Novel radiation sensors based on bio/nanomaterials

X-ray sensors are essential to many applications which are not limited to diagnostics and imaging technologies. Such sensors are extensively used in industry, medicine, research and space technology for applications such as safety, security, quality control, imaging and treatment. Depending on the effect of the radiation on the matter employed in the sensor, different types of X-ray sensors are fabricated. However, available techniques of X-ray detection have been under development due to specific shortcomings such as finite life time, low sensitivity, and post-processing requirements. This thesis is focused on design, fabrication and characterization of novel radiation sensors based on bio/nanomaterials. Bacteriorhodopsin (BR), a proton pump protein in the cell membrane of Halobacterium Salinarum, has been used to fabricate a sensor to measure dose and dose rate of X-ray beam in the kilovoltage and megavoltage energy range. The mass attenuation coefficients, effective atomic numbers and electron densities of BR and its comprising amino acids have been calculated for 1 keV-100 GeV photons to better understand the interaction of BR with X-ray photons. A theoretical formulation for calculating the change in the conductivity of nanoparticles under radiation is also provided. In particular, the dependence of radiation induced conductivity to irradiated particle size is given. In addition to that, an X-ray sensor based on thin film of bismuth sulfide has been fabricated using laser micromachining and chemical deposition techniques. This sensor has been characterized under a diagnostic X-ray machine with kilovoltage energy beam.1 yea

Characterization of the Imaging Performance of the Simultaneously Counting and Integrating X-ray Detector CIX

The CIX detector is a direct converting hybrid pixel detector designed for medical X-ray imaging applications. Its defining feature is the simultaneous operation of a photon counter as well as an integrator in every pixel cell. This novel approach offers a dynamic range of more than five orders of magnitude, as well as the ability to directly obtain the average photon energy from the measured data. Several CIX 0.2 ASICs have been successfully connected to CdTe, CdZnTe and Si sensors. These detector modules were tested with respect to the imaging performance of the simultaneously counting and integrating concept under X-ray irradiation. Apart from a characterization of the intrinsic benefits of the CIX concept, the sensor performance was also investigated. Here, the two parallel signal processing concepts offer valuable insights into material related effects like polarization and temporal response. The impact of interpixel coupling effects like charge-sharing, Compton scattering and X-ray uorescence was evaluated through simulations and measurements

Design and Implementation of a High Resolution CMOS X-Ray Imager with Amorphous Selenium Sensor

This thesis presents a novel system for high resolution X-ray imaging in medical and industrial applications. Complementary metal-oxide-semiconductor (CMOS) technology is a standard technology used in most state of the art electronic systems including imagers. In addition, amorphous selenium (a-Se) is a photoconductor that is sensitive to a wide range of X-ray photon energies. Increasing the e ective spatial resolution is one the primary goals of state of the art imaging systems. The objective of this thesis is to integrate the a-Se sensor and CMOS readout to make an ultra high resolution X-ray imager. Other features of the imager like noise, dynamic range, imaging speed, and ll factor are competitive with existing X-ray imaging systems. All of the signal reading circuitry is implemented on a custom CMOS chip and the a-Se sensor is deposited on top of it through post processing. This thesis also describe the design of external hardware and software needed to properly operate the imager. We demonstrate our imager with a 64 × 64 pixel array prototype containing 5.6 × 6.25 μm2 and 11.2 × 6.25 μm2 pixel. Our results include characterization of the electronic and X-ray imaging performance of our system. We also show X-ray images with e ective resolution down to 14 μm.1 yea

The Dexela 2923 CMOS X-ray detector: A flat panel detector based on CMOS active pixel sensors for medical imaging applications

