Flash Forward to Toshiba’s High-K

Toshiba is the first flash manufacturer to incorporate a high-K dielectric in their product. Their innovative inter-poly dielectric has allowed Toshiba to scale their floating gate flash memory to 43nm. The 16Gbit multi-level cell (MLC) device from Toshiba sets the new high watermark for NAND flash bit density at 139Mbits/mm².

Samsung claimed the first implementation of high-K dielectric for flash. However, that was for a charge-trapping (CTF) device they expected to roll out for 4Xnm. By now, we have all heard a lot about TANOS flash from Samsung. There is no floating gate with CTF, so the high-K material is in the tunnel oxide between the silicon channel and the control gate of the memory cell. The TANOS concept first announced by Samsung at IEDM 2005 was an extension to the generic SONOS approach of an oxide/nitride/oxide sandwich for charge trapping much like the so-called O-N-O inter-poly dielectric routinely used to separate the control and floating gate in traditional flash devices. The SONOS acronym was derived from the silicon on top (poly gate) of the dielectric and the silicon substrate underneath. SANOS CTF devices increased the dielectric constant of the charge trapping dielectric to allow the layers to electrically scale without sacrificing reliability by physically thinning the layers. The ‘A’ in SANOS comes from the aluminum-oxide high-K material. The last step to get to TANOS was for Samsung to substitute a tantalum-nitride metal gate in their CTF.

The bottom line from that wordy, acronym-laden paragraph is that floating gate was supposedly running out of steam and CTF devices were going to replace them. That’s what generated all the buzz and all the lovely new acronyms. Despite many “expert” predictions over the years, reports of the death of floating gate flash are greatly exaggerated. On the contrary, floating gate technology continues to dominate the market. I wonder if the floating gate technologists at Toshiba are having a good laugh because they were first to market with high-K which was a big part of the CTF that was supposed to put them out of business.

Many more details on this innovative flash process from Toshiba are available from Semiconductor Insights.

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