Understanding the Different Types of Nanoimprinting Techniques

Nanoimprint lithography is based on surface structuring with a template that includes multi-level patterns. The topographic patterns are to be transferred using the imprint method with the aim to obtain different functionalities. In regard to the current scenario, there are several methods by which Nanoimprinting is done. However, its two main types are hot embossing and UV-based Nanoimprint lithography.

• Hot Embossing: It is the process of structuring polymer films by embossing stamp into the polymer when it is heated above the glass transition temperature.

Process: A polymer sheet is heated on a substrate at a temperature above the glass transition temperature. Then the characters are imprinted on the substrate by pressing the scale mask or applying a contact force on the stack. Before releasing the template material, it is allowed to cool down naturally. However, it’s important to note that the type of stamp material or substrate depends on the required size, thickness, and features of the material.

Advantages: Hot embossing is less prone to defects as compared to other techniques. Also, the technique is not limited to nano or microstructures. It is considered best for optical applications where high precision and high-quality are important. Additionally, hot embossing has the potential to decrease the production costs with the enlargement and automation of the molding process.

Applications: Microfluidics, lab-on-chip systems, life sciences, patterned media, and rapid prototyping.

• UV-based Nanoimprint technique: In it, a photo-curable resist is used to withstand the UV-light exposure.

Process: First, the chamber is pre-heated at the temperature higher than the glass transition of the polymer. During the heating time, the substrate or the material is placed in the embossing chamber. Once the temperature reaches the imprinting heat, contact force is applied, which is applied until the characters are properly imprinted. Finally, the substrate is removed from the chamber. The total cycle time for this process is 3 to 20 minutes, including the heating and cooling capabilities of the equipment.

Advantages: It facilitates multi-level patterning with high precision and high-quality. The process of this technique is much easier and can be performed at room temperature, without generating thermal gradients. Also, the cycle time of this technique is shorter and stamps can be easily obtained by casting and curing a liquid precursor onto a silicon master.

Applications: Biological applications, Telecommunication, and 3D Screening.

Both the processes can be performed with either hard template materials like nickel, Silicon, and quartz glass or soft working stamp materials. Depending on the available equipment and type of imprint material, either hot embossing or UV-based technique can be chosen.