P. Alpuim

AMORPHOUS AND MICROCRYSTALLINE SILICON FILMS GROWN AT LOW TEMPERATURES BY RADIO-FREQUENCY AND HOT-WIRE CHEMICAL VAPOR DEPOSITION

The effect of hydrogen dilution on the optical, transport, and structural properties of amorphous and microcrystalline silicon thin films deposited by hot-wire (HW) chemical vapor deposition and radio-frequency (rf) plasma-enhanced chemical vapor deposition using substrate temperatures (Tsub) of 100 and 25 °C is reported. Microcrystalline silicon (μc-Si:H) is obtained using HW with a large crystalline fraction and a crystallite size of ∼30 nm for hydrogen dilutions above 85% independently of Tsub. The deposition of μc-Si:H by rf, with a crystallite size of ∼8 nm, requires increasing the hydrogen dilution and shows decreasing crystalline fraction as Tsub is decreased. The photoconductivity, defect density, and structure factor of the amorphous silicon films (a-Si:H) are strongly improved by the use of hydrogen dilution in the Tsub range studied. a-Si:H films with a photoconductivity-to-dark conductivity ratio above 105, a deep defect density below 1017 cm−3, an Urbach energy below 60 meV and a structure fa...

Fabrication of flexible thermoelectric microcoolers using planar thin-film technologies

The present work reports on the fabrication and characterization of a planar Peltier cooler on a flexible substrate. The device was fabricated on a 12 µm thick Kapton(c) polyimide substrate using Bi2Te3 and Sb2Te3 thermoelectric elements deposited by thermal co-evaporation. The cold area of the device is cooled with four thermoelectric junctions, connected in series using metal contacts. Plastic substrates add uncommon mechanical properties to the composite film–substrate and enable integration with novel types of flexible electronic devices. Films were deposited by co-evaporation of tellurium and bismuth or antimony to obtain Bi2Te3 or Sb2Te3, respectively. Patterning of the thermoelectric materials using lift-off and wet-etching techniques was studied and compared. The performance of the Peltier microcooler was analysed by infrared image microscopy, on still-air and under vacuum conditions, and a maximum temperature difference of 5 °C was measured between the cold and the hot sides of the device.

Influence of the chemical and electronic structure on the electrical behavior of zirconium oxynitride films

This work is devoted to the investigation of decorative zirconium oxynitride, ZrOxNy, films prepared by dc reactive magnetron sputtering, using a 17:3 nitrogen-to-oxygen-ratio gas mixture. The color of the films changed from metallic-like, very bright yellow pale, and golden yellow, for low gas mixture flows [from 0 to about 9SCCM (SCCM denotes cubic centimeter per minute at STP)] to red brownish for intermediate gas flows (values up to 12SCCM). Associated to this color change there is a significant decrease of brightness. With further increase of the reactive gas flow, the color of the samples changed from red brownish to dark blue (samples prepared with 13 and 14SCCM). The films deposited with gas flows above 14SCCM showed only apparent colorations due to interference effects. This change in optical behavior from opaque to transparent (characteristic of a transition from metallic to insulating-type materials), promoted by the change in gas flow values, revealed that significant changes were occurring in...

Amorphous and microcrystalline silicon deposited by hot-wire chemical vapor deposition at low substrate temperatures: application to devices and thin-film microelectromechanical systems

Abstract Amorphous silicon and microcrystalline silicon have been deposited on glass and plastic (PET) substrates using hot-wire chemical vapor deposition (HW) at substrate temperatures ( T sub ) of 100°C and 25°C. The optoelectronic and structural properties of intrinsic and doped films are reviewed. Intrinsic HW a-Si:H is incorporated into a p-i-n diode processed at a maximum temperature of 100°C, achieving a rectification ratio of 10 6 . The mechanical (residual stress) properties of low- T sub HW layers are compared to those of low- T sub radio-frequency-deposited layers. Doped-microcrystalline films of low- T sub HW layers deposited on plastic substrates show piezoresistive behavior. The resistance of n-type films decreases with applied tensile stress and increases with applied compressive stress, while p-type films show the opposite behavior. The mechanical properties of low- T sub HW layers are adequate for their use as structural layers in thin-film microelectromechanical systems (MEMS). The electrical actuation of surface micromachined bridge structures and the mechanical actuation of thin-film microresonators on large area substrates are demonstrated.

