Tin Oxide Channel Research Articles

Impact of ambient moisture on gate controllability in ferroelectric-gate field-effect transistors with bottom-gate geometry

Ferroelectric-gate field-effect transistors (FeFETs) with a bottom-gate geometry consisting of a ferroelectric HfO2 gate and an oxide channel have been intensively studied in recent years. However, there has been no detailed investigation into the impact of atmospheric exposure on device performance, even though the channel is often exposed to ambient air for process simplification, especially at the research stage. In this study, the ambient stability of an indium tin oxide channel FeFET with a ferroelectric Ce-HfO2 bottom gate was investigated. We found that ambient degradation of the gate controllability was caused by an increase in physisorbed water in the device owing to the intrusion of moisture. Mobile ions, such as H+, which can easily move through a network of hydrogen bonds formed by adjacent physisorbed water, may compensate for ferroelectric polarization. Finally, we demonstrated that the observed degradation can be managed effectively without compromising the original device characteristics using Al2O3 passivation gently formed via plasma-free deposition.

High-performance ferroelectric field-effect transistors with ultra-thin indium tin oxide channels for flexible and transparent electronics

With the development of wearable devices and hafnium-based ferroelectrics (FE), there is an increasing demand for high-performance flexible ferroelectric memories. However, developing ferroelectric memories that simultaneously exhibit good flexibility and significant performance has proven challenging. Here, we developed a high-performance flexible field-effect transistor (FeFET) device with a thermal budget of less than 400 °C by integrating Zr-doped HfO2 (HZO) and ultra-thin indium tin oxide (ITO). The proposed FeFET has a large memory window (MW) of 2.78 V, a high current on/off ratio (ION/IOFF) of over 108, and high endurance up to 2×107 cycles. In addition, the FeFETs under different bending conditions exhibit excellent neuromorphic properties. The device exhibits excellent bending reliability over 5×105 pulse cycles at a bending radius of 5 mm. The efficient integration of hafnium-based ferroelectric materials with promising ultrathin channel materials (ITO) offers unique opportunities to enable high-performance back-end-of-line (BEOL) compatible wearable FeFETs for edge intelligence applications.

Interfacial Engineering of High-Performance, Solution-Processed Sb2S3 Phototransistors.

Antimony sulfide, as a binary chalcogenide, has attracted great attention in the field of optoelectronics in recent years, particularly in photovoltaics, because of its striking merits such as earth elements abundance, excellent stability, chemical versatility, and solution processability. With the rapid development of fabrication techniques and device engineering, the device performance of Sb2S3 solar cells has experienced an unprecedented success. However, photodetectors based on Sb2S3 were barely reported, especially based on the transistor configuration. In this work, we prepared high quality Sb2S3 thin films via a sol-gel method, and Sb2S3 thin films were deposited on zinc-tin oxide based field-effect transistors. Furthermore, an additional electron transport layer was inserted between the Sb2S3 layers and the zinc-tin oxide channels and archived high-performance phototransistors with proper interfacial engineering. The optimized devices exhibited extremely high photosensitivity (106), low dark current (∼10 pA) and noise (∼11 fA Hz-1/2), high detectivity (1 × 1013 Jones), and superior device stability, indicating great potential for next generation solution-processed photodetectors.

High-stability flexible radio frequency transistor and mixer based on ultrathin indium tin oxide channel

In this work, a high-performance flexible radio frequency transistor using an ultrathin indium tin oxide film channel based on a solution-cast thin polyimide substrate has been demonstrated. The 60 nm short channel transistor shows a record high cut-off frequency of 5 GHz and a maximum oscillation frequency of 11 GHz with high uniformity among 40 devices. The radio frequency characteristics under various bending conditions have been systematically studied under a bending radius of 5 mm for 10 000 times and a bending radius of 1 mm for 1000 times, showing excellent stability with only 20% decrease in the cut-off frequency. Furthermore, a flexible frequency mixer has also been demonstrated at 2.4 GHz with decent conversion gains.

High-Performance 3D Vertically Oriented Graphene Photodetector Using a Floating Indium Tin Oxide Channel.

