Porous silicon-based cathode electron source and preparation method and equipment thereof

Abstract

The present invention provides a porous silicon-based cathode electron source and a preparation method and preparation equipment thereof, and relates to the technical field of cathode electron emission sources. The preparation method of the porous silicon-based cathode electron source comprises: preparing a porous silicon layer by an anodic oxidation method; in a first electrolyte, performing a cathode reduction treatment on the porous silicon layer so that specific ions in the first electrolyte passivate the porous silicon layer, which is beneficial to the oxidation of the porous silicon layer; electrochemically oxidizing the passivated porous silicon layer so that the passivated porous silicon layer is uniformly and fully oxidized; and thermally annealing the porous silicon layer after the electrochemical oxidation treatment. The preparation method first uses cathode reduction to passivate the porous silicon layer before the electrochemical oxidation treatment, which helps the electrochemical oxidation to oxidize the porous silicon layer more completely and fully, and reduces the random scattering effect of electrons in the porous silicon layer caused by defect states during the tunneling acceleration process, thereby greatly improving the repeatability and stability of the device current and emission current.

Description

Technical Field

[0001] The invention relates to the technical field of cathode electron sources, and in particular to a porous silicon-based cathode electron source and a preparation method thereof and equipment for preparing the porous silicon-based cathode electron source. Background Art

[0002] High-power and high-frequency vacuum micro / nanoelectronic devices require efficient and stable on-chip electron sources. Compared with traditional cathode electron sources such as thermionic field emission sources, surface conduction emission sources, and nanotube emission sources, the planar porous silicon electron source is a silicon-based field emission electron source with a standard MIS structure. This electron source has attracted much attention for its solid silicon process foundation and advantages such as small electron emission angle, low operating voltage, and insensitivity to the atmosphere. In the porous silicon electron source, the porous silicon layer prepared by electrochemical anodization is its core part. The full and uniform passivation of the porous silicon layer and the nanocrystals filled inside it is the key to forming an electron acceleration tunneling channel.

[0003] However, due to the complex microscopic morphology and structural characteristics of the porous silicon layer itself and the random distribution and poor controllability of the nanocrystals inside, it is difficult to obtain uniform and sufficient passivation characteristics using traditional processes such as rapid thermal oxidation, high-pressure water vapor annealing, and surface thermal carbonization treatment. Silicon dioxide films of different thicknesses and oxidation degrees will be formed inside it. At the same time, the high-pressure and high-temperature environment involved in the above processes will also damage the surface of the porous silicon to varying degrees, causing the tunneling channel used for electron acceleration to be damaged near the surface area, thereby affecting the effective emission area of ​​the electron source, and the uniformity of the electron source's planar emission will also deteriorate. In addition, the thermal stability of the tunneling channel structure damaged by the high-temperature and high-pressure environment will also deteriorate, and the repeatability and stability of the device during operation will be greatly affected.

[0004] As a liquid-phase oxidation method, electrochemical oxidation can avoid high temperature and high pressure processes, but its unidirectional oxidation characteristics usually cause one side of the porous silicon to be over-oxidized while the other side is not oxidized, resulting in uneven oxidation of the porous silicon layer and insufficient oxidation of local nano-silicon, especially for thicker porous silicon layers. This uneven oxidation characteristic inside and outside will increase the random scattering effect caused by defect states when electrons tunnel. At the same time, insufficient oxidation of nanocrystals will reduce their interconnection performance, resulting in enhanced phonon scattering of electrons at the interface of the oxide layer on its outer surface. These factors will lead to the degradation of the field emission performance of the device, and the stability and repeatability of the device will deteriorate, making it difficult to meet the needs of future vacuum microelectronic chips for high-performance on-chip electron sources. Summary of the invention

[0005] In view of this, an embodiment of the present invention provides a porous silicon-based cathode electron source and a preparation method and preparation equipment thereof, aiming to solve the technical problem of poor stability of the porous silicon cathode electron source in the prior art.

[0006] In order to achieve the above-mentioned purpose, the first aspect of an embodiment of the present invention provides a method for preparing a porous silicon-based cathode electron source, comprising: preparing a porous silicon layer by an anodic oxidation method; performing a cathode reduction treatment on the porous silicon layer in a first electrolyte so that specific ions in the first electrolyte passivate the porous silicon layer, which is beneficial to the oxidation of the porous silicon layer; performing an electrochemical oxidation on the passivated porous silicon layer so that the passivated porous silicon layer is uniformly and fully oxidized; and performing a thermal annealing on the porous silicon layer after the electrochemical oxidation treatment.

[0007] In some embodiments, preparing the porous silicon layer by anodization includes: connecting a silicon wafer placed in a first electrolyte to an anode of an electrochemical power source, and corroding the silicon wafer to form a porous silicon layer.

[0008] In some embodiments, the specific ions include hydrogen ions; in the first electrolyte, performing cathode reduction treatment on the porous silicon layer includes: reversing the electrodes of the electrochemical power source so that the porous silicon layer is connected to the cathode of the electrochemical power source to drive the hydrogen ions to passivate the porous silicon layer.

[0009] In some embodiments, the first electrolyte includes pure hydrofluoric acid or a mixed solution of hydrofluoric acid and ethanol, wherein the proportion of hydrofluoric acid in the mixed solution is not less than 20%; the silicon wafer includes n-type silicon or p-type silicon, and the resistance of the silicon wafer does not exceed 10 6 Ω·cm; The method of etching the silicon wafer includes constant current etching method or pulse etching method, wherein the peak current of the etching is less than 200mA / cm 2 ; The current density during the cathode reduction treatment of the porous silicon layer does not exceed 100 mA / cm 2 , the time of cathode reduction treatment shall not exceed 20 min.

