general structure and functionality of the TTM shown and described above in relation to the drawings, with or without having the metal layer for reduced lead resistance. As shown in  FIG. 8A , TTM  800   a  has an emitter region  802 , a base region  804 , and a collector region  806 . A first barrier layer  808  is located between emitter region  802  and base region  804 , and a second barrier layer  826  is located between collector region  806  and base region  804 . First barrier layer  808  may be a Schottky barrier (electrically conductive material) or a tunnel barrier (insulator material). Similarly, second barrier layer  826  may be a Schottky barrier (electrically conductive material) or a tunnel barrier (insulator material). Emitter region  802  has one or more emitter layers  828  which may be or include a silicon layer or an FM layer such as nickel-iron. 
     In this embodiment, base region  804  includes a free layer structure  814 , a pinned layer structure  812 , an AFM pinning layer  818 , and a non-magnetic spacer layer  820 . Pinned layer structure  812  is adjacent first non-magnetic spacer layer  820 , which is in turn adjacent free layer structure  814 . An FM pinned layer of pinned layer structure  812  is magnetically pinned by exchange-coupling with AFM pinning layer  818 . AFM pinning layer  818  is located between and adjacent pinned layer structure  812  and first barrier layer  808 . The pinning field generated by AFM pinning layer  818  should be greater than demagnetizing fields to ensure that the magnetization direction of the FM pinned layer remains fixed during application of external fields (e.g. fields from bits recorded on the disk). The magnetization of free layer structure  814  is not fixed and is free to rotate in response to the field from the information recorded on the magnetic medium (i.e. the signal field). Pinned layer structure  812  may be a single FM layer or, alternatively, a multi-layer structure. In particular, pinned layer structure  812  may be an AP pinned layer structure as shown and described earlier in relation to  FIG. 11 . 
     Collector region  806  has an in-stack LBL structure  816 . Collector region  806  may also have one or more other collector layers  830  which may be or include a silicon layer or an FM layer such as nickel-iron. Being formed “in-stack” with the sensor layers, LBL structure  816  of collector region  806  is formed within the central region of the sensor but not within side regions thereof. LBL structure  816  includes a pinned layer structure  828  and an AFM pinning layer  824 . Second barrier layer  826  is formed between LBL structure  816  and free layer structure  814 , causing pinned layer structure  822  and free layer structure  814  to be physically separated but in close proximity to each other. As apparent, second barrier layer  826  simultaneously serves as a spacer layer for LBL structure  816 ; no separate spacer layer is needed. Note that since base region  806  does not contain LBL structure  816 , base region  806  has a smaller thickness for an improved signal in the TTM  800 . 
     Pinned layer structure  822  of LBL structure  816  is magnetically pinned by exchange-coupling with AFM pinning layer  824 . In particular, AFM pinning layer  824  pins a magnetic moment of pinned layer structure  822  parallel to the ABS and parallel to the planes of the sensor layers as indicated. Because of pinned layer structure  822 , the magnetic moment of free layer structure  814  is magnetically stabilized parallel to the ABS and parallel to the major planes of the sensor as indicated by the dashed arrows. This biasing is uniform from the sides of free layer structure  814  so that the biasing does not cause a limitation on narrow track width sensors. Pinned layer structure  822  may be a single FM layer or alternatively a multi-layer structure, and may include an AP pinned structure as previously shown and described in relation to  FIG. 11 . 
     Note that AFM pinning layer  824  of LBL structure  816  should preferably magnetically pin at a different temperature than AFM pinning layer  818 . The reason is so that, during TTM fabrication, the pinning achieved for AFM pinning layer  824  will not be adversely affected by the subsequent pinning process utilized for AFM pinning layer  818 . As is known, the pinning of AFM pinning layers is typically achieved by heating the AFM materials to a predetermined temperature and applying a magnetic field at the same time. Preferably, to obtain the difference in pinning temperatures, AFM pinning layer  824  is made of a different material than that of AFM pinning layer  818 . For example, AFM pinning layer  818  may be made of platinum-manganese (PtMn) and AFM pinning layer  824  may be made of iridium-manganese (IrMn). A similar result may be achieved by utilizing the same materials for AFM pinning layers  818  and  824  with different thicknesses. More generally, the choice of any AFM material and its thickness may vary. The AFM layers may be the same material or alternatively have the same thickness. Preferably, the AFM layers are made of different materials and have different thicknesses. 
