2D layered materials may spawn a revolution in the field of solid-state micro/nano-electronic devices and circuits, owing to their outstanding electronic, physical, chemical, and thermal properties.^[1] Some top scientists and companies have suggested that 2D materials could be used to mitigate the limitations of silicon technologies, help to extend Moore's law, and create new concept devices beyond the complementary metal–oxide–semiconductor (CMOS) technology.^[2] Top microchip manufacturers like TSMC, Samsung, Intel, and IBM and semiconductor research institutes like IMEC have already reported prototype field-effect transistors with 2D semiconducting channels^{[3, 4]} (Figure 1). The International Roadmap for Devices and Systems (IRDS)—a document written by a world-class group of industry-led experts (who foreshadow important developments in the past)—lists 2D materials as an option for commercial transistors and other beyond-CMOS devices around 2028 (see Figure 2).^[5]

The current status is: electronic devices made of 2D materials produced by mechanical exfoliation of small crystals have exhibited outstanding performance, such as transistors with 2D semiconducting channels that achieve high mobility (700 cm² V⁻¹ s⁻¹), high current on/off ratio (>10⁵), and low subthreshold swing (74 mV per decade).^[6] However, when nanosized devices (area of <0.1 µm²) are produced using scalable fabrication techniques, such as chemical vapor deposition (CVD), the performance remarkably degrades. For example, some of the best 2D-materials-based nanosized transistors (channel area of ≈0.0075 µm²) fabricated by industry show low mobility of ≈20 cm² V⁻¹ s⁻¹ and high subthreshold swing ≈134 mV per decade,^[7] with very high device-to-device variability. The reason is the presence of local defects in the 2D materials and contamination.^[3] Interestingly enough, 2D materials show promise for lower variability compared to silicon technology because of the amazing electrostatic control associated with these very thin channels.^[8]

By now, we have seen that 2D materials have started to be integrated in some commercial products that do not require a high integration density, such as sensors^[9] and speciality cameras^[10]—in these bigger devices the effect of local defects in the 2D material is not so detrimental. However, commercial high-integration-density electronic circuits exploiting the properties of 2D materials are still a matter or research. Hopefully, as 2D materials start to enter in industrial laboratories with more controlled environments and materials processing (lithography, etching, deposition), the density of local defects and contamination can be reduced and ultrascaled devices might exhibit better performance and reliability.

In terms of exploratory research, the next steps to be taken in the field of 2D materials are to develop reliable device-fabrication flows and to prototype electronic circuits capable of performing operations that single devices cannot do, such as logic gates using transistors or vector matrix multiplication using crossbar arrays of memristors (among many others). In this special issue, Advanced Materials brings you some of the most advanced knowledge in the field of 2D-materials-based electronic circuits. The special issue includes 21 articles from leading experts, touching upon multiple aspects related to fabrication, characterization, and modelling of electronic circuits made of 2D materials.

The first group of articles in this special issue focuses on materials synthesis and their integration in micro/nano-electronic devices and circuits. Dr. Hyeon-Jin Shin from Samsung (article number 2103286) and Prof. Xixiang Zhang from King Abdullah University of Science and Technology (KAUST) (article number 2201253) present two research articles on material synthesis, the first one about precise layer control in 2D semiconductors and the second one about graphene-mesh metamaterials. Prof. Mario Lanza, also from KAUST (article number 2104138), shows that the evaporation of metal can damage the crystallographic structure of even the most stable 2D materials (multilayer hexagonal boron nitride); and that, quite to the contrary, the deposition of the same type of metal via inkjet printing does not produce any damage. This section is complemented with a Perspective article from Dr. Tom Schram from Imec (article number 2109796) describing the process modules to follow for a correct integration of 2D semiconductors on silicon wafers to build integrated circuits.

The second group of articles focuses on the development of electronic memories. This is one of the most important circuits in microelectronics, and its market has reached a size of ≈166.5 billion USD in 2021,^[11] only counting standalone memories. Prof. Yanqing Wu from Peking University (article number 2106321) presents a nonvolatile logic and ternary content-addressable memory based on complementary black phosphorus and rhenium disulphide transistors. One of the most striking features of their work is that they developed a Schmidt-like flip-flop using only two transistors, while conventional silicon counterparts typically use six transistors. Prof. Pi-Ho Hu from National Taiwan University (article number 2107894) foresees that 2D-materials-based static random access memories designed with state-of-the-art contact resistance, mobility, and equivalent oxide thickness might achieve excellent stability and operation speed at the 1 nm node. The status of 2D-materials-based electronic memories is further discussed in two review articles coming from the groups of Prof. Han Wang from University of Southern California (article number 2202371), and Prof. Xixiang Zhang from KAUST (article number 2201880). The first review discusses the advantage of introducing 2D materials in static random access memories, dynamic random access memories, and flash memories, and the second review touches on electronic memories based on principles that are in a more embryonic stage, such as the ferroelectric memristive effect and magnetic skyrmions.

