Qimonda created a stir last week when it unveiled a new DRAM technology called “Buried Wordline Technology” which purportedly consumes less power than conventional stacked capacitor DRAMs. This is achieved by reducing the capacitive coupling between the bitline and wordline by burying the wordline in the substrate of the device. An image of the buried wordline in Qimonda’s presentation appears to show tungsten as the wordline material. The middle of line process in the memory array is greatly simplified compared to standard stacked capacitor devices resulting in reduced process complexity.
Another surprising feature was the absence of a trench capacitor. Qimonda has responded to skepticism regarding the scalability of trench technology by switching to a cylindrical stacked capacitor for its DRAM roadmap down to the 3xnm generation. Qimonda plans to ramp its 65nm buried wordline technology with cell size of 6F2 in parallel with its 58nm 8F2 trench capacitor technology in the second half of 2008. The 65nm 1Gb device sports a die size of 55mm2 comparable to Micron’s 68nm 1Gb DDR2 chip size of 56mm2.
Subsequent 46nm and 3xnm 6F2 generations will be introduced in 2009 and 2010 respectively with a 3xnm 4F2 technology targeted for 2011. According to Qimonda, the 46nm technology is expected to effectively double the number of die per wafer versus the 58nm trench technology allowing the company to take the lead in productivity vis-à-vis the competition. This productivity boost is particularly important for driving down costs, especially in light of the massive €598 million net loss the company posted in the fourth quarter of calendar year 2007 on net sales of €513 million.
Qimonda stated that an incremental investment of €100 million over its existing investment for trench technology would be required to make the transition to the new technology. This would include deposition and etch tooling for hi-k capacitor formation.
The company hinted that the new technology opens up partnering opportunities which is expected to include Qimonda’s manufacturing and foundry partners, Winbond and SMIC although Inotera's participation is questionable given the recent tie-up between Nanya and Micron Technology. If licensing deals with these parties are reached, they would be expected to make similar investments for the conversion from trench to stack technology.
Currently, Qimonda, along with partner Nanya Technology, are the sole remaining DRAM players engaged in the development and production of trench capacitor DRAM technology accounting for a combined 18% of the DRAM market in 2007. The remaining 82% consists of Samsung, Hynix/ProMOS, Elpida/Powerchip and Micron Technology, which are all part of the stacked capacitor camp. With Qimonda’s announcement, trench technology is expected to be phased out of the market in the next three years.
It is also difficult to ignore the timing of the announcement. It appears that Qimonda was pressured to reveal details of its roadmap plans after rumors of a joint development and production agreement between its partner, Nanya Technology and Micron Technology surfaced. The rumors were subsequently confirmed when a memorandum of understanding was announced between the two parties on March 3.