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circuitry is the TOAS zinc-tin-oxide (ZTO) since it can be deposited at room temperature (RT) enabling the low-cost fabrication of transparent, flexible circuits. [3,4] So far, several ZTO-based metal-insulator field-effect transistors (MISFETs) and related inverters have been reported in the literature, however, those devices required a deposition at elevated temperatures or post-growth annealing processes in order to perform well. [5][6][7] Reports on associated integrated circuits comprising ZTO MISFETs are restricted to thin film transistor (TFT) logic technology, based on depletion and enhancement transistors, as well as complementary metal oxide semiconductor logic technology, requiring compatible p-type and n-type FETs. Further, an additional fabrication step is necessary for the preparation of the gate insulator. Such MISFETs and related integrated circuits usually require high operating voltages due to the voltage drop across the insulator as well as a limited switching speed due to carrier scattering at the channel-insulator interface. [8] Previously reported ZTO-based ring oscillators, consisting of five or seven stages, exhibited oscillation frequencies between 0.85 and 800 kHz at operating voltages ranging from 5 to 60 V. [9][10][11] Single stage delay times, resulting in oscillation frequencies compatible with an ISM band, have so far not been reported for ZTObased ring oscillators.Recently, first metal-semiconductor field-effect transistors (MESFETs) and simple inverter circuits, comprising depletion-type MESFETs based on room temperature-deposited ZTO channel layers, have been reported. [12,13] Concerning device performance and fabrication efficiency, the absent gate insulator in case of MESFETs enables improved switching behavior as well as more fail-safe and faster processing. However, in case of inverters consisting of depletion-type FETs only, a shifting of the output signal is necessary to cover the voltage range required for switching a subsequent inverter. In the current work, we employ the Schottky diode FET logic (SDFL) approach that facilitates a sufficient level shift of the inverters output signal to enable a successful cascading of a series connection of inverters (see Figure 1). Since the SDFL layout consists of unipolar devices only, transistor channels can be deposited using a single photolithographic patterning process.Schottky diode FET logic (SDFL) ring oscillator circuits comprising metalsemiconductor field-effect transistors (MESFETs) based on amorphous zinc-tin-oxide (ZTO) n-channels are presented. The ZTO channel layers are deposited entirely at room temperature by long-throw magnetron sputtering. Best MESFETs exhibit on/off current ratios as high as 8.6 orders of magnitude, a sub-threshold swing as low as 250 mV dec −1 , and a maximum transconductance of 205 µS. Corresponding inverters show peakge gain magnitude (pgm) values of 83 with uncertainty levels as low as 0.5 V at an operating voltage of 5 V. Single stage delay times down to 277 ns are measured for three-stage ring...

TSOs are ZnO, SnO 2 , Ga 2 O 3 , and In 2 O 3 as well as several related compound materials and alloy systems, due to their broad application potential in the field of optoelectronic devices. [1-3] Especially transparent amorphous oxide semiconductors (TAOSs) have emerged into a thriving distinct area of research over the last few years, and since then, the field has grown rapidly toward, for instance, novel thin-film transistor (TFT) backplanes for next-generation flat-panel displays. [4,5] Alongside their high transparency, TAOSs exhibit a superior, at least tenfold higher free-carrier mobility compared to conventional amorphous silicon thin films and allow homogeneous large-scale deposition at sufficiently low temperatures, enabling the fabrication of transparent devices on flexible substrates. The by far most mature and already widely commercially exploited representative indium gallium zinc oxide (IGZO); however, contains scarce elements such as indium which innovative research is attempting to substitute by material systems consisting of abundant cations only. [6] One suitable candidate that meets these requirements and gained popularity particularly in the recent couple of years is amorphous zinc tin oxide (ZTO). ZTO is composed of earth-abundant, nontoxic elements only and exhibits, in addition to its optical transparency, a reasonably high free-carrier mobility with reported values up to 12.7 cm 2 V −1 s −1 in case of ZTO thin films fabricated at room temperature. [7] The first TFTs implementing amorphous ZTO as channel material have been reported by Chiang et al. back in 2005, followed by numerous studies on ZTO-based TFTs or rather metal-insulator-semiconductor field-effect transistors (MIS-FETs), fabricated using various deposition methods. [8-13] According to previous reports, however, the realization of MISFETs based on amorphous ZTO, including transparent devices, has up to date exclusively been limited to deposition at elevated temperatures or postdeposition annealing treatment in order to achieve sufficient functionality. [8,14-16] As alternatives to MISFET structures, metal-semiconductor fieldeffect transistors (MESFETs), implementing an n-ZTO/AgO x Schottky barrier diode as gate contact, have been reported by

Recent advances in the field of integrated circuits based on sustainable and transparent amorphous oxide semiconductors (AOSs) are presented, demonstrating ultrahigh performance operating state-of-the-art integrated inverters comprising metal–semiconductor field-effect transistors (MESFETs) with amorphous zinc tin oxide (ZTO) as a channel material. All individual circuit layers have been deposited entirely at room temperature, and the completed devices did not require undergoing additional thermal annealing treatment in order to facilitate proper device functionality. The demonstrated ZTO-based MESFETs exhibit current on/off ratios of over 8 orders of magnitude a field-effect mobility of 8.4 cm2 V−1 s−1, and they can be switched within a voltage range of less than 1.5 V attributed to their small subthreshold swing as low as 86 mV decade−1. Due to adjustments of the circuit layout and, thus, the improvement of certain geometry-related transistor properties, the associated Schottky diode FET logic inverters facilitate low-voltage switching by exhibiting a remarkable maximum voltage gain of up to 1190 with transition voltages of only 80 mV while operating at low supply voltages ≤3 V and maintaining a stable device performance under level shift. To the best of our knowledge, the presented integrated inverters clearly exceed the performance of any similar previously reported devices based on AOS, and thus, prove the enormous potential of amorphous ZTO for sustainable, scalable low-power electronics within future flexible and transparent applications.

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