Indium Gallium Zinc Oxide Thin-film Transistors Research Articles

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).

Specific contact resistivity reduction in amorphous IGZO thin-film transistors through a TiN/IGTO heterogeneous interlayer

Oxide semiconductors have gained significant attention in electronic device industry due to their high potential for emerging thin-film transistor (TFT) applications. However, electrical contact properties such as specific contact resistivity (ρC) and width-normalized contact resistance (RCW) are significantly inferior in oxide TFTs compared to conventional silicon metal oxide semiconductor field-effect transistors. In this study, a multi-stack interlayer (IL) consisting of titanium nitride (TiN) and indium-gallium-tin-oxide (IGTO) is inserted between source/drain electrodes and amorphous indium-gallium-zinc-oxide (IGZO). The TiN is introduced to increase conductivity of the underlying layer, while IGTO acts as an n+-layer. Our findings reveal IGTO thickness (tIGTO)-dependent electrical contact properties of IGZO TFT, where ρC and RCW decrease as tIGTO increases to 8 nm. However, at tIGTO > 8 nm, they increase mainly due to IGTO crystallization-induced contact interface aggravation. Consequently, the IGZO TFTs with a TiN/IGTO (3/8 nm) IL reveal the lowest ρC and RCW of 9.0 × 10−6 Ω·cm2 and 0.7 Ω·cm, significantly lower than 8.0 × 10−4 Ω·cm2 and 6.9 Ω·cm in the TFTs without the IL, respectively. This improved electrical contact properties increases field-effect mobility from 39.9 to 45.0 cm2/Vs. This study demonstrates the effectiveness of this multi-stack IL approach in oxide TFTs.

Floating body effect in indium–gallium–zinc–oxide (IGZO) thin-film transistor (TFT)

In this paper, the floating body effect (FBE) in indium-gallium-zinc-oxide (IGZO) thin-film transistor (TFT) and the mechanism of device failure caused by that are reported for the first time. If the toggle AC pulses are applied to the gate and drain simultaneously for the switching operation, the drain current of IGZO TFT increases dramatically and cannot show the on/off switching characteristics. This phenomenon was not reported before, and our study reveals that the main cause is the formation of a conductive path between the source and drain: short failure. It is attributed in part to the donor creation at the drain region during the high voltage (Vhigh) condition and in part to the donor creation at the source region during the falling edge and low voltage (Vlow) conditions. Donor creation is attributed to the peroxide formation in the IGZO layer induced by the electrons under the high lateral field. Because the donor creation features positive charges, it lowers the threshold voltage of IGZO TFT. In detail, during the Vhigh condition, the donor creation is generated by accumulated electrons with a high lateral field at the drain region. On the other hand, the floating electrons remaining at the short falling edge (i.e., FBE of the IGZO TFT) are affected by the high lateral field at the source region during the Vlow condition. As a result, the donor creation is generated at the source region. Therefore, the short failure occurs because the donor creations are generated and expanded to channel from the drain and source region as the AC stress accumulates. In summary, the FBE in IGZO TFT is reported, and its effect on the electrical characteristics of IGZO TFT (i.e., the short failure) is rigorously analyzed for the first time.

Flexible multi-electrode neural probe using active-matrix design of transistor array

To realize a brain-machine interface, a neural probe is one of key hardware. For the neural probe, a high spatial resolution of an electrode array, high electrical sensitivity, and mechanical flexibility remain challenging and essential issues. In regard to these, implantable multi-electrode neural probe employing active-matrix design with field effect transistors (FETs) can attract attention due to their advantages of a suitable integration density and good signal-amplifying abilities. Therefore, we developed a flexible multi-electrode neural probe employing an active-matrix design based on a two-transistor (2T) scheme for application to a flexible neural signal recording probe. As a proof of concept, 4 × 8 electrode array (32 channels) with TFTs was demonstrated. For the flexible active-matrix design, back-gate indium-gallium-zinc-oxide (IGZO) thin film transistors (TFTs) were fabricated on a polyimide (PI). The TFTs used here can amplify signals and achieve a switching function to drive the active matrix. The probe structure was encapsulated by the same PI material again to achieve flexibility with good reliability, as the sandwich-like structure can induce a neutral plane on the TFT and electrodes. To ensure a high signal-to-noise ratio, the structural and process parameters of the TFT were studied. Among different annealing times and temperatures of the IGZO TFT, the optimized annealing condition of the TFT was found to be 250 °C a 1 hour on a flexible substrate. The width over length of the transistors was optimized to 50 μm/10 μm, and the field-effect mobility was 8.33 cm2/V·s. The on current was 2.28 × 10−6 A at a low driving voltage of 5 V. The transconductance was 2.16 μS and the threshold voltage (Vth) was 1.6 V. By applying 5 V, the switching TFT was turned on, and a doubly amplified signal (> 2.4 times) could be measured on the drain line. The electrode array probe with the active-matrix design can use for accurate neural recording and herald a new generation of flexible neural probes with high spatial resolutions.

