Gallium Zinc Oxide Thin Film Research Articles

Trap Assessment and Mobility Simulation of Amorphous Indium Gallium Zinc Oxide Thin Film Transistors

Ultra-broadband photoconduction (UBPC) is used to measure the sub-gap trap density of amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) across the bandgap, from the valence band mobility edge to within 0.15 eV (~6kBT) of the conduction band mobility edge. Figure (a) is a plot of the total integrated trap density (Ntraps, green) and the sub-gap density of states (dNtraps/dE, blue) as measured by UBPC for traps located just below the conduction band mobility edge (E-EC = 0). Three Gaussian sub-gap states are observed with peak energies of 0.9, 0.7, and 0.4 eV below the conduction band mobility edge. Note that the width of the 0.4 eV peak (180 meV) is much larger than that of the other two deeper peaks (45 meV). All three of these peaks are likely associated with oxygen vacancies, but it is unclear why the 0.4 eV trap is so much broader than all the other deeper oxygen vacancy derived donor trap states.The black dotted curves included in Figure (b) are experimental EKV mobility (μEKV) versus overvoltage (VG-VON) plots obtained at three different temperatures (0 °, 20 °, and 100 °C). The red dashed curves are simulated mobility curves obtained assuming that only conduction band tail states act as electron traps to degrade the mobility. Since these red simulated curves grossly overestimate the experimental mobility, other traps must be operative in establishing the black experimental mobility curves. In fact, the inclusion of the 0.4 eV trap measured by UBPC in addition to the conduction band tail states in the simulation (blue curves) leads to excellent agreement between experimental and simulated mobility for all three temperatures (0 °, 20 °, and 100 °C). In summary, it is demonstrated how the mobility of a-IGZO can be simulated by including the experimentally observed DoS of a 0.4 eV centered Gaussian trap state.

Bottom-Up Design of a Supercycle Recipe for Atomic Layer Deposition of Tunable Indium Gallium Zinc Oxide Thin Films

Bottom-Up Design of a Supercycle Recipe for Atomic Layer Deposition of Tunable Indium Gallium Zinc Oxide Thin Films

Enhanced Electrical Properties and Stability in IGZO TFTs via Low-Temperature Activation with MgOx Layer.

We propose the introduction of a magnesium oxide (MgOx) layer to reduce the temperature required for the activation of indium gallium zinc oxide (IGZO) thin films. By incorporating the MgOx layer between the IGZO channel layer and the gate insulator layer, the required activation temperature is lowered from 300 to 200 °C while enhancing the electrical performance of the IGZO thin-film transistor (TFT). Specifically, the field effect mobility is improved from 6.40 to 16.12 cm2/(V s), the on/off current ratio is enhanced from 1.62 × 109 to 7.16 × 109, and subthreshold swing is enhanced from 0.48 to 0.46 V/decade. Furthermore, IGZO TFTs with the MgOx layer exhibit enhancements in threshold voltage (VTH) shift compared to TFTs without the MgOx layer under positive bias stress (VGS = 20 V and VDS = 0.1 V for 10,000 s) and negative bias stress (VGS = -20 V and VDS = 0.1 V for 10,000 s): the VTH shifts are decreased from 2.40 to 1.72 V and from 0.56 to 0.53 V, respectively. These enhancements are verified through various analyses and are attributed to the diffusion of Mg atoms into the IGZO front channel during the low-temperature activation process, which results in the formation of Mg-doped IGZO between the MgOx and IGZO channel layers.

97‐3: Late‐News Paper: Enhanced IGZO TFT Performance with Atomic Layer Deposition Parameter Optimization for Large OLED Displays

In this comprehensive study, we rigorously evaluated the applicability of amorphous indium gallium zinc oxide (a‐IGZO) thin films synthesized using atomic layer deposition (ALD) technology in the field of large‐area organic light‐emitting diode (OLED) TVs. The key term to display production is the distribution of device characteristics, and maintaining uniformity can improve productivity yield and product quality. The purpose of this paper is to present guidelines for early application in industry through the process variable exploration results of ALD deposition equipment. The process parameters studied are process pressure and oxygen partial pressure (PO2). We have secured a method to secure device characteristics suitable for display technology through the correlation between a‐IGZO thin film characteristics and device characteristics through corresponding parameters. Our empirical data strongly demonstrate that the threshold voltage (Vth) stabilizes near 0.0 V and consistently achieves device mobility exceeding 15 cm2/Vs. In particular, this study shows that the variability of the Vth characteristic, which is limited to a narrow range of less than ±0.1V, is greatly reduced, and the mobility dispersion is also greatly reduced to less than ±1cm2/Vs. A deeper analytical exploration revealed that the pivotal factors affecting device performance are closely related to oxygen vacancies (Vo) and their dynamic interactions with oxygen molecules. These results will improve the uniformity of device characteristics, and it is believed that the introduction of ALD technology into future display technology will demonstrate improvements in the performance and quality of display products.

