Photo: Gears, laser-cut in 1 mm silica glass
The component has to be processed
right up to the edge to ensure the
channel has an entry and exit
©Fraunhofer ILT

This process enables micrometer-fine structures to be created in transparent material like silica glass, borosilicate glass, sapphire and ruby.

Biochips with microchannels measuring 100 micrometers in diameter, the same thickness as a strand of human hair, are used for quick tests in medical research. The channels in the small thin plates hold around a drop of fluid – blood in most cases – which is analyzed with the aid of specialized medical equipment.

At present, biochips made out of plastic are used for this kind of application. However, substances from the plastic can diffuse into the test fluid and distort test results. Partners from the field of medical engineering are therefore increasingly asking for biochips made out of glass. These glass biochips are chemically neutral and essentially better suited for medical analysis applications than their plastic counterparts. The only problem so far, however, has been the lack of a suitable process for manufacturing microchannels in glass components.

The ISLE process from Fraunhofer ILT now for the first time provides a manufacturing process for microchannels, shaped holes and cuts in transparent glass material. Selective laser-induced etching first involves irradiating the transparent component internally with a laser at the point where a structure, a channel for instance, will subsequently be created. It is important that the component is also processed right up to the edge to ensure the channel has an entry and exit. At the irradiated points, the material now has a different structure than at the untreated points. It exhibits 300-times higher etchability than the unexposed material. The component is then immersed in a bath containing special, environmentally friendly etching fluid, enabling the exposed material to be etched away.

Next, the component is cleaned, leaving behind the required geometry, in this case a fine system of channels. But this process can also be used to drill holes, to manufacture tiny pipes with a wall thickness of eight 8 micrometers and measuring one millimeter in both diameter and length, or to produce miniature gears for the watchmaking industry.

"The greatest challenge is to avoid damaging the glass", says Doctor Jens Gottmann, project manager at the Fraunhofer ILT. "The remelting in the glass produces stresses that cause the material to crack and make the component unusable. It's all about finding the optimum irradiation parameters, something we are constantly working on."; Source: Fraunhofer Institute for Laser Technology ILT