Thermoelectric micro converters for cooling and energy scavenging systems

This paper describes the fabrication process of thermoelectric microconverters, based on n-type bismuth telluride (Bi2Te3) and p-type antimony telluride (Sb2Te3) thin films. The films are fabricated by thermal co-evaporation with thermoelectric properties comparable to those reported for the same materials in bulk form (used in conventional macro-scale Peltier modules). The absolute value of the Seebeck coefficient in the range of 150–250 µV K−1 and an in-plane electrical resistivity of 7–15 µΩ m were obtained. The influence of fabrication parameters on thermoelectric properties is reported. The films were patterned by photolithography and wet-etching techniques, using HNO3/HCl-based etchants. The influence of composition and concentration of etchants in the lithographic process is reported. A microcooler was fabricated.

Doping of amorphous and microcrystalline silicon films deposited at low substrate temperatures by hot-wire chemical vapor deposition

The gas phase doping of amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon thin films deposited at substrate temperatures of 25 °C and 100 °C by hot-wire chemical vapor deposition is studied. Phosphine was used for n-type doping and diborane for p-type doping. The electronic and structural properties of the doped films are studied as functions of hydrogen dilution. Films were deposited on glass and polyethylene terephthalate. Similar dark conductivities, σd, were obtained for the doped films deposited on either substrate. σd above 10−6 Ω−1 cm−1 were obtained for a-Si:H films doped n-type at 25 °C and 100 °C (σd>10−4 Ω−1 cm−1) and for a-Si:H doped p-type only at 100 °C. σd, equal or above 10−1 Ω−1 cm−1, were obtained for μc-Si:H doped p-type at 25 °C and 100 °C for μc-Si:H doped n-type only at 100 °C. Isochronal annealing at temperatures up to 200 °C reveals that, while the dopants are fully activated in microcrystalline samples, they are only partially activated in amorphous films deposited at a lo...

Electronic and structural properties of doped amorphous and nanocrystalline silicon deposited at low substrate temperatures by radio-frequency plasma-enhanced chemical vapor deposition

The gas phase doping of hydrogenated amorphous silicon and hydrogenated nanocrystalline silicon thin films deposited on glass and on plastic (polyethylene terephthalate) substrates is reported. Two substrate temperatures were used during deposition: 25 °C and 100 °C. Films were deposited by radio-frequency plasma-enhanced chemical vapor deposition using phosphine or diborane for n- or p-type doping, respectively. Similar electronic and structural properties are obtained for the doped films deposited on either substrate. Hydrogen dilution of silane is used to improve the electronic and structural properties of the amorphous films and to obtain nanocrystalline films. The most conductive amorphous films have n-type dark conductivity at room temperature ∼10−3 Ω−1 cm−1 and ∼10−5 Ω−1 cm−1 when deposited at 100 °C and 25 °C, respectively, or p-type room-temperature dark conductivity ∼10−7 Ω−1 cm−1 at both substrate temperatures. The most conductive nanocrystalline films deposited at 100 °C have n- and p-type dark conductivity at room temperature above 10−2 Ω−1 cm−1 while nanocrystalline films deposited at 25 °C only have p-type conductivity higher than 10−2 Ω−1 cm−1 at room temperature. Isochronal annealing at temperatures up to 300 °C showed that the dopants are fully activated at the deposition temperature in doped nanocrystalline samples and that they are only partially activated in amorphous films deposited at low substrate temperatures.The gas phase doping of hydrogenated amorphous silicon and hydrogenated nanocrystalline silicon thin films deposited on glass and on plastic (polyethylene terephthalate) substrates is reported. Two substrate temperatures were used during deposition: 25 °C and 100 °C. Films were deposited by radio-frequency plasma-enhanced chemical vapor deposition using phosphine or diborane for n- or p-type doping, respectively. Similar electronic and structural properties are obtained for the doped films deposited on either substrate. Hydrogen dilution of silane is used to improve the electronic and structural properties of the amorphous films and to obtain nanocrystalline films. The most conductive amorphous films have n-type dark conductivity at room temperature ∼10−3 Ω−1 cm−1 and ∼10−5 Ω−1 cm−1 when deposited at 100 °C and 25 °C, respectively, or p-type room-temperature dark conductivity ∼10−7 Ω−1 cm−1 at both substrate temperatures. The most conductive nanocrystalline films deposited at 100 °C have n- and p-type dar...

