Field-emission electron gun for a MEMS electron microscope

摘要

This article presents a field-emission electron gun in tended for use in a MEMS(microelectromechanical system)electron microscope.Its fabricati on process follows the tech no logy of a miniature device under development built from silicon electrodes and glass spacers.The electron gun contains a silicon cathode with a single very sharp protrusion and a bundle of disordered CNTs deposited on its end(called a sharp silicon/CNT cathode).It was tested in diode and triode con figurations.For the diode con figuration,a low threshold voltage<1000V and a high emission current that reached 90 pA were obtained.After 30 min of operation at 900 V,the emission current decreased to 1.6 pA and was stable for at least 40 min,with RMS fluctuation in the anode current lower than 10%.The electron beam spot of the source was observed on the phosphor screen.In the diode configuration,the spot size was the same as the emission area(~10 pm)z which is a satisfactory result.In the triode configuration,an extraction electrode(gate)control function was reported.The gate limited the emission current and elongated the lifetime of the gun when the current limit was set.Moreover,the electron beam current fluctuations at the anode could be reduced to〜1%by using a feedback loop circuit that controls the gate voltage,regulating the anode current.The developed sharp silicon/CNT cathodes were used to test the MEMS electron source demonstrator,a key component of the MEMS electron microscope,operating under atmospheric pressure conditions.Cathodoluminescence of the phosphor layer(ZnS:Ag)deposited on the thin silicon nitride membrane(anode)was observed.