Amorphous-InGaZnO Thin-Film Transistors Operating Beyond 1 GHz Achieved by Optimizing the Channel and Gate Dimensions

Abstract

Amorphous indium-gallium-zinc oxide (a-InGaZnO or a-IGZO) has already started replacing amorphous silicon in backplane driver transistors for large-area displays. However, hardly any progress has been made to commercialize a-IGZO for electronic circuit applications mainly because a-IGZO transistors are not yet capable of operating at GHz frequencies. Here, nanoscale a-IGZO thin-film transistors (TFTs) are fabricated on a high-resistivity silicon substrate with a Ta2O5 gate dielectric. Carrier mobilities up to 18.2 cm 2 V-1 s-1 have been achieved. By optimization of the TFT channel length and contact overlap, we are able to demonstrate current-gain and power-gain cutoff frequencies at 1.24 and 1.14 GHz, respectively, both beyond the 1 GHz benchmark. Such a performance may have implications in developing at least medium-performance, a-IGZO-TFTs-based circuits for low-cost or flexible electronics.

Air Stable Indium-Gallium-Zinc-Oxide Diodes With a 6.4 GHz Extrinsic Cutoff Frequency Fabricated Using Adhesion Lithography

“…TFTs have significant overlap capacitance and so for higher frequencies Schottky diodes are normally preferred. A recent study has, however, optimized the contact overlaps and produced fT values over 1 GHz [6]. Previous Schottky diodes that have used a-IGZO as the active material have shown good air stability and high rectification ratios (10 6 -10 8 ) [7]- [9].…”

8.4: Invited Paper: Oxide devices for displays and low power electronics

“…Thus it is necessary to improve the operation frequency of oxide-semiconductor TFTs in order to commercialize IGZO for applications in the 'internet of things' (IoT). The current-gain cut-off frequency can be described by , where g m is the transconductance, V G is the gate voltage, V TH is the threshold voltage, µ eff is the effective field-effect mobility, C G is the total gate capacitance, L CH is the channel length and L OV is the overlap length between the source/drain contact and the gate electrode [4] . It is plausible that the cut-off frequency can be improved by reducing the channel length and the overlap length.…”

“…Besides, reducing L CH may introduce the short-channel effect which makes the device difficult to pinch off. Thus optimising the channel length and overlap length is critical to realizing a high operating frequency [4] .…”

“…Here, we review our recent work on a) high-performance oxidebased Schottky diodes with an ideality factor of 1.09, ultra-low noise, and operating speed >20 GHz on glass [2] and 2.45 GHz on flexible substrate [3] ; b) IGZO TFTs capable of reaching a benchmark speed of 1 GHz [4] , which are, to the best of our knowledge, the fastest oxide-based diodes and transistors to date; c) a few different methods to achieve IGZO TFTs capable of onevolt operations [5][6][7][8][9] ; d) CMOS-like oxide logic gates and functional circuits including inverters with a gain up to 150 [10,11] , NAND gate [12] , D-latch [13] , 51 stage ring oscillator [13] , complementary static random access memories [14] , and a one-bit full adder [13] , etc, by integrating SnO-based p-type TFTs with IGZO-based n-type TFTs; and finally e) novel oxide TFTs with a Schottky source contact that show no short channel effect, almost total immunity to negative bias illumination stress, and have a gain over two orders of magnitude higher than that of a typical silicon transistor [15] .…”

Research Progress on Flexible Oxide-Based Thin Film Transistors

“…The technological advance in TFTs is a significant factor for promoting the development of such displays [42][43][44][45][46][47][48][49][50]. Researchers around Nomura et al [42], the earliest engaged in this field, have successfully fabricated the first transparent and flexible oxide-based TFTs, which have rapidly attracted the interest of numerous researchers all over the world [51][52][53][54][55][56][57][58][59][60][61]. Compared with hydrogenated amorphous silicon (a-Si:H) TFTs and low-temperature polysilicon (LTPS) TFTs [62][63][64][65][66][67][68][69][70][71][72][73], oxide TFTs are reputed as the next-generation displays TFT technology due to their high performance, such as relatively high carrier mobility, good uniformity, low process temperature, optical transparency, low cost and flexibility [74][75][76][77][78][79].…”