ABSTRACT
The first miniaturized chip was fabricated on a Si wafer for gas chromatography (GC; see Figure 6.1) [1]. Isotropic etch on a 200-
µ
m thick Si <100> wafer (5 cm diameter) produced a spiral GC channel (200
µ
m wide, 30
µ
m deep, 1.5 m long). A relatively short capillary length (1.5 m) with an OV-101 stationary phase was used for GC analysis of hydrocarbons. An etched Si miniature valve with a Ni diaphragm (activated by a solenoid plunger) was used for injections. The separation was completed in less than 10 s. However, the plate numbers only range from 385 to 2300, and n-hexane and chloroform were not resolved. The GC chip was incorporated with a thermal conductivity detector (TCD) which was separately fabricated on another Si chip. It consisted of an etched cavity in order to reduce thermal mass and to shorten the thermal time constant to about 1 ms. The cavity was insulated by thermal SiO
(100 nm), sputtered with Pyrex glass (1.5
µ
m) and patterned with a Ni thin-film (100 nm) resistor [1]. GC analysis was also carried out on a Si-glass chip using an off-chip flame
ionization detector (FID). Figure 6.2 shows the Golay plots (cf. Van Deemter plots) of the n-C
peak when both the native and oxidized Si surfaces were used. H
is lower in native Si because of the less polar stationary phase. Figure 6.2
FIGURE 6.1
Photograph of a gas chromatograph integrated on silicon [1]. Reprinted with permission from IEEE.
