Two-Transistor Active Pixel Sensor for High Resolution Large Area Digital X-ray Imaging

Taghibakhsh, Farhad; Karim, K.S.

doi:10.1109/iedm.2007.4419126

Cited by 15 publications

(11 citation statements)

References 4 publications

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“…2) in order to discharge the deposited charge after the sensor value is read out. When the Reset TFT is turned on, it discharges the charge gate to the output, which is virtually grounded (or held at a constant reset voltage V RST ), by the column amplifiers connected to the output [7]. In similar, the charge gate can be reset to a nonzero voltage.…”

Section: Resultsmentioning

confidence: 99%

“…2. 2T-APS die micrograph and circuit diagrams for 2T [7] and 1T high resolution current mode APS circuits, using a-Si CG-TFT. The drain, source, and gate terminals of the CG-TFT are outlined in white on the micrograph, and the charge gate is outlined in black for clarity.…”

Section: Resultsmentioning

confidence: 99%

“…Here, we introduce a charge-gated TFT (CG-TFT) for both integrating the sensor charge and switching the TFT output current on and off. The CG-TFT replaces the amplifier and selects TFT in the 3T APS architecture [7]. Manuscript …”

Section: Introductionmentioning

confidence: 99%

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Charge-Gated Thin-Film Transistors for High Resolution Digital Imaging Applications

Taghibakhsh

Karim

2008

IEEE Electron Device Lett.

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A field-effect thin-film transistor (TFT) with two gates, which are charge and voltage gates, is introduced. By applying a proper voltage to the voltage gate, the device is biased at a desired operating point or turned on and off, whereas the amount of charge deposited on the charge gate, which is embedded inside the dielectric, shifts the threshold voltage and therefore modulates the drain-source current. Such device finds application in sensor circuits, particularly high resolution sensor arrays, where it replaces both the tranconducting amplifier and the addressing switch transistor, thus reducing transistor count per pixel. Device structure, operation, and characteristics are derived and discussed. A planar configuration of the charge-gated TFT was fabricated by using top-gate amorphous silicon TFTs and implemented in a 100-µm-pitch two-transistor active pixel sensor test structure.Index Terms-Amorphous silicon (a-Si), digital imaging, high resolution, thin-film transistor (TFT).

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Charge-Gated Thin-Film Transistors for High Resolution Digital Imaging Applications

Taghibakhsh

Karim

2008

IEEE Electron Device Lett.

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“…The TFT was assumed to be liner operation mode to ensure the linearity of the detector and minimize the V Th shift effect from a-Si:H metastability effect [7]. Typically, the transconductance of a TFT is considered as 0.1 μS range and the readout period (T s ) needs to be stay under a few tens of μs range for protein crystallography applications.…”

Section: Readout Validationmentioning

confidence: 99%

Novel silicon x-ray detector with TFT readout

Shin

Wang²,

Allec

et al. 2012

SPIE Proceedings

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Crystalline Silicon Drift Detectors (SDDs) have been used for spectroscopy and particle physics applications since they were first reported in the 1980s[1] [2]. However, spatial resolution and a complex fabrication process are two major hurdles that prevent SDDs from seeing widespread use in diffraction imaging and protein crystallography. To overcome the issues with SDDs, we proposed a new type of silicon radiation detector integrated with a hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) readout technology intended for low X-ray energy detection with high spatial resolution [3]. This work aims to extend our previous effort by examining in detail the operation of the proposed integrated silicon TFT detector and to evaluate its X-ray sensitive performance via numerical analysis. In this research we simulate a 250-μm-thick slightly doped p-type silicon substrate that also functions as an X-ray detector integrated with a TFT readout having a channel length of 15 μm and a source/drain width of 15 μm. The simulations performed focus on the potential distribution and band structure at the heterostructure interface between the TFT and the silicon detector, and also on the current-voltage characteristics of the TFT due to X-ray exposure. Based on simulation results, the expected lower and upper limits of performance will be presented. In particular, the feasibility of a single 6 keV photon detection (arguably the minimum signal for a crystallography application) with such a device will be examined.

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“…The charge generated in the photoconductor, henceforth the detector, upon the absorption of x-rays, is stored on the del storage capacitor, C pix which also couples the Read pulse (the APS addressing signal) to the gate of transistor T 1 . T 1 operates as a switch-amplifier, i.e., the pixel transconductance amplifier as well as the pixel access switch transistor [11]. The reset transistor, T 2 , is used to discharge the del stored charge to the virtually grounded output, thus resetting the pixel.…”

Section: The Active-passive Detector Architecture and Operationmentioning

confidence: 99%

Evaluation of the x-ray response of amorphous selenium coated 100-μm pitch a-Si active pixel sensors for tomosynthesis applications

et al. 2009

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We detail the integration of hydrogenated amorphous silicon (a-Si:H) active pixel sensor (APS) test arrays with an overlying amorphous selenium (a-Se) x-ray photoconductor, and report on results of their x-ray response and imaging properties. The a-Se/a-Si:H APS arrays incorporate a two-transistor (2T) gate-switched pixel amplifier architecture designed to provide high detector array resolution, as well as a controllable on-pixel gain. The direct x-ray detectors consist of in-house fabricated, dual mode active and passive sensor arrays with detector element (del) pitches of 100 μm and 200 μm, coated with an 80 μm thick stabilized amorphous selenium layer. These selenium layers were selected for preliminary work and represent a quantum efficiency (QE) of 69% for x-ray spectra (tungsten target, 0.44 mm Al filtration) of 35 kV. Detector response was evaluated for a-Se bias fields of both 5 V/μm and 10 V/μm. A detector dark current of 110 pA/cm 2 (0.01 pA/100 μm del) at 10V/µm electric field, a controllable detector conversion gain up to 15.3 nA/mR at 30 kVp were measured. Active pixel gains of 6.7 and 9.6 were measured for 100 μm and 200 μm pitch detectors respectively. The amplified readout exhibits a better detection limit (by one order of magnitude) compared to the passive readout implemented on the same pixel. Capabilities of amplified pixels such as nondestructive readout, as well as programmable pixel conversion gain, and dynamic range control are demonstrated. In light of their adaptable gain and dynamic range, these detectors represent a promising technology for high-resolution high gain x-ray digital imaging, particularly in mammography tomosynthesis.

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Two-Transistor Active Pixel Sensor for High Resolution Large Area Digital X-ray Imaging

Cited by 15 publications

References 4 publications

Charge-Gated Thin-Film Transistors for High Resolution Digital Imaging Applications

Charge-Gated Thin-Film Transistors for High Resolution Digital Imaging Applications

Novel silicon x-ray detector with TFT readout

Evaluation of the x-ray response of amorphous selenium coated 100-μm pitch a-Si active pixel sensors for tomosynthesis applications

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