Particle detector based on semiconductors with electrical properties dedicated to particle differentiation

Abstract

Disclosed is a particle detector comprising: - a semiconductor substrate comprising a sensitive volume for producing charges on passage of a particle, at least one front contact island under a front side of the substrate, and at least one back contact island under a back side of the substrate, - at least one front electrode making contact with the front contact island; - at least one back electrode making contact with the back contact island; - an acquisition chain for detecting transient signals coming from the front electrode. The front electrode is an electrode for applying voltage and detecting transient signals. It is produced on only part of the front side of the semiconductor substrate, without guard electrodes, such that a non-uniform electric field is created in the sensitive volume when the electrode is supplied with a voltage.

Description

Description Title of the invention: Semiconductor-based particle detector with electrical properties dedicated to particle differentiation. technical field

[0001] The present invention relates to a particle detector.

[0002] Such a detector is designed to measure energy deposits generated by the passage of ionizing or non-ionizing radiation. These detectors are used in numerous technical fields where knowledge of the ambient radiation environment (flux, particle nature, etc.) is desired, such as radiation monitors onboard satellites dedicated to studying radiation belts. However, the invention has a broader scope, as it also applies to the calibration of particle beams in radiation protection, or to the study of other types of radiation besides electrons or protons, in space or on the ground. Prior art

[0003] In general, commonly used ionizing radiation detectors comprise a sensitive volume, typically corresponding to the substrate of a solid-state detector (SSD) made of semiconductor material, usually silicon, and an amplification chain. When only the deposited energy is sampled, the amplification chain acts as an integrator to converge to a value directly comparable to the quantities of charge generated and, therefore, to the energy deposited by the incident particle.

[0004]

[0005] Sometimes, the data measured by radiation monitors is erroneous. Indeed, in a mixed environment such as the radiation belts, radiation monitors can encounter significant difficulties in discriminating between electrons and protons, especially when they deposit the same amount of energy in the detector. This is due to the commonly used measurement method, where the only information gathered upon particle detection is the total energy deposited in the diode. This misidentification of the particle type leads to contamination of the monitor's data. Data contamination occurs when measurements attributed to protons are actually due to electrons, and vice versa; thus, the wrong type of particle is not being measured. This results in unreliable measurements of particle fluxes in the radiation belts at any given time.

[0006]

[0007] It is known that observing transient signals allows us to extract information about the nature and energy of the incident ionizing particle. These detectors include an amplification chain designed to preserve the integrity of the dynamics of the charge collection generated by the incident particle. Therefore, the function is no longer to act as an integrator but solely to amplify the signal as it is at the output of the SSD.

[0008] The generation of transient signals in a semiconductor detector relies on the Shockley-Ramo theorem. This theorem allows us to calculate the current measured on a given electrode as a function of time t, according to the following expression:

[0011] With i(t) the current induced on the electrode, q the electric charge of the carriers moving in the electric field of the sensing volume with a velocity v(t), and E* the virtual electric field or "Weighting Field," normalized by a potential of 1 Volt. This virtual field is calculated individually for each measuring electrode of the detector, by removing all charges, setting the potential of the electrode in question to 1 V, and the potential of all other electrodes to 0 V. Each electrode thus has its own "weighting field," defining the current generated on it independently of the electric field actually applied in the detector.

[0012] The electric field in the sensitive volume and the movement of the carriers in this field are calculated from the solution of the Poisson drift-diffusion equations:

[0018] With n and p being the electron and hole densities, J nand J p electron and hole current densities, V the electrostatic potential, IVp and the density of donor and acceptor sites, D n and D p the diffusion coefficients for electrons and holes, and p n and p p the mobilities of electrons and holes.

[0019] This type of detector is used in accelerators, particularly to identify the isotopes of an incident ion. However, identifying the nature of the particle often relies on the signal generated when it is immobilized in the detector, which does not allow discrimination between particles passing through the detector.

[0020] In the case of the detectors described above, the first makes it completely impossible to discriminate between particles depositing the same amount of energy, and the second depends on post-processing applied to the captured transients. Currently, scientists' efforts have focused solely on heavy particles and in controlled environments. There is no solution for measurements in uncontrolled environments (such as in radiation belts) and for distinguishing lighter particles.

[0021]

[0022] Figure 1 shows the LET (Linear Energy Transfer) of 200 keV electrons and 500 MeV protons in a volume of silicon. The LET is the amount of energy per unit length transferred by the incident particle to the target material. In Figure 1, we can see that the electrons and protons in this example deposit the same amount of energy in a volume up to several tens of micrometers thick. Thus, if these two particles were to pass through a detector that only analyzed the amount of energy deposited, the detector would be unable to distinguish the electron from the proton. However, if we consider the details of the particle's path, and not just the amount of energy deposited, it is possible to identify trends specific to each type of particle.Indeed, low-energy electrons will mostly interact elastically with the matter they traverse, while protons will very often interact inelastically. Consequently, electrons will tend to have a very diffuse path, while protons will traverse the volume in a very straight line. These differences lead to different tracks, and therefore different ways of depositing the same amount of energy, as illustrated in Figure 2.