Complementary metal-oxide-semiconductors (CMOS) active pixel sensors (APS) have been introduced recently in many scientific applications. This work reports on the performance (in terms of signal and noise transfer) of an X-ray detector that uses a novel CMOS APS which was developed for medical X-ray imaging applications. For a full evaluation of the detector's performance, electro-optical and X-ray characterizations were carried out. The former included measuring read noise, full well capacity and dynamic range. The latter, which included measuring X-ray sensitivity, presampling modulation transfer function (pMTF), noise power spectrum (NPS) and the resulting detective quantum efficiency (DQE), was assessed under three beam qualities (28 kV, 50 kV (RQA3) and 70 kV (RQA5) using W/Al) all in accordance with the IEC standard. The detector features an in-pixel option for switching the full well capacity between two distinct modes, high full well (HFW) and low full well (LFW). Two structured CsI:Tl scintillators of different thickness (a “thin” one for high resolution and a thicker one for high light efficiency) were optically coupled to the sensor array to optimize the performance of the system for different medical applications. The electro-optical performance evaluation of the sensor results in relatively high read noise (∼360 e−), high full well capacity (∼1.5×106 e−) and wide dynamic range (∼73 dB) under HFW mode operation. When the LFW mode is used, the read noise is lower (∼165) at the expense of a reduced full well capacity (∼0.5×106 e−) and dynamic range (∼69 dB). The maximum DQE values at low frequencies (i.e. 0.5 lp/mm) are high for both HFW (0.69 for 28 kV, 0.71 for 50 kV and 0.75 for 70 kV) and LFW (0.69 for 28 kV and 0.7 for 50 kV) modes. The X-ray performance of the studied detector compares well to that of other mammography and general radiography systems, obtained under similar experimental conditions. This demonstrates the suitability of the detector for both mammography and general radiography, with the use of appropriate scintillators. The high DQE values obtained under low mammographic exposures (up to 0.65 for 22.3 μGy) matches the demand for high detectability in imaging of the dense breast

Innovating Advanced Radiation Instruments

STREAM is a 4-year multi-site training network that aims at career development of Early Stage Researchers (ESRs) on scientific design, construction manufacturing and of advanced radiation instrumentation. STREAM targets the development of innovative radiation-hard, smart CMOS sensor technologies for scientific and industrial applications. The platform technology developed within the project will be tested in the demanding conditions posed by the CERN LHC detectors' environment as well as European industry leaders in the field of CMOS imaging, electron microscopy and radiation sensors. This leveraging factor will allow to fine-tune the technology to meet the requirements of industrial application cases on demand such as electron microscopy and medical X-ray imaging, as well as pathway towards novel application fields such as satellite environments, industrial X-ray systems and near-infrared imaging. The project will train a new generation of creative, entrepreneurial and innovative early-stage researchers and widen their academic career and employment opportunities. The STREAM consortium is composed of 10 research organisations and 5 industrial partners; the network will provide training to 17 ESRs. STREAM structures the research and training in four scientific work-packages which span the whole value-chain from research to application: CMOS Technologies Assessment, Smart Sensor Design and Layout, Validation and Qualification, Technology Integration, and Valorization

Performance of a novel wafer scale CMOS active pixel sensor for bio-medical imaging

Recently CMOS Active Pixels Sensors (APSs) have become a valuable alternative to amorphous Silicon and Selenium Flat Panel Imagers (FPIs) in bio-medical imaging applications. CMOS APSs can now be scaled up to the standard 20 cm diameter wafer size by means of a reticle stitching block process. However despite wafer scale CMOS APS being monolithic, sources of non-uniformity of response and regional variations can persist representing a significant challenge for wafer scale sensor response. Non-uniformity of stitched sensors can arise from a number of factors related to the manufacturing process, including variation of amplification, variation between readout components, wafer defects and process variations across the wafer due to manufacturing processes. This paper reports on an investigation into the spatial non-uniformity and regional variations of a wafer scale stitched CMOS APS. For the first time a per-pixel analysis of the electro-optical performance of a wafer CMOS APS is presented, to address inhomogeneity issues arising from the stitching techniques used to manufacture wafer scale sensors. A complete model of the signal generation in the pixel array has been provided and proved capable of accounting for noise and gain variations across the pixel array. This novel analysis leads to readout noise and conversion gain being evaluated at pixel level, stitching block level and in regions of interest, resulting in a coefficient of variation ≤ 1.9%. The uniformity of the image quality performance has been further investigated in a typical X-ray application, i.e. mammography, showing a uniformity in terms of CNR among the highest when compared with mammography detectors commonly used in clinical practise. Finally, in order to compare the detection capability of this novel APS with the currently used technology (i.e. FPIs), theoretical evaluation of the Detection Quantum Efficiency (DQE) at zero-frequency has been performed, resulting in a higher DQE for this detector compared to FPIs. Optical characterization, X-ray contrast measurements and theoretical DQE evaluation suggest that a trade off can be found between the need of a large imaging area and the requirement of a uniform imaging performance, making the DynAMITe large area CMOS APS suitable for a range of bio-medical applications

