The Experts below are selected from a list of 11499 Experts worldwide ranked by ideXlab platform
Kai Wang - One of the best experts on this subject based on the ideXlab platform.
-
backside illuminated 3 d photosensitive thin film transistor on a scintillating glass substrate for Indirect Conversion x ray detection
IEEE Electron Device Letters, 2020Co-Authors: Qi Qian, Jun Chen, Zhongmin Yang, Kai WangAbstract:A conventional large-area Indirect-Conversion X-ray detector usually adopts front side illumination (FSI) of a scintillator atop a photodiode-integrated thin-film transistor (TFT) array. This work however proposes a backside illuminated (BSI) three-dimensional dual-gate photosensitive a-Si:H TFT (3-D DGTFT) on a scintillating glass substrate, aiming for Indirect-Conversion X-ray detection. It not only improves the sensitivity with a 3-D photosensitive TFT as an active pixel sensor, but also enhances the resolution and photon utilization by reducing photon scattering and optical crosstalk. Backside illumination of 3-D photosensitive TFT-integrated scintillating glass therefore provides an alternative approach to large-area Indirect-Conversion X-ray imaging.
-
highly sensitive Indirect Conversion x ray detector with an embedded photodiode formed by a three dimensional dual gate thin film transistor
Journal of Lightwave Technology, 2020Co-Authors: Qi Zhou, Jun Chen, Jia Huang, Kai WangAbstract:This article reports on a highly-sensitive Indirect-Conversion X-ray detector with an embedded photodiode formed by a scintillator-coupled 3-D photosensitive thin-film transistor. A high X-ray sensitivity up to 2.5 × 105 μC·Gy−1·cm−2 at a dose of 1 mGy is achieved due to full photon utilization and a high photo gain of ∼104 by operating it in an active pixel sensor format. These performance characteristics make it a great promise for low-dose and high-spatial resolution large-area Indirect-Conversion X-ray detection.
-
A Flat Panel Photodetector Formed by a ZnS Photoconductor and ZnO Nanowire Field Emitters Achieving High Responsivity From Ultraviolet to Visible Light for Indirect-Conversion X-Ray Imaging
Journal of Lightwave Technology, 2018Co-Authors: Zhipeng Zhang, Keshuang Zheng, Ningsheng Xu, Shaozhi Deng, Kai Wang, Jun ChenAbstract:Flat panel photodetectors have been well studied for their applications in large area detection such as Indirect-Conversion X-ray imaging. Even though a few of photodetectors have become commercially available, there is still a room for advancement in responsive wavelength range and sensitivity. This paper reports a sensitive broadband flat panel photodetector that integrates a ZnS photoconductor with an array of ZnO nanowire field emitters. The photodetector exhibits a spectral responsivity of 5.93 × 102-3.79 × 103 A/W with an external quantum efficiency of 1.03 × 105-1.34 × 106% from 350 to 700 nm wavelengths. Additionally, a short signal rise time of 55 ms and a fall time of 1.03 s are demonstrated. The flat panel photodetector with broadband detection and a high responsivity shows a great promise for use in Indirect-Conversion X-ray detector incorporated with a broad range of X-ray scintillators.
-
dual gate photosensitive a si h thin film transistor with a pi shape channel for large area imaging and sensing
IEEE Electron Device Letters, 2015Co-Authors: Kai Wang, Shaozhi Deng, Cairong Ding, Jun ChenAbstract:This letter reports on a photosensitive dual-gate amorphous silicon (a-Si:H) thin-film transistor (TFT) for low-level light detection. It differs from a conventional dual-gate TFT in that a 760-nm $\pi $ -shape channel layer is implemented instead of a typically thin a-Si:H layer of 50 $\sim $ 100 nm in the conventional TFTs. Not only such a device improves the photoabsorption, it also preserves the transfer characteristics of the TFT. Upon the low-level light exposure, the photosensitivity can be multiplied by operating the device in the subthreshold region. In addition, resetting the device can minimize the residual photocurrent and improves the photoresponse. The device can be, therefore, sensitive and fast enough to enable optical applications, such as low-dose Indirect-Conversion X-ray imaging and large-area document scanning.
-
evaluation of a single pixel one transistor active pixel sensor for low dose Indirect Conversion x ray imaging
2015 International Conference on Optical Instruments and Technology: Optoelectronic Imaging and Processing Technology, 2015Co-Authors: Xinghui Liu, Jun Chen, Kai WangAbstract:We designed and fabricated a dual-gate photosensitive TFT with active amorphous silicon thickness of 240nm and W/L ratio of 250μm/20μm by using a conventional six-mask photography microfabrication process. A single-pixel sensor was tested under different light conditions to mimic the real situation of X-ray exposure via the scintillator. The results demonstrate the capability of using dual-gate photosensitive TFT to acquire an X-ray image Indirectly.