     Exemplary thicknesses and materials of TTM  800   a  are indicated in  FIG. 8A . In-stack longitudinal bias layer structure  816  has AFM pinning layer  824  made of platinum-manganese (PtMn) with a thickness of about 180 Angstroms and pinned layer  822  made of cobalt-iron (CoFe) with a thickness of about 20 Angstroms. AFM pinning layer  818  is made of iridium-manganese (IrMn) with a thickness of about 80 Angstroms, pinned layer  812  made of cobalt-iron (CoFe) with a thickness of about 20 Angstroms, and spacer layer  820  made of copper (Cu) with a thickness of about 20 Angstroms. Free layer structure  814  is made of nickel-iron (NiFe) with a thickness of about 40 Angstroms. 
     Preferably, there is a predetermined relationship established between the magnetic thickness of the pinned layer structure  822  of LBL structure  816  and the magnetic thickness of free layer structure  814 . In particular, the magnetic thickness of pinned layer structure  822  is made to be substantially the same as the magnetic thickness of free layer structure  814 . However, the magnetic thickness of the pinned layer may be between 50-500% of the thickness of the free layer. 
     One variation of the TTM  800   a  of  FIG. 8A  is a TTM  800   b  shown in  FIG. 8B . TTM  800   b  of  FIG. 8B  is the same as TTM  800   a  of  FIG. 8A  except that the layers are inverted as shown, such that an emitter region  802   b  includes in-stack LBL structure  816  and base region  804   b  includes free layer structure  814  and pinned layer structure  812 . Another variation of the TTM  800   a  of  FIG. 8A  is a TTM  800   c  shown in  FIG. 8C . TTM  800   c  of  FIG. 8C  is the same as TTM  800   a  of  FIG. 8A  except that a base region  804   c  includes a self-pinned layer structure  812   c  as the pinned layer structure. For TIM  800   c , the AFM pinning layer  818  of the TIM  800   a  of  FIG. 8A  is not needed for pinning purposes. A sensor of the self-pinned type relies on magnetostriction of the self-pinned structure and the ABS stress for a self-pinning effect. The AFM pinning layer, which is typically as thick as 150 Angstroms, is no longer necessary for pinning purposes so that a thinner sensor can be made. TTM  800   d  of  FIG. 8D  is another structural variation where LBL structure  816   d  also has a self-pinned layer structure  822   d . Note that the self-pinned layer structure  822   d  of  FIG. 8D  may include one or multiple layers of materials. In this variation, structure  812   c  may or may not be self-pinned. 
       FIG. 9A  is a sensing plane (or ABS) view of yet another embodiment of a TTM  900   a  of the present application. TTM  900   a  of  FIG. 9A  has the general structure and functionality of the TTM shown and described above in relation to the drawings, with or without having the metal layer for reduced lead resistance. As shown in  FIG. 9A , TTM  900   a  has an emitter region  902 , a base region  904 , and a collector region  906 . A first barrier layer  920  is located between emitter region  902  and base region  904 , and a second barrier layer  926  is located between collector region  906  and base region  904 . First barrier layer  920  may be a Schottky barrier (electrically conductive material) or a tunnel barrier (insulator material). Similarly, second barrier layer  926  may be a Schottky barrier (electrically conductive material) or a tunnel barrier (insulator material). 
     In this embodiment, base region  904  consists of a free layer structure  914 . Since free layer structure  914  is the only structure provided within base region  904 , the base region has a relatively small thickness for an improved signal in the TTM  900 . Emitter region  902  has a pinned layer structure  912  and an AFM pinning layer  918 . Emitter region  902  may also have one or more other emitter layers  928  which may be or include a silicon layer or an FM layer such as nickel-iron. Pinned layer structure  912  is adjacent first barrier layer  920 , which is in turn adjacent free layer structure  914 . As apparent, first barrier layer  920  simultaneously serves as a spacer layer between pinned layer structure  912  and free layer structure  914 . 
