cfaed Seminar Series

Abstract

The use of solution-based fabrication processes for the realisation of (opto-)electronic devices and circuits based on metal oxide semiconductors has become an attractive alternative to conventional manufacturing technologies allowing for the reduction of manufacturing costs by large-area production. Field-effect mobilities of metal oxide transistors are already well beyond those of amorphous silicon and the performance of such devices is steadily increasing due to material and process optimisation. However, solution-deposition of state-of-the-art metal oxide semiconductors typically require high curing temperatures (>200 °C) for prolonged periods of time (>60 min) in order to reach the desired electrical properties needed for high performance transistors which makes the use of inexpensive substrates such as plastic incompatible and severely hampers the production throughput. In this presentation we will demonstrate a promising approach to overcome these issues by using high-power xenon flash lamps for the rapid photo-thermal conversion of carefully selected precursor materials to semiconducting metal oxides. For the first time, we are able to fabricate low operating voltage (≤2 V) electron transporting In2O3 and ZnO transistors on glass substrates with electron mobilities of 6 cm2/Vs and 1.7 cm2/Vs, respectively with processing times for the semiconductor annealing of less than 18 seconds by using this technology. Moreover, a significant performance improvement is achieved by the photonic annealing of In2O3/ZnO heterostructure devices with field-effect mobilities of up to 35 cm2/Vs. We will show that these level of performances are comparable to reference devices fabricated via conventional thermal annealing at 250 °C for 60 min. Besides the electrical characterisation, the influence of the high intensity flash exposure on the surface topography and elemental composition of the resulting semiconductors are investigated by atomic force microscopy and x-ray photoelectron spectroscopy. Using a numerical model we are able to analyse the temperature profile in time within the thin film stack revealing a remarkable increase of the temperature up to 1000 °C in less than 1 ms on top of the device surface within the metal oxide films during each pulse while the backside of the glass substrate is nearly unaffected. Our work demonstrates the tremendous potential of photonic processing for the rapid manufacturing of metal oxide electronics on arbitrary substrate materials.