X-ray vertical channel field effect transistor detector

Abstract

The utility model discloses an X-ray vertical channel field effect transistor detector, which comprises an X-ray sensing part, a current modulation part and a charge coupling induction part, the X-ray sensing part is composed of a high-atomic-number semiconductor crystal and a corresponding semiconductor structure, absorbs high-energy X-rays and generates electron / hole pairs; the current modulation part is composed of a porous source electrode, a semiconductor channel and a drain electrode; the charge coupling induction part is composed of a gate electrode, a dielectric layer and a porous source electrode. The dielectric layer is over the X-ray sensing layer. According to the utility model, the photocurrent is amplified by utilizing the gain of the field effect transistor, so that high-sensitivity X-ray detection is obtained; the X-ray sensing layer is arranged between the grid electrode and the dielectric layer, dark current is blocked through the dielectric layer, an incident X-ray signal is transmitted to light current through charge coupling induction, and low-noise X-ray detection is achieved.

Description

Technical Field

[0001] This utility model relates to the field of photoelectric detection, and in particular to X-ray detection technology. Background Technology

[0002] Because X-ray photons have very high energy, they have a strong penetrating ability to target objects. Therefore, X-ray imaging is widely used in medical and industrial manufacturing to achieve non-destructive testing of diseases and industrial products. Generally speaking, X-ray detection has two methods: direct detection and indirect detection, such as... Figure 1a and Figure 1b As shown. In direct detection, the semiconductor layer absorbs the energy of the incident X-rays and converts it into electron / hole pairs. These photogenerated electron / hole pairs separate under the influence of an electric field and drift to form a detection electrical signal. In indirect X-ray detection, X-ray photons first incident on the scintillator, exciting visible fluorescence, and then the visible fluorescence signal is detected by a semiconductor detector.

[0003] Compared to indirect X-ray detectors, direct X-ray detectors do not require the conversion of X-rays into visible fluorescence, thus offering higher detection external quantum efficiency. Furthermore, direct X-ray detectors avoid visible fluorescence scattering, resulting in higher imaging spatial resolution. However, in direct X-ray detectors, a relatively thick absorbing semiconductor (~mm) is required to fully absorb and convert high-energy X-ray photons. To ensure complete separation and drift of electrons and holes generated by the absorbing semiconductor to form an electrical signal, a high bias voltage (hundreds of volts) is required across the direct detector. Figure 1a The X-ray direct detector shown is subjected to a high bias voltage across its terminals, resulting in relatively high dark current and noise caused by current fluctuations. Therefore, in conventional X-ray direct detectors, the detection sensitivity (proportional to photocurrent) and signal-to-noise ratio (inversely proportional to noise signal) are mutually constrained. Achieving high-sensitivity, low-noise X-ray detection is a pressing problem that needs to be solved. Utility Model Content

[0004] Purpose of the utility model: This utility model addresses the problems of conventional X-ray direct detectors by proposing an X-ray vertical channel field-effect transistor detector. It utilizes the gain of the field-effect transistor to amplify the photocurrent, thereby achieving high-sensitivity X-ray detection. By placing the X-ray sensing layer between the gate and the dielectric layer, and using the dielectric layer to block dark current, the incident X-ray signal is transmitted to the photocurrent through charge coupling induction, resulting in low-noise X-ray detection.

[0005] The technical solution adopted in this utility model is: an X-ray vertical channel field-effect transistor detector, including an X-ray sensing part, a current modulation part, and a charge coupling sensing part;

[0006] The X-ray sensing part is composed of semiconductor materials and corresponding semiconductor structures for X-ray absorption. It absorbs high-energy X-rays and generates electron / hole pairs.

[0007] The current modulation section consists of a porous source electrode, a semiconductor channel, and a drain electrode. The semiconductor channel is disposed between the porous source electrode and the drain electrode, and photocurrent is obtained through the semiconductor channel.

[0008] Without X-ray irradiation, electrons cannot be injected into the channel from the source electrode due to the potential barrier between the source electrode and the semiconductor channel, resulting in a very low dark current. When X-rays irradiate the sensing area, the potential barrier between the source electrode and the semiconductor channel is reduced and thinned due to charge coupling induction, so a large number of electrons are injected into the semiconductor channel from the source electrode, forming a photocurrent.

[0009] The charge-coupled sensing part consists of a gate electrode, a dielectric layer and a porous source electrode. The gate electrode is disposed below the X-ray sensing part and a passivation layer is disposed on the gate electrode. The dielectric layer is disposed above the X-ray sensing part and a porous source electrode is disposed above the dielectric layer.

