Rodrigo Martins

Molybdenum (0.5at%) doped indium oxide thin films deposited by spray pyrolysis technique were irradiated by 100MeV O 7+ ions with different fluences of 5×10 11, 1×10 12 and 1×10 13ions/cm 2. Intensity of (222) peak of the pristine film was decreased with increase in the ion fluence. Films irradiated with the maximum ion fluence of 1×10 13ions/cm 2 showed a fraction of amorphous nature. The surface microstructures on the surface of the film showed that increase in ion fluence decreases the grain size. Mobility of the pristine molybdenum doped indium oxide films was decreased from  122 to 48cm 2/Vs with increasing ion fluence. Among the irradiated films the film irradiated with the ion fluence of 5×10 11ions/cm 2 showed relatively low resistivity of 6.7×10 -4Ωcm with the mobility of 75cm 2/Vs. The average transmittance of the as-deposited IMO film is decreased from 89% to 81% due to irradiation with the fluence of 5×10 11ions/cm 2. © 2012 Elsevier Ltd.

The microstructural aspects related to crystalline or amorphous structure of as-deposited and annealed films of sol-gel-derived WO 3 are shown in the literature to be critical for electrochromic (EC) performance. In consideration of ion insertion materials, there is a need for developing light and at the same time nanocrystalline structures to improve both coloration efficiency and switching kinetics. By controlling microstructure and morphology, one could design a material with optimal EC performance. This report compares the microstructural and morphological characteristics of standard WO 3 wet deposition techniques versus inkjet printing technology (IPT), correlating these features with their optical and electrochemical performances, emphasizing the importance of the dual-phase a-WO 3/TiO 2/WO X film composition proposed in this work for high-performance EC applications. The effect of the type and content of metal oxide nanoparticles in the precursor sols formulated in various peroxopolytungstic acid (PTA) and oxalic acid (OAD) proportions on film properties is comprehensively studied using multi-factorial design of experiment (DOE). To the authors' knowledge, no other report on sol-gel deposition of inorganic EC materials via the inkjet printing technique exists, in which furthermore the film crystallinity can be controlled under low-temperature process conditions. The proposed method enables development of EC films which irrespective of their composition (a-WO 3, a-WO 3/TiO 2 or a-WO 3/TiO 2/WO X) outperform their amorphous or nanocrystalline analogues presented as the state-of-the-art due to their superior chemical and physical properties. © 2012 The Royal Society of Chemistry.

Reduction in the accumulation capacitance value was more in Si metal-oxide-semiconductor devices than that of Ge metal-oxide-semiconductor devices after a thermal treatment irrespective of the annealing environment. Relatively, thermal treatment in oxygen environment improves the interface quality of HfO2/Ge stacks considerably, when compared with HfO 2/Si stacks. Whereas, the forming gas annealing at a temperature of 400 °C was not so effective in improving the interface quality at HfO 2/Si stack. The presence of induced negatively charged hydrogen atom in Ge lessens the Fermi level pinning at HfO2 and Ge interface. © 2011 Elsevier B.V. All rights reserved.

In this work we present sputtered multicomponent dielectrics based on mixtures of HfO 2 and SiO 2. This way it is possible to get stable amorphous structure up to 800°C, that does not happen for pure HfO 2, for instance, that present a polycrystalline structure when deposited without any intentional substrate heating. Besides, also the band gap of the resulting films is increased when compared with pure HfO2 that theoretically is an advantage in getting a suitable band offset with the semiconductor layer on oxide TFTs. Concerning the electrical characterization, the leakage current on c-Si MIS structures is low as 10 -9 Acm -2 at 10 V. The amorphous structure of the films also lead to better dielectric/semiconductor interfaces, as suggested by C-V characteristics on GIZO MIS structures, which do not present strong variation with frequency. On other hand, the dielectric constant decreases due to the incorporation of SiO 2 and Al 2O 3. Further improvement on insulating and interface characteristics is achieved using multilayer stacks and substrate bias during deposition. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

This paper presents the results of a preliminary study to examine the ability of post-silicon devices for analog processing. It is focused on the latest thin-film transistors (TFTs) with amorphous gallium-indium-zinc oxide (a-GIZO) as active layer. Three circuit configurations are presented: a differential pair and two multiplier topologies. Both triode and saturation regions of operation are included in the analysis, with the devices set to remain in strong accumulation. A neural model, which is developed based on the measured data of the TFTs, is used for the circuit simulations in the Cadence Virtuoso environment. The analog multipliers simulation results are compared against the expected functional results. © 2012 IEEE.