Jun Chen - One of the best experts on this subject based on the ideXlab platform.
-
backside illuminated 3 d photosensitive thin film transistor on a scintillating glass substrate for Indirect Conversion x ray detection
IEEE Electron Device Letters, 2020Co-Authors: Qi Qian, Jun Chen, Zhongmin Yang, Kai WangAbstract:A conventional large-area Indirect-Conversion X-ray detector usually adopts front side illumination (FSI) of a scintillator atop a photodiode-integrated thin-film transistor (TFT) array. This work however proposes a backside illuminated (BSI) three-dimensional dual-gate photosensitive a-Si:H TFT (3-D DGTFT) on a scintillating glass substrate, aiming for Indirect-Conversion X-ray detection. It not only improves the sensitivity with a 3-D photosensitive TFT as an active pixel sensor, but also enhances the resolution and photon utilization by reducing photon scattering and optical crosstalk. Backside illumination of 3-D photosensitive TFT-integrated scintillating glass therefore provides an alternative approach to large-area Indirect-Conversion X-ray imaging.
-
highly sensitive Indirect Conversion x ray detector with an embedded photodiode formed by a three dimensional dual gate thin film transistor
Journal of Lightwave Technology, 2020Co-Authors: Qi Zhou, Jun Chen, Jia Huang, Kai WangAbstract:This article reports on a highly-sensitive Indirect-Conversion X-ray detector with an embedded photodiode formed by a scintillator-coupled 3-D photosensitive thin-film transistor. A high X-ray sensitivity up to 2.5 × 105 μC·Gy−1·cm−2 at a dose of 1 mGy is achieved due to full photon utilization and a high photo gain of ∼104 by operating it in an active pixel sensor format. These performance characteristics make it a great promise for low-dose and high-spatial resolution large-area Indirect-Conversion X-ray detection.
-
A Flat Panel Photodetector Formed by a ZnS Photoconductor and ZnO Nanowire Field Emitters Achieving High Responsivity From Ultraviolet to Visible Light for Indirect-Conversion X-Ray Imaging
Journal of Lightwave Technology, 2018Co-Authors: Zhipeng Zhang, Keshuang Zheng, Ningsheng Xu, Shaozhi Deng, Kai Wang, Jun ChenAbstract:Flat panel photodetectors have been well studied for their applications in large area detection such as Indirect-Conversion X-ray imaging. Even though a few of photodetectors have become commercially available, there is still a room for advancement in responsive wavelength range and sensitivity. This paper reports a sensitive broadband flat panel photodetector that integrates a ZnS photoconductor with an array of ZnO nanowire field emitters. The photodetector exhibits a spectral responsivity of 5.93 × 102-3.79 × 103 A/W with an external quantum efficiency of 1.03 × 105-1.34 × 106% from 350 to 700 nm wavelengths. Additionally, a short signal rise time of 55 ms and a fall time of 1.03 s are demonstrated. The flat panel photodetector with broadband detection and a high responsivity shows a great promise for use in Indirect-Conversion X-ray detector incorporated with a broad range of X-ray scintillators.
-
dual gate photosensitive a si h thin film transistor with a pi shape channel for large area imaging and sensing
IEEE Electron Device Letters, 2015Co-Authors: Kai Wang, Shaozhi Deng, Cairong Ding, Jun ChenAbstract:This letter reports on a photosensitive dual-gate amorphous silicon (a-Si:H) thin-film transistor (TFT) for low-level light detection. It differs from a conventional dual-gate TFT in that a 760-nm $\pi $ -shape channel layer is implemented instead of a typically thin a-Si:H layer of 50 $\sim $ 100 nm in the conventional TFTs. Not only such a device improves the photoabsorption, it also preserves the transfer characteristics of the TFT. Upon the low-level light exposure, the photosensitivity can be multiplied by operating the device in the subthreshold region. In addition, resetting the device can minimize the residual photocurrent and improves the photoresponse. The device can be, therefore, sensitive and fast enough to enable optical applications, such as low-dose Indirect-Conversion X-ray imaging and large-area document scanning.
