1. Ag/Si/a-Si Rectified Nonvolatile Crossbar Switches
Crossbar switches, in which switching media was sandwiched between two crossed electrodes, employ the resistance change at the crosspoints to memorize and process information. Crossbar has been regarded as an ideal architecture for nanoelectronics because of its inherent simplicity, potential 3D scalability and defect tolerance capability. Amorphous silicon, along with many other switching media, were once studied in a Metal/insulator/Metal (MIM) structure and showed promising switching performance. However, before working as a switch, the MIM structure requires a high voltage critical forming process which is not fully controllable and reduces the device yield and endurance. Moreover, like most other MIM resistive switch, Metal/a-Si/Metal structure has a sneak current problem which necessitates complicated additional selector circuit for the crossbar array.
The Ag/a-Si/c-Si nanowire crossbar switch was discovered to require no special forming process and its self-rectified features avoided the sneak current issues and made crossbar arrays feasible without complicated selector circuits. The switch can have device size as small as 20 X 20 nanometers, fast switching speed (<100 nano seconds), long endurance cycles (>104 times), intrinsic rectification ratio higher than 104, on/off ratios greater than 104 and a long retention time of several weeks. These important memory parameters, at the time of the discovery (2004), were state of the art in the field, indicating that denser, faster, more reliable, yet cheaper memories could be feasible with this system.
The discovery of Ag/a-Si/c-Si crossbar switches opened up many research and development opportunities for highly scalable nonvolatile memory and programmable nanoprocessors. Specifically, the discovery has “inspired” Dr. Wei Lu‘s research on identical Ag/a-Si/c-Si crossbar memory arrays in CMOS compatible planar structures, which directly led to the founding of the silicon valley startup Crossbar Inc., an advanced memory development company, that has been listed as one of the 10 Startups to Follow in 2014 by Electronics360.