     An FM pinned layer of pinned layer structure  912  is magnetically pinned by exchange-coupling with AFM pinning layer  918 , which is formed adjacent pinned layer structure  912 . The pinning field generated by AFM pinning layer  918  should be greater than demagnetizing fields to ensure that the magnetization direction of the FM pinned layer remains fixed during application of external fields (e.g. fields from bits recorded on the disk). The magnetization of free layer structure  914  is not fixed and is free to rotate in response to the field from the information recorded on the magnetic medium (i.e. the signal field). Pinned layer structure  912  may be a single FM layer or, alternatively, a multi-layer structure. In particular, pinned layer structure  912  may be an AP pinned layer structure as shown and described earlier in relation to  FIG. 11 . 
     Collector region  906  has an in-stack LBL structure  916 . Collector region  906  may also have one or more other collector layers  930  which may be or include a silicon layer or an FM layer such as nickel-iron. Being formed “in-stack” with the sensor layers, LBL structure  916  of collector region  906  is formed within the central region of the sensor but not within side regions thereof. LBL structure  916  includes a pinned layer structure  922  and an AFM pinning layer  924 . Second barrier layer  926  is formed between LBL structure  916  and free layer structure  914 , causing pinned layer structure  922  and free layer structure  914  to be physically separated but in close proximity to each other. As apparent, second barrier layer  926  simultaneously serves as a spacer layer for LBL structure  916 ; no separate spacer layer is needed to provide such separation. 
     Pinned layer structure  922  is magnetically pinned by exchange-coupling with AFM pinning layer  924 . In particular, AFM pinning layer  924  pins a magnetic moment of pinned layer structure  922  parallel to the ABS and parallel to the planes of the sensor layers as indicated. Because of pinned layer structure  922  the magnetic moment of free layer structure  914  is magnetically stabilized parallel to the ABS and parallel to the major planes of the sensor as indicated by the dashed arrows. This biasing is uniform from the sides of free layer structure  914  so that the biasing does not cause a limitation on narrow track width sensors. Pinned layer structure  922  may be a single FM layer or alternatively a multi-layer structure, and may include an AP pinned structure as previously shown and described in relation to  FIG. 11 . 
     Note that AFM pinning layer  924  of LBL structure  916  should preferably magnetically pin at a different temperature than AFM pinning layer  918 . The reason is so that, during TTM fabrication, the pinning achieved for AFM pinning layer  924  will not be adversely affected by the subsequent pinning process utilized for AFM pinning layer  918 . As is known, the pinning of AFM pinning layers is typically achieved by heating the AFM materials to a predetermined temperature and applying a magnetic field at the same time. Preferably, to obtain the difference in pinning temperatures, AFM pinning layer  924  is made of a different material than that of AFM pinning layer  918 . For example, AFM pinning layer  918  may be made of platinum-manganese (PtMn) and AFM pinning layer  924  may be made of iridium-manganese (IrMn). A similar result may be achieved by utilizing the same materials for AFM pinning layers  918  and  924  with different thicknesses. More generally, the choice of any AFM material and its thickness may vary. The AFM layers may be the same material or alternatively have the same thickness. Preferably, the AFM layers are made of different materials and have different thicknesses. 
     Exemplary thicknesses and materials of TTM  900   a  are indicated in  FIG. 9A . In-stack longitudinal bias layer structure  916  has AFM pinning layer  924  made of platinum-manganese (PtMn) with a thickness of about 150 Angstroms and pinned layer  922  made of cobalt-iron (CoFe) with a thickness of about 20 Angstroms. AFM pinning layer  918  is made of iridium-manganese (IrMn) with a thickness of about 80 Angstroms and pinned layer  912  made of cobalt-iron (CoFe) with a thickness of about 40 Angstroms. Free layer structure  914  is made of nickel-iron (NiFe) with a thickness of about 40 Angstroms. 
     Preferably, there is a predetermined relationship established between the magnetic thickness of the pinned layer structure  922  of LBL structure  916  and the magnetic thickness of free layer structure  914 . In particular, the magnetic thickness of pinned layer structure  922  is made to be substantially the same as the magnetic thickness of free layer structure  914 . However, the magnetic thickness of the pinned layer may be between 50-500% of the thickness of the free layer. 
