Rodrigo Martins

A novel compact linear thin film position sensitive detector with 128 elements, based on p-i-n a-Si:H devices was developed. The proper incorporation of this sensor into an optical inspection camera makes possible the acquisition of three dimension information of an object, using laser triangulation methods. The main advantages of this system, when compared with the conventional charge-coupled devices, are the low complexity of hardware and software used and that the information can be continuously processed (analogue detection).

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.

Zinc oxide is a well-known wide band gap semiconductor material (3.4 eV at room temperature, in the crystalline form), which has many applications, such as for transparent conductors, varistors, surface acoustic waves, gas sensors, piezoelectric transducers and UV detectors. More recently, it is attracting considerable attention for its possible application to thin film transistors. In this paper, we present some of the recent results already obtained as well as the ones that are being developed in our laboratory. The main advantage presented by these new thin film transistors is the combination of high channel mobility and transparency produced at room temperature which makes these thin film transistors a very promising low cost device for the next generation of invisible and flexible electronics. Moreover, the processing technology used to fabricate this device is relatively simple and it is compatible with inexpensive plastic/flexible substrate technology. © 2005 Elsevier B.V. All rights reserved.

Transparent and highly conducting gallium-doped zinc oxide films were successfully deposited by rf sputtering at room temperature. The lowest resistivity achieved was 2.6×10-4 Ω cm for a thickness of 1100 nm (sheet resistance ≈1.6 Ω/sq), with a Hall mobility of 18 cm2/Vs and a carrier concentration of 1.3×1021 cm-3. The films are polycrystalline with a hexagonal structure and a strongly preferred orientation along the c-axis. A linear dependence between the mobility and the crystallite size was obtained. The films present a transmittance in the visible spectra between 80 and 90% and a refractive index of approximately 2, which is very close to the value reported for bulk material. © 2003 Elsevier B.V. All rights reserved.

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.

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.

In this paper we present the first results of thin film transistors produced completely at room temperature using ZnO as the active channel and silicon oxynitride as the gate dielectric. The ZnO-based thin film transistors (ZnO-TFT) present an average optical transmission (including the glass substrate) of 84% in the visible part of the spectrum. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 1.8 V. A field effect mobility of 70 cm2/Vs, a gate voltage swing of 0.68 V/decade and an on-off ratio of 5×105 were obtained. The combination of transparency, high field-effect mobility and room temperature processing makes the ZnO-TFT very promising for the next generation of invisible and flexible electronics. © 2004 Elsevier B.V. All rights reserved.