This chapter gives an overview about GIZO TFTs, comprising an introductory section about generic TFT structure and operation, different semiconductor technologies for TFTs - with special emphasis on AOSs and particularly on GIZO - and then some experimental results obtained for GIZO TFTs fabricated in CENIMAT. Thin-film transistors (TFTs) are important electronic devices which are predominantly used as On/Off switches in active matrix backplanes of flat panel displays (FPDs), namely liquid crystal displays (LCDs) and organic light emitting device (OLED) displays. Even if a-Si:H is still dominating the TFT market in terms of semiconductor technology, oxide semiconductors are emerging as one of the most promising alternatives for the next generation of TFTs, bringing the possibility of having fully transparent devices, low processing temperature, low cost, high performance and electrically stable properties [1, 2]. Amorphous oxide semiconductors (AOS) such as Gallium-Indium-Zinc oxide (GIZO) [3, 4], even if fabricated at temperatures below 150°, are currently capable of providing transistors with field-effect mobility (μFE) exceeding 20 cm2V-1 s-1, threshold voltage (VT) close to 0V, On/Off ratios above 108, subthreshold swing (S) around 0:20V dec-1 and fully recoverable VT shift (ΔVT) lower than 0.5V after 24 h stress with constant drain current of 10 μA. © Springer-Verlag Berlin Heidelberg 2012.

Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper. Transparent electronics is one of the most advanced science topics for a broad range of device applications. In this article an overview is presented of state-of-the-art n- and p-type oxides for TFTs and their integration, processed by physical vapor deposition and by solution processing techniques. Some of the most relevant emerging applications are also presented, including CMOS devices based on oxide TFTs fabricated on glass and even on paper. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thin-films of copper oxide Cu x were sputtered from a metallic copper (Cu) target and studied as a function of oxygen partial pressure. A metallic Cu film with cubic structure obtained from 0% O PP has been transformed to cubic Cu x phase for the increase in O PP to 9% but then changed to monoclinic CuO phase (for. The variation in crystallite size (calculated from x-ray diffraction data) was further substantiated by the variation in grain size (surface microstructures). The Cu x films produced with O PP ranging between 9% and 75% showed p-type behavior, which were successfully applied to produce thin-film transistors. © 2006 IEEE.

P-type thin-film transistors (TFTs) using room temperature sputtered tin and copper oxide as a transparent oxide semiconductor have been produced on rigid and paper substrates. The SnO x films shows p-type conduction presenting a polycrystalline structure composed with a mixture of tetragonal β-Sn and α-SnO x phases, after annealing at 200°C. These films exhibit a hole carrier concentration in the range of ≈ 10 16-10 18 cm -3, electrical resistivity between 101-102 Ωcm, Hall mobility of 4.8 cm 2/Vs, optical band gap of 2.8 eV and average transmittance ≈ 85 % (400 to 2000 nm). Concerning copper oxide Cu xO thin films they exhibit a polycrystalline structure with a strongest orientation along (111) plane. The Cu xO films produced between an oxygen partial pressure of 9 to 75% showed p-type behavior, as it was measured by Hall effect and Seebeck measurements. The bottom gate p-type SnO x TFTs present field-effect mobility above 1.24 cm 2/Vs (including the paper p-type oxide TFT) and an on/off modulation ratio of 10 3 while the Cu xO TFTs exhibit a field-effect mobility of 1.3×10 -3 cm 2/Vs and an on/off ratio of 2×10 2. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

