ICMCTF2018 Session CP: Symposium C Poster Session

We report novel photo-elastic method for measurement of the stress in polyimide (PI) based flat panel displays (FPD) and flexible displays (FD) structures. Method is based on measurement of the change of the state of polarization of the light undergoing reflection (or transmission) in the structures containing PI layer(s). Commonly used FPD and FD contain layers of 5 um or thicker PI layers. PI has stress optic coefficient of about 3.4E-10 Pa^-1 [1], which is almost 100 times larger than glass [2]. This allows easily measurement of stress with sensitivity of the order of 5 MPa and less. We present apparatus for local stress measurements having lateral resolution of 3 cm, and stress resolution of 5 MPa. Presented tool gives promise to become capable of measuring glass panels of the size 1.5 m x 1.85 m does not contained any moving parts. Our tool can be combined with more traditional stress induced deflection based stress measurement [3]. We discuss also methods of numerical analysis of optical data, including stress separation algorithm optimized for this problem, and practical problems related to analysis of the data.

[1] Noe, Susan Cunningham. A prism coupling study of optical anisotropy in polymide including moisture, stress, and thickness effects. Diss. Massachusetts Institute of Technology, 1992.

[2] Sun, Lan, and Samad Edlou. "Low birefringence lens design for polarization sensitive optical systems." Proc. SPIE. Vol. 6289. 2006.

[3] Walecki, Wojtek J Stress Metrology for Flat Panel Displays G6 and Bigger . Abstract submitted to Photonics West 2018 SPIE OPTO (PW18O) .

Chemical bath deposition (CBD) is an advantageous thin film deposition technique for depositing compound semiconductors at low temperature. In this paper, nickel oxide (NiO) thin films were prepared by CBD method under aqueous solution containing nickel sulfate, potassium persulfate, and ammonia water at room temperature. Prepared NiO thin film has porous structure with two dimensionally networked nanoflake arrays. In this process, concentration of ammonia water and nickel sulfate significantly affect on morphological features. Increase of ammonia concentration cause the growth kinetics until 30 ml of ammonia. Over 30 ml, however, it tended to not only decrease the thickness of films but also change the growth direction of flakes. In addition, lower concentration of nickel sulfate form a thicker NiO thin film but high concentration forms a lower thickness. This phenomenon is derived from Oswald ripening between crystal growth and aggregation at the CBD process. Each prepared NiO thin films were characterized by electrochemical measurement to apply on elctrochromic window. Optimized NiO thin film shows good elctrochromic performance with fast switching speed (11.0 s and 7.5 s), high optical modulation (T_bleaching: 80% and T_coloring: 17 %) and high cycling durability (over 5000 cycle).

Lead halide perovskite is an excellent candidate for use as a light harvester in solar cells. The perovskite structure (CH₃NH₃)PbX₃ (X = halogen) consists of organic components at cuboctahedral sites and inorganic components at octahedral sites, and perovskites exhibit the chemical properties of the organic component. Solid-state hybrid organic–inorganic solar cells often employ a layered structure of nanoparticulate titania, an organometal halide perovskite, and a spiro-MeOTAD hole transport material (HTM). One concern, however, is the potential toxicity of lead, an important component of conventional perovskite solar cells. Currently, the most likely substitute is a tin, and it is a Group 14 metal, similar to lead. In this paper, we develop a new type of perovskite photoresist for non - toxic perovskite solar cell applications. This is also a non-toxic material for solar cells compared to conventional materials used for perovskite solar cells. The perovskite precursor solution was prepared by dissolving CH₃NH₃I and SnI₂ in N-dimethylformamide (DMF). The application of the perovskite layer produced by the sequential deposition technique through the perovskite produced by using the tin is likely to replace the Pb-based perovskite, which is a safety and commercialization of the perovskite solar cell Improve technological progress.

