Rodrigo Martins

In this paper we report by the first time tunneling tranport on vertical μcSi/aSixCyOz:H/μcSi (μcaμc) heterostructures produced in a Two consecutive Decomposition and Deposition Chamber system where a Negative Differential Conductance is observed even at room temperature. Giant bias anomalies are observed, that decrease with temperature. Tunneling spectroscopy data are also reported for samples measured at low temperatures. A qualitative information of the recorded data is obtained and related with main features of the heterostructure. Nevertheless in this stage is hard to take quantitative information. © 1989.

We report, for the first time, results on transparent ZnO:Al thin films deposited on polyester (Mylar type D, 100 μm thickness) substrates at room temperature by magnetron sputtering. The structural, optical and electrical properties of the deposited films have been studied. The samples are polycrystalline with a hexagonal wurtzite structure and a strong crystallographic c-axis orientation (0 0 2) perpendicular to the substrate surface. The ZnO:Al thin films with 83% transmittance in the visible region and a resistivity as low as 3.6 × 10-2 Ωcm have been obtained, as deposited. The obtained results are comparable to those obtained on glass substrates, opening a new field of low cost, light weight, small volume, flexible and unbreakable large area optoelectronic devices. © 2002 Elsevier Science Ltd. All rights reserved.

Pd-metal/insulator/semiconductor based on hydrogenated amorphous silicon were produced by plasma enhanced chemical vapour deposition with two different oxidised surfaces: thermal in ambient air and chemical with hydrogen peroxide. The diode characteristics have been investigated using dark and light current as f(v) measurements in the temperature range from 300 K to 380 K, from which it was possible to infer the electron barrier height. The data obtained show that the incorporation of a thin insulator layer between the semiconductor and the metal improves the performances of the devices by preventing the formation of suicides at the interface. Apart from that we also show that the MIS structures with the thermal oxide presents 'better' performances than the ones with the chemical oxide due to the type of interface states and of the oxide charges associated with the interface between the insulator and the semiconductor. © 1998 Elsevier Science B.V. All rights reserved.

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. The key components are wide band gap semiconductors, where oxides of different origin play an important role, not only as passive component but also as active component, similar to what we observe in conventional semiconductors like silicon. In this paper we present the recent progress in n- and p-type oxide based thin film transistors (TFT) produced by rf magnetron sputtering and we will summarize the major milestones already achieved with this emerging and very promising technology. © 2015 IEEE.

Thin film transistors (TFTs) have been produced by rf magnetron sputtering at room temperature, using non conventional oxide materials like amorphous indium-zinc-oxide (IZO) semiconductor, for the channel as well as for the drain and source regions. The obtained TFTs operate in the enhancement mode with threshold voltages of 2.4 V, saturation mobility of 22.7 cm2/Vs, gate voltage swing of 0.44 V/dec and an ON/OFF current ratio of 7×10 7. The high performances presented by these TFTs associated to a high electron mobility, at least two orders of magnitude higher than that of conventional amorphous silicon TFTs and a low threshold voltage, opens new doors for applications in flexible, wearable, disposable portable electronics as well as battery-powered applications.

Tensile tests were performed on PET films coated with Al doped zinc oxide films by RF magnetron sputtering. During the tensile elongation, the electrical resistance of the oxide was evaluated in situ. The results indicate that the increase in the electrical resistance is related to the crack debsity and crack width, which also depends on the film thickness.

Gallium-doped zinc oxide (GZO) thin films have been deposited onto polyethylene naphthalate (PEN) substrates by r.f. magnetron sputtering at room temperature. The influence of the film thickness (from 70 to 890 nm) on the electrical, structural and morphological properties are presented. The lowest resistivity obtained was 5 × 10-4 Ω cm with a Hall mobility of 13.7 cm2/Vs and a carrier concentration of 8.6 × 1020 cm-3. These values were obtained by passivating the surface of the polymer with a thin silicon dioxide, so preventing the moisture and oxygen permeation inside the film. © 2003 Elsevier B.V. All rights reserved.

The application of hydrogenated amorphous silicon (a-Si:H) to optoelectronic devices are now well established as a viable low cost technology and is presently receiving much interest. Taking advantage of the properties of a-Si:H based devices, single and dual axis large area (up to 80×80 mm 2) thin film position sensitive detectors (TFPSD) based on a-Si:H p-i-n diodes have been developed, produced by plasma enhanced chemical vapor deposition. In this study, the main optoelectronic properties presented by the TFPSD as well as their behavior under operation conditions, concerning its linearity and signal to noise ratio, are reported. © 1994 American Institute of Physics.

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.

We have developed a rectangular dual-axis large area Position Sensitive Detector (PSD), with 5 cm×5 cm detection area, based on PIN hydrogenated amorphous silicon (a-Si:H) technology, produced by Plasma Enhanced Chemical Vapor Deposition (PECVD). The metal contacts are located in the four edges of the detected area, two of them located on the back side of the ITO/PIN/Al structure and the others two located in the front side. The key factors of the detectors resolution and linearity are the thickness uniformity of the different layers, the geometry and the contacts location. Besides that, edge effects on the sensor's corner disturb the linearity of the detector. In this paper we present results concerning the linearity of the detector as well as its optoelectronic characteristics and the role of the i-layer thickness on the final sensor performances.

