Ge₂Sb₂Te₅ p-Type Thin-Film Transistors on Flexible Plastic Foil.

Alwin Daus,Stefan Knobelspies,Giuseppe Cantarella,Gerhard Tröster,Songyi Han

doi:10.3390/ma11091672

Abstract

In this work, we show the performance improvement of p-type thin-film transistors (TFTs) with GeSbTe (GST) semiconductor layers on flexible polyimide substrates, achieved by downscaling of the GST thickness. Prior works on GST TFTs have typically shown poor current modulation capabilities with ON/OFF ratios ≤20 and non-saturating output characteristics. By reducing the GST thickness to 5 nm, we achieve ON/OFF ratios up to ≈300 and a channel pinch-off leading to drain current saturation. We compare the GST TFTs in their amorphous (as deposited) state and in their crystalline (annealed at 200 °C) state. The highest effective field-effect mobility of 6.7 cm/Vs is achieved for 10-nm-thick crystalline GST TFTs, which have an ON/OFF ratio of ≈16. The highest effective field-effect mobility in amorphous GST TFTs is 0.04 cm/Vs, which is obtained in devices with a GST thickness of 5 nm. The devices remain fully operational upon bending to a radius of 6 mm. Furthermore, we find that the TFTs with amorphous channels are more sensitive to bias stress than the ones with crystallized channels. These results show that GST semiconductors are compatible with flexible electronics technology, where high-performance p-type TFTs are strongly needed for the realization of hybrid complementary metal-oxide-semiconductor (CMOS) technology in conjunction with popular n-type oxide semiconductor materials.

Highlights

Flexible electronics have received increased attention in the last years, promising great innovations in emerging display technology [1], healthcare [2,3,4], human-machine interfaces [4,5], textiles [6]and flexible sensor systems for Internet-of-Things (IoT) applications [7]
The GST thin-film transistors (TFTs) have been fabricated on a free-standing flexible 50 μm thick polyimide foil as described above
We have reported a significant performance improvement for GST TFTs by lowering the semiconductor thickness down to 5 nm

Summary

Introduction

Flexible electronics have received increased attention in the last years, promising great innovations in emerging display technology [1], healthcare [2,3,4], human-machine interfaces [4,5], textiles [6]. Flexible sensor systems for Internet-of-Things (IoT) applications [7] The latter requires high-frequency operation (13.56 MHz) to enable wireless data transmission via radio frequency identification (RFID) and near-field communication (NFC). Recent reports have shown that unipolar circuit technology based on oxide semiconductors can be employed for NFC and RFID applications [12,13]. Several groups of materials have been studied to realize flexible hybrid CMOS together with n-type oxide semiconductors involving p-type SnO [14] or carbon nanotubes [15,16,17,18]. We study GST TFTs on a flexible substrate and demonstrate performance improvements through downscaling of the GST thickness to 5 nm. We compare the device characteristics before and after thermal annealing above the crystallization temperature, which leads to an increased conductivity and mobility for GST thin-films ≥10 nm

Device Fabrication

Material Characterization

Thin-Film Transistor Characterization

Results and Discussion

Conclusions and Outlook