In this work, the nonisothermal sintering behavior of as-received commercial high purity ZnO micrometric (m-ZnO), submicrometric (sm-ZnO) and nanometric (n-ZnO) powders was studied. The sintering behavior for sputtering target production was evaluated by changing the green density of samples from 62% of theoretical density (TD) to 35%. We observed that for n-ZnO powder, the maximum shrinkage rate (MSR) temperature (T MSR) was not affected by the green density, and that it was reached at lower temperatures (∼710°C) compared with m-ZnO and sm-ZnO powders. For these powders, the temperature of MSR increased from 803°C to 934°C and from 719°C to 803°C as TD changed from 62% to 35% TD, respectively. Small grain size (∼0.560 μm) and high density targets were obtained for n-ZnO when sintered at temperatures below the T MSR. Heating rate from 1°C to 15°C/min led to lower activation energy for n-ZnO (∼201 ± 3 kJ/mol) than for the submicrometric (sm-ZnO) (∼332 ± 20 kJ/mol) and micrometric (m-ZnO) (∼273 ± 9 kJ/mol) powders. Using the model proposed by Bannister and Woolfrey, an n value of 0.75 was found, which was correlated with a combination of viscous flow and volume diffusion mechanisms that should control the initial stage of n-ZnO sintering. No significant differences were observed for n-ZnO powder in terms of density when the size of targets (scale-up effect) was increased, while in the case of m-ZnO and sm-ZnO, a delay in the densification was observed, which was related to the higher sinterability of n-ZnO powder. Two inches ZnO ceramic targets with different particle sizes and final densities were used in an rf magnetron sputtering system to produce ZnO films under the same deposition conditions. Films with thickness around 100 nm and good uniformity were produced using those targets, and no variation was observed in the optical and morphological properties. However, low electrical resistivity (1.4 Omega;·cm) films were obtained with n-ZnO targets, which could be explained in terms of a nonstoichiometric Zn:O composition of the started powders. © 2011 The American Ceramic Society.

This paper reports the application of a polymethacrylate hydroxyethylene resin based electrolyte in electrochromic (EC) devices. The electrolyte is characterized by electrochemical impedance spectroscopy, visible spectroscopy, TGA, DSC, and DRX and tested as an ionic conductor in an EC device with the following configuration: Substrate/IZO/WO 3/Polymer Electrolyte/(CeO 2)TiO 2/IZO/Substrate. The electrolyte presents an ionic conductivity of 10 -7S/cm at room temperature and TGA analysis show that electrolyte is thermally degraded at 200°C. The EC device based on this polymethacrylate hydroxyethylene resin electrolyte system shows memory effect and exhibits an excellent optical density. © 2011 John Wiley & Sons, Ltd.

Transparent electronics is emerging as one of the most promising technologies for the next generation of electronic products, away from the traditional silicon technology. It is essential for touch display panels, solar cells, LEDs and antistatic coatings. The book describes the concept of transparent electronics, passive and active oxide semiconductors, multicomponent dielectrics and their importance for a new era of novel electronic materials and products. This is followed by a short history of transistors, and how oxides have revolutionized this field. It concludes with a glance at low-cost, disposable and lightweight devices for the next generation of ergonomic and functional discrete devices. Chapters cover: Properties and applications of n-type oxide semiconductors P-type conductors and semiconductors, including copper oxide and tin monoxide Low-temperature processed dielectrics n and p-type thin film transistors (TFTs) - structure, physics and brief history Paper electronics - Paper transistors, paper memories and paper batteries Applications of oxide TFTs - transparent circuits, active matrices for displays and biosensors Written by a team of renowned world experts, Transparent Oxide Electronics: From Materials to Devices gives an overview of the world of transparent electronics, and showcases groundbreaking work on paper transistors. © 2012 John Wiley & Sons, Ltd.

We have projected and fabricated a microfluidic platform for DNA sensing that makes use of an optical colorimetric detection method based on gold nanoparticles. The platform was fabricated using replica moulding technology in PDMS patterned by high-aspect-ratio SU-8 moulds. Biochips of various geometries were tested and evaluated in order to find out the most efficient architecture, and the rational for design, microfabrication and detection performance is presented. The best biochip configuration has been successfully applied to the DNA detection of Mycobacterium tuberculosis using only 3. l on DNA solution (i.e. 90. ng of target DNA), therefore a 20-fold reduction of reagents volume is obtained when compared with the actual state of the art. © 2013 Elsevier B.V.

We demonstrate fully transparent, highly rectifying contacts (TRC) on amorphous GaInZnO and compare them to TRC fabricated on single crystalline bulk ZnO and heteroepitaxial ZnO thin films. The contacts' transparency in the visible spectral range exceeds 70%. From numerical simulations, we conclude that thermionic emission is the dominating transport mechanism, however, for several samples with low net doping density diffusion theory must be applied. The detailed investigation of the rectification properties of the TRC using temperature-dependent current-voltage and capacitance-voltage measurements reveals that barrier inhomogeneities govern the IV-characteristics of all diodes irrespective of the sample crystallinity. Assuming a Gaussian barrier height distribution, the extracted mean barrier heights typically range between 1.1 and 1.3 V. The width of the barrier distribution correlates with the mean barrier height and ranges from 110 to 130 mV. By compiling literature data, we found that this correlation holds also true for Schottky diodes on elemental and III-V semiconductors. © 2013 American Institute of Physics.

