We detail the integration of amorphous silicon (a-Si) 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 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 80 μm thick stabilized amorphous selenium. These selenium layers were selected for preliminary work and
represent a quantum efficiency (QE) of 69% for x-ray spectra (tungsten target, 2 mm Al filtration) of 30 kVp. Detector
response was evaluated for a-Se biasing electric fields of both 5 V/μm and 10 V/μm.
A detector dark current of 110 pA/cm2 (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 100μm and
200μm 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.