Hybrid detectors consist of two key components, a semiconductor sensor and a readout Application Specific Integrated Circuit (ASIC). X-ray photons that have passed through, been scattered by, or emitted from the sample are stopped in the sensor material, creating a cloud of charge where the number of free electrons created is proportional to the energy of the X-ray. These charge clouds then drift across the sensor and the ASIC can measure the amount of charge and its position.
The HEXITEC ASIC is a novel energy-resolving pixelated readout chip, with 80 × 80 pixels on a 250µm pitch. Unlike single photon counting detectors, HEXITEC detects both the presence of an X-ray photon and the magnitude of the induced charge it has created, providing information on the energy of the initial X-ray. This gives HEXITEC its excellent energy-resolving capability, allowing for simultaneous imaging of a wide range of X-ray energies that provide an extra dimension of “colour” information across the 80x80 pixels per detector module, allowing direct access to the sample’s chemical composition and microstructure.
Another key capability of HEXITEC is the ability to work at high-X-ray energies. Many direct conversion X-ray imaging systems rely on silicon-based sensors whose efficiency drops dramatically at energies of about 15 keV. HEXITEC makes use of sensors produced from high density compound semiconductor materials like cadmium zinc telluride (CdZnTe), allowing operation across a broad range of energies from 4 keV up to 600 keV.
(Left) HEXITEC GigE system (Right) HEXITEC 2x2 system with Cadmium Zinc Telluride (CZT)
The HEXITEC family of technologies covers both low-flux (<104 photons s-1mm-2) and high-flux (<108 photons s-1mm-2) applications. The original low-flux HEXITEC technology provides <1 keV FWHM energy resolution at 60 keV with detector modules of 80 x 80 pixels on a 250 µm pitch; it operates at a maximum frame rate of 9.5 kHz.
The high-flux HEXITEC system, HEXITECMHz, maintains the same pixel pitch and array size as the original system. To provide a spectroscopic imaging capability at higher fluxes, the detector system works at a continuous frame rate of 1 million frames a second and delivers a spectroscopic resolution of 1 keV at 60 keV. No other detector system has this capability.
HEXITECMHz camera system
Stages of Development
The original HEXITEC detector is an established technology since 2012; it is fully developed and ready for licensing (Technology Readiness Level (TRL) = 9). The detector system has been characterised in laboratory settings and at large-scale facilities such as Diamond Light Source (DLS) synchrotron, the European Synchrotron Radiation Facility (ESRF), and the NASA Goddard Space Flight Centre.
The original HEXITEC ASIC has also been incorporated into a range of camera systems with varying numbers of detectors per system, currently available to purchase from Quantum Detectors or from STFC directly. These camera systems have been purchased and used by over 30 academic institutes worldwide for research purposes.
As of Summer 2024, the HEXITECMHz system is at TRL = 5. A prototype of the high-flux HEXITECMHz detector has been characterised in a laboratory setting as well as at DLS and ESRF synchrotrons. A new, fully productised, camera system has been produced and was used in initial scientific experiments at DLS in October 2024 – it will be ready for commercial sales soon.
