Co/$Al_O_3$/NiFe and CO/$Al_O_3$/Co tunnel junctions were fabricated by a radio frequency magnetron sputtering at room temperature with hard mask on glass and $4^{circ}$ tilt cut Si (111) substrates. The barrier layer was formed through two steps. After the Al layer was deposited, it was oxidized in the chamber of a reactive ion etching system (RIE) with $O_2$plasma at various conditions. The dependence of the TMR value and junction resistance on the thickness of Al layer (before oxidation) and oxidation parameters were investigated. Magnetoresistance value of 7% at room temperature was obtained by optimizing the Al layer thickness and oxidation conditions. Circular shape junctions on $4^{circ}$tilt cut Si (111) substrate showed 4% magnetoresistance. Photovoltaic energy conversion effect was observed with the cross-strip geometry junctions on Si substrate.