The fabrication of high sensitive spin-valve sensor for magnetic bead detection

Manipulation and detection of magnetic beads on a chip open up new perspectives for analysis of magnetically labeled specimens in biological and medical applications. This work has studied to achieve the high sensitive spin-valve (SV) sensor detecting the stray field from a spherical-shaped superparamagnetic bead magnetized by external field. First of all, SV structures of Ta(50)/NiFe(45)/CoFe(15)/Cu(26)/ CoFe(40)/IrMn(150)/Ta(50) [unit of ( ) is A] with 8 - 9% magnetoresistive ratio (MR) were deposited on substrate Si/SiO 2 (1500) by UHV magnetron sputter system. SV sensor was fabricated through photolithographic techniques and ion milling processes. The working of sensor was confirmed by obtaining the output signal as a function of sense current under the external field parallel to magnetization direction of pinned layer. The sensitivity of the fabricated SV sensor was about 0.3%/Oe (sense current 10 mA). Sensor signal (AV) output of 2 mV was obtained for 2.8 μm magnetic beads positioned over the SV sensor using an external in-plane field and 10 mA sense current.