X-ray energy detector
By introducing a timing control unit into the X-ray detector, the internal noise problem is solved, the signal-to-noise ratio and sensitivity of the detector are improved, and the high-precision needs of energy spectrum CT imaging are met.
Patent Information
- Application Number
- CN202411284897.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-13
- Publication Date
- 2024-12-31
AI Technical Summary
Existing X-ray detectors have problems such as internal carrier noise, which affects the signal-to-noise ratio and detection sensitivity, and is difficult to meet the high-precision requirements in the field of energy spectrum CT imaging.
By adding a timing control unit, the transfer and cyclic multiplication of photogenerated charges are realized, the charge collection and transfer of the transfer layer is controlled by the first timing control unit, and the charge of the doubling layer is cyclically multiplied and read out through the second timing control unit, thereby improving the charge of the doubling layer. The signal-to-noise ratio and sensitivity of the detector.
It effectively reduces the internal noise of the detector, improves the signal-to-noise ratio and detection sensitivity, and improves imaging accuracy and reliability of clinical applications.
Smart Images
Figure CN119224820A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of semiconductor X-ray detectors, and in particular to an X-ray energy detector. Background Art
[0002] With the discovery of X-rays, X-ray imaging has been widely used in the field of modern medical imaging, and higher requirements have been put forward for the quantitative detection of X-rays. In the field of spectral CT imaging, detectors with X-ray energy analysis function are an important component. At present, there are two main types of X-ray detectors: indirect and direct. Indirect detectors use scintillator materials to absorb X-rays and convert them into visible light signals, and then convert them into electrical signals through photodiodes. Direct detectors directly realize the conversion of X-rays to electrical signals. Due to the shortcomings of scintillators such as afterglow effect and long response time, a large number of studies are currently focused on direct X-ray detectors based on semiconductor materials.
[0003] X-ray detectors made of semiconductor materials can divide the energy range of X-rays and are suitable for spectral CT imaging. Among them, the photon counting detector (PCD) counts the photocurrent pulses by setting the energy threshold, providing high-resolution images, but is also limited by the pulse pile-up effect, photon overflow and the influence of carrier noise inside the semiconductor. As another type of multi-spectrum detector, the tomographic X-ray detector has the following main principles: X-rays are incident from the edge of the semiconductor detector, interact with the atoms in the substrate, generate electron-hole pairs, and apply a suitable bias voltage to the electrode, and the generated electrons will be collected in the potential well to form charge packets, realizing the collection of charge packets. According to the absorption characteristics of X-rays of different energies in semiconductor materials of different thicknesses, the semiconductor detector is divided into energy layers of different depths vertically. Several electrodes are arranged in sequence in each layer and connected to the timing control unit. Through the periodic change of the timing control unit, the sequential readout of the charge packets of different energy layers is realized, and the X-ray components of different energies are calculated through the energy analytical equation. The detector is less affected by the light source and signal stacking, effectively improving the imaging accuracy and reducing the difficulty of clinical application, but there are still problems such as internal carrier noise. Summary of the invention
[0004] In view of the technical problems existing in the prior art, the present invention provides an X-ray energy detector, which realizes the transfer and cyclic multiplication of the photogenerated charge of the total energy through the control of an additional timing control unit, thereby further improving the signal-to-noise ratio and detection sensitivity of the detector.
[0005] In order to solve the problems of the prior art, the present invention adopts the following technical solutions:
[0006] A low-dose X-ray energy detector, the detector is composed of a body; a base layer, an oxide layer and a circuit output module are arranged on the detector; the detector also includes: a first timing control unit and a second timing control unit; wherein: the base layer is divided into a plurality of transfer layers and multiplication layers according to the needs of X-ray energy analysis; the transfer layer is connected to the first timing control unit through an electrode group of three electrodes; the multiplication layer is connected to the second timing control unit through five electrodes; wherein:
[0007] The first timing control unit is connected to the positive electrode of each electrode group and is used to control the collection and transfer of photogenerated charges;
[0008] The second timing control unit is connected to each electrode of the multiplication layer and is used for controlling the multiplication and reading of the transferred charge packets.
