Miniature high-dose radiation detector structure of piezoresistive MEMS, method and application

Abstract

The invention belongs to the technical field of radioactivity detection, and particularly relates to a piezoresistive MEMS miniature high-dose radiation detector structure which comprises a radiation sensitive layer, a strain amplification layer and a base layer which are arranged in sequence, a radiation sensitive material (3) arranged on the radiation sensitive layer generates controllable volume expansion after absorbing radiation, and the strain amplification layer is arranged on the base layer. And the strain amplification layer converts volume expansion into mechanical strain, converts the strain into resistance change by utilizing a piezoresistive effect, and is connected with a Wheatstone bridge and an external detection circuit to measure the variable quantity of output voltage so as to realize radiation dose measurement. The capability of measuring high-dose and high-energy radiation (greater than 10 kGy) and the advantage of direct sensing are combined together, miniaturization (the chip scale size is less than or equal to 5 mm * 5 mm * 1 mm) and high-dose range coverage (1 kGy to 100 kGy) are realized, and the distributed dose monitoring requirement in an extreme environment is met; the device is passive, free of maintenance, resistant to radiation damage and suitable for monitoring the accumulated radiation dose in the fields of nuclear industry, aerospace, medical irradiation and the like.

Description

Technical Field

[0001] This invention belongs to the field of radioactivity detection technology, specifically relating to the structure, method and application of a piezoresistive MEMS miniature high-dose radiation detector. Background Technology

[0002] High-energy radiation doses exceeding 10 kGy are found in experimental research facilities such as nuclear power plants, the Large Hadron Collider, the European Free Electron Laser Project, and the International Thermonuclear Experimental Reactor, as well as at nuclear facility decommissioning sites. Measuring these doses presents a significant practical challenge. High-energy radiation can severely damage the structural materials of these facilities; therefore, it is essential to measure the radiation dose absorbed by these materials to ensure their safe operation.

[0003] Currently known electronic dosimeters for detecting high-dose ionizing radiation mainly consist of conductive sensors. The interaction between high-energy radiation and π-conductor elements limits the measurement of the maximum radiation dose to tens of kGy. Passive dosimeters, such as thermoluminescent dosimeters, optically stimulated luminescent dosimeters, and alanine dosimeters, can measure radiation doses exceeding tens of kGy, but continuous measurements are not possible because the detector must be moved from the monitoring area to the readout device.

[0004] With the rapid development of IoT technology, the demand for low-power, high-precision sensor systems in the environmental monitoring field is increasing. MEMS sensors, with their advantages of small size, light weight, low power consumption, high reliability, high sensitivity, easy integration, and resistance to harsh working environments, are gradually replacing the dominant position of traditional mechanical sensors.

[0005] As can be seen from the above introduction, with the development of nuclear energy and particle accelerators, in order to ensure the safe operation of facilities such as reactors and accelerators and to assess the radiation damage effect of high-dose high-energy radiation on the structural materials of the facilities, it is necessary to develop a new detector structure to measure the high-dose radiation that occurs in the above facilities in real time. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention aims to propose a piezoresistive MEMS sensor based on the chain of "radiation-material volume expansion-mechanical strain-resistance change-dose change". It combines the ability to measure high-dose, high-energy radiation (>10kGy) with the advantages of direct sensing, providing a passive, maintenance-free, radiation-damage-resistant MEMS detector structure, method, and application. It achieves miniaturization (chip-level size ≤5mm×5mm×1mm) and high dose range coverage (1kGy~100kGy), meeting the needs of distributed dose monitoring in extreme environments. It is suitable for cumulative radiation dose monitoring in fields such as nuclear industry, aerospace, and medical irradiation.

[0007] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0008] A micro high-dose radiation detector structure of piezoresistive MEMS includes a radiation-sensitive layer, a strain amplification layer and a base layer arranged in sequence. The radiation-sensitive material (3) in the radiation-sensitive layer absorbs radiation and generates controllable volume expansion. The strain amplification layer converts the volume expansion into mechanical strain. The strain is converted into a change in resistance by utilizing the piezoresistive effect. The radiation dose is measured by measuring the change in output voltage through connection with a Wheatstone bridge and an external detection circuit.

