Tin Oxide Thin Film Transistors Research Articles

High-Performance Tin Oxide Thin-Film Transistors Realized by Codoping and Their Application in Logic Circuits.

Tin oxide is a promising channel material, offering the advantages of being low-cost and environmentally friendly and having a wide band gap. However, despite the high electron mobility of SnO2 in bulk, the corresponding thin-film transistors (TFTs) generally exhibit moderate performance, hindering their widespread application. Herein, we proposed a codoping strategy to improve both the electrical property and the stability of SnO2 TFTs. A comparative analysis between doped and undoped SnO2 was conducted. It is observed that taking advantage of the difference in ionic radii between two dopants (indium and gallium) and the tin ions in the host lattice can effectively reduce impurity-induced strain. Additionally, we investigated the effect of codoping content on SnO2 TFTs. The optimal codoped SnO2 (TIGO) TFTs demonstrate high performance, featuring a field-effect mobility of 15.9 cm2/V·s, a threshold voltage of 0.2 V, a subthreshold swing of 0.5 V/decade, and an on-to-off current ratio of 2.2 × 107. Furthermore, the devices show high stability under both positive and negative bias stress conditions with a small threshold voltage shift of 1.8 and -1.2 V, respectively. Utilizing the TIGO TFTs, we successfully constructed a resistor-loaded unipolar inverter with a high gain of 10.76. This study highlights the potential of codoped SnO2 TFTs for advanced applications in electronic devices.

Dual-Gate Operation and Configurable Logic From Solution Pattern-Based Zinc Tin Oxide Thin-Film Transistors

Dual-Gate Operation and Configurable Logic From Solution Pattern-Based Zinc Tin Oxide Thin-Film Transistors

Graded-Band-Gap Zinc-Tin Oxide Thin-Film Transistors with a Vertically Stacked Structure for Wavelength-Selective Photodetection.

Filter-free wavelength-selective photodetectors have garnered significant attention due to the growing demand for smart sensors, artificial intelligence, the Internet of Everything, and so forth. However, the challenges associated with large-scale preparation and compatibility with complementary metal-oxide-semiconductor (CMOS) technology limit their wide-ranging applications. In this work, we address the challenges by constructing vertically stacked graded-band-gap zinc-tin oxide (ZTO) thin-film transistors (TFTs) specifically designed for wavelength-selective photodetection. The ZTO thin films with various band gaps are fabricated via atomic layer deposition (ALD) by varying the ALD cycle ratios of zinc oxide (ZnO) and SnO2. The ZTO film with a small Sn ratio exhibits a decreased band gap, and the resultant TFT shows a degraded performance, which can be attributed to the Sn4+ dopant introducing a series of deep-state energy levels in the ZnO band gap. As the ratio of Sn increases further, the band gap of the ZTO also increases, and the mobility of the ZTO TFT increases up to 30 cm2/V s, with a positive shift of the threshold voltage. The photodetectors employing ZTO thin films with distinct band gaps show different spectral responsivities. Then, vertically stacked ZTO (S-ZTO) thin films, with gradient band gaps increasing from the bottom to the top, have been successfully deposited using consecutive ALD technology. The S-ZTO TFT shows decent performance with a mobility of 18.4 cm2/V s, a threshold voltage of 0.5 V, an on-off current ratio higher than 107, and excellent stability under ambient conditions. The resultant S-ZTO TFT also exhibits obviously distinct photoresponses to light at different wavelength ranges. Furthermore, a device array of S-ZTO TFTs demonstrates color imaging by precisely reconstructing patterned illuminations with different wavelengths. Therefore, this work provides CMOS-compatible and structure-compact wavelength-selective photodetectors for advanced and integrable optoelectronic applications.

Mobility enhancement of tin oxide thin-film transistor by indium-doping

Herein, indium-doped tin oxide (TIO) thin films were prepared using the solution process. The structural characteristics, surface morphologies, and chemical compositions of the prepared films were systematically investigated as a function of indium-doping contents. The films were integrated as a channel layer into thin-film transistors (TFTs). Results show that indium can be used as a carrier suppressor as well as a mobility enhancer for SnO2. The optimal devices exhibited satisfactory performance, achieving field-effect mobility of 8.94 cm2/V·s, positive threshold voltage of 0.25 V, small subthreshold swing of 0.4 V/decade, and on-to-off current ratio of 1.5 × 106. The results of this study suggest that TIO-TFTs are very promising for use in next-generation displays.

Spinel Single Phase Indium Zinc Tin Oxide Thin-Film Transistors with High Mobility and Excellent Uniformity

Spinel Single Phase Indium Zinc Tin Oxide Thin-Film Transistors with High Mobility and Excellent Uniformity

Manufacturing and Electrical Performance of TFTs

<p>This research is to discuss the sputtering of zinc tin oxide (ZTO) thin film under different oxygen flow conditions in the RF sputtering chamber to conduct a series of verifications and inferences and try to find the best sputtering conditions. Next, we deposited hafnium dioxide (HfO2) as an insulating layer, and processed zinc tin oxide (ZTO) thin film transistors. By measuring the electrical properties for material analysis, we found that the thin film transistors made of ZTO thin films with an argon-oxygen ratio of 45:5 have a better saturation zone. At the same time, we observe that the transmittance of the film will increase with the increase of the oxygen flow rate, and the transmittance is above 80~85% at the wavelength of visible light. By measuring the Hall effect, we can see that under the condition of an argon-oxygen ratio of 45:5, there is a better carrier concentration of 6.45 ൈ 10ଵଵ . This is because the oxygen vacancies in the ZTO film will provide the film carrier. Therefore, when the oxygen concentration is high, the original oxygen vacancies will be filled, thereby alleviating the problem of excessive carrier concentration, and reaching a saturated and cut-off state.</p> <p> </p>

Multifunctional Crystalline InGaSnO Phototransistor Exhibiting Photosensing and Photosynaptic Behavior Using Oxygen Vacancy Engineering.

A multifunctional optoelectronic device implementing photodetector, photosynapse, and photomemory is of increasing attention for neuromorphic system. This enables multiple devices to be replaced with a single device, which simplifies the structure of complex, highly integrated electronics. Here, a multifunctional c-axis-aligned crystalline indium gallium tin oxide thin-film transistor (TFT) optoelectronic device is demonstrated. The photodetecting and photosynaptic behaviors could be demonstrated by tuning of gate pulse. The device shows a high responsivity of 1.1×106 AW-1 to blue light (467nm) and cutoff frequency (f-3dB ) of 2400Hz exhibiting high frequency switching using a gate reset pulse. It is possible to implement photosynaptic behavior using persistent photoconductivity effect by applying a gate bias to make the TFT depletion mode. When potentiation and depression of synaptic weight are implemented with light pulse and gate voltage pulse, respectively, 64-state potentiation-depression curves are demonstrated with excellent nonlinearity of 1.13 and 2.03, respectively. When an artificial neural network is constructed with this device for the Modified National Institute of Standards and Technology training pattern recognition simulation, it shows a high pattern recognition accuracy of 90.4%.

Effects of Ti Doping on the Electrical Properties and Gate-Bias Stability of Amorphous Zinc–Tin–Oxide Thin-Film Transistors

Multicationic oxide semiconductors are receiving considerable interest in electronic and optoelectronic devices owing to their tunability of physical properties by the cation compositions. Here, we investigated the effects of Ti doping on the electrical properties and gate-bias stability of amorphous zinc–tin–oxide (a-ZnSnO, Zn/Sn = 7:3) thin-film transistors (TFTs) using a cosputtering process. Particularly, by using cosputtering, controllable doping of Ti in a-ZnSnO films was possible in the range of 0.87–3.87 atom %. From various electrical analyses, it was found that the key metrics of Ti-doped ZnSnO (TiZnSnO) TFTs, such as field-effect mobility and gate-bias stability, were highly dependent on the Ti concentration, showing a mobility–stability tradeoff. Based on X-ray photoelectron spectroscopy analysis, the mobility–stability tradeoff is ascribed to the suppression of oxygen vacancy formation by Ti doping. Considering the overall electrical performance and stability of TiZnSnO TFTs, which were processed at 450 °C, the optimal Ti concentration was determined as ∼1.14 atom % with Zn, Sn, and O concentrations of 15.87, 22.92, and 60.07 atom %, respectively. The device exhibited a field-effect mobility of 8.2 cm2 V–1 s–1, a subthreshold slope of 0.208 V decade–1, an on/off ratio of 3.38 × 108, a hysteresis of 2.8 V, and a threshold voltage shift of +5.61 and −2.24 V under positive- and negative-bias stresses, respectively.

