Contact resistance and overlapping capacitance in flexible sub-micron long oxide thin-film transistors for above 100 MHz operation

Abstract

(2014) Contact resistance and overlapping capacitance in flexible sub-micron long oxide thin-film transistors for above 100 MHz operation. Applied Physics Letters, 105 (26).

Flexible InGaZnO TFTs With ${f}$ $_{\textsf{max}}$ Above 300 MHz

“…Both, the MSG and GTU measurements show the expected behavior, namely a decrease of f max in longer TFTs. This is also in line with corresponding transit frequency measurements [12]. In particular the GTU measurement also exhibits larger error bars at smaller frequencies.…”

“…However, it has to be mentioned that due to the extremely short channel some of the parameters are deteriorated. In particular the effective mobility is reduced by a contact resistances of 12 Ω cm (same order of magnitude as the channel resistance) [12]. Simultaneously, the output resistance is only ≈5.5 kΩ (V GS =2 V).…”

“…organic or oxide TFTs are desirable in the future. This calls for more aggressive scaling, including: planar nanoscale TFTs on plastic foils without deteriorated contact resistance (known from vertical TFTs [11]), electrostatic control of the channel, minimized parasitic resistances and capacities [12], control of the effective channel length reduction [17], and optimized overall ductility of flexible TFTs. This requires new techniques such as thinner layers to improve the pinch off behavior, self-alignment of additional layers to reduce parasitic capacities, or the use of plasma treatment and double gate structures to minimize the contact resistances [18], [19].…”

“…These dimensions represent a trade-off between processability on free-standing plastic foils (large tolerances + lateral dimensions), high transconductance (short channels), current saturation (long TFT channels), low capacitance (small overlaps), and low contact resistance (large overlaps) [11]. They are the result of an optimization process involving test structures, characterization of TFTs with different channel length, as well as Comsol and Spice simulations [12]. The TFT layout comprises ground-signal-ground (GSG) contacts with a pitch size of 150 µm to ensure reliable AC measurements.…”

Metal oxide semiconductor thin-film transistors for flexible electronics

“…Controlling the contact resistance is especially important in short-channel devices (L Շ 5 lm), since a high R C value can lead to the degradation of both the device l FE and f T . 105,106 In a TFT, the contact resistance depends on the source/drain electrodes, 107,108 the interface metal/semiconductor, 107 the source/drain to gate contact area, 106,108 as well as specific contact treatments (plasma, temperature, etc.) performed.…”