Silicon Spintronics

"Electronics" uses our ability to control electrons with electric fields via interaction with their fundamental charge. Because we can manipulate the electric fields within semiconductors, they are the basis for microelectronics, and silicon (Si) is the most widely-used semiconductor for integrated microelectronic circuits. The electron's magnetic moment, called spin, has been known for over eighty years, and its existence explains (among other things) the static magnetic field of permanent magnets. Our understanding of electron spin manipulation has led to information-storage applications such as high-sensitivity magnetic field sensors for hard-drives (Giant Magneto-Resistance - or GMR - devices), and devices for non-volatile random-access memory called Tunnel Magneto-Resistance (TMR) devices; however, it has not yet found use in information-processing circuits. To enable spin-based integrated circuits, long spin lifetimes are necessary to enable multiple logic operations before depolarization and decoherence sets in. In addition, long spin transport coherence lengths are needed to enable integration of multiple devices in a circuit. Silicon has been broadly viewed as the ideal material for spintronics due to its low atomic weight, lattice inversion symmetry, and near lack of nuclear spin. Despite this appeal, however, the experimental difficulties of achieving coherent spin transport in silicon were overcome only recently (in our lab here at Delaware), by using unique spin-polarized hot-electron injection and detection techniques with nano-scale ferromagnetic metal spin "polarizers".[1] Using these methods, we have observed unprecedented coherence in spin precession measurements, and extracted very long spin lifetimes of conduction electrons traveling over macroscopic distances.[2] Whereas transistor scaling limits will soon suppress progress in microelectronics using Si, its favorable spintronics properties may secure this semiconductor's dominance for the future.