Large-area thin-film position-sensitive detectors (TFPSDs) using the hydrogenated amorphous silicon (a-Si:H) technology are presented. The detection accuracy of these devices (lengths of about 80 mm) is better than ±0.5% of the value of the full scale of the sensor, the spatial resolution is better than ±20 μm, the non-linearities measured are below ±2% and the frequency response is in the range of a few kilohertz, compatible with the sampling frequency of most electromechanical assembling/control systems. The obtained results are quite promising regarding the application of these sensors to a wide variety of optical inspection systems.

Copper oxide (Cu2 O) thin films were used to produce bottom gate p-type transparent thin-film transistors (TFTs). Cu2 O was deposited by reactive rf magnetron sputtering at room temperature and the films exhibit a polycrystalline structure with a strongest orientation along (111) plane. The TFTs exhibit improved electrical performance such as a field-effect mobility of 3.9 cm2 /V s and an on/off ratio of 2× 102. © 2010 American Institute of Physics.

Aluminium doped zinc oxide thin films (ZnO:Al) have been deposited on polyester (Mylar type D, 100 μm thickness) substrates at room temperature by r.f. magnetron sputtering. The structural, morphological, optical and electrical properties of the deposited films have been studied. The samples are polycrystalline with a hexagonal wurtzite structure and a strong crystallographic c-axis orientation (002) perpendicular to the substrate surface. The ZnO:Al thin films with 85% transmittance in the visible and infra-red region and a resistivity as low as 3.6×10-2 Ωcm have been obtained, as deposited. The obtained results are comparable to those ones obtained on glass substrates, opening a new field of low cost, light weight, small volume, flexible and unbreakable large area optoelectronic devices.

Staggered bottom gate transparent thin film transistors (TTFTs) have been produced by rf magnetron sputtering at room temperature, using amorphous indium zinc oxide (IZO) semiconductor, for the channel as well as for the drain and source regions. The obtained TTFTs operate in the enhancement mode with threshold voltages of 2.4 V, saturation mobility of 22.7 cm2/V s, gate voltage swing of 0.44 V/dec and an ON/OFF current ratio of 7 × 107. The high performances presented by these TTFTs produced at room temperature, make these TFTs a promising candidate for flexible, wearable, disposable portable electronics as well as battery-powered applications. © 2007 Elsevier Ltd. All rights reserved.

Large area thin film position sensitive detectors based on amorphous silicon technology have been prepared on polyimide substrates using the conventional plasma-enhanced chemical vapour deposition. The sensors have been characterized by spectral response, light intensity dependence and linearity measurements in a bent state in order to evaluate the properties in real working conditions. The obtained one-dimensional (1D) position sensors with 10 mm width and 20 mm length present a non-linearity of ±1% which are comparable to the ones produced on glass substrates.

The present paper describes the properties of a photochemical sensor based on amorphous silicon MIS (Metal-Insulator-Semiconductor) diodes. The structure of the sensors used in this work are based on glass/Cr/a-SiH(n +)/a-Si:H(i)SiOx/Pd, where the amorphous silicon layers have been deposited by conventional plasma r.f. techniques. The proposed photochemical sensors present a 2-3 orders of magnitude change in the saturation current and a decrease of up to 40% on the open circuit voltage when in the presence of 400 ppm of hydrogen. The overall performance of these sensors, associated with the low cost fabrication technology, suggests that, in the near future, it will be possible to use them in several industrial applications. © 1998 Elsevier Science Ltd. All rights reserved.

In this paper we present results of indium zinc oxide deposited at room temperature by rf magnetron sputtering, with an electron mobility as high as 60 cm2/Vs. The films present a resistivity as low as 5 × 10 - 4 Ω cm with an optical transmittance of 85%. The structure of these films seems to be polymorphous (mix of different amorphous and nanocrystalline phases from different origins) as detected from XRD patterns with a smooth surface and from SEM micrographs, is highly important to ensure a long lifetime when used in display devices. © 2005 Elsevier B.V. All rights reserved.

P-type thin-film transistors (TFTs) using room temperature sputtered SnOx (x<2) as a transparent oxide semiconductor have been produced. The SnOx films show p-type conduction presenting a polycrystalline structure composed with a mixture of tetragonal Β-Sn and α -SnOx phases, after annealing at 200 °C. These films exhibit a hole carrier concentration in the range of ≈ 1016 - 1018 cm-3; electrical resistivity between 101 - 102 cm; Hall mobility around 4.8 cm2 /V s; optical band gap of 2.8 eV; and average transmittance ≈85% (400 to 2000 nm). The bottom gate p-type SnOx TFTs present a field-effect mobility above 1 cm2 /V s and an ON/OFF modulation ratio of 103. © 2010 American Institute of Physics.

