Stress Management in Thin-Film Gas-Permeation Barriers
Andreas Behrendt1, Jens Meyer2, Peter van de Weijer3
1Institute of Electronic Devices, University of Wuppertal , Rainer-Gruenter-Str. 21, 42119 Wuppertal, Germany.
ACS Applied Materials & Interfaces
|January 22, 2016
Summary
Atomic layer deposition (ALD) creates gas diffusion barriers (GDBs) with high tensile stress. Adding compressive layers enhances GDB robustness, preventing cracking in organic electronics under harsh conditions.
Area of Science:
- Materials Science
- Nanotechnology
- Mechanical Engineering
Background:
- Gas diffusion barriers (GDBs) are critical for protecting sensitive materials, particularly organic electronic devices, from environmental factors like oxygen and moisture.
- Atomic layer deposition (ALD) is a widely used technique for fabricating thin-film barriers due to its precise control over layer thickness and conformality.
Purpose of the Study:
- To investigate the mechanical properties, specifically intrinsic stress, of GDBs fabricated using ALD.
- To determine the critical mechanical force threshold for cracking and delamination of ALD GDBs on organic electronic devices.
- To develop strategies for enhancing the robustness of GDBs to ensure long-term device stability under operational stress.
Main Methods:
- Fabrication of GDBs using various ALD processes.
- Measurement of intrinsic mechanical tensile stress in ALD-grown barrier layers.
- Derivation of the critical membrane force for GDB failure (cracking and delamination).
- Introduction of compressively strained layers (e.g., metals, SiNx) to counteract tensile stress.
- Testing of the enhanced GDBs on organic light-emitting diodes (OLEDs) under accelerated damp heat conditions (85 °C/85% relative humidity).
Main Results:
- ALD-processed barrier layers exhibit significant intrinsic tensile stress, typically in the range of 400-500 MPa.
- A critical membrane force of 1200 GPaÅ was determined for the onset of cracking and delamination, corresponding to approximately 300 nm thickness.
- Thicker GDBs are beneficial for encapsulating defects but increase the risk of mechanical failure due to higher tensile stress.
- The integration of compressively strained layers effectively reduced the overall membrane force below the critical threshold.
- The modified GDBs demonstrated excellent robustness, preventing cracking and delamination even under severe damp heat conditions.
Conclusions:
- Intrinsic tensile stress in ALD GDBs poses a significant challenge for their application on flexible and organic electronics.
- A novel approach using compressively strained layers successfully mitigates the detrimental effects of tensile stress, leading to highly robust gas diffusion barriers.
- These robust GDBs are crucial for enhancing the long-term reliability and performance of organic electronic devices in demanding environments.