[0010] In some embodiments, electrochemically oxidizing the passivated porous silicon layer includes placing the passivated porous silicon layer in a second electrolyte and passing a specific current into the second electrolyte.

[0011] In some embodiments, the second electrolyte includes a sulfuric acid solution, a nitric acid solution, or a sodium hydroxide solution, and the concentration of the second electrolyte is between 0.1-5 mol / L; the specific current does not exceed 150 mA / cm 2 , the electrochemical oxidation time does not exceed 60 min.

[0012] In some embodiments, electrochemically oxidizing the passivated porous silicon layer further includes: during the electrochemical oxidation treatment of the porous silicon layer, irradiating the porous silicon layer with a light source to provide holes required for oxidation of the porous silicon layer.

[0013] In some embodiments, after thermal annealing the porous silicon layer after electrochemical oxidation treatment, the preparation method further comprises: depositing a top electrode on the surface of the porous silicon layer and depositing a bottom electrode on the back side of the silicon wafer.

[0014] A second aspect of an embodiment of the present invention provides a porous silicon-based cathode electron source, comprising a bottom electrode, a silicon substrate, a porous silicon layer and a top electrode stacked in sequence. The porous silicon-based cathode electron source is prepared by the preparation method in the above embodiment.

[0015] The third aspect of an embodiment of the present invention provides an apparatus for preparing a porous silicon-based cathode electron source, comprising: an anodizing apparatus for preparing a porous silicon layer by an anodizing method; a cathode reduction apparatus for performing a cathode reduction treatment on the porous silicon layer in a first electrolyte so that specific ions in the first electrolyte passivate the porous silicon layer, thereby facilitating the oxidation of the porous silicon layer; an electrochemical oxidation apparatus for performing an electrochemical oxidation on the passivated porous silicon layer so that the passivated porous silicon layer is uniformly and fully oxidized; and a thermal annealing apparatus for performing a thermal annealing on the porous silicon layer after the electrochemical oxidation treatment.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects:

[0017] (1) Performing cathode reduction treatment before electrochemical oxidation treatment of the porous silicon layer, that is, first using cathode reduction to effectively passivate the inner surface of the porous silicon layer, which helps electrochemical oxidation to oxidize the porous silicon layer more completely and fully, helps to improve the density of electronic defect states at the interface and inside the porous silicon layer, and can reduce the random scattering effect caused by defect states during the tunneling acceleration process of electrons injected from the silicon substrate into the porous silicon layer, thereby greatly improving the repeatability and stability of the device current and emission current;

[0018] (2) The preparation method disclosed in the present invention only involves an electrochemical process and does not require expensive equipment involved in processes such as rapid thermal oxidation and high-temperature steam annealing. The process is simple and convenient and can be carried out at room temperature, meeting the process requirements of large-scale and low-cost processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0020] Figure 1 This is a schematic diagram of electrical characteristics testing using a porous silicon-based cathode electron source according to an embodiment of the present invention;

[0021] Figure 2 is a schematic flow chart of a method for preparing a porous silicon-based cathode electron source according to an embodiment of the present invention;

[0022] Figure 3is a schematic diagram comparing the electron emission characteristics test results of two groups of samples according to an embodiment of the present invention and a control example;

[0023] Figure 4 Schematic diagram comparing the oxidation degree and chemical state of two groups of samples according to the embodiment of the present invention and the control example. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] The endpoints and any values ​​of the ranges invented in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically invented in the present invention.

[0026] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0027] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0028] Similarly, in order to simplify the present invention and help understand one or more of the various inventive aspects, in the above description of exemplary embodiments of the present invention, the various features of the present invention are sometimes grouped together into a single embodiment, figure or description thereof. The description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0029] Please refer to Figure 1 , Figure 1Schematic diagram of electrical characteristic test of porous silicon-based cathode electron source 100 according to an embodiment of the present invention. In this embodiment, porous silicon-based cathode electron source 100 comprises a bottom electrode 110, a silicon substrate 120, a porous silicon layer 121 and a top electrode 130 stacked in sequence.

[0030] like Figure 1 As shown, a DC bias voltage V may be applied between the top electrode 130 and the bottom electrode 110. ps , the electrons injected from the silicon substrate 120 into the porous silicon layer 121 are accelerated by tunneling through the oxidized interconnected silicon nanocrystals, and some electrons obtain sufficient kinetic energy to penetrate the top electrode 130 and are emitted into the vacuum. When the electrical characteristics of the porous silicon-based cathode electron source 100 are tested, the entire device can be placed in a vacuum chamber, and the vacuum degree can be about 3×10 -4 Pa, a collector 10 is arranged at a distance h (h can be 5 mm, for example) above the top electrode 130 of the device, and a positive voltage V can be applied relative to the top electrode 130 c (V c For example, it can be 200 V) to collect the emitted electrons, and the emission current density J e and device current density J d As the DC bias voltage V ps The function of is recorded, the electron emission efficiency η of the porous silicon-based cathode electron source 100 is η=J e / J d .

[0031] The study found that in the porous silicon-based cathode electron source 100, the porous silicon layer 121 and the nanocrystals filled therein have a significant effect on the electron emission performance of the electron source. Oxidation treatment of the porous silicon layer 121 can improve the electron emission performance of the device. Electrochemical oxidation is a room temperature liquid phase oxidation method. The porous silicon layer 121 can be placed in a specific electrolyte as an anode, and a certain amplitude of current or voltage is applied by an external power supply to attract oxygen-containing anions in the electrolyte to the inner surface of the porous silicon layer 121 to passivate it. Electrochemical oxidation can avoid high temperature and high pressure processes, but its unidirectional oxidation characteristics usually cause one side of the porous silicon layer 121 to be over-oxidized while the other side is not oxidized, especially for thicker porