Joule heating induced local electrodeposition for microelectronic circuits

A fundamental study is performed for local electrodeposition of copper utilizing thermal potential induced by Joule heating. The feasibility of the process for microelectronic applications is assessed by both experiment and mathematical modeling. The results of the investigation show that (i) a copper wire is coated under conditions of a.c. 50 Hz Joule heating in electrolyte containing 1.0 M CuSO₄ and 0.5m H₂SO₄ with relatively high deposition rate of about 0.4 µm min^–1, (ii) the Joule heating current should be kept below the boiling point of the solution to realize uniform deposition, and (iii) results of calculations by the present model based on one-dimensional heat conduction agree well with experimental results.Nomenclature D diameter of wire (m) - D ₀ initial diameter of wire (m) - F Faraday constant (96 487 C mol¹ ) - g acceleration due to gravity (9.807 m s²) - Gr Grashof number - H thickness of electrodeposit (m) - I current (A) - i ₀ exchange current density (Am^–2) - i _n current density normal to electode (Am^–2) - J current density (I/S) (Am^–2) - L length of wire (m) - M molar concentration of electrolyte (mol dm^–3 or M) - m atomic weight (kg mol^–1) - n number of electrons participating - n unit normal vector to boundary - Nu Nusselt number - Pr Prandtl number - q heat per unit volume (W m^–3) - R universal gas constant (8.314 3 J mol^–1 K^–1) - (r, z) cylindrical coordinate (m) - S cross section of wire (m²) - T temperature (K) - T ₀ fixed temperature at both ends of wire (K) - T _y temperature of electrolyte (K) - t time (s) - x longitudinal coordinate over wire (m) Greek symbols heat transfer coefficient (W m^–2 K^–1 - _a,c anodic (a) and cathodic (c) transfer coefficient - thermal expansion coefficient of solution (K^–1) - specific heat (J kg^–1K^–1) - potential (V) - _e electrode potential (V) - thermal conductivity (W m^–1 K^–1 ) - _y ionic conductivity of electrolyte (^–1m^–1) - _e electronic conductivity of electrode (^–1 m^–1) - kinematic viscosity (m²s^–1) - surface overpotential ( _e – ) (V) - time constant (s) - density (kg m^–3) This work was presented at The 7th International Microelectronics Conference, Yokohama, Japan (1992).     

Electrostatic Cleaning System for Removing Lunar Dust Adhering to Space Suits

Removing lunar dust adhering to astronaut space suits is critically important for long-term lunar exploration. We are developing an automatic cleaning system that uses electrostatic force. It employs an alternating electrostatic field that forms a barrier on the surface of fabrics. In this study, we applied single-phase rectangular voltage to parallel wire electrodes stitched into the insulating fabric of space suits. By applying mechanical vibration and operating the system in a vacuum, we realized high performance: the cleaning rate exceeded 80%. Flicking out particles smaller than 10?μm in diameter that were trapped between fibers was difficult, but this system can perform preliminary space suit cleaning and save precious time for astronauts on the moon.     

Initial phoneme versus whole-word criterion to initiate pronunciation: Evidence based on response latency and initial phoneme duration.

Undergraduates participated in 4 speeded naming experiments investigating 2 criteria to initiate articulation–initial phoneme (IP) or whole word (WW). These criteria make different response latency and IP duration predictions for words with regular vs irregular vowel pronunciations (e.g., "pump" vs "pint"). The EP criterion predicts no latency differences but longer IP durations for irregulars, whereas the WW criterion predicts no EP duration differences but longer latencies for irregulars. The latencies and IP durations of words beginning with plosives are measured (a) indirectly by exploiting the conflation of latency and EP duration in the standard naming task and (b) directly by determining when closure begins and ends in the postvocalic naming task (participants say "uuhhh" until responding). Results support both criteria: Response latencies and IP durations are longer for irregular words compared with regular words. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Femoral vein stasis during laparoscopic cholecystectomy: effects of graded elastic compression leg bandages in preventing thrombus formation

Venous stasis of the legs during laparoscopic cholecystectomy was compared between patients without graded compression leg bandages (Group 1; n = 12) and patients with such bandages (Group 2; n = 12) by measuring mean blood flow velocity and cross-sectional area of the femoral vein using a color Doppler ultrasonography. In Group 1, when velocity and area were measured in the supine position, a significant decrease in velocity (p < .05) and a significant increase in area (p < .05) occurred after abdominal insufflation to 10 mm Hg. These changes were greater during abdominal insufflation in the reverse Trendelenburg position than during abdominal insufflation in the supine position. In Group 2, flow velocity was significantly higher (p < .05) before abdominal insufflation as compared with Group 1. After abdominal insufflation to 10 mm Hg and a postural change, velocity significantly decreased (p < .05) and area significantly increased (p < .05) in Group 2, similar to the results in Group 1. During abdominal insufflation at 5 mm Hg or lower, the use of the graded compression bandage was found to be useful for preventing femoral vein stasis. During abdominal insufflation at 10 mm Hg or in the reverse Trendelenburg position, the bandage did not prevent femoral vein stasis.     

Sintering chemical reactions to increase thermal conductivity of aluminium nitride

Chemical reactions to increase thermal conductivity by decreasing oxygen contents during AlN sintering with an Y₂O₃ additive in a reducing nitrogen atmosphere with carbon were investigated. They were: Al₂O₃ + N₂ + 3CO ⇋ 2AlN + 3CO₂, Al₂Y₄O₉ + N₂ + 3CO ⇋ 2AlN + 2Y₂O₃ + 3CO₂ and Y₂O₃ + N₂ + 3CO ⇋ 2YN + 3CO₂. Some of the CO₂ gas reduced to CO gas in the presence of carbon by a chemical reaction: CO₂ + C ⇋ 2CO. These reactions were confirmed by examining oxygen contents, the grain boundary phases of the sintered AlN, and the trapped CO and CO₂ gases in the sintered bodies. These reducing reactions proceed with increasing sintering temperature and periods, and hence the thermal conductivity is increased.     

A study of the buying price of photovoltaic electricity under a carbon tax regime

Assuming that photovoltaic (PV) systems are adopted in residential houses under a carbon tax regime, the economic performance of PV systems is investigated from the standpoint of an electric utility. The economic performance is estimated by using the buying price of PV electricity and the PV economic index, which is defined as the ratio of the buying price to the generation cost of the electric utility. Because these values depend on electric power development and operation, the best mix and the operation of power plants are obtained by linear programming subject to restrictions on power generation. Then, the buying price of PV electricity is calculated from the total cost of the electric utility. The buying price means the upper limit at which the electric utility never suffers a loss. The buying price is also compared with the power generation cost. The parameters are the prevalence attainment ratio of PV systems (0 to 100%), the upper limit of newly developed nuclear power plants (0 to 4 GW/10 y), and the generated energy ratio of coal‐fired thermal plants (0 to 15%). Chubu Electric Power Company, Inc. is used as the electric utility. The calculation results show that the buying price of PV electricity increases linearly with increasing carbon tax rate, and its values are 9 and 11.5 yen/kWh when the carbon tax rate is 0 and 25 thousand yen/t‐C, respectively, which does not depend on the prevalence attainment ratio of PV systems and the upper limit of newly developed nuclear power plants. It is not the carbon tax rate but the newly developed nuclear power plant that influences the PV economic index. The values of the PV economic index are 1.35 to 1.45 and 1.50 to 1.60 when the newly developed nuclear power plant capacity is 0 and 4 GW/10 y, respectively. These results show that the economic performance of PV systems is increased by developing nuclear power plants at a certain rate and introducing a carbon tax. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(2): 38–49, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10067