  The readout electronics of the ATLAS Hadronic Endcap Calorimeter (HEC) will
have to withstand an about 3-5 times larger radiation environment at the future
high-luminosity LHC (HLLHC) compared to their design values. The preamplifier
and summing boards (PSBs), which are equipped with GaAs ASICs and comprise the
heart of the readout electronics, were irradiated with neutrons and protons
with fluences surpassing several times ten years of operation of the HL-LHC.
Neutron tests were performed at the NPI in Rez, Czech Republic, where a 36 MeV
proton beam was directed on a thick heavy water target to produce neutrons. The
proton irradiation was done with 200 MeV protons at the PROSCAN area of the
Proton Irradiation Facility at the PSI in Villigen, Switzerland. In-situ
measurements of S-parameters in both tests allow the evaluation of frequency
dependent performance parameters, like gain and input impedance, as a function
of fluence. The linearity of the ASIC response was measured directly in the
neutron tests with a triangular input pulse of varying amplitude. The results
obtained allow an estimation of the expected performance degradation of the
HEC. For a possible replacement of the PSB chips, alternative technologies were
investigated and exposed to similar neutron radiation levels. In particular,
IHP 250 nm Si CMOS technology has turned out to show good performance and match
the specifications required. The performance measurements of the current PSB
devices, the expected performance degradations under HL-LHC conditions, and
results from alternative technologies will be presented.
