Pixel high-purity germanium detector with rotary strip-shaped electrode

Abstract

The invention belongs to the technical field of high-energy X-ray detection, and particularly relates to a pixel high-purity germanium detector with a rotary strip-shaped electrode. The detector base is in the shape of a regular quadrangular prism, P-type lightly-doped high-purity germanium is selected as a base material, a cathode plate is attached to the bottom of the detector base, an anode plate is attached to the top of the detector base, a strip-shaped electrode in the middle of the anode plate is distributed in a roundabout strip-shaped folded shape, and the unoccupied part is filled with Al2O3 to achieve the isolation effect; the distance G1 between the strip-shaped electrode in the middle of the anode plate and the edge of the detector is set to be 4 microns, the width W of the strip-shaped electrode is set to be 8 microns, and the distance G2 between the strip-shaped electrodes is set to be 8 microns. The high electric field around the electrode is reduced, and the influence on the performance of the detector due to the overhigh local electric field is avoided. Meanwhile, the distance between the cathode and the anode is shortened, so that the problem of incomplete charge collection is obviously improved.

Description

Technical Field

[0001] The invention belongs to the technical field of high-energy X-ray detection, and in particular relates to a pixel high-purity germanium detector with gyroscopic strip electrodes. Background Art

[0002] X-ray pulsars can emit extremely stable periodic pulse signals, becoming the most accurate astronomical clock in nature. Pulsars can provide autonomous navigation services for deep space spacecraft. Compared with navigation methods such as GPS and Beidou, X-ray pulsar navigation is not affected by the position of the spacecraft and is a new navigation mechanism that will never be destroyed. Therefore, pulsar navigation technology has received extensive attention from researchers around the world. The principle of X-ray pulsar navigation is to detect X-ray pulse signals for a long time, compare the acquired pulse profile with the standard pulse profile, and thus obtain the X-ray pulse arrival time (TOA).

[0003] The core component of pulsar navigation technology is the semiconductor detector, whose main function is to capture and record the high-energy particle X-ray frequency band emitted by pulsars. Semiconductor detectors usually use germanium and silicon materials as detection matrices. Compared with silicon, germanium has a larger atomic number, a smaller bandgap, an average ionization energy much lower than silicon, and a higher charge mobility. In the sensitive area of ​​germanium-based detectors, the same radiation energy can generate more electron-hole pairs. Therefore, in theory, germanium-based detectors have better energy resolution, faster charge collection speed, higher response sensitivity and signal strength. Due to the impurity content of 10 10 / cm 3 -10 15 / cm 3 Made of the following germanium crystals, the extremely high purity germanium detector can be stored at room temperature and work in a low temperature liquid nitrogen environment. The process is simple and easy to use, and it is now widely used in radiation detection of high energy x-rays and gamma rays.

[0004] At present, a variety of high-purity germanium detectors have been developed, including two representative structures: planar and coaxial. Figure 1 The planar high-purity germanium detector has larger dimensions in the length and width directions, but smaller dimensions in the thickness direction. It is mainly used to detect X-rays and low-energy gamma rays. Referring to patent application number CN202211435148, the coaxial high-purity germanium detector has a relatively large axial dimension, which can effectively expand the volume of the sensitive area and has a good detection effect on high-energy X-rays.

[0005] However, high-purity germanium detectors are committed to detection in a higher energy range, further expanding the volume of their sensitive area, which makes the phenomenon of incomplete charge collection more obvious. In order to avoid this situation, the method of increasing the reverse bias voltage is usually adopted, but since the leakage current increases significantly with the increase of the reverse bias voltage, the energy resolution of the detector will decrease; another method is to improve the purification process of semiconductor materials to reduce the substrate impurity concentration and thus increase the resistivity. In addition, in the field of deep space exploration, large-sized high-purity germanium detectors have limited position resolution capabilities, and this position resolution capability directly affects the performance of the entire detector. Within a specific radiation range, reducing the size of a single detector unit and integrating it into a pixel unit array is an optional way to solve this problem. Summary of the invention

[0006] In order to design a high-purity germanium detector that can accurately sense the energy range of X-rays required for X-ray pulsar navigation technology, the purpose of the present invention is to provide a solution, that is, to design the high-purity germanium detector into a small-sized pixel unit structure with a cyclotron strip electrode. In this way, while maintaining the small capacitance of the detector structure, the high electric field around the electrode is reduced to avoid the impact on the detector performance due to excessive local electric field. At the same time, the distance between the anode and cathode is reduced, which significantly improves the problem of incomplete charge collection.