Curcuma longa L., also known as turmeric, is widely used as a food colorant and has been reported to have antioxidant, anti-inflammatory, anti-mutagenic and anti-cancer properties. The aim of this study was to evaluate the effects of the spray drying on curcuminoid and curcumin contents, antioxidant activity, process yield, the morphology and solubility of the microparticulated solid dispersion containing curcuma extract using a Box Behnken design. The microparticles were spherical in shape, and an increase in outlet temperature from 40 to 80 °C resulted in a significant increase in the yield of microparticles from 16 to 53%. The total curcuminoid content (17.15 to 19.57. mg/g), curcumin content (3.24 to 4.25. mg/g) and antioxidant activity (530.1 to 860.3 μg/mL) were also affected by the spray drying process. The solubility of curcuminoid from C. longa remarkably improved 100-fold in the microparticles, confirming the potential of the ternary solid dispersion technique to improve the dyeing and nutraceutical properties of these compounds. Furthermore, the microparticles were obtained using the spray drying process, can be easily scaled up. © 2011 Elsevier Ltd.

The present work focuses on a qualitative analysis of localised I-V characteristics based on the nanostructure morphology of highly dense arrays of p-type NiO nano-pillars (NiO-NPs). Vertically aligned NiO-NPs have been grown on different substrates by using a glancing angle deposition (GLAD) technique. The preferred orientation of as grown NiO-NPs was controlled by the deposition pressure. The NiO-NPs displayed a polar surface with a microscopic dipole moment along the (111) plane (Tasker's type III). Consequently, the crystal plane dependent surface electron accumulation layer and the lattice disorder at the grain boundary interface showed a non-uniform current distribution throughout the sample surface, demonstrated by a conducting AFM technique (c-AFM). The variation in I-V for different points in a single current distribution grain (CD-grain) has been attributed to the variation of Schottky barrier height (SBH) at the metal-semiconductor (M-S) interface. Furthermore, we observed that the strain produced during the NiO-NPs growth can modulate the SBH. Inbound strain acts as an external field to influence the local electric field at the M-S interface causing a variation in SBH with the NPs orientation. This paper shows that vertical arrays of NiO-NPs are potential candidates for nanoscale devices because they have a great impact on the local current transport mechanism due to its nanostructure morphology. © 2013 The Royal Society of Chemistry.

The aim of this study was to investigate the influence of ultrasound and high-shear mixing on the properties of microparticles obtained by spray congealing. Dispersions containing 10% carbamazepine and 90% carrier Gelucire® 50/13 (w/w) were prepared using magnetic stirring, high-shear mixing, or ultrasound. Each preparation was made using hot-melt mixing spray congealing to obtain the microparticles. All microparticles presented a spherical shape with high encapsulation efficiency (>99%). High-shear mixing and ultrasound promoted a decrease in the size of microparticles (D90) to 62.8 ± 4.1 μm and 64.9 ± 3.3 μm, respectively, while magnetic stirring produced microparticles with a size of 84.1 ± 1.4 μm. The use of ultrasound led to microparticles with increased moisture content as identified through sorption isotherm studies. In addition, rheograms showed distinct rheological behaviour among different dispersion preparations. Therefore, the technique used to prepare dispersions for spray congealing can affect specific characteristics of the microparticles and should be controlled during the preparation. © 2013 Informa UK Ltd. All rights reserved.

Nitrogen and Phosphorus co-doped (N+P)- zinc oxide (ZnO) films were RF sputtered on corning glass substrates at 350 °C and comparatively studied with undoped, N-, and P- doped ZnO. X-ray diffraction spectra confirmed that the ZnO structure with a preferred orientation along <002> direction. Scanning electron microscope analysis showed different microstructure for the N+P co-doping, and thus probably confirming the co-existence of both the dopants. X-ray photoelectron spectroscopy spectra revealed that the chemical composition in N+P co-doped ZnO are different from that found in undoped, N-, and P- doped ZnO. The atomic ratio of N and P in N+P co-doped ZnO is higher than that in single N or P doped ZnO. One broad ZnO emission peak around 420 nm is observed in photoluminescence spectra. The relative intensity of the strongest peak obtained from co-doped ZnO films is about twice than the P- doped and thrice than the pure and N- doped films. © (2013) Trans Tech Publications, Switzerland.

