Project Acronym: PROXIMA
Full title: Portable RObust X-ray IMAge detector based on a flexible TFT array with organic and metal oxide semiconductors and an X-ray convertor.
Project duration: 30 months
Coordinator: Agfa N.V., Septestraat 27, B-2640 Mortsel, Belgium
Contact: dirk.vandenbroucke@agfa.com
Project website address: n/a
Executive summary
A completely new and disruptive X-ray photonic sensor for medical applications will be demonstrated by PROXIMA presenting the following advantages over state of the art: 1) low-cost to facilitate its adoption by low-budget hospitals and in developing countries where healthcare budgets are limited, 2) lightweight and robust allowing it to be easily carried to point of care and remote trauma 3) of high image quality in the low exposure limit to allow for dose reduction 4) conformable to enable advantages in cone-beam CT, tomosynthesis, dental or NDT applications. These benefits will arise by manufacturing the active matrix arrays with a flexible complementary and hybrid thin-film transistor technology consisting of organic and non-critical metal oxide semiconductors with organic dielectrics on plastic substrates and combine it with a flexible X-ray photoconductor.
Main work packages are: 1) the deposition of the n-type metal oxide semiconductor on the plastic substrate, and its integration with the p-type organic semiconductor to form a CMOS type backplane; 2) the development of a pigment in binder (PiB) coated X-ray photoconductor layer and its integration on the backplane; 3) the development of prototype read-out hardware and software to image-wise read-out the X-ray detector prototype. The final demonstrator, as well as intermediate demonstrators based on the combination of an organic p-type backplane and a PiB X-ray photoconductor or a hybrid complementary logic backplane combined with an organic photodiode and a flexible X-ray scintillator as intermediate test frame for the final concept will be evaluated in a medical relevant environment.
Final project summary
Realizing a complementary circuit on a flexible substrate required in the first place the development of a deposition method of the n-type metal oxide semiconductor compatible with the restrictions imposed by plastic substrates. The performance of the resulting TFT did match the specification as fixed in the WP1. The integration with the p-type organic transistor was more difficult than expected. Factors negatively influencing the performance of the complementary TFT’s were identified and eliminated for 90%. However, finalizing the complementary logic in a demonstrator was not possible within the project time and budget, mainly due to the COVID-19 pandemic.
We mainly focused on a CsPbBr3 perovskite to check the feasibility of developing a low cost X-ray photoconductor based on pigment in binder (PiB) coated layers. We developed a method to make the material via aqueous HBr precipitation. This leads to an orange 100% pure microcrystalline powder, with well-defined crystal morphology. An optimized coating of the material with a specific binder demonstrated high photoconductivity vs. dark current (PC/DC) efficiency, both for visual light and for X-rays. This high quality was demonstrated even for an A4 format when the material was coated on a PEN/ITO substrate. Single pixel 1.5 cm x 1.5 cm samples tested in a medical X-ray modality at RQA 5 beam quality indicated a nearly 100% collection efficiency of the photocharges. Alternative lead-free perovskites were also tested, but did not demonstrate high PC/DC efficiencies when coated in PiB layers. Agfa was in contact with flat panel detector (FPD) manufacturers in trying to valorize the concept of the CsPbBr3 PiB coated photoconductor as a component for a direct type FPD. A co-development with a potential partner was proposed, but so far an agreement is pending.
To demonstrate the PROXIMA concepts, a read-out system and associated software was developed to read all planned FPD prototypes with a single set-up. An organic p-type flexible backplane in combination with the coated photoconductor was tested, but did not show image-wise X-ray information in the first test of the prototype read-out hardware/software. Due to the pandemic, further demonstrators could not be prepared and tested.
The cooperation between FE and UNINOVA has accelerated the hybrid complementary technology that has been on FE’s roadmap. For UNINOVA, a unique platform was given for fundamental research resulting in new directions for future fundamental research, namely on ultra-low temperature processes for flexible electronics and device integration. Without FE and UNINOVA, Agfa could have not evaluated the potential of the low cost X-ray photoconductors for the use with innovative backplanes on plastic.