-
evaluation of a single pixel one transistor active pixel sensor for low dose Indirect Conversion x ray imaging
2015 International Conference on Optical Instruments and Technology: Optoelectronic Imaging and Processing Technology, 2015Co-Authors: Xinghui Liu, Jun Chen, Kai WangAbstract:We designed and fabricated a dual-gate photosensitive TFT with active amorphous silicon thickness of 240nm and W/L ratio of 250μm/20μm by using a conventional six-mask photography microfabrication process. A single-pixel sensor was tested under different light conditions to mimic the real situation of X-ray exposure via the scintillator. The results demonstrate the capability of using dual-gate photosensitive TFT to acquire an X-ray image Indirectly.
J. A. Rowlands - One of the best experts on this subject based on the ideXlab platform.
-
direct Conversion flat panel x ray image sensors for digital radiography
Proceedings of the IEEE, 2002Co-Authors: S O Kasap, J. A. RowlandsAbstract:Advances in active-matrix array flat panels for displays over the last decade have led to the development of flat-panel X-ray image detectors. Recent flat-panel detectors have shown image quality exceeding that of X-ray film/screen cassettes. They can also permit the instantaneous capture, readout, and display of digital X-ray images and, hence, enable the clinical transition to digital radiography. There are two general approaches to flat panel detector technology: 1) direct and 2) Indirect Conversion. The present paper outlines the operating principles for direct-Conversion detectors based on the use of photoconductors. It formulates and reviews the required X-ray photoconductor properties for such applications and examines to what extent potential materials fulfill these requirements. The quantum efficiency, X-ray sensitivity, noise, and detective quantum efficiency factors are discussed with reference to current and potential large area X-ray photoconductors.
-
effect of depth dependent modulation transfer function and k fluorescence reabsorption on the detective quantum efficiency of Indirect Conversion flat panel x ray imaging systems using csi
Medical Imaging 2001: Physics of Medical Imaging, 2001Co-Authors: J. A. Rowlands, Wei ZhaoAbstract:A theory of the imaging behavior of structured phosphor layers is developed based on linear analysis and Carlo model modeling and tested by comparison with experiments. The experiments include: the evaluation of Swank factor; modulation transfer function (MTF) measured as a function of spatial frequency f on CsI phosphor layers of different thicknesses and optical properties (e.g. presence or absence of reflective backing layer). These measurements on structured screens were used to establish phosphor parameters (e.g. absorption and scattering lengths). In addition, MTF(f), Wiener noise power spectra [NPS(f)] and detective quantum efficiency [DQE(f)] measurements were obtained from the literature for x-ray image intensifiers and Indirect Conversion flat panel detectors constructed using CsI layers. These results were compared with the theory using the previously established phosphor parameters. The effects of K-fluorescence and depth dependence of the MTF on DQE (i.e. Lubberts' effect) were investigated.
Karim S. Karim - One of the best experts on this subject based on the ideXlab platform.
-
invited Indirect Conversion digital x ray imager using an amorphous selenium photoconductor
5th International Symposium on Graphene Ge III-V and Emerging Materials For Post-CMOS Applications - 223rd ECS Meeting, 2013Co-Authors: Shiva Abbaszadeh, Kai Wang, Rasoul Keshavarzi, Karim S. KarimAbstract:In this work, we report preliminary results from a 32×32 pixel prototype array that integrates a-Si:H TFT pixels with optically sensitive lateral a-Se MSM detectors. The array was in-house fabricated and characterized. Recent advances in improving the wavelength sensitivity, dark current, photocurrent and quantum efficiency of the a-Se optically sensitive lateral device are also presented together with system-level characterization and the first image captured by the array.
-
amorphous selenium photodetector on a flexible substrate for Indirect Conversion medical imaging
Proceedings of SPIE, 2012Co-Authors: Shiva Abbaszadeh, Nicholas Allec, Shaikh Hasibul Majid, Karim S. KarimAbstract:Amorphous selenium photodetectors, in both lateral and vertical structures, have been investigated for Indirect Conversion medical imaging applications. The low dark current, high responsivity for blue light, and possibility for gain are all among the attractive features of these devices. Typically these devices are deposited on a solid glass substrate and are read out using thin-film-transistors (TFTs). With the advent of flexible TFTs, flexible electronics have become a viable technology. This technology may be leveraged for flexible imaging, however the detection and Conversion materials that serve to convert the incident x-rays to collectable charge will also need to be flexible. In this paper, we investigate the use of amorphous selenium photodetectors on flexible substrates and compare their performance with amorphous selenium photodetectors deposited on glass.
