Efficient infrared imaging system with simple structure

Abstract

The utility model discloses a high-efficiency infrared imaging system with a simple structure. The high-efficiency infrared imaging system comprises an infrared detection part for converting incident infrared photons into photo-generated charges; the gain modulation part is used for modulating the Schottky barrier by utilizing space charge accumulation so as to regulate and control the emission current; an electron / hole composite visible light emission part and a silicon-based visible light detection part are utilized. The infrared imaging system is simple in structure and low in cost; by adopting the ITO transparent conductive particles, the specific surface area embedded into the electron transfer layer is increased, the injection current of the ITO transparent conductive particles is increased, and the gain of an up-conversion system is increased; the transparent grid electrode, the dielectric layer, the mesh source electrode, the electron transport layer and the reflective top electrode are adopted to emit all the generated visible light from the bottom, so that the light emitting efficiency of the visible light is improved; and an infrared thermoelectric sensing layer can also be adopted, so that the device can be used for medium and long wave infrared detection imaging at room temperature.

Description

Technical Field

[0001] The utility model relates to the field of optoelectronic imaging, especially infrared imaging technology. Background Art

[0002] Infrared imaging refers to the process in which a detector converts the infrared ray signal (with a wavelength between 900nm and 100um) radiated by a target object into an electrical signal. According to the infrared radiation theory, any target object with a certain temperature can radiate infrared rays. The radiation spectral distribution of an ideal black body at different temperatures is as Figure 1 shown. It can be seen from the figure that when the object temperature is relatively low, such as 300K, the infrared radiation energy is mainly concentrated in the short-wave infrared and mid-wave infrared. Since infrared imaging can help people detect heat-emitting objects in a dark environment, it has important applications in the fields of security detection, national defense, medical imaging, etc.

[0003] According to different detection principles, infrared detection can generally be divided into two categories: photoelectric detection and pyroelectric detection. The so-called infrared photoelectric detection means that a narrow-band semiconductor material is used to absorb the incident infrared photons, and through the photoelectric effect, photo-generated electrons / holes are generated, and then the electrons and holes are separated by an electric field to form a detection current. Figure 2 is a typical infrared photoelectric detector structure, including a transparent top substrate 1, an infrared sensing pn junction 2, a passivation layer 3, flip-chip solder indium pillars 4, an insulating layer 5, a unit silicon readout circuit 6, an infrared sensing array 7, a silicon array readout circuit 8, and a pixel readout circuit 9. The infrared photoelectric sensing principle is exactly the same as that of visible light photoelectric detection. However, since the energy of infrared photons is relatively low (<1.5eV), narrow-bandgap semiconductor materials are required to absorb infrared photons. However, the lattice structure of narrow-bandgap semiconductor materials does not match that of silicon. Therefore, an infrared detector needs to epitaxially grow an infrared sensing layer (such as a mercury cadmium telluride layer) lattice-matched on an infrared transparent substrate (such as a cadmium zinc telluride substrate) to form an infrared sensing array. Then, the infrared sensing array is coupled with the silicon CMOS readout circuit through processes such as flip-chip soldering. This structural feature makes the manufacturing process relatively complex. Not only is the detector cost expensive, but it also restricts the imaging resolution. In addition, because narrow-band semiconductor materials are used, the influence of thermal noise on the detector is relatively serious. Most high-performance infrared photoelectric detectors need to work under refrigeration conditions.

[0004] In order to achieve uncooled infrared imaging, the working mode of infrared pyroelectric detection has been proposed. It uses the pyroelectric effect to convert the absorbed infrared photons into a resistance change or differential voltage change of the semiconductor material, and finally obtains a detection electrical signal. Since the pyroelectric detector does not need to use the photoelectric effect, this detector does not require narrow-band semiconductors and does not necessarily need to work under refrigeration. However, due to some physical restrictions of the pyroelectric effect itself, the response speed of infrared pyroelectric detectors is generally relatively slow, and the imaging spatial resolution is also relatively low.Figure 3a and Figure 3b is a comparison between an infrared pyroelectric image and an infrared optoelectronic image.

[0005] In order to further improve the imaging quality of infrared images, people are constantly exploring new infrared imaging methods. For example, Patent CN 108831905 A discloses an infrared detection-visible light display integrated system based on semiconductor quantum dots. Its essence is to connect a quantum dot infrared detector and a quantum dot light-emitting diode through a vertical trench field-effect transistor, thereby converting incident infrared photons into visible photons and obtaining a certain detection signal gain through the field-effect transistor.

