Integrated circuits based on organic thin-film transistors (OTFTs) have been in development for over 15 years with development scientists working on both the speed and complexity of integrated circuits for a range of electronics applications. However, one of the main barriers to the growth of printed electronic circuits was the ability to manufacture circuits using high-throughput, solution-coating techniques with the necessary semiconductor performance to allow fast logic circuits to be realised in standard digital circuits such as ring oscillators.
SmartKem has just fabricated a tru-FLEX-based all-organic 5‑stage OTFT ring oscillator using solution coating that operates with an oscillation frequency above 500kHz and stage delay of less than 200ns. This is the highest frequency reported to date for a unipolar ring oscillator fabricated using a solution-processed organic semiconductor and gate dielectric. It is also expected that with trivial optimisation of the circuit design, oscillator frequencies well above 1MHz can be easily attained.
This result demonstrates that the historic barrier to realising fast, solution-printed electronics no longer exists, opening the door to a wide range of application possibilities. For instance, with the emergence of the Internet of Things, one market requirement that has not been met is for low-cost, thin, flexible and disposable RFID and NFC tags for the transmission of data from devices, sensors or objects. To achieve the necessary bit rate of 53kbits/s for a RFID or NFC device operating at the standardised frequency of 13.6MHz, a stage gate delay in the logic of less than 400ns is needed. SmartKem’s ring oscillator operates well below this requirement, at 200ns.
A more immediate and pressing application is as a TFT backplane platform for the manufacture of conformal LCD and flexible AMOLED displays. Narrow bezels can now be achieved by the use of ‘integrated gate drivers’ fabricated on the display backplane. Whilst it was once thought that this could only be achieved using inorganic materials such as LTPS, this new result shows that tru-FLEX would allow the manufacture of integrated gate drivers that would not only drive 4K2K displays, but would offer the unique capability of true physical flexibility.
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