Enhancing the fill-factor of CMOS SPAD arrays using microlens integration

Arrays of single-photon avalanche diode (SPAD) detectors were fabricated, using a 0.35 μm CMOS technology process, for use in applications such as time-of-flight 3D ranging and microscopy. Each 150 x 150 μm pixel comprises a 30 μm active area diameter SPAD and its associated circuitry for counting, timing and quenching, resulting in a fill-factor of 3.14%. This paper reports how a higher effective fill-factor was achieved as a result of integrating microlens arrays on top of the 32 x 32 SPAD arrays. Diffractive and refractive microlens arrays were designed to concentrate the incoming light onto the active area of each pixel. A telecentric imaging system was used to measure the improvement factor (IF) resulting from microlens integration, whilst varying the f-number of incident light from f/2 to f/22 in one-stop increments across a spectral range of 500-900 nm. These measurements have demonstrated an increasing IF with fnumber, and a maximum of ~16 at the peak wavelength, showing a good agreement with theoretical values. An IF of 16 represents the highest value reported in the literature for microlenses integrated onto a SPAD detector array. The results from statistical analysis indicated the variation of detector efficiency was between 3-10% across the whole f-number range, demonstrating excellent uniformity across the detector plane with and without microlenses

LA PLASTICA ESTERNA DELLA VALVOLA PRETERMINALE DELLA VENA GRANDE SAFENA

FIRENZ

Traffic engineering with OSPF-TE and RSVP-TE: Flooding reduction techniques and evaluation of processing cost

This paper considers two important aspects related to the control plane of Traffic Engineered IP/MPLS networks: the "flooding reduction" mechanisms and the evaluation of processing cost for signaling and routing protocols. The flooding reduction mechanisms are needed to reduce the amount of information exchanged by Traffic Engineering enabled routing protocols. The trade-off between the amount of information exchanged and the network performance (connection blocking probability) is discussed in the light of specific aspects of OSPF-TE routing protocol and RSVP-TE signaling protocol. Different mechanisms are analyzed and a suggestion is given for the best one. The dynamic aspects related to the time needed to distribute the routing and signaling information are considered. Finally, the combined processing cost of routing and signaling is analyzed, and the possible bottlenecks of the architecture are discussed. It is worth mentioning that the discussed results have been derived not only with simulation/analysis but also with measurements coming from a testbed implementation. (c) 2005 Elsevier B.V. All rights reserved

Optimization of epitaxial growth for thick Ge-on-Si structures used for single photon avalanche diode applications

SPAD structures have been grown by RP-CVD and shown to have: excellent crystallinity, with low TDD; a smooth surface, suitable for device incorporation; and sharp doping profiles required to maximize performance. Device measurements have produced the highest SPDE of any Ge on Si SPAD recorded