Importance of Electrical Feedthroughs

High voltage electrical feedthroughs are used extensively in high vacuum and ultra high vacuum conditions. They enable the transmission of high voltages into and out of hermetically-sealed chambers without presenting a point of potential pressure loss due to the ingress of atmospheric gas.

Importance of High Voltage Electrical Feedthroughs

High vacuum conditions extend from approximately 10-5mbar – 10-9mbar. This pressure regime is achieved by evacuating a chamber to all but residual gaseous molecules. Collisions between these molecules and the walls of the vacuum chamber dominate the pressure regime, this requires a series of pumps to effectively evacuate the chamber. A rough vacuum pump is used to exhaust the bulk of the gases; however, at the onset of the high vacuum regime, a different pump is required to evacuate residual molecules once they have entered the pump aperture.

Ultra high vacuum conditions are even more severe, extending above 10-9mbar in almost entirely dry conditions. This pressure range is on an order of trillionths of the atmosphere. Whilst water molecules persist in high vacuum processes, it is primarily hydrogen (H2) which remains in ultra high vacuum conditions due to the high mobility and lightness of the gas. This requires specialist ultra high vacuum pumps and bakeout to achieve high purity vacuum conditions of greater than 10-9mbar.

Achieving high vacuum and ultra high vacuum conditions is a highly energy-intensive process which requires the backing of multiple pumps and hermetically-sealed processing chambers. High voltage electrical feedthroughs are required to adjust process conditions in real time without compromising the integrity of the vacuum. The designs of high voltage feedthroughs vary significantly depending on the chamber architecture and application requirements.

An electrical feedthrough connection might need to withstand considerable pressure differences across its length. Systems that operate under high vacuum conditions, such as electron microscopes, require electrical connections through the pressure vessel.

Types of Electrical Feedthroughs

Electrical feedthroughs are available as wire feedthroughs, as multiple feedthroughs with a plug or a feedthrough with a coaxial connector. There are different types of electrical feedthroughs used for different applications, including; coaxial, power, and thermocouple.

Coaxial Feedthroughs – in coaxial feedthroughs, one conductor is insulated with a dielectric material and is then surrounded by the other conductor. This is commonly referred to as the center conductor and shield; the shield is typically a serve, braid or foil braid configuration. The typical applications for this type of feedthrough include, video, RF and microwave.

Power Feedthroughs – power feedthroughs are solid or stranded conductors which are surrounded by insulation, shielding and a protective jacket. These feedthroughs are designed for high voltages, and are found in many applications including vacuum furnaces, sample heating, biasing and in-vacuum coating applications such as electron beam evaporation, resistive heating evaporation and DC plasma sputtering.

Thermocouple Feedthroughs Рas the name suggests, thermocouple feedthroughs are used for measuring temperatures. They function via a pair of wires of dissimilar metals (such as copper and iron), that are joined, with the free ends of the wires connected to an instrument (as a voltmeter) that measures the difference in potential created at the junction of the two metals. Thermocouple feedthroughs are not specifically temperature sensing devices, they are components used to conduct the thermocouple’s voltage (EMF) through the bulkhead of a chamber to external instrumentation.