Holst Centre, imec, Evonik Develop Thin-Film Hybrid Oxide-Organic Microprocessor

Holst Centre, imec and Evonik have realized a general-purpose 8-bit microprocessor, manufactured using complementary thin-film transistors (TFTs) processed at temperatures compatible with plastic foil substrates (250°C). The new “hybrid” technology integrates two types of semiconductors – metal-oxide for n-type TFTs (iXsenic, Evonik) and organic molecules for p-type TFTs – in a CMOS microprocessor circuit, operating at unprecedented for TFT technologies speed – clock frequency 2.1kHz. The breakthrough results were published online in Scientific Reports, an open access journal from the publisher of Nature.

Low temperature thin-film electronics are based on organic and metal-oxide semiconductors. They have the potential to be produced in a cost effective way using large-area manufacturing processes on plastic foils. Thin-film electronics are, therefore, attractive alternatives for silicon chips in simple IC applications, such as RFID and NFC tags and sensors for smart food packaging, and in large-area electronic applications, such as flexible displays, sensor arrays and OLED lamps. Holst Centre’s research into thin-film electronics aims at developing a robust, foil-compatible, high performance technology platform, which is key to making these new applications become a reality.

The novel 8-bit microprocessor performs at a clock frequency of 2.1 kHz. It consists of two separate chips: a processor core chip and a general-purpose instruction generator (P2ROM). For the processor core chip, a complementary hybrid organic-oxide technology was used (p:n ratio 3:1). The n-type transistors are 250°C solution-processed metal-oxide TFTs with typically high charge carrier mobility (2 cm2/Vs). The p-type transistors are small molecule organic TFTs with mobility of up to 1 cm2/Vs. The complementary logic allows for a more complex and complete standard cell library, including additional buffering in the core and the implementation of a mirror adder in the critical path. These optimizations have resulted in a high maximum clock frequency of 2.1kHz.

The general-purpose instruction generator or P2ROM is a one-time programmable ROM memory configured by means of inkjet printing, using a conductive silver ink. The chip is divided into a hybrid complementary part and a unipolar n-TFT part and is capable of operating at frequencies up to 650 Hz, at an operational voltage of Vdd=10V.