A simple method for microlens fabrication by the modified LIGA process

TLDR

Irradiation of PMMA with deep x‑rays reduces its molecular weight and glass transition temperature. Microlenses were fabricated by exposing PMMA to deep x‑rays followed by thermal treatment, where volume change, surface tension, and reflow shape the lenses and geometry is controlled by x‑ray dose, lens diameter, heating temperature, time, and cooling rate, enabling hemispherical, rectangular, star‑shaped, and other structures via a modified LIGA process. The method yields simple, high‑quality microlenses and arrays with surface roughness below 1 nm and diameters from 30 to 1500 µm.

Abstract

Microlenses and microlens arrays were fabricated using a novel fabrication technology based on the exposure of a resist (usually PMMA) to deep x-rays and subsequent thermal treatment. The fabrication technology is very simple and produces microlenses and microlens arrays with good surface roughness (less than 1 nm). The molecular weight and glass transition temperature of PMMA is reduced when it is irradiated with deep x-rays. The microlenses were produced through the effects of volume change, surface tension, and reflow during thermal treatment of irradiated PMMA. The geometry of the microlens was determined by parameters such as the x-ray dose applied to the PMMA, the diameter of the microlens, along with the heating temperature, heating time and cooling rate in the thermal treatment. Microlenses were produced with diameters ranging from 30 to 1500 μm. The modified LIGA process was used to construct not only hemispherical microlenses, but also structures that were rectangular-shaped, star-shaped, etc.