[0009] Furthermore, the radiation-sensitive layer includes a radiation-sensitive layer frame and a radiation-sensitive material. The radiation-sensitive layer frame is made of a strong and rigid material, which covers the surface and sides of the radiation-sensitive material in contact with it, causing the radiation-sensitive material exposed to radiation to expand directionally away from the radiation-sensitive layer frame.

[0010] Furthermore, the radiation-sensitive material is a polymer or composite material, selected according to the type of radiation to be measured; the polymer is PMMA or polyimide.

[0011] Furthermore, the strain amplification layer includes a piezoresistor, a pressure-sensitive diaphragm, and an air cavity. The piezoresistor is disposed in a high stress concentration area formed in the pressure-sensitive diaphragm and is connected to a Wheatstone bridge and an external detection circuit to convert the resistance change of the piezoresistor into an output voltage change.

[0012] Furthermore, the pressure-sensitive diaphragm includes a pressure-sensitive diaphragm, square islands, narrow beams, and a supporting substrate frame. The pressure-sensitive diaphragm, which has multiple narrow beams and square islands inside, is disposed within the supporting substrate frame. The square islands are connected to each other and to the supporting substrate frame through narrow beams.

[0013] Furthermore, the narrow beam is used to form a high stress concentration area in the pressure-sensitive diaphragm for placing the varistor.

[0014] Furthermore, the square island is used to increase the local stiffness of the pressure-sensitive diaphragm and improve its overload resistance.

[0015] Furthermore, the varistor is made of lightly doped P-type silicon, the pressure-sensitive diaphragm is made of lightly doped N-type silicon, and the base layer is made of borosilicate glass resistant to high-energy radiation.

[0016] A method for detecting high-dose radiation using the above-described detector structure includes the following steps:

[0017] Step 1: calibrate the detector structure in a standard radiation field and give the calibration factor between the ionizing radiation dose and the change in output voltage.

[0018] Step 2: High-energy radiation irradiates the radiation-sensitive material, causing the material to expand in volume, which in turn causes a change in the varistor.

[0019] Step 3: Measure the change in output voltage by connecting to a Wheatstone bridge and an external detection circuit;

[0020] Step 4: Based on the change in output voltage in Step 3 and the calibration factor obtained in Step 1, obtain the ionizing radiation dose.

[0021] In a specific implementation, the piezoresistive MEMS miniature high-dose radiation detector structure described above is applied to the monitoring of cumulative radiation dose in nuclear industry, aerospace, or medical irradiation.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. Combining the ability to measure high-dose, high-energy radiation (>10kGy) with the advantages of direct sensing, miniaturization (chip-level size ≤5mm×5mm×1mm) and high-dose range coverage (1kGy~100kGy) are achieved to meet the needs of distributed dose monitoring in extreme environments.

[0024] 2. Passive, maintenance-free, and radiation-resistant, suitable for cumulative radiation dose monitoring in fields such as nuclear industry, aerospace, and medical irradiation. Attached Figure Description

[0025] Figure 1 This is a cross-sectional view of a micro high-dose radiation detector structure of a piezoresistive MEMS.

[0026] Figure 2 for Figure 1 Top view of the structure of a medium-pressure diaphragm;

[0027] Figure 3 for Figure 1 Cross-sectional view of the medium-pressure diaphragm;

[0028] Figure 4 This is a flowchart illustrating the measurement principle of a miniature high-dose radiation detector structure for a piezoresistive MEMS.

[0029] In the above figures, 1 is the outer frame of the radiation-sensitive layer; 2 is the piezoresistor; 3 is the radiation-sensitive material; 4 is the pressure-sensitive diaphragm; 5 is the air cavity; 6 is the base layer; 7 is the pressure-sensitive diaphragm; 8 is the square island; 9 is the narrow beam; and 10 is the supporting substrate frame. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] A micro high-dose radiation detector structure of piezoresistive MEMS includes a radiation-sensitive layer, a strain amplification layer and a base layer arranged sequentially. The radiation-sensitive material 3 in the radiation-sensitive layer absorbs radiation and generates controllable volume expansion. The strain amplification layer converts the volume expansion into mechanical strain. The strain is converted into a change in resistance using the piezoresistive effect. By connecting with a Wheatstone bridge and an external detection circuit, the change in output voltage is measured to achieve radiation dose measurement.