The influence of disordered grain boundary on carrier transport is investigated for degenerated polycrystalline Al-doped ZnO (AZO) thin films prepared using two magnetron sputtering deposition (MSD) apparatuses . The AZO thin films with an Al content of 3 at.% and a thickness of 500 nm were prepared on glass substrates at a substrate temperature of room temperature (RT) in a pure Ar gas atmosphere at a pressure of 0.6 Pa using a dc and an r.f. (13.56 MHz) power supply applied either separately or in combination; dc-MSD and rf-MSD or rf+dc-MSD. When the electrical properties were evaluated by the van der Pauw method, the obtained mobility (μ^Hall) and carrier concentration (n^Hall) in polycrystalline AZO thin films prepared by MSD methods exhibited the location dependences (distributions) on the substrate surface, when moved from the location corresponding to the center on the target surface to one corresponding to the erosion area on the target. The location dependences of μ^Hall and n^Hall were also controlled by rf+dc-MSDs carried out with varying superimposed r.f. power. However, we found that the μ^Hall-n^Hall relationship resulting from those location dependences always exhibited a positive slope. In addition, we found that the main scattering mechanism, which limits the mobility of AZO thin films is attributed to grain boundary scattering caused by the reflection of electron s from the potential barrier at the grain boundary between crystallites. The obtained μ^Hall-n^Hall relationships with a positive slope in degenerated AZO thin films prepared by various MSDs always exhibited fair agreement with those calculated using Mayadas and Shatzkes (MS) theory. However, the significance and reliability of reflectivity used as a fitting parameter in the semi-classical MS theory seem questionable. Munoz’s group recently reported that the increase in the resistivity of a metallic specimen must be estimated under the effect of electron scattering from disordered grain boundaries based upon Kubo formalism. Disordered grain boundaries were represented by a one-dimensional periodic array of Dirac delta functions separated by a distance producing a Krönig-Penney (KP) potential. They used Green’s function built from the wave functions, which are solutions of the KP potential. In quantum theory, the positively sloped μ^Hall-n^Hall relationship in degenerated semiconductors such as AZO thin films is attributed to Anderson localization, induced by electron grain boundary scattering from disordered successive grains.

A novel amorphous indium-tungsten-oxide thin film transistor with a multi-stacked active layer is well discussed in this work. A multi-layer channel is proposed to effectively enhance the carrier mobility and device stability, simultaneously. A top capping oxygen-rich a-IWO thin film is used for suppressing the plasma damage to channel layer during backchannel passivation layer deposition process or the oxygen desorption from channel layer by the backchannel passivation material. In addition, a bottom buffer oxygen-rich a-IWO thin film is deposited to avoid the oxygen vacancy formation during the following thermal process. On the other hand, a 1-nm thick WO₃ layer is inserted between the high-k gate insulator and the multi-stacked active layer, which plays important roles as interfacial layer for improving the interface quality and reducing the surface roughness. Besides, a HfO₂ dielectrics film is chosen as gate insulator for realizing low-voltage operation. In this research, the sample with multi-stacked active layer exhibits a high On/Off current ratio of ∼ 1×10⁷ for low gate leakage current, attributing to the bottom oxygen-rich thin film. Then, a high field-effect mobility of ∼ 21 cm²/V.s is achieved by a low surface roughness. Due to the good interface quality, the subthreshold swing is about 0.1 V/decade. This multi-stacked active layer structure exhibits its potential application for the future high-resolution and large-size display manufacture.

Co-Fe-Ni alloys form a family of soft magnetic material with a large magnetic saturation (~20 kG) and very low coercive field (< 10 Oe) that can play an important role in developing micro electromechanical systems and other novel device structures. For example, integration of magnetic structures into vacuum electronic traveling wave amplifier circuits may dramatically reduce the bulk magnetic material needed in these devices, thereby producing favorable scaling opportunities in larger systems . Vacuum electronic devices have been made using ultraviolet photolithography and electroforming (UV-LIGA) to form bulk copper structures. Magnetic components to aid in directing the electron beam passing through the electromagnetic circuit are traditionally machined, brazed together and drilled out to accept the copper circuit structure. To explore the integration of magnetic materials into these circuits by additive manufacturing, we explore tuning the elemental and structural composition of the electroformed Co-Ni-Fe magnetic films. The resulting films were assessed using x-ray photoemission, x-ray diffraction, scanning electron microscopy, vibrating sample magnetometry, and ferromagnetic resonance techniques.

Samples were formed using a sulfate electrolyte bath consisting primarily of cobalt sulfate, nickel sulfate and iron sulfate with several additives to act as a buffer, improve adhesion, and reduce stress. The pH was varied from 2.8 to 3.2, and the galvanic methods were varied. The plating was carried out in a nitrogen glovebox to exclude oxygen in the atmosphere. The effects of hydrogen annealing are also studied, since vacuum electronic devices are often hydrogen brazed at temperatures up to 1050 deg C.

We present the study of nanostructured metal-oxide films prepared using a gas aggregation cluster source. The main advantage of the use of the cluster source is the possibility to prepare films with a high reactive area without the need for the use of wet techniques (often used for preparing nanostructured sensors). The films with the desired stoichiometry can be prepared directly without the need for subsequent thermal and/or chemical treatment.