A ternary gate-connected threshold switching thin-film transistor

Multi-valued logic has been a significant focus of research in various fields with the advancement of information technology. One approach to realizing ternary logic is integrating of a threshold switching (TS) device with a transistor, but this method often entails a complex fabrication process. This work suggests a ternary gate-connected threshold switching thin-film transistor (TS-TFT) by serially connecting the TS device with a bottom-gate thin-film transistor (TFT). The fabrication process is simplified with a structure that shares electrodes and insulators. Different threshold voltages from TS and TFT devices produce stable multiple states. The Pt/HfO2/TiN TS device has an electronic trapping/detrapping switching mechanism that exhibits low power consumption and high reliability. With the superior electrical performance of an amorphous indium gallium zinc oxide TFT, the TS-TFT has stable endurance. Furthermore, pulse switching and ternary inverter are demonstrated from the practical point of view.

Innovations in thin‐film electronics for the new generation of displays

AbstractToday's display industry faces transistor‐level challenges similar to those of complementary metal‐oxide semiconductor (CMOS) metal‐oxide semiconductor field‐effect transistors (MOSFETs) in the mid‐1990s. Learnings from MOSFETs inform the display industry's response to the limitations of silicon‐based thin‐film transistors (TFTs). Improvements sustaining Moore's Law drove the need to rethink MOSFET materials and structures. The display industry needs fundamental innovation at the device level. New thin‐film devices enable an inflection point in the use of displays, just as fin field‐effect transistor (FinFET) defined the inflection point in CMOS in the 2000s. This paper outlines two innovations in thin‐film device technology that offers improvement in image quality and power consumption of flat panel displays: amorphous metal gate TFTs (AMeTFTs) and amorphous metal nonlinear resistors (AMNRs). Linked through a single core material set based on mass‐producible, thin‐film amorphous metals, these two innovations create near‐ and long‐term roadmaps simplifying the production of high‐image quality, low‐power consumption displays on glass (now) and plastic (future). In particular, the field‐effect mobility of indium gallium zinc oxide (IGZO) AMeTFTs (55–72 cm2/Vs) exceeds that of IGZO TFTs developed by existing display manufacturers without the need for atomic layer deposition or vertical stacking of heterostructure semiconductor films, making AMeTFTs a natural choice for the new G8.5–G8.7 fabs targeting IGZO backplanes.

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.

A low-temperature photoresist-based film-profile engineering scheme for fabricating bottom- and double-gated indium–gallium–zinc oxide TFTs

We proposed a novel low-temperature (<110 °C) process scheme based on the film-profile engineering technique for fabricating indium–gallium–zinc oxide thin-film transistors (TFTs) with both bottom-gated (BG) and double-gated (DG) configurations. An organic photoresist (PR) suspended bridge is constructed to shadow the depositing species during the deposition processes of the bottom gate-oxide, channel, and source/drain metal films. An Al2O3 layer deposited at 110 °C using atomic-layer deposition is employed as the bottom gate-oxide layer. Such a low-temperature process allows us to deposit the Al2O3 layer following the formation of the PR suspended bridge, preventing the formation of organic residues between the gate-oxide and channel layers. As a result, excellent device performance in terms of field-effect mobility of 12.1 cm2 V−1 s−1 and subthreshold swing of 141 mV/dec is achieved. Our proposed low-temperature process scheme is readily applicable for fabricating DG TFTs which show substantial enhancements in driving currents.

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.

Rapid thermal annealing effect on performance variations of solution processed indium–gallium–zinc-oxide thin-film transistors

In this paper, the 1 min annealing effect on the electrical characteristics of solution-processed amorphous indium–gallium–zinc-oxide thin-film transistors (a-IGZO TFTs) was analyzed in an ambient gas environment comprising He, Ar, N2, and O2 and an annealing temperature range from 400 to 600 °C for different active layer thicknesses. Even for the short annealing time of 1 min, the He-annealed TFTs show good performance with a threshold voltage of −1.27 V, a subthreshold slope of 605 mV/dec, and a field-effect mobility of 7.19 cm2/Vs under the thick active layer condition. The resulting good performance of the He-annealed TFT originates from the high thermal velocity of the He atom, which can be confirmed from the x-ray photoelectron spectroscopic measurement by the sharp definition of the active layer near the a-IGZO/gate insulator interface.