[0007] To achieve the above object, the technical solution adopted by the present invention is: it comprises a detector base, a cathode sheet, a cathode contact layer, an anode sheet, and an anode contact layer; the detector base is in the shape of a regular quadrangular prism, with a size of 80 μm×80 μm×120 μm, and uses P-type lightly doped high-purity germanium as the base material, with a doping concentration of 1×10 12 / cm 3 The bottom of the detector base is attached with a cathode sheet with a thickness of 1 μm. The cathode sheet uses P-type heavily doped high-purity germanium as the cathode with a doping concentration of 1×10 19 / cm 3 ; A 1 μm thick anode sheet is attached to the top of the detector base. N-type heavily doped high-purity germanium is used as the anode with a doping concentration of 1×10 19 / cm 3 The surfaces of the cathode sheet and the anode sheet are respectively provided with a cathode contact layer and an anode contact layer, wherein the strip electrode in the middle of the anode sheet is distributed in a circuitous strip folded shape, and the remaining part is filled with Al2O3 to achieve an isolation effect.

[0008] Preferably, the distance between the strip electrode in the middle of the anode sheet and the edge of the detector is set to G1 = 4 μm, the width of the strip electrode is set to W = 8 μm, and the spacing between the strips is set to G2 = 8 μm.

[0009] Preferably, a contact electrode having the same structure as the strip electrode is arranged in the middle of the anode contact layer.

[0010] Preferably, the contact electrode adopts Al as the contact material, and the blank part uses Al2O3 as the passivation layer to realize the insulation and isolation functions.

[0011] Preferably, the cathode contact layer and the anode contact layer are combined with the cathode sheet and the anode sheet by coating on the surface of high-purity germanium using magnetron sputtering technology.

[0012] Preferably, the anode contact layer coating on the surface of the anode sheet needs to be coated in steps due to different materials.

[0013] Preferably, the anode contact layer on the surface of the anode sheet needs to be evaporated in steps due to different materials.

[0014] Preferably, the overall size of the detector base after being combined with the cathode sheet, cathode contact layer, anode sheet and anode contact layer is 80 μm×80 μm×122 μm.

[0015] Preferably, the detector base 1 can be combined into four units to form a 2X2 detector matrix.

[0016] After adopting the above structure, the beneficial effects of the present invention are as follows: the cyclotron electrode pixel high-purity germanium detector designed in the present application can form a detector array by integrating pixel units; at the same time, the detector array has the characteristics of fast signal response speed and fast charge collection speed in heavy ion incidence research, and uses multiple sensing electrodes to provide more accurate position resolution capability, and can judge the position information of external energy by the current changes between units. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the present invention is described in detail through the following specific implementations and drawings.

[0018] Figure 1 It is a schematic diagram of the technical drawings structure of the present invention;

[0019] Figure 2 It is a structural schematic diagram of the present invention;

[0020] Figure 3 It is a schematic diagram of the cyclotron electrode distribution of the present invention;

[0021] Figure 4 It is a cross-sectional schematic diagram of the present invention;

[0022] Figure 5 It is a schematic diagram of a 2X2 matrix of the present invention.

[0023] Figure 6 This is an electrical simulation image of a high-purity germanium detector with square collection electrode pixels and a high-purity germanium detector with spiral strip electrode pixels according to Example 1 of the present invention.

[0024] Figure 7 This is a curve showing the change in capacitance of the high-purity germanium detector with a spiral strip electrode pixel as a function of thickness in Example 2 of the present invention.

[0025] Figure 8 This is the change in electron concentration inside the detector before and after heavy ion incidence in Example 3 of the present invention.

[0026] Fig. 9 This is a curve showing how the total collection current of the 2X2 detector array changes with time after heavy ions are incident on unit I of the cyclotron electrode pixel high-purity germanium detector in Example 3 of the present invention, and a curve showing how the collection current of the four adjacent units changes with time. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is described below by the specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0028] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions according to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0029] See also Figure 1-Figure 5 As shown, this specific embodiment adopts the following technical scheme: it comprises a detector base 1, a cathode sheet 2, a cathode contact layer 3, an anode sheet 4, and an anode contact layer 5; the detector base 1 is in the shape of a regular quadrangular prism, with a size of 80 μm×80 μm×120 μm, and uses P-type lightly doped high-purity germanium as the base material, with a doping concentration of 1×10 12 / cm 3 The bottom of the detector base 1 is attached with a cathode plate 2 with a thickness of 1 μm. The cathode plate 2 uses P-type heavily doped high-purity germanium as the cathode with a doping concentration of 1×10 19 / cm 3 ; A 1 μm thick anode sheet 4 is attached to the top of the detector base 1, and N-type heavily doped high-purity germanium is selected as the anode with a doping concentration of 1×10 19 / cm 3The surfaces of the cathode sheet 2 and the anode sheet 4 are respectively provided with a cathode contact layer 3 and an anode contact layer 5, wherein the strip electrode 6 in the middle of the anode sheet 4 is distributed in a circuitous strip folded shape, and the remaining part is filled with Al2O3 to achieve an isolation effect.