This work describes the fabrication and characterization of an improved version of large area (5mm×80mm with an active length of 70mm) flexible position sensitive detectors deposited onto polymeric substrates (polyimide-Kapton® VN). The new configuration presented by the sensor is based on a heterostructure of a-Si:H/ZnO:Al. The sensors were characterized by spectral response, photocurrent dependence as a function of light intensity and position detection measurements. The set of data obtained on one-dimensional position sensitive detectors based on the heterostructure show excellent performances with a maximum spectral response of 0.12A/W at 500nm and a non-linearity of ±10% over 70mm length. The produced sensors present a non-linearity higher than those ones produced on glass substrates, due to the different thermal coefficients exhibited by the polymer and the amorphous silicon film. In order to prove this behaviour, it was measured the defect density obtained by the constant photocurrent method on amorphous silicon deposited on polymeric substrates bended with different radius of curvature. © 2004 Elsevier B.V. All rights reserved.

Highly textured transparent conducting ZnO:Al thin films have been prepared by r.f. magnetron sputtering. The films were deposited on polyester (Mylar type D, 100 μm thickness) and glass substrates at room temperature. Surface stylus profiling, X-ray diffraction, scanning electron microscopy, transmission electron microscope and Hall effect measurements as a function of temperature, using the van der Pauw technique have characterized the films. The samples are polycrystalline with a hexagonal wurtzite structure and a strong crystallographic c-axis orientation (002) perpendicular to the substrate surface (columnar structure). The ZnO:Al thin films with a resistivity as low as 3.6×10-2 Ωcm have been obtained, as deposited. © 2001 Materials Research Society.

A Linear array Thin Film Position Sensitive Detector (LTFPSD) based on hydrogenated amorphous silicon (a-Si:H) is proposed for the first time, taking advantage of the optical properties presented by a-Si:H devices we have developed a LTFPSD with 128 integrated elements able to be used in 3D inspections/measurements. Each element consists on a 1D LTFPSD, based on a p.i.n. diode produced in a conventional PECVD system, where the doped layers are coated with thin resistive layers to establish the required device equipotentials. By proper incorporation of the LTFPSD into an optical inspection camera it will be possible to acquire information about an object/surface, through the optical cross- section method. The main advantages of this system, when compared with the conventional CCDs, are the low complexity of hardware and software used and that the information can be continuously processed (analogue detection).

The aim of this work is to present the main optoelectronic characteristics of large area 1D position sensitive detectors based on amorphous silicon p-i-n diodes. From that, the device resolution, response time and detectivity are derived and discussed concerning the field of applications of the 1D thin film position sensitive detectors.

Transparent electronics is today one of the most advanced topics for a wide range of device applications, where the key components are wide band gap semiconductors, where oxides of different origin play an important role, not only as passive components but also as active components similar to what we observe in conventional semiconductors. As passive components they include the use of these materials as dielectrics for a wide range of electronic devices and also as transparent electrical conductors for use in several optoelectronic applications, such as liquid crystal displays, organic light emitting diodes, solar cells, optical sensors etc. As active materials, they exploit the use of truly electronic semiconductors where the main emphasis is being put on transparent thin film transistors, light emitting diodes, lasers, ultraviolet sensors and integrated circuits among others. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report high performance ZnO thin film transistor (ZnO-TFT) fabricated by rf magnetron sputtering at room temperature with a bottom gate configuration. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 19 V, a field effect mobility of 28 cm2/Vs, a gate voltage swing of 1.39 V/decade and an on/off ratio of 3×105. The ZnO-TFT present an average optical transmission (including the glass substrate) of 80% in the visible part of the spectrum. The combination of transparency, high field-effect mobility and room temperature processing makes the ZnO-TFT a very promising low cost optoelectronic device for the next generation of invisible and flexible electronics.

In this paper we report the use of a sheet of cellulose fiber-based paper as the dielectric layer used in oxide based semiconductor thin film field-effect transistors (FETs). In this new approach we are using the cellulose fiber-based paper in an "interstate" structure since the device is build on both sides of the cellulose sheet. Such hybrid FETs present excellent operating characteristics such as high channel saturation mobility (>30 cm 2/Vs), drain-source current on/off modulation ratio of approximately 104, near-zero threshold voltage, enhancement n-type operation and sub-threshold gate voltage swing of 0.8 V/decade. The cellulose fiber-based paper FETs characteristics have been measured in air ambient conditions and present good stability. The obtained results outpace those of amorphous Si TFTs and rival with the same oxide based TFTs produced on either glass or crystalline silicon substrates. The compatibility of these devices with large-scale/large-area deposition techniques and low cost substrates as well as their very low operating bias delineates this as a promising approach to attain high-performance disposable electronics like paper displays, smart labels, smart packaging, RFID and point-of-care systems for self analysis in bio-applications, among others. © 2009 SPIE.