[0032] The working principle of the micro high-dose radiation detector structure of piezoresistive MEMS is to use high-energy rays or high-energy radiation (such as gamma rays, electron beams, proton beams, etc.) to induce changes in the molecular structure of sensitive materials, resulting in volume expansion. The expansion is converted into mechanical strain through MEMS microstructure, and the strain is converted into resistance change based on the piezoresistive effect. Radiation dose measurement is achieved through the resistance-dose relationship.

[0033] Example 1

[0034] This invention discloses a micro high-dose radiation detector structure for piezoresistive MEMS, designed as a chip-level "sandwich" structure, such as... Figure 1 As shown, it includes a radiation-sensitive layer, a strain amplification layer, and a base layer arranged sequentially from top to bottom.

[0035] The radiation-sensitive layer comprises a radiation-sensitive layer frame 1 and a radiation-sensitive material 3. The radiation-sensitive layer frame 1 is a rigid material that hardly deforms. An insulating ceramic coating is sprayed onto the surface of the radiation-sensitive layer frame 1 to ensure insulation. The radiation-sensitive material 3 can be a polymer or composite material that undergoes controlled volume expansion upon absorbing radiation. Controlled volume expansion refers to a linear proportional relationship between the volume expansion rate (or length change rate) of the radiation-sensitive material and the absorbed radiation dose within a certain radiation dose range. The radiation-sensitive material 3 adopts a planar layered structure, with the radiation-sensitive layer frame 1 positioned above it, completely covering the upper surface and sides of the radiation-sensitive material 3. Placing the radiation-sensitive material 3 below the rigid radiation-sensitive layer frame 1, with only its lower surface uncovered, allows it to undergo downward directional expansion when irradiated by ionizing radiation.

[0036] The radiation-sensitive material 3 can be a high molecular polymer or composite material such as PMMA (polymethyl methacrylate) or polyimide, which produces a controllable volume expansion after absorbing radiation. Different radiation-sensitive materials 3 can be selected depending on the type of radiation or rays to be measured.

[0037] For example:

[0038] When PMMA is irradiated with high-energy radiation (such as gamma rays or electrons), its internal polymer chain structure is disrupted, resulting in microscopic fractures and defects. Simultaneously, the broken molecular chains release internal stress and may form tiny bubbles (primarily gases such as CO, CO2, H2, and CH4). These changes in microstructure collectively lead to macroscopic volume expansion. Within a certain radiation dose range (e.g., 10 kGy to 1000 kGy, depending on the type and formulation of the PMMA), its volume expansion rate (or length change rate) exhibits a strong linear proportional relationship with the absorbed radiation dose.

[0039] When neutrons irradiate quartz glass, they undergo nuclear reactions with silicon and oxygen atoms, disrupting its ordered crystal structure (or glassy network structure) and creating numerous vacancies and defects. This leads to an increase in interatomic spacing, which macroscopically manifests as a decrease in density and volume expansion. Within a certain flux range, the volume expansion rate is approximately proportional to the neutron flux (which can be converted into absorbed dose), but it remains unchanged after reaching saturation.

[0040] The strain amplification layer includes a piezoresistor 2, a pressure-sensitive diaphragm 4, and an air cavity 5. The air cavity 5 is located inside the pressure-sensitive diaphragm 4, providing space for deformation. A cantilever beam or diaphragm structure, fabricated using MEMS technology, converts expansion into localized strain. A piezoresistor 2 is integrated into the strain region; four piezoresistors 2 are interconnected with leads to form a Wheatstone bridge.

[0041] The pressure-sensitive diaphragm 4 adopts a beam-membrane-three-island structure, such as Figure 2 and 3 As shown, it includes a pressure-sensitive diaphragm 7, square islands 8, narrow beams 9, and a supporting substrate frame 10. The pressure-sensitive diaphragm 7, which has multiple narrow beams 9 and square islands 8 inside, is disposed within the supporting substrate frame 10. The square islands 8 are connected to each other and to the supporting substrate frame 10 through the narrow beams 9.

[0042] The pressure-sensitive diaphragm 7 is designed as a square diaphragm, which can achieve higher mechanical stress compared to a circular diaphragm. The pressure-sensitive diaphragm 7 is fixed inside the support substrate frame 10 with a square frame structure, and the height of the upper surface of the pressure-sensitive diaphragm 7 is slightly lower than the height of the upper end of the surrounding support substrate frame 10.

