Highly conductive SnO2 thin films for flat‐panel displays

Abstract— SnO₂ is considered to be a promising alternative material for indium tin oxide (ITO), which is used for thin‐film transparent electrodes in flat‐panel displays (FPDs) and is facing a serious indium depletion problem. However, annealing processes in the manufacture of plasma‐display panels (PDPs), which are major FPDs, cause high resistivity in SnO₂ films. To obtain lower resistivity after the annealing processes, the relationship between deposition conditions and resistivity and the influences of annealing on resistivity, both theoretically and experimentally, were investigated. As a solution, a method involving the formation of a coating of SiO₂ on SnO₂ is proposed, and a SnO₂ resistivity as low as 6.60 × 10^?5 Ω‐m was obtained after annealing.     

Effect of deep UV laser treatment on silicon‐doped Tin oxide thin film

In this paper, the effect of deep ultraviolet (UV) laser on physical and electrical properties of amorphous Silicon‐doped tin oxide (amorphous Si‐Sn‐O, a‐STO) thin films were studied. Surface morphology, thickness, crystallinity, and optical band gap of a‐STO thin films treated by laser were investigated. Results showed that the decrease of thickness and surface roughness of a‐STO thin films after deep UV laser treatment, and the films maintained an amorphous structure, which implied that the quality of a‐STO thin films were improved. The peak position of oxygen vacancy binding energy became lower; this is caused by an increase in oxygen vacancies resulting in a decrease in coordination number. And the oxygen vacancy content of the a‐STO thin films was increased after deep UV laser treatment. In addition, the optical band gap of a‐STO films was broaden after the deep UV laser treatment. It exploits a new application of deep UV laser in oxide semiconductor.     

Solution‐processed oxide thin‐film transistors using aluminum and nitrate precursors for low‐temperature annealing

Abstract— In this article, a solution process for oxide thin‐film transistors (TFTs) at low‐temperature annealing was investigated. Solution‐process engineering, including materials and precursors, plays an important role in oxide thin‐film deposition on large glass and flexible substrates at low temperature. Reactive material could reduce the alloy reaction temperature for a multicomponent oxide system. A volatile precursor could also reduce annealing temperature in the formation of metal‐oxide thin films. A solution process with reactive Al and a volatile nitrate precursor can demonstrates competitive oxide TFTs at 350°C.     

Letter: Solution‐processed flexible zinc‐tin oxide thin‐film transistors on ultra‐thin polyimide substrates

In this letter, solution‐processed flexible zinc‐tin oxide (Z_0.35T_0.65O_1.7) thin‐film transistors with electrochemically oxidized gate insulators (AlOx:Nd) fabricated on ultra‐thin (30 µm) polyimide substrates are presented. The AlOx:Nd insulators exhibited wonderful stability under bending and excellent insulating properties with low leakage current, high dielectric constant, and high breakdown field. The device exhibited a mobility of 3.9 cm²/V · s after annealing at 300 °C. In addition, the flexible device was able to maintain the electricity performance under various degrees of bending, which was attributed to the ultra‐thin polyimide substrate.     

Highly reliable a‐IGZO TFTs on a plastic substrate for flexible AMOLED displays

We have successfully reduced threshold voltage shifts of amorphous In–Ga–Zn–O thin‐film transistors (a‐IGZO TFTs) on transparent polyimide films against bias‐temperature stress below 100 mV, which is equivalent to those on glass substrates. This high reliability was achieved by dense IGZO thin films and annealing temperature below 300 °C. We have reduced bulk defects of IGZO thin films and interface defects between gate insulator and IGZO thin film by optimizing deposition conditions of IGZO thin films and annealing conditions. Furthermore, a 3.0‐in. flexible active‐matrix organic light‐emitting diode was demonstrated with the highly reliable a‐IGZO TFT backplane on polyimide film. The polyimide film coating process is compatible with mass‐production lines. We believe that flexible organic light‐emitting diode displays can be mass produced using a‐IGZO TFT backplane on polyimide films.     