[0006] In Figure 4 In the detection structure shown, it is proposed to use two-dimensional materials such as graphene to form a grid source electrode, so that the electric field formed in the infrared detector part can penetrate into the visible light emission region and modulate the emission intensity of visible light. Since this grid-like source electrode needs to simultaneously consider the functions of electric field penetration and current emission modulation, the source-drain current emission ability obtained by using graphene or metal nanowires to construct the grid electrode is relatively low, and the amplification gain of the input infrared signal is generally less than 10, far from meeting the actual application requirements.

[0007] In summary, although infrared optoelectronic imaging has high image quality, it often requires a refrigerated working condition, and the preparation process is complex and the cost is high. The infrared pyroelectric imaging structure is relatively simple and can work at room temperature, but the imaging response speed and spatial resolution are not as good as those of infrared optoelectronic images. The detection method of infrared-visible light upconversion has a relatively simple structure, but the infrared signal gain is small and cannot meet the actual application requirements. Summary of the Invention

[0008] The present utility model aims at the problems existing in the existing infrared imaging system and proposes a simple-structured and high-efficiency infrared imaging system. Its core content is to convert the input infrared signal into a visible light signal with a higher power density through a high-gain upconversion structure, and then use a conventional silicon image sensor or a charge-coupled image sensor to detect the visible light signal.

[0009] The technical solution adopted by the present utility model is: a simple-structured and high-efficiency infrared imaging system, comprising:

[0010] An infrared detection part that converts incident infrared photons into photo-generated charges;

[0011] A gain modulation part that modulates the emission current by using space charge accumulation to modulate the Schottky barrier;

[0012] A visible light emission part;

[0013] And a silicon-based visible light detector;

[0014] The infrared detection part includes a transparent bottom substrate, a transparent bottom electrode, an infrared sensing layer, a dielectric layer, and a porous source electrode; the transparent bottom electrode is disposed on the transparent bottom substrate, the infrared sensing layer and the dielectric layer are disposed on the transparent bottom electrode, and the porous source electrode is disposed on the dielectric layer; when incident infrared rays are incident on the infrared sensing layer from bottom to top, the electrical characteristics are changed through the photoelectric effect or the pyroelectric effect, so that charges are accumulated at the lower end area of the dielectric layer, and opposite charges are induced at the upper end surface of the dielectric layer by induction.

[0015] The gain modulation part includes a porous source electrode and an electron transport layer. The porous source electrode is composed of transparent conductive nanoparticles, and a Schottky junction is formed between it and the electron transport layer; when the amount of charge induced on the dielectric layer is regulated, the barrier height and width of the Schottky junction can be changed, and further the current injected from the porous source electrode into the electron transport layer can be regulated, and the gain modulation of the emission current is realized by using the electric field induction effect.

[0016] The visible light emission part includes a visible light emitting layer, a hole transport layer, a hole injection layer, and a top electrode. Its working mechanism is similar to that of a quantum dot light emitting diode or an organic light emitting diode. The electrons injected by the porous source electrode reach the visible light emitting layer through the electron transport layer, and the top electrode injects holes, which also reach the visible light emitting layer through the hole injection layer and the hole transport layer. Electrons and holes recombine in the visible light emitting layer. The band gap of the visible light emitting layer is between 1.6 and 3.1 eV, and the electron / hole recombination will emit visible light. The top electrode is set as a reflective electrode, and the upward transmitted radiation light is reflected when it encounters the top electrode and exits from the transparent bottom electrode.

[0017] Further, the silicon-based visible light detector is a conventional silicon-based CMOS image sensor (CIS) or a charge coupled sensor (CCD), and it responds to visible light.

[0018] Further, the porous source electrode is composed of transparent conductive nanoparticles, and its particle size should be less than 20 μm to increase the specific surface area of the porous source electrode / electron transport layer.

[0019] Further, the material of the infrared sensing layer can adopt a photoelectric sensing material (such as narrow bandgap semiconductor quantum dots, etc.), or a pyroelectric material (such as bismuth telluride, etc.).

[0020] Further, the transparent bottom electrode adopts an ITO electrode, the infrared sensing layer adopts PbS quantum dots, the dielectric layer adopts HfO 2 , the porous source electrode adopts ITO nanoparticles, the electron transport layer adopts a ZnO thin film, the visible light emitting layer adopts CdSe / ZnS core-shell structure quantum dots, the hole transport layer adopts PVK, the hole injection layer adopts TFB, and the top electrode adopts an Au thin film.

