ICMCTF2013 Session CP: Syposium C Poster Session

Recently, transfer printing has been widely used to form metal electrodes on various plastic substrates. This process can be applied to flexible display or organic solar cell application. Only a few metals such as Au, Ag and Cu have been employed in these applications because these metals have the property of 'glues' and 'releases' with substrate materials. The surface energy difference and cross-linking between metal and organic materials are key factors. Pure metals have better electrical properties but less optical transparency than transparent conducting oxides (TCO) and thus new structures such as TCO/Metal bilayer or TCO/Metal/TCO tri-layer have been studied. In this work, we have demonstrated that a structure of TCO/metal bilayer can be prepared successfully by a transfer printing method. A bilayer of Al-doped ZnO(AZO) and silver films sequentially deposited on poly(dimethyl siloxane) (PDMS) mold by RF magnetron sputtering is transferred onto polyester film(Obducat UV sheet) at 120^oC. Anti-sticking layer (METAX fz-610, Kanto kasei) are coated on PDMS mold pattern. The AZO layer thicker than 8 nm cannot be transferred because of film cracking, and Ag layer thinner than 5 nm is not enough for an adhesion layer. I-V characteristics of line patterns of AZO/Ag bilayer lines were measured. It is found that the transferred bilayer line has higher electrical resistance due to poor uniformity of METAX films formed by spin-coating and that optical transmittance of the bilayer is decreased as thickness of AZO layer is increase at the fixed thickness of Ag layer. As AZO becomes thicker surface roughness becomes larger and causes more scattering of the incident light.

Lately, zinc oxide (ZnO)-based semiconductors have been investigated as active channels of transparent thin-film transistors (TFTs) for organic light-emitting diodes and transparent displays because of their excellent electrical and optical properties at room temperature. Most of the researches have mainly been focused on improving the device performances of the TFTs. However, the electrical instability such as the threshold voltage shift due to the hysteresis phenomenon in the current-voltage characteristics of oxide-TFTs may need to be considered for practical applications. It is known that the electrical hysteresis may occur through several processes, such as electron injection and trapping within the gate insulator or deep state creation for the explicit case of a metal vacancy or electron trapping within the oxide channel layer. However, the exact mechanism responsible for the hysteresis is not clear yet.

In this study, we have investigated the hysteresis in the oxide-TFT which uses amorphous indium zinc oxide ( IZO) as the active channel. The IZO-based TFTs were fabricated with a bottom-gate structure. The IZO channel layers were deposited on thermally oxidized Si substrates (gate) via RF sputtering. Some of the IZO-TFTs had double channels which were formed by two-step deposition procedures. Here, the 1^st-IZO layer was deposited at relatively low oxygen contents in the O₂/Ar gas mixture. Then, the 2^nd-IZO layer was deposited at the higher oxygen contents without stopping the vacuum. The source/drain electrodes were also deposited with IZO films using the same RF sputtering system under a pure Ar environment. The forward and reverse voltage-sweep transfer characteristics of the fabricated IZO-TFTs were measured. The threshold voltage shift (ΔV_th) caused by the hysteresis was increased with the thickness and oxygen content of the IZO layer. The charge trapping mechanism responsible for the ΔV_th was examined by constructing the small-signal equivalent circuits for the single- and double-channel structures of IZO-TFTs and also measuring their capacitance-voltage (C-V) characteristics in the frequency range of 1 kHz – 10 MHz. From the C-V measurement, the interface trap density (D_it) and channel trap density (D_ch) were estimated in terms of the oxygen contents used for deposition of IZO-channel layers. The results indicate that more metal vacancies and oxide interstitials can be created for the IZO-channel layers with the greater incorporation of oxygen and the larger thickness. It is also noted that the channel trapping is dominant at the higher oxygen contents, but the interfacial trapping becomes a majority trap at the lower oxygen contents.