The third group of articles focuses on neuromorphic computation and development of artificial neural networks. This field is gaining a lot of attention because it can compute a lot of data in parallel to avoid the von Neuman bottleneck,^[12] sparing time and energy. Prof. Saptarshi Das from Penn State University (article number 2202535) connected 21 memtransistors made of photosensitive molybdenum disulfide to form two cascaded three-stage inverters and one XOR logic gate. The proposed circuit was employed to encode visual information in a spiking neural network. Prof. Yuchao Yang from Peking University (article number 2108826) connected two ferroelectric semiconductor field-effect transistors with two series resistors, all of them made of α-phase indium (III) selenide (α-In₂Se₃), and, based on its experimental figures-of-merit, concluded that a multilayer recurrent neural network made of such building blocks could offer high-harmonic generation and progressive low-pass filtering effect, suitable for reservoir computing. Prof. Yang Chai from The Hong Kong Polytechnic University (article number 2107754) designed and fabricated a complementary cell with two transistors (one n-type and another p-type) using a thin film of tungsten diselenide and polyvinylidene fluoride as dielectric. Despite being small, this circuit exhibited 6 bit storage capability, low nonlinearity, and high conductance modulation range, and could be successfully used to solve classical computation exercises (like the cart-pole problem) consuming very low power (32 pJ per forward process). This section is complemented with one Review article from Prof. Mark Hersam from Northwestern University (article number 2108025) describing the recent progress on memtransistors for neuromorphic circuits and systems, as well as the main challenges to be solved.

The fourth group of articles focuses on applications in different fields. Prof. Husam Alshareef from KAUST (article number 2201253) synthesized titanium carbide (Ti₃C₂T_X) inks by the liquid-phase exfoliation (LPE) method, and deposited them by spray-coating and vacuum annealing to form thin films with high conductivity (≈11 000 S cm⁻¹) and low work function (≈4.5 eV). These films proved to be useful for the fabrication of transistors, and their application in different types of inverters and rectifiers was successfully demonstrated. Prof. Wenzhong Bao from Fudan University (article number 2202472) used the CVD method to synthesize monolayer molybdenum disulfide sheets on 4 inch wafers, which exhibited mobilities between 3 and 30 cm² V⁻¹ s⁻¹. More importantly, his team managed to construct inverters, ring oscillators, logic gates, multiplexers, and demultiplexers. Prof. Max Lemme from RWTH Aachen university (article number 2108469) also brings us a prototype based on semiconducting molybdenum disulfide films synthesized by the CVD-method, but in this case on flexible substrates for high-frequency circuits. More specifically, his team fabricated power-detectors with a voltage responsivity of 45 V W⁻¹ at 18 GHz and a dynamic range of 30 dB, even better than that achieved using CMOS transistors and GaAs Schottky diodes. Prof. Zengfeng Di from Chinese Academy of Sciences (article number 2201630) exploited the piezoelectric potentials generated in strained molybdenum tungsten disulfide sheets with different concentrations to produce nanogenerators, and used them to build self-powered real-time arterial pulse sensors. This section is complemented with two reviews, the first one from Prof. Renato Negra, also from RWTH Aachen (article number 2108473), on different graphene-based microwave circuits, and the second one from Prof. David Jiménez from Universitat Autonoma de Barcelona (article number 2201691) on compact modelling for the simulation of integrated circuits based on graphene field-effect transistors.

The special issue is completed with three review articles sharing, from different perspectives, the overall vision of the field, the main challenges to be overcome, and the possible strategies to follow in order to see 2D materials in commercial integrated circuits. In the first two Prof. He Tian from Tsinghua University (article number 2201916) and Prof. Peng Zhou from Fudan University (article number 2106886) discuss the status and prospects of 2D semiconductors, focusing on the development of transistors and how these can complement the mainstream silicon technology. In the third one, Prof. Tibor Grasser from TU Wien (article number 2201082) discusses whether this entire field of 2D-materials-based electronic devices and circuits is a scientific pipe dream or a disruptive technology. One should bear in mind that, after showing some “promising” performance, many other nanomaterials received huge public and private investment and, due to the difficult manipulation and processing, never ended up delivering benefits to the micro-/nanoelectronics industry.