Electrical properties of diamond films grown at low temperature

The unique electronic properties of diamond, associated with the emergence of chemical vapour deposition (CVD) methods for the growth of thin films on non-diamond substrates, have led to considerable interest in electronic devices fabricated from this material. In our previous work, we found that polycrystalline diamond films can be deposited at 250 °C using CH₄---CO₂ gas mixtures. Studying the electrical properties and the upcoming problems of applications of low-temperature diamond films are relevant concerns.

In this work, the electrical properties of diamond films grown at low temperatures were studied and compared with those of conventional diamond films. Platinum was used as the upper electrode. The resistivity of low-temperature diamond was around three orders of magnititude lower than that of conventional diamond. However, both the low temperature and conventional growth diamond exihibited rectifying behavior when platinum was used as the upper electrode.     

Effect of B/C ratio on the physical properties of highly boron-doped diamond films

Highly boron-doped diamond films were deposited on silicon substrate by hot filament chemical vapor deposition in a gas mixture of hydrogen and methane. The chemical bonding states, surface texture, and electrical resistivity of these films were analyzed by X-ray photoelectron spectroscopy, scan electron microscope, and four-point probe method. It was found that boron dopants play an important role in the texture and chemical bonding states of the diamond films. An appropriate concentration of boron dopants (B/C ratio of 10 000 ppm) can simultaneously improve crystal quality and reduce resistivity of the diamond films. The minimum resistivity of diamond films reaches 1.12 × 10⁻² Ω cm, which is applicable as electrodes.     

Filament-assisted growth of diamond films

Filament-assisted pyrolytic growth of diamond films on (100) Si wafers was investigated in an attempt to grow quality layers for semiconductor applications. The work was carried out in hydrogen ambient under a reduced pressure condition of about 100 torr (133, 322×10² Pa). Using isopropanol and methanol as carbon source chemicals, the growth process and film properties were characterized as functions of reactant concentration, filament and substrate temperature, reaction pressure and the total gas flow rate. Diamond films of good quality were grown under condition of low source concentration and small flow rate. However, the growth rates were generally slow. The films were polycrystalline. The filament and substrate temperatures were fairly critical to the nucleation and growth processes. The substrate surface finishing from diamond paste polishing predominated the nucleation site and grain size of the deposits.     

Dielectric Behavior of Diamond Films

Nanostructured diamond films have been synthesized using microwave plasma enhanced chemical-vapor-deposition methods. The dielectric behavior has been investigated by using impedance spectroscopy up to 500°C. Impedance data are presented in the form of a Cole–Cole plot. It is found that: (i) The resistivity contributed from both the grain interior and the grain boundary decreases with an increase of temperature. (ii) Above 250°C, the impurities at grain boundaries are thermally activated, and thus contribute to the dielectric relaxation. (iii) The electrical conductivity of diamond films follows an Arrhenius law with an activation energy transition from 0.13 and 0.67 eV at 250°C. A similar activation energy is found for the Arrhenius plot of relaxation frequencies from 0.14 to 0.73 eV. Possible physical mechanisms responsible for the dielectric behavior are presented and discussed.     

fabrication of diamond membranes for MEMS using reactive ion etching of silicon

Polycrystalline diamond thin film has been grown on a silicon substrate using high pressure microwave plasma-assisted chemical vapor deposition from a gas mixture of methane and hydrogen at a substrate temperature of 950°C. A simple process flow has been developed to fabricate optically transparent polycrystalline synthetic diamond membranes/windows employing reactive ion etching (RIE) of a single crystal silicon substrate using an electron beam evaporated aluminum thin film mask pattern formed by photolithography. Scanning electron microscopy has been used to study the morphology of as-grown diamond thin films.     

Low temperature synthesis of sol–gel derived Al-doped ZnO thin films with rapid thermal annealing process

A series of sol–gel derived Al-doped ZnO (AZO) thin films with rapid thermal annealing process at low temperature were studied to examine the influence of annealing temperature and the Al doping concentration on their microstructure, electrical and optical transport properties. Crystalline AZO thin films were obtained following an annealing process at temperatures between 400 and 600 °C for 10 min in argon gas ambient. AZO thin films with Al doping of 1 at% were oriented more preferentially along the (002) direction, and have larger grain size and lower electrical resistivity, while the highest average optical transmittances of 92% were observed in AZO films with Al doping of 2 at%. With the annealing temperature increasing from 400 to 600 °C, the grain size of AZO films increased, the optical transmittance became higher, and the electrical resistivity decreased to a lowest value of 1.2 × 10⁻⁴ Ω cm resulting from the increase of the carrier concentration and the mobility.     

