Thin film transistors (TFTs) with bottom gate and staggered electrodes using atomic layer deposited Al2O3 as gate insulator and radio frequency sputtered In–Ga–Zn Oxide (IGZO) as channel layer are fabricated in this work. The performances of IGZO TFTs with different deposition temperature of Al2O3 are investigated and compared. The experiment results show that the Al2O3 deposition temperature play an important role in the field effect mobility, Ion/Ioff ratio, sub-threshold swing and bias stability of the devices. The TFT with a 250 °C Al2O3 gate insulator shows the best performance; specifically, field effect mobility of 6.3 cm2/Vs, threshold voltage of 5.1 V, Ion/Ioff ratio of 4×107, and sub-threshold swing of 0.56 V/dec. The 250 °C Al2O3 insulator based device also shows a substantially smaller threshold voltage shift of 1.5 V after a 10 V gate voltage is stressed for 1 h, while the value for the 200, 300 and 350 °C Al2O3 insulator based devices are 2.3, 2.6, and 1.64 V, respectively.

•Sputtered AlOx film as the gate insulator.•Effect of rf power on the electrical properties of AlOx insulator.•Electrical performance and bias stability of InGaZnO-TFTs.•Interfacial properties using C–V method.We reported on the electrical and surface characteristics of radio frequency (rf) AlOx film and their applications in InGaZnO-based thin film transistors (TFTs). By optimizing the rf power, AlOx film with the low leakage current density and smooth surface was obtained. The leakage current density for the 180 W AlOx film was observed to be ∼2.0 × 10−9 A/cm2 at electrical field strength of 2 MV/cm. The root mean square (rms) roughness of 180 W AlOx film was about 1.36 nm. InGaZnO-TFTs with different AlOx insulators were fabricated. The InGaZnO-TFT with 180 W AlOx insulator exhibits a field-effect mobility of 6.9 cm2/V s, a threshold voltage of 4.2 V, an on/off ratio of 2.7 × 107, and a much smaller Vth shift of 6.6 V for 20 V bias stress duration of 10,800 s. The improvement of InGaZnO-TFT with 180 W AlOx film is attributed to smooth surface of AlOx film and smaller trap charges. The results indicate that AlOx is a promising candidate insulator for InGaZnO-TFTs.

•The Al2O3 gate insulator is fabricated by ALD.•The effect of channel thickness on performance of TFT is studied.•The proper channel thickness enhances the performance of TFT.•58 nm will be a proper channel thickness for IGZO TFT.We report on the electrical properties of bottom-gate InGaZnO (IGZO) thin film transistors (TFTs) with different channel layer thicknesses. The IGZO channel layer with thickness varied from 25 to 120 nm were deposited by radio frequency sputtering. Al2O3 films were deposited on highly-doped n-Si substrate by atomic layer deposition (ALD) as gate insulator in this work. The influence of the IGZO channel layer thickness on the performance of TFTs is studied. The performance of devices is found to be thickness dependent. The best performance of devices is obtained from a 58 nm thick IGZO TFT, which shows a field-effect mobility in the saturation region of 6.2 cm2/Vs, a threshold voltage of 2.1 V, an Ion/Ioff ratio of approximately 6.4 × 107, and a subthreshold swing of 0.6 V/dec.

A copper phthalocyanine (CuPc) organic semiconductor is capped onto an amorphous indium–gallium–zinc-oxide (InGaZnO) thin film transistor (TFT) to enhance the photosensitivity of InGaZnO-TFT. The CuPc organic semiconductor is served as a light absorption layer and forms a p–n junction with the InGaZnO film. After 60 s white light illumination, light responsivity (R) of InGaZnO-TFT with a CuPc light absorption layer reaches a value of 148.5 A/W at a gate-source voltage (VGS) of 20 V, which is much larger than that (31.2 A/W) of the conventional InGaZnO-TFT. The results are attributed to the following mechanism. First, a CuPc layer is employed as the light absorption layer. Second, CuPc/InGaZnO p–n junction enables the injection of electron into InGaZnO film. Our results indicate that using CuPc as light absorption layer is an effective approach to improve the photosensitivity of InGaZnO-TFT.Highlights► Enhanced photosensitivity with a CuPc light absorption layer. ► Calculating the light responsivity. ► Studying the mechanism of light responsivity.