Vertically oriented graphene (VG), owing to its sharp edges, non-stacking morphology, and high surface-to-volume ratio structure, is promising as a consummate material for the application of photoelectric detection. However, owing to high defect and fast photocarrier recombination, VG-absorption-based detectors inherently suffer from poor responsivity, severely limiting their viability for light detection. Herein, we report a high-performance photodetector based on a VG/indium tin oxide (ITO) composite structure, where the VG layer serves as the light absorption layer while ITO works as the carrier conduction channel, thus achieving the broadband and high response nature of a photodetector. Under the illumination of infrared light, photoinduced carriers generated in VG could transfer to the floating ITO layer, which makes them separate and diffuse to electrodes quickly, finally realizing large photocurrent detectivity. This kind of composite structure photodetector possesses a room temperature photoresponsivity as high as ~0.7 A/W at a wavelength of 980 nm, and it still maintains an acceptable performance at temperatures as low as 87 K. In addition, a response time of 5.8 s is observed, ~10 s faster than VG photodetectors. Owing to the unique three-dimensional morphology structure of the as-prepared VG, the photoresponsivity of the VG/ITO composite photodetector also presented selectivity of incidence angles. These findings demonstrate that our novel composite structure VG device is attractive and promising in highly sensitive, fast, and broadband photodetection technology.

Extremely high-gain source-gated transistors

Despite being a fundamental electronic component for over 70 years, it is still possible to develop different transistor designs, including the addition of a diode-like Schottky source electrode to thin-film transistors. The discovery of a dependence of the source barrier height on the semiconductor thickness and derivation of an analytical theory allow us to propose a design rule to achieve extremely high voltage gain, one of the most important figures of merit for a transistor. Using an oxide semiconductor, an intrinsic gain of 29,000 was obtained, which is orders of magnitude higher than a conventional Si transistor. These same devices demonstrate almost total immunity to negative bias illumination temperature stress, the foremost bottleneck to using oxide semiconductors in major applications, such as display drivers. Furthermore, devices fabricated with channel lengths down to 360 nm display no obvious short-channel effects, another critical factor for high-density integrated circuits and display applications. Finally, although the channel material of conventional transistors must be a semiconductor, by demonstrating a high-performance transistor with a semimetal-like indium tin oxide channel, the range and versatility of materials have been significantly broadened.

Low-Temperature Plasma-Enhanced Atomic Layer Deposition of Tin(IV) Oxide from a Functionalized Alkyl Precursor: Fabrication and Evaluation of SnO2-Based Thin-Film Transistor Devices.

A bottom-up process from precursor development for tin to plasma-enhanced atomic layer deposition (PEALD) for tin(IV) oxide and its successful implementation in a working thin-film transistor device is reported. PEALD of tin(IV) oxide thin films at low temperatures down to 60 °C employing tetrakis-(dimethylamino)propyl tin(IV) [Sn(DMP)4] and oxygen plasma is demonstrated. The liquid precursor has been synthesized and thoroughly characterized with thermogravimetric analyses, revealing sufficient volatility and long-term thermal stability. [Sn(DMP)4] demonstrates typical saturation behavior and constant growth rates of 0.27 or 0.42 Å cycle-1 at 150 and 60 °C, respectively, in PEALD experiments. Within the ALD regime, the films are smooth, uniform, and of high purity. On the basis of these promising features, the PEALD process was optimized wherein a 6 nm thick tin oxide channel material layer deposited at 60 °C was applied in bottom-contact bottom-gate thin-film transistors, showing a remarkable on/off ratio of 107 and field-effect mobility of μFE ≈ 12 cm2 V-1 s-1 for the as-deposited thin films deposited at such low temperatures.

