The Japanese research institute Riken uses a laser to expose microfluidic 3D structures in FOTURAN^® samples. The goal is to produce novel 3D biochips for use in biotechnology research. Photo: SCHOTT/C. Costard

Material with unlimited possibilities

Biochips, nanosatellites, micro-assembly tools – the photostructurable FOTURAN^® is emerging as a material for innovative applications beyond microfluidics.

Thilo Horvatitsch

More than 1,000 hits in the scientific database Google Scholar show how well known FOTURAN^® photostructurable glass is to materials scientists. Developed back in 1984, this technical glass has found a home thousands of times, especially in microfluidics for medical analyses. For example, samples are placed in the tiny wells of microtiter plates or fluids are guided through fine channels, mixed and analyzed.

This material is ideal for producing these types of microstructures. The glass system consisting of lithium and aluminosilicates is doped with silver and cerium oxides and is highly photosensitive. If ultraviolet (UV) light lands on the glass through a photomask, silver nuclei form in the exposed sectors. Subsequent heat treatment triggers fast crystalline nucleus growth. These crystallized areas can now be etched away using hydrofluoric acid. This results in very fine structures of only a few micrometers in size without using photoresists such as conventional glass or silicon.

The Aerospace Corporation in the United States uses FOTURAN^® to produce components for nanosatellites: to the right a multiwafer from the structurable material, to the left a control unit. Photo: Aerospace Corporation

Its photostructurability, high transmittance and chemical and temperature resistance have made FOTURAN^® the material of choice as an alternative to plastics for very interesting developments. SCHOTT learned how interesting it is by conducting a comprehensive market survey. ”We were surprised to learn how our material is being used by the demanding material science community and what impressive products can be produced with it,” says Fredrik Prince, Director Global Product Management Thin Glass&Wafer at SCHOTT.

They range from nanosatellites (see page 35), micro-assembly tools and micromachining to pioneering biotechnological applications based on 3D laser structuring. RIKEN, Japan’s largest institute for extensive research in science and technology, for example, uses a femtosecond laser to expose microfluidic 3D structures in FOTURAN^®. A combination of heat treatments and etching can create not only microchannels, but also movable elements such as micro valves or pumps for controlling fluids, for example. In addition, researchers use special processes to produce microstructures and extremely small biomimetic flow structures made of plastic in the 3D glass channels.

”With FOTURAN^® II unmatched microgeometry
ratios can now be achieved.”

Fredrik Prince,
Vice President Thin Glass&Wafer

Enhanced manufacturing for improved benefits

SCHOTT’s photo-sensitive FOTURAN^® II glass wafers can be structured and processed in three steps: UV-exposure, tempering, etching, and optionally ceramization.

”The goal of these developments is ultimately to produce novel, multi-layered and multi-functional 3D biochips for use in advanced biotechnology research. Here, FOTURAN^® photostructurable glass used as a chip substrate offers several advantages over quartz glass. It is extremely important to be able to achieve high surface quality and optical quality through the thermal treatment of the material after etching.

The sensor manufacturer Innovative Sensor Technology IST AG (www.ist-ag.com) produces extremely small flow sensors for thermal mass flow measurement of gases. This is where FOTURAN^® leverages its precise structurability and its high temperature and chemical resistance. Thousands of these types of sensors are already being used. Photo: SCHOTT/C. Costard

This is essential for our biotech applications, including close monitoring of biological cells or microorganisms and their behavior,” explains Koji Sugioka, Senior Research Scientist at RIKEN Center for Advanced Photonics. But these are not the only types of projects that prove the 30-year old FOTURAN^® photostructurable glass holds future potential, however. SCHOTT has also seen an increase in demand from the semiconductor industry in recent years. For example, this material can be used as a substrate in chip packaging, where the goal is also to produce microstructures.

Against this backdrop, SCHOTT has developed an improved melting technique and increased the quality of the glass. First and foremost, FOTURAN^® II offers greater homogeneity and thus more stable photosensitivity. ”Much finer microstructures and unmatched microgeometry ratios can now be produced,” says Fredrik Prince. Directly available from SCHOTT as wafers and square substrates, or as finished components from a broad partner network, the improved glass is highly promising for use in high-frequency technology, such as filter elements for efficient separation of channels in frequency ranges for mobile data communication thanks to its high-precision structurability. It opens up many possibilities – for a proven material with a bright future. —