[0023]

[0024] The design of SSDs (Solid State Detectors) is primarily geared towards meeting "static" criteria (typically leakage current, which is desired to be as low as possible). Figure 3 shows the classic structure of an SSD: an n- or p-doped substrate, and junctions (n+ or p+) for the contacts.

[0025] Such SSDs, combined with transient signal processing during particle passage through the detector, have already been used for heavy-ion discrimination in controlled environments. Signals are generated in the device when the particle passes through the semiconductor diode(s) composing the detector and deposits charges in the diode's sensitive volume. These signals are measured using a detection track integrated into each diode. Each measurement track is connected to a signal acquisition and processing chain capable of sampling the The shape of the transient signal generated on the detection track can be used to analyze the characteristics of these signals. Through a method of analyzing and classifying the collected signals and their characteristics, these devices are able to identify the incident particle and its initial energy. However, this identification is only possible when the particle has not completely passed through the detector.

[0026]

[0027] Thus, current transitional measures do not allow for effective discrimination of particle types in uncontrolled environments and / or for light particles.

[0028]

[0029] We are familiar with document CN103954988B, which describes a detector designed to discriminate between particles. This detector comprises several SSD diodes in parallel. One of the three diodes has an input window for the radiation to be measured. The radiation enters through the first and second diodes and is then blocked by the third. The recovered signals allow for the discrimination of particles and their energies.

[0030] We know that document CN104656117B exploits the shape of the signal generated by alpha particles and protons (heavy particles) to differentiate them.

[0031] We also know of document EP3821278B 1, which describes a guard ring-based detector for particle detection. The guard rings serve to ensure a homogeneous magnetic field within the volume of the SSD diode.

[0032]

[0033] The present invention aims at a new detector capable of efficiently discriminating between heavy and light particles.

[0034] Another objective of the invention is a new detector capable of operating in controlled or uncontrolled environments.

[0035] Description of the invention

[0036] At least one of the aforementioned objectives can be achieved with a particle detector comprising:

[0037] - a semiconductor substrate comprising a sensitive volume capable of producing charges during the passage of a particle, at least one front contact island made under a front face of the semiconductor substrate, and at least one rear contact island made under a rear face of the semiconductor substrate,

[0038] - at least one front electrode made on the front face of the semiconductor substrate, in contact with the front contact island;

[0039] - at least one rear electrode made on all or part of the rear face of the semiconductor substrate, in contact with the rear contact island;

[0040] - an acquisition chain capable of detecting transient signals from said at least one front electrode.

[0041] Said at least one front electrode is a voltage application and transient signal detection electrode, and said at least one front electrode is made on only a portion of the front face of the semiconductor substrate, without guard electrodes, so that a non-homogeneous electric field is created in the sensitive volume when said at least one electrode is voltage-energized.

[0042]

[0043] Transient signals are obtained, for example, by connecting at least one front electrode and at least one rear electrode to the acquisition chain.

[0044]

[0045] With the detector according to the invention, an inhomogeneous electric field is generated within the detector's sensitive volume to enhance the dynamics of charge collection, these charges being generated by the passage of an incident particle through the detector's sensitive volume. The electrode geometry is designed to make the electric field non-homogeneous.

[0046] With enhanced dynamics, it is possible to discriminate between different types of particles using signal processing techniques familiar to those skilled in the art. Indeed, a non-homogeneous electric field within the detector's sensitive volume induces unique behaviors in the measured signals, thus facilitating discrimination. Each particle generates a highly distinctive signal shape measured by the electrode.

[0047] The electrode in the invention plays a dual role of perturbing the field to make it inhomogeneous and detecting the measured signal.

[0048]

[0049] The principle of the invention is to allow manipulation of the two terms governing the current collected by the detector during the passage of a particle, which are given by the Shockley-Ramo equation. By modulating the electric field, the transport of charges created within the sensitive volume is modified. This allows, among other things, the charge carriers to be directed towards the measuring electrode(s), and limits information loss. This modulation depends on the voltage applied to the measuring electrode, as well as the geometry of the detector.

[0050]

[0051] According to an advantageous feature, said at least one front electrode has a geometric shape having at least an inter-electrode spacing suitable for creating a non-homogeneous electric field in the sensitive volume.

[0052] Inter-electrode spacing means that the electrode comprises at least two parts separated by a zone that leaves the surface of the semiconductor substrate uncovered. This zone can be linear, circular, or any other shape. This allows for the creation of a non-homogeneous distribution on the surface of the semiconductor substrate and, when an electric field is created by applying voltage, an inhomogeneous electric field in the sensitive volume.

[0053] According to one embodiment, said at least one front electrode is a spiral covering at least a part of the surface of the sensitive volume.

[0054] When the spiral covers the surface of the sensitive volume, there is the inter-electrode spacing which ensures inhomogeneity.

