Toshiba Corp delivered an invited lecture on the "BiCS (bit cost scalable)" next-generation NAND flash memory, which stacks memory cells in multiple layers in three-dimensional directions, at the 2013 Symposium on VLSI Technology, which runs from June 11 to 13, 2013, in Kyoto, Japan (lecture number: T6-1).
Akihiro Nitayama from Toshiba Semiconductor & Storage Products Company took the podium. The title of the lecture was "Bit Cost Scalable (BiCS) Technology for Future Ultra High Density Storage Memories."
Toshiba announced the concept of the BiCS in 2007 as "post-NAND memory" for an era when the scaling of existing floating gate technology-based NAND flash memory reaches its limit. One of the distinguished features of the BiCS is that multiple layers of memory cells can be formed at one time with multilayer formation and etching technologies. The company is expected to start to ship samples of the BiCS within 2013.
In the lecture, Nitayama explained how Toshiba made improvements to the original structure to overcome disadvantages such as low operation speed and data retention properties.
For example, the company improved memory cell properties by employing a structure called "P-BiCS." It solved the problem of the cell current degradation caused by an increase in the number of memory cell layers by improving the channel mobility of polysilicon TFT. And it enhanced data retention properties by making improvements to the method of forming a SONOS film.
Then, Nitayama compared the BiCS with other 3D NAND flash memories being developed by other companies and said that the BiCS is the most promising technology for Tbit-class storage devices in terms of the number of manufacturing processes, memory cell area, disturbance resistance, etc.
In regard to the scalability of the BiCS, he said, "We would like to extend the life of the technology to five generations."
Nitayama pointed out that 3D ReRAMs (resistive random-access memories) and PRAMs (phase-change random access memories) using process technologies similar to the BiCS technology have been recently introduced. And he said that the concept of the BiCS will possibly be applied to various new memories.