Thermoelectric Properties of Bi2Te3/Sb2Te3 Thin Films

The deposition and characterization of n-type Bi2Te3 and p-type Sb2Te3 semiconductor films are reported. The films were deposited by thermal co-evaporation on a 25 µm thick polyimide (kapton) substrate. The co-evaporation method is inexpensive, simple, and reliable, when compared to other techniques that need longer time periods to prepare the starting material or require more complicated and expensive deposition equipment. Seebeck coefficients of -189 µVK-1 and +140 µVK-1 and electrical resistivities of 7.7 µ0m and 15.1 µ0m were measured at room temperature on n-type and p-type films, respectively. These values are better than those reported for films deposited by co-sputtering or electrochemical deposition, and are close to those reported for films deposited by metal-organic chemical vapour deposition or flash evaporation. Because of their high figures of merit, these films will be used for the fabrication of a micro-Peltier element, useful in temperature control and laser-cooling for telecommunications.

Thermal stability of zirconia/alumina thin coatings produced by magnetron sputtering

Abstract Thin ZrO 2 -Al 2 O 3 -Y 2 O 3 coatings were deposited by reactive magnetron sputtering technique onto steel substrates. Annealing at 1273 K the ceramic ZrO 2 -Al 2 O 3 mixtures in air crystallise in the tetragonal phase and grain growth is observed. The Al 2 O 3 content limits the maximum observed grain size between 25 and 30 nm during the observation time of this study of about 1.8 × 10 6 s (500 h). In contrast, the ZrO 2 -Y 2 O 3 coatings revealed tetragonal grains with a size of about 200 nm. Diffusion processes cause the grain growth as well as the observed decrease of the intrinsic coating stress. Zirconia coatings stabilised by Al 2 O 3 (without Y 2 O 3 ) generally show tetragonal grains but prolonged annealing at 1273 K decreases the effect of the rigid Al 2 O 3 matrix and the zirconia transforms into its monoclinic phase modification. Multilayered coatings of ZrO 2 with layer thickness lower to 6 nm also retained the tetragonal phase. Nevertheless, 1-nm thick Al 2 O 3 spacing layers are not sufficient to suppress the diffusion, growth and subsequent phase transformation of the zirconia.

All-Inkjet-Printed Bottom-Gate Thin-Film Transistors Using UV Curable Dielectric for Well-Defined Source-Drain Electrodes

Technological restrictions of the inkjet printing technology for printed electronics can hinder its application potential, mainly due to the limited resolution and layer homogeneity in comparison to conventional manufacturing techniques for electronics. The manufacturing of active devices such as thin-film transistors with appropriate performance using printing technologies is still one of the current challenges towards industrial applications. This work demonstrates the application of an ultraviolet (UV) curable ink as insulating material for the gate dielectric. The advantage of the UV curable ink is its fast curing and the smooth surface enabling high resolution patterns on top of it. In this way, all-inkjet-printed organic thin-film transistors (OTFTs) were fabricated with silver electrodes, UV curable gate dielectric, and 6,13-bis(triisopropylsilylethynyl)pentacene for the active semiconductor layer. By fine tuning of processing parameters and pattern geometries, a stable channel length of about 10 μm was obtained in the bottom-gate configuration without the need of additional steps, suggesting a way to build low-cost all-inkjet-printed OTFTs with well-defined source-drain electrodes and fast UV curable dielectric without any additional steps. The inkjet-printed device is characterized by an electron mobility of 0.012 cm2 V−1 s−1 and on/off ratio of 103.