[0009] Furthermore, the first timing control unit is connected to the positive electrode of each electrode group, and is used for the collection and transfer process of the photogenerated charges, including:
[0010] The first positive electrode p1 of each electrode group is connected to the first timing control unit, and a transfer voltage signal is applied.
[0011] V1, the second positive electrode p2 is connected to the first timing control unit, applying the transfer voltage signal V2, and so on; wherein:
[0012] At time t2, V3 starts to apply transfer voltage. At time t3, the voltage of V2 decreases slowly, and the transfer voltage applied by V3 remains unchanged. The charges collected by the p2 electrode will continue to flow to the p3 (P3) electrode. At time t4, V1 starts to apply transfer voltage. At time t5, the voltage of V3 decreases slowly, and the charges under the p3 (P3) electrode are continuously transferred to p1. At time t6, V2 starts to apply transfer voltage. Repeating this step can realize the simultaneous vertical downward transfer of charges collected in the transfer layer until charge packets are transferred to the multiplication layer.
[0013] Furthermore, the second timing control unit is connected to each electrode; it is used to multiply and read out the transferred charge packets, including: the five electrodes of the multiplication layer are respectively connected to the second timing control unit, and five voltage signals B1, B2, B3, B4, and B5 are applied to each of them, wherein: the first electrode is used to collect or transfer charges, and the transfer voltage signal B1 is applied; the second electrode is used to transfer and multiply charges, which is mainly achieved by applying the transfer and multiplication voltage B2; the third electrode is used to transfer charges, and the transfer voltage signal B3 is applied; the fourth electrode temporarily stores the charges that have undergone a multiplication cycle at this electrode and waits for the next multiplication; the fifth electrode is a read-out charge switch, and the threshold voltage B5 is applied to transfer the charges to the subsequent read-out circuit.
[0014] Furthermore, the second timing control unit performs a circulation process for the transferred charge to be multiplied, including:
[0015] The first transfer cycle multiplication sequence starts at time t5, at which time the charge stored in p3 (P3) begins to transfer to the multiplication layer; at time t5, the potential of B4 is pulled down, and a threshold voltage pulse is applied to B5. At the same time, for the transferred charge to be multiplied, first B1, B2, B3, and B4 apply transfer voltages in sequence. The cycle multiplication process is realized through the three electrodes B2, B3, and B4, starting from time t6, which is also the start time ta of the cycle multiplication period;
[0016] B2 applies a multiplication voltage, B3 applies a low level, at time tb, B3 applies a transfer voltage, and at the same time B4 is pulled down, the charge is multiplied and transferred from B4 to B2, then at time tc, B2 potential drops, and the charge flows to B3, at time td, B4 applies a transfer voltage, then B3 is pulled down, and the charge flows to B4;
[0017] Among them: ta to te is a doubling period, and the time of the doubling period is adjusted according to the set doubling times;
[0018] After repeating the above doubling steps for a preset fixed number of times, the doubling process ends, i.e., at time tf;
[0019] Waiting for the moment when the charge packet transferred from the next transfer layer is located in the potential well of the p3 (P3) electrode;
[0020] At time t11, when the charge packet transferred from the next transfer layer is in the potential well of the p3 (P3) electrode, B5 applies a threshold voltage to transfer the multiplied charge stored in B4 to the subsequent readout circuit;
[0021] The above process is repeated until all collected charges are read out.
