Applied Physics

Mokhtar Chmeissani

The focus of the applied physics research at IFAE is to develop sensor technologies with applications in medical imaging, high-energy physics and other scientific or industrial fields by exploting the valuable knowledge available at IFAE and fostering collaborations with other research centres in Catalonia like the Centro Nacional de Microelectronica (CNM), medical centers like Hospital Parc Taulí, or companies like Multiscan Technologies.

Introduction

In 2021, the medical imaging/applied physics group at IFAE has been very active, though COVID-19 has hampered the working efficiency especially when it comes to hardware construction and debugging. The team was very busy concluding the LINDA project, developing an ASIC for adaptive retinal implant, Simulation of Helmet-PET Scanner for brain imaging, and the initiation of Softpix project to detect soft X-ray photons. 3 patents have been granted, one in Japan and two in the US

LINDA (X-ray LINe Detector with novel photon counting ASIC)

LINDA project was funded by the EU through the FEDER program and the SUR department of the Generalitat de Catalunya (call PRODUCTE 2018), and it was concluded successfully in June 2021. The LINDA project delivered a 20 cm long Spectral X-ray Line Camera and it was mounted in a dedicated commercial X-ray scanner machine for food quality control. Soon after commissioning the LINDA Camera, Deep Detection SL, an IFAE startup started operating it and tuning its performance. In fig. 1, the 20 cm LINDA sensor can be seen and in fig. 2 is the installation and the commissioning of the LINDA camera with the Line scan X-ray machine and in fig.3 one can see preliminary results of detecting the anomalies in some products

Figure 1: shows a close-up view of the camera PCB with a protection box for the sensors. On the right hand side one can see the full view of the LINDA box camera which has two isolated compartments, above each other, in order to keep the sensors at controlled temperature. The top cover of the LINDA camera is made of carbon fiber to allow the X-ray photon to reach the LINDA sensor with minimal attenuation.

Figure 2: shows the integration of the LINDA Camera Box inside an X-ray Line scan machine for food quality control. IFAE mechanical workshop has designed a dedicated platform to hold the camera box firmly and accurately under the X-ray tube.

Figure 3: shows two sample products with contamination that have been identified with LINDA Camera. On the left-hand-side a chicken fillet with little bones. On the right-hand-side show mini-burgers with fragments of bones that have been easily identified. These images were produced by Deep Detection SL.

The LINDA line Scan X-ray machine is hosted in IFAE workshop to facilitate Deep-Detection team with Space and technical support during the evaluation of LINDA camera and the preparation for LINDA++ camera (40 cm long).

ASIC for Epi-retinal Implant for Vision Restoration

The Institut de Física d’Altes Energies (IFAE) and in collaboration with Catalan Institute of Nanoscience and Nanotechnology (ICN2), The Institute of Photonic Sciences (ICFO), Barraquer Foundation (BF) are developing the technology and the know-how for epi-retinal implant for vision restoration, figure 4. The prosthesis technology is capable of providing high-acuity artificial vision to individuals blinded by eye retinitis disease. In such eye disease, neurons responsible for conveying information to the brain remain alive. A retinal prosthesis electrically stimulates these neurons in a precise pattern to re-create vision sensation. IFAE is leading the development of a wireless (power and data) retinal prosthesis, patent protected. The project is funded by La Caxias Health Research Program.

Figure 4: shows schematically an array of electrodes (red color) made of graphene and are sandwiched between an ASIC (blue color) and the top layer of the retina and close to Ganglion cells. An external camera (mounted on a dedicated eyeglasses) captures an image frame and it gets sent to the ASIC wirelessly , via modulated light at high frequency that follow the pattern of data string (…00110001111….) to program each pixel/electrode on the ASIC. The same light is used as well to power the ASIC itself using Photo-Voltaic cell

In 2021 IFAE succeeded in the production of the 2nd prototype of epi-retinal implant ASIC with 1260 electrodes that can sense the activity on the neurons as shown in fig.5. The ASIC has been bonded to a fan-out signals substrate, designed and produced by ICN2 team, to make it possible to connect the ASIC to the rat retina at ICFO. It was possible to detect the neuron activation when the retina gets exposed to flashes of light. This will allow mapping the type of Retina Ganglion Cells beneath every pixel electrode.