Electrical properties of thin film transistors with zinc tin oxide channel layer

We have investigated thin film transistors (TFTs) with zinc tin oxide (ZTO) channel layer fabricated by using an ultra-high vacuum radio frequency sputter. ZTO thin films were grown at room temperature by co-sputtering of ZnO and SnO2, which applied power for SnO2 target was varied from 15 W to 90 W under a fixed sputtering power of 70 W for ZnO target. A post-annealing treatment to improve the film quality was done at temperature ranges from 300 to 600 °C by using the electrical furnace. The ZTO thin films showed good electrical and optical properties such as Hall mobility of more than 9 cm2/V·s, specific resistivity of about 2 × 102 Ω·cm, and optical transmittance of 85% in visible light region by optical bandgap of 3.3 eV. The ZTO-TFT with an excellent performance of channel mobility of 19.1 cm2/V·s and on-off ratio (I on /I off ) of 104 was obtained from the films grown with SnO2 target power of 25 W and post-annealed at 450 °C. This result showed that ZTO film is promising on application to a high performance transparent TFTs.

Bipolar Conduction in Tin-Oxide Semiconductor Channel Treated by Oxygen Plasma for Low-Power Thin-Film Transistor Application

In this paper, we investigated the bipolar conduction mechanism in thin-film transistors (TFTs) with oxygen plasma treatment on tin-oxide channel. The optimized p-type thin-oxide TFTs showed an on/off ratio of ${>}{\hbox{10}}^{4}$ , a threshold voltage of $-$ 1.05 V, and a field-effect mobility of ${\hbox{2.14}} {\hbox{cm}}^{2}{\cdot}{\hbox{V}}^{-1}{\cdot}{\hbox{s}}^{-1}$ . By increasing the exposure time of oxygen plasma, excess oxygen was incorporated to thin-oxide channel and converted thin monoxide to oxygen-rich n-type thin dioxide, which in turn led to n-type operation. It indicated that oxygen plasma was the critical factor to determine oxygen concentration, oxygen vacancies, metal ions and channel polarity. This proposed oxygen-content tuning through plasma treatment approach shows great promise in simplification of TFT process that can achieve n-type and p-type TFTs under the same device process.

Improvement in the Positive Bias Temperature Stability of SnOx-Based Thin Film Transistors by Hf and Zn Doping.

We investigated the performance of tin oxide thin film transistors (TFTs) using DC magnetron sputtering. A remarkable improvement in the transfer characteristics was obtained for the Hf-doped tin oxide (HTO) TFT. We also developed amorphous hafnium-zinc-tin oxide (HZTO) thin film transistors and investigated the effects of hafnium doping on the electrical characteristics of the HTO TFTs. Doping with hafnium resulted in a reduced defect density in the tin oxide channel layer related to oxygen vacancies, which may result from increased field effect mobility. Zinc atoms have relatively higher oxidation potential compared to tin atoms, so more oxygen molecules can be absorbed and more electrons are trapped in the HZTO films. The HZTO TFTs exhibited good electrical characteristics with a field effect mobility of 10.98 cm2/Vs, and a high ION/IOFF ratio over 10(8).

Low temperature processed complementary metal oxide semiconductor (CMOS) device by oxidation effect from capping layer.

In this report, both p- and n-type tin oxide thin-film transistors (TFTs) were simultaneously achieved using single-step deposition of the tin oxide channel layer. The tuning of charge carrier polarity in the tin oxide channel is achieved by selectively depositing a copper oxide capping layer on top of tin oxide, which serves as an oxygen source, providing additional oxygen to form an n-type tin dioxide phase. The oxidation process can be realized by annealing at temperature as low as 190°C in air, which is significantly lower than the temperature generally required to form tin dioxide. Based on this approach, CMOS inverters based entirely on tin oxide TFTs were fabricated. Our method provides a solution to lower the process temperature for tin dioxide phase, which facilitates the application of this transparent oxide semiconductor in emerging electronic devices field.