A comparative study of p-type diamond films using Raman and transport measurements

The influence of deposition temperature in the properties of synthetic diamond films grown by two different chemical vapor deposition (CVD) techniques, hot-filament- and microwave-plasma-assisted, was investigated. These samples were obtained using the optimal growth conditions previously achieved in this work. Raman spectroscopy was employed in order to investigate the diamond film quality as a function of the deposition temperature. It was found that the nondiamond carbon bands decrease as the deposition temperature increases for both the deposition methods, leading to higher-quality diamond films. The micro- and macro-Raman spectra showed that the nondiamond band is already present in a single diamond grain. Both techniques provided well homogeneous diamond films and with equivalently good quality. Boron-doped diamond films with different carrier concentration levels were also studied. In order to get details about the electrical properties of the films, resistivity as a function of the boron concentration—in association with Raman spectra—and temperature-dependent transport measurements were employed. The results showed that the boron doping is the main responsible for the conductivity and that the variable range hopping (VRH) mechanism dominates the transport in these doped diamond films.     

Electrical properties of electroplated Cu(Ag) thin films

To increase the electromigration resistance of copper interconnects copper alloy systems are of interest. In the present paper electrical properties of Cu(Ag) films will be discussed with respect to heat treatment and in comparison to copper and other alloy systems. The investigations show that the electrical resistivity of Cu(Ag) films is very low in comparison to other copper alloy systems. Up to an alloy content of about 2 at.% Ag the International Technology Roadmap for Semiconductors criterion of 2.2 μΩcm (scattering by geometrical constraints neglected) can be fulfilled after heat treatment. The various components of the electrical resistivity will be discussed in detail. The investigations show that grain growth and the redistribution of silver and impurities dominate the electrical resistivity evolution.     

Nitrogen-incorporation induced changes in the microstructure of nanocrystalline WO3 thin films

Nitrogen incorporated tungsten oxide (WO₃) films were grown by reactive magnetron sputter-deposition by varying the nitrogen content in the reactive gas mixture keeping the deposition temperature fixed at 400 °C. The crystal structure, surface morphology, chemical composition, and electrical resistivity of nitrogen doped WO₃ films were evaluated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and electrical conductivity measurements. The results indicate that the nitrogen-incorporation induced changes in the microstructure and electrical properties of WO₃ films are significant. XRD measurements coupled with SEM analysis indicate that the increasing nitrogen content decreases the grain size and crystal quality. The nitrogen concentration increases from 0 at.% to 1.35 at.% with increasing nitrogen flow rate from 0 to 20 sccm. The corresponding dc electrical conductivity of the films had shown a decreasing trend with increasing nitrogen content.     

Low-temperature preparation of polycrystalline silicon from silicon tetrachloride

Polycrystalline silicon has been prepared by zinc reduction of silicon tetrachloride at a low temperature (≈550° C) in a vertical vapour phase reactor. Characterisation of the remelted polycrystalline ingot by X-ray, SEM and electrical methods shows that the material is p-type with an average grain size of 0.5 μm having a room-temperature resistivity in the range 1.0–1.5 Ω cm suitable for solar cell fabrication.     

Preparation and characterization of sputtered Cu films containing insoluble Nb

Copper films containing various amounts of insoluble Nb (up to 24.7 at.%) were prepared by r.f. magnetron sputtering. The crystallography and microstructure of the films were investigated for as-deposited and annealed Cu(Nb) thin films. Cu(Nb) thin films are found to consist of non-equilibrium supersaturated solid solution of Nb in Cu with a nanocrystalline microstructure. X-ray diffraction and scanning electron microscope analyses revealed a reduction in the grain sizes of the films with increasing Nb content in the films leading to a grain refinement. The electrical resistivity of as-deposited and annealed Cu(Nb) thin films is found to be low for an Nb content 2.7 at.%. Significant drops in the resistivity were observed for the high Nb contents after annealing at 530 °C which may be due to grain growth and formation of Nb-bearing phase in the film. Microhardness of the films was found to increase with the Nb concentration due to the combined effects of grain refinement and the solute strengthening of Nb.     