[0021] Compared with the infrared / visible light up-conversion structure based on vertical-channel transistors proposed in the reference CN 108831905 A, the innovation points of the present utility model are as follows: a single-sided emission structure is proposed, that is, the input infrared light is incident from the bottom, and the output visible light is also emitted from the bottom. This structure can improve the light extraction efficiency; transparent conductive nanoparticles are used as the source electrode, which not only meets the requirement of bottom light emission, but also increases the specific surface area of the Schottky junction of the source electrode, enhancing the current injection ability; it is proposed to compound the infrared sensing layer and the gate insulating layer, and the visible light brightness is modulated by using the space charge accumulation effect, improving the modulation sensitivity.

[0022] The beneficial effects of the present utility model are as follows:

[0023] (1). An efficient infrared imaging system with a simple structure according to the present utility model obtains a high-gain amplified infrared / visible light image conversion through simple vertical-channel transistors, and then uses a mature silicon-based detector to detect the visible light pattern. Compared with conventional infrared imaging devices, it has a simple structure and low cost.

[0024] (2). An efficient infrared imaging system with a simple structure according to the present utility model improves the specific surface area embedded with the electron transport layer by using ITO transparent conductive particles, increases the injection current of the ITO transparent conductive particles, and increases the gain of the up-conversion system.

[0025] (3). An efficient infrared imaging system with a simple structure according to the present utility model emits all the generated visible light from the bottom through the adoption of a transparent gate, a dielectric layer, a mesh source electrode, an electron transport layer, and a reflective top electrode, improving the light extraction efficiency of the visible light.

[0026] (4). An efficient infrared imaging system with a simple structure according to the present utility model can also adopt an infrared thermoelectric sensing layer in addition to the infrared photoelectric sensing layer, so it can also be used for medium- and long-wave infrared detection imaging at room temperature. Description of the Drawings

[0027] Figure 1 is the radiation spectral distribution of blackbody;

[0028] Figure 2 is a typical infrared photoelectric detection structure;

[0029] Figure 3a is a typical infrared image (infrared thermoelectric image);

[0030] Figure 3b is a typical infrared image (infrared photoelectric image);

[0031] Figure 4It is an infrared detection-visible light display integrated system based on semiconductor quantum dots;

[0032] Figure 5a It is an infrared imaging system based on high-gain upconversion (infrared imaging system structure);

[0033] Figure 5b It is an infrared imaging system based on high-gain upconversion (a typical energy band structure);

[0034] Figure 6a It uses ITO nanoparticles as a porous source electrode (ITO nanoparticles and ZnO electron transport layer);

[0035] Figure 6b It uses ITO nanoparticles as a porous source electrode (specific surface area corresponding to nanoparticles of different particle sizes);

[0036] Figure 7a It is the electrical characteristics of the infrared imaging system (transfer characteristic curve);

[0037] Figure 7b It is the electrical characteristics of the infrared imaging system (output characteristic curve);

[0038] Figure 8a It is the visible light emission obtained by using the infrared imaging system of the present utility model (visible light emission photo);

[0039] Figure 8b It is the visible light emission obtained by using the infrared imaging system of the present utility model (uniformity distribution of light spots);

[0040] In the figure: 1. Transparent top substrate; 2. Infrared sensing pn junction; 3. Passivation layer; 4. Flip-chip solder indium pillar; 5. Insulating layer; 6. Unit silicon readout circuit; 7. Infrared sensing array; 8. Silicon array readout circuit; 9. Pixel readout circuit; 10. Incident infrared rays; 11. Emitted visible light; 12. Transparent bottom substrate; 13. Transparent bottom electrode; 14. Infrared sensing layer; 15. Dielectric layer; 16. Porous source electrode; 17. Electron transport layer; 18. Visible light emitting layer; 19. Hole transport layer; 20. Hole injection layer; 21. Top electrode; 22. Silicon-based visible light detector; 23. ITO nanoparticles. Detailed implementation mode

[0041] The present utility model will be described in detail below. This embodiment is implemented on the premise of the technical solution of the present utility model, and the detailed implementation mode and specific operation process are given, but the protection scope of the present utility model is not limited to the following embodiments.

[0042] As Figure 5a shown, a simple and efficient infrared imaging system includes:

[0043] An infrared detection part that converts incident infrared photons into photo-generated charges;

[0044] A gain modulation part that uses space charge accumulation to modulate the Schottky barrier and then regulates the emission current;

[0045] A visible light emission part;

[0046] And a silicon-based visible light detector 22;

[0047] The infrared detection part includes a transparent bottom substrate 12, a transparent bottom electrode 13, an infrared sensing layer 14, a dielectric layer 15, and a porous source electrode 16; the transparent bottom electrode 13 is disposed on the transparent bottom substrate 12, the infrared sensing layer 14 and the dielectric layer 15 are disposed on the transparent bottom electrode 13, and the porous source electrode 16 is disposed on the dielectric layer 15; when the incident infrared ray 10 is incident on the infrared sensing layer 14 from bottom to top, the electrical characteristics change through the photovoltaic effect or the pyroelectric effect, so that charges accumulate at the lower end area of the dielectric layer 15, and opposite charges are induced on the upper end surface of the dielectric layer 15 by induction.