Controlling the flow of oxygen to explore the study of zinc tin oxide thin film transistors

本研究討論在射頻濺鍍腔體內，控制氬氣氧氣比(Ar:O2)，沉積氧化鋅錫(ZTO)薄膜，透過厚度、穿透率找到最佳條件。接著使用二氧化鉿(HfO2)作為絕緣層，製成氧化鋅錫(ZTO)電晶體，藉由測量電性進行材料分析，發現利用氮氧比為45:5的ZTO薄膜製作而成的薄膜電晶體，有很好的飽和區，臨界電壓為1.26V。<br>我們發現氧氣含量越高時，薄膜的穿透率會越來越高，在可見光的波長間穿透率有85%。再透過量測霍爾效應看出45:5的條件下有較好的載子濃度6.45x1011。原因是在氧氣濃度高的情況下，許多的氧空缺被填滿，改善了載子濃度過高的問題，進而達到飽和且截止的功能。This study discusses in the RF sputtering chamber, controlling the ratio of argon to oxygen (Ar:O2), depositing zinc tin oxide (ZTO) film, and finding the best conditions through thickness and penetration.Then use hafnium dioxide (HfO2) as an insulating layer to make zinc tin oxide (ZTO) transistors. By measuring the electrical properties for material analysis, it is found that the thin film made of ZTO film with a nitrogen-to-oxygen ratio of 45:5 is used. The crystal has a good saturation zone and the critical voltage is 1.26V.We found that the higher the oxygen content, the higher the penetration rate of the film, and the penetration rate between visible light wavelengths is 85%. Through the measurement of the Hall effect, it can be seen that the carrier concentration is 6.45x1011 under the condition of 45:5. The reason is that in the case of high oxygen concentration, many oxygen vacancies are filled, which improves the problem of excessive carrier concentration, and then achieves the function of saturation and cut-off.

High-Performance Amorphous InGaSnO Thin-Film Transistor with ZrAlOx Gate Insulator by Spray Pyrolysis

Here, we report the high-performance amorphous gallium indium tin oxide (a-IGTO) thin-film transistor (TFT) with zirconium aluminum oxide (ZAO) gate insulator by spray pyrolysis. The Ga ratio in the IGTO precursor solution varied up to 20%. The spray pyrolyzed a-IGTO with a high-k ZAO gate insulator (GI) exhibits the field-effect mobility (μFE) of 16 cm2V−1s−1, threshold voltage (VTH) of −0.45 V subthreshold swing (SS) of 133 mV/dec., and ON/OFF current ratio of ~108. The optimal a-IGTO TFT shows excellent stability under positive-bias-temperature stress (PBTS) with a small ΔVTH shift of 0.35 V. The enhancements are due to the high film quality and fewer interfacial traps at the a-IGTO/ZAO interface. Therefore, the spray pyrolyzed a-IGTO TFT can be a promising candidate for flexible TFT in the next-generation display.

Solution processed low operating voltage SnO2 thin film transistor by using Li2SnO3/TiO2 stacked gate dielectric

A thin layer of sol–gel derived lithium stannate (Li2SnO3) was deposited by a spin coating method that shows high areal capacitance with low DC conductivity which originated due to the mobile lithium ion (Li+) and low carrier concentration. The DC conductivity of this Li2SnO3 thin film has been reduced further by adding a sol–gel derived titanium-oxide (TiO2) layer. Moreover, bilayer thin film effective areal capacitance also increases due to the higher relative permittivity of TiO2 layer. The measured areal capacitance of such Li2SnO3 /TiO2 bilayer thin films is 518 nF/cm2 with a low current density of 3.8 X 10-5 A/cm2 under 5 V external bias, can fulfil the requirement as gate dielectric of a low operating voltage (≤3V) thin film transistor (TFT). For identifying its applicability as gate insulator, a solution-processed tin oxide (SnO2) thin film transistor (TFT) was fabricated with Li2SnO3/TiO2 stacked gate dielectric. In this TFT structure, thin film of TiO2, SnO2 and Li2SnO3 are all polycrystalline in nature. The electrical characterization of TFT has been done under DC mode operation in ambient atmosphere measurement which remain almost unaltered under 11 cyclic measurements. The optimized TFT required only 3.0 V external bias that shows an electron mobility of 3.47 cm2 V−1 s−1 with on/off ratio of 50.