Insight into the evolution of electrical properties for Schottky-barrier IGZO thin-film transistors with Cu-based Schottky contacts

In this work, we performed systematic electrical characterization and analysis of indium–gallium–zinc oxide (IGZO) Schottky-barrier thin-film transistors (SBTFTs) with different Cu-based Schottky contact structures. It was found that the Schottky barrier height (ΦB) between the IGZO layer and the Cu electrode could be modulated notably by changing the thickness of the AlOx tunnel layer, and the variation in ΦB significantly changed the saturation drain current (Idsat) of the IGZO SBTFTs based on the Schottky contacts but only had a minor influence on the saturation voltage (Vdsat) of the devices. Furthermore, Cu/Al stacked source/drain electrodes and silicon nitride (SiNx) passivation were employed to tailor the contact resistance and channel resistance of the IGZO SBTFTs, which led to an increase in Idsat and a variation in Vdsat. A universal resistance–capacitance network model was proposed to explain the observed evolution of Vdsat of the SBTFTs with different device structures. This work provides meaningful insight into developing low-cost metal oxide SBTFTs with tailored device performances.

Enhancing photodetection performance of UV photodetectors with stacked Pt/NiO dual capping layers on IGZO thin-film transistors

This paper proposes a solution to mitigate the trade-off between dark and photocurrents in the indium gallium zinc oxide (IGZO) thin-film transistor (TFT) applications, such as ultraviolet photodetectors, by using a stacked Pt/NiO dual capping layer (CL). The Pt CL forms a Schottky contact with the IGZO channel, which maximizes the depletion width on the channel layer and allows the use of a thicker channel to suppress both dark current and channel resistance. On the other hand, the NiO CL forms a pn heterojunction with the IGZO channel, which provides additional space for generating electron–hole pairs and is forward biased by the photovoltaic voltage under UV irradiation, resulting in a further negative shift in the threshold voltage and a significant increase in photocurrent. Experimental results show that the proposed CL scheme exhibits excellent photoresponsivity, photosensitivity, and specific detectivity in a 40 nm-thick IGZO TFT, with the values of 1888 A/W, 3.37 × 108 A/A, and 3.99 × 1016 Jones, respectively, which are about 55%, 83%, and 68% higher than a traditional 30 nm-thick IGZO TFT using only NiO CL under 275 nm UV irradiation.

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.

Accurate determination of band tail properties in amorphous semiconductor thin film with Kelvin probe force microscopy

The disordered microscopic structure of amorphous semiconductors causes the formation of band tails in the density of states (DOS) that strongly affect charge transport properties. Such band tail properties are crucial for understanding and optimizing thin-film device performance with immense relevance for large area electronics. Among the available techniques to measure the DOS, Kelvin Probe Force Microscopy (KPFM) is exceptional as it enables precise local electronic investigations combined with microscopic imaging. However, a model to interpret KPFM spectroscopy data on amorphous semiconductors of finite thickness is lacking. To address this issue, we provide an analytical solution to the Poisson equation for a metal–insulator–semiconductor junction interacting with the atomic force microscope tip. The solution enables us to fit experimental data for semiconductors with finite thickness and to obtain DOS parameters, such as band tail width, doping density, and flat band potential. To demonstrate our method, we perform KPFM experiments on Indium–Gallium–Zinc Oxide (IGZO) thin-film transistors (IGZO-TFTs). DOS parameters compare well with values obtained with photocurrent spectroscopy. We demonstrate the relevance of the developed method by investigating the impact of ionizing radiation on DOS parameters and TFT performance. Our results provide clear evidence that the observed shift in threshold voltage is caused by static charge in the gate dielectric, leading to a shift in flat band potential. Band-tails and doping density are not affected by the radiation. The developed methodology can be easily translated to different semiconductor materials and paves the way for quantitative microscopic mapping of local DOS parameters in thin-film devices.

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.

