Bidirectional Selector Realized Through Multilayer Tunnel Barrier Engineering

The selector plays an important role in solving the leakage current issue in a large-scale memory crossbar array. Especially, the bidirectional selector has a broader application scope than the unidirectional one, since it can be connected with both unipolar and bipolar memory devices. In this letter, two engineering approaches to realize bidirectional tunneling barrier selectors were investigated: the crested barrier and variable oxide thickness (VARIOT). It is found that the selectors based on the crested barrier exhibit much higher nonlinearity and lower off-current than those fitting the VARIOT approach. The associated tunneling mechanisms have been proposed to explain the electrical properties of the crested barrier devices. The excellent multilayer barrier bidirectional selector has been realized in the ZnO/Ta
₂
O
₅
/ZnO stack with pA-level off current and high nonlinearity (>10
⁴
). It is worth noting that the present ZnO/Ta
₂
O
₅
/ZnO selector shows the best performances compared with previously reported tunnel barrier selectors.