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X-rays are produced when accelerated electrons hit a positively biased target. For over a hundred years, the electron beam in X-ray tubes has been produced by heating a tungsten filament to over 2000°C (hence the “Hot Cathode” X-ray tube). This is now about to change: the tech company Nanox Imaging Ltd is developing amulti-source Digital Tomosynthesis system where the electron stream is generated by a field-emission chip (Hence a “Cold Cathode” tube). Tomosynthesis enhances anatomy visualization with multiple layers and reduces the super-imposition of structures. The chip containing the field emitter array for the new system is microfabricated at CSEM’s specialized MEMS foundry services, among others.
Scanning electron microscope picture of an array of nano cones. Each nano cone is located inside a nano cavity. Electrons are extracted from the nano cones by applying a voltage to the top gate electrode.
CSEM, in partnership with Nanox, has now been capable of producing fully functional MEMS chips to be integrated into the Nanox.ARC system and other applications as well. The MEMS chip consists of millions of homogeneous nano-cones, regularly spaced and uniformly shaped refractory metal cones – each only a few hundred nanometers in size – arranged on an area of about seven square millimeters. For electron emission, a positive voltage is applied to the grid and pulls a stream of electrons from the tips of the cones.
“For the generation of millions of nano-cones of exactly the same height we had to develop a unique electro-chemical etching,” says senior project leader Thomas Overstolz, Senior R&D Engineer at CSEM. “The etching process had to be very precise and timed to the second.” The production took place at the state-of-the-art cleanroom of the specialized MEMS foundry at CSEM.
As Thomas Overstolz reports, the initial tests of the microfabricated MEMS delivered promising results. CSEM and Nanox have produced and performed positive functional testing on the first wafers and chips .
The project team around Thomas Overstolz is ready to refine the micromanufacturing process in collaboration with the Nanox technical team, as he stated, “CSEM is also prepared to eventually produce the MEMS chip in industrial volume for Nanox.”
NANOX General Manager of Source & Services Division & Head of Nanox USA, Jim Dara, has high praise for the good partnership with CSEM. “We greatly appreciate the professionalism demonstrated by the team at CSEM. They exhibited exceptional expertise both technically and in business. Their validation of Nanox technology enabled the production of a functional MEMS chip in under a year.”.
Nanox.ARC: 3D tomosynthesis imaging system.
The innovative Nanox.ARC system developed by NANOX has several advantages compared to the conventional imaging system. As mentioned, a tungsten filament must be heated to 2000°C. In contrast, the cold cathode tube does not need a standby current and can be turned on and off instantly with low voltage and milliamps current consumption. Also, because there is no need for a standby current, several vacuum tubes (or even several chips within a single tube) can be placed closely together while connected to the High kV and switched one by one with no X-ray radiation from the neighboring source. This is not possible to achieve with hot-cathode sources. Nanox intends to build tubes with CSEM chips in them, for testing and validation in the next stage.
The novel digital X-ray source is the basis of core technology in the imaging systems Nanox is developing. Nanox’s mission is to improve early detection and treatment, which they believe is key to helping people achieve better health outcomes Their goal is to enable medical institutions to incorporateend-to-end systems, or to adopt a modular approach by acquiring or licensing components to integrate Nanoxtechnologies into their specific products.
The team at CSEM is very pleased with finding an innovative solution for the microfabrication of a functional MEMS chip for industrial partner Nanox. This project is an excellent showcase for our specialized MEMS foundry services. If you are looking for a competent and experienced partner for prototyping and industrializing your next-generation MEMS chip, please get in touch!