[0048] The gain modulation part includes a porous source electrode 16 and an electron transport layer 17. The porous source electrode 16 is composed of transparent conductive nanoparticles, and a Schottky junction is formed between it and the electron transport layer 17; when the amount of charge induced on the dielectric layer 15 is regulated, the barrier height and width of the Schottky junction can be changed, and then the current injected from the porous source electrode 16 into the electron transport layer 17 can be regulated, and the gain modulation of the emission current is realized by using the electric field induction effect.

[0049] The visible light emission part includes a visible light emitting layer 18, a hole transport layer 19, a hole injection layer 20, and a top electrode 21. Its working mechanism is similar to that of a quantum dot light emitting diode or an organic light emitting diode. The electrons injected from the porous source electrode 16 reach the visible light emitting layer 18 through the electron transport layer 17, and holes are injected from the top electrode 21 and also reach the visible light emitting layer 18 through the hole injection layer 20 and the hole transport layer 21. Electrons and holes recombine in the visible light emitting layer 18. Since the band gap of the visible light emitting layer 18 is between 1.6 and 3.1 eV, this electron / hole recombination will radiate out the emitted visible light 11. The top electrode 21 is set as a reflective electrode, such as Au, Ag, etc., so the upwardly transmitted radiation light is reflected by the top electrode and exits from the bottom electrode.

[0050] The silicon-based visible light detector 22 is a conventional silicon-based CMOS image sensor (CIS) or charge coupled sensor (CCD), and it responds to visible light.

[0051] The described simple-structured and high-efficiency infrared imaging system, its typical structure and energy band distribution are asFigure 5b As shown. It uses an ITO electrode as the transparent bottom electrode, PbS quantum dots as the infrared sensing layer, and HfO 2 as the dielectric layer. HfO 2 has good light transmittance for both visible light and infrared light, which can meet the requirement of single-sided emission proposed by the present utility model; since HfO 2 has a very wide bandgap, the photo-generated holes generated after PbS quantum dots absorb infrared photons will accumulate at the end face of HfO 2 close to the incident end face, and negative charges will be induced at the other end face; ITO nanoparticles are used as the porous source electrode, ZnO thin film as the electron transport layer, CdSe / ZnS core-shell structure quantum dots as the visible light emission layer, PVK as the hole transport layer, TFB as the hole injection layer, and Au thin film as the top electrode; due to having Figure 5b the energy band structure as shown, the electrons injected from the ITO nanoparticles and the holes injected from the Au electrode can be smoothly transported to the CdSe / ZnS quantum dot layer and recombine here to emit visible light; since there is a large specific surface area between the ITO nanoparticles and ZnO, the incident infrared rays have a sensitive regulation on the injection current of the ITO nanoparticles; since both the ITO nanoparticles and the ZnO electron transport layer are transparent to visible light, it meets the requirement of single-sided emission proposed by the present utility model; since the Au electrode has good reflection for the outwardly radiated visible light, it enhances the ability to emit light from one end of the transparent substrate.

[0052] The present utility model first deposits a whole transparent bottom electrode 13 (such as an ITO thin film) on a transparent bottom substrate 12 (such as glass) that is transparent to both infrared and visible light by sputtering or evaporation deposition. An infrared sensing layer 14 is deposited on the transparent bottom electrode by spin coating or printing. The sensing layer can be an infrared photoelectric sensing layer (such as a PbS quantum dot layer) or an infrared thermoelectric sensing layer (such as a bismuth telluride layer); a dielectric layer 15 (such as an HfO 2 layer) that is transparent to visible light is deposited on the infrared sensing layer by spin coating or evaporation coating. Transparent conductive nanoparticles (such as ITO nanoparticles) are spin-coated on the transparent dielectric layer and used as the porous source electrode 16; alternatively, the infrared sensing material (such as PbS quantum dots) can be mixed with HfO 2 nanoparticles and then directly spin-coated on the transparent bottom electrode to replace Figure 5aTwo components, an infrared sensing layer 14 and a dielectric layer 15; on the porous source electrode 16, a granular n-type semiconductor material layer (such as ZnO nanoparticles) that is transparent to visible light is deposited by spin coating or printing as the electron transport layer 17. The transparent conductive particles are completely embedded in the n-type semiconductor layer and form a Schottky junction; a visible light emitting layer 18 (such as a CdSe / ZnS quantum dot layer) is spin coated and deposited on the electron transport layer 17; a p-type hole transport layer 19 (such as TFB) and a hole injection layer 20 (such as PVK) are spin coated and deposited thereon, and a top electrode 21 is then evaporated thereon. The top electrode layer has good smoothness and reflects the visible light radiating upward, so that all visible light exits from the transparent bottom substrate 12, enhancing the light extraction efficiency of the visible light.