     One variation of the TTM  900   a  of  FIG. 9A  is a TTM  900   b  shown in  FIG. 9B . TTM  900   b  of  FIG. 9B  is the same as TTM  900   a  of  FIG. 9A  except that the layers are inverted as shown, such that an emitter region  902   b  includes in-stack LBL structure  916  and collector region  906   b  includes pinned layer structure  918 . Another variation of the TTM  900   a  of  FIG. 9A  is a TTM  900   c  shown in  FIG. 9C . TTM  900   c  of  FIG. 9C  is the same as TTM  900   a  of  FIG. 9A  except that emitter region  902   c  includes a self-pinned layer structure  912   c  as the pinned layer structure. For TTM  900   c , the AFM pinning layer  918  of the TTM  900   a  of  FIG. 9A  is not needed for pinning purposes. A sensor of the self-pinned type relies on magnetostriction of the self-pinned structure and the ABS stress for a self-pinning effect. The AFM pinning layer, which is typically as thick as 150 Angstroms, is no longer necessary for pinning purposes so that a thinner sensor can be made. TTM  900   d  of  FIG. 9D  is another structural variation where LBL structure  916   d  also has a self-pinned layer structure  922   d . Note that the self-pinned layer structure  922   d  of  FIG. 9D  may include one or multiple layers of materials. In this variation, structure  912   c  may or may not be self-pinned. 
       FIG. 10  is a sensing plane (or ABS) view of yet another embodiment of a TTM  1000  of the present application. TTM  1000  of  FIG. 10  has the general structure and functionality of the TTM shown and described above generally in relation to the drawings, with or without having the metal layer for reduced lead resistance. Specifically, TTM  1000  is a specific embodiment of that shown and described in relation to  FIG. 9A  and is of the double tunnel junction type. As shown in  FIG. 10 , TTM  1000  has an emitter region  1002 , a base region  1004 , and a collector region  1006 . A first insulative tunnel barrier layer  1008  is located between emitter region  1002  and base region  1004 , and a second insulative tunnel barrier layer  1026  is located between collector region  1006  and base region  1004 . Since TTM  1000  is of the double tunnel junction type, first and barrier layers  1008  and  1026  are insulative tunnel barriers made of a suitable electrically insulative material (e.g. Al 2 O 3  or alumina). 
     In this embodiment, base region  1004  consists of a free layer structure  1014 . Since free layer structure  1014  is the only structure provided within base region  1004 , the base region has a relatively small thickness for an improved signal in the TTM  1000 . Emitter region  1002  has a pinned layer structure  1012  and an AFM pinning layer  1018 . Emitter region  1002  may also have one or more other emitter layers  1028  which may be or include a silicon layer or an FM layer such as nickel-iron. Pinned layer structure  1012  is adjacent first insulative tunnel barrier layer  1008 , which is in turn adjacent free layer structure  1014 . As apparent, first insulative tunnel barrier layer  1008  simultaneously serves as a spacer layer between pinned layer structure  1012  and free layer structure  1014 . 
     An FM pinned layer of pinned layer structure  1012  is magnetically pinned by exchange-coupling with AFM pinning layer  1018 , which is formed adjacent pinned layer structure  1012 . The pinning field generated by AFM pinning layer  1018  should be greater than demagnetizing fields to ensure that the magnetization direction of the FM pinned layer remains fixed during application of external fields (e.g. fields from bits recorded on the disk). The magnetization of free layer structure  1014  is not fixed and is free to rotate in response to the field from the information recorded on the magnetic medium (i.e. the signal field). Pinned layer structure  1012  may be a single FM layer or, alternatively, a multi-layer structure. In particular, pinned layer structure  1012  may be an AP pinned layer structure as shown and described earlier in relation to  FIG. 11 . The FM pinned layer of pinned layer structure  1012  may alternatively be “self-pinned” where AFM pinning layer  1018  is not needed for pinning purposes, as described earlier above. 