[0010] Photogenerated holes created by the X-ray sensing layer are blocked by the dielectric layer and accumulate below it. Due to charge-induced coupling, electrons of equal charge are induced near the porous source electrode above the dielectric layer. The large number of electrons induced near the porous source electrode lowers the potential barrier between the source electrode and the semiconductor channel, allowing electrons to be injected from the porous source electrode into the semiconductor channel.

[0011] Furthermore, the atomic number of the X-ray absorbing semiconductor material is ≥30, and the mass density is ≥3 g / cm³. 3 .

[0012] Furthermore, the semiconductor junction sensing structure in the X-ray sensing part is as follows: a p-type top semiconductor junction layer and an n-type bottom semiconductor junction layer are prepared on a semiconductor material to form a pin junction, or the top semiconductor junction layer and the bottom semiconductor junction layer are simultaneously set to p-type or n-type to form a pip or nin junction.

[0013] Furthermore, the porous source electrode is a metal electrode that is electrically grounded. The porous source electrode is not a continuous conductive layer. In order to achieve charge coupling induction, some holes are provided on the surface of the electrode. The size and density of the holes are determined by the metal material properties of the porous source electrode and the material properties of the semiconductor channel. The drain electrode is a common metal electrode.

[0014] Furthermore, the dielectric layer has a very high resistivity and dielectric constant, and is an HfO2 dielectric layer.

[0015] Furthermore, the passivation layer is SiO2 or SiN. x layer.

[0016] Furthermore, the semiconductor channel is a ZnO layer.

[0017] The above-mentioned method for fabricating an X-ray vertical channel field-effect transistor detector includes the following steps:

[0018] Step 1. Perovskite crystal MAPbBr3 is grown in solution using the inverse temperature method and used as the semiconductor material for the X-ray sensing part;

[0019] Step 2. A semiconductor junction layer is prepared on the perovskite crystal using metal ion doping.

[0020] Step 3. A continuous metal film is deposited on the bottom surface of the X-ray sensing part by vacuum evaporation or sputtering to form a gate electrode;

[0021] Step 4. A stable oxide or nitride layer is sputtered onto the gate electrode as a passivation layer;

[0022] Step 5. Prepare a dielectric layer on the top surface of the X-ray sensing part by spin coating or sputtering;

[0023] Step 6. A patterned metal layer is sputtered onto the dielectric layer using a mask to serve as a porous source electrode;

[0024] Step 7. Deposit semiconductor channels on the porous source electrode using a spin-coating method;

[0025] Step 8. Deposit a metal layer as a drain electrode on the semiconductor channel layer using vacuum evaporation or sputtering methods.

[0026] The beneficial effects of this utility model are:

[0027] (1) This invention proposes a vertical channel field-effect phototransistor structure, which obtains photocurrent through the semiconductor channel between the source electrode and the drain electrode. Because the field-effect phototransistor has a gain amplification effect on the incident X-ray signal at the gate, the X-ray detector proposed in this invention can obtain a higher photocurrent and achieve high-sensitivity detection of X-rays.

[0028] (2) In the X-ray detector structure proposed in this invention, the X-ray sensing part is inserted between the gate electrode and the dielectric layer. Due to the high potential barrier of the dielectric layer, the current between the gate electrode and the porous source electrode can be ignored. The photogenerated electron / hole pairs caused by X-rays in the sensing part do not directly inject into the channel and affect the detection current, but modulate the photocurrent through charge coupling effect. The X-ray detector proposed in this invention can suppress dark current and achieve low-noise detection of X-rays. Attached Figure Description

[0029] Figure 1a For direct detection by X-ray detectors;

[0030] Figure 1b Indirect detection using X-ray detectors;

[0031] Figure 2a This invention relates to a photoconductive X-ray sensor for the X-ray sensing part.

[0032] Figure 2b This invention relates to a semiconductor junction X-ray sensor for the X-ray sensing part of the present invention.

[0033] Figure 3a This is the device structure of the current modulation section of this utility model;

[0034] Figure 3b This is the dark-state potential barrier distribution of the current modulation section of this utility model.

[0035] Figure 3c The potential barrier distribution of the current modulation section of this utility model after X-ray irradiation;

[0036] Figure 4a This is the dark-state structure of the charge-coupled sensing part of this utility model;

[0037] Figure 4b This invention relates to the charge coupling induction of the charge coupling induction part after X-ray incidence;

[0038] Figure 5 This invention relates to an X-ray vertical channel field-effect phototransistor detector.

[0039] In the figure, 1. Semiconductor material; 2. Top semiconductor junction layer; 3. Bottom semiconductor junction layer; 4. Porous source electrode; 5. Semiconductor channel; 6. Drain electrode; 7. Gate electrode; 8. Dielectric layer; 9. Passivation layer. Detailed Implementation

[0040] The present invention will now be described in detail. This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiment.