[0030] The distance between the strip electrode 6 in the middle of the anode sheet 4 and the edge of the detector is set to G1 = 4 μm, the width of the strip electrode is set to W = 8 μm, and the spacing between the strips is set to G2 = 8 μm.

[0031] Furthermore, a contact electrode 7 having the same structure as the strip electrode 6 is provided in the middle of the anode contact layer 5. The contact material of the contact electrode 7 is Al, and Al2O3 is selected as a passivation layer in the blank part to realize the insulation and isolation functions. The cathode contact layer 3 and the anode contact layer 5 are combined with the cathode sheet 2 and the anode sheet 4 by coating on the surface of high-purity germanium using magnetron sputtering technology. The coating of the anode contact layer 5 on the surface of the anode sheet 4 needs to be coated in steps due to different materials. The evaporation of the anode contact layer 5 on the surface of the anode sheet 4 needs to be evaporated in steps due to different materials. The overall size of the detector base 1 after being combined with the cathode sheet 2, the cathode contact layer 3, the anode sheet 4, and the anode contact layer 5 is 80μm×80μm×122μm. The detector base 1 can be combined into four units to form a 2X2 detector matrix.

[0032] Example 1: Study on electrical characteristics of detector

[0033] In this study, the semiconductor simulation software Sentaurus TCAD (P-2019.03) was used to conduct an in-depth study of the electrical properties of pixel high-purity germanium detectors. We used the carrier transport equation, SRH recombination model and state density model to analyze the device. In terms of material parameters, we directly used the built-in material parameters of the Sentaurus TCAD software. In the mobility model, we considered the carrier scattering on ionic impurities, and introduced the carrier mobility degradation model (DopingDep), the carrier velocity saturation model in high electric fields (HighFieldSat), and the mobility degradation model caused by surface roughness scattering (Enormal). For the state density model, we used the effective intrinsic density model (OldSlotboom) to consider the doping effect during the simulation process. In the recombination model (Recombination), the corresponding carrier generation and recombination process is realized through the carrier continuity equation, and the SRH recombination mechanism is selected. In addition, the interface charge density between Al2O3 and Ge is set to -4×10 11 q / cm 2 .

[0034] like Figure 6As shown, Figure 6 a. Figure 6 b shows the three-dimensional images of the two detectors when a -80V reverse bias is applied between the two poles. As the electrons gradually move toward the anode, the matrix electron concentration inside the detector decreases. When the depletion voltage is reached, the matrix electron concentration is the lowest, causing the detector to be in a fully depleted state.

[0035] Figure 6 c shows the IV curves of the two detectors, describing the change in detector current as the voltage increases. Previous literature reported that the depletion voltage of a coaxial high-purity germanium detector with a diameter of 50 mm was 1800 V. The pixel high-purity germanium detector proposed in this article has a lower full depletion voltage of -5 V. To ensure that the charge generated inside the detector is completely absorbed, the voltage applied in practical applications should be higher than the full depletion voltage of the detector. It can be observed from the figure that as the reverse bias voltage gradually increases, the leakage current of the detector increases significantly, and enters a full depletion state when the full depletion voltage is reached. At this time, the leakage current value tends to saturation and no longer changes significantly. There is no obvious difference in the leakage current value of the two detectors, which is 0.19 μA.

[0036] Figure 6 d. Figure 6 e shows the three-dimensional potential distribution of the two detectors on the XZ plane (Y = 0μm), where the X axis represents the width of the detector and the Z axis represents the thickness of the detector. From the perspective of potential and electric field distribution, although the difference between the two types of detectors in the matrix is ​​not significant, the potential and electric field changes near the edge of the detector anode are very obvious.

[0037] Figure 6 f shows the potential curves of the two detectors at Z = -5μm, which can more intuitively observe that the square collection electrode pixel high-purity germanium detector has a potential mutation phenomenon near the edge of the collection anode, which may affect its performance. The improved gyroscopic strip electrode pixel high-purity germanium detector presents a more uniform potential distribution.

