  The high-luminosity operation of the Tracker in the Compact Muon Solenid
(CMS) detector at the Large Hadron Collider (LHC) experiment calls for the
development of silicon-based sensors. This involves implementation of
AC-coupling to micro-scale pixel sensor areas to provide enhanced isolation of
radiation-induced leakage currents. The motivation of this study is the
development of AC-pixel sensors with negative oxides (such as aluminium oxide -
Al$_2$O$_3$ and hafnium oxide - HfO$_2$) as field insulators that possess good
dielectric strength and provide radiation hardness. Thin films of Al$_2$O$_3$
and HfO$_2$ grown by atomic layer deposition (ALD) method were used as
dielectrics for capacitive coupling. A comparison study based on dielectric
material used in MOS capacitors indicate HfO$_2$ as a better candidate since it
provides higher sensitivity (where, the term sensitivity is defined as the
ratio of the change in flat-band voltage to dose) to negative charge
accumulation with gamma irradiation.
  Further, space charge sign inversion was observed for sensors processed on
high resistivity p-type Magnetic Czochralski silicon (MCz-Si) substrates that
were irradiated with gamma rays up to a dose of 1 MGy. The inter-pixel
resistance values of heavily gamma irradiated AC-coupled pixel sensors suggest
that high-$K$ negative oxides as field insulators provide a good electrical
isolation between the pixels.