[0041] An X-ray vertical channel field-effect transistor detector includes the following components:

[0042] Part 1, X-ray sensing section, such as Figure 2a and 2b As shown. This section includes those with larger atomic numbers (≥30) and higher mass density (≥3g / cm³).3 The X-ray sensing element is composed of semiconductor material 1, which can fully absorb incident X-rays and form photogenerated electron / hole pairs through physical processes such as the photoelectric effect. Under the action of an applied electric field, these electron / hole pairs separate and drift in a specific direction. To reduce dark current and noise in the X-ray sensing section, a semiconductor junction sensing structure is also employed, in which a p-type top semiconductor junction layer 2 and an n-type bottom semiconductor junction layer 3 are fabricated on semiconductor material 1 to form a pin junction. Alternatively, a unipolar carrier transport mode can be used, where the top semiconductor junction layer 2 and the bottom semiconductor junction layer 3 are both p-type or n-type, forming a pip or nin junction.

[0043] The second part is the current modulation section. It consists of a porous source electrode 4, a semiconductor channel 5, and a drain electrode 6. The porous source electrode 4 is a metal electrode that is electrically grounded. The porous source electrode is not a continuous conductive layer; to achieve charge coupling induction, pores are formed on its surface. The size and density of these pores are determined by the metal material properties of the porous source electrode 4 and the material properties of the semiconductor channel 5. The semiconductor channel 5 forms a carrier channel. Since it does not require X-ray photoelectric conversion, there are no special requirements for the atomic number and mass density of the semiconductor channel 5. However, the semiconductor channel 5 is required to have a high carrier mobility to meet the needs of fast switching. The drain electrode 6 is a common metal electrode, such as... Figure 3a As shown.

[0044] In the absence of X-ray irradiation, a potential barrier exists between the porous source electrode 4 and the semiconductor channel 5, such as Figure 3b As shown, this potential barrier prevents electrons from being injected from the porous source electrode 4 into the semiconductor channel 5. When X-rays are incident, electron / hole pairs are generated in the X-ray sensing layer 1. Through charge-coupled induction, induced electrons are generated near the porous source electrode 4, increasing the electron concentration. The increased electron concentration lowers the potential barrier between the porous source electrode 4 and the semiconductor channel 5, so under the influence of the electric field, some electrons can cross the barrier and be injected from the porous source electrode 4 into the semiconductor channel layer 5, forming a photocurrent I. photo ,like Figure 3c As shown.

[0045] The third part is the charge-coupled induction section. This part has the following structure: Figure 4a As shown, a gate electrode 7 is positioned at the bottom, above which is the X-ray sensing element, and on top of that, a dielectric layer 8 is placed. Above the dielectric layer 8 is a porous source electrode 4. The dielectric layer 8 has a high resistivity and a large dielectric constant. When X-rays are incident on the sensing layer, photogenerated electrons drift downwards under the influence of the electric field and are received by the gate electrode 7. Photogenerated holes drift upwards, and due to the obstruction of the dielectric layer 8, the holes accumulate on the lower surface of the dielectric layer 8. These accumulated holes induce an equal number of electrons on the upper surface of the dielectric layer 8, such as... Figure 4b As shown. The electrons induced near the porous source electrode 4 are... Figure 3c Sources of increased electron concentration in the middle.

[0046] Combining the above three parts, this utility model proposes a high-sensitivity, low-noise X-ray vertical channel field-effect phototransistor detector, such as... Figure 5 As shown. A gate electrode 7 is disposed on the bottom surface of the X-ray sensing section, and a passivation layer 9 is disposed on the gate electrode 7; a dielectric layer 8 is disposed on the top surface of the X-ray sensing section; a current modulation section is disposed on the dielectric layer 8. The porous source electrode 4 is grounded, and a bias voltage V is applied between the porous source electrode 4 and the gate electrode 7. gs A bias voltage V is applied between the porous source electrode 4 and the drain electrode 6. ds .

[0047] The fabrication process of the aforementioned X-ray vertical channel field-effect transistor detector is as follows:

