Low-temperature (150 °C) processed metal-semiconductor field-effect transistor with a hydrogenated In–Ga–Zn–O stacked channel

Abstract

We developed low-temperature (150 °C) processed top-gate and coplanar metal-semiconductor field-effect transistors (MES-FETs) with a stacked In-Ga-Zn-O (IGZO) channel consisting of a hydrogenated IGZO (IGZO:H) on conventional IGZO (IGZO). The IGZO and IGZO:H films were prepared by Ar + O 2 and Ar + O 2 + H 2 sputtering, respectively. By applying an IGZO:H on IGZO (IGZO:H/IGZO) stacked channel, the on-current of the MES-FET significantly increased while maintaining a low off-current. An on-off current ratio of 4.2 × 10 8 , a turn-on voltage of −5.9 V and a subthreshold swing of 155 mV decade −1 were achieved by the IGZO:H/IGZO = 25/25 nm stacked channel. The carrier concentration of the IGZO: H/IGZO stacked film dramatically increased to 1.4 × 10 19 cm −3 by stacking the IGZO:H (4.4 × 10 17 cm −3 ) film on the IGZO (7.6 × 10 17 cm −3 ) film. It was suggested that diffused hydrogens from IGZO:H to IGZO enhanced carrier concentration in the IGZO near the IGZO:H/IGZO interface, which acts as a pseudo two dimensional electron gas. Moreover, a potential barrier was formed at the IGZO:H/IGZO interface, which could have helped to maintain the low off-current of the MES-FETs. Therefore, the IGZO:H/IGZO stacked channel plays an important role in improving the performance of the MES-FETs.

Defect Passivation and Carrier Reduction Mechanisms in Hydrogen-Doped In-Ga-Zn-O (IGZO:H) Films upon Low-Temperature Annealing for Flexible Device Applications

“…Hereafter, we will focus on the properties of hydrogen-doped IGZO films (IGZO:H), which were deposited by sputtering in Ar/O 2 /H 2 gases, to discuss the mechanism for low-temperature activation of the IGZO:H TFTs [ 22 , 23 , 24 ]. Figure 2 shows the in situ Hall measurement results of the N e in the IGZO:H films deposited with R[H 2 ] of (a) 2%, (b) 5% and (c) 8%.…”

“…Figure 2 d shows the annealing time dependence of the N e in the IGZO:H films with different R[H 2 ] values. Annealing was carried out at 150 °C in ambient air since this temperature can effectively activate the IGZO:H TFTs with good electrical properties and reliability as we previously reported [ 22 , 23 , 24 ]. A minor change in the N e of about 10 18 cm −3 was observed within the whole range of the annealing time for the film deposited at R[H 2 ] of 2%.…”

“…Several methods have already been proposed (these methods are referred to as “activation process of IGZO”), such as active IGZO layer oxidation at low temperatures by O 2 wet and O 3 annealing [ 15 , 16 ], high-pressure O 2 and N 2 gas annealing [ 17 ], hydrogen injection and oxidation for low-temperature aqueous solution-processed IGZO TFT [ 18 ], microwave and e-beam annealing [ 19 ], capacitive coupled plasma-assistant IGZO magnetron sputtering [ 20 ], and mechanochemical and thermal treatment [ 21 ]. Our research group has recently reported that adding hydrogen to the sputtering atmosphere can effectively reduce the activation temperature of IGZO films [ 22 , 23 , 24 ]. Table 1 shows the recent progress in different activation methods and the obtained TFT mobility.…”

High-mobility hydrogenated polycrystalline In2O3 (In2O3:H) thin-film transistors

“…Wide-bandgap oxide semiconductors (OSs) have been extensively studied as active channel layers of thin-film transistors (TFTs) for next-generation flat-panel displays 1 , 2 , nonvolatile memories 3 , inverters 4 , various sensors 5 , 6 , Schottky devices 7 , 8 , and so on. Among OSs, amorphous In–Ga–Zn–O (a-IGZO) TFTs have now become the backplane standard for active-matrix liquid-crystal displays (AMLCDs) and active-matrix organic light-emitting diode (AMOLED) displays because of their reasonable field-effect mobility ( μ FE ) of over 10 cm 2 V −1 s −1 , extremely low leakage current, low process temperature (<350 °C), and large-area scalability 9 , 10 .…”

P‐12: Activation of IGZO Devices at 150°C via Reduction Process Using Hydrogen Gas During Sputtering

“…The radius of the Schottky contact was 100 μm for Schottky diodes, and L of 10 μm and W of 100 μm for MES-FETs. The detailed fabrication process of the devices appears elsewhere [14][15][16][17]. To investigate the electronic states in IGZO:H films, hard X-ray photoelectron spectroscopy (HAXPES) analysis with an excitation X-ray energy of 7940 eV was performed.…”