Another day, another technology patent fight. Toshiba has filed infringement lawsuits in Japan and the US against rival Hynix.

The Japanese suit alleges that Hynix violated three of Toshiba's patents covering NAND-type flash memory chips. It seeks monetary damages and a halt to sales of the infringing products.

A broader suit against Hynix and some of its US subsidiaries was also filed in Texas. That suit alleges Hynix has infringed on four patents for NAND-type flash memory and three relating to DRAM. Like the Japanese suit, it asks for an injunction against sale of the products and monetary damages.

Both lawsuits stem from a patent cross-licensing agreement signed by both of them in August 1996. That agreement expired on 31 December 2002, and despite negotiations the two companies have been unable to agree on a revision of the arrangement.

"Toshiba want money, and they want to protect their technology," said Kim Soo-Kyoum, program director for semiconductor research at market research company IDC. Kim said that the suits filed by Toshiba are in support of legal moves made in mid-October by its flash memory development and production partner SanDisk against STMicroelectronics, which partners Hynix in making flash chips.

On 18 October, SanDisk filed a complaint with the US International Trade Commission alleging that NAND-type flash memory chips made by STMicroelectronics infringed a SanDisk patent. SanDisk requested that STMicroelectronics' NAND flash memory chips be barred from sale in the US. SanDisk also filed suit in California involving the same patent, and sought an order declaring that its products did not infringe 14 US patents assigned to STMicroelectronics.

Flash memory has the ability to maintain its contents even after power to the chip has been turned off. This has made it one of the most commonly used types of memory chip in devices such as consumer electronics products, cellular telephones and digital music players. DRAM is the most commonly used type of memory in personal computers.

Toshiba is the world's second biggest NAND flash memory maker with about 34 percent market share. Meanwhile, Hynix, which has started volume production of NAND flash recently has only a very small share, according to Kim. If Toshiba forces Hynix to pay royalties through successfully prosecuting the patent dispute, Toshiba will benefit from any success Hynix and STMicroelectronics have in the market. "It's a win-win situation for Toshiba," Kim said.