Ha!! Too funny!! There's NO DOUBT that NLM steps all over 70+ LWLG Patents!!! funny how you used to tout that Lumera had the patents and LWLG would have to pay the royalties!!!! Also, there are disadvantages to crosslinking that have not been discussed, here
Disadvantages of Crosslinking in NLM Photonics' Materials
1. Reduced Electro-Optic Coefficient (r33?) 📉
One of the primary purposes of NLM's materials is their high electro-optic coefficient, which dictates how efficiently they can convert electrical signals into optical ones. Crosslinking, while beneficial for stability, can sometimes reduce this key performance parameter. For example, some materials might show a decrease from 460 pm/V without crosslinking to 290 pm/V with it. This trade-off between stability and performance is a significant consideration.
2. Potential for Increased Absorption (Optical Losses) 💡
Crosslinking can lead to a slight increase in optical absorption within the material. This means more light energy is lost as heat rather than being transmitted or modulated, which can reduce the efficiency of the photonic device. For instance, absorption might increase from <0.0001 to <0.0002 at a specific wavelength after crosslinking.
3. Processing Complexity and Specific Requirements 🧪
The crosslinking process adds an extra step to the fabrication of photonic devices. This step often requires specific conditions, such as:
UV light exposure: Many photo-crosslinking reactions are initiated by UV light, requiring specialized equipment and careful control of dosage and uniformity.
Photoinitiators: The use of photoinitiators can be necessary, and their choice affects the polymerization efficiency and the specific wavelength of light needed.
Oxygen inhibition: Photo-radical curing methods are often susceptible to inhibition by molecular oxygen, potentially leading to incomplete curing or tacky surfaces. This might necessitate an oxygen-free environment, adding cost and complexity.
Temperature control: While photo-crosslinking offers low-temperature processing advantages over thermal curing, precise temperature control during the reaction is still important.
4. Material Shrinkage and Heterogeneity 📏
The crosslinking process can induce shrinkage in the material as it forms a more compact network. This shrinkage can create stress within the device, potentially affecting its optical properties or long-term reliability. Additionally, chain-growth crosslinking can lead to a more heterogeneous network, which is also prone to more shrinkage and can reduce control over the final material properties.
5. Limited Design Flexibility in Some Cases 📐
Once a material is crosslinked, it forms a thermoset polymer, meaning its shape is largely fixed and cannot be easily re-melted or re-processed. This limits the ability to reshape or repair the material after crosslinking, which can be a disadvantage in certain manufacturing or application scenarios.
6. Compatibility with Other Fabrication Steps 🏭
While crosslinking makes the material resistant to common solvents, enabling subsequent processing steps, the thermal stability of NLM's materials (e.g., typically not withstanding temperatures >300 °C) can be a limitation for integration with certain high-temperature semiconductor foundry processes. However, NLM addresses this by integrating their materials post-foundry.
Despite these disadvantages, the benefits of enhanced thermal stability, chemical resistance, and mechanical strength provided by crosslinking are often crucial for the long-term performance and reliability of high-performance photonic devices. The challenge lies in optimizing the crosslinking process to minimize these drawbacks while maximizing the desired material properties.
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