When was the Memory Stick invented and was it co-invented by Sony and SanDisk?

Sony launched the Memory Stick, a type of flash memory, in October of 1998. It is their idea, and only later did they team up with SanDisk to further develop it. The invention may have come a year or so earlier, as there is (obviously) a short delay between the invention and the release of a product. A link can be found below.