-
Study of the transient response of PI/a-Se photodetectors for Indirect Conversion medical imaging
2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS MIC), 2012Co-Authors: Shiva Abbaszadeh, Nicholas Allec, Karim S. KarimAbstract:Previously two different amorphous selenium (a-Se) photodetector designs were proposed for Indirect Conversion medical imaging using polyimide (PI) as blocking contacts: a lateral comb structure where a PI layer covers both electrodes and a vertical structure where a PI layer is placed between the positively biased electrode and a-Se. These detectors have raised interest due to their simple structure, ease of fabrication, very low dark current at high electric fields, and high quantum efficiency. In this study we examine the transient behavior of these detectors for fluoroscopic or tomographic applications. The photo response to a short light pulse (10-100 μs) is examined in both structures. The presence of charge accumulation at the PI/a-Se interface is investigated by observing the photo response of consecutive light pulses under different electric fields. This work demonstrates the promise of low-cost a-Se devices for use in Indirect Conversion large area digital medical X-ray imaging applications such as real-time fluoroscopy and computed tomography.
-
integration of an amorphous silicon passive pixel sensor array with a lateral amorphous selenium detector for large area Indirect Conversion x ray imaging applications
Proceedings of SPIE, 2011Co-Authors: Kai Wang, Shiva Abbaszadeh, Mohammad Y Yazdandoost, Rasoul Keshavarzi, Kyung Wook Shin, Christos Hristovski, Feng Chen, Shaikh Hasibul Majid, Karim S. KarimAbstract:Previously, we reported on a single-pixel detector based on a lateral a-Se metal-semiconductor-metal structure, intended for Indirect Conversion X-ray imaging. This work is the continuous effort leading to the first prototype of an Indirect Conversion X-ray imaging sensor array utilizing lateral amorphous selenium. To replace a structurally-sophisticated vertical multilayer amorphous silicon photodiode, a lateral a-Se MSM photodetector is employed which can be easily integrated with an amorphous silicon thin film transistor passive pixel sensor array. In this work, both 2×2 macro-pixel and 32×32 micro-pixel arrays were fabricated and tested along with discussion of the results.
-
study of gain phenomenon in lateral metal semiconductor metal detectors for Indirect Conversion medical imaging
Proceedings of SPIE, 2011Co-Authors: Shiva Abbaszadeh, Kai Wang, Nicholas Allec, Feng Chen, Karim S. KarimAbstract:Previously, metal-semiconductor-metal (MSM) lateral amorphous selenium (a-Se) detectors have been proposed for Indirect detector medical imaging applications. These detectors have raised interest due to their high-speed and photogain. The gain measured from these devices was assumed to have been photoconductive gain; however the origin of this gain was not fully understood. In addition, whether or not there was any presence of photocurrent multiplication gain was not investigated. For integration-type applications photocurrent multiplication gain is desirable since the total collected charge can be greater than the total number of absorbed photons. In order to fully appreciate the value of MSM devices and their benefit for different applications, whether it is counting or integration applications, we need to investigate the responsible mechanisms of the observed response. In this paper, we systematically study, through experimental and theoretical means, the nature of the photoresponse and its responsible mechanisms. This study also exposes the possible means to increase the performance of the device and under what conditions it will be most beneficial.
Shiva Abbaszadeh - One of the best experts on this subject based on the ideXlab platform.
-
thickness uniformity and stability of amorphous selenium films on flexible substrates for Indirect Conversion x ray detection
Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, 2021Co-Authors: Maryam Farahmandzadeh, Steven Marcinko, Davide Curreli, Shiva AbbaszadehAbstract:Amorphous selenium (a-Se) possesses unique features that have been leveraged for medical imaging applications. Previously, it was shown that having a soft interface with a-Se will reduce the stress generated from the creation of crystalline nucleus, prevent radiation-induced crystallization, and improve long-term stability of the device. The aim of this study is to develop a uniform thickness of a-Se on a flexible substrate, polyethylene terephthalate coated with indium tin oxide (ITO-PET), for future investigations of the effect of substate on stability of the a-Se against radiation-induced defects and long-term storage. In order to fabricate the a-Se-based detector, we have developed a dedicated thermal evaporator for a-Se deposition. The dependence of the source-to-substrate distance on film uniformity has been investigated. Experimentally, following modeling results, a-Se samples over a 2-inch diameter were deposited on ITOPET and thickness uniformity was compared to simulation.
