FE, or field emission, refers to a phenomenon where high-density electrons are emitted when a strong electric field is applied to a cathode (electron emission element) with a sharpened tip.

FE technology provides an electron beam that is approximately 1,000 times more dense (high intensity) than conventional thermionic electron cathodes. This technology has been applied to the development of FE electron beam sources. However, given the difficulty of stabilizing FE electron beam sources, it was considered to be extremely challenging to develop practical FE technology at the time. That was when Hitachi realized that FE electron beam sources could be stabilized by housing the cathode in an ultra-high vacuum. Hitachi thus stabilized FE electron beam sources by concentrating on establishing ultra-high vacuum technology. By applying this technology to an electron beam source for an electron microscope, Hitachi achieved the world's highest level of resolution at the time. Today, Hitachi has dramatically improved the stability and reliability of FE electron beam sources by rigorously investigating and addressing all factors that could compromise the vacuum. While further boosting the performance of electron microscopes in terms of high resolution, this vacuum technology has become an important fundamental technology ensuring the stability and reliability of Hitachi's electron microscopes.