- Different materials to match different ambient conditions
- Pirani for higher pressures, Bayard-Alpert for UHV
- Supplied with accessories (connectors, cables) to get a complete measurement function
Bayard Alpert gauges are workhorses’ components in UHV measurements. Their technology enable very low-pressure measurement, down in the 10-12 Torr range.
Working principle is based on ionization of gas molecules, which are attracted by a collector; measurement of current intensity is directly linked to the gas molecule density, ie, the pressure.
There are two types of materials commonly used for filaments cathodes in Bayard Alpert gauges (vacuum measurements), tungsten or iridium. Two types of coatings are also used on the filaments : thorium or yttrium.
Generally, filaments are thoria- coated iridium, and yttria-coated or uncoated tungsten. The most common style is coated iridium: it operates at lower temperature than tungsten and, therefore, is less reactive. Coated iridium filaments are also more burnout resistant when exposed to a harsh environment or to atmospheric pressure.
Riber recommendations are to install tungsten filaments in the growth chambers when no harsh environment and iridium filament in all other chambers like load lock chambers, buffer and degassing chambers.
Another type of gauge which is traditionally used in vacuum measurement, for higher pressure (atmosphere down to 10-3/10-4 Torr range) is the Pirani technology, It is linked to thermal loss measurement from a heated filament towards gas molecules; the higher the losses, the higher the pressure.
|Characteristics||Bayard Alpert gauge||Pirani-type gauge||Dual BA/Pirani gauge|
|Filament type||Tungsten (W) or Thoria-coated Iridium (Ir/Th)||Gold-plated Tungsten||Yttria-coated Iridium|
|Typical pressure range||10-3 to 2.10-11 Torr||Atm to 10-4 Torr||Atm to 10-9 Torr|
|Typically used in||Growth Chamber pumping well, buffer chamber, transfershuttle, cluster, loading chamber||Growth Chamber pumping well, buffer chamber, transfer shuttle, cluster, loading chamber||Loading chamber, flip chamber, cold finger|