Fabrication of 120-nm-channel-length ferroelectric-gate thin-film transistor by nanoimprint lithography

Nanoimprint lithography (NIL) is one of the most promising device fabrication techniques because it has a high resolution and moderate fabrication cost. Oxide-based thin-film transistors (TFTs) with various physical properties have the potential to outperform Si-based large-scale integration (LSI) devices. In this study, we focus on the miniaturization of oxide-based TFTs by NIL. A ferroelectric-gate thin-film transistor (FGT) was prepared by incorporating a chemical-solution-deposition (CSD)-processed indium tin oxide channel, a Pb(Zr,Ti)O3 (PZT) gate insulator, and sputtered Pt electrodes. The Pt source–drain electrodes and ITO channel were patterned by the NIL process. The results show that we successfully fabricated an FGT with a channel length of 120 nm by NIL. The 120 nm channel length was confirmed by scanning electron microscopy (SEM). The fabricated NIL-FGT showed typical n-channel transistor characteristics. The obtained ON/OFF current ratio, threshold voltage, subthreshold voltage, and field-effect mobility were 103, 0.5 V, 1.0 V/decade, and 0.1–0.2 cm2·V−1·s−1, respectively.

Atomic layer deposited zinc tin oxide channel for amorphous oxide thin film transistors

Bottom-gate thin film transistors with amorphous zinc tin oxide channels were grown by atomic layer deposition. The films maintained their amorphous character up to temperatures over 500 °C. The highest field effect mobility was ∼13 cm2/V·s with on-to-off ratios of drain current ∼109–1010. The lowest subthreshold swing of 0.27 V/decade was observed with thermal oxide as a gate insulator. The channel layers grown at 170 °C showed better transistor properties than those grown at 120 °C. Channels with higher zinc to tin ratio (∼3–4) also performed better than ones with lower ratios (∼1–3).

Flexible Electronics Based on InGaZnO Transparent Thin Film Transistors

There is increasing interest in use of conducting oxide materials in new forms of transparent, flexible or wearable electronics on cheap substrates, including paper. While Si-based thin film transistors (TFTs) are widely used in displays, there are some drawbacks such as light sensitivity and light degradation and low field effect mobility (<1 cm2/Vs). For example, virtually all liquid crystal displays (LCDs) use TFTs imbedded in the panel itself. One of the promising alternatives to use of Si TFTs involves amorphous or nanocrystalline n-type oxide semiconductors. There have been promising results with zinc oxide, indium gallium oxide and zinc tin oxide channels. In this paper, recent progress in these new materials for TFTs on substrates such as paper is reviewed. In addition, InGaZnO transistor arrays show promise for driving laminar electroluminescent, organic light-emitting diode (OLED) and LCD displays. These transistors may potentially operate at up to an order of magnitude faster than Si TFTs. We have fabricated bottomgate amorphous (α-) indium-gallium-zinc-oxide (InGaZnO4) thin film transistors (TFTs) on both paper and glass substrates at low processing temperature (≤100°C). As a water and solvent barrier layer, cyclotene (BCB 3022-35 from Dow Chemical) was spin-coated on the entire paper substrate. TFTs on the paper substrates exhibited saturation mobility (μsat) of 1.2 cm2.V-1.s-1, threshold voltage (VTH) of 1.9V, subthreshold gate-voltage swing (S) of 0.65V.decade-1, and drain current onto- off ratio (ION/IOFFSubscript text) of ~104. These values were only slightly inferior to those obtained from devices on glass substrates (μsat~2.1 cm2.V-1.s-1, VTH ~0 V, S~0.74 V.decade-1, and ION/IOFF=105- 106). The uneven surface of the paper sheet led to relatively poor contact resistance between source-drain electrodes and channel layer. Future areas for development are identified.

Improvement in the Device Characteristics of Tin Oxide Thin-film Transistors by Adopting Ultralow-Pressure Sputtering

Here in, thin film transistors (TFTs) were fabricated with the tin oxide channel, deposited by using ultralow-pressure sputtering (ULPS), are reported. The effect of ULPS on the device performance of the tin oxide TFTs was investigated. The TFTs with tin oxide channel, deposited by conventional sputtering pressure (CSP), did not show a promising performance. However, the saturation mobility and threshold voltage of the ULPS SnOx TFTs were improved to ~ 3.9 cm2/Vs and ~ 0.6 V, respectively. The improved device performance of ULPS film was attributed to the decreased carrier concentration, which was originated from the formation of nano-crystalline phase and the higher film density compared to CSP film. We also compared the crystalline structure of ULPS and CSP film by using high-resolution transmission electron microscopy