Advancements in image sensor technology for soft X-ray spectroscopy in space: CIS detectors for the Auroral X-ray Imaging Spectrometer

Soft X-rays with energies below 2 keV are of tremendous scientific utility for planetary science but are particularly challenging to detect and analyse due to their low energies and short attenuation lengths. Solid state image sensor based X-ray detectors, derived from charge coupled devices (CCDs) and CMOS image sensors (CISs), have the potential to capture information about a soft X-ray flux in the time, spatial, and energy domains, and so are a potent scientific tool. Developing X-ray detector technology is enabling the application of soft X-ray imaging spectrometers in ever more demanding environments, with the current state of the art CIS promising the potential for high temperature, Fano-limited, performance. This thesis investigates the use of solid state image sensors for soft- X-ray imaging spectroscopy in space-based applications. Specifically: an evaluation of the radiation damage experienced by the swept charge devices (SCDs) of the Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS) which was shown to be within expectations and consistent with the requirements for continued science operation; and a study of X-ray detectors for the Auroral X-ray Imaging Spectrometer (AXIS) instrument aboard the Disturbed and quiet-time Ionosphere System at High Altitudes (DISHA) mission, resulting in the adoption of a novel CIS X-ray detector into the instrument design. The AXIS study has found that the newly developed CISs are now equal to their CCD counterparts in some soft X-ray imaging spectroscopy applications, potentially enabling new science targets to be pursued. The successful recommendation to change the AXIS instrument X-ray detector from the more mature EMCCD CCD201-20 of the baseline design, to the less mature but better performing CIS221-X and its derivatives represents a milestone in the development of CIS X-ray detector technology

Characterisation of CMOS APS Technologies for Space Applications

In recent years, the performance of scientific CMOS active pixel sensors has been improved to the point that it is now approaching that of the current silicon sensor of choice, CCDs. For some applications, CMOS APSs is believed to present significant advantages over CCDs, such as improved radiation hardness. In this work, the effect of radiation damage on a ‘baseline’ commercial APS, e2v technologies’ Jade APS, is characterised in response to gamma, proton and heavy ion irradiation. Specific performance problems encountered during this radiation characterisation, such as dark current non-uniformity under gamma irradiation, random telegraph signals under proton irradiation, and single event effects under heavy ion irradiation are described and analyzed. The X-ray spectroscopic imaging performance of the device is measured and compared to the Ocean Colour Imager APS test array showing progress towards a high frame rate spectroscopic X-ray imager for space science. The implications of these results for using similar devices in space applications are considered. Furthermore, possible novel techniques for measuring inter-pixel responsivity non-uniformity, heavy ion detection and spectroscopy, and measuring the dynamics of radiation-induced trap formation are discussed

Foreign Object Detection and Quantification of Fat Content Using A Novel Multiplexing Electric Field Sensor

There is an ever growing need to ensure the quality of food and assess specific quality parameters in all the links of the food chain, ranging from processing, distribution and retail to preparing food. Various imaging and sensing technologies, including X-ray imaging, ultrasound, and near infrared reflectance spectroscopy have been applied to the problem. Cost and other constraints restrict the application of some of these technologies. In this study we test a novel Multiplexing Electric Field Sensor (MEFS), an approach that allows for a completely non-invasive and non-destructive testing approach. Our experiments demonstrate the reliable detection of certain foreign objects and provide evidence that this sensor technology has the capability of measuring fat content in minced meat. Given the fact that this technology can already be deployed at very low cost, low maintenance and in various different form factors, we conclude that this type of MEFS is an extremely promising technology for addressing specific food quality issues

2D Detectors for Particle Physics and for Imaging Applications

The demands on detectors for particle detection as well as for medical and astronomical X-ray imaging are continuously pushing the development of novel pixel detectors. The state of the art in pixel detector technology to date are hybrid pixel detectors in which sensor and read-out integrated circuits are processed on different substrates and connected via high density interconnect structures. While these detectors are technologically mastered such that large scale particle detectors can be and are being built, the demands for improved performance for the next generation particle detectors ask for the development of monolithic or semi-monolithic approaches. Given the fact that the demands for medical imaging are different in some key aspects, developments for these applications, which started as particle physics spin-off, are becomming rather independent. New approaches are leading to novel signal processing concepts and interconnect technologies to satisfy the need for very high dynamic range and large area detectors. The present state in hybrid and (semi-)monolithic pixel detector development and their different approaches for particle physics and imaging application is reviewed