ترانزیستورهای گرافنی متاثر از میدان برای الکترونیک قابل انعطاف فرکانس رادیویی Graphene Field-Effect Transistors for Radio-Frequency Flexible Electronics

I. INTRODUCTION The desire to integrate wireless communications into flexible electronics requires field-effect transistors (FETs) which both demonstrate unity-power-gain cut-off frequencies, fmax, in the gigahertz frequency range and can withstand high levels of strain. While the highest electronic performance for flexible radio-frequency FETs (RF-FETs) have been achieved in thin films of Si and III-V semiconductors laminated on polymer substrates, poor mechanical flexibility has restricted strain limits in these devices typically to below ∼۰٫۲۵% [۱], [۲], with pre-straining resulting in slightly improved strain limits in tension up to 1.08% [3]. In contrast, graphene is an ideal candidate for use in flexible RF-FETs, because it offers both exceptional electronic properties (room temperature mobility in excess of 10,000 cm2 V−۱ s−۱ and saturation velocity of 1-5 x107 cm s−۱), as well as outstanding mechanical performance (strain limits up to 25%) [4], [5]. Furthermore, largearea films of graphene can be produced in commercially scalable processes by chemical vapor deposition (CVD) [6], which demonstrate equivalent electronic and mechanical properties to pristine graphene crystals [7], [8]. Indeed, flexible RF-FETs have been fabricated from CVD graphene which demonstrated fmax up to 3.7 GHz with strain limits up to 1.75% [9]. Strain limits up to 8% have been achieved in flexible GFETs with fmax = 2.1 GHz [10]. While graphene RF-FETs have demonstrated improved mechanical performance over those fabricated from Si and III-V semiconductors, electronic performance has remained in the low gigahertz frequency range. However, flexible graphene RF-FETs have only been fabricated with modestly scaled channel lengths down to 500 nm [9], [10], allowing for the potential to improve fmax to a level competitive with traditional semiconductors by channel length scaling [4]. In this work, we fabricate flexible RF-FETs with CVD graphene as the active channel material with a 260-nm channel length. The devices demonstrate extrinsic fmax up to 7.6 GHz, with strain limits up to 2%. This work not only achieves the highest extrinsic RF performance reported for flexible GFETs to date, but also demonstrates a strain limit an order of magnitude higher than in thin films of InAs, the flexible RF-FET technology with best competing fmax [2].