[0038] Figure 6 g and Figure 6 h shows the three-dimensional electric field distribution of the two detectors. There is a uniform electric field around the anode of the spiral strip high-purity germanium detector, which promotes the collection process of internal carriers.

[0039] from Figure 6Figure 1 shows the electric field comparison curves of the two detectors at Z = -5 μm. It can be observed that at Z = -5 μm, the square collection electrode high-purity germanium pixel detector has a sudden increase in the local electric field value, and the outermost edge shows a lower local electric field. This unevenly distributed electric field will affect the charge collection speed and efficiency. Therefore, in comparison, the gyroscopic strip electrode pixel high-purity germanium detector has obvious advantages.

[0040] Example 2: Study on the relationship between detector capacitance and thickness

[0041] Capacitance is an important factor that determines the noise level of the detector and directly affects the performance of the detector. Therefore, the size of the capacitor needs to be fully considered when designing the detector. A smaller capacitor can effectively reduce the noise level, thereby improving the performance of the detector. The present invention studies the effect of the thickness change of the detector sensitive area on the capacitance of the high-purity germanium detector with gyroscopic strip electrode pixels.

[0042] like Figure 7 The curve of the detector capacitance changing with voltage under different detector thicknesses shown in a. A -80V reverse bias is applied to the cyclotron strip electrode pixel high-purity germanium detector. We select the detector thickness t as a variable, and its value range is 105-125μm, with an increase of 2.5μm, and observe the curve of the detector capacitance changing with thickness. It can be observed from the curve in the figure that as the voltage gradually increases, the value of the detector capacitance gradually decreases and eventually tends to a horizontal straight line. This is because in the sensitive area of ​​the detector, electrons move to the anode and holes move to the cathode until most of the carriers are absorbed by the two poles, causing the detector matrix to tend to a depleted state, and the capacitance value no longer changes significantly.

[0043] according to Figure 7 When the voltage applied to the two poles of the detector reaches -80V, the capacitance values ​​corresponding to different thicknesses are shown in b. When the voltage applied to the two poles of the high-purity germanium detector of the spiral strip electrode pixel reaches -80V, the capacitance value shows a decreasing trend as the thickness of the detector increases. This is because the high-purity germanium detector is based on the working principle of the PN junction. When the voltage increases, the internal depletion region gradually expands and eventually reaches a fully depleted state. When the detector is in a depleted state, its sensitive area achieves charge balance. At this time, the capacitance of the high-purity germanium detector is similar to that of a parallel plate capacitor, that is, the capacitance is inversely proportional to the thickness of the detector. At the same time, the capacitance values ​​of all experimental groups are less than 1.3fF, indicating that this type of high-purity germanium detector has a very small capacitance.

[0044] Example 3: The detector array was used for heavy ion injection research

[0045] like Figure 8 As shown in a, a 2×2 detector array is selected as the research object. Figure 8As shown in Figure 2, a beam of heavy ions is incident from the middle of the cathode into the interior of unit I along the direction perpendicular to the substrate. The initial time of the incident is 5 ns, the incident depth is 100 μm, the radius of the action range is set to 0.2 μm, and the linear energy conversion rate is set to 1×10 -5 pC / μm. Due to the incidence of heavy ions, the detector, which was originally in a fully depleted state, triggers an energy change inside the matrix and excites electron-hole pairs. Under the action of reverse bias, the electron-hole pairs move to the anode and cathode respectively, among which the electrons drift to the central anode and are collected to generate electrical signals.

[0046] like Figure 8 Figure c shows the changes in the electron concentration inside the detector before and after the heavy ion incident. At 3ns, the detector is in a fully depleted state. At 5ns, the heavy ion enters the detector matrix. From 5ns to 8ns, a high-concentration electron region is formed inside the detector, and gradually moves toward the central anode over time until it is completely absorbed.

[0047] like Fig. 9 The figure shows the curve of the current signal generated by the 2×2 detector array. The green line represents the total collected current curve over time. At 5ns, heavy ions enter the detector, causing the current value to rise rapidly to the maximum value. Subsequently, due to the absorption of a large number of induced electrons by the anode, the current value gradually stabilizes and decreases until the induced electrons are completely absorbed by the anode, causing the current to reach the minimum value and no longer change significantly. The charge collection time in this process is 2.5ns, and the detector eventually returns to a fully depleted state.

