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Advances in medical imaging require utilizing reliable and pioneering radiation detector technology. At STFC, in collaboration with US-based company MH3D Inc, we are helping to develop their world's first pre-clinical scanner, the Alpha-SPECT$^{TM}$ Mini. This scanner can select, measure and visualise the distribution of radionuclides during TAT (Targeted Alpha Therapy), a selective form of cancer treatment that is currently undergoing clinical trials.
The detector modules for the Alpha-SPECT$^{TM}$ Mini are fully assembled and radiation tested at STFC before integrating to the scanner. STFC has previously assembled radiation detectors with pitch as small as 55µm[1][2]. The hybrid detector module consists of a HEXITEC Application Specific Integrated Circuit read-out chip (ASIC)[3] and a compound semiconductor Cadmium Zinc Telluride (CZT) sensor for detecting gamma rays. The assembly process of the module starts with triple gold ball studding of the ASIC. The average height of the triple studs are ~40µm. For minimizing failure rates, first the ASICs are wire bonded to a PCB and then subjected to a Voltage pulse test before assembling on to a sensor. Afterwards, the tested module is assembled to a 6mm thick CZT printed uniformly with thixotropic silver epoxy on a pitch of 500µm and assembled on to the wirebonded ASIC using precise flip-chip technology, capable of placing a chip to an accuracy of 0.5µm. Finally, the assembled hybrid module is tested using Americium-241 and Cobalt-57 radiation sources. The tested full module has a spectroscopic energy resolution of 2keV full width half maximum (FWHM) measured at 60keV and a bond yield of 99.9%. STFC Technology department's detector integration facility has developed and implemented an advanced and improved assemble process that has now a capability of assembling hundreds of modules with high yield.
[1] Veale, Matthew Charles, et al. "Characterization of the uniformity of high-flux CdZnTe material." Sensors 20.10 (2020): 2747.
[2] Schneider, Andreas, et al. "Single Die Process Using Shadow Masks for a 55µm Fine Pitch Array of 4µm-Tall Indium Bumps Across an Entire Chip." 2024 IEEE 10th Electronics System-Integration Technology Conference (ESTC). IEEE, 2024.
[3] Jones, Laurence, et al. “HEXITEC ASIC - a pixellated readout chip for CZT detectors,” Nucl. Inst. Meth. Phys. Res. A: Accelerators, Spectrometers, Detectors and Associated Equipment vol. 604 issue 1-2, pp. 34-37, June 2009.