Effects of Laser Treatment of Terbium-Doped Indium Oxide Thin Films and Transistors.

In this study, a KrF excimer laser with a high-absorption coefficient in metal oxide films and a wavelength of 248 nm was selected for the post-processing of a film and metal oxide thin film transistor (MOTFT). Due to the poor negative bias illumination stress (NBIS) stability of indium gallium zinc oxide thin film transistor (IGZO-TFT) devices, terbium-doped Tb:In2O3 material was selected as the target of this study. The XPS test revealed the presence of both Tb3+ and Tb4+ ions in the Tb:In2O3 film. It was hypothesized that the peak of the laser thermal effect was reduced and the action time was prolonged by the f-f jump of Tb3+ ions and the C-T jump of Tb4+ ions during the laser treatment. Studies related to the treatment of Tb:In2O3 films with different laser energy densities have been carried out. It is shown that as the laser energy density increases, the film density increases, the thickness decreases, the carrier concentration increases, and the optical band gap widens. Terbium has a low electronegativity (1.1 eV) and a high Tb-O dissociation energy (707 kJ/mol), which brings about a large lattice distortion. The Tb:In2O3 films did not show significant crystallization even under laser energy density treatment of up to 250 mJ/cm2. Compared with pure In2O3-TFT, the doping of Tb ions effectively reduces the off-state current (1.16 × 10-11 A vs. 1.66 × 10-12 A), improves the switching current ratio (1.63 × 106 vs. 1.34 × 107) and improves the NBIS stability (ΔVON = -10.4 V vs. 6.4 V) and positive bias illumination stress (PBIS) stability (ΔVON = 8 V vs. 1.6 V).

Effect of sputtering working pressure on the reliability and performance of amorphous indium gallium zinc oxide thin film transistors

In this study, the reliability and electrical properties of indium gallium zinc oxide (IGZO) thin film transistors (TFTs) are investigated when the working pressure of the sputtering system is varied. As IGZO is deposited at a low working pressure, the sputtering yield increases and the film density increases from 5.84 to 6.00 g/cm3 based on x-ray reflectivity measurements. IGZO TFT sputtered at low working pressure has a mobility of 8.05 cm2/V s, a threshold voltage of 1.25 V, and a subthreshold swing of 0.25 V/dec. In addition, x-ray photoelectron spectroscopy analysis shows that the oxygen content in the film decreases when IGZO is deposited at a low working pressure, resulting in improved positive bias stress reliability due to the oxygen-poor film. Furthermore, the IGZO film deposited at a low working pressure effectively prevents the formation of defects caused by the environment such as H2O molecules.

Design and simulation of a nano biosensor based on amorphous indium gallium zinc oxide (a-IGZO) thin film transistor

In this study, a biosensor utilizing a dielectric-modulated amorphous indium gallium zinc oxide (a-IGZO) thin film transistor (TFT) is introduced. TFT biosensors have garnered significant attention due to their heightened sensitivity, scalable nature, low power consumption, rapid electrical detection capabilities, and cost-effective means of mass production. By embedding a nano-cavity within the gate insulator of the TFT, biomolecules can accumulate within. As each biomolecule possesses its own dielectric constant, it modulates the effective gate capacitance and, subsequently, changes the channel conductance. To assess the sensitivity of the biosensor, variation in saturation current after the absorption of biomolecules with respect to the drain current in the case of an air-filled cavity has been considered as a precise measure. The efficient operation of a biosensor is contingent upon the sensitivity being highly dependent on the dielectric constant of the biomolecules that are accumulated within the nano-cavity. Consequently, a comprehensive evaluation has been conducted to ascertain the impact of critical design parameters which have the potential to affect the sensitivity of the biosensor. Additionally, a statistical analysis based on coefficient of variation measure has been performed to evaluate the susceptibility of the biosensor’s sensitivity to variations in geometrical and physical design parameters. The utilization of label-free detection methodology in this device presents a notable advantage due to its compatibility with the fundamental CMOS processing technology and its cost-effective potential for macro production.

