Holst Centre, imec and their partner Evonik have prototyped 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 2.1 kHz.
The breakthrough results were published online in Scientific Reports, an open access journal from the publisher of Nature.
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 optimisations have resulted in a high maximum clock frequency of 2.1 kHz. 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.
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 radio frequency identification (RFID) and near field communication (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 (imec and TNO) 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.
A thin-film microprocessor with inkjet print-programmable memory
Kris Myny | Steve Smout | Maarten Rockelé | Ajay Bhoolokam | Tung Huei Ke | Soeren Steudel | Brian Cobb | Aashini Gulati | Francisco Gonzalez Rodriguez | Koji Obata | Marko Marinkovic | Duy-Vu Pham | Arne Hoppe | Gerwin H. Gelinck | Jan Genoe | Wim Dehaene | Paul Heremans
Scientific Reports 4, Article number: 7398 | doi:10.1038/srep07398
Received 29 August 2014 | Accepted 14 November 2014 | Published 10 December 2014
Abstract
The Internet of Things is driving extensive efforts to develop intelligent everyday objects. This requires seamless integration of relatively simple electronics, for example through ‘stick-on’ electronics labels. We believe the future evolution of this technology will be governed by Wright's Law, which was first proposed in 1936 and states that the cost of a product decreases with cumulative production. This implies that a generic electronic device that can be tailored for application-specific requirements during downstream integration would be a cornerstone in the development of the Internet of Things. We present an 8-bit thin-film microprocessor with a write-once, read-many (WORM) instruction generator that can be programmed after manufacture via inkjet printing. The processor combines organic p-type and soluble oxide n-type thin-film transistors in a new flavor of the familiar complementary transistor technology with the potential to be manufactured on a very thin polyimide film, enabling low-cost flexible electronics. It operates at 6.5 V and reaches clock frequencies up to 2.1 kHz. An instruction set of 16 code lines, each line providing a 9 bit instruction, is defined by means of inkjet printing of conductive silver inks.
