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Capacitance diaphragm gauges have been realized by microelectromechanical system (MEMS) technology. The full-scale pressure ranges of the developed sensor chips are four types (1, 10, 100 and 1,000mbar) and all these sensor chips were produced by the same process except for one etching process. This technique has brought advantages on cost and mass production. The vacuum sensor chips are composed of single crystal silicon and glass, and are as small as 20mm x 20mm in size and only 2grams in weight. Nevertheless, their performances are as well as or better than conventional capacitance diaphragm gauges.
As one of our major interests in the characteristics of MEMS capacitance diaphragm gauge is a mechanical stability, the change in full-scale voltage through the repeat between atmospheric pressure and vacuum (< 0.2mbar) of one million times was evaluated, and resulted in the change of full-scale voltage within 0.5%. This result confirms that the single crystal diaphragm is free from creep or plastic deformation.
The performances of these capacitance diaphragm gauges were also evaluated on a practical vacuum chamber for sputtering. The monitored output signal properly showed the pressure change in accordance with the process events such as Argon gas introduction, discharge start and stop, etc.
On the process of these evaluations, comparison with conventional metal diaphragm capacitance gauge has been carried out, and an interesting difference has been found out. That is, the MEMS capacitance diaphragm gauges are hardly affected by mechanical vibrations. It has been seen that the output signals of conventional metal diaphragm gauge contains some noises derived from a mechanical pump's vibration, but on the contrary those of MEMS diaphragm gauge contains less noise from mechanical pumps. It is thought that the realization of small and lightweight diaphragm enables the gauges to avoid mechanical synchronization at certain frequencies which general mechanical pumps generate.
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