OXFORD, England Sharp Laboratories Europe, the European R&D arm for Japan's Sharp Corp., has established a road map for the miniaturization of integrated circuits manufactured on the glass substrate used in displays.
The benefits of miniaturization which is proving increasingly difficult in bulk silicon ICs that have progressed to 0.13-micron minimum geometries could be more readily achieved with emerging process technology that is about to migrate to 0.8-micron design rules, researchers said.
Progress seems likely to follow a path similar to Moore's Law, the empirical observation that monolithic ICs tend to double in complexity about every 18 months. It uses polycrystalline silicon thin films laid down on the periphery of display panels to sweep up display and system circuitry.
Sharp researchers said they have already demonstrated a 13,000-transistor Z80 microcontroller implemented on glass and built using 2-micron design rules. The controller was reported at ISSCC in February 2003, and achieves a clock frequency of 3-MHz when operated from a 5-V supply voltage.
Silicon-on-glass technology is typically being applied to liquid-crystal displays, although it could be applied to most displays that use a glass substrate.
The system-on-panel road map is based on Sharp's continuous grain (CG) polysilicon, which can provide mobility that is more than 300 times higher than amorphous silicon an early form of semiconductor film used on glass and more than three times higher than low-temperature polysilicon, according to Graham Cairns, a Sharp researcher.
The CG material's mobility is about half that of bulk silicon, which has allowed Sharp to contemplate putting significant amounts of system functionality on a chip.
CG material is used for thin-film transistors both for the active matrix of the display and for peripheral circuitry.
The first generation of CG silicon display introduced in 2001 used 3-micron design rules and a maximum logic frequency of about 3-MHz. The technology was used to sweep up solid-state drivers for 2-inch quarter VGA displays used in mobile telephones, Cairns said.
The current generation unveiled in 2003 moved to 1.5-micron design rules and supports 5-MHz logic frequency. Analog amplifiers for the audio subsystem and the display controller are being added to the driver circuits, Cairns said. Improvements in the CG silicon enhanced display resolution.
A third generation with improved CG silicon mobility will be manufactured using 0.8-micron design rules beginning in 2005. Circuits for maximum clock frequencies of 30 MHz would be more than adequate for large parts of the interface chain. The display would likely include image sensing and capacitive touch sensing with related signal conditioning, conversion and digital signal processing on the same glass substrate.
Cairns said Sharp researchers reported at the recent Society of Information Display conference on a 2.6-inch diagonal VGA display with peripheral circuitry integrated using 1.5-micron design rules.