X-rays on a chip: characterization of a monolithically integrated MEMS X-ray source

• The first MEMS X-ray source integrated on a chip has been demonstrated. • Each parameter of the X-ray radiation can be independently controlled. • Emission currents, vacuum conditions and X-ray spectra are stabile in time. • MEMS X-ray source enables compact XRF analysis with milliwatt-level power use. Miniaturization of X-ray sources developed using MEMS (Micro-electro-mechanical Systems) technology hold significant potential to advance many measurement methods, applied for material analysis, portable diagnostics, and space exploration, through their compactness, low power consumption, and ease of integration. However, it may come true, only if the parameters of the miniature instruments will not be worse than the ones of the classical counterparts. In this work, we present a monolithically integrated MEMS X-ray source that combines a field emission cathode, an electron-optical column, a transmission target, and an integrated ion-sorption pump into a single, self-contained vacuum structure. We demonstrate that the source operates stably and repetitively thanks to the proper choice of the field emission material, device construction as well as thanks to providing and maintaining high vacuum conditions by the use of an integrated micropump. Within the article we characterize the source, and correlate how its parameters (emission stability, voltage control, spot size, vacuum conditions) translate into key properties of the generated X-rays, and how to tune them for different applications, especially for various measurement and analytical methods, especially to X-ray fluorescence (XRF) measurements. Spectral analysis confirms the generation of X-rays with well-controlled intensities and energies from several hundred eV to several tens of keV, including a sharp Si Kα line at 1.71 keV and continuous bremsstrahlung radiation. This fulfils perfectly the requirements of the XRF system.