A method to observe field-region oxide charge and inter-electrode isolation from CV-characteristics of n-on-p devices

Abstract N -on- p silicon sensors will be utilized in the Compact Muon Solenoid (CMS) detector's tracker and High Granularity Calorimeter (HGCAL) in the High Luminosity upgrade of the Large Hadron Collider (HL-LHC). Among their several advantages in terms of radiation hardness over the traditional p -on- n sensors in the extreme radiation environment of the HL-LHC are electron collection instead of holes and overlapping maxima of weighting and electric fields at the charge-collecting electrodes. The disadvantage of the multi-channel SiO 2 -passivated n -on- p sensors is the generation of an inversion layer under the Si/SiO 2 -interface by a positive interface-oxide-charge ( N ox ) that at high densities can compromise the position resolution by creating a conduction channel between the electrodes. This issue is typically addressed by including additional isolnts ( p -stp, p -spray) between n + -electrodes. Focusing on the guard-ring regions of n -on- p sensors where no isolation implants are applied between the electrodes, a capacitance-voltage ( CV ) characterization study of both 6-inch wafer test diodes and 8-inch HGCAL prototype and pre-series sensors showed a distinct threshold voltage ( V th,iso ) in the CV -characteristics of a biased n + -electrode when its enclosing guard-ring was left floating. When reproduced by simulations, the measured V th,iso was found to contain information on the field-region N ox and indicate the threshold where the two electrodes become electrically isolated by the influence of the reverse bias voltage. Together with previous studies on the inter-electrode isolation of irradiated n -on- p sensors, the results indicate that position sensitive n -on- p sensors without isolation implants may be feasible in future HEP experiments.