Design of an integrated low-noise ultra-fast charge-sensitive micro-probe for semiconductor detectors

A low-noise wide-bandwidth charge-sensitive micro-probe is being developed, able to capture the charge signals of semiconductor detectors. The micro-probe works on a single terminated coaxial cable of whatever length, whose quality is key to achieving a good dynamic performance. The cable carries both the power supply (DC signal component) and the event pulses (AC signal component). No power-supply filtering capacitor is required. The micro-probe is particularly compact, consisting of a few devices, including a GΩ surface-mount resistor. Both a discrete-component and an ASIC version are under development. The ASIC version is designed in a 0.35μm 5V CMOS technology and is expected to be fully functional also at cryogenic temperatures. Thanks to such a large degree of integration the micro-probe can be placed very close to the detector electrode and is particularly light, compact and hence suited for hostile environments and for applications where a high radio-purity of the front-end is required, like in rare-decay research in underground laboratories. The rise time of the integrated version, as obtained from computer simulation, is < 1ns with a detector capacitance of 16pF. The energy range is beyond 20 MeV, and the power consumption is ∼35 mW per channel.