Zinc oxide (ZnO)-based semiconductors as active channel layers for thin film transistors (TFTs) recently have attracted much attention due to their excellent characteristics such as higher mobility than amorphous silicon, the ability to perform room-temperature deposition, and high transparency. However, most of the successful ZnO-based TFTs incorporate indium (In), e.g. indium zinc oxide (IZO), indium zinc tin oxide (IZTO), and indium gallium zinc oxide (IGZO), which is relatively rare on Earth. This makes those technologies easily subject to a material shortage. Recently, some researchers have reported experimental results which demonstrate new oxide semiconductors free of In, such as aluminum zinc tin oxide (AZTO), magnesium zinc oxide (MZO), and titanium oxide (TiO_x), as another alternative channel layers for oxide TFTs. Also, it has been known that the group IV elements (such as Si, Ge, Ti, Zr, Hf) may act as effective donors in the ZnO lattice because they may be substitutionally placed on the Zn sites and then enhance the carrier concentration and conductivity.

In this study, we suggest a novel transparent oxide TFT which has a silicon zinc oxide (SZO) channel layer. The SZO-based TFTs with a bottom-gate structure were fabricated by the following procedures. An n-type Si (100) wafer with a low resistivity (below 0.002 Ωcm) was used as a gate electrode, and a gate insulating layer was formed by thermally oxidizing the Si substrate. Then, the SZO channel layers were deposited via a co-sputtering method using two separated targets of ZnO (99.999 % of purity, 4 inch of diameter) and boron (B)-doped Si (99.999 % of purity, 0.1 Ωcm of resistivity), by varying the applied RF powers and the flow rates of oxygen gas. Finally, aluminum (Al) films were deposited via DC magnetron sputtering, followed by a lift-off process to form the source-drain electrodes. The various methods, such as four-point probe, X-ray diffraction (XRD), UV/visible spectrophotometer, secondary ion-mass spectrometry (SIMS), and x-ray photoelectron spectroscopy (XPS), were used to investigate the effects of the rf power and oxygen gas on the electrical, structural, and optical properties of the deposited SZO films. The output and transfer current-voltage characteristics of the fabricated SZO-TFTs were measured using a semiconductor parameter analyzer (4200-SCS, Keithley). The role of Si incorporation in determining the device characteristics of the SZO-TFTs was extensively examined. In addition, the relationship between the material properties of the SZO films and the device characteristics of the SZO-TFTs was discussed in detail.

Hafnium oxide (HfO₂) is a high temperature refractory material with excellent physical, electronic and chemical properties. The outstanding chemical stability, electrical and mechanical properties, high dielectric constant (high-k), and wide band gap of HfO₂ makes it suitable for several industrial applications in the field of electronics, magneto-electronics, structural ceramics, and optoelectronics. HfO₂ has been identified as one of the most promising dielectric to replace SiO₂ in nano-electronics. Hafnium oxide exhibits various polymorphs; monoclinic, tetragonal, and cubic. Doping a small amount of yttrium stabilizes the HfO₂ cubic phase. The high temperature cubic HfO₂ phase stabilized by Y-doping has been shown to exhibit increased dielectric constant compared to that in monoclinic phase. In the present work, yttrium-doped hafnium oxide (YDH) films were produced by sputter deposition on quartz and sapphire substrates at 400 °C by varying the deposition time in a wide range. YDH films with a thickness range ~20-1000 nm were produced by sputter-deposition. The grown YDH films were analyzed using X-ray diffraction, scanning electron microscopy (SEM) and optical spectrophotometry to understand the effect of film thickness on the microstructure and optical properties of YDH films. The XRD and SEM results indicate that the phase evolution and grain size were dependent on the film thickness. The cubic phase of YDH is seen for films with a thickness ≥60 nm. An increase in band gap from 5.2 to 5.5 eV is observed with film thickness. A correlation between growth conditions, thicknesses, and optical properties of the YDH is discussed.

This work studies impact of mechanical strain on hot carrier (HC) degradation for partially depleted silicon-on-insulator (SOI) n-channel metal-oxide-semiconductor-field-effect-transistors (MOSFETs). In general, conventional floating body (FB) effect can aggravate HC effect for SOI FB-type MOSFETs. For ultra-thin gate oxide, gate-induced-floating-body-effect (GIFBE) becomes a candidate to influence device performance under HC stress. By measurement of body current (I­_B), we can examine the body charging behavior and clarify mechanism. Additionally, it can be found that the maximum of I_B (I_Bmax) shows two stage trends under application of V_D. While V_D<1V, I_Bmax decreases as V_D increases, since GIFBE is diminished by expansion of depletion region. Beyond V_D=-1V, I_Bmax increases with V_D due to impact ionization. Therefore, aggravated HC degradation for FB device is attributed to conventional FB effect instead of GIFBE, even for ultra-thin gate oxide low power devices. Furthermore, we study the influence of mechanical strain on HC stress for SOI MOSFETs. It can be seen that performance of grounder body (GB) device with strain shows more significant degradation than that without strain during stress. This is because band gap narrowing enhances impact ionization. However, FB device shows invariant under HC stress before and after strain, since FB effect could make a competition between enhancement of impact ionization rate and electric field of depletion region lowing.

