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Sharp, SEL integrate processor into system-on-glass device

Posted: 25 Oct 2002 ?? ?Print Version ?Bookmark and Share

Keywords:sharp? semiconductor energy laboratory? processor? transistors? glass substrate?

Sharp Corp. and Semiconductor Energy Laboratory Co. Ltd (SEL) have integrated an 8-bit Z80 processor composed of 13,000 transistors onto a glass substrate with an LCD, demonstrating the feasibility of "system-on-glass" devices for future applications.

The circuitry was built using 35m design rules and continuous-grain silicon technology, for which the two companies hold hundreds of patents. "Circuitry on glass will bring new applications that a silicon wafer cannot offer," said Shumpei Yamazaki, president of SEL. Sharp said it will consider building business card-sized display panels with the technology.

The integrated Z80, which covers a 17mm square on the substrate, "shows the possibility of fabricating various functions on glass panels as new LSIs," said Shigeo Misaka, chief technology and production officer of Sharp.

Sharp and SEL said CG-silicon technology enables electron mobility that is about three times faster than what is now possible in low temperature polysilicon LCDs, which can achieve 500 cm2/V mobility in the laboratory. In the 35m process, CG-silicon can realize 200 cm2/V mobility. "LT-polysilicon still has atomic-level discontinuity at the crystal-grain boundaries, and transistors have to be formed avoiding those grain boundaries," said Mikio Katayama, group general manager of Sharp's mobile LCD group. "CG-silicon grain maintains atomic-level continuity at grain boundaries, which enables electrons to travel smoothly through the boundaries, resulting in high mobility. We believe CG-silicon LCDs have an advantage over LT-polysilicon, especially in LSI."

Replaced aged silicon

To demonstrate the CPU-on-glass, SEL and Sharp replaced a silicon Z80 in a personal computer Sharp had marketed in the late 1970s, and ran an old computer game on the system. "It has equal or better performance than its silicon-based correspondent," SEL president Yamazaki said of the chip-on-glass.

Because a glass substrate functions as an insulator, transistors fabricated on it have all the merits of those fabricated on a silicon-on-insulator wafer, Sharp and SEL said. But the temperatures required to build on a glass substrate are much lower than those required for an SOI process, they said. "CG-silicon transistors have the merits of SOI and metal gates, so when the technology goes into submicron rules with large glass substrates, CG-silicon LSIs would be advantageous over silicon LSIs," Yamazaki said.

Three micron design rules are the most advanced available for CG-silicon. The Z80 produced in the process runs at 3MHz. "It is impossible to make CPUs these days with these design rules," Sharp's Misaka said. "We fabricated the Z80 for demonstration. In the future, we will target something like ARM-7 and ARM-9."

In a road map for their CG-silicon technology, the companies indicated that electron mobility would increase to 400cm2/V by 2005, when design rules shrink to 0.85m and logic frequency reaches 20MHz or 30MHz.

No sheet computer

The companies described applications they expect to pursue for system-on-glass devices, and dismissed notions of a so-called "sheet computer."

"I do not think a sheet computer with a 10GHz CPU-on-glass can be realized with CG-silicon technology by 2005," said Sharp's Katayama. "And anyway, we do not think a sheet computer in the present PC concept is important. Rather, we want to offer a card-type display." Such an information viewer would be 3mm to 5mm thick and the size of a business card, with such circuitry as a signal processor, font generator, CPU, memory, a touch panel and some communication blocks, he said.

Sharp has begun mass production of CG-silicon LCDs in October at its fabrication facility in Tenri, which has a capacity of 2.5 million two-inch panels per month. The company is building a second fab in Taki that is scheduled to begin operation next October, with a capacity of 4 million two-inch panels per month.

- Yoshiko Hara

EE Times

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