Ultraflexible Monolithic Three-Dimensional Static Random Access Memory.

Flexible static random access memory (SRAM) plays an important role in flexible electronics and systems. However, achieving SRAM with a small footprint, high flexibility, and high thermal stability has always been a big challenge. In this work, an ultraflexible six-transistor SRAM with high integration density is realized based on a monolithic three-dimensional (M3D) design. In this design, vertical stacked n-type indium gallium zinc oxide thin film transistors and p-type carbon nanotube transistors share common gate and drain electrodes, respectively, saving interlayer vias used in traditional M3D designs. This compact architecture reduces the footprint of the SRAM cell from a six-transistor to a four-transistor area, saving 33% of the area, and significantly enables the SRAM to have the highest flexibility among the reported ones, withstanding a harsh deforming process (6000 cycles of bending at a radius of 500 μm) without performance degradation. Moreover, this design facilitates the thermal stability of the SRAM under high temperature (333 K). It also exhibits great static and dynamic performance, with the highest normalized hold noise margin of 73.6%, a maximum gain of 151.2, and a minimum static power consumption of 3.15 μW in hold operation among the reported flexible SRAMs. This demonstration provides possibilities for SRAMs to be used in advanced wearable system applications.

PEALD deposited aluminum hafnium mixed oxide dielectrics for amorphous-IGZO TFTs

(Al–Hf) mixed oxide thin films (HfAlO) are attracted by many researchers because of their outstanding optical and electrical properties compared to hafnium oxide (HfO2). This study prepared HfAlO films at 300 °C using plasma-enhanced atomic layer deposition (PEALD). Changing the cycle ratio of HfO2 and aluminum oxide (Al2O3), the mixing effect on the properties of HfAlO film was studied. The characterization of the HfAlO films was investigated using spectroscopic ellipsometry (SE), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray reflectivity (XRR), scanning electron microscopy (SEM), and UV–vis spectroscopy. The results show that the aluminum content and optical bandgap of the HfAlO films increased with the increase of the Al2O3 cycle ratio. The dielectric constant of the HfAlO film with a 20 % Al2O3 cycle ratio (cycles of Al2O3/(cycles of Al2O3 + cycles of HfO2)) reaches ∼ 26, and the breakdown electric field is about 6.5 MV/cm. Pure HfO2 and 20 % Al2O3 cycle ratio deposited HfAlO was used as the gate dielectric layer, and the influence on the performance of amorphous indium gallium zinc oxide (a-IGZO) thin film transistor (TFT) was studied. A-IGZO TFT with a 20 % Al2O3 cycle ratio mixed HfAlO film as the gate dielectric exhibits the best performance, showing a high Ion/Ioff ratio of 1.3 × 109, a saturation mobility of ∼5.8 cm2/Vs, a subthreshold slope of 88 mV per decade and a low threshold voltage of −0.1V.

Effect of Channel Shape on Performance of Printed Indium Gallium Zinc Oxide Thin-Film Transistors.

Printing technology will improve the complexity and material waste of traditional deposition and lithography processes in device fabrication. In particular, the printing process can effectively control the functional layer stacking and channel shape in thin-film transistor (TFT) devices. We prepared the patterning indium gallium zinc oxide (IGZO) semiconductor layer with Ga, In, and Zn molar ratios of 1:2:7 on Si/SiO2 substrates. And the patterning source and drain electrodes were printed on the surface of semiconductor layers to construct a TFT device with the top contact and bottom gate structures. To overcome the problem of uniform distribution of applied voltages between electrode centers and edges, we investigated whether the circular arc channel could improve the carrier regulation ability under the field effect in printed TFTs compared with a traditional structure of rectangular symmetry and a rectangular groove channel. The drain current value of the IGZO TFT with a circular arc channel pattern was significantly enhanced compared to that of a TFT with rectangular symmetric source/drain electrodes under the corresponding drain-source voltage and gate voltage. The field effect properties of the device were obviously improved by introducing the arc-shaped channel structure.

A Comprehensive Large Signal, Small Signal, and Noise Model for IGZO Thin Film Transistor Circuits.