[0055]

[0056] According to an advantageous characteristic, the semiconductor substrate is circular, square, or rectangular in shape and:

[0057] - said at least one front electrode consists of a plurality of annular front electrodes distributed concentrically around a central front electrode, with an inter-electrode spacing present between any two front electrodes and

[0058] - said at least one rear electrode consists respectively of a plurality of annular rear electrodes distributed concentrically around a central rear electrode; each front-rear electrode pair being capable of receiving a bias voltage different from that intended to be applied to the neighboring front-rear electrode pair, an inter-electrode spacing being present between two rear electrodes.

[0059] Using multiple front or rear electrodes further allows for the decomposition of the virtual collection field. This enables the acquisition of individual signals across the entire width of the detector and allows for the reconstruction of the particle's track shape. Each front-rear electrode pair constitutes an individual measurement track, enabling the measurement to be discretized.

[0060] Ideally, for each front-rear electrode pair, the voltage applied to the front electrode is different from the voltage applied to the rear electrode. Preferably, one electrode is grounded and the other is held at a specific potential.

[0061]

[0062] The semiconductor substrate can be circular, square, or rectangular in shape, and:

[0063] - said at least one front electrode comprises a first central front electrode of circular, square or rectangular shape and at least a second front electrode, peripheral or not, of circular, square or rectangular shape; an inter-electrode spacing being present between the two front electrodes; and

[0064] - said at least one back electrode consists of a single back electrode distributed over the entire back face of the semiconductor substrate.

[0065] Such a design has the advantage of limiting the number of measurement tracks and to ensure, however, an active in-homogenization.

[0066]

[0067] According to one embodiment, where the semiconductor substrate can be a diode structure, at least one front electrode is an anode or a cathode; at least one rear electrode is respectively a cathode or an anode. Those skilled in the art will understand that converting from an anode+cathode assembly to a cathode+anode assembly requires adapting the voltage direction.

[0068]

[0069] Advantageously, the semiconductor substrate can have a thickness between 30 µm and 5 mm, ideally 300 µm. This range of values ​​has been shown to be optimal. Too thin a thickness risks the detector failing to detect charges. Too thick a thickness risks detector failure due to an excessively high applied voltage.

[0070]

[0071] The semiconductor substrate can also have a width ranging from 30 µm to 5 cm, ideally 1.5 mm. A width that is too small risks resulting in an insufficient particle flux. A width that is too large risks an excessively large detector size, leading to integration difficulties.

[0072]

[0073] According to one embodiment, the inter-electrode spacing may have a width between 30 pm and 1 mm, ideally 200 pm.

[0074] An inter-electrode spacing that is too narrow would result in an excessively high electric field, risking detector failure. A spacing that is too wide would lead to a loss of efficiency, with a risk of charge loss in the sensitive volume area below the spacing.

[0075]

[0076] Advantageously, when this detector includes several front electrodes, the acquisition chain can be configured to apply voltages respectively to the front electrodes with a voltage difference between two consecutive front electrodes of between 0 and 20 V, ideally 0 V.

[0077] It is possible to have zero voltage at the center and 100V at an i-th ring.

[0078]

[0079] According to a preferred embodiment, the sensitive volume has a doping level between 10 10 and 10 14 cm 3 ideally 10 11 cm 3 These values ​​correspond to relatively low doping levels, resulting in a completely depleted zone. This ensures full collection of the generated charges within the sensitive volume.

[0080]

[0081] Furthermore, each contact island can present a doping level between 1010 and 10 18 cm 3 ideally 10 16 cm 3 Preferably, the doping level of the islands is different from the doping level of the sensitive volume. This can help to obtain an inhomogeneous electric field in the sensitive volume.

[0082]

[0083] The detector can include as many front electrodes as there are front contact islands.

[0084]

[0085] According to another aspect of the invention, a system for detecting and discriminating particles is proposed. This system comprises:

[0086] - a particle detector as described above,

[0087] - a processing unit configured to compare one or more parameters of an acquired transient signal with one or more predetermined parameters in order to identify the nature of the particle at the origin of this acquired transient signal.

[0088]

[0089] A method for detecting and discriminating particles is also provided. Advantageously, the method comprises the following steps implemented by a processing unit of the above system:

[0090] - application of one or more voltages to one or more front electrodes of the particle detector such that a non-homogeneous electric field is created in the sensitive volume,

[0091] - acquisition of a transient signal on said one or more front electrodes following the passage of a particle through the sensitive volume,

[0092] - comparison of one or more parameters of the transient signal to one or more predetermined parameters in order to identify the nature of the particle at the origin of this acquired transient signal.

[0093]

[0094] The parameters can be characteristics of the measured signals: slope, amplitude, derivative, mean, area, ... Description of the figures and methods of implementation.

