  The barrel section of the novel MIP Timing Detector (MTD) will be constructed
as part of the upgrade of the CMS experiment to provide a time resolution for
single charged tracks in the range of $30-60$ ps using LYSO:Ce crystal arrays
read out with Silicon Photomultipliers (SiPMs). A major challenge for the
operation of such a detector is the extremely high radiation level, of about
$2\times10^{14}$ 1 MeV(Si) Eqv. n/cm$^2$, that will be integrated over a decade
of operation of the High Luminosity Large Hadron Collider (HL-LHC). Silicon
Photomultipliers exposed to this level of radiation have shown a strong
increase in dark count rate and radiation damage effects that also impact their
gain and photon detection efficiency. For this reason during operations the
whole detector is cooled down to about $-35^{\circ}$C. In this paper we
illustrate an innovative and cost-effective solution to mitigate the impact of
radiation damage on the timing performance of the detector, by integrating
small thermo-electric coolers (TECs) on the back of the SiPM package. This
additional feature, fully integrated as part of the SiPM array, enables a
further decrease in operating temperature down to about $-45^{\circ}$C. This
leads to a reduction by a factor of about two in the dark count rate without
requiring additional power budget, since the power required by the TEC is
almost entirely offset by a decrease in the power required for the SiPM
operation due to leakage current. In addition, the operation of the TECs with
reversed polarity during technical stops of the accelerator can raise the
temperature of the SiPMs up to $60^{\circ}$C (about $50^{\circ}$C higher than
the rest of the detector), thus accelerating the annealing of radiation damage
effects and partly recovering the SiPM performance.