High‐mobility self‐aligned top‐gate oxide TFT for high‐resolution AM‐OLED

High‐mobility and highly reliable self‐aligned top‐gate oxide thin‐film transistor (TFTs) were developed using the aluminum reaction method. Al diffusion to the oxide semiconductor and homogenization of the oxygen concentration in the depth direction after annealing were confirmed by laser‐assisted atom probe tomography. The high mobility of the top‐gate TFT with amorphous indium tin zinc oxide channel was demonstrated to be 32 cm²/V s. A 9.9‐in. diagonal qHD active‐matrix organic light‐emitting diode (AM‐OLED) display was fabricated using a five‐mask backplane process to demonstrate an applicable solution for large‐sized and high‐resolution AM‐OLEDs.     

The effect of the crystallization of indium tin oxide on indium tin oxide wet etching based on gate line with the structure of copper/indium tin oxide

In thin film transistor-liquid crystal display (TFT-LCD), the copper/indium tin oxide (Cu/ITO) layer was often used to be gate line. In this event, the patterning of ITO is necessary and important. However, the high temperature generated during Cu deposition will cause ITO to crystallize, which is not conducive to ITO etching. In this paper, the ITO films prepared by radio frequency (RF) magnetron sputtering were annealed according to the monitoring results of production line to simulate and study the effect of crystallization on the etching properties of ITO film. When the annealing temperature was less than 200°C, no large size grains were detected in ITO films, and the ITO films could be easily etched by etchant. However, the ITO films transformed from amorphous structure to polycrystalline structure after being annealed more than 200°C. After wet etching experiments, the polycrystalline ITO films could be hardly removed by etchant. The X-ray photoelectron spectroscopy (XPS) results showed that high temperature annealing induced a large amount of Sn⁴⁺ on ITO films surface. The Sn⁴⁺ was difficult to be dissolved by acid under normal conditions, which might be the most important factors that led to the greatly decreased etching rate for polycrystalline ITO films.     

Transparent and conducting SWNT thin films for flexible electronics

Abstract— Thin films from low‐density networks of single‐walled carbon nanotubes (SWNTs) are intriguing new two‐dimensional electronic materials because they have excellent tunable electrical, optical, and mechanical properties. Such properties coupled with room‐temperature deposition from solution ensure that the material will have profound impact on emerging technologies such as cheap, flexible plastic electronics and smart fabrics and windows. These optoelectronic properties of SWNT thin films make them a potentially good replacement for indium tin oxide (ITO), used widely in photovoltaics, organic, and inorganic light‐emitting diodes, displays, touch screens, and smart windows.     

Electrical properties of nickel oxide thin films for flow sensor application

In this work, Ni oxide thin films, with thermal sensitivity superior to Pt and Ni thin films, were formed through annealing of Ni films deposited by a r.f. magnetron sputtering. The annealing was carried out in the temperature range of 300–500 °C under atmospheric conditions. Resistivity of the resulting Ni oxide films were in the range of 10.5 μΩ cm/°C to 2.84 × 10⁴ μΩ cm/°C, depending on the extent of Ni oxidation. The temperature coefficient of resistance (TCR) of the Ni oxide films also depended on the extent of Ni oxidation; the average TCR of Ni oxide resistors, measured between 0 and 150 °C, were 5630 ppm/°C for the 300 °C and 2188 ppm/°C for 500 °C films. Because of their high resistivity and very linear TCR, Ni oxide thin films are superior to pure Ni and Pt thin films for flow and temperature sensor applications.     

Ferroelectric thin film fabrication by direct UV-lithography

Due to their use in the fields of sensors, energy harvesting, capacitors and FeRAMs the fabrication of microstructured ferroelectric thin films is an important research field. Therefore a modified sol–gel process chain has been developed to produce fine patterned ferroelectric PZT (PbZr_0.52Ti_0.48O₃) thin films by direct UV-lithography. A sol based on methacrylic acid was developed to provide a photosensitive metal organic PZT precursor. The sol was used to obtain photosensitive xerogel films by spin-coating, which were patterned using conventional UV-photolithography equipment. After development the patterned xerogel films were pyrolized and crystallized in air via rapid thermal annealing in order to obtain crystalline PZT thin films. The patterned PZT films were investigated by XRD technique and SEM-micrographs. Finely patterned, crack free, crystalline PZT thin films were obtained.     

