Abstract
The simplification of fabrication processes that can define very fine patterns for large-area flexible radio-frequency (RF) applications is very desirable because it is generally very challenging to realize submicron scale patterns on flexible substrates. Conventional nanoscale patterning methods, such as e-beam lithography, cannot be easily applied to such applications. On the other hand, recent advances in nanoimprinting lithography (NIL) may enable the fabrication of large-area nanoelectronics, especially flexible RF electronics with finely defined patterns, thereby significantly broadening RF applications. Here we report a generic strategy for fabricating high-performance flexible Si nanomembrane (NM)-based RF thin-film transistors (TFTs), capable of over 100 GHz operation in theory, with NIL patterned deep-submicron-scale channel lengths. A unique 3-dimensional etched-trench-channel configuration was used to allow for TFT fabrication compatible with flexible substrates. Optimal device parameters were obtained through device simulation to understand the underlying device physics and to enhance device controllability. Experimentally, a record-breaking 38 GHz maximum oscillation frequency fmax value has been successfully demonstrated from TFTs with a 2 μm gate length built with flexible Si NM on plastic substrates.
Highlights
In recent years, flexible electronics have gained popularity with various applications ranging from flexible displays, wearable electronics and identification tags, biomedical devices, to structural health monitoring[1,2,3,4,5,6]
Patterning deep submicron scale features on the nanomembranes on flexible substrates using conventional fine lithography techniques[9,10,11] has been very challenging due to the difficulties encountered in the fabrication process, such as the diffraction of exposed light on the plastic substrate and the thermal plasticity of the flexible substrates under even moderate temperatures that are essential for photolithography
The flexible RF thin-film transistors (TFTs) were fabricated on flexible Si NM employing a nano trench structure produced via nano-imprinting lithography (NIL) technology and were transfer printed onto a polyethylene terephthalate (PET) substrate
Summary
Flexible electronics have gained popularity with various applications ranging from flexible displays, wearable electronics and identification tags, biomedical devices, to structural health monitoring[1,2,3,4,5,6]. One key feature of this novel TFT device structure is the nano trench formed in the Si NM via NIL, which is used to define a very small effective channel (as narrow as 100 nm)[18,19].
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