[0095] Other advantages and features of the invention will become apparent upon reading the detailed description of implementations and embodiments, which are by no means limiting, and the following attached drawings:

[0096] Figure 1 is a graph illustrating the linear energy transferred by 200keV electrons and 500MeV protons according to the prior art,

[0097] Figure 2 includes a map of the charge densities generated by 500 MeV protons (left) and a map of the charge densities generated by 200 keV electrons (right),

[0098] Figure 3 is a schematic view of a typical SSD structure.

[0099] Figure 4 includes three examples of calculated electric field maps for a classical geometry (a) and for multi-electrode geometries (b and c),

[0100] Figure 5 includes four examples of virtual potential maps calculated for (a) a simple electrode made over the entire front surface of a particle detection diode, (b) a central electrode covering half the front surface of the diode, (c) a central electrode covering one-third of the front surface of the diode, and (d) for a ring electrode surrounding the electrode of example (c),

[0101] Figure 6 is a graphical representation illustrating the curves of the effect of the virtual electric field on the current collected by a central junction of variable width: 100% (a); 50% (b); and 30% (c) of the front surface of the diode,

[0102] Figure 7 is a schematic view of a system for detecting and discriminating particles,

[0103] Figure 8 is a schematic view of a semiconductor substrate according to the invention with front and rear measuring electrodes,

[0104] Figure 9 includes a) a schematic top view of a semiconductor substrate with a serpentine front electrode, and b) a schematic cross-sectional view of the same semiconductor substrate with the front electrode and a rear electrode,

[0105] Figure 10 includes a) a schematic top view of a semiconductor substrate with front electrodes in the shape of concentric circles, b) a schematic bottom view of the same semiconductor substrate with rear electrodes in the shape of concentric circles, and c) a schematic cross-sectional view of the same semiconductor substrate.

[0106] Figure 11 includes a) a schematic bottom view of a semiconductor substrate with two rear electrodes of square and annular shape respectively, and b) a schematic cross-sectional view of the same semiconductor substrate with an anode on the front surface and the rear electrodes on the rear surface,

[0107] Figure 12 includes a) a schematic top view of a semiconductor substrate with two front electrodes of circular and annular shapes respectively, and b) a schematic cross-sectional view of the same semiconductor substrate with the front electrodes and a rear cathode, and

[0108] Figure 13 is a graphical representation illustrating the curves of the transient signals generated by the passage of a proton and an electron depositing the same amount of energy.

[0109] The embodiments described below are by no means limiting; in particular, variants of the invention may be implemented comprising only a selection of features described below, isolated from the Other described features, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one preferably functional feature without structural details, or with only some of the structural details if that part alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0110] The principle of the invention is to allow manipulation of the two terms governing the current collected by the detector during the passage of a particle, which are given by the Shockley-Ramo equation. To this end, the invention provides a detector comprising a semiconductor substrate and at least one measuring electrode formed on a surface of the substrate. The geometry of the electrode on the substrate is such that the electric field created in the sensitive volume of the substrate when the substrate is powered via the electrode is inhomogeneous. The electric field in the sensitive volume is modulated according to the shape of the electrode formed on the surface of the substrate.

[0111] By modulating the electric field within the sensitive volume of a particle detector, the transport of charges created within that volume is consequently modified. This allows, among other things, the charge carriers to be directed towards the measuring electrodes, thus limiting information loss. This modulation depends on the geometry of the detector and / or the voltage applied to the measuring electrodes.

[0112] Figure 4 presents examples of electric field maps calculated for different detector geometries. Figure 4(a) shows an example of the electric field in a classic S-SD structure such as that of Figure 3. Figures 4(b) and (c) show the electric field obtained from multi-electrode geometries, but with different dimensions of the measuring electrode and different voltage values ​​applied to the measuring electrode. It is therefore possible to manipulate the different geometric parameters to change the electric field and charge transport, and thus the shapes of the transient signals.

[0113]

[0114] By changing, in particular, the number and dimensions of the measuring electrodes, it is possible to influence the virtual field associated with each measuring electrode and to modify their individual response. Figure 5 shows some examples of virtual potential maps calculated for a single electrode spanning the entire width of the diode (a), a central electrode spanning half (b) or one-third (c) of the diode surface width, and for a ring electrode (d).

[0115] We can first observe a significant difference between the uniform virtual field of the classical case (a), and the distorted fields in the case of the other tracks (b), (c), and (d), which will lead to very different signal shapes measured on the electrodes according to the Shockley-Ramo relation. Indeed, the collected signal is directly proportional to the virtual electric field.

[0116] Figure 6 shows the effect of the virtual field on the signal generated by a 1.56 MeV proton with an angle of incidence of 19° injected into the center of the sensitive volume of a detector, in the case of the geometries shown in Figures 5a), 5b), and 5c), corresponding respectively to a simple junction representing 100%, 50%, or 30% of the total diode width (300 µm in this example). A junction is the contact area of ​​an electrode on the surface of the semiconductor substrate. It can be seen that the smaller the junction width, the weaker the generated signal. Furthermore, the amount of energy collected by the junction also decreases. With a full junction (100%, Figure 5a), all of the energy is collected (1.56 MeV). A 50% junction, figure 5 b) collects only 20% of the total charge and a 30% junction, figure 5 c) collects only 5% of the total charge.This is due to the fact that the angle of incidence of the proton is such that it passes by the partial junctions (not totally covering the surface of the diode), which reduces the proportion of charges recovered by the electrode.

