Printed sensors are among the most successful groups of devices within the domain of printed electronics, both in terms of their application versatility and the emerging market share. However, reports on fully printed gas sensors are rare in the literature, even though it can be an important development toward fully printed multisensor platforms for diagnostics, process control, and environmental safety-related applications. In this regard, here, we present the traditional tin oxide-based completely inkjet-printed co-continuous and mesoporous thin films with an extremely large surface-to-volume ratio and then investigate their NO 2 sensing properties at low temperatures. A method known as evaporation-induced self-assembly (EISA) has been mimicked in this study using pluronic F127 (PEO 106 -PPO 70 -PEO 106 ) as the soft templating agent and xylene as the micelle expander to obtain highly reproducible and spatially homogeneous co-continuous mesoporous crystalline SnO 2 with an average pore diameter of the order of 15−20 nm. The fully printed SnO 2 gas sensors thus produced show high linearity for NO 2 detection, along with extremely high average response of 11,507 at 5 ppm NO 2 . On the other hand, the sensors show an ultralow detection limit of the order of 20 ppb with an easy to amplify response of 31. While the excellent electronic transport properties along such co-continuous, mesoporous structures are ensured by their well-connected (co-continuous) ligaments and pores (thereby ensuring high surface area and high mobility transport at the same time) and may actually be responsible for the outstanding sensor performance that has been observed, the use of an industrial printing technique ascertains the possibility of high-throughput manufacturing of such sensor units toward inexpensive and widerange applications.

Inkjet-printed co-continuous mesoporous structures have been demonstrated for a large set of functional oxides. Channel-length-independent electronic transport was achieved when the mesoporous oxides were used to obtain printed, vertical edge FETs.

Here, the first term, V GS S ψ ∂ ∂ , known as the "body factor", cannot be less than 1 for standard MOSFET electrostatics, and the second term log I ( ) S 10 D ψ ∂ ∂ that is equals ln(10) β K T q and is 60 mV dec −1 at room temperature, determines the minimum limit of the subthreshold swing for the thermionic emission over the Boltzmann barrier. This in turn defines the steepness/slope of the transfer curves, the signal gain and the dynamic power dissipation of the electronic switches. One way to circumvent this limit is to allow tunneling through the barrier; in this case band-to-band-tunneling (BTBT) would be required as single career tunneling cannot lead to subthermionic transport. [2] However, the BTBT field-effect transistors (FETs) typically show low Oncurrents; while there are large number of subthermionic tunnel FETs reported in the literature, [3][4][5][6][7][8][9][10][11][12][13] the recent ones based on 2D dichalcogenides demonstrate particularly high performance. [2,14,15] An alternative approach to achieve subthermionic transport, originally proposed by Salahuddin and Datta [16] and later experimentally demonstrated by various research groups, [16][17][18][19][20][21][22][23][24][25][26][27] deals with concept that can actually reduce the body factor to values less than 1. This involves stabilizing a negative capacitance regime by placing a ferroelectric and dielectric layer in series to comprise the MOS capacitor. In this case, the Boltzmann activation barrier remains intact; however, an artificial voltage amplifier or step-up transformer is created using the sharp switching of the dipoles (i.e., exploiting the square-shaped P-E loop) of the ferroelectric and thereby a faster change in Ψ S (surface potential) becomes possible, as compared to the applied ∂V GS . However, in either of these approaches, specific requirements in terms of semiconductors (e.g., single sheet of 2D material), dielectrics or interfaces (e.g., ferroelectric/dielectric interface in case of negative capacitance (NC)-gate FETs) are there, which are certainly nontrivial to be replicated, when the complete device is to be solution processed/printed. Consequently, subthermionic transport Subthreshold slope of field-effect transistors (FETs) less than the fundamental Boltzmann limit (60 mV dec −1 at 300 K) is demonstrated either using band-to-band tunneling or negative capacitance (NC) ferroelectric-gate transistors. However, it is difficult to replicate both of these strategies in solution-processed/printed FETs. Nonetheless, it is shown that the use of a metal-insulator-metal-semiconductor architecture alongside electrolyte gating can simultaneously create highly reproducible static negative capacitance behavior in printed FETs, resulting in subthermionic transport for over four decades of drain currents with a subthreshold slope as low as 16 mV dec −1 , and thereafter a strong thermionic transport regime, characterized by an unprecedented On-current of 195 µA µm −1 , a transconductance of 215 µS µm, and a metal-like On-state res...

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Significant developments have also been noted in the printed/flexible electronics domain, where the performance of solution-processed thin film transistors (TFTs) may now easily be compared with their vacuum deposited (e.g. sputtered or pulsed-laser deposited) counterparts. [6] Notably, these solutionprocessed devices are of high interest for a wide range of portable electronic or Internet of Things (IoT) related devices. However, any digital electronic component essentially requires complementary metal oxide semiconductor (CMOS) technology to ensure high noise immunity and low power consumption. [7] Unfortunately, it is only the oxygen deficient n-type oxide semiconductors, the performance of which nearly matches that of polycrystalline silicon, whereas the performance of the p-type materials is substantially lower in comparison. In fact, the problem associated with the absence of matching/comparable p-type oxide semiconductors range beyond the CMOS electronics to other p-n junction devices, for example, solar cells. Here, the transport properties of p-type oxide semiconductors are primarily limited by their highly localized oxygen 2p orbitals in the valence band maximum (VBM), deep VBM, rigorous environmental and fabrication conditions and difficulties in high-quality film formation. [8][9][10][11] It should also be noted that the examples of solutionprocessed p-type oxide semiconductors are essentially limited to NiO, Cu x O, SnO, and delafossite-type CuMO 2 (M = Al and Cr). [8][9][10][11] Among these, Cu x O has been the most promising candidate owing to its high theoretical Hall mobility, non-toxicity, suitable optical properties, and low cost. [12,13] Although it has been a well-known semiconductor even in the pre-silicon era, resurgent interest in Cu 2 O has been spurred when Matsuzaki et al. demonstrated a Hall mobility of 90 cm 2 V −1 s −1 for epitaxial Cu 2 O films on MgO in 2008. [14] The subsequent studies have reported about p-type Cu x O deposition via sputtering, [14] pulsed laser deposition [15,16] and thermal oxidation techniques. [17] Solution-based fabrication techniques involving either spin/spray coating or inkjet printing have also been reported. [15,[18][19][20][21][22][23] However, when it comes to Cu x O-based TFTs, the typical process temperatures (≥400 °C) or reported operating voltages have always been very high. [24][25][26] Oxide semiconductors are becoming the materials of choice for modern-day display industries. The performance of solution-processed oxide thin film transistors (TFTs) has also improved dramatically over the last few years. However, while oxygen deficient n-type semiconductors can demonstrate excellent electronic transport, the performance of p-type materials has remained unsatisfactory. Consequently, only the n-type semiconductor-based pseudo-complementary metal oxide semiconductor (CMOS) technology has attracted tremendous interests recently; yet, the high power dissipation remains a problem. Here, this work demonstrates all-oxide CMOS invertors with high-performa...