Keywords: Hot Carrier Stress, GIFBE, PD SOI, n-MOSFETs, Strain

We investigated on the physical characteristics and electrical performance of nitrogen doped amorphous In-Ga-Zn-O thin film transistor (IGZO:N TFT) without any channel passivation layer. By using microwave annealing technology instead of thermal furnace annealing, the electrical characteristics of a-IGZO:N (N₂ = 2sccm) thin film transistor could improve obviously from normally off to a transfer characteristic with a carrier mobility of 4.97 cm²/Vs, threshold voltage of 3.98 V and subthreshold swing of 0.39 V/decade. This TFT performance with microwave annealing of 300s is well competitive with its counterpart with furnace annealing at 450℃ for 1 hr. The a-IGZO:N TFT performance especially in mobility could further improve by increasing the microwave annealing time from 100s to 600s. Besides, we also discussed the nitrogen containment in a-IGZO with different flow rate of nitrogen gas mixed with argon gas during thin film deposition by DC sputtering system. With the nitrogen flow rate increased from 0 to 2sccm, the mobility of device is enhanced significantly from 2.06 to 4.97 cm²/Vs and the threshold voltage is lowered from 8.83 to 3.89 V. The effective carrier concentration in a conductive oxide semiconductor might be increased due to the doping of nitrogen with low electronegativity.

Fabrication of Zn-Cd-S films by Chemical bath deposited (CBD) has been studied for use as buffer layers in Cu(In,Ga)Se₂ (CIGS)-based solar celldevices.The Zn-Cd-S films were grown using zinc sulfate, thiourea , cadmium acetate and ammonia water in the temperature 70℃.The process gives good control of thickness and [Cd]/([Cd]+[Zn]) content of the films.

The prepared films were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and UV–vis spectroscopy.The band gap increased from 2.4 to 3.8eV with increasing [Cd]/([Cd]+[Zn]) from 0 to 1. The Zn-Cd-S buffer layer of efficiency enhance and it was shared better the lattice matched with CIGS.

Recently, nonvolatile memory (NVM) has been widely used in electronic devices. Nowadays, the prevailing NVM is Flash memory. However, it is generally believed that the conventional Flash memory will approach its scaling limit within about a decade. The resistive random access memory (RRAM) is emerging as one of the potential candidates for future memory replacement because of its high storage density, low power consumption as well as simple structure.

The purpose of this work is to develop a reliable a-InGaZnO based resistive switching memory. We investigate the resistive switching characteristics of TiN/Ti/IGZO/Pt structure and TiN/IGZO/Pt structure. The device with TiN/Ti/IGZO/Pt structure exhibits stable bipolar resistive switching. The impact of inserting a Ti interlayer is studied by material analyses. The device shows excellent resistive switching properties. For example, the DC sweep endurance can achieve over 1,000 times; and the pulse induced switching cycles can reach at least 10,000 times. In addition, we demonstrate the possibility of MLC IV operation for the device. By controlling the compliance current, multi-level operation can be achieved. Besides, the pulse induced switching is also performing on the MLC operation by adjusting the pulse amplitude. Furthermore, the impact of different sputtering ambient, the temperature instability, and the conduction mechanisms are also investigated. According to our experiment s, we propose a model to explain the resistive switching phenomenon observed in our devices.

Finally, because the whole fabricating process of the RRAM device is under room temperature, it holds the potential for flexible electronics applications. The TiN/Ti/IGZO/Pt RRAM device is fabricated on flexible stainless steel to test its flexibility and mechanical endurance.