Novel top‐gate zinc oxide thin‐film transistors (ZnO TFTs) for AMLCDs

Abstract— High‐performance top‐gate thin‐film transistors (TFTs) with a transparent zinc oxide (ZnO) channel have been developed. ZnO thin films used as active channels were deposited by rf magnetron sputtering. The electrical properties and thermal stability of the ZnO films are controlled by the deposition conditions. A gate insulator made of silicon nitride (SiN_x) was deposited on the ZnO films by conventional P‐CVD. A novel ZnO‐TFT process based on photolithography is proposed for AMLCDs. AMLCDs having an aperture ratio and pixel density comparable to those of a‐Si:H TFT‐LCDs are driven by ZnO TFTs using the same driving scheme of conventional AMLCDs.     

Silicon‐nanocrystal‐based photosensor integrated on low‐temperature polysilicon panels

Abstract— A photodetector using a silicon‐nanocrystal layer sandwiched between two electrodes is proposed and demonstrated on a glass substrate fabricated by low‐temperature poly‐silicon (LTPS) technology. Through post excimer‐laser annealing (ELA) of silicon‐rich oxide films, silicon nanocrystals formed between the bottom metal and top indium thin oxide (ITO) layers exhibit good uniformity, reliable optical response, and tunable absorption spectrum. Due to the quantum confinement effect leading to enhanced phonon‐assisted excitation, these silicon nanocrystals, less than 10 nm in diameter, promote electron‐hole‐pair generation in the photo‐sensing region as a result resembling a direct‐gap transition. The desired optical absorption spectrum can be obtained by determining the thickness and silicon concentration of the deposited silicon‐rich oxide films as well as the power of post laser annealing. In addition to obtaining a photosensitivity comparable to that of the p‐i‐n photodiode currently used in LTPS technology, the silicon‐nanocrystal‐based photosensor provides an effective backlight shielding by the bottom electrode made of molybdenum (Mo). Having a higher temperature tolerance for both the dark current and optical responsibility and maximizing the photosensing area in a pixel circuit by adopting a stack structure, this novel photosensor can be a promising candidate for realizing an optical touch function on a LTPS panel.     

Annealing effect of low‐temperature (<150°C) Cat‐CVD gate dielectric silicon nitride films diluted with atomic hydrogen

Abstract— The effect of in‐situ hydrogen pretreatment on dielectric properties of silicon nitride (SiN^x) thin films for a gate dielectric layer has been studied. SiN^xthin films were grown at a low temperature (150°C) by Catalytic CVD followed by conventional furnace annealing at 150°C for 2 hours. The in‐situ hydrogen pretreatment was performed without vacuum break before the sample was transferred to the furnace for thermal annealing. Capacitance—voltage (C‐V) and current‐density—voltage (J‐V) measurement showed that the hydrogen pretreatment was effective in reducing the hysteresis in the C‐V curve and in increasing the breakdown voltage. Without the treatment, the 150°C annealing failed to produce reliable C‐V and I‐V characteristics. The C‐V hysteresis and the threshold voltage shift of SiN^x were improved by furnace annealing as the hydrogen dilution ratio increased. Also, addition of hydrogen to the deposition gas mixture helped to improve the dielectric properties of the SiN^x films after thermal annealing. The combination of hydrogen dilution of the source gas and the in‐situ hydrogen treatment was successful in producing low‐temperature SiN^x films applicable to a‐Si TFTs. The TFT fabricated by using these films showed a field‐effect mobility of 0.23 cm²/V‐sec and a Vth of 3.1 V.     

Properties and cathodoluminescence of Y2O2S:Eu thin films

Abstract— Europium‐activated yttrium oxysulfide thin films were fabricated by electron‐beam deposition of Y₂O₂S:Eu with consequent annealing in an H₂S/Ar gas mixture. Transformations in film composition and surface morphology as well as corresponding changes in the optical, photoluminescent, and cathodoluminescent properties were studied and will be discussed. It is shown that 248‐nm laser irradiation of heat‐treated films improves cathodoluminescence by as much as 30%, supposedly due to annealing. The developed phosphor films have a luminance comparable to that of annealed europium‐activated yttrium oxide films and improved color properties (CIE color coordinates: x = 0.624, y = 0.329), and are suitable for display and optoelectronics applications.     