We fabricated the indium-gallium-zinc oxide (IGZO) thin film transistor (TFT) with reactive sputtered SiOx as passivation layer, and investigated the role of the SiOx passivation layer in the IGZO-TFT under gate bias stress. The bias stability of IGZO-TFT with passivation layer is much better than that of IGZO-TFT without passivation layer. After applying positive bias stress of 20 V for 10000s, the device without passivation layer shows a larger positive Vth shift of 7.3 V. However, the device with passivation layer exhibits a much smaller Vth shift of 1.3 V. It suggests that Vth instability is attributed to the interaction between the exposed IGZO back surface and oxygen in ambient atmosphere during the positive gate voltage stress. The results indicate that reactive sputtered SiOx passivation layer can effectively improve the bias stability of IGZO-TFT.Highlights► Reactive sputtered SiOx film for passivation. ► Improving bias stress stability of IGZO-TFT. ► Impact of passivation layer on device stability. ► Calculation of energy activation.

We demonstrated the tunable contact resistance in pentacene thin film transistor (TFT) by inserting an organic–inorganic hybrid interlayer between Au electrode and pentacene layer. The contact resistance of pentacene-TFT varies with concentration of pentacene-TFT varies with concentration of MoOx in organic–inorganic hybrid interlayer. MoOx in organic–inorganic hybrid interlayer. The contact resistance of the device with 55 wt% MoOx doped pentacene interlayer is about 7.8 times smaller than that of device without interlayer at the gate voltage of −20 V. Comparing the properties of pentacene-TFT without interlayer, the performance of the pentacene-TFT with 55 wt% MoOx doped pentacene was significantly improved: saturation mobility increased from 0.39 to 0.87 cm2/V s, threshold voltage reduced from −21.3 to −7.2 V, and threshold swing varied from 3.75 to 1.39 V/dec. Our results indicated that the organic–inorganic hybrid interlayer is an effective way to improve the performance of p-channel OTFTs.Highlights► Tuning the contact resistance with an organic–inorganic hybrid interlayer. ► The calculation of contact resistance. ► Improving the device performance.

We demonstrated that the electrical properties of pentacene-thin film transistors with low-cost Cu electrodes can be enhanced by inserting a thin MoOx interlayer layer between pentacene and Cu source/drain (S/D) electrodes. In comparison with the device having Cu-only electrodes, the performance of the device with MoOx/Cu electrodes was significantly improved. The saturation mobility increased from 0.13 to 0.61 cm2/V s, threshold voltage reduced from −14.5 to −7.3 V, on/off ratio shifted from 8.9 × 105 to 1.6 × 106 and threshold swing varied from 1.92 to 1.33 V/decade. The improvement was attributed to the reduction of contact resistance and the enhancement of hole-injection efficiency. The results suggest modification of Cu S/D electrodes is a simple and effective way to improve device performance and reduce the fabrication cost.

Organic thin film transistors (OTFTs) with different concentrations of tetrafluorotetracyanoquinodimethane (F4-TCNQ) doped pentacene interlayer were fabricated. When a 2 wt% F4-TCNQ doped pentacene layer was incorporated between gold electrodes and a pentacene layer, the performance of the OTFT was significantly improved. The saturation mobility increased from 0.21 to 0.63cm2/Vs, the threshold voltage was reduced from −31.9 to −7.6 V, and the threshold swing varied from 5.09 to 2.40 V/dec as compared with an OTFT without interlayer. This improvement was ascribed to the reduction of the hole-injection barrier and contact resistance. Our results indicated that contact-area-limited doping is an effective way to improve OTFT performance.