Paper TF2-TuA2
Evaluation of Al2O3 ALD Gas Diffusion Barriers and Visualization of Barrier Defects Using the Ca Test
Tuesday, November 10, 2009, 2:20 pm, Room B4
| Session: |
ALD/CVD: Oxides and Barriers |
| Presenter: |
J.A. Bertrand, University of Colorado, Boulder |
| Authors: |
J.A. Bertrand, University of Colorado, Boulder
S.H. Jen, University of Colorado, Boulder
D. Seghete, University of Colorado, Boulder
S.M. George, University of Colorado, Boulder
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| Correspondent: |
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Flexible gas diffusion barriers are required on polymers. One key application area for these barrier films is organic electronics, especially organic light emitting diodes (OLED) for flexible displays.The necessary water vapor transmission rate (WVTR) for OLEDs is <10-6 g/m2/day. In collaboration with DuPont, we earlier measured low WVTR values of ~6.5 x 10-5 g/m2/day for single Al2O3 ALD films at 60°C/85% RH using the Ca test with optical transmission probing (Appl. Phys. Lett.89, 031915 (2006)). Our current measurements have employed the Ca test with electrical resistance probing. The electrical resistance probing method is based on previous work by Paetzold and coworkers (Rev. Sci. Instrum. 74, 5147 (2003)). The change of the electrical resistance of the Ca film versus time can be related to the WVTR.
The current results are also obtained using a new ALD reactor that is connected to a glove box that is interfaced to a PVD chamber. This apparatus allows Ca test films to be prepared, transferred into the glove box and then positioned in the ALD reactor all under oxygen-free conditions. The glove box also helps to reduce particle contamination that may be the dominant factor in determining the WVTR. Using this apparatus, we have measured even lower WVTR values of ~2 x10-5 g/m2/day at 70oC/28% RH with an Al2O3 ALD film thickness of 25 nm. This is the lowest WVTR value measured at elevated temperature for a single layer barrier film.
The Al2O3 ALD barriers are also deposited directly on the Ca films. This configuration allows the Ca test film to visualize the defects in the Al2O3 ALD barrier. As the calcium oxidizes, the transition from shiny metal to clear calcium oxide can monitor the number and distribution of defects in the Al2O3 ALD film. The experiments demonstrate that the calcium oxidation is dominated by a few pinhole defects. The WVTR value of ~2 x 10-5 g/m2/day is consistent with several defects per cm2 in the Al2O3 ALD film. The resistance increases as these pinholes lead to the oxidation of circular regions of the Ca film that grow with time.