We report a new physics-based model for dual-gate amorphous-indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) which we developed and fine-tuned through experimental implementation and benchtop characterization. We fabricated and characterized a variety of test patterns, including a-IGZO TFTs with varying gate widths (100-1000 μm) and channel lengths (5-50 μm), transmission-line-measurement patterns and ground-signal-ground (GSG) radio frequency (RF) patterns. We modeled the contact resistance as a function of bias, channel area, and temperature, and captured all operating regimes, used physics-based modeling adjusted for empirical data to capture the TFT characteristics including ambipolar subthreshold currents, graded interbias-regime current changes, threshold and flat-band voltages, the interface trap density, the gate leakage currents, the noise, and the relevant small signal parameters. To design high-precision circuits for biosensing, we validated the dc, small signal, and noise characteristics of the model. We simulated and fabricated a two-stage common source amplifier circuit with a common drain output buffer and compared the measured and simulated gain and phase performance, finding an excellent fit over a frequency range spanning 10 kHz-10 MHz.

High Performance and High Yield Solution Processed IGZO Thin Film Transistors Fabricated with Low‐Temperature Annealed Hafnium Dioxide Gate Dielectric

AbstractSolution‐processed microelectronics offer advantages, including cost‐effectiveness, higher energy efficiency, and compatibility with rapid prototyping compared to their counterparts fabricated through traditional semiconductor manufacturing processes. Unfortunately, solution‐processed transistors exhibit wide performance variability and low yield. In this work, a solution‐processed transparent indium gallium zinc oxide (IGZO) thin film transistor with a low temperature‐annealed hafnium oxide dielectric layer is described. Post‐annealing temperatures for the sol–gel hafnium dioxide thin film are reduced to below 200 °C, significantly expanding the range of substrates on which the metal oxide dielectric can be deposited. The fabricated devices exhibit excellent characteristics with high field‐effect mobilities of over 85 cm2 V−1 s−1, along with low subthreshold swing below 140 mV dec−1, high on/off ratios, and near‐zero threshold voltages when operating stably at low‐operating voltages of 2 V. The solution processed transparent hafnium dioxide gate dielectric IGZO transistors are shown to exhibit comparatively significantly lower device variation and high yield, allowing for the reproducible fabrication of large‐area and transparent solution processed microelectronics systems.

Highly Sensitive Wireless NO2 Gas Sensing System

There is a need for reliable and accurate air quality monitoring systems in order to secure human health from the air pollutants such as nitrogen dioxide (NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). The development of low-cost and modern technology-compatible sensing systems is essential. In this work, a highly sensitive and selective Indium Gallium Zinc oxide (IGZO) thin film transistor has been used to design an efficient and wireless NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensing system. The sensing system uses the IGZO TFT as a current source for the current-starved ring oscillator where exposed NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentration determines the oscillation frequency. The presented NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas sensing system exhibited excellent sensitivity of 5.39 MHz/ppm with the lowest detection limit (LOD) of 50 ppb at room temperature. To the best of the authors’ knowledge, the achieved sensitivity is the best-reported performance for frequency-based NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensors. The sinusoidal output of the sensor obviates the need for costly peripheral signal conditioning circuits and allows direct integration with wireless systems. The 13.56 MHz RFID antenna connected to the output of the sensor is used to show wireless sensing compatibility and highlights the excellent candidacy of the proposed work for the growing Internet of Things (IoT) and untethered sensor applications.

Highly sensitive biosensor based on IGZO thin-film transistors for detection of Parkinson's disease

α-Synuclein (α-Syn) is a major biomarker of Parkinson's disease (PD). Concentration detection of α-Syn in cerebrospinal fluid and plasma of patients are used as a clue for early PD detection. Herein, we propose a thin-film transistor (TFT) biosensor based on an indium gallium zinc oxide (IGZO) thin film fabricated by the sol-gel method. The IGZO TFT biosensor is used for the early detection of PD after surface functionalization for α-Syn. The surface functionalization worked on the surface of the extended gate indium tin oxide sensing platform instead of the channel layer of TFT. Depending on concentrations of α-Syn in human cerebrospinal fluid and plasma, we diluted six different concentrations of α-Syn for detection, ranging from 1 pg ml−1 to 100 ng ml−1. The result shows that the biosensor exhibits high sensitivity and selectivity for α-Syn, a reliable sensing performance with a sensitivity of 189.9 mV dec−1, and a coefficient of determination R2 of 99.7% between 10 pg ml−1 and 100 ng ml−1.

