Miniaturization of Polymer Shape Memory Patterns

The Journal Article:

Constrained shrinking of nanoimprinted pre-stressed polymer films to achieve programmable, high-resolution, miniaturized nanopatterns

Shady Sayed et al., Nanotechnology 32, 505301 (2021)

DOI: https://doi.org/10.1088/1361-6528/ac244d

Featured Image by Barbara A Lane from Pixabay

Why should I care about this article?

I would bet that most people reading this blog post has, at some point in their life, enjoyed coloring and creating miniaturized crafts with Shrinky Dinks. After all, it is much easier to color and cut out a large icon and THEN shrink it for your charm bracelet. The idea behind this nifty kid’s craft has expanded into an ever-growing field of research. While there are many types of ‘Smart Materials’, this article focuses on shape memory polymers. Aside from artistic applications, these polymers are being researched and produced for aerospace instruments such as self-unfolding hinges for spacecraft solar panels, biomedical tools such as surgical grippers, flexible electronics and wearable devices, and 4D printed tools and furniture, among other fantastic things. To read a lot more detail about these applications, check out this great review article²; click here and head to section 4 at the end of page 16.

For some cool videos of 4D printed ‘Smart Materials’ items, check out this video³!

How does this article address these applications/concerns?

As electronic device fabrication gets smaller and smaller, researchers are always looking for new and novel ways to get small, reproducible features. The authors of this article present combining two techniques, one that is used for high throughput and reproducibility of patterns and another that shrinks patterns to smaller sizes.

Nanoimprint lithography (NIL) is a technique that uses a master pattern mold fabricated by electron-beam lithography to stamp reproducible patterns into a polymer material coated on another substrate. Each new pattern requires a new mold, and anything smaller than ~100 nm significantly increases the complexity of the master mold fabrication.

Shape memory polymers (SMPs) is a material that can be molded and then returned to its original shape using heat, light, or electricity. However, use of these types of materials in the past has lead to loss of pattern definition and problems with returning to the original shape.

By combining these two techniques, the authors show a way to use one master mold to create tailored sub 100 nm patterns with SMPs.

What are the results from this article¹?

The patterns are made with the following process shown in Figure 1 from the journal article. A. The master mold is applied to the substrate. B. The substrate is heated under pressure from the master mold to transfer the pattern. C. The new pattern is held in one direction and heated to shrink the opposite direction. D. The hold and heat process is repeated for the opposite direction. During the shrinking process, patterns were shown to shrink up to ~50% of the original master mold. By using the two step shrink process, the authors were able to keep pattern definition unlike previous research.

The authors showed this process using patterns of arrayed lines and holes. Shown here is Figure 4 from the article which uses an array of patterned holes. A. and D. show the original pattern. B. and E. show the corresponding shrunk patterns. And C. and F. show the shrunk patterns from an inclined view.

The authors also showed the ability to tailor the size of the shrunk pattern by changing the heating time. In this case, the new patterns were heated to 130 °C. When heated for 4.5 minutes in each direction the pattern shrunk 17%. At 6 min of heating it was shrunk by 32%. And finally the full 50% reduction was achieved at 9 min of heating. This demonstrates the ability of one master mold to imprint the SMP and tailor the resultant pattern size.

The Takeaway.

The authors combined a master pattern mold with shrinky dink polymer films to create sub ~100 nm patterns of tailorable size, for applications in nanoscale electronic devices.

Citations

(1) Shady Sayed et al., Nanotechnology 32, 505301 (2021)

(2) Y. Xia et al., Advanced Materials 33, 2000713 (2021)

(3) https://www.youtube.com/watch?v=CLjUHrx7amc