-
Indirect Conversion amorphous selenium photodetectors for medical imaging applications
2014Co-Authors: Shiva AbbaszadehAbstract:The innovative design of flat panel volume computed tomography (CT) systems has recently led to the emergence of a wide spectrum of new applications for both diagnostic and interventional purposes, such as ultra-high resolution bone imaging, image guided interventions, dynamic CT angiography, and interventional neuroradiology. Most of these applications require low X-ray dose to limit potential harm to the patient. One of the main challenges of low dose imaging is to maintain a quantum noise limited system to achieve the highest possible signal to noise ratio (SNR) at a given dose. One potential method to achieve a quantum noise limited system is to employ a high gain detector. Current flat panel CT technology is based on Indirect Conversion detectors that contain a scintillator and hydrogenated amorphous silicon (a-Si:H) p-i-n photodetectors which have a gain below unity and require a specialized p-layer. In this thesis, an alternative detector to the p-i-n photodetector, which can achieve gain above unity and thus aid in achieving quantum noise limited systems is investigated for large area flat panel imaging. The proposed detector is based on amorphous selenium (a-Se). Amorphous selenium is the most highly developed photoconductor for large area direct Conversion X-ray imaging and is still the only commercially available large area direct Conversion flat panel X-ray detector. However, the use of a-Se for Indirect Conversion imaging has not been significantly explored. Amorphous selenium has field dependent mobility and Conversion efficiency, which increase with increasing electric field. It is also the only large area compatible avalanche-capable material; a property that was discovered more than 30 years ago. This unique property could be leveraged to provide the gain necessary for low dose medical imaging applications. The only current commercial avalanche capable a-Se optical detector uses electron beam readout in vacuum, which is not large area compatible and makes integration with pixelated readout electronics challenging. The detector structure proposed in this research seeks to address the challenges associated with integration of an avalanche capable a-Se detector with large area X-ray imager. One important aspect in the development of a-Se avalanche detectors is reducing the dark current and preventing a-Se breakdown as the electric field across the device is increased. A high dark current reduces the dynamic range of the detector, it increases the noise level, and it can lead to crystallization of the detector due to joule heating. To overcome the dark current problem, different blocking layers that allow for integration with large area flat panel imagers were investigated. Experimental results from fabricated devices provided the basis for the choice of the most suitable blocking layer. Two device structures are proposed using the selected blocking layer, a vertical structure and a lateral structure, each having associated benefits and drawbacks. It was shown that introducing a polyimide blocking…
-
invited Indirect Conversion digital x ray imager using an amorphous selenium photoconductor
5th International Symposium on Graphene Ge III-V and Emerging Materials For Post-CMOS Applications - 223rd ECS Meeting, 2013Co-Authors: Shiva Abbaszadeh, Kai Wang, Rasoul Keshavarzi, Karim S. KarimAbstract:In this work, we report preliminary results from a 32×32 pixel prototype array that integrates a-Si:H TFT pixels with optically sensitive lateral a-Se MSM detectors. The array was in-house fabricated and characterized. Recent advances in improving the wavelength sensitivity, dark current, photocurrent and quantum efficiency of the a-Se optically sensitive lateral device are also presented together with system-level characterization and the first image captured by the array.
-
amorphous selenium photodetector on a flexible substrate for Indirect Conversion medical imaging
Proceedings of SPIE, 2012Co-Authors: Shiva Abbaszadeh, Nicholas Allec, Shaikh Hasibul Majid, Karim S. KarimAbstract:Amorphous selenium photodetectors, in both lateral and vertical structures, have been investigated for Indirect Conversion medical imaging applications. The low dark current, high responsivity for blue light, and possibility for gain are all among the attractive features of these devices. Typically these devices are deposited on a solid glass substrate and are read out using thin-film-transistors (TFTs). With the advent of flexible TFTs, flexible electronics have become a viable technology. This technology may be leveraged for flexible imaging, however the detection and Conversion materials that serve to convert the incident x-rays to collectable charge will also need to be flexible. In this paper, we investigate the use of amorphous selenium photodetectors on flexible substrates and compare their performance with amorphous selenium photodetectors deposited on glass.
-
Study of the transient response of PI/a-Se photodetectors for Indirect Conversion medical imaging
2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS MIC), 2012Co-Authors: Shiva Abbaszadeh, Nicholas Allec, Karim S. KarimAbstract:Previously two different amorphous selenium (a-Se) photodetector designs were proposed for Indirect Conversion medical imaging using polyimide (PI) as blocking contacts: a lateral comb structure where a PI layer covers both electrodes and a vertical structure where a PI layer is placed between the positively biased electrode and a-Se. These detectors have raised interest due to their simple structure, ease of fabrication, very low dark current at high electric fields, and high quantum efficiency. In this study we examine the transient behavior of these detectors for fluoroscopic or tomographic applications. The photo response to a short light pulse (10-100 μs) is examined in both structures. The presence of charge accumulation at the PI/a-Se interface is investigated by observing the photo response of consecutive light pulses under different electric fields. This work demonstrates the promise of low-cost a-Se devices for use in Indirect Conversion large area digital medical X-ray imaging applications such as real-time fluoroscopy and computed tomography.