[0022] Beneficial Effects
[0023] The present invention realizes the transfer of the photogenerated charge of the total energy by controlling the transfer layer through the first timing control unit, and realizes the charge cyclic multiplication of the multiplication layer through the second control unit; reduces the noise generated inside the detector; and improves the signal-to-noise ratio and detection sensitivity of the detector. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 The present invention provides a basic structure of a low-dose X-ray energy detector with a charge cyclic multiplication mechanism;
[0025] Figure 2 The timing diagram of the timing control unit of the detector 106 of the present invention;
[0026] Figure 3 Timing diagram of the timing control unit of the detector 107 of the present invention. DETAILED DESCRIPTION
[0027] The following is combined with Figure 1 -Attached Figure 3 The present invention is described as follows:
[0028] The present invention is based on the improvement of the tomographic X-ray detector, the basic structure is as follows Figure 1 (b) As shown. 101 is the detector substrate, i.e., the base layer; it is used to complete the reception of X-rays and the conversion of photoelectric signals. A layer of oxide 102, i.e., the oxide layer, is grown on the upper surface of the substrate; the oxide realizes the electrical insulation isolation between the substrate and the electrode. 103 is the electrode group, and the positive and negative electrodes are discretely arranged on the lower surface of the substrate and the upper surface of the oxide, as shown in FIG. Figure 1 As shown in (a), all positive electrodes are distributed on the same surface, all negative electrodes are distributed on another surface, the positive electrodes are connected to the corresponding first timing control unit 106, and the negative electrodes are connected to a low potential.
[0029] According to the depth of the semiconductor detector, it is divided into several transfer layers 104 and a multiplication layer 105 in the longitudinal direction, wherein the multiplication layer is located below the several transfer layers and close to the circuit output module 108. The electrode group 103 of each transfer layer and the multiplication layer are arranged in sequence with several electrodes, wherein each transfer layer 104 is provided with 3 electrodes for collecting and transferring photogenerated charges, which are controlled by the first timing control unit 106. 105 is a multiplication layer, which is provided with 5 electrodes for multiplying and reading the transferred charge packets, which are controlled by the second timing control unit 107.
[0030] The first positive electrode p1 of each electrode group is uniformly connected to the first timing control unit 106, and a transfer voltage signal V1 is applied. The second positive electrode p2 is also uniformly connected to the first timing control unit 106, and a transfer voltage signal V2 is applied, and so on. The five electrodes of the multiplication layer 105 are respectively connected to the second timing control unit 107, and five voltage signals B1, B2, B3, B4, and B5 are applied to each of them, wherein: the first electrode is used to collect or transfer charges, and a transfer voltage signal B1 is applied; the second electrode is used to transfer and multiply charges, which is mainly achieved by applying a transfer and multiplication voltage B2; the third electrode is used to transfer charges, and a transfer voltage signal B3 is applied; the fourth electrode temporarily stores the charges after a multiplication cycle at this electrode and waits for the next multiplication; the fifth electrode is a readout charge switch, and a threshold voltage B5 is applied to transfer the charges to the subsequent readout circuit.
[0031] X-rays are incident from the incident interface 201 of the semiconductor detector. Due to the different penetration capabilities of X-ray photons of different energies, the electrode potential wells of different transfer layers collect X-ray photogenerated charges of different energies. In order to improve the detection sensitivity of all energies, a transfer voltage is applied to transfer the charges to the multiplication electrode area, and the charges are read out after a fixed number of cyclic multiplication processes. The specific implementation process is as follows:
[0032] Set the voltage of each electrode of the detector to zero and clear the charge stored in the potential well of each electrode;
[0033] Apply a collection voltage to the second electrode V2 of each electrode group in the transfer layer, start exposure, X-rays are incident from the incident interface 201 of the detector, and the photogenerated charges are collected and stored in the potential well of each second electrode group. At the same time, a collection voltage is applied to the B4 electrode;
[0034] After the exposure is completed, the charges collected in each transfer layer are transferred across the layers in an orderly manner. The specific timing is as follows: Figure 2 As shown, at t2, V3 starts to apply the transfer voltage. At t3, the voltage of V2 slowly decreases, and the transfer voltage applied by V3 remains unchanged. The charges collected by the p2 electrode will continue to flow to the p3 electrode. At t4, V1 starts to apply the transfer voltage. At t5, the voltage of V3 slowly decreases, and the charges under the p3 electrode continue to transfer to p1. At t6, V2 starts to apply the transfer voltage. Repeating this step can realize the simultaneous vertical downward transfer of the charges collected in the transfer layer until a charge packet is transferred to the multiplication layer.