Figure 5: shows on the left hand side a small fraction of the fan-out substrate developed by ICN2 with 40um solder balls deposited in the IFAE clean room. On the right one see the retina ASIC bonded to the fan-out substrate to get interfaced with rat retina setup at ICFO. The flip-chip was carried out in the IFAE clean room.

Figure 6-2: the photo-receivers on the retina ASIC

Figure 6-2: the response of the photo-receiver for different modulations.

Due to the high risk of failing to operate the implant wirelessly, and thus putting a premature end to the project, the IVISION consortium inclined to a more conservative approach and to do the test in-vivo with the retina ASIC encapsulated in a polyimide flex-cable. IFAE has taken the lead of this task and has done the design and the layout of the flex-cable as shown fig. 7-top. With this flex-cable the consortium will have a real assessment of the ASIC performance in true environment, beside its life time in the aqueous humor (the transparent liquid in eye) which is a tricky issue. The right end of the flex cable is the encapsulated retina ASIC. At 3 corners of the ASIC there are 3 holes which are meant to be used by the ophthalmologist to fix the encapsulated ASIC to the retina via tacks as shown in figure 7-bottom

Figure 7: the design/layout of the polyimide flex-cable of 40um thick and 50mm long. The right end of the flex-cable, where the retina ASIC is encapsulated insider the polyimide, one can see 3 holes which are meant to for tack pins to fix the flex the ASIC against the retina.

Helmet PET scanner

It is a study funded by the Ministerio de Ciencia e Innovación, based on simulation, to assess the performance of a Helmet PET scanner design, using a highly segmented detector with a stack of pixel CdTe sensors. To carry out a more realistic and convincing simulation of the PET scanner, a true PET/CT brain scan in DICOM format was imported and put as an object with FDG radiotracer in the Helmet PET scanner. The image reconstructed from the scanner shows it is able to reproduce the FDG uptake map by the brain as shown in fig. 8. Next step is to use a DICOM image of small animal PET that has a very high spatial resolution image. Though the gantry of Helmet PET is 270 mm, which is much bigger than that of small animal, usually has a gantry of 100 mm, nonetheless one should expect to achieve comparable results because the detector modules use for the Helmet PET scanner have excellent accuracy in detecting the position of the absorbed photon and with high energy resolution to reduce the impact of the scattered photos.

SOFTPIX

Softpix project is funded by the Ministerio de Ciencia e Innovación and has started September 2021. It is a coordinated project between IFAE and CNM-IMB to develop a spectral photon counting pixel sensor for very soft X-ray photons, or in another word a very low energy photons. Detection a low energy photon is possible by using pixel ASIC like Timepix4/Medipix4.

Both ASICs have low noise level and the minimum threshold is around 2 keV. If one bonds LGAD (Low Gain Avalanche Detector) sensor with a gain factor of 10 with Timepix4/Medipix4, as shown in fig. 9, then one can have a Spectral X-ray imaging in the range of 0.5keV down to 0.2keV. This range of soft X-ray photons has plenty of applications in Synchrotron Labs and on the table-top setup, such as X-ray diffraction and radiography for small/soft objects. In Softpix project, CNM-IMB will develop the LGAD sensors and IFAE, as member of Medipix Collaboration, will provide the Timepix4/Medipix4 ASIC, the readout electronics, and as well the hybridization of the LGAD to the Timepix4/Medipix4 ASICs.

Figure 9: shows the detections of the soft X-ray photons with LGAD sensor bonded to Timepix4. The LGAD sensor should have no passive material that blocks the software X-ray from reaching the avalanche zone

Deep Detection SL

Deep Detection SL was founded in July 2020 and its main domain of activities is X-ray detectors for industrial quality control and security. It will exploit the LINDA camera. (www.deeptech.tech).

During 2021 Deep Detection (DD) obtained private financing from international VCs, and public financing, between soft loans and grants and ended the year with 5 full-time workers. The market analysis shows a clear business opportunity for multispectral cameras that work at high speeds and this is what DD is focusing on 2021. Along this line, DD is pursuing an industrial design and production of LINDA++, an upgraded version of LINDA and with dual energy capability. The first prototype is expected to be ready in the 4th quarter of 2022.