1. A multilayer memristive device comprising: a first electrode ( 410 ); a second electrode ( 405 ); a first memristive region ( 430 ); a second memristive region ( 435 ), said first memristive region ( 430 ) and said second memristive region ( 435 ) being created by directional ion implantation of dopants ( 420 , 430 ) into a memristive matrix ( 415 ); said first memristive region ( 430 ) and said second memristive region ( 435 ) being interposed between said first electrode ( 410 ) and said second electrode ( 405 ); and mobile dopants ( 315 ); said mobile dopants ( 315 ) moving within said first memristive region ( 430 ) and said second memristive region ( 435 ) in response to an applied electrical field.