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imec details flexible 6502 plastic processor

imec details flexible 6502 plastic processor

Technology News |
By Nick Flaherty



imec in Belgium has detailed the design of an 8bit 6502 plastic processor developed with foundry PragmatIC Semiconductor and KU Leuven.

The 8bit microprocessor detailed at ISSCC 2022 this week was built in a 0.8µm metal-oxide flexible technology and is capable of running real-time complex assembly code at a clock frequency 71.4kHz. The microprocessor was implemented with a unique digital design flow with a new standard cell library for NMOS metal-oxide thin-film indium-gallium-zinc-oxide (IGZO) transistors with a ‘quasi-CMOS’ structure.

This is relevant for designing a broad range of loT applications, integrating around 16,000 metal-oxide thin-film transistors on a 24.9mm2 flexible chip.

Flexible electronics based on thin-film transistor technology is preferred over Si CMOS-based electronics for applications requiring low-cost, thin, flexible and/or conformable devices. The technology is already being used for health sensors and RFID labels and as a driver for flat panel displays.

imec designed the flexible 8-bit microprocessor based on the source file of the MOS6502 chip.

“Our flexible microprocessor shows excellent characteristics for IoT applications, including high speed, low power consumption of 11.6mW when running at 10kHz, 134.9mW at max operating speed, and high transistor integration density,” said Kris Myny, Principal Scientist at imec. “At ISSCC 2022, we will showcase real-time correct operation of our circuit by running the complex assembly code of the popular Snake game.”

“Metal-oxide thin-film transistors based on IGZO are inherently n-type. This results in circuits with a higher static power consumption compared to complementary technologies. To address this, we created our own design flow starting from the open-source file of the MOS6502 microprocessor – one of the most influential microprocessors ever designed,” he said.

“We engineered the number of cells and logic gates to obtain the most optimal design for our flexible6502 microprocessor in terms of area, power, and speed – using pseudo-CMOS as our logic family. This unique design flow allowed us to create a new standard cell library for metal-oxide thin-film technology that can be used to innovate applications based on metal-oxide thin-film technology.”

The chip was built by UK foundry and flexible chip developer PragmatIC Semiconductor, which showed the chip last year and also worked with ARM on a plastic version of the Coretex-M0 processor.

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“Until recently, there was no mature and robust technology available for integrating such a large number of thin-film transistors with sufficient yield. Our FlexLogIC fab now enables the rapid turnaround of such complex new designs at an ultra-low cost, delivering ICs on thin and flexible wafers. Our FlexIC Foundry service continues to be instrumental in enabling design teams like the one at imec to expand the range of design and use cases for flexible electronics,” said Brian Cobb, VP Product Development at PragmatIC.

The processor was developed as part of a E1.5m Horizon 2020 grant targeting amorphous oxide TFTs on plastic substrates for very large scale flexible integrated circuits. The project developed a new logic style, called “quasi-CMOS”, based on unipolar, oxide dual-gate thin-film transistors. This achieved lower power consumption in unipolar logic gates in a novel way by taking advantage of dynamic backgate driving and of the transistor’s unique low off-state leakage current, without compromising on switching speed.

“As such, this work nicely wraps up my ERC Starting Grant which aimed at opening up new horizons in the field of thin-film transistor technology,” said Myny.

www.imec-int.com; www.pragmaticsemi.com

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