[0035] When the charge packet is transferred to the potential well of the electrode of electrode group p3 (P3), B1-B5 applies a timing signal to realize the multiplication of the charge transfer cycle, such as Figure 3 As shown. The first transfer cycle multiplication sequence starts at t5, when the charge stored in p3 (P3) begins to transfer to the multiplication layer. At t5, the potential of B4 is pulled down, and a threshold voltage pulse is applied to B5. At the same time, for the transferred charge to be multiplied, B1, B2, B3, and B4 are first applied in sequence and transferred to B4 in a similar transfer sequence as in the above steps.
[0036] The cyclic multiplication process is mainly realized by the three electrodes B2, B3 and B4, starting from time t6, which is also the starting time ta of the cyclic multiplication cycle. When B2 applies the multiplication voltage and B3 applies the low level, at time tb, B3 applies the transfer voltage, and at the same time, the level of B4 is pulled down, and the charge is multiplied and transferred from B4 to B2. Then at time tc, the potential of B2 drops, and the charge flows to B3. At time td, B4 applies the transfer voltage, and then the level of B3 is pulled down, and the charge flows to B4. Among them: ta to te is a multiplication cycle, and the time of the multiplication cycle is adjusted according to the set multiplication times. After repeating the above multiplication steps for a preset fixed number of times, the multiplication process ends, that is, time tf in the figure. Wait for the moment when the charge packet transferred from the next transfer layer is located in the potential well of the p3 (P3) electrode. At time t11, when the charge packet transferred from the next transfer layer is located in the potential well of the p3 (P3) electrode, B5 applies the threshold voltage to transfer the multiplied charge stored in B4 to the subsequent readout circuit. The above process is repeated until all collected charges are read out.
[0037] After the charge transfer readout, in order to obtain the X-ray energy analysis results, the photogenerated charges generated in the semiconductor at different depths need to be grouped and accumulated, that is, the charges collected by each transfer layer electrode need to be grouped and accumulated. The form of charge grouping depends on the division of the energy spectrum interval of the X-rays required in the actual application and the absorption of the rays in the semiconductor. Generally, X-rays are divided into several energy spectrum intervals, and the accumulated charges are divided into several groups. The position of the corresponding charge grouping is preferably such that the X-rays in the corresponding energy interval are completely absorbed within the depth of the semiconductor. Finally, the energy attenuation information of each energy spectrum interval is obtained by calculating the total amount of the accumulated photogenerated charges in each group.
[0038] Example 1
[0039] The detector structure proposed in the present invention can use Si semiconductor materials with a length of 5-6cm. This example takes 5cm as an example, with a thickness and width of 0.5-1mm. 0.005mm of oxide is deposited on it, and finally polysilicon or metal is etched to complete the electrode interconnection, wherein: the three-dimensional size, number and spacing between electrodes depend on the size of the detector substrate, the collection efficiency of photogenerated charges and the charge coupling ability. The typical values in this example are that the thickness of the electrode is 0.01mm, the length of the electrode is 0.4mm, the width of the electrode is 0.1mm, and the spacing between adjacent electrodes is 0.001mm. Taking the medical X-ray energy spectrum of 10Kev-100Kev as an example, assuming that the energy spectrum interval is divided into 3, namely (10Kev-30Kev), (30Kev-60Kev), and (60Kev-100Kev), the photogenerated charges in the semiconductor are divided into three groups in longitudinal order, and the three groups correspond to semiconductor lengths of 1cm, 1.5cm, and
[0040] 2.5cm, the transfer layer length at the end is 0.6mm. Among them: the typical voltage of the multiplication voltage signal B2 is 12.5V, and the transfer voltage used for transfer is 3.3V. The standard voltage of the collection voltage and transfer voltage of the remaining transfer electrodes is 3.3V, and the typical value of the threshold voltage is 2.5V. The collision ionization rate of a single multiplied electron is 4.2%. 50 multiplications can be set to achieve tenfold multiplication of the charge packet, where the multiplication period is set to 1us, the total time of 50 multiplications is 50us, and the corresponding transfer charge period is the total time of 50 multiplications plus the transfer time and readout time of 52us.
