Abstract
Due to their low-temperature processing capability and ionic bonding configuration, amorphous oxide semiconductors (AOS) are well suited for applications within future mechanically flexible electronics. Over the past couple of years, amorphous zinc tin oxide (ZTO) has been proposed as indium and gallium-free and thus more sustainable alternative to the widely deployed indium gallium zinc oxide (IGZO). The present study specifically focuses on the strain-dependence of elastic and electrical properties of amorphous zinc tin oxide thin-films sputtered at room temperature. Corresponding MESFETs have been compared regarding their operation stability under mechanical bending for radii ranging from 5 to 2 mm. Force-spectroscopic measurements yield a plastic deformation of ZTO as soon as the bending-induced strain exceeds 0.83 %. However, the electrical properties of ZTO determined by Hall effect measurements at room temperature are demonstrated to be unaffected by residual compressive and tensile strain up to 1.24 %. Even for the maximum investigated tensile strain of 1.26 %, the MESFETs exhibit a reasonably consistent performance in terms of current on/off ratios between six and seven orders of magnitude, a subthreshold swing around 350 mV/dec and a field-effect mobility as high as 7.5 cm2V−1s−1. Upon gradually subjecting the transistors to higher tensile strain, the channel conductivity steadily improves and consequently, the field-effect mobility increases by nearly 80 % while bending the devices around a radius of 2 mm. Further, a reversible threshold voltage shift of about −150 mV with increasing strain is observable. Overall, amorphous ZTO provides reasonably stable electrical properties and device performance for bending-induced tensile strain up to at least 1.26 % and thus represent a promising material of choice considering novel bendable and transparent electronics.
Highlights
With the rapid evolution of active-matrix flat-panel display technology, significantly advanced by the replacement of commonly deployed silicon by indium gallium zinc oxide (IGZO) approximately a decade ago, amorphous oxide semiconductors (AOS) have considerably gained interest leading to the development of a distinct, thriving research area (Hosono, 2018)
This study focuses on evaluating the effect of bending-induced strain on the properties of amorphous zinc tin oxide (ZTO) thin-films as well as the limits to excessive bending stress on the performance of ZTO based metalsemiconductor field-effect transistor (MESFET)
In order to investigate the impact of bending induced strain on the mechanical properties of amorphous ZTO, force-distance curves of 24 nm thick ZTO thin-films, deposited on polyimide substrates, have been recorded via force spectroscopy using atomic force microscopy (AFM) to monitor the tip-sample interactions via perpendicular cantilever deflection
Summary
With the rapid evolution of active-matrix flat-panel display technology, significantly advanced by the replacement of commonly deployed silicon by indium gallium zinc oxide (IGZO) approximately a decade ago, amorphous oxide semiconductors (AOS) have considerably gained interest leading to the development of a distinct, thriving research area (Hosono, 2018). A few flexible devices implementing ZTO have so far been demonstrated, including MISFETs fabricated between 180°C and 300 °C and junction field-effect transistor (JFET) based inverters (Jackson et al, 2005; Jackson et al, 2006; Fernandes et al, 2018; Lee et al, 2018; Schlupp et al, 2020). Over the past couple of years, JFET and especially metalsemiconductor field-effect transistor (MESFET) technology has proven to be a viable approach to obtain high-performance ZTO based electronics providing both low-power operation and fabrication at room temperature (Dang et al, 2017; Vogt et al, 2018; Lahr et al, 2019a; Lahr et al, 2020a). The successful implementation of amorphous ZTO within integrated circuits such as logic inverters and ring oscillators yielded a remarkable voltage gain as high as 1190 as well as single stage delay times as low as 277 ns, respectively, rendering amorphous ZTO a reasonable competitor within the scope of future AOS based electronic applications (Lahr et al, 2019b; Lahr et al, 2020b)
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