Improving the Performance of Tin Oxide Thin-Film Transistors by Using Ultralow Pressure Sputtering

Thin-film transistors (TFTs) are fabricated with a tin oxide channel deposited by using ultralow pressure sputtering (ULPS). The effect of sputtering pressure on the device performance of the tin oxide TFTs was investigated. The TFTs with tin oxide channel deposited by conventional sputtering pressure did not show a promising performance. However, the saturation mobility and the threshold voltage of the ULPS-deposited TFTs were improved to and , respectively. The better device performance of the ULPS-deposited TFT was attributed to the reduced free electron density resulting from the formation of a nanocrystalline phase.

Encapsulation of Zinc Tin Oxide Based Thin Film Transistors

In this paper, we study the effect of thin film encapsulation on transparent thin film transistors (TFTs) with zinc tin oxide channel layers deposited by oxygen plasma assisted pulsed laser deposition (PAPLD). Chemisorption and desorption of oxygen are identified as the most important physical processes governing the impact of surface passivation on the device characteristics. For an in-depth study, we apply three different methods to remove chemisorbed oxygen from the channel surface: thermally activated desorption in vacuum; light induced desorption; and chemical reaction with the highly reactive agent trimethyl aluminum (TMA) during atomic layer deposition (ALD) thin film encapsulation. In each case, the removal of chemisorbed oxygen significantly shifts the threshold voltage of the TFTs on the order of 1−2 V. On the basis of the understanding gained in these experiments, a two-step encapsulation process is proposed that enables the application of high-performance ALD grown permeation barriers layers without alteration of the device characteristics. This finding is an essential step toward active matrix OLED displays with metal oxide driving electronics.

Transparent Thin Film Transistors Based on InZnO for Flexible Electronics

There is strong interest in new forms of transparent, flexible or wearable electronics using non-Si materials deposited at low temperature on cheap substrates. While Si-based thin film transistors (TFTs) are widely used in displays, there are some drawbacks such as light sensitivity and light degradation and low field effect mobility (<1 cm2/Vs). For example, virtually all liquid crystal displays (LCDs) use TFTs imbedded in the panel itself. One of the promising alternatives to use of Si TFTs involves amorphous or nanocrystalline n-type oxide semiconductors. For example, there have been promising results with zinc oxide, indium gallium oxide and zinc tin oxide channels. In this paper, recent progress in these new materials for TFTs is reviewed. It is expected that GaInZnO transistor arrays will be used for driving laminar electroluminescent, organic lightemitting diode (OLED) and LCD displays. These transistors may potentially operate at up to an order of magnitude faster than Si FTFs.

Functional Porous Tin Oxide Thin Films Fabricated by Inkjet Printing Process

The highly transparent SnO 2 thin films were deposited through solution-based inkjet printing using a simple precursor solution. We were able to fabricate porous tin oxide thin film that has a thin nanoporous layer on top and a thicker meso- and macroporous layer beneath the top layer. The thin-film transmittance is over 98% in the visible wavelength range. A mechanism based on gas evolution was proposed to explain the formation of porous structure. A depletion-mode thin-film transistor using the porous tin oxide channel layer was fabricated with a field-effect mobility of 3.62 cm 2 /V s.

Zinc tin oxide thin-film transistors via reactive sputtering using a metal target

Zinc tin oxide based thin-film transistors are fabricated via reactive magnetron sputtering using a metallic zinc/tin alloy target. The oxygen partial pressure and total sputtering pressure are explored. An oxygen partial pressure and total sputtering pressure of 0.8 and 30mTorr, respectively, are found to be optimal. Devices with a reactively sputtered zinc tin oxide channel layer and channel layer annealing of 500°C exhibit incremental mobilities of ∼32cm2V−1s−1, turn-on voltage of ∼−4V and drain current on-to-off ratios of ∼107. Both direct current and radio frequency magnetron sputtering are explored showing similar characteristics.