Extraction Technique for the Conduction Band Minimum Energy in Amorphous Indium–Gallium–Zinc–Oxide Thin Film Transistors

The conduction band minimum energy in amorphous oxide semiconductor-based thin film transistors (AOS TFTs) is a key parameter governing the accurate extraction of energy distribution for the subgap density-of-states (DOSs) and carrier mobility. We report a technique for extraction of the gate voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {CBM}}{)}$ </tex-math></inline-formula> and corresponding energy ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {F},{\text {CBM}}}$ </tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {C}-{\text {EREF}}}{)}$ </tex-math></inline-formula> for the quasi-Fermi level ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {F}}{)}$ </tex-math></inline-formula> equal to the conduction band minimum ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {C}}{)}$ </tex-math></inline-formula> as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {CBM}}$ </tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {GS}}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {F}}$ </tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {C}}{)}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {F},{\text {CBM}}}$ </tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {F}}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {GS}}$ </tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {CBM}}{)}$ </tex-math></inline-formula> . In order to confirm this technique through optoelectronic experimental data, amorphous indium–gallium–zinc–oxide (a-IGZO)-based thin film transistor was irradiated with various wavelengths and power, and obtained <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {CBM}}$ </tex-math></inline-formula> = 7.1 V and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {F} {\text {CBM}}}$ </tex-math></inline-formula> = 71 meV in the dark state. This technique is expected to be useful in the accurate characterization of the subgap DOS and the effective mobility in AOS TFTs through a simple and effective extraction process.

Performance of Transparent Indium–Gallium–Zinc Oxide Thin Film Transistor Prepared by All Plasma Enhanced Atomic Layer Deposition

Transparent indium–gallium–zinc oxide thin film transistor (IGZO-TFT) prepared by all plasma enhanced atomic layer deposition (PEALD) has been firstly investigated. As the chemical composition has a considerable impact on the performance of IGZO TFTs, the properties of IGZO film and IGZO-TFT based on different In2O3 cycle ratios are investigated. The IGZO film prepared by PEALD shows amorphous state with excellent conformity and uniformity. Moreover, the a-IGZO films with different In2O3 cycle ratios are applied to TFT fabrication. When the a-IGZO thin film with 35% In2O3 cycle ratios, the transistor presents satisfactory electrical performance with a threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\text {th}}$ </tex-math></inline-formula> ) of 1.7 V, a saturation mobility ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{\text {sat}}$ </tex-math></inline-formula> ) of 8.8 cm2/Vs, a subthreshold swing (SS) of 0.2 V/decade and an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{I}_{ON}/\text{I}_{OFF}$ </tex-math></inline-formula> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.2\times 10^{{8}}$ </tex-math></inline-formula> . This work provides a new way to achieve transparent TFT which better for practical commercial applications.

A Multi-Finger GHz Frequency Doubler Based on Amorphous Indium Gallium Zinc Oxide Thin Film Transistors

A Multi-Finger GHz Frequency Doubler Based on Amorphous Indium Gallium Zinc Oxide Thin Film Transistors

Effect of passivation layer on back channel etching InGaZnO thin film transistors

Amorphous indium gallium zinc oxide (IGZO) thin film transistors (TFT) are widely used in active-matrix displays because of their excellent stability, low off-current, high field-effect mobility, and good process compatibility. Among IGZO TFT device structures, back channel etching (BCE) is favorable due to low production cost, short channel length and small SD-to-gate capacitance. In this work, prepared are the BCE IGZO TFTs each with the passivation layer of silicon dioxide (SiO&lt;sub&gt;2&lt;/sub&gt;), polyimide (PI) or SiO&lt;sub&gt;2&lt;/sub&gt;-PI stacked structure to study their difference in back channel hydrogen impurity and diffusion behavior. Comparing with the conventional SiO&lt;sub&gt;2&lt;/sub&gt; passivation BCE TFT, the performance of PI passivation TFT is improved greatly, specifically, the saturation field effect mobility increases from 4.7 to 22.4 cm&lt;sup&gt;2&lt;/sup&gt;/(V·s), subthreshold swing decreases from 1.6 to 0.28 V/decade, and the an on-off current ratio rises dramatically from 1.1×10&lt;sup&gt;7&lt;/sup&gt; to 1.5×10&lt;sup&gt;10&lt;/sup&gt;. After the SiO&lt;sub&gt;2&lt;/sub&gt; passivation layer is substituted with PI, the I&lt;sub&gt; off&lt;/sub&gt; decreases from 10&lt;sup&gt;–11&lt;/sup&gt; A to 10&lt;sup&gt;–14&lt;/sup&gt; A, which indicates that there exist less shallow-level donor states of hydrogen impurities, which might be explained by the following three mechanisms: first, in the film formation process of PI, the direct incorporation of hydrogen-related radicals from SiH&lt;sub&gt;4&lt;/sub&gt; precursor into the back channel is avoided; second, the hydrogen content in the PI film is lower and harder to diffuse into the back channel; third, the hydrogen impurity of back channel that is introduced by the H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;-based etchant in the SD etching process could diffuse more easily toward the PI layer. The TFTs with PI passivation layer also shows the less electrical degradation after the annealing treatment at 380 ℃ and better output performance, which confirms less defects and higher quality of the back channel. The bias stabilities of PI devices are improved comprehensively, especially negative bias illumination stability with the threshold voltage shifting from –4.8 V to –0.7 V, which might be attributed to the disappearance of hydrogen interstitial sites and hydrogen vacancies that are charged positively in the back channel. The PI passivation layer is effective to avoid back channel hydrogen impurities of BCE TFT and promises to have broad applications in the display industry.

