High tunneling magnetoresistance ratios (TMR) up to 44.6% were observed at room temperature on magnetic tunnel junctions (MTJs) with Ta20/Ni 8 1 Fe 1 9 20/Co 9 0 Fe 1 0 2/Al(1nm)-oxide/Co 9 0 Fe 1 0 2/Ni 8 1 Fe 1 9 7/ Fe 5 0 Mn 5 0 20/Ta5 (the thickness of other layers is in nm) structures fabricated by using an inductively coupled plasma sputtering system operating at a base pressure of 5x10 - 1 0 Torr. High field sensitivity up to 6.1%/Oe has been achieved in these MTJs with dimensions of 120μmx120μm by using extremely soft ferromagnetic (FM) Ni 8 1 Fe 1 9 /Co 9 0 Fe 1 0 electrode. Small ferromagnetic coupling field (11Oe) between the top and bottom FM electrodes, high breakdown electrical field (1.2x10 7 V/cm), and high V h (340-414mV) at which the TMR decreases to 50% of its initial value, were obtained as the surface roughness of the bottom FM electrode (R m s <3Å) and Al-oxide (R m s <1Å) layer have been improved.