Pulsed laser fabrication of 3D diamond sensors

3D detectors, whose electrodes extend perpendicularly to the sensor surface, represent one of the solution proposed for the challenges of radiation-harsh environments in high energy physics [1-4]. We report on the fabrication and characterization of prototypes of 3D diamond detector, which add to the 3D architecture the advantages of diamond as a sensor for tracking purposes. Two different laser sources, a Nd:YAG 1064 Q-switched laser with 8 ns pulse-width and a Ti:sapphire laser source with 30 fs pulse duration have been used to fabricate arrays of graphitic columns in the bulk of a polycrystalline and a single crystal diamond sample. The columns are staggered and connected to graphitic combs which have been fabricated as well by laser irradiation and used as electric contacts. On each sample, an identical pattern of graphitic combs without columns (2D structure) has also been fabricated as a reference. The charge collection efficiency of each 3D sensor has been measured at different voltages and compared with the corresponding 2D structures. The much lower saturation voltages of the 3D sensors compared to those of the planar ones confirm that charge collection takes place at the columnar electrodes. Moreover, an efficiency of 100% is assured by the sensors fabricated with the fs- laser source, while a loss in efficiency up to 30% is observed with the sensors fabricated with the ns-laser. The expected behaviour of 3D diamond sensors after strong radiation damage is discussed.