Particle detector capable of separating in-time signals from out-of-time signals

Abstract

Silicon Particle Detector, comprising an absorption region (10) capable of generating electrical charges in response to a particle passing therethrough, a first and a second electrode (20, 30) arranged on opposite sides of the absorption region (10), wherein the first electrode (20) is segmented into a plurality of pads (20a), and a plurality of multiplication layers (40) able to avalanche-multiply the electric charges generated in the absorption region (10), each of the multiplication layers (40) being arranged beneath a respective pad (20a) and interposed between it and the absorption region (10), each multiplication layer (40) is surrounded by a respective protection ring (50) formed by the material of the pad (20a). The protection ring (50) is laterally interposed between the multiplication layer (40) and the absorption region (10).

Claims

1. A silicon particle detector comprising: an absorption region capable of creating electric charges as a response to a particle passing therethrough, a first and a second electrode on opposite sides of the absorption region, one of said first and second electrode being an anode and the other of said first and second electrode being a cathode, wherein the first electrode is formed by a plurality of pads arranged in array, neighboring pads being separated from each other by a gap formed by material of the absorption region, and a plurality of multiplication layers capable of avalanche-multiplying the electric charges created in the absorption region, each multiplication layer of the plurality of multiplication layers being arranged under a respective pad of the plurality of pads and interposed between the respective pad of the plurality of pads and the absorption region, wherein each multiplication layer of the plurality of multiplication layers is surrounded by a respective protection ring formed of the same type material as the respective pad, the respective protection ring being laterally interposed internally between the plurality of multiplication layers and the absorption region.

2. The detector according to claim 1, wherein the respective protection rings that surrounds each multiplication layer of the plurality of multiplication layers forms a plurality of protection rings, wherein the absorption region, the first and second electrode, the plurality of multiplication layers and the plurality of protection rings are made of silicon, the first electrode and plurality of protection rings having a first type of doping, and the plurality of multiplication layers, absorption region and second electrode have a second type of doping, opposite to the first type of doping.

3. The detector according to claim 2, wherein the first and second electrode and plurality of protection rings have a higher doping concentration than the plurality of multiplication layers, the plurality of multiplication layers having a higher doping concentration than the absorption region.

4. The detector according to claim 3, wherein a doping concentration in the first and second electrode and plurality of protection rings is of the order of magnitude of 10.sup.18 cm.sup.3, a doping concentration in the plurality of multiplication layers is of the order of magnitude of 10.sup.16 cm.sup.3, and a doping concentration in the absorption region is of the order of magnitude of 10.sup.12-10.sup.14 cm.sup.3.

Description

(1) Further features and advantages of the detector according to the invention will become more apparent in the following detailed description of an embodiment of the invention, made with reference to the appended drawings, provided purely to be illustrative and non-limiting, wherein

(2) FIGS. 1 and 2 is a structural diagram of a known particle detector;

(3) FIG. 3 is a structural diagram of a detector according to the invention; and

(4) FIG. 4 is a plan view of a part of the detector of FIG. 3.

(5) With reference to FIGS. 3 and 4, a silicon particle detector is shown, in particular, an ultra-fast silicon detector UFSD.

(6) The detector comprises an absorption region 10 capable of generating electrical charges in response to a particle passing therethrough, and a first and second electrode 20, 30 arranged on opposite sides of the absorption region 10. Depending on the possible configurations of the detector, one of such electrodes 20, 30 is an anode while the other is a cathode.

(7) The first electrode 20 is segmented into a plurality of pads 20a arranged in an array. Each pad, generally square or rectangular, has lateral dimensions that may vary from tens of microns to several millimeters.

(8) As used in this description, the term lateral means any direction in a plane orthogonal to the direction that goes from the anode to the cathode.

(9) The neighboring pads 20a are separated from each other by a gap 10a formed by material from the absorption region 10. The distance d between two pads, i.e. the width of the gap, is normally kept as small as possible, with typical distances of 50-100 m. In FIGS. 1 to 3, such distance is exaggerated for clarity of representation.

(10) Below each pad 20a, and interposed between it and the absorption region 10, there is arranged a respective multiplication layer 40, capable of avalanche-multiplying the electric charges generated in the absorption layer 10.

