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Title: Passivation Coatings for RF Power Devices

 [1];  [1];  [1]
  1. Advanced Cooling Technologies, Inc.
Publication Date:
Research Org.:
Advanced Cooling Technologies, Inc.
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
Report Number(s):
DOE Contract Number:
Type / Phase:
Resource Type:
Technical Report
Country of Publication:
United States

Citation Formats

Flannery, Matt, Desai, Tapan, and Weyant, Jens. Passivation Coatings for RF Power Devices. United States: N. p., 2014. Web.
Flannery, Matt, Desai, Tapan, & Weyant, Jens. Passivation Coatings for RF Power Devices. United States.
Flannery, Matt, Desai, Tapan, and Weyant, Jens. 2014. "Passivation Coatings for RF Power Devices". United States. doi:.
title = {Passivation Coatings for RF Power Devices},
author = {Flannery, Matt and Desai, Tapan and Weyant, Jens},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2014,
month =

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  • Using a highly sensitive residual gas analyzer, the off-gassing of hydrogen, water, and hydrocarbons from surface-treated storage vessels containing deuterium was measured. The experimental storage vessels were compared to a low-off-gassing, electro-polished 304L canister. Alternative vessels were made out of aluminum, or were coatings on 304L steel. Coatings included powder pack aluminide, electro-plated aluminum, powder pack chromide, dense electro-plated chromium, copper plated, and copper plated with 25 and 50 percent nano-diamond. Vessels were loaded with low pressure deuterium to observe exchange with protium or hydrogen as observed with formation of HD and HDO. Off gas of D 2O or possiblemore » CD 4 was observed at mass 20. The main off-gas in all of the studies was H 2. The studies indicated that coatings required significant post-coating treatment to reduce off-gas and enhance the permeation barrier from gases likely added during the coating process. Dense packed aluminum coatings needed heating to drive off water. Electro-plated aluminum, chromium and copper coatings appeared to trap hydrogen from the plating process. Nano-diamond appeared to enhance the exchange rate with hydrogen off gas, and its coating process trapped significant amounts of hydrogen. Aluminum caused more protium exchange than chromium-treated surfaces. Aluminum coatings released more water, but pure aluminum vessels released small amounts of hydrogen, little water, and generally performed well. Chromium coating had residual hydrogen that was difficult to totally outgas but otherwise gave low residuals for water and hydrocarbons. Our studies indicated that simple coating of as received 304L metal will not adequately block hydrogen. The base vessel needs to be carefully out-gassed before applying a coating, and the coating process will likely add additional hydrogen that must be removed. Initial simple bake-out and leak checks up to 350° C for a few hours was found to be inadequate. All of the studies indicated that vessels needed several days of vacuum baking at 350-450° C to fully outgas the residual gases, which were mostly hydrogen. The current standard practice of out-gassing from ultra-clean, electro-polished 304L vessels with both vacuum bake-out and followed by an oxidative bake out to enhance the chromium surface performed the best in these studies.« less
  • Grain boundary barrier heights and other properties were measured on a variety of Wacker poly-Si to test the contention of Redfield that as received samples had no potential barriers and that temperature anneals activate the impurities in the boundaries. Our results show that these generalizations are not true and that a variety of barrier behaviors are found. Several of our new analytical techniques for studying grain boundaries and their passivation have been upgraded, including a new cell for Fourier Transform Infrared (FTIR) studies, electrochemical techniques, and a laser scanning apparatus for imaging grain boundaries. Grain boundaries in a variety ofmore » samples have been successfully passivated by the use of both the Kaufman ion source and a dc discharge apparatus. 20% improvements in cell efficiencies have been observed in large grained poly-Si cells, and the time of treatment has been drastically reduced.« less
  • Several aspects of the electrical properties of silicon grain boundaries have been studied. The temperature dependence of the zero-bias conductance and capacitance of single boundaries has been measured and shown to be in good agreement with a simple double depletion layer/thermal emission (DDL/TE) model developed to predict the transport properties of such structures. In addition, it has been shown that deconvolution of the I-V properties of some boundaries via a deconvolution scheme suggested by Pike and Seager yields effective one-electron densities of trapping states which are in good agreement with estimates obtained by low temperature electron emission measurements. Experiments havemore » also been performed which indicate that diffusion of atomic hydrogen into silicon grain boundaries greatly reduces this density of trapping states. In properly prepared, large grained polycrystalline samples all measurable traces of grain boundary potential barriers can be removed to substantial penetration depths after several hours exposure to a hydrogen plasma at elevated temperatures. Initial experiments on prototype polysilicon solar cells have shown that this passivation process can improve AM1 efficiencies. In order to more fully understand and develop this process for improving practical multigrained cells, several device research efforts with other DOE/SERI funded contractors have been initiated.« less
  • Theoretical studies of grain boundaries subject to uniform illumination have been completed. Barrier heights and recombination velocities for silicon grain boundaries have been calculated and are shown to be in good agreement with recently obtained transport measurements on uniformly illuminated silicon bicrystals. Improved calculations of the Hall effect in polycrystalline solids are also presented along with assessments of the ability of effective circuit models to account for the anomalously low carrier concentrations measured in small grain polycrystalline silicon. Preliminary optimization of some new methods for hydrogen passivation has been completed. Almost complete removal of EBIC grain boundary losses can nowmore » be achieved in times as short as twenty minutes. In addition, progress has been made in the identification and characterization of infrared vibrational modes associated with grain boundary-bonded hydrogen. The effects of fluorine and oxygen treatments on silicon grain boundaries have also been determined. These agents appear to increase grain boundary potential barrier heights in n-type silicon in marked contrast to the effect of hydrogen.« less
  • Calculations have been made of the a.c. properties of silicon grain boundaries based on the simple DDL/TE model. Experimental data obtained on bicrystals are shown to be in good agreement with these predictions. The anomalously large values of the low frequency capacitance are shown to be due to modulation of the barrier height by injected charge. Calculations of the properties of illuminated grain boundaries are also detailed and some preliminary conclusions are presented. Several new improved methods for the introduction of atomic hydrogen into polysilicon are discussed. By using EBIC characterization of polysilicon diodes it has been demonstrated that themore » hydrogen passivation process not only removes substantial amounts of trapped grain boundary charge, but also eliminates essentially all minority carrier recombination in these regions. Methods for reducing the hydrogen exposure time necessary to achieve this passivated condition are discussed.« less