[0048] By comparison Fig. 9 From the current signal curves of the four units, it can be observed that unit I reaches the forward current peak first. This is because the external energy quickly excites a large number of electron-hole pairs at the incident position, causing a large number of induced electrons to enter unit I and generate a forward current. When heavy ions are incident inside unit I, it will affect the adjacent units. At 5ns, current signals appear in the four units at the same time, and the response peak of each unit reaches the maximum. Subsequently, since a large number of electrons generated inside unit I are quickly absorbed by its anode, the electron filling movement in the adjacent units increases, thereby generating a large number of hole currents in other units, which causes the negative current values ​​of units II-IV to rise rapidly until negative values ​​appear.

[0049] Units II and III, which are close to the incident position and at equal distances, are most affected, and their collected anode current values ​​are very close; while unit IV, which is located at a farther position, has a relatively high current minimum. This phenomenon shows that this type of detector has excellent position resolution and can determine the incident position by comparing the current signals between each unit. If the pixel high-purity germanium unit is made small enough and sufficient in number, the position information and energy size of the incident particle can be accurately determined.

[0050] In conjunction with specific embodiments 1-3, in the context of X-ray pulsar navigation applications, this article proposes an innovative method to address the problems of incomplete charge collection and limited position resolution in traditional high-purity germanium detectors: by designing the high-purity germanium detector into a thin pixel unit structure and adopting a spiral strip-shaped collection electrode design, we have achieved a more uniform potential and electric field distribution inside the detector, thereby significantly improving the incomplete charge collection phenomenon. Experiments have also confirmed that the detector has a small capacitance value, which decreases with increasing thickness. This low capacitance value effectively reduces the noise level. At the same time, through research on pixel high-purity germanium detector arrays, we found that this type of detector has a fast response speed to external radiation signals and a short collection time. It can locate the incident unit according to the changes in the collection current of different units and has excellent position resolution. Because the process is simple and can be stored at room temperature, it has the potential for wide application.

Claims

1. A pixel high-purity germanium detector with gyroscopic strip electrodes, characterized in that: The invention comprises a detector base, a cathode sheet, a cathode contact layer, an anode sheet and an anode contact layer; the detector base is in the shape of a regular quadrangular prism, with a size of 80 μm×80 μm×120 μm, and uses P-type lightly doped high-purity germanium as the base material, with a doping concentration of 1×10 12 / cm 3 The bottom of the detector base is attached with a cathode sheet with a thickness of 1 μm. The cathode sheet uses P-type heavily doped high-purity germanium as the cathode with a doping concentration of 1×10 19 / cm 3 ; A 1 μm thick anode sheet 4 is attached to the top of the detector base. N-type heavily doped high-purity germanium is used as the anode with a doping concentration of 1×10 19 / cm 3 The surfaces of the cathode sheet and the anode sheet are respectively provided with a cathode contact layer and an anode contact layer, wherein the strip electrode in the middle of the anode sheet is distributed in a circuitous strip folded shape, and the remaining part is filled with Al2O3 to achieve an isolation effect.

2. The pixel high-purity germanium detector with convoluted strip electrodes according to claim 1, characterized in that: The distance between the strip electrode in the middle of the anode sheet and the edge of the detector is set to G1 = 4 μm, the width of the strip electrode is set to W = 8 μm, and the spacing between the strips is set to G2 = 8 μm.

3. The pixel high-purity germanium detector with gyroscopic strip electrodes according to claim 1, characterized in that: A contact electrode having the same structure as the strip electrode is arranged in the middle of the anode contact layer.

4. The pixel high-purity germanium detector with convoluted strip electrodes according to claim 3, characterized in that: The contact electrode adopts Al as the contact material, and the blank part selects Al2O3 as the passivation layer to realize the insulation and isolation functions.

5. The pixel high-purity germanium detector with convoluted strip electrodes according to claim 1, characterized in that: The cathode sheet adopts Al as the contact material, and the whole sheet is a rectangular sheet-shaped coating.

6. The pixel high-purity germanium detector with convoluted strip electrodes according to claim 1, characterized in that: The cathode contact layer and the anode contact layer are combined with the cathode sheet and the anode sheet by coating on the surface of high-purity germanium using magnetron sputtering technology.

7. The pixel high-purity germanium detector with convoluted strip electrodes according to claim 6, characterized in that: The anode contact layer coating on the surface of the anode sheet needs to be coated in steps due to different materials.

8. The pixel high-purity germanium detector with convoluted strip electrodes according to claim 1, characterized in that: The overall size of the detector base after being combined with the cathode sheet, cathode contact layer, anode sheet and anode contact layer is 80 μm×80 μm×122 μm.

9. According to the pixel high-purity germanium detector with convoluted strip electrodes as described in claim 1, the detector base can be combined into four units to form a 2X2 detector matrix.

Images