Mixtures of tungsten oxide (WO₃) and cupric oxide (CuO) were deposited by cluster source and/or by conventional reactive dc sputter deposition. Sputtering conditions were tuned to vary the chemical composition and structure of the prepared films. The prepared films were characterized by means of X-ray diffraction, scanning electron microscopy, atomic force microscopy and Raman spectroscopy. The elemental composition was determined by energy and wave dispersive spectroscopy. The oxidation state of metals was studied by X-Ray Photoemission Spectrometry. Subsequently, the films were examined for their sensorial response when assembled into a hydrogen gas sensor. Noble-metal catalysts (Pd, Pt) deposited by dc magnetron sputtering were used to support the response and to lower the working temperature.

The layers were tested for response to a time-varied hydrogen concentration in synthetic air at various temperatures. The response sensitivity and the response time were evaluated. It is shown that optimization of the structure and composition results in enhanced sensorial properties.

Gallium oxide (Ga­₂O₃), which is a stable oxide of Ga, has been attracting the scientific and research community in view of its interesting physical, chemical and electrical properties. β-Ga­₂O₃ thin films find numerous applications in high temperature sensors, photovoltaics, optoelectronics, and anti-reflection coatings. The structural and electrical properties β-Ga₂O₃ thin films are quite important for their integration into optoelectronics, photovoltaics and sensors. Recently, we proposed an approach to obtain tunable structural and electronic properties of β-Ga₂O₃ thin films using refractory metal incorporation. In this work, we performed a comprehensive study of the electrical properties of molybdenum (Mo) doped β-Ga­₂O₃ (GMO) thin films. The results indicate that the resistivity, sheet resistance, conductivity, charge carrier concentration, and mobility are dependent on the microstructure, chemistry and Mo-content. Most importantly, the variable Mo content from 0 to 12 at% found to influence the electrical properties and allow us to obtain GMO films with a wide range of electrical properties. The results and implications for utilizing GMO films in electronic and optoelectronic devices will be discussed.

Ellipsometry is an optical technique for determining properties of laminar reflecting (or transmitting) structures from the measurement of light polarization state change resulting from the light-sample interaction. In all but the simplest of cases, the measurements must be followed by data processing in which the measured data is compared to an appropriate mathematical model of the sample derived from Maxwell’s equations and measurement conditions. Thus a key common problem is determining how many and which measurements to make. A single ellipsometer measurement consists of a single complex data point and therefore usually more than one measurement is required. Previously we have addressed these problems using Complex Analysis in the n-k plane for homogeneous isotropic films. One of the key findings was that certain angles and wavelengths are useful and others are not. The purpose of the work here is to extend that analysis to anisotropic films. These films have a greater number of unknowns and consequently require more measurements. The central question remains, how many measurements are needed and which specific measurements will provide sufficiently independent equations considering the unknowns. It can be that additional measurements vary to such a small degree that they are not useful considering measurement error tolerance. The work to be presented will show how to identify useful measurements based upon the anticipated sample configuration. The approach avoids making unnecessary measurements which can actually reduce rather than increase the solution accuracy.

Flexible strain sensors have many applications such as structural health monitoring, mechanical testing, and pulse power suppliers. Piezotronic strain sensors, which consist of a metal–semiconductor– metal interface, are well-suited for these applications due to their high sensitivity and fast response times. Zinc oxide (ZnO) nanowires (NWs) are a popular material for use in piezotronic strain sensors.[3] However, Zinc oxide has relatively high work function, so we can enhance its field electron emission with titanium nitride (TiN) coating, which has good electrical conductivity and relatively low work function.[1][4][5] Therefore, TiN thin film makes it potential in ideal field emitters. In our research, we want to develop the new material which has piezo-related properties and low work function simultaneously.

In this work, piezophotocatalytic and piezoelectric performance of Titanium Zinc Nitride Nanorod thin films deposited by RF magnetron sputtering were described. TiN and ZnN have centrosymmetric structure. However, thin film capacitors fabricated by sputtering Zn doped TiN nanorods from Zinc and Titanium targets in N2 ambient has non-centrosymmetric structure, because electric polarization and relative permittivity measurements yield distinct ferroelectric properties.

Based on various measurements including piezopotential, piezotronic, piezophototronic, and piezophotocatalytic analyses obtained by characterization tools, (i.e. X-ray diffraction, X-ray photoelectron spectroscopy, Raman scattering, Scanning electron microscope, Transmission electron microscopy, Secondary-ion mass spectrometry, UV-Vis, and I-V methods) we found that the base pressure of vacuum chamber, the chamber pressure and temperature, the sputtering power, and gas flow significantly influenced this material’s crystallinity, morphology (i.e. surface roughness), structure properties (i.e. crystallite size), electrical properties (i.e. refractive index), optical, and mechanical properties. In addition, we use combinatorial methodology to fabricate the material [6], which has significant piezoelectric properties in the specific concentration of Zinc, for use as a piezoelectric sensor.

