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Room temperature fabrication of amorphous oxide semiconductors enables a cost-efficient production of devices on flexible and large-area substrates. Metal-semiconductor field-effect transistors using amorphous zinc-tin-oxide (ZTO) thin films with a cation composition of 1:1 Zn:Sn are presented. The n-type ZTO channel is deposited by long-throw magnetron sputtering from a ceramic target at room temperature on glass substrates. Reactively sputtered platinum is used as a gate contact material. We report on/off current ratios as high as 1.8 × 106, a threshold voltage of 0.47 V, and a sub-threshold swing of 124 mV dec−1 for as-fabricated devices. Using negative bias treatment, an improvement in device properties is observed, namely, a decrease in the off-current by two orders of magnitude and a reduction of the sub-threshold swing. An inverter based on as-deposited ZTO metal-semiconductor field-effect transistors exhibits a high peak gain magnitude of 119 and a small uncertainty level of 160 mV for a supply voltage of 3 V.

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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...

Deposition of semiconductors on bendable substrates is a crucial step toward flexible circuitry and deposition by a roll-to-roll process. Since most bendable substrates have limited temperature stability (normally degradation starts between 150 °C and 300 °C), processing temperatures are typically below that of rigid substrates. Amorphous oxide semiconductors (AOSs) such as indium gallium zinc oxide (IGZO) can be fabricated at room temperature (RT) and exhibit electron mobilities >10 cm2 V−1 s−1 being a pre-requisite for application in backplanes of displays. While IGZO is already commercially exploited, the search for alternative materials is highly relevant because indium and gallium are rare and expensive. Zinc tin oxide (ZTO) is a promising AOS since zinc and tin are highly abundant and cheap. In this letter, we discuss RT-fabricated n-type ZTO thin films used as the channel material in flexible inverter circuits based on junction field-effect transistors. RT-fabricated nickel oxide is used as a semitransparent p-type gate material. The devices are fabricated on flexible polyimide and exhibit an excellent peak gain magnitude of 464 and uncertainty level as low as 130 mV at a supply voltage of only 3 V. They are characterized before and after bending at various radii. Even after bending at 2 mm radius, the inverters behave still very well.