Effects of composition on optical and electrical properties of amorphous In-Ga-Zn-O films deposited using radio-frequency sputtering with varying O2 gas flows

This study used powders containing various In₂O₃-Ga₂O₃-ZnO (IGZO) chemical compositions to manufacture targets by using a metallurgical process. The resulting targets were used to deposit amorphous In-Ga-Zn-O (a-IGZO) channel films using a radio frequency (r.f.) magnetron sputtering process. The average transmittance increased and achieved saturation; the resistivity increased in conjunction with the O₂ flow ratio of less than 6%; and subsequently, the resistivity decreased with increasing the O₂ flow ratio larger than 6%. This study examined the effects of compositions on electrical characteristics and optical properties of a-IGZO films at varied O₂ flow rates. The effects of composition on optical and electrical characteristics of a-IGZO films indicate that the average transmittance of a-IGZO films with more zinc atoms (approximately 50%) had more than 80% at various O₂ flow ratios because of the higher oxygen absorption of the zinc atoms. However, the average transmittance of a-IGZO film with a lower zinc atomic ratio (approximately 20%) without an O₂ flow ratio decreased to below 10% because of the indium and indium oxide crystalline precipitation in the indium-rich a-IGZO films. The results revealed that the resistivity increased when the gallium atomic ratio increased and the indium atomic ratio decreased.     

Physical properties of hydrogenated Al-doped ZnO thin layer treated by atmospheric plasma with oxygen gas

Hydrogenated Al-doped ZnO (H:AZO) thin films were deposited on glass substrates at room temperature by radio-frequency magnetron sputtering at various hydrogen flow rates. The addition of hydrogen improved the resistivity of the H:AZO films significantly. A thin insulating layer was produced on H:AZO films by atmospheric pressure plasma with Ar/O₂ reactive gas. The resistivity degenerated and the optical band gap of the oxygen plasma-treated H:AZO films decreased from 3.7 eV to 3.4 eV. This was attributed to a decrease in the hydrogen concentration at the film surface according to elemental depth analysis.     

The substrate temperature dependent electrical properties of titanium dioxide thin films

Titanium dioxide thin films were obtained by a dc sputtering technique onto heated glass substrates. The relationship between the substrate temperature and the electrical properties of the films was investigated. Electrical resistivity measurements showed that three types of conduction channels contribute to conduction mechanism in the temperature range of 13–320 K. The temperature dependence of electrical resistivity between 150 and 320 K indicated that electrical conduction in the films was controlled by potential barriers caused by depletion of carriers at grain boundaries. The conduction mechanism of the films was shifted from grain boundary scattering dominated band conduction to the nearest neighbor hopping conduction at temperatures between 55 and 150 K. Below 55 K, the temperature dependence of electrical resistivity shows variable range hopping conduction. The correlation between the substrate temperature and resistivity behavior is discussed by analyzing the physical plausibility of the hopping parameters and material properties derived by applying different conduction models. With these analyses, various electrical parameters of the present samples such as barrier height, donor concentration, density of states at the Fermi level, acceptor concentration and compensation ratio were determined. Their values as a function of substrate temperature were compared.     

Effects of substrate position and oxygen gas flow rate on the properties of ZnO: Al films prepared by reactive co-sputtering

Al-doped zinc oxide (ZnO: Al) thin films are deposited at room temperature on rotating glass substrates by direct current co-sputtering of metallic targets under various oxygen partial pressures in the range 0.05-0.067 Pa. The films are polycrystalline with wurtzite structure and show preferential (001) orientation when they are transparent. The electrical resistivity is strongly influenced by sample position with the lowest value of 6.6 × 10^− 4 Ω cm far from the magnetron axis, where it is directly linked to grain size. As the oxygen gas flow rate is enhanced, the optical transparency rises up and both the electrical conductivity facing the magnetron axis and its lateral homogeneity decrease. A significant reduction in heterogeneity as the draw distance increases suggests an influence of the energy of impinging metal atoms, the instantaneous deposition rate and oxygen reactivity on the electrical behaviour.     

正偏压对纳米金刚石薄膜结构和电阻率的影响

采用电子辅助热丝化学气相沉积工艺, 在1kPa反应气压和施加不同的偏流条件下, 沉积了纳米金刚石薄膜. 用X射线衍射, 场发射扫描电镜和半导体特性表征系统对该薄膜进行了表征和分析. 结果表明, 施加偏流可以使薄膜晶粒呈现明显的(110)晶面择优取向, 表面形貌发生较大变化. 当偏流为8A时, 薄膜晶粒达到最小值, 约为20nm, 薄膜表面也最光滑. 本文讨论了在低气压和电子轰击条件下(110)晶面择优取向的形成机制及其对薄膜显微形貌和电阻率的影响关系.     

Optical and electrochemical properties of optically transparent,boron-doped diamond thin films deposited on quartz

The optical and electrochemical properties of transparent, boron-doped diamond thin film, deposited on quartz, are discussed. The films were deposited by microwave-assisted chemical vapor deposition, for 1-2 h, using a 0.5% CH4/H2 source gas mixture at 45 Torr and 600 W of power. A high rate of diamond nucleation was achieved by mechanically scratching the quartz. This pretreatment leads to the formation of a continuous film, in a short period of time, which consists of nanometer-sized grains of diamond. The thin-film electrode was characterized by cyclic voltammetry, atomic force microscopy, and UV-visible absorption spectrophotometry. The film's electrochemical response was evaluated using Ru(NH3)6(3+/2+) in 1 M KCl, Fe(CN)6(3-/4-) in 1 M KCl, and chlorpromazine (CPZ) in 10 mM HClO4. The film exhibited a low voltammetric background current and a stable and active voltammetric response for all three redox systems. The optical transparency of the polycrystalline film in the visible region was near 50% and fairly constant between 300 and 800 nm. The optical and electrical properties were extremely stable during 48-h exposure tests in various aqueous (HNO3, NaOH) solutions and nonaqueous (e.g., chlorinated) solvents. The properties were also extremely stable during anodic and cathodic potential cycling in harsh aqueous environments. This stability is in stark contrast to what was observed for an indium-doped tin oxide thin film coated on quartz. The spectroelectrochemical response (transmission mode) for CPZ was studied in detail, using a thin-layer spectroelectrochemical cell. Thin-layer voltammetry, potential step/ absorption measurements, and detection analytical figures of merit are presented. The results demonstrate that durable, stable, and optically transparent diamond thin films, with low electrical resistivity (approximately 0.026 omega x cm) laterally through the film, can be deposited on quartz.     

Control of electrical resistivity of TaN thin films by reactive sputtering for embedded passive resistors

Tantalum nitride thin films were deposited by radio frequency (RF) reactive sputtering at various N₂/Ar gas flow ratios and working pressures to examine the change of their electrical resistivity. From the X-ray diffraction (XRD) and four-point probe sheet resistance measurements of the TaN_x films, it was found that the change of the crystalline structures of the TaN_x films as a function of the N₂ partial pressure caused an abrupt change of the electrical resistivity. When the hexagonal structure TaN thin films changed to an f.c.c. structure, the sheet resistance increased from 16 Ω/sq to 1396 Ω/sq. However, we were able to control the electrical resistivity of the TaN thin film in the range from 69 Ω/sq to 875 Ω/sq, with no change in crystalline structure, within a certain range of working pressures. The size of the grains in the scanning electron microscopy (SEM) images seemed to decrease with the increase of working pressure.     

Electrical conductivity of copper nanoparticle thin films annealed at low temperature

Copper nanoparticles with a mean diameter of 20 nm were used to prepare electrical conductive films at low temperature. After dispersal in an organic solvent, the copper nanoparticle pastes were coated onto a glass substrate, which was then annealed under various conditions to investigate the effects of various atmospheric conditions, such as air, nitrogen gas or hydrogen gas, as well as different annealing temperatures. Two-step annealing, which first involves oxidation in air followed by reduction, is effective in the preparation of high electrical conductive copper nanoparticle films. The copper nanoparticle films that were calcined in air for 1 h and then hydrogen gas for 1 h at a low temperature of 200 °C showed a low resistivity of 2 × 10^-5 Ω cm.     

Ar流量对磁控溅射制备Al掺杂ZnO薄膜的影响

Al掺杂ZnO(AZO)具有电导率高、光学透射率高的优点,且原料来源丰富、制备成本低廉,被认为是最有应用潜力的透明导电薄膜.本文利用射频磁控溅射制备30 cm×30 cm尺寸大面积AZO薄膜,研究了气压恒定时,Ar流量对薄膜晶粒生长机制、电学和光学性能的影响.结果表明,AZO薄膜晶粒均表现出垂直基片方向的c轴择优取向生...