[0117]

[0118] It is thus possible to observe the effect of the detector's geometric parameters by comparing the signals from the geometries in Figures 5b and 5c. In Figure 5c, the central measuring electrode is narrower than that in Figure 5b, which tends to reduce the proportion of charge collected by the electrode, as observed in the case of a proton with a given angle of incidence. However, this central measuring electrode can be combined with an annular measuring electrode (see Figure 6d) arranged around it. The annular measuring electrode allows for the measurement of the signal induced on the sides of the diode. Measurement capability is thus found over almost the entire surface of the diode, but with electric field perturbations according to the invention.

[0119] Given the significant difference between the potential maps 5c) and 5d), the response of the annular track in Figure 5d) will also be very different from that of the central electrode 5c).

[0120] By manipulating the two parameters, the real electric field and the virtual electric field, it is possible to modify the shapes of the signals measured by the electrodes, which is then used to optimize electron / proton discrimination. Unlike prior art designs that used guard rings to control the electric field (to keep it uniform within the sensitive volume) and separate electrodes to measure the With charge deposited, the electrodes according to the invention have a dual function: deformation of the electric field and measurement of the signal generated in the diode.

[0121]

[0122] Figure 7 shows an example of an embodiment of a system according to the invention. A semiconductor substrate, such as a diode 4, is shown, suitable for receiving ionizing particles to be measured. Each ionizing particle interacts within the semiconductor substrate by transferring energy into the sensitive volume of the substrate. This energy creates electron-hole pairs, which are charge carriers. When an electric field is applied to the sensitive volume of the semiconductor substrate via the electrodes, the electrons and holes move in opposite directions. This movement of charge carriers results in the generation of an electrical signal across the electrodes.

[0123] This electrical signal is collected by an acquisition chain 5 which includes hardware and software components capable of processing this signal, in particular by digitizing it and recording it over time in order to preserve its dynamics.

[0124] A processing unit 6 retrieves the measured signal and applies a classification, correlation, comparison or deep learning technique to identify, based on the shape and dynamics of the signal, whether the particle at the origin of the signal is an electron 7 or a proton 8. The processing unit 6 is also capable of determining the energy N R. J generated by the ionizing particle at the origin of the measured signal.

[0125]

[0126] Figure 8 shows in more detail an assembly according to the invention comprising a semiconductor substrate 9 on which are arranged front measuring electrodes 10 and rear measuring electrodes 11. Under each measuring electrode is an island 12, 13, that is to say, a region of the semiconductor substrate doped inversely to the doping of the sensitive volume 14 forming the interior of the semiconductor substrate. Each island can have a width of a few tens to a few hundred micrometers. The doping of the islands can range from 1E+11 to 1E+14 # / cm 3 .

[0127]

[0128] At least one measuring electrode can be installed on one side of the semiconductor substrate to apply a voltage that creates an electric field and to measure the signal generated by an ionizing particle detected by the substrate. The other side can be equipped with a grounded electrode, a measuring electrode, or a floating electrode.

[0129] Different compatible configurations are possible as long as the electric field can be made inhomogeneous in the substrate. semiconductor. For example, when the semiconductor substrate is designed as a diode, one or more measuring electrodes can be made on the anode (front face) and / or on the cathode (rear face).

[0130] For example, with a single measuring electrode 10 in Figure 8, the electric field is sufficiently perturbed within the sensitive volume to allow for effective discrimination of particles based on the measured signals. Several configurations are possible to further perturbed the electric field.

[0131] Figure 9 describes a very schematic embodiment in which a parallelepiped-shaped diode 15 is distinguished, with a rectangular upper and lower face. The diode includes a sensitive volume 16 in which particles passing through the diode deposit charges. The electric field in the sensitive volume is created by applying a voltage V to a measuring electrode 17. An island (not shown), substantially symmetrical to the shape of electrode 17, is formed within the sensitive volume 16, in contact with electrode 17. Electrode 17 is a spiral-shaped detection anode, as illustrated in the top view of Figure 9 on the left. The spiral covers a large part of the front surface of the diode 15, thus enabling the collection of almost all the charges generated during the passage of a particle. The spiral shape has an inter-electrode spacing 19.The bias voltage V applied to electrode 17 generates, thanks to the inter-electrode spacing, an inhomogeneous electric field in the sensitive volume 16.

[0132] Unlike the design with guard rings, whose role was to homogenize the electric field, the use of a spiral shape here allows the electric field within the diode to be distorted. This has the effect of modifying the propagation of charge carriers, and according to the Shockley-Ramo relation, of changing the shape of the measured signal. It can be advantageous, however, to use multiple measurement anodes or cathodes to also decompose the virtual collection field. Figure 10 illustrates such an implementation.