[0041] Although the present invention has been described above, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many modifications without departing from the purpose of the present invention, which are all within the protection of the present invention.
Claims
1. An X-ray energy detector, the detector is composed of a body; the detector is provided with a base layer, an oxide layer and a circuit output module; characterized in that: The detector further comprises: a first timing control unit and a second timing control unit; wherein: the base layer is divided into a plurality of transfer layers and multiplication layers according to the needs of X-ray energy analysis; the transfer layer is connected to the first timing control unit through an electrode group consisting of three electrodes; the multiplication layer is connected to the second timing control unit through five electrodes; wherein: The first timing control unit is connected to the positive electrode of each electrode group and is used to control the collection and transfer of photogenerated charges; The second timing control unit is connected to each electrode of the multiplication layer and is used for controlling the multiplication and reading of the transferred charge packets.
2. An X-ray energy detector according to claim 1, characterized in that: The first timing control unit is connected to the positive electrode of each electrode group and is used for collecting and transferring photogenerated charges, including: The first positive electrode p1 of each electrode group is connected to the first timing control unit and applied with a transfer voltage signal V1, the second positive electrode p2 is connected to the first timing control unit and applied with a transfer voltage signal V2, and so on; wherein: At time t2, V3 starts to apply transfer voltage. At time t3, the voltage of V2 decreases slowly, and the transfer voltage applied by V3 remains unchanged. The charges collected by the p2 electrode will continue to flow to the p3 electrode. At time t4, V1 starts to apply transfer voltage. At time t5, the voltage of V3 decreases slowly, and the charges under the p3 electrode are continuously transferred to p1. At time t6, V2 starts to apply transfer voltage. Repeating this step can realize the simultaneous vertical downward transfer of charges collected in the transfer layer until a charge packet is transferred to the multiplication layer.
3. A low-dose X-ray energy detector according to claim 2, characterized in that: The second timing control unit is connected to each electrode; it is used to multiply and read out the transferred charge packets, including: the five electrodes of the multiplication layer are respectively connected to the second timing control unit, and five voltage signals B1, B2, B3, B4, and B5 are applied to each of them, wherein: the first electrode is used to collect or transfer charges, and the transfer voltage signal B1 is applied; the second electrode is used to transfer and multiply charges, which is mainly achieved by applying the transfer and multiplication voltage B2; the third electrode is used to transfer charges, and the transfer voltage signal B3 is applied; the fourth electrode temporarily stores the charges that have passed a multiplication cycle at this electrode and waits for the next multiplication; the fifth electrode is a read-out charge switch, and the threshold voltage B5 is applied to transfer the charges to the subsequent read-out circuit.
4. A low-dose X-ray energy detector according to claim 3, characterized in that: The second timing control unit performs a circulation process of the transferred charge to be multiplied, including: The first transfer cycle multiplication sequence starts at t5, when the charge stored in p3 (P3) begins to transfer to the multiplication layer; at t5, the potential of B4 is pulled down, and a threshold voltage pulse is applied to B5. First, B1, B2, B3, and B4 apply transfer voltages in sequence, and the cyclic multiplication process is achieved through the three electrodes B2, B3, and B4. Starting from time t6, which is also the starting time ta of the cycle doubling period; B2 applies a multiplication voltage, B3 applies a low level, at time tb, B3 applies a transfer voltage, and at the same time B4 is pulled down, the charge is multiplied and transferred from B4 to B2, then at time tc, B2 potential drops, and the charge flows to B3, at time td, B4 applies a transfer voltage, then B3 is pulled down, and the charge flows to B4; Among them: ta to te is a doubling period, and the time of the doubling period is adjusted according to the set doubling times; After repeating the above doubling steps for a preset fixed number of times, the doubling process ends, i.e., at time tf; Waiting for the moment when the charge packet transferred from the next transfer layer is located in the potential well of the p3 (P3) electrode; At time t11, when the charge packet transferred from the next transfer layer is in the potential well of the p3 (P3) electrode, B5 applies a threshold voltage to transfer the multiplied charge stored in B4 to the subsequent readout circuit; The above process is repeated until all collected charges are read out.