PUNCH-THROUGH CHARACTERISTICS OF FOXFET BIASED DETECTORS

The main punch-through characteristics have been studied on Field OXide FETs (FOXFETs) used for microstrip biasing in Si detectors. The voltage-current DC curves have been studied on devices with different channel width/length ratios, fabricated on Si substrates with different doping levels. The punch-through threshold voltage depends on the positive charge in the gate oxide, device layout and temperature. The relation between punch-through current and dynamic resistance is insensitive to charge accumulation in the gate oxide induced by irradiation and to different Si donor doping levels. Dynamic resistance however varies as the doping changes from n- to p-type, and it also depends on the Si bulk damage induced by neutron irradiation. The AC impedance will reproduce the DC dynamic resistance, but show also large effects due to parasitic capacitance, which dominates the FOXFET response at high frequency and can affect the detector performance.