(11) Each multiplication layer 40 has lateral dimensions smaller than those of the overlying respective pad 20a and is surrounded by a respective protection ring 50 formed of the material of the pad 20a. The protection ring 50 is therefore laterally interposed between the multiplication layer 40 and the absorption region 10. The width b of the ring is about 10-30 m.

(12) The thickness of the various layers is generally on the order of microns or tens of microns.

(13) The absorption region 10, the first and second electrodes 20, 30, the multiplication layers 40 and the protection rings 50 are made of the same semiconductor material, in particular, silicon.

(14) The first electrode 20 and the protection rings 50 have a first type of doping, for example n, and the multiplication layers 40, the absorption region 10 and the second electrode 30 have a second type of doping opposite to the first, for example p.

(15) The first and second electrodes 20, 30 and the protection rings 50 have a concentration of charge carriers greater than that of the multiplication layers 40. The multiplication layers 40 exhibit a concentration of charge carriers greater than that of the absorption region 10.

(16) For the purposes of this description, the term concentration of charge carriers means the concentration of the majority carriers in each individual detector region.

(17) For example, the concentration of charge carriers at room temperature in the first and second electrodes 20, 30 and in the protection rings 50 may be on the order of 10.sup.18 cm.sup.3. The concentration of charge carriers at room temperature in the multiplication layers 40 may be on the order of 10.sup.16 cm.sup.3. The concentration of charge carriers at room temperature in the absorption region 10 may be on the order of 10.sup.12 cm.sup.3.

(18) The symbols n++ and p++ are therefore used to refer to doping levels (charge carrier concentration) of the silicon of approximately 10.sup.18 cm.sup.3 for silicon of type n and of type p, respectively.

(19) On the other hand, symbols n+ and p+ are used to refer to silicon doping levels of about 10.sup.16 cm.sup.3 per silicon of type n and of type p, respectively.

(20) Finally, the symbols n and p are used to refer to silicon doping levels of about 10.sup.12-10.sup.14 cm.sup.3 per silicon of type n and of type p, respectively.

(21) For example, a detector may be provided wherein the absorption region 10 is of doped silicon p, the first electrode 20 (or more specifically, the individual pads 20a) of doped silicon n++, the second electrode 30 of doped silicon p++, the multiplication layer 40 of doped silicon p+ so as to create a contact n+/p+ between the overlying pad and the multiplication layer, and the silicon protection ring 50 doped in the same manner as the pad, i.e. n++.

(22) The structure that is generated in this detector is therefore of the type n++/p+/p/p++ in the central region of each pad, while it is of the type n++/p/p++ in the peripheral region of each pad, where the ring is positioned.

(23) Naturally, it is possible to provide a detector having an inverted doping type with respect to the one indicated above, i.e. of the type p++/n+/n/n++, in the central region of each pad, and of the type p++/n/n++ in the peripheral region of each pad, where the ring is located.

(24) For the operation of the detector described above, a potential difference between the first and second electrode is applied. For example, a negative voltage is applied to the second electrode 30 with respect to the first electrode 20, if the first electrode is doped n++ and the second p++.

(25) The electrical field generated in the detector causes the movement of free charges created by radiation: if the free charges are created directly under the multiplication layer 40, then they are collected by passing through the multiplication layer 40 and their signal is multiplied. If, however, as shown in FIG. 3, the free charges are created in a region between two neighboring pads, they are collected by the protection ring 50 without being multiplied.

(26) The use of the protection ring 50 therefore allows multiplying only the radiation hitting the part of the absorption region 10 which lies between the absorption layer 40 and the second electrode 30, leaving the signal of the particle which hit elsewhere unaltered and thus easily recognizable.

(27) It is interesting to point out a second effect due to the addition of the protection ring around each pad in a segmented detector: with this design, the segmented detector becomes more resistant to the effects of electric breakdowns as the edge terminations of each pad are deeper and therefore, in the vicinity thereof, the electric field is smaller.

BIBLIOGRAPHICAL REFERENCES

(28) [1] G. F. Dalla Betta et al, Design and TCAD simulation of double-sided pixelated low gain amplification detectors, https://indico.cern.ch/event/313925/contributions/1687301/attachments/601603/827991/G F_DALLA_BETTA.pdf

(29) [2] P. Fernndez-Martinez et al, Design and Fabrication of an Optimal Peripheral Region for the LGAD, https://indico.cern.ch/event/313925/contributions/1687306/attachments/601607/827995/6_4_FernandezMartinez_LGAD_Design.pdf.