PureB multi-guard ring structures for detector applications

• PureB technology offers damage free doping, shallow junctions, low leakage current and high responsivity photodiodes.
• PureB multi-guard rings were used in SDDs to obtain high breakdown voltage.
• Field plate in the inward direction offers a higher breakdown voltage.
• Fabricated PureB multi-guard rings showed no breakdown till 1100 V.
• PureB SDD showed very low leakage current in the range of 1.5–3 nA/cm2.

The breakdown voltage is an important parameter in designing X-ray detectors such as silicon drift detectors (SDDs). In SDDs the complete thickness of the wafer has to be depleted to enable the detection of different energies of X-rays. A high voltage is required to have a fully depleted region while keeping the leakage current low. Multi-guard ring structures are designed to meet both a low leakage current and a high breakdown voltage using deposited PureB layers. To obtain a low leakage current, PureB layers were used. In multi-guard ring structures, parameters such as gap width, number of the rings and overlap of the metal field plate with the oxide have been designed to obtain higher breakdown voltage. Parameters such as gap size, oxide charge, bulk doping concentration and field plate design have an influence on the potential distribution of the guard rings. The designed structure works up to the limit of the measurement systems (1100 V) with very low leakage current in the range of 1.5–3 nA/cm2 for the detector.