[0048] 1. Preparation of semiconductor materials. It is a semiconductor crystal with high carrier mobility, high average atomic number, and high mass density. A typical semiconductor material is perovskite MAPbBr3 crystal, which can be grown in solution using a temperature-inverse method. Temperature-inverse epitaxial growth of perovskite crystals: Methylamine aqueous solution and hydrobromic acid aqueous solution are mixed in a molar ratio of 1:1.2 in a water bath at 0℃. After the reaction is complete, the mixture is allowed to stand for 10 minutes. The resulting solution is then evaporated to dryness on a rotary evaporator, and the precipitated white powder is collected. The white powder is washed successively with ether and ethanol, and then evaporated again on a rotary evaporator to obtain CH3NH3Br powder. The CH3NH3Br powder is dissolved in DMF at a concentration of 1 mol / L, stirred with a glass rod, and sonicated until completely dissolved. PbBr2 is weighed in a 1:1 molar ratio and slowly poured into the DMF solution. The solution is then stirred and sonicated until completely dissolved, yielding a clear and transparent solution. The crystal is grown using a water bath method with a relatively low initial temperature. The first stage of heating was performed at 20℃ with a heating rate of 0.5℃ / min. When the solution reached 60℃, the temperature was kept constant until single crystal nuclei began to appear in the solution, and then growth was allowed to continue for 30 minutes. The heating power was increased for the second stage of heating with a heating rate of 0.2℃ / min. When the solution reached 65℃, the temperature was kept constant for 30 minutes. The heating power was increased again for the third stage of heating with a heating rate of 0.2℃ / min. When the solution reached 70℃, the temperature was kept constant for 30 minutes. The heating power was increased again for the fourth stage of heating with a heating rate of 0.1℃ / min. When the solution reached 80℃, the temperature was kept constant until the MAPbBr3 crystal size reached the design requirements.

[0049] 2. Fabrication of an X-ray semiconductor junction layer. The semiconductor junction layer exhibits p-type or n-type semiconductor properties. A typical fabrication method involves doping the MAPbBr3 crystal prepared in step 1 with metal ions, such as Ag. + Obtain a p-type layer by doping with Bi. 3+ Obtain an n-type layer;

[0050] 3. A continuous metal film is deposited on the bottom surface of the X-ray sensing section by vacuum evaporation or sputtering to form a gate electrode;

[0051] 4. A stable oxide or nitride layer, such as SiO2 and SiN, is sputter-deposited on the gate electrode. x The layer serves as a passivation layer;

[0052] 5. A dielectric layer is prepared on the top surface of the X-ray sensing part by spin coating or sputtering. The dielectric layer needs to have high resistivity and dielectric constant. A typical dielectric layer is HfO2 dielectric layer.

[0053] 6. A patterned metal layer is deposited on the dielectric layer by sputtering through a mask to serve as a porous source electrode;

[0054] 7. A semiconductor channel is deposited on a porous source electrode using a spin-coating method. The semiconductor channel layer has a high carrier mobility and exhibits n-type semiconductor characteristics. A typical semiconductor channel layer is a ZnO layer.

[0055] 8. A metal layer is deposited on the semiconductor channel layer using vacuum evaporation or sputtering methods, and it is used as the drain electrode.

[0056] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. An X-ray vertical channel field-effect transistor detector, characterized in that: It includes an X-ray sensing section, a current modulation section, and a charge-coupled sensing section; The X-ray sensing part is composed of semiconductor materials and corresponding semiconductor structures for X-ray absorption. It absorbs high-energy X-rays and generates electron / hole pairs. The current modulation section consists of a porous source electrode, a semiconductor channel, and a drain electrode. The semiconductor channel is disposed between the porous source electrode and the drain electrode, and photocurrent is obtained through the semiconductor channel. The charge-coupled sensing part consists of a gate electrode, a dielectric layer and a porous source electrode. The gate electrode is disposed below the X-ray sensing part and a passivation layer is disposed on the gate electrode. The dielectric layer is disposed above the X-ray sensing part and a porous source electrode is disposed above the dielectric layer.

2. The X-ray vertical channel field-effect transistor detector according to claim 1, characterized in that: The atomic number of the X-ray absorbing semiconductor material is ≥30, and the mass density is ≥3g / cm³. 3 .

3. The X-ray vertical channel field-effect transistor detector according to claim 2, characterized in that: The semiconductor junction sensing structure in the X-ray sensing part is as follows: a p-type top semiconductor junction layer and an n-type bottom semiconductor junction layer are prepared on a semiconductor material to form a pin junction, or the top semiconductor junction layer and the bottom semiconductor junction layer are simultaneously set to p-type or n-type to form a pip or nin junction.

4. The X-ray vertical channel field-effect transistor detector according to claim 3, characterized in that: The porous source electrode is a metal electrode that is electrically grounded, and the surface of the porous source electrode has holes. The drain electrode is a metal electrode.

5. An X-ray vertical channel field-effect transistor detector according to claim 4, characterized in that: The dielectric layer has high insulation and high dielectric constant.

6. The X-ray vertical channel field-effect transistor detector according to claim 5, characterized in that: The dielectric layer is an HfO2 dielectric layer.

7. An X-ray vertical channel field-effect transistor detector according to claim 6, characterized in that: The passivation layer is SiO2 or SiN. x layer.

8. An X-ray vertical channel field-effect transistor detector according to claim 7, characterized in that: The semiconductor channel is a ZnO layer.

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