Keywords: Titanium Zinc Nitride, Zinc doped, nanocolumn, morphology control, composition spread, combinatorial magnetron sputtering, piezotronic / piezophototronic effects, photocatalysis / piezophotocatalysis.

According to previous researches, two-step hydrothermal method was used to deposit ZnSnO₃ on the different kinds of substrate and control their alignment with different conditions such as substrate, temperature, surfactant, and others. ^[1,2] In this research, a novel way was proposed to fabricate ZnSnO₃/polymer nanocomposites by simple hydrothermal and polymer epitaxy method. This research emphasized on improving the alignment of ZnSnO₃ nanorods^[3,4] by polymer epitaxy^[5] such as PVDF and its synergistic piezo-related performance of the ZnSnO₃/PVDF nanocomposites.^[6] PVDF was used to control the alignment of the fabricated ZnSnO₃ nanorods and enhance its piezo-related performance including piezopotential, piezotronic, piezophototronic, and piezophotocatalytic analyses.

XRD and SEM were used to characterize the ZnSnO₃/PVDF nanocomposites. The results from the XRD confirmed the presence of ZnSnO_3. SEM analysis showed the morphologies and alignments of the ZnSnO₃ nanorods and PVDF. These nanocomposites exhibited average piezopotentials. Piezotronic analysis was also conducted on ZnSnO₃/PVDF nanocomposites, exhibiting high current density when the ZnSnO₃ are well-aligned. When under UV light illumination, the output current density obtained were several times higher for ZnSnO₃/PVDF. These confirmed the alignment control and synergistic piezophototronic property of the material.

In a piezophotocatalytic experiment, the decomposition of methylene blue (MB) was also investigated. The ZnSnO₃/PVDF nanocomposites exhibited better degradation property than pure ZnSnO_3. All the promising enhancement was attributed to the well-aligned ZnSnO_3, whichreduced the recombination of photogenerated electron−hole pairs and enhanced the mobility of these pairs resulting from the energy band distortion caused by applied stresses. Finally, we can use this nanocomposites or this epitaxially fabricating method to other materials on various electronic applications, such as multifunctional electronic-skin.^[7]

Keywords: ZnSnO₃/PVDF nanocomposites, epitaxy, ZnSnO₃ nanorods, piezophotocatalysis, electronic-skin

REFERENCES

[1] M.K. Lo, S.Y. Lee and K.S. Chang, J. Phys. Chem. C, 119 (2015) 5218-5224

[2] Y.T. Wang and K.S. Chang, J. Am. Ceram. Soc., 99 (2016) 2593-2600

[3] C. Fang, B. Geng, J. Liu, F. Zhan, Chem. Commun., (2009) 2350–2352

[4] Z. Zhang, J. Huang, B. Dong, Q. Yuan, Y. He, O.S. Wolfbeis, Nanoscale Res. Lett., 7 (2015) 4149-4155

[5] W.C. Cheng, C.Y. Yang, B.Y. Kang, M.Y. Kuo and J. Ruan, Soft Matter, 9 (2013) 10822-10831

[6] H.M. Lin, K.S. Chang, RSC Adv., 7 (2017) 30513-30520

[7] H. He, Y. Fu, W. Zang, Q. Wang, L. Xing, Y. Zhang, X. Xue, Nano Energy, 31 (2017) 37-48

Surface plasmons at metal-dielectric interfaces can efficiently confine and amplify electromagnetic (EM) energy in deep sub-wavelength volumes. Concomitant with the large EM field enhancement, Joule heating occurs which severely limits performance for applications such as miniaturized optical circuits. However, the same effect provides a great opportunity to remotely control temperature distributions in the micro- to nano- scale. These highly localized thermal fields have applications to research in catalysis, heat-assisted magnetic recording, phononic circuitry, and photothermal medical therapy among others. A fundamental step to advance the emerging applications of thermoplasmonics is the capability to provide fast, quantitative, contactless experimental determination of the resulting temperature distributions.^[i]

Spectroscopic ellipsometry (SE) is a phase sensitivity and self-referenced technique expected to have tremendous impact for contactless, marker-free, optical characterization at the nano-scale. ^[ii] However, numerical, fully-vectorial SE data analysis is required for non-layered samples with characteristic lateral dimensions (L) between l/10 and 10(l). To date, two systematic approaches seem favorable and will be reviewed; namely, the rigorous coupled-wave analysis (RCWA) method which was highly successful to study optical critical dimension (OCD) of 1D gratings by the semiconductor industry,^[iii] and, more recently, the Finite-Difference Time-Domain that is being systematically investigated by our group. ^[iv]

In tis presentation we will provide an assessment of the expected capabilities of SE to provide quantitative optical characterization in plasmonic metamaterials including changes in refractive index and thermal expansion effects based on the known instrumentation and computational limitations currently available.

