Toward Printed Integrated Circuits based on Unipolar or Ambipolar Polymer Semiconductors

Abstract

For at least the past ten years printed electronics has promised to revolutionize our daily life by making cost-effective electronic circuits and sensors available through mass production techniques, for their ubiquitous applications in wearable components, rollable and conformable devices, and point-of-care applications. While passive components, such as conductors, resistors and capacitors, had already been fabricated by printing techniques at industrial scale, printing processes have been struggling to meet the requirements for mass-produced electronics and optoelectronics applications despite their great potential. In the case of logic integrated circuits (ICs), which constitute the focus of this Progress Report, the main limitations have been represented by the need of suitable functional inks, mainly high-mobility printable semiconductors and low sintering temperature conducting inks, and evoluted printing tools capable of higher resolution, registration and uniformity than needed in the conventional graphic arts printing sector. Solution-processable polymeric semiconductors are the best candidates to fulfill the requirements for printed logic ICs on flexible substrates, due to their superior processability, ease of tuning of their rheology parameters, and mechanical properties. One of the strongest limitations has been mainly represented by the low charge carrier mobility (μ) achievable with polymeric, organic field-effect transistors (OFETs). However, recently unprecedented values of μ ∼ 10 cm(2) /Vs have been achieved with solution-processed polymer based OFETs, a value competing with mobilities reported in organic single-crystals and exceeding the performances enabled by amorphous silicon (a-Si). Interestingly these values were achieved thanks to the design and synthesis of donor-acceptor copolymers, showing limited degree of order when processed in thin films and therefore fostering further studies on the reason leading to such improved charge transport properties. Among this class of materials, various polymers can show well balanced electrons and holes mobility, therefore being indicated as ambipolar semiconductors, good environmental stability, and a small band-gap, which simplifies the tuning of charge injection. This opened up the possibility of taking advantage of the superior performances offered by complementary "CMOS-like" logic for the design of digital ICs, easing the scaling down of critical geometrical features, and achieving higher complexity from robust single gates (e.g., inverters) and test circuits (e.g., ring oscillators) to more complete circuits. Here, we review the recent progress in the development of printed ICs based on polymeric semiconductors suitable for large-volume micro- and nano-electronics applications. Particular attention is paid to the strategies proposed in the literature to design and synthesize high mobility polymers and to develop suitable printing tools and techniques to allow for improved patterning capability required for the down-scaling of devices in order t...

Experimental evidence that short-range intermolecular aggregation is sufficient for efficient charge transport in conjugated polymers

“…S10). To the best of our knowledge these values are among the best ever reported for solution-processed organic CMOS-like inverters (37).…”

Inkjet Printed Single‐Walled Carbon Nanotube Based Ambipolar and Unipolar Transistors for High‐Performance Complementary Logic Circuits

“…Direct printing technologies, compatible with mass production, [ 1,2 ] can enable large-area electronics for wearable, portable, and distributed micro/opto-electronics and sensing applications. [3][4][5][6][7][8] Different solution-processable semiconductors are being developed and tested in fi eld-effect transistors (FETs), among which conjugated small-molecule and polymer semiconductors are one of the most investigated approaches.…”

Toward Perceptive Soft Robots: Progress and Challenges

“…In most soft sensing systems, electronic interfaces are placed on rigid bases far away from the sensing sites because conventional silicon‐based electronics are inherently incompatible with soft material–based systems. Substantial progress has been made in flexible organic electronics,123 but it is still far away to be massively utilized in sensing systems because of the limited performance, functionality, and stretchability. Very recently, the intrinsically stretchable transistor‐based skin electronics124 from Bao and co‐workers would be promising to develop truly stretchable electronics to be fully integrated into soft systems.…”