ABSTRACT
The scanning tunneling microscopy experiment has proved that a process of vacuum tunnel can inject spin-polarized electrons into a semiconductor effectively. In traditional transistors, the electron's movement is classical. But when the scale of the device is so small that its scale is about equal to or smaller than some characteristic lengths, there will be distinct quantum effects of current. Experiments found that for a small quantum dot, only when the electric voltage is larger than a certain value, the electron can pass through the dot. The reason is that the Coulomb interaction between the electron in a quantum dot and the electron in a circuit will reject the entry of the second electron to the quantum dot. The proposition of spin-vales and room-temperature magnetic sensor utilizing anisotropic magnetoresistance makes for great success of giant magnetoresistance in commerce. In 1995 scientists found a new phenomenon, tunneling magnetoresistance, which has larger magnetoresistance and smaller coercive force.
