Demonstration of 8-bit flexible MCU for low-power applications

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imec, KU Leuven, and PragmatIC Semiconductor, a specialist in flexible electronics, are to demonstrate the fastest 8-bit microprocessor in 0.8µm metal-oxide flexible technology that's capable of running real-time complex assembly code at this week’s International Solid-State Circuits Conference.

The microprocessor was implemented with a unique digital design flow that has allowed the creation of a new standard cell library for metal-oxide thin-film technologies – relevant for designing a broad range of loT applications.

The robust thin-film technology offered by imec’s foundry partner PragmatIC Semiconductor was said to be to integrating the approximately ~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 has already made inroads in terms of health-patch sensors and RFID labels, for example, and as a driver for flat panel displays. The missing piece has been a flexible microprocessor to perform more complex signal processing calculations – as such adding compute functionality to a broad range of IoT applications.

In response, imec has designed a flexible 8-bit microprocessor in 0.8µm indium-gallium-zinc-oxide (IGZO)-transistor technology, that’s able to perform such complex computations.

Commenting Kris Myny, Principal Scientist at imec said, “Our flexible microprocessor shows excellent characteristics for IoT applications, including high speed (71.4kHz max operating speed), low power consumption (11.6mW when running at 10kHz, 134.9mW at max operating speed), and high transistor integration density (~16,000 transistors with 0,8µm gate length in a 24.9mm2 chip). Moreover, at ISSCC 2022, we will showcase real-time correct operation of our circuit by running the complex assembly code of the popular Snake game.”

With the microprocessor, imec has been able to address numerous challenges related to the design of unipolar systems.

Myny said, “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. 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. 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.”

To fabricate the flexible microprocessor, imec turned to foundry partner PragmatIC, whose FlexIC Foundry offers rapid prototyping and high-yield volume manufacturing of flexible integrated circuits.

Brian Cobb, VP Product Development at PragmatIC said, “Until recently, there was no mature and robust technology available for integrating such a large number of thin-film transistors with sufficient yield. Our pioneering 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.”

This research was performed in the framework of the ERC starting grant FLICs under grant agreement No 716426 under the European Union's Horizon 2020 research and innovation programme.