Modulation of carrier density in indium–gallium–zinc-oxide thin film prepared by high-power impulse magnetron sputtering

Amorphous indium-gallium-zinc-oxide (α-IGZO) thin films were prepared by high-power impulse magnetron sputtering. The film composition and properties were investigated. The films were zinc-rich when compared to the target material due to the highest sputtering yield, least collision scattering and lowest self-sputtering yield of zinc species among the metallic sputtered species. The carrier-density in the thin film was modulated by the process pressure. Increasing process pressure raised more oxygen radicals and enhanced the oxygen binding ability of the Ga additives. Therefore, the oxygen vacancies were passivated thereby the carrier density was inhibited. Specifically, the carrier density markedly decreased from 8.4 × 1018/cm3 to 9.9 × 1016/cm3 as the process pressure increased. Meanwhile, the electron mobility only slightly decreased from 11.9 cm2/V·s to 8.0 cm2/V·s. Inverted staggered IGZO-TFTs were fabricated. The switch characteristic of the TFTs can be effectively modulated by the pressure during the preparation of IGZO channel.

Process Development of Amorphous Indium Tin Gallium Oxide (ITGO) Thin Film Transistors

The invention of portable electronic devices had a huge impact on the growing interest in flat panel displays. Since the first report in 2004 on amorphous Indium Gallium Zinc Oxide (a-IGZO) thin film transistors (TFTs), many companies have become interested in this material. The main advantage of a-IGZO over conventional amorphous silicon TFTs is its steep subthreshold, low off state current, and high channel mobility. However, the demand for larger displays with higher resolution and refresh rates is driving the demand for TFTs with higher performance, while avoiding the cost and complexity associated with low temperature polycrystalline silicon. There is an increased focus on alternative amorphous oxide semiconductors for use as TFT channel materials, due to the success of a-IGZO.The focus of this study is an investigation on Indium-Tin-Gallium-Oxide (ITGO) TFTs. Unpassivated bottom-gate devices were fabricated with a 30nm a-ITGO film, sputter deposited with 1% and 10% oxygen gas ambient, followed by a 2 hour anneal at 300oC in oxygen. Devices fabricated with PO2 = 1% resulted in a highly conductive channel. Devices with PO2 = 10% displayed semiconducting behavior and a shallow subthreshold. This trend held for all device dimensions tested; lengths of 24µm, 12µm, and 6µm with a width of 24µm. Compared to a-IGZO devices with a length of 4µm, ITGO devices with a length of 12µm exhibit an equivalent current drive, implying a 3 to 4 times improvement in mobility.Following aging in room ambient for multiple days, a-ITGO devices displayed improved yet left-shifted transfer characteristics. In unpassivated a-IGZO devices, similar behavior can also be observed and is attributed to an inhomogeneous trap distribution across the channel. As the exposed channel reacts with room air, oxygen vacancies are filled resulting in a more homogeneous trap distribution. A radial variation of device performance from the center of the wafer to the edge was also observed. When measuring devices towards the edge of the wafer a considerable left shift in transfer characteristics was observed. This variation in device performance is believed to be attributed to non-uniformities in the as deposited ITGO film and will be related to material optical parameters. Figure 1