     Collector region  1006  has an in-stack LBL structure  1016 . Collector region  1006  may also have one or more other collector layers  1030  which may be or include a silicon layer or an FM layer such as nickel-iron. Being formed “in-stack” with the sensor layers, LBL structure  1016  of collector region  1006  is formed within the central region of the sensor but not within side regions thereof. LBL structure  1016  includes a pinned layer structure  1022  and an AFM pinning layer  1024 . Second insulative tunnel barrier layer  1026  is formed between LBL structure  1016  and free layer structure  1014 , causing pinned layer structure  1022  and free layer structure  1014  to be physically separated but in close proximity to each other. As apparent, second insulative tunnel barrier layer  1026  simultaneously serves as a spacer layer for LBL structure  1016 ; no separate spacer layer is needed to provide such separation. 
     Pinned layer structure  1022  is magnetically pinned by exchange-coupling with AFM pinning layer  1024 . In particular, AFM pinning layer  1024  pins a magnetic moment of pinned layer structure  1022  parallel to the ABS and parallel to the planes of the sensor layers as indicated. Because of pinned layer structure  1022 , the magnetic moment of free layer structure  1014  is magnetically stabilized parallel to the ABS and parallel to the major planes of the sensor as indicated by the dashed arrows. This biasing is uniform from the sides of free layer structure  1014  so that the biasing does not cause a limitation on narrow track width sensors. Pinned layer structure  1022  may be a single FM layer or alternatively a multi-layer structure, and may include an AP pinned structure as previously shown and described in relation to  FIG. 11 . 
     Note that AFM pinning layer  1024  of LBL structure  1016  should preferably magnetically pin at a different temperature than AFM pinning layer  1018 . The reason is so that, during TTM fabrication, the pinning achieved for AFM pinning layer  1024  will not be adversely affected by the subsequent pinning process utilized for AFM pinning layer  1018 . As is known, the pinning of AFM pinning layers is typically achieved by heating the AFM materials to a predetermined temperature and applying a magnetic field at the same time. Preferably, to obtain the difference in pinning temperatures, AFM pinning layer  1024  is made of a different material than that of AFM pinning layer  1018 . For example, AFM pinning layer  1018  may be made of platinum-manganese (PtMn) and AFM pinning layer  1024  may be made of iridium-manganese (IrMn). A similar result may be achieved by utilizing the same materials for AFM pinning layers  1018  and  1024  with different thicknesses. More generally, the choice of any AFM material and its thickness may vary. The AFM layers may be the same material or alternatively have the same thickness. Preferably, the AFM layers are made of different materials and have different thicknesses. 
     Exemplary thicknesses and materials of TTM  1000  are indicated in  FIG. 10 . In-stack longitudinal bias layer structure  1016  has AFM pinning layer  1024  made of platinum-manganese (PtMn) with a thickness of about 150 Angstroms and pinned layer  1022  made of cobalt-iron (CoFe) with a thickness of about 20 Angstroms. AFM pinning layer  1018  is made of iridium-manganese (IrMn) with a thickness of about 80 Angstroms and pinned layer  1012  made of cobalt-iron (CoFe) with a thickness of about 40 Angstroms. Free layer structure  1014  is made of nickel-iron (NiFe) with a thickness of about 40 Angstroms. 
     A TTM of the present application may be fabricated using conventional lithographic techniques, as now described. In the following description, a TTM of the type shown and described in relation to  FIG. 4  and  FIG. 7A  is specifically made; these techniques are easily applied for the fabrication of all TTM types. Referring to  FIG. 12A , collector region  20  is shown with an insulating oxide layer  1010 / 1012  deposited thereon. A resist pattern  43  is then used to remove a middle portion of the insulating layer  1010 / 1012  which creates, as shown in  FIG. 12B , a via  44  down to the semiconductor substrate  20  as well as insulating layers  1010  and  1012 . The removal of the insulating layer materials may be performed using conventional etching techniques. Optionally, a metal layer  1050  is then formed over at least a portion of insulating layer  1012 . Metal layer  1050  may be formed using sputter-deposition or electroplating steps, as well as lithography steps with a patterned resist and etching. An air bearing surface (ABS)  11  of the sensor structure is represented by a dotted line in  FIGS. 13A and 13B  as well as in the subsequent drawings. 