The effect of substrate temperature (Ts) on the properties of pyrolytically deposited nitrogen (N) doped zinc oxide (ZnO) thin films was investigated. The Ts was varied from 300 °C to 500 °C, with a step of 50 °C. The positive sign of Hall coefficient confirmed the p-type conductivity in the films deposited at 450 °C and 500 °C. X-ray diffraction studies confirmed the ZnO structure with a dominant peak from (1 0 0) crystal plane, irrespective of the variation in Ts. The presence of N in the ZnO structure was evidenced through X-ray photoelectron spectroscopy (XPS) analysis. The obtained high N concentration reveals that the 450 °C is the optimal Ts. Atomic force microscope (AFM) analysis showed that the surface roughness was increased with the increasing Ts until 400 °C but then decreased. It is found that the transmittance of the deposited films is increased with the increasing Ts. The optical band gap calculated from the absorption edge showed that the films deposited with T s of 300 °C and 350 °C possess higher values than those deposited at higher Ts. © 2012 Elsevier B.V.

We present the results obtained with an extended-gate ISFET totally based on amorphous oxides (GIZO as the semiconductor, +{\hbox{Ta}}-{2}{\hbox{O}}-{5}{\ hbox{:SiO}}-inf2-inf as the dielectric and +{\hbox{Ta}}-{2}{\hbox{O}}-inf5-inf as the sensitive layer). A full characterization of the device was performed with constant ionic strength pH buffer solutions, revealing a sensitivity of 40 mV/pH with small hysteresis, and good linearity in the pH 4-pH 10 range buffer solutions. These results clearly show that it is possible to produce room-temperature disposable and low cost bio-sensors. © 2005-2012 IEEE.

The present work is focused on gelatin-based electrolytes doped with a range of concentration of zinc triflate (Zn(CF3SO3)2). The transparent-thin-film samples have been represented by the notation GelatinnZn(CF3SO3)2, where n represents the zinc triflate salt concentration in the electrolyte membranes from 0.00 wt% to 10.93 wt% The samples have been characterized by conductivity measurements, thermal analysis, cyclic voltammetry, X-ray diffraction (XRD), polarized optical microscopy (POM) and scanning electron microscopy (SEM). The gelatin-based electrolytes were also tested as ionic conductors in electrochromic devices with the glass/ITO/WO3/gelatin-based electrolyte/CeO2-TiO2/ITO/glass configuration. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A high-gain amplifier topology, with all single n-type enhancement transistors, is proposed in this paper. This type of circuits are essential in transparent TFT technologies, such as GIZO and ZnO that lack complementary type transistor. All circuits were simulated using BSIM3V3 model of a 0.35 μm CMOS technology, due to the absence of a complete electrical model for the TFTs. Results reveal that the proposed circuit promise more gain, lower power consumption and higher bandwidth than the existing solutions under identical bias conditions. © 2013 IEEE.

Transparent TFT technologies, with amorphous semiconductor oxides are lacking a complementary type transistor. This represents a real challenge, when the design of high-gain amplifiers are considered, without resorting to passive resistive elements. However, some solutions do exist to overcome the lack of a p-type transistor. This paper then presents a comparison analysis of two high-gain single-stage amplifier topologies using only n-type enhancement transistors. In these circuits, high gain is achieved using positive feedback for the load impedance. The comparison is carried out in terms of bandwidth, power consumption and complexity under identical bias conditions. Further, the same load impedance is used to develop a novel high-gain multiplier. All the circuits are simulated using a 0.35 μm CMOS technology, as it is easy to test the reliability of the methods, since CMOS transistors have trustworthy models. © 2013 IEEE.

Metallic nanoparticles (NPs) have received recently considerable interest of photonic and photovoltaic communities. In this work, we report the optoelectronic properties of gold NPs (Au-NPs) obtained by depositing very thin gold layers on glass substrates through thermal evaporation electron-beam assisted process. The effect of mass thickness of the layer was evaluated. The polycrystalline Au-NPs, with grain sizes of 14 and 19 nm tend to be elongated in one direction as the mass thickness increase. A 2 nm layer deposited at 250 C led to the formation of Au-NPs with 10-20 nm average size, obtained by SEM images, while for a 5 nm layer the wide size elongates from 25 to 150 nm with a mean at 75 nm. In the near infrared region was observed an absorption enhancement of amorphous silicon films deposited onto the Au-NPs layers with a corresponding increase in the PL peak for the same wavelength region.