In‐Depth Studies on Rapid Photochemical Activation of Various Sol–Gel Metal Oxide Films for Flexible Transparent Electronics

Abstract

Despite intensive research on photochemical activation of sol–gel metal oxide materials, the relatively long processing time and lack of deep understanding of the underlying chemical courses have limited their broader impact on diverse materials and applications such as thin‐film electronics, photovoltaics, and catalysts. Here, in‐depth studies on the rapid photochemical activation of diverse sol–gel oxide films using various spectroscopic and electrical investigations for the underlying physicochemical mechanism are reported. Based on the exhaustive chemical and physical analysis, it is noted that deep ultraviolet‐promoted rapid film formation such as densification, polycondensation, and impurity decomposition is possible within 5 min via in situ radical‐mediated reactions. Finally, the rapid fabrication of all‐solution metal oxide thin‐film‐transistor circuitry, which exhibits stable and reliable electrical performance with a mobility of >12 cm2 V−1 s−1 and an oscillation frequency of >650 kHz in 7‐stage ring oscillator even after bending at a radius of <1 mm is demonstrated.

Metal oxide semiconductor thin-film transistors for flexible electronics

“…Due to their high T G % 360 C, PI substrates with thickness ranging from %3 to 50lm are widely used. 83,145,191,193,[197][198][199][220][221][222][223] Polyarylate (PAR) foils have also been employed, 192,200,224,225 given their good temperature stability (T G % 330 C), combined with a colorless transparency in the visible range. If the semiconductor deposition is performed at lower temperatures ( 150 C), also PES foils (T G around 200 C) can be utilized.…”

“…The few available examples include Al 2 O 3 196,197 and PMMA layers. 220,221 In particular, 400 nm thick PMMA layers have been utilized to encapsulate flexible solution-processed In 2 O 3 and IGZO TFTs fabricated on thin spin coated PI. 220,221 In particular, PMMA encapsulations allow reducing the mechanical stress (and therefore crack formation) during the release of the PI foil from the rigid glass carrier.…”

“…145,191,193,197,199,222 Alternatively, polymers can be spin coated onto a carrier substrate (thickness of %3-18 lm) and subsequently peeled off after the device fabrication has been completed. 83,220,221 b. General remarks on solution-processing.…”

“…To grow barrier, gate dielectrics, and passivation layers, vacuum-deposition tools like ALD (for Al 2 O 3 ) 83,145,196,197,200 and PECVD (for SiO 2 and SiN x ) 76,83,145,199,222 are commonly utilized. For source/ drain and gate contact deposition, thermal and e-beam evaporation 145,193,220,221,231 as well as sputtering 76,83,190,192,196,197,220,221 are mainly employed. With regards to solution-deposition processes on flexible substrates, there are several techniques in use.…”

“…As a drawback, however, spin coating can only be carried out in batch processes and becomes more challenging when the substrate size is increased. 83,191,192,195,220,221,224 To realize flexible fully solution-processed devices, also spin coated ITO source/drain and gate electrodes have been reported. 83 (II) Drop casting is probably the simplest deposition technique in which a defined volume of solution is manually dispensed at the desired location.…”