Freestanding microheaters in Si with high aspect ratio microstructures

Freestanding, high aspect ratio microstructures in Si were micromachined as thick microheaters. These microheaters, combined with adsorbents, can be used as preconcentrators in a micromachined gas chromatography system. Dry etching of Si using etch and passivation cycles has been developed to produce 240 μm thick Si microheaters with 3 μm wide wires, achieving a high aspect ratio of 80:1. This optimized dry etching technology results in high etch rates with vertical profiles for thick Si microheaters up to 535 μm. Microheaters with 40 μm wide wires, 110 μm gaps, 400 μm thick, and an area of 9 mm2 have been fabricated. With the heater on a 140 μm thick Si membrane, it takes 1320 mW to increase the temperature by 290 °C. The power consumption is reduced to 447 mW for the same temperature raise with a freestanding Si microheater. Heating response for freestanding Si microheaters with different thicknesses is also studied. These Si microheaters have fast response times and reach 75% of the final temperature in 5 s. Microheaters consisting of Si wires and posts show similar response time and heating uniformity. In addition, power consumption is reduced by thermal isolation of the microheaters. These thick, freestanding high aspect ratio Si microheaters can provide high power efficiency, large adsorbent capacity, and high mechanical strength.