The present invention relates to a magneto-resistive device, and a magnetic head and a head suspension assembly using the same. 
With the trend to a larger capacity and a smaller size of hard disk drives (HDD), heads are required to have a higher sensitivity and larger output.  To meet this requirement, strenuous efforts have been made to improve characteristics of GMR head (Giant Magneto-Resistive Head) currently available on the market.  On the other hand, intense development is under way for a tunnel magneto-resistive head (TMR head) which can be expected to have a resistance changing ratio twice or more higher than the GMR head. 
Generally, the GMR head differs from the TMR head in the head structure due to a difference in a direction in which a sense current is fed.  A head structure adapted to feed a sense current in parallel with a film plane, as in a general GMR head, is referred to as a CIP (Current In Plane) structure, while a head structure adapted to feed a sense current perpendicularly to a film plane, as in the TMR head, is referred to as a CPP (Current Perpendicular to Plane) structure.  Since the CPP structure can use a magnetic shield itself as an electrode, it is essentially free from short-circuiting between the magnetic shield and a device (defective insulation) which is a serious problem in reducing a lead gap in the CIP structure.  For this reason, the CPP structure is significantly advantageous in providing a higher recording density. 
The TMR head, which anticipates the CPP head, has drawn attention because of its high MR ratio, but is confronted by a grave problem of a reduction in resistance. 
On the other hand, a CPP-GMR head which employs a spin valve (SV) film, used in the CIP structure, for a magneto-resistive device, though in the CPP structure, can be reduced in resistance because of the employment of the spin valve film which does not include an insulating film in the magneto-resistive device.  An article entitled “Giant Magnetoresistance Properties of Spin Valve Films in Current-perpendicular-to-plane Geometry” by Nagasaka et al. ( Journal of Magnetics Society of Japan, Vol.  25, No.  4-2, pp.  807-810, 2001) discloses a magneto-resistive device which has a CPP structure using a spin valve film. 
In such a conventional magneto-resistive device which has the CPP structure using a spin valve film, a cap layer, a pin layer, a pinned layer, a non-magnetic layer, and a free layer formed between an upper electrode and a lower electrode, which make up the spin valve film, are formed substantially only in regions in which they overlap with one another, and the respective layers have substantially the same dimensions in a plane direction which is largely smaller than the area of the upper electrode and lower electrode. 
However, the conventional magneto-resistive device having the CPP structure using the spin valve film significantly excels the TMR device in the ability to reduce the resistance, whereas an actual MR ratio of the conventional magneto-resistive device, provided as the whole device between the upper electrode and lower electrode, is prohibitively low, for example, several percent. 
While the aforementioned article states that the MR ratio can be increased, the MR ratio referred to in the article is not the actual MR ratio provided as the whole device between the upper electrode and lower electrode, but the MR ratio only for a portion which exhibits a magneto-resistive change (i.e., a laminate made up of the pinned layer, non-magnetic layer and free layer).  Specifically, while the pin layer, cap layer and the like exist between the upper electrode and lower electrode, the aforementioned article refers to the MR ratio without taking into account the influence of these fixed resistive components.  This is why the MR ratio referred to in the article is apparently higher.