IMEC, VUB Create On-wafer Chromatograph with Sub-micron Micromachining

IMEC and the VUB (Vrije Universiteit Brussel) have built and demonstrated an on-wafer liquid phase chromatograph, using sub-micron micromachining. Measurements show a 5- to 10-fold increase in speed of analysis and an improved separation capacity compared to state-of-the-art macroscopic chromatographs.

The device has 56 separation channels with a length of 4cm, a width of 50-150µm, and a depth of 5-18µm. The channels are packed with vertical micro-cylinders. These pillars are 1-5µm thick, and are separated by gaps of 1-0.1µm. Within one channel, all pillars have an identical shape, size, and distance. The chromatograph was implemented on a 200mm Si wafer. First, a Si oxide layer was deposited on the wafer, on which the submicron structures of the chromatograph were patterned and etched. Next, with the silicon (Si) oxide layer as hard mask, the separation channels and the pillars were etched with deep reactive ion etching (DRIE). The separation channels were then connected via wider interconnecting supply channels. A 200mm glass wafer was bonded to the Si wafer, serving as a roof to close off the open separation channels. And last, access holes were etched through the back of the Si wafer.

A comparison with commercial chromatographs with macroscopic tubes shows that the micro-chromatograph is 5 to 10 times as fast, and has a better separation capacity. Also, unlike with macro-chromatographs, the separation does not degrade with higher velocities of molecule transport. The performance of the chromatograph was tested by injecting a fluid with tracer molecules in the chromatograph and following the velocity and width of the resulting tracer band.

Liquid phase chromatography is a powerful technique to separate and identify molecules. It is used, for example, in biochemistry labs to separate proteins. The molecules — suspended in a liquid — are separated by forcing them through macroscopic columns filled with micron-sized, randomly packed spherical particles. This sub-micro chromatograph validates fluid dynamic computations that predict that injecting molecules though a submicron maze of perfectly ordered structures will considerably increase the separation speed of liquid phase chromatography.

Cylindrical pillars in the separation channel, etched with DRIE, using Si oxide as hard mask.

About IMEC
IMEC is a world-leading independent research center in nanoelectronics and nanotechnology. Its research focuses on the next generations of chips and systems, and on the enabling technologies for ambient intelligence. IMEC’s research bridges the gap between fundamental research at universities and technology development in industry. Its unique balance of processing and system know-how, intellectual property portfolio, state-of-the-art infrastructure and its strong network of companies, universities and research institutes worldwide position IMEC as a key partner for shaping technologies for future systems. IMEC vzw is headquartered in Leuven, Belgium, has a sister company in the Netherlands, IMEC-NL, concentrating on wireless autonomous transducer solutions, and has representatives in the US, China and Japan. Its staff of more than 1500 people includes more than 500 industrial residents and guest researchers. In 2006, its revenue (P&L) was EUR 227 million.