By Hank Hogan
For disk-drive makers, contamination control is part of fighting the law, Hwang’s law to be precise. Samsung Semiconductor President Chang-Gyu Hwang predicted flash memory chips would double in capacity every year and his law has held for the last half decade. The 32-gigabit chips introduced late in 2006 were double the capacity of those available the year before and 64 times the capacity of those available in 2000.
According to Joseph Unsworth, a principal analyst in the semiconductor group of Gartner Dataquest, the trend will continue until 2010, with flash prices dropping more than 50 percent annually. Such a scenario, notes Unsworth, challenges disk-drive makers. “As prices become lower and capacities increase, you then begin to target new applications, hard drives being one of them,” he says.
Partly in response to this but mostly due to competition within the industry, hard-disk manufacturers are implementing more stringent contamination controls. Clint Dyer, vice president of operations for disk-drive maker Hitachi Global Storage Technologies (San Jose, CA), notes that a key metric is areal density, the amount of data stored in disk real estate, and driving that value up is important. “We need to increase our areal density and, thus, cleanliness levels to stay competitive,” he says.
The most critical dimensions in a hard disk are the distance between the read/write head and the rotating platter, and the spacing of magnetic domains on that platter. Both are in the range of a few nanometers. The contamination control solutions involve Class 10 (ISO Class 4) cleanrooms for the most critical areas, careful selection of materials, automated assembly lines, and other strategies.
Forrest Monroy, a spokesperson for hard-disk manufacturer Seagate Technology (Scotts Valley, CA), notes his company’s cleanrooms in Singapore are Class 100 (ISO 5), but are upgradeable to ISO 4. Seagate has nine cleanrooms at the site, with a typical size of 150 by 100 square feet. Contamination abatement efforts include strict control of electrostatic discharge, thorough training of personnel, and as much automation as is warranted.
Such contamination control techniques boost areal density and product yield, notes John Monroe, research vice president at Gartner. They also pay off because disk drives are mechanical devices that outgas and vibrate, yet are expected to last for years. “Contamination can cause field failures that can really be catastrophic,” says Monroe.
For all of these efforts, though, disk-drive makers face a problem, one that makes flash memory tough to beat in some applications. Hard disks have a fixed manufacturing cost, which today runs about $40. For low-capacity needs, flash memory may be cheaper than that minimum. However, better contamination control that leads to higher manufacturing yields could help drop that fixed cost.
On the other hand, hard-drive manufacturers are taking advantage of Hwang’s law themselves. Several have announced hybrid drives, ones that have both a rotating platter and flash memory. This arrangement allows the drive to save power by sleeping most of the time, spinning up less than a minute for every hour of typical use. Hybrids are expected to see increasing deployment over the next few years.