Cu(InGa)Se₂ (CIGSe)-based chalcopyrite thin film has been employed as a desirable light absorber for thin film solar cell, recently yielding 20.3% cell efficiency (2010, ZSW). Typically, either the selenization of CuGaIn metal precursor selenization or elemental co-evaporation is used to fabricate CIGSe layers. Especially, selenization using the rapid thermal processing (RTP) of Se-coated CuGaIn precursors followed by sufurization by H₂S was successfully scaled up by Avancis company, reporting a conversion efficiency of 13.9% at 65ⅹ165 cm² module. It is assumed that the partial substitution of Se with S is intended to improve Ga depth uniformity within absorber and increase band gap energy at the surface of absorber layer.

In this contribution, the sulfurization process of CuGaIn/Se precursors by H₂S was investigated with a particular emphasis on the phase evolution and compositional depth profile. The CuGaIn metal precursors were prepared by either sequential or simultaneous sputtering of CuGa and element In target, followed by thermal evaporation of Se. The reactive selenization and sulfurization of precursors were carried out in a tube-type rapid thermal process system at the temperatures of 450-570 °C and 570-600 °C, respectively. In-situ phase evolution during sulfurization was observed by high-temperature X-ray diffraction scan. Compositional depth profile was measured by transmission electron microscope and secondary ion mass spectrometer. Morphology during sulfurization was analyzed by scanning electron microscopy of samples obtained by intentional quenching during reactive annealing. It was found that replacing Se of CIGSe structure by S would affect the formation of MoSe₂ and Ga incorporation. Also, the degree of S dosing would be affected by the degree of selenization at the first stage, which is controlled by selenization conditions such as the thickness of Se layer, reaction time and temperature.

Transparent conducting oxides (TCOs) are materials with rather high electronic conductivity and low optical absorption of the visible light which can be used in many applications in transparent electronics, e.g. light emitting diodes, photovoltaics, smart windows or flat panel displays.

The p-type TCOs mainly consist in spinel and delafossite materials with AB₂O₄ and ABO₂ stoichiometry, respectively. Very few papers deal with the deposition of delafossite structure coatings which however are of strong importance for the development of new transparent devices which are not feasible with n-type materials alone, e.g. transparent diodes, transistors or heterojunctions.

In this paper, we investigate the feasibility of magnesium doped p-type delafossite structure CuCr_1-xMg_xO₂ coatings by co sputtering of metallic targets in argon-oxygen reactive gas mixtures.

After a short description of the experimental device were the substrates are positioned on a rotating substrate holder, the coatings are performed in so called compound sputtering mode by fixing the discharge current of the Cr target and by modifying that of the Cu or Ag one. Hence, the chemical, structural, microstructural and morphological features of the coatings are investigated via scanning electronic energy dispersive X-ray spectroscopy, X-ray diffraction and scanning electron microscopy on thick films. Complementary structural data are assessed by Fourier transmission infrared spectroscopy and Raman spectrometry. The optical properties of the films are assessed by optical transmission spectrophotometry and their electrical conductivity is determined by using four point probe method.

Finally, the influence of annealing performed in air at different temperatures is investigated owing to the structural, optical and electrical properties of CuCr_1-xMg_xO₂ coatings.

In the study, we used the polyol method to synthesize silver nanowire, and the use of silver nitrate (AgNO₃) as the precursor for seeds. The experimental results show that the different synthesis temperature, Poly(N-vinylpyrrolidone) (PVP) molecular weight, the concentration of reactants and the addition rate of silver nitrate will affect the growth characteristics of silver nanowires. Field-emission scanning electron microscopy, UV-vis spectrophotometer and x-ray diffractometer have been employed to characterize the silver nanowires. When the synthesis temperature is higher than 180℃, the nucleation rate is too fast. Therefore, the particles are homogeneous nucleation and the formation of silver particles. When increasing the concentration of PVP, the diameter of the silver nanowires will be widened to cause a smaller aspect ratio. This study successfully prepared silver nanowires with a diameter of 120 nm and a length of 20 μm. Finally, the transmittance and sheet resistance were measured by UV-vis spectrophotometer and four-point probe I-V test, respectively. The solution-type silver nanowire thin film shows high transmittance, low sheet resistance and can be used for transparent conductive film application.