[0043] The pressure-sensitive diaphragm 7 is designed with a narrow beam 9 and three square islands 8. The three square islands 8 are arranged in a straight line between the parallel and opposite frames of the supporting substrate frame 10. The square islands 8 are connected to each other and to the supporting substrate frame 10 through the narrow beam 9.

[0044] The narrow beam 9 structure forms a high stress concentration area in the pressure-sensitive diaphragm 7. The piezoresistor 2 is placed in this area and connected to the Wheatstone bridge and external detection circuits to measure the voltage value of the piezoresistor 2, which helps to improve the sensitivity of the detector structure.

[0045] The square island 8 structure in the pressure-sensitive diaphragm 7 helps increase the local stiffness of the diaphragm 7, thereby improving the overload resistance of the detector structure, reducing the deformation deflection of the pressure-sensitive diaphragm 7 caused by external pressure, reducing the nonlinearity of the detector structure, and also providing protection for the pressure-sensitive diaphragm 7. In MEMS, the minute deformation of the pressure-sensitive diaphragm 7 is used to sense pressure. If overloaded (excessive pressure is applied), it will cause permanent deformation or damage to the pressure-sensitive diaphragm 7, and the entire detector structure will fail.

[0046] The two adjacent square islands 8 are connected by a narrow beam 9 structure. The upper surfaces of the narrow beam 9 and the square islands 8 are on the same horizontal line as the upper surface of the supporting substrate frame 10, which is beneficial to the processing and manufacturing of the pressure-sensitive diaphragm 7 and the optimization of the structural dimensions of the pressure-sensitive diaphragm 7.

[0047] Varistor 2 is made of lightly doped P-type silicon.

[0048] The pressure-sensitive diaphragm 4 is made of lightly doped N-type silicon.

[0049] The base layer 6 is made of borosilicate glass that is resistant to high-energy radiation.

[0050] High-energy radiation irradiation of the radiation-sensitive material 3 causes the material's volume to expand, driving deformation of the MEMS microstructure. The varistor 2 converts the mechanical strain of the microbeam into a change in resistance, and the change in resistance of the varistor 2 is converted into a change in voltage through a Wheatstone bridge. The change in output voltage is positively correlated with the ionizing radiation dose. Before use, it is calibrated in a standard radiation field, and the ionizing radiation dose can be obtained by measuring the change in output voltage.

[0051] The measurement principle and workflow of a piezoresistive MEMS miniature high-dose radiation detector structure are as follows: Figure 4 As shown. During use, when ionizing radiation interacts with radiation-sensitive materials, it generates gas microbubbles or causes the material's microcrystalline structure to loosen, resulting in controllable volume expansion, thereby driving the deformation of the MEMS microstructure. The mechanical strain of the microbeam is converted into a resistance change by a varistor integrated on the microstructure, and the resistance change of the varistor is converted into an output voltage change by a Wheatstone bridge. After temperature compensation, the change in ionizing radiation dose can be obtained.

[0052] The aforementioned piezoresistive MEMS miniature high-dose radiation detector structure can be applied to cumulative radiation dose monitoring in the nuclear industry, aerospace, or medical irradiation.

[0053] Example 2

[0054] The method for detecting high-dose radiation using this detector structure includes the following steps:

[0055] Step 1: calibrate the detector structure in a standard radiation field to obtain the calibration factor between the ionizing radiation dose and the change in output voltage; place the detector device in the standard radiation field, measure the voltage value of the detector structure when it is not irradiated, irradiate the detector structure with a standard source of known activity, and read the voltage value of the detector structure at regular intervals to obtain the correspondence between the change in the voltage value of the detector structure and the cumulative radiation dose of the standard source, i.e., the calibration factor.

[0056] Step 2: High-energy radiation irradiates the radiation-sensitive material, causing the material to expand in volume, which in turn causes a change in the piezoresistor. The detector structure and the object to be monitored are placed in the same position, and the radiation source irradiates the detector structure. When the ionizing radiation interacts with the radiation-sensitive material, it generates gas microbubbles or causes the material's microcrystalline structure to loosen, resulting in controllable volume expansion, which drives the deformation of the MEMS microstructure. The piezoresistor integrated on the microstructure converts the mechanical strain of the microbeam into a change in resistance.

[0057] Step 3: Measure the change in voltage of the detector structure; after being irradiated by the radiation source for a period of time, record the voltage value of the detector structure to obtain the change in voltage of the detector structure.