Effects of gate‐bias stress on ZnO thin‐film transistors

Abstract— The effects of gate‐bias and thermal stress on the stability issues of zinc oxide thin film transistors (ZnO TFTs) deposited on glass substrates were investigated. The shift in threshold voltage for devices undergoing various post‐growth annealing conditions using a stretched‐exponential formalism was analyzed. The analysis indicated that the extracted parameters such as the time constant and the effective energy barrier (E^τ) can be correlated to the device trap states associated with the annealing conditions. Improvement in the channel conductance and interface quality, hence the resultant device stability, can therefore be resumed when subject to a thermal treatment at 400°C for 30 minutes compared with those annealed for a shorter time.     

Rapid thermal annealing of polysilicon thin films

In comparison with conventional heat treatment, high-temperature rapid thermal annealing (RTA) in a radio frequency (RF) induction-heated system can reduce or eliminate residual stresses in thin films in a few seconds. In this work, changes in the stress level due to the RTA of polycrystalline silicon thin films were studied as a function of annealing time and temperature. The corresponding variations in the microstructure and surface layer of the thin films were experimentally investigated by a variety of analytical tools. The results suggest that the residual stress evolution during annealing is dominated by two mechanisms: 1) microstructure variations of the polysilicon thin film and 2) effects of a surface layer formed during the heat treatment. The fact that the microstructure changes are more pronounced in samples after conventional heat treatment implies that the effects of the formed surface layer may dominate the final state of the residual stress in the thin film     

Fabrication and electrical properties of polymer-derived ceramic (PDC) thin films for high-temperature heat flux sensors

In this paper, we describe the fabrication of ceramic thin films for high-temperature heat flux sensors. The polymer-derived ceramic (PDC) thin films are prepared by using soft lithography on pre-ceramic polymer precursors followed by pyrolysis and heat treatment. Processing routes have been developed which lead to thin film resistance-thermal detectors (RTD) that have sufficient mechanical strength for handling and for use in thermal sensing. The effect of annealing temperatures on the electric resistivity of the PDC sensors was investigated. The electrical resistivity of the sensors was measured at different temperatures.     

The electrical and optical properties of AZO thin film under different post-annealing temperatures

In this study, the Aluminum element doped zinc oxide (Al:ZnO) thin film was deposited on the Corning glass substrate by RF magnetron sputtering technology and annealing treatment. After sputtering, all thin films are then annealed on nitrogen atmosphere and temperature of 300, 500 and 550 °C, respectively. The structural, electric and optical characteristics were then investigated. All films illustrate strong (002) for ZnO and (335) for Al preferential orientation by using XRD analysis. The lower resistivity can be observed at nitrogen annealing and temperature of 400 °C. The transmittance property of AZO thin film exhibited an excellent transparency in the visible light range. The transmittance reached to nearly 81.4 % for all Al:ZnO film. It can be clearly observed that the grain size of AZO thin film is very uniform by utilizing SEM technology.     

Structural, optical and electrical properties of CdO/Cd(OH)2 thin films grown by the SILAR method

Successive Ionic Layer Adsorption and Reaction (SILAR) was used to form Cd(OH)₂ thin films from aqueous cadmium–ammonia complex on glass substrates at room temperature and the thermal annealing effect on thin films was studied. The as-deposited films were annealed at 200, 300 and 400 °C for 1 h in an oxygen atmosphere for conversion from Cd(OH)₂ to CdO and change in the structural, optical and electrical properties of the films and the effect of the light on the electrical properties of the films were investigated. The structural and surface morphological properties of the films were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that Cd(OH)₂ phase is converted into the cubic CdO films by annealing. The band gap energy values of films decreased from 3.59 to 2.13 eV through increasing annealing temperature. It was found that the current increased with increasing light intensity and CdO films were more conductive than the as-deposited films.     

Negative bias illumination stress assessment of indium gallium zinc oxide thin‐film transistors

Electrical performance stability of indium gallium zinc oxide (IGZO) thin‐film transistors (TFTs) is evaluated under negative bias illumination stress (NBIS). A bottom‐gate IGZO TFT whose top surface is passivated with zinc tin silicon oxide (ZTSO) exhibits a dramatic improvement in NBIS stability compared with that of an unpassivated, bottom‐gate IGZO TFT. Oxygen chemisorption/desorption at the channel layer top surface is proposed to explain why an unpassivated TFT exhibits significantly more NBIS than a passivated TFT.