Flex6502: A Flexible 8b Microprocessor in 0.8µm Metal-Oxide Thin-Film Transistor Technology Implemented with a Complete Digital Design Flow Running Complex Assembly Code

Abstract

Integrated circuits based on thin-film transistors (TFTs) are attractive for use in many areas, including the Internet-of-Things (loT), where ultra-thin circuits on flexible substrates at a low-cost per unit area provide significant advantages over silicon CMOS. A complete loT circuit based on TFTs requires complex digital circuits to perform embedded control and signal-processing calculations. In this work, we have demonstrated a microprocessor capable of such complex computations and showcase it by running a complex assembly code. We selected the MOS 6502 for this, as it was one of the most commonly used microprocessors in the late 1970s, when applications with embedded software started to emerge. The 6502 came in various, more advanced iterations through the following decades [1]. The Flex6502 has been fabricated in an 800nm Indium-Gallium-Zinc-Oxide (IGZO) TFT process technology, manufactured on a flexible polyimide substrate, with total thickness less than 30µm. Based on the comparison of two logic styles, pseudo-CMOS logic [2] and resistive load logic [3], we selected pseudo-CMOS as the better-suited logic family for robustness and energy efficiency. We used the assembly code of the well-known Snake game to demonstrate real-time correct operation of the circuit.