Two Dimensional Amorphous Silicon Image Sensor Arrays

Street, R. A.; Wu, X.D.; Weisfield, Richard L.; Ready, S. E.; Apte, Raj B.; Nguyen, Manh-Cuong; Nylen, P.

doi:10.1557/proc-377-757

Cited by 59 publications

(15 citation statements)

References 19 publications

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“…For the case of indirect detection, each pixel switch is coupled to either a discrete optical sensing element 1 or, alternatively, to an overlying, continuous, optically sensitive layer. 13,14 An x-ray converter, such as a phosphor screen or CsI:Tl, is placed or deposited upon the array allowing the imaging pixels to sense light generated in the converter by interacting x rays. Thus far, optically sensitive arrays, which are compatible with the indirect detection approach, have primarily incorporated discrete n-i-p or p-i-n photodiodes coupled to either a-Si:H TFTs, [1][2][3][4] to single diodes, [8][9][10] or to back-toback diodes.…”

Section: Introductionmentioning

confidence: 99%

“…11 There has also been an initial examination of a-Si:H TFTs coupled to discrete phototransistors 5 and to a continuous photodiode layer. 14 As in the case of AMLCDs, the pixel count of AMFPIs, led by the photodiode ϩTFT approach, has increased in an exponential manner since the creation of the first imaging arrays in 1988. 15,16 Recently, our research on this approach has progressed to the point where a large-area, high spatial resolution array design has been realized.…”

Section: Introductionmentioning

confidence: 99%

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Empirical investigation of the signal performance of a high‐resolution, indirect detection, active matrix flat‐panel imager (AMFPI) for fluoroscopic and radiographic operation

et al. 1997

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Signal properties of the first large-area, high resolution, active matrix, flat-panel imager are reported. The imager is based on an array of 1536 x 1920 pixels with a pixel-to-pixel pitch of 127 microns. Each pixel consists of a discrete amorphous silicon n-i-p photodiode coupled to an amorphous silicon thin-film transistor. The imager detects incident x rays indirectly by means of an intensifying screen placed over the array. External acquisition electronics send control signals to the array and process analog imaging signals from the pixels. Considerations for operation of the imager in both fluoroscopic and radiographic modes are detailed and empirical signal performance data are presented with an emphasis on exploring similarities and differences between the two modes. Measurements which characterize the performance of the imager were performed as a function of operational parameters in the absence or presence of illumination from a light-emitting diode or x rays. These measurements include characterization of the drift and magnitude of the pixel dark signal, the size of the pixel switching transient, the temporal behavior of pixel sampling and the implied maximum frame rate, the dependence of relative pixel efficiency and pixel response on photodiode reverse bias voltage and operational mode, the degree of linearity of pixel response, and the trapping and release of charge from metastable states in the photodiodes. In addition, X-ray sensitivity as a function of energy for a variety of phosphor screens for both fluoroscopic and radiographic operation is reported. Example images of a line-pair pattern and an anthropomorphic phantom in each mode are presented along with a radiographic image of a human hand. General and specific improvements in imager design are described and anticipated developments are discussed. This represents the first systematic investigation of the operation and properties in both radiographic and fluoroscopic modes of an imager incorporating such an array.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Empirical investigation of the signal performance of a high‐resolution, indirect detection, active matrix flat‐panel imager (AMFPI) for fluoroscopic and radiographic operation

et al. 1997

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“…1 Therefore, in an effort to optimize fill factor, the TFT are assumed to be embedded under the sensor to provide high fill factor imaging systems, which follows from the continuous layer sensor architecture concept suggested previously. This could undermine fill factor if conventional methods of placing the sensor and TFTs are used.…”

Section: Active Pixel Sensormentioning

confidence: 99%

“…Amorphous silicon ͑a-Si͒ active matrix flat-panel imagers ͑AMFPIs͒ have gained considerable significance in digital imaging, 1 and more recently in diagnostic medical imaging applications, 2 in view of their large area readout capability. The pixel, forming the fundamental unit of the active matrix, consists of a detector and readout circuit to efficiently transfer the collected electrons to external electronics for data acquisition.…”

Section: Introductionmentioning

confidence: 99%

Active pixel sensor architectures in a-SiH for medical imaging

Karim

Nathan

Rowlands

2002

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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High dynamic range active pixel sensor arrays for digital x-ray imaging using a -Si : H J. Vac. Sci. Technol. A 24, 850 (2006); 10.1116/1.2192526 High dynamic range pixel architecture for advanced diagnostic medical x-ray imaging applications Low noise signal-to-noise ratio enhancing readout circuit for current-mediated active pixel sensorsThe most widely used architecture in large area amorphous silicon ͑a-Si͒ flat panel imagers is the passive pixel sensor ͑PPS͒, which consists of a detector and a readout switch. While the PPS has the advantage of being compact and amenable towards high-resolution imaging, reading the low PPS output signal requires external circuitry such as column charge amplifiers that produce additional noise and reduce the minimum readable sensor input signal. This work presents a voltage mediated active pixel sensor ͑APS͒ on-pixel readout circuit for diagnostic medical imaging to minimize external component count and hence external readout noise sources. Preliminary results indicate excellent APS linearity along with a pixel readout time suitable for mammography or radiography.

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“…Pixelated arrays of electronics in amorphous silicon (a-Si : H) technology, routinely used for liquid crystal displays, are now being extended to several new and significant application areas in large area digital imaging [1,2]. Large area active matrix flat panel imagers (AMFPIs) with area *30 × 40 cm 2 have been demonstrated for radiography [3].…”

Section: Introductionmentioning

confidence: 99%

Large Area Digital X‐ray Imaging

et al. 2003

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This chapter reviews amorphous silicon devices for large area flat panel imaging technology. We present Schottky and p-i-n diode image sensors and elaborate on their operating principles, electrical and optoelectronic characteristics including stability, along with the challenges associated with reduction of the dark current. Issues pertinent to sensor-thin film transistor integration for different active matrix pixel architectures for high fill factor imaging arrays are presented along with optimization of materials and processing conditions for reduced threshold voltage shift, reduced parasitics and leakage current, and enhanced mechanical integrity. Extension of the current fabrication processes to low (*120 8C) temperature, enabling fabrication of flexible imaging array (on plastic substrates), is also discussed.

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Two Dimensional Amorphous Silicon Image Sensor Arrays

Cited by 59 publications

References 19 publications

Empirical investigation of the signal performance of a high‐resolution, indirect detection, active matrix flat‐panel imager (AMFPI) for fluoroscopic and radiographic operation

Empirical investigation of the signal performance of a high‐resolution, indirect detection, active matrix flat‐panel imager (AMFPI) for fluoroscopic and radiographic operation

Active pixel sensor architectures in a-SiH for medical imaging

Large Area Digital X‐ray Imaging

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