[0133] Figure 10 shows a circular diode 20, composed of a sensitive volume 21. Seven annular detection anodes 22 are distributed concentrically around a central anode 23. Seven annular detection cathodes 24 are distributed concentrically around a central cathode 25. A gap or inter-electrode spacing 26 is present between the two consecutive electrodes.

[0134] Each anode 22 can receive a bias voltage V n Each cathode can receive a bias voltage V' n different from V n ...The bias voltages V n and V' n are determined in such a way as to create an inhomogeneous electric field in the sensitive volume 21. The voltage difference between two bias voltages applied to two neighboring rings can be between zero and 20 volts. This allows modification of their charge collection properties and control of the deformation of the electric field in the sensitive volume.

[0135] The use of multiple electrodes allows us to manipulate both terms of the Shockley-Ramo relationship. Indeed, in addition to the distortion of the actual electric field, each electrode possesses a specific virtual collection field and therefore its own unique signal. Compared to the previous spiral design, we can thus decompose the total signal with each electrode, allowing us to obtain individual signals across the entire width of the detector and to reconstruct the shape of the particle's track.

[0136] To improve upon the example in Figure 10, a smaller number of measuring electrodes can be used. This would reduce manufacturing and operational complexity, particularly since each anode and cathode would need its own signal acquisition chain. In the example shown in Figure 10, sixteen acquisition chains would therefore be required.

[0137]

[0138] The device in Figure 11 comprises a square diode 30, consisting of a sensitive volume 31 and a single anode 32. The cathode is divided into two square measuring electrodes: a first central electrode 33 and a second electrode 34 extending along the perimeter of the diode around the first electrode. Each electrode 33 or 34 can receive an individual bias voltage (V1 or V2, respectively) to modify its charge-collecting properties. A gap or inter-electrode spacing 35 is present between electrodes 33 and 34. Electrode 34 can be located at the periphery of the diode or simply around electrode 33 without being at the edge of the diode surface.

[0139] Using two measuring electrodes, unlike the sixteen in the example in Figure 10, simplifies the use of the diode and reduces the complexity of the electronics required for its operation. Since the device has several electrodes, it is always possible both to distort the electric field in the sensitive volume and to decompose the virtual collection field. Here, decomposing the cathode into two electrodes allows for modulation of the hole collection. However, since holes are less mobile than electrons, it is more difficult to make them converge towards a given measuring electrode, and there is a risk of charge loss in the band gap. This loss could be reduced by decomposing the anode instead of the cathode. Furthermore, the square geometry of the diode creates peak areas where the local electric field can be very strong. Therefore, an alternative geometry could be considered to limit the risk of breakdown.

[0141] The device in Figure 12 comprises a circular diode 40, consisting of a sensitive volume 41 in which particles passing through the diode deposit charges. A central sensing anode 42 and a second sensing track 43, forming a ring around the first, are included at the end of the diode. A gap or inter-electrode spacing 44 is present between electrodes 42 and 43. The second sensing track is a measuring electrode located at the periphery (edge) or not of the diode surface. Each electrode 42 or 43 can receive an individual bias voltage (V1 or V2, respectively) to modify its charge-collecting properties.

[0142]

[0143] To optimize the device according to the different embodiments, the following properties can be used: A diode thickness between 30 µm and 5 mm, a diode width between 30 µm and 5 cm, and an inter-electrode gap (between two electrodes or between two parts of the same electrode on the same surface) with a width between 30 µm and 1 mm. A voltage delta of 0 to 20 V between two electrodes on the same surface, A doping level of the semiconductor substrate between 1E+10 and 1E+14 # / cm3, A doping level of the islands associated with the electrodes between 1E+10 and 1E+18 # / cm3.

[0144] An example of optimal values ​​for the geometry of Figure 12 can be given below: A diode thickness of 300 µm, A diode width of 1.5 mm, an inter-electrode gap or spacing between the two electrodes 42 and 43 of 200 pm, A voltage delta of 0 V between the two electrodes 42 and 43, A doping level of the semiconductor substrate of 1E+11 # / cm3, A doping level of the islands associated with the electrodes of 1E+16 # / cm3.

[0145]

[0146] In the example in Figure 12, the leakage current can be kept around nA, ten times lower than when the optimization according to the invention is not applied. The leakage current can be on the order of 1–10 nA. Although higher, this current remains on the order of 0.1% to 1% of the amplitude of the signal generated by a particle passing through the detector (pA). Thus, the detector properties are not significantly degraded by the leakage current. The intensity of the leakage current depends on the gap size, as well as the difference in potential between the two electrodes. If the potential difference between the electrodes is too high and if the gap is sufficiently narrow, the resulting electric field in this area can be strong enough to disrupt the formation of the depletion region between the anodes and the cathode and generate a significant leakage current.

