Speaker
Description
Modern Free Electron Laser (FEL) facilities produce X-ray light pulses at MHz
repetition rates. The LCLS-II accelerator, which is currently under
commissioning, will operate at a continuous rate of 1 MHz with X-ray energies
between 250 eV and 5 keV. Experiments conducted at LCLS-II will require
detectors with a unique set of features, such as high-spatial resolution, low-noise
performance (single photon resolution at X-ray energies down to 250 eV),
high-dynamic range (up to 10^3 photons) and high-frame rates (from 5 kHz up to 1
MHz).
We present the design of ePixM, a charge-integrating imaging detector developed
for soft X-rays applications. It consists of 384 x 192 active pixel sensors,
with a pixel size of 50x50 um and a total sensitive area of 2 x 1 cm. ePixM has
been designed in LFoundry 150 nm CMOS technology on high-resistivity substrate
to enable full depletion of the substrate: This results in a lower detector
capacitance (~ 50 fF) and a charge-collection time on-the-order of a few ns.
Each pixel includes a Charge Sensitive Amplifier (CSA) with gain auto-ranging
capability and a noise-shaper performing Correlated Double Sampling
(CDS). The performance in terms of Equivalent Noise Charge (ENC) has been
evaluated through post-layout simulations and meets the experimental
requirements of 15 electrons, thus allowing single-photon resolution at X-ray
energies down to 250 eV. Moreover, the dynamic range exceeds 10^3 photons at 500
eV thanks to the auto-ranging circuitry. We present the architecture of the
front-end electronics and report the first preliminary results.