Write-Once-Read-Many-Times Memory Characteristics with a Large Memory Window Operating at a Low Voltage by Li-Ion Incorporation from the LiCoOx Ion-Supplying Layer into the InGaZnO Channel of a Thin-Film Transistor

Write-once-read-many-times (WORM) memory characteristics with a large memory window are demonstrated in a thin-film transistor (TFT) composed of an indium-gallium-zinc oxide (IGZO) channel and a lithium-cobalt oxide (LiCoOx) ion-supplying layer in the gate oxide. While the device with a thicker (5 nm) tunneling oxide showing a threshold voltage shift (ΔVT) of about 5 V by electron charging upon positive gate voltage (VGS) sweep to +25 V, the device with a 2 nm-thick tunneling oxide exhibits a large memory window with ΔVT > 20 V by Li-ion migration from LiCoOx to IGZO channel, which can be controlled as multilevel states with respect to the VGS amplitude. Incorporation of Li ions into the IGZO channel acting as p-type dopants reduces carrier concentration in the channel and consequently increases VT. The increased VT and the consequently reduced drain current are not instantly restored back by applying negative VGS, featuring WORM memory characteristics. Although the device undergoes partial retention loss, the retention remains up to about 90% after 100 min of retention time. These results verify WORM memory operations in the IGZO TFTs through gate voltage-driven Li-ion incorporation into the IGZO channel to modify its conductive states instead of using a typical electrical charging route.

IGZO thin-film transistors with tunneling contacts: towards power efficient display

We report the fabrication and characterization of indium gallium zinc oxide (IGZO) tunneling thin-film transistors. Both the IGZO channel and an Al2O3 tunneling barrier layer were deposited using the radio-frequency magnetron sputtering method. Compared with a conventional device, our device exhibited rapid saturation at a much smaller drain bias. Interestingly, we observed two different current saturation mechanisms within a single device, which can be explained as competition between the depletion envelope near the source electrode and channel depletion near the drain electrode. This work represents an industry-friendly method for implementing the tunnel-contact approach in the display industry.

9.1: Effect of Nitrogen Doping Content on Electrical Properties and Stability of a‐IGZO TFT

To improve the electrical properties and stability of thin‐film transistor (TFT) based on the indium gallium zinc oxide (IGZO) channel, the effect of nitrogen‐doping content on the electrical properties of IGZO films and the IGZO TFT were evaluated. It is found that the mobility and carrier concentration of IGZO films gradually decreases ( μ from 18.11 to 11.25 cm2/ V.s, n from 1.76×107 to 4.38×107 cm‐3 ) with the increase of N2 flow content (0‐8sccm). N‐doping can evidently improve the positive bias stress(PBS) stability of IGZO TFT. Typically, the low‐content N‐doping (1 sccm) can significantly boost the stability of IGZO:N TFT (ΔVth = 3.3 V vs ΔVth=9.54 V for the undoped counterpart), while the electrical properties is at almost no degradation with the mobility and on‐off current ratio (Ion/Ioff)as high as 16.59 cm2 /V.s and 3.55×107, and the sub‐threshold swing (SS) and threshold voltage (Vth) as low as 0.32 V/dec and 1.49 V, respectively. These outstanding reliability performance indicates that the N‐doping with appropriate low‐content is a facile and economical way to improve the electrical properties and stability of IGZO TFT.

An Integrated Analog Front-End System on Flexible Substrate for the Acquisition of Bio-Potential Signals.

The application of a versatile, low-temperature thin-film transistor (TFT) technology is presently described as the implementation on a flexible substrate of an analog front-end (AFE) system for the acquisition of bio-potential signals. The technology is based on semiconducting amorphous indium-gallium-zinc oxide (IGZO). The AFE system consists of three monolithically integrated constituent components: a bias-filter circuit with a bio-compatible low cut-off frequency of ≈1Hz, a 4-stage differential amplifier offering a large gain-bandwidth product of ≈955kHz, and an additional notch filter exhibiting over 30dB suppression of the power-line noise. Respectively built using conductive IGZO electrodes with thermally induced donor agents and enhancement-mode fluorinated IGZO TFTs with exceptionally low leakage current, both capacitors and resistors with significantly reduced footprints are realized. Defined as the ratio of the gain-bandwidth product of an AFE system to its area, a record-setting figure-of-merit of ≈86kHzmm-2 is achieved. This is about an order of magnitude larger than the < 10kHzmm-2 of the nearest benchmark. Requiring no supplementary off-substrate signal-conditioning components and occupying an area of ≈11mm2 , the stand-alone AFE system is successfully applied to both electromyographyand electrocardiography (ECG).

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.