[0058] Step 4: Obtain the ionizing radiation dose based on the voltage change in Step 3. Based on the recorded voltage change of the detector structure, and through the relationship between the voltage change of the detector structure and the cumulative radiation dose of the standard source (scale factor), obtain the ionizing radiation dose of the detector structure.

[0059] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. Thus, the invention also intends to include any such variations, uses, or adaptations that fall within the scope of the claims and their equivalents.

[0060] The above embodiments are merely illustrative examples of the present invention. The present invention may also be implemented in other specific ways or forms without departing from its spirit or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of protection of the present invention should be defined by the claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A micro high-dose radiation detector structure for piezoresistive MEMS, characterized in that: It includes a radiation-sensitive layer, a strain amplification layer and a base layer arranged in sequence. The radiation-sensitive material (3) in the radiation-sensitive layer absorbs radiation and generates a controllable volume expansion. The strain amplification layer converts the volume expansion into mechanical strain and uses the piezoresistive effect to convert the strain into a change in resistance. By connecting with a Wheatstone bridge and an external detection circuit, the change in output voltage is measured to realize radiation dose measurement.

2. The piezoresistive MEMS micro high-dose radiation detector structure as described in claim 1, characterized in that: The radiation-sensitive layer includes a radiation-sensitive layer frame (1) and a radiation-sensitive material (3). The radiation-sensitive layer frame (1) is made of a strong and rigid material and covers the surface and surrounding area of ​​the radiation-sensitive material (3) in contact with it, so that the radiation-sensitive material (3) subjected to radiation irradiation will produce directional expansion away from the radiation-sensitive layer frame (1).

3. The piezoresistive MEMS miniature high-dose radiation detector structure as described in claim 2, characterized in that: The radiation-sensitive material (3) is a polymer or composite material, selected according to the type of radiation to be measured; the polymer is PMMA or polyimide.

4. The micro high-dose radiation detector structure of a piezoresistive MEMS as described in claim 1, characterized in that: The strain amplification layer includes a piezoresistor (2), a pressure-sensitive diaphragm (4), and an air cavity (5). The piezoresistor (2) is disposed in the high stress concentration area formed in the pressure-sensitive diaphragm (4) and is connected to a Wheatstone bridge and an external detection circuit to convert the resistance change of the piezoresistor (2) into an output voltage change.

5. The micro high-dose radiation detector structure of a piezoresistive MEMS as described in claim 4, characterized in that: The pressure-sensitive diaphragm (4) includes a pressure-sensitive diaphragm (7), a square island (8), a narrow beam (9), and a supporting substrate frame (10). The pressure-sensitive diaphragm (7), which has multiple narrow beams (9) and square islands (8), is located inside the supporting substrate frame (10). The square islands (8) are connected to each other and to the supporting substrate frame (10) through the narrow beams (9).

6. The piezoresistive MEMS miniature high-dose radiation detector structure as described in claim 5, characterized in that: The narrow beam (9) is used to form a high stress concentration area in the pressure-sensitive diaphragm (7) for placing the varistor (2).

7. The piezoresistive MEMS miniature high-dose radiation detector structure as described in claim 5, characterized in that: The square island (8) is used to increase the local stiffness of the pressure-sensitive diaphragm (7) and improve its overload resistance.

8. The micro high-dose radiation detector structure of a piezoresistive MEMS as described in claim 5, characterized in that: The varistor (2) is made of lightly doped P-type silicon, the pressure-sensitive diaphragm (4) is made of lightly doped N-type silicon, and the base layer is made of borosilicate glass resistant to high-energy radiation.

9. A method for detecting high-dose radiation using the detector structure described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: calibrate the detector structure in a standard radiation field and give the calibration factor between the ionizing radiation dose and the change in output voltage. Step 2: High-energy radiation irradiates the radiation-sensitive material (3), causing the radiation-sensitive material (3) to expand in volume, which in turn causes the varistor (2) to change. Step 3: Measure the change in output voltage by connecting to a Wheatstone bridge and an external detection circuit; Step 4: Based on the change in output voltage in Step 3 and the calibration factor obtained in Step 1, obtain the ionizing radiation dose.

10. An application of the piezoresistive MEMS miniature high-dose radiation detector structure according to any one of claims 1-8, characterized in that: It can be applied to the monitoring of cumulative radiation dose in nuclear industry, aerospace or medical irradiation.

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