Threshold voltage tuning of IGZTO thin-film transistors deposited by RF sputtering for high-resolution flexible displays using deep ultraviolet light

Development of DUV/Thermal dual treatment (DTT) process to improve the electrical performance and stability of oxide thin film transistors while efficiently controlling the threshold voltage of the device.

Solution-processed amorphous zinc indium tin oxide thin-film transistors with high stability under AC stress

Amorphous zinc–indium–tin oxide thin-film transistors with various Zn : In : Sn ratios are investigated to improve AC stress stability by suppressing hot carrier effects in the channel layer.

Physico-Chemical Origins of Electrical Characteristics and Instabilities in Solution-Processed ZnSnO Thin-Film Transistors

We investigate the physico-chemical origins that determine the transistor characteristics and stabilities in sol-gel processed zinc tin oxide (ZTO) thin-film transistors (TFTs). ZTO solutions with Sn/(Sn+Zn) molar ratios from 0.3 to 0.6 were synthesized to demonstrate the underlying mechanism of the electrical characteristics and bias-induced instabilities. As the Sn/(Sn+Zn) ratio of ZTO is increased, the threshold voltage of the ZTO TFTs negatively shifts owing to the gradual increase in the ratio of oxygen vacancies. The ZTO TFTs with an Sn/(Sn+Zn) ratio of 0.4 exhibit highest saturation mobility of 1.56 cm2/Vs lowest subthreshold swing and hysteresis of 0.44 V/dec and 0.29 V, respectively, due to the desirable atomic states of ZTO thin film. Furthermore, these also exhibit outstanding positive bias stability due to the low trap density at the semiconductor-dielectric interface. On the other hand, the negative bias stress-induced instability gradually increases as the proportion of tin increases because the negative bias stress instability originates from the ionization of oxygen vacancies. These results will contribute to the optimization of the composition ratio in rare-metal-free oxide semiconductors for next-generation low-cost electronics.

Importance of Solvent Evaporation Temperature in Pre-Annealing Stage for Solution-Processed Zinc Tin Oxide Thin-Film Transistors

We focused on the importance of solvent evaporation governed by the temperature of the pre-annealing stage (TS) in solution-processed zinc tin oxide (ZTO) thin-film transistors (TFTs). We controlled TS based on the boiling point (BP) of the solvent used. When TS reaches the BP, the field effect mobility is found to be about 1.03 cm2/V s, which is 10 times larger than the TS < Bp case (0.13 cm2/V s). The reason is presumed to be that residual organic defects are effectively removed as TS increases. In addition, when Ts is beyond Bp, the mobility is rather decreased due to structural defects such as pores and pinholes. Based on our results, it is noted that TS plays a significant role in the enhancement of electrical performance and stability of solution-processed ZTO TFTs.

Importance of Structural Relaxation on the Electrical Characteristics and Bias Stability of Solution-Processed ZnSnO Thin-Film Transistors.

Effect of structural relaxation (SR) on the electrical characteristics and bias stability of solution-processed zinc–tin oxide (ZTO) thin-film transistors (TFTs) were systematically investigated by controlling the annealing time of the ZTO semiconductor films. Note that SR was found to increase with increased annealing time. Due to the increased SR, the ratio of oxygen vacancies (VO) increased from 21.5% to 38.2%. According to increased VO, the mobility in the saturation region was exhibited by a sixfold increase from 0.38 to 2.41 cm2 V−1 s−1. In addition, we found that the threshold voltage negatively shifted from 3.08 to −0.95 V. Regarding the issue of bias stability, according to increased SR, positive-bias stress of the ZTO TFTs was enhanced, compared with reverse features of negative-bias stress. Our understanding is expected to provide a basic way to improve the electrical characteristics and bias stability of rare-metal-free oxide semiconductor TFTs, which have not been sufficiently studied.

The effect of gamma-ray irradiation on the electrical characteristics of sol-gel derived zinc tin oxide thin film transistors

The effect of different doses of gamma-ray irradiation has been investigated on zinc tin oxide thin film transistors fabricated via the sol–gel spin-coating method. A negative threshold voltage shift was observed for 10 MRad gamma irradiation dose but the shift became positive after higher radiation doses (50 MRad and 100 MRad). The drain current showed a slight increase at 10 MRad (air) irradiation but reduced at further higher doses of irradiation. Field effect mobility degraded slightly as the irradiation dose increased. The subthreshold swing and the corresponding interfacial defects increased with increasing the dose of irradiation. The ZTO TFT demonstrated only a moderate degradation after 100 MRad (air), making it a viable candidate for radiation-hard electronics applications.