     In  FIG. 14A , a sensor stack  18  is formed over insulating layers  1010  and  1012 , into via  44 , and over metal layer  1050 . Sensor stack  18  includes base region  15  and emitter region  5 , with the barrier regions (e.g. barrier region  10 ) deposited in the stack where appropriate. Behind the sensing plane, base region  15  is formed over and in contact with metal layer  1050 . The top-down view of  FIG. 14B  illustrates the upper cap of sensor stack  18 , which is top the surface of emitter region  5 . Next, as depicted in  FIGS. 15A and 15B , another resist  46  is used to pattern sensor stack  18 , where portions of emitter region  5  are removed using known techniques such as ion milling or reactive ion etching (RIE). This exposes base layer  15  along the sides and defines the stripe height H S  of the device. As shown in  FIGS. 16A and 16B , an insulator  25  (such as alumina) is then filled in the areas over exposed base layer  15 . 
     In the next stage of processing, as illustrated in  FIGS. 17A and 17B , a patterned resist  47  is used to pattern the structure along a trackwidth (TW) axis  1600  with an etch. Patterned resist  47  is best viewed in the top-down view of  FIG. 12B  where the exposed portions of insulator  25  and emitter  5  are shown. Once the exposed material is removed, an insulating layer  29  is deposited as depicted in the ABS view of  FIG. 18A  and a top plan view of  FIG. 18B . In the ABS view of  FIG. 19A  and in  FIG. 19B , portions of insulator layer  29  are removed along with portions of refill alumina  25  and base region  15 , such that only emitter region  5  and a remaining portion of base region  15  are located between insulator layer  29 . Another resist  48  is then used to pattern the device and another insulator  38  fills the exposed portions.  FIGS. 20A and 20B  illustrate the device where yet another resist  49  used to pattern (etch) a via  56  to base region  15  and a via (not visible) to collector region  20 . This step may etch through metal layer  1050  as shown or, alternatively, refrain from etching through metal layer  1050 . After the patterning is completed, the transistor device is plated with emitter lead  35  and base lead  36  as shown in  FIGS. 21A and 21B , wherein these leads  35 ,  36  are preferably made of nickel-iron (NiFe). Other leads, such as the collector lead (not shown) can also be included in this lead-plating step. 
     Final Comments. As described herein, a three terminal magnetic sensor (TTM) of the present application which is suitable for use in a magnetic head has a base region, a collector region, and an emitter region. A first barrier layer separates the emitter region from the base region, and a second barrier layer separates the collector region from the base region. A sensing plane is defined along sides of the base region, the collector region, and the emitter region. The base region consists of a free layer structure so as to have a relatively small thickness. A pinned layer structure is made part of the emitter region. An in-stack longitudinal biasing layer (LBL) structure which magnetically biases the free layer structure is made part of the collector region. In one variation, the emitter region has the in-stack LBL structure and the collector region has the pinned layer structure. The TTM may comprise a spin valve transistor (SVT), a magnetic tunnel transistor (MTT), or a double junction structure. 
     A disk drive of the present application includes a slider, a magnetic head carried on the slider, a write head portion of the magnetic head, and a read head portion of the magnetic head which includes a three terminal magnetic sensor (TTM). The TTM has a base region, a collector region, and an emitter region. A first barrier layer separates the emitter region from the base region, and a second barrier layer separates the collector region from the base region. An air bearing surface (ABS) plane is defined along sides of the base region, the collector region, and the emitter region. The base region consists of a free layer structure so as to have a relatively small thickness. A pinned layer structure is made part of the emitter region. An in-stack longitudinal biasing layer (LBL) structure which magnetically biases the free layer structure is made part of the collector region. The TTM may comprise a spin valve transistor (SVT), a magnetic tunnel transistor (MTT), or a double junction structure. 
     It is to be understood that the above is merely a description of preferred embodiments of the invention and that various changes, alterations, and variations may be made without departing from the true spirit and scope of the invention as set for in the appended claims. For example, although the TTM is described as a three-leaded device, it may actually have three or more leads. Few if any of the terms or phrases in the specification and claims have been given any special particular meaning different from the plain language meaning to those ordinarily skilled in the art, and therefore the specification is not to be used to define terms in an unduly narrow sense.