[0147]

[0148] The advantage of the optimized geometry according to the invention compared to the conventional geometry of SSDs is evident when comparing their particle identification performance. The confusion matrices calculated in both cases (without and with optimization) are presented below for different energy ranges. The values ​​are given for incident protons between 100 and 250 MeV and incident electrons between 0.1 and 7 MeV, which corresponds to the ranges where the total energy deposited by the electrons and protons is very similar. The prediction results are classified by the total energy deposited in the detector by the particles according to three ranges: Table 1: 0-150 keV, Table 2: 150-300 keV, and Table 3: 300-450 keV.

[0149] Confusion matrices allow us to quantify the accuracy of the prediction of the particle's nature. They show the proportion of electrons and protons correctly identified.

[0150] In the example of the first matrix (a) for the 0-150 keV range (Table 1), the method used correctly identifies 47% of the protons, while 53% are identified as electrons. In the second row of the matrix, 32% of the electrons are identified as protons, and 68% are correctly identified.

[0151] Table 1

[0152]

[0153] The confusion matrices for the classic single-track detection design (a) are derived solely from the total amount of energy deposited by the particles, which is the only available information in this case. The confusion matrices allow for a comparison of the percentages of correctly identified particles (columns) with the true nature of the particles. (lines). These matrices demonstrate a significant improvement in the prediction of particle nature by analyzing the shape of transient signals.

[0154] The confusion matrices for the optimized design according to the invention with multiple detection tracks are obtained using statistical processing of the shapes of the transient signals induced by the particles. This processing first examines the characteristic quantities of the signals (maximum amplitude, rise time, full width at half maximum, integral, proportion of the total charge deposited on the ring, etc.) by comparing their distributions for electrons and protons. By calculating the overlap of these distributions, the sorting criteria for which the electron-proton separation is most pronounced can be selected, and the probability that a signal is associated with one particle or the other can be calculated. For example, from the distributions of the maximum amplitudes of the electron and proton signals, ranges of values ​​where protons are more prevalent than electrons, and vice versa, can be identified.Next, when a signal from an unidentified particle is measured, its maximum amplitude can be extracted and placed within the previously established distribution, giving us the probability of having measured a proton. There are, of course, ranges of values ​​where the maximum amplitudes of the electron and proton signals are identical, making it impossible to determine the identity of the measured signal. In such cases, the discrimination must be refined using other criteria. It is possible to further improve the efficiency of the discrimination by using machine learning methods, which automate the logical path to follow to discriminate a measured signal.

[0155] Table 2 Table 3

[0156] It is also possible to demonstrate the contribution of the present invention by examining more closely the different forms of transient signals generated by particles depositing the same amount of energy in the diode's sensitive volume. Figure 13 shows examples of transient signals calculated for the passage of a 240 MeV proton and a 1 MeV electron through a sensitive volume 300 pm thick, having deposited the same amount of energy (200 keV). Current conventional detectors only allow measurement of the total amount of energy deposited in the sensitive volume, making differentiation impossible with this type of detector in the example presented here. In Figure 13, it is possible to compare the transient signal that would be obtained with a conventional geometry (Figure 3) with the multiple signals obtained using the multi-track geometry of the embodiment shown in Figure 12.

[0157]

[0158] The solid curves show the transient signal obtained with the geometry of a conventional detector shown in Figure 3, namely a single measurement track spanning the entire width of the diode. The shapes of these signals remain similar, and it is difficult to distinguish the proton signal (thin line) from the electron signal (thick line). This shows that, even using a conventional diode geometry connected to an acquisition chain capable of obtaining transient signal shapes (instead of an acquisition chain that only returns the integral of this signal), electron / proton separation remains complex due to the similarity of the transient signals.

[0159] The advantage of the optimized geometry of the invention is that it allows the total signal to be decomposed, yielding the shape of the signals generated on each track. In the case of Figure 13, the annular track has been divided in two to provide three measurement tracks (left, center, and right), thus determining the direction from which the particle passes. If this information is not required, the left and right tracks can be combined into a single annular electrode. This has the advantage of reducing the number of acquisition chains required (one per electrode).

[0160] The shapes of the signals generated on each individual track are very different between the proton and the electron. The signal generated in the center by the proton is wider than that of the electron, while the signal generated on the left by the electron is not symmetrical with the signal generated on the right, unlike the In the case of the proton, this is due to the fact that the path of electrons is much more chaotic than the straight path of protons. This example shows that this difference in behavior between electrons and protons has a more pronounced effect on signals measured with an optimized geometry than with a standard geometry, which would make it easier to identify trends specific to each type of particle. In this particular example, it is easy to differentiate the electron from the proton using only the central measuring electrode, since the proton passed straight through the center of the diode while the electron was deflected. In more realistic situations, where particles arrive at an angle of incidence and do not necessarily enter through the center of the diode, the electron-proton distinction is no longer so easy, and it becomes necessary to combine the information from several electrodes.

