2, Imperial College London, London, , United Kingdom
3, University of Oxford, Oxford, , United Kingdom
4, Nanjing Tech University, Nanjing, , China
5, King Abdullah University of Science and Technology (KAUST), Thuwal, , Saudi Arabia
In an effort to address the fast-growing demand for data storage within the emerging sector of printed electronics and its wider deployment in the Internet of Things, solution-processable polymer-electret based charge-trapping organic field-effect transistor (OFET) memory technologies have been attracting increasing attention owing to their intriguing characteristics, including non-destructive read-out, easily integrated structures for circuitry, inexpensive fabrication processes for large-area manufacturing. However, to date a polymer electret OFET memory often requires multiple fabrication steps, including both vacuum- and solution-phase deposition techniques. This is mainly because full solution-processing is limited by solvent orthogonality during the sequential depositions of organic layers (i.e. polymer electrets and organic semiconductors). To simplify fabrication protocols, hence reducing manufacturing costs, alternative processing approaches and/or materials systems for polymer electret OFET memory are urgently needed.
Here we report a universal approach for developing an alternative semiconducting system based on organic blends using small molecules and polymer electrets and its application in non-volatile OFET memories. Such blend systems are known to self-assemble into two vertically separated components due to the phase separation occurring during the film deposition, hence forming a high mobility semiconductor layer (small-molecule) and a charge trapping layer (polymer electret). Using this approach, solution-grown 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-PEN)/polystyrene (PS) blend OFET memory devices exhibit excellent non-volatile memory characteristics with a fast switching speed (~50 µs, despite the long channel length, 30 µm, employed), low operation voltages (<15 V), and highly-stable 8-level (i.e. 3 bits) data storage characteristics. This development paves the way to high-density data storage using single memory cells and could potentially minimize the overall system cost without the need for device-size downscaling and/or complex integration.
Furthermore, we were able to demonstrate flexible, non-volatile TIPS-PEN/PS based OFET memories with superb operating characteristics, such as highly-reliable memory operation with programming/erasing cycles well in excess of 10,000. Finally, the same blend material approach is successfully extended to other high-mobility organic semiconductors such as 2,7-Dioctylbenzothieno[3,2-b]benzothiophene (C8-BTBT) blended with PS, further demonstrating the universal nature of the proposed technology. The development of such single-step deposited charge-trapping polymer electret and organic semiconductor systems not only simplifies the manufacturing protocols but also creates a new promising direction for future research in the emerging area of printed memory systems.
 W.-C. Chen, Electrical Memory Materials and Devices, Royal Society of Chemistry, Cambridge, 2015.