Effects of change of oxygen vacancy on hysteresis voltage and stability under time-temperature dependence positive bias stress in amorphous SZTO transistors

The study on voltage hysteresis (VHys) and instability under the time dependence positive bias stress at a fixed temperature (PBTS) in amorphous silicon zinc tin oxide (a-SZTO) thin-film transistors (TFTs) has been investigated by varying the oxygen flow rate (OFR) during the a-SZTO channel material growth via radio frequency (RF) sputtering. Current-voltage (I-V) measurement was initially taken to study the VHys, which revealed that the VHys was widened by increasing the OFR. The threshold voltage (Vth) shift in a-SZTO TFTs and the impact of OFR on electrical properties and electrical stability of a-SZTO TFTs were analyzed by the PBTS measurement. From PBTS, we observed that the threshold voltage shift difference (∆Vth) increases as the OFR increases. We conclude that a plausible reason for these results may be due to the acceptor-like trap states induced by OFR. The density of Gaussian-like states, excess or weakly bonded oxygen acting as acceptor-like states, is increased by increasing OFR during the deposition of channel material. These results are expected to be of general importance for future works of other amorphous oxide based TFTs.

Microwave and furnace annealing in oxygen ambient for performance enhancement of p-type SnO thin-film transistors

In this study, we investigated the effect of microwave-irradiation annealing (MWA) and thermal furnace annealing (FA) in oxygen ambient on the active channel layer of p-type tin-oxide (SnO) thin-film transistors. At very low source-drain voltage of −0.1 V, the MWA at 1200 W and FA at 300 °C samples have exhibited significant improvement in the electrical characteristics such as subthreshold swing (SS) of 0.93 and 0.485 V dec−1, the I on/I off ratio of 1.65 × 104 and 3.07 × 104, the field-effect mobility (μ FE) of 0.16 and 0.26 cm2 V−1 s and ultra-low off-state current of 1.9 and 2.0 pA respectively. The observed performance enhancement was mainly attributed to the reduction of interface trap density (N t) by tuning the power of MWA and optimizing the temperature in FA. From the result, we observed the optical band gap (E g) increased by 6% in FA, and 12% in MWA, which confirms improved crystallinity and reduction of defect states. Additionally, a low thermal budget microwave anneal process has shown high transmittance of more than 86% in the visible region (380–700 nm). The physical characterization indicates the partial phase transformation of SnO to SnO2 with retaining p-type conductivity in both annealing processes. The results demonstrate that both the annealing process could be highly promising to be used in the complementary logic circuits of new generation flexible/transparent displays.

Effects of Active Layer Thickness on the Electrical Characteristics and Stability of High-Mobility Amorphous Indium–Gallium–Tin Oxide Thin-Film Transistors

Herein, we investigated the effects of active layer thickness (tS) on the electrical characteristics and stability of high-mobility indium–gallium–tin oxide (IGTO) thin-film transistors (TFTs). IGTO TFTs, with tS values of 7 nm, 15 nm, 25 nm, 35 nm, and 50 nm, were prepared for this analysis. The drain current was only slightly modulated by the gate-to-source voltage, in the case of the IGTO TFT with tS = 50 nm. Under positive bias stress (PBS), the electrical stability of the IGTO TFTs with a tS less than 35 nm improved as the tS increased. However, the negative bias illumination stress (NBIS) stability of these IGTO TFTs deteriorated as the tS increased. To explain these phenomena, we compared the O1s spectra of IGTO thin films with different tS values, acquired using X-ray photoelectron spectroscopy. The characterization results revealed that the better PBS stability, and the low NBIS stability, of the IGTO TFTs with thicker active layers were mainly due to a decrease in the number of hydroxyl groups and an increase in the number of oxygen vacancies in the IGTO thin films with an increase in tS, respectively. Among the IGTO TFTs with different tS, the IGTO TFT with a 15-nm thick active layer exhibited the best electrical characteristics with a field-effect mobility (µFE) of 26.5 cm2/V·s, a subthreshold swing (SS) of 0.16 V/dec, and a threshold voltage (VTH) of 0.3 V. Moreover, the device exhibited robust stability under PBS (ΔVTH = 0.9 V) and NBIS (ΔVTH = −1.87 V).