[0161]

[0162] With this invention, it is possible to manipulate the shapes of transient signals using optimized geometry by modifying the electric field in the detector (Figure 4) or the virtual field of each measurement track (Figure 6). This allows for the optimization of the detector's dimensions (sensitive volume, track size, etc.) as well as the applied voltages, in order to distort the signals and further highlight the transport differences between electrons and protons, as seen, for example, in Figure 8.

[0163] In the case of the geometry used in the invention, the optimal design is the one that allows for the most marked separation possible between the shapes of the signals generated by electrons and protons, while maintaining a leakage current low enough not to degrade the performance of the detector.

[0164]

[0165] Of course, the invention is not limited to the examples just described. Many modifications can be made to these examples without departing from the scope of the present invention as described.

Claims

Demands

1. 1. Particle detector comprising: - a semiconductor substrate comprising a sensitive volume capable of producing charges during the passage of a particle, at least one front contact island made under a front face of the semiconductor substrate, and at least one rear contact island made under a rear face of the semiconductor substrate, - at least one front electrode made on the front face of the semiconductor substrate, in contact with the front contact island; - at least one back electrode made on all or part of the back face of the semiconductor substrate, in contact with the back contact island; - an acquisition chain capable of detecting transient signals from said at least one front electrode, characterized in that said at least one front electrode is a voltage application and transient signal detection electrode, and in that said at least one front electrode is made on only a part of the front face of the semiconductor substrate, without guard electrodes, so that a non-homogeneous electric field is created in the sensitive volume when said at least one front electrode is supplied with voltage.

2. 2. Detector according to claim 1, characterized in that said at least one front electrode has a geometric shape having at least one inter-electrode spacing suitable for creating a non-homogeneous electric field in the sensitive volume.

3. 3. Detector according to claim 2, characterized in that said at least one front electrode is a spiral covering at least a part of the surface of the sensitive volume.

4. 4. Detector according to claim 1 or 2, characterized in that the semiconductor substrate is circular, square or rectangular in shape and: - said at least one front electrode consists of a plurality of annular front electrodes distributed concentrically around a central front electrode, with an inter-electrode spacing present between any two front electrodes and - said at least one rear electrode consists respectively of a plurality of annular rear electrodes distributed concentrically around a central rear electrode; each front-rear electrode pair being capable of receiving a bias voltage different from that intended to be applied to the neighboring front-rear electrode pair, an inter-electrode spacing being present between two rear electrodes.

5. 5. Detector according to claim 1 or 2, characterized in that the semiconductor substrate is circular, square or rectangular in shape, and: - said at least one front electrode comprises a first central front electrode of circular, square or rectangular shape and at least a second front electrode, peripheral or not, of circular, square or rectangular shape; an inter-electrode spacing being present between the two front electrodes; and - said at least one back electrode consists of a single back electrode distributed over the entire back face of the semiconductor substrate.

6. 6. Detector according to any one of the preceding claims, characterized in that, where the semiconductor substrate is a diode structure, said at least one front electrode is an anode or a cathode; said at least one rear electrode being respectively a cathode or an anode.

7. 7. Detector according to any one of the preceding claims, characterized in that the semiconductor substrate has a thickness of between 30 pm and 5 mm, ideally 300 pm.

8. 8. Detector according to any one of the preceding claims, characterized in that the semiconductor substrate has a width between 30 pm and 5 cm, ideally 1.5 mm.

9. 9. Detector according to any one of claims 2 to 8, characterized in that the inter-electrode spacing has a width between 30 pm and 1 mm, ideally 200 pm.

10. 10. Detector according to any one of the preceding claims, characterized in that when this detector comprises several front electrodes, the acquisition chain is configured to apply voltages respectively to the front electrodes with a voltage difference between two consecutive front electrodes of between 0 and 20 V, ideally 0 V.

11. 11. Detector according to any one of the preceding claims, characterized in that the sensitive volume has a doping level between 10 10 and 10 14 cm 3 ideally 10 11 cm 3 .

12. 12. Detector according to any one of the preceding claims, characterized in that each contact island has a doping level between 10 10 and 10 18 cm 3 ideally 10 16 cm 3 .

13. 13. Detector according to any one of the preceding claims, characterized in that it comprises as many front electrodes as front contact islands.

14. 14. A system for detecting and discriminating particles, characterized in that it comprises: - a particle detector according to any one of the preceding claims, - a processing unit configured to compare one or more parameters of an acquired transient signal with one or more predetermined parameters in order to identify the nature of the particle at the origin of this acquired transient signal.

15. 15. A method for detecting and discriminating particles, characterized in that it comprises the following steps implemented by a processing unit of a system according to claim 14: - application of one or more voltages to one or more electrodes in front of the particle detector so that a non-homogeneous electric field is created in the sensitive volume, - acquisition of a transient signal on said one or more electrodes before following the passage of a particle through the sensitive volume, - comparison of one or more parameters of the transient signal to one or more predetermined parameters in order to identify the nature of the particle at the origin of this acquired transient signal.

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