Anti bacterial surfaces are of increasing importance for various applications. Among the coatings able to ensure antibacterial activity, both crystallized titanium dioxide that allows photocatalytic destruction of bacteria under UV irradiation and noble metals such as Cu or Ag introduced into a ceramic matrix are known as suitable alternatives.

Association of titanium dioxide with a noble metal in a nanocomposite coating is an alternative susceptible to allow both effects. Among the technologies able to produce nanocomposite TiO₂-Cu(Ag) coatings, reactive co sputtering is known as a powerful technique.

In this paper, after a short description of the industrial vessel used for the deposition of TiO₂-Cu(Ag) nanocomposite coatings using plasma emission monitoring, we investigate the effect of emission setpoint of the titanium target and discharge current dissipated on the noble metal target on the structure of as-deposited TiO₂-noble metal coating.

Finally, anti bacterial tests are performed using two model bacteria, i.e. escherichia coli and staphylococcus aureus, to give tendancies owing to the nanocomposite structure on the anti bacterial activity.

This work was to study to test the application of three coatings, deposited in arrays conformation, for the manufacture of fastening elements in austenitic stainless steels 302 HQ. One of the problems that occur during the forming process is the adhesion of conformal material (stainless steel 302HQ), forming the arrays were coated with TiN, TiAlN and TiAlSiN. Forming Matrices were machined by a polishing process, to reduce the roughness. To analyze the behavior of the coatings were used the following tests: integrity analysis tools through superficial roughness; tests microstructures characterization by scanning electron microscope (SEM); assay adhesion of the coating, embossing tests; Metallographic analysis: the substrate tool Steel AISI D6, the lines of deformation of a screw formed by the first matrix tested in a tool sectioned regions of: substrate layer of the coating. It was determined that the matrices must have a roughness pattern to avoid wear and improve the process. In the forming process is crucial that no flaws, a variable that must be controlled is the alignment between the tool and blank.

This study investigates the self current compliance bipolar resistance switching behaviors of resistive random access memory with ITO/SiO_x:Gd/TiN and Pt/SiO_x:Gd/TiN devices. Generally, because the set process of filament-type resistance switching has to accompany a current compliance, the transistor is a common element to achieve the function of current compliance (1T-1R structure). However, the 1T-1R structure suffers from certain physical limitations from its continual scaling down limit. Hence, a self-formation current compliance structure should be developed. ITO/SiOx:Gd/TiN structure can exhibit a self current compliance property due to an interface formation between ITO/bulk, which can form a self-build series resistor to achieve the current compliance. Moreover, the electroforming process with a higher current compliance can compose a better self-formation current compliance property, one which can reduce the operation current and voltage. Additionally, the Pt/SiO_x:Gd/TiN device exhibits an interface-type bipolar resistive switching, one which has not only a size effect, but also a but also a lower operating current. The resistance transitions are due to the variation in conductance of the switching layer, which also shows a self current compliance phenomenon. Finally, compared with 1T-1R structure, the self-formation current compliance can reduce the cost of the fabrication process.

Bismuth Titanate Oxide (Bi_xTi_yO_z) compounds have been the subject of many studies due to their ferroelectric, piezoelectric and optical properties, which make them interesting material s for the fabrication of optical devices, ferroelectric memories and lead-free piezoelectric sensors and actuators. However, there have been few studies on the corrosion resistance of these materials . Therefore, the main aim of this work is to report on our preliminary data on the corrosion resistance of Bi_xTi_yO_z thin films and to correlate the observed results with their chemical surface compositionand crystallinity

The BixTiyOz thin films were deposited by RF magnetron sputtering onto stainless steel and titanium alloy (Ti6Al4V) substrates. The structural properties were studied by x-ray diffraction (XRD); the surface chemical composition was determined by x-ray photoelectron spectroscopy (XPS) and the corrosion resistance was evaluated by potentiodynamic polarization Tafel tests.

The XRD preliminary results i ndicate that the films are amorphous or poorly crystalline in nature . The XPS analysis show that the uppermost part of the deposited film s is mainly composed by bismuth oxide (Bi₂O₃) and titanium oxide (TiO₂) and the corrosion tests show that the current density is lower by two orders of magnitude than that shown by the uncovered substrates.