Researchers Turn to the Humble MOS 6502 to Prove a Multi-Project Foundry Model for Flexible Chips

Researchers from KU Leuven are hoping to increase interest in flexible semiconductors — by showing that a foundry production model with multiple different projects on each wafer is as applicable to flexible chips as it is to their more rigid counterparts.

"We will not compete with silicon-based chips, we want to stimulate and accelerate innovation based on flexible, thin-film electronics," says KU Leuven professor Kris Myny, corresponding author on the paper detailing the team's investigation into a foundry-based model for flexible semiconductors. "This field can benefit hugely from a foundry business model similar to that of the conventional chip industry."

A traditional semiconductor chip is built on a rigid silicon wafer at a foundry — with most chip design firms, including industry giants like AMD and NVIDIA, lacking their own fabrication facilities and instead sending the designs off for production at companies like Taiwan Semiconductor (TSMC). To reduce costs and maximize yields, a single wafer may be home to multiple different chip designs — creating what is known as a Multi-Project Wafer, or MPW.

This same model can apply to flexible semiconductors, the researchers argue, where rather than a rigid silicon wafer the chips are made on a bendable substrate. To prove it, the team designed an implementation of the classic MOS Technology 6502 eight-bit microprocessor and had it produced at two different flexible chip foundries — one using a wafer with amorphous indium-gallium-zinc-oxide and the other a plate with low-temperature polycrystalline silicon. In both cases, the 6502 sat on the substrate alongside other projects — just like a traditional silicon foundry wafer.

While the team readily admits that the 6502, found in beloved vintage computing devices from Commodore, Apple, and Nintendo, among others, isn't in high demand for performance-sensitive applications these days, the thickness of their flexible implementation — under 30 micrometers, less than the width of a human hair — shows promise for building something more complicated for wearable sensors and other skin-applied devices.

They're not the first to build a bendable version of the 6502, either: three years ago PragmatIC, which was one of the two companies chosen to build the research chip along with PanelSemi, teamed up with 6502 co-designer Bill Mensch to build their own implementation on a flexible plastic substrate, and a year later announced a partnership with Imec to build 6502-based flexible chips for energy-efficient Internet of Things (IoT) devices.

The team's work has been published in the journal Nature under open-access terms.