[0053] To illustrate that using ITO transparent conductive particles to construct a porous source electrode can improve the regulation sensitivity of incident infrared rays, Figure 6a and 6b shows the structure and specific surface area change of the nanoparticles and the surrounding thin film. It can be seen from Figure 6a that ITO nanoparticles 23 are deposited on the HfO 2 dielectric layer 15, and a ZnO electron transport layer 17 is deposited on the ITO nanoparticles 23. As a result, the ITO nanoparticles are completely embedded in the ZnO layer. There is a Schottky barrier between the ITO nanoparticles and the ZnO layer. By regulating the width and height of the Schottky barrier through incident infrared rays, the injection current of the porous source electrode can be changed. Assume that the mass density of the ZnO layer is 3.5 g / cm 3 , Figure 6b shows the change in the specific surface area of the Schottky junction under different nanoparticle diameters. It can be seen from the figure that when the diameter of the nanoparticles is less than 12 μm, the specific surface area increases rapidly. The increase in the effective area of the Schottky junction helps to draw more current from the porous source electrode and can improve the gain of the vertical channel transistor.

[0054] Figure 7a and 7b are the typical transfer characteristic curve and output characteristic curve obtained by the infrared imaging system shown in Figure 5b . It can be seen from the curve that by changing the gate voltage, the change in the source-drain current density can reach ~A / cm 2 . Such a sensitive current modulation can generate visible light emission with a very high brightness, as shown in Figure 8a and 8b , where the luminous intensity of the visible light can reach ~10 3 Cd / m 2 .

[0055] It should be understood that those of ordinary skill in the art can make improvements or transformations based on the above description, and all such improvements and transformations shall fall within the protection scope of the appended claims of this utility model.

Claims

1. A simple and efficient infrared imaging system, characterized by: include: The infrared detection part converts incident infrared photons into photogenerated charges; The gain modulation part uses space charge accumulation to modulate the Schottky barrier and thus regulate the emission current; Visible light emitting part; and silicon-based visible light detectors; The infrared detection part comprises a transparent bottom substrate, a transparent bottom electrode, an infrared sensing layer, a dielectric layer and a porous source electrode; the transparent bottom substrate is provided with a transparent bottom electrode, the infrared sensing layer and the dielectric layer are provided on the transparent bottom electrode, and the porous source electrode is provided on the dielectric layer; The gain modulation part includes a porous source electrode and an electron transport layer, wherein the porous source electrode is composed of transparent conductive nanoparticles and a Schottky junction is formed between the porous source electrode and the electron transport layer; The visible light emitting part includes a visible light emitting layer, a hole transport layer, a hole injection layer and a top electrode. The electrons injected by the porous source electrode reach the visible light emitting layer through the electron transport layer. The holes injected by the top electrode also reach the visible light emitting layer through the hole injection layer and the hole transport layer. The electrons and holes recombine in the visible light emitting layer. The top electrode is configured as a reflective electrode.

2. According to claim 1, a simple and efficient infrared imaging system is characterized by: The silicon-based visible light detector is a conventional silicon-based CMOS image sensor or a charge coupled sensor.

3. The high-efficiency infrared imaging system with a simple structure according to claim 1, characterized in that: The porous source electrode is composed of transparent conductive nanoparticles, and the particle size thereof is less than 20 μm.

4. The high-efficiency infrared imaging system with a simple structure according to claim 3 is characterized by: The infrared sensing layer material is made of narrow-bandgap semiconductor quantum dots or bismuth telluride.

5. The high-efficiency infrared imaging system with a simple structure according to claim 4, characterized in that: The transparent bottom electrode adopts ITO electrode, the infrared sensing layer adopts PbS quantum dots, the dielectric layer adopts HfO2, the porous source electrode adopts ITO nanoparticles, the electron transport layer adopts ZnO film, the visible light emitting layer adopts CdSe / ZnS core-shell structure quantum dots, the hole transport layer adopts PVK, the hole injection layer adopts TFB, and the top electrode adopts Au film.

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