Financial support from the RGC of the HKSAR, China (Project CityU- 122812) and CityU Strategic Research Grant for unfunded GRF/ECS (SRG-Fd, 7004961) is acknowledged.

[i] G Baffou, R Quidant: “Thermoplasmonics”, Laser Photonics Rev. 7 (2013) 171.

[ii] Ellipsometry at the Nanoscale, Maria Losurdo, Kurt Hingerl (Editors), Springer-Verlag Berlin Heidelberg 2013, 978-3-642-33956-1 (eBook), DOI 10.1007/978-3-642-33956-1.

[iii] Elson Liu and Fred L. Terry, Jr. “Immersion scatterometry for improved nano-scale topography measurements” Phys. Stat. Sol. (a) 205 (2008) 784.

[iv] Y. Foo, and J. A. Zapien “Convergence and precision characteristics of Finite Difference Time Domain Method for the Analysis of Spectroscopic Ellipsometry Data at Oblique Incidence” Appl. Surf. Sci. 421 (2017) 878.

The optical coatings with excellence performance would be achieved more easily when the materials chosen have relatively adjustable refractive index. In this study, Al₂O₃/ZnO/Al₂O₃ structures were fabricated using electron beam evaporation and 800^oC post-annealing treatments were carried out. According to the inter-diffusion, the ZnO layer became a high refractive index material with porous structure and the ZnAl₂O₄ spinel was formed as low refractive index material and the refractive index contrast of the multilayer was increased. In the Al₂O₃/ZnO/Al₂O₃ structure, the porous ZnO layer with an average porosity of 19.78% was successfully prepared and the refractive index was from 2 reduced to 1.357 by 800^oC post-annealing process due to solid state diffusion mechanism.

Currently, electronics and semiconductor studies have focused a great effort to overcome the intrinsic disadvantages of bulk-Si to develop optoelectronic devices. The non-stoichiometric Silicon dioxide (SiO_X) has been proposed as a cheap and effective alternative to develop ultraviolet absorbers or silicon-based light emitters. SiO_X can be deposited by several physical vapor deposition techniques but Sputtering technique particularly allows a great control on film thickness. SiO_x films can be obtained by simultaneous co-sputtering of Si and fused quartz (SiO₂) targets. The Si content in the SiO_X layers can be modified by a variation on RF-power applied to Si (Psi) target and keeping constant the RF-power applied to SiO₂ target.

In this work, we studied the effect of the increase of silicon content on the optical, structural and electrical properties of thin SiO_x films obtained by Sputtering. The Psi was changed between 10 and 50 W. All the films were annealed at 1100 ºC in N₂ for 3 hours. Ellipsometry and step measurements were applied to calculate thickness and the refractive index. Fourier transform infrared (FTIR) measurements were obtained from all the SiO_x films to confirm a change on stoichiometry. Absorbance spectra of SiO_x films showed rocking and bending vibration modes similar to stoichiometric silicon dioxide but an asymmetric stretching mode revealed the non-stoichiometric nature of our SiO_x films. X-ray photoelectron spectroscopy (XPS) measurements in depth profile revealed that Si content was increased from 3.5 to 10.7% in the SiO_x films. AFM images were obtained to calculate and relate the surface roughness according to Si content. SiO_X films showed a wide photoluminescence (PL) at room temperature (RT) between 575 nm to 875 nm. The PL intensity and peak position also showed a dependence on Silicon content and the possible presence of defects.

An Indium-Zinc Oxide (IZO) gate, optically semitransparent in the visible range, was deposited onto the SiO_X films surface. Also, Aluminum backside contact was added by Sputtering. Current–voltage (I–V) measurements of IZO/SiO_x/Si devices were obtained. A high conduction regime was measured even for low gate voltages. Electroluminescent (EL) emission was observed with the naked eye as discrete shining points on the surface of the devices. The intensity of the shining points showed a dependence on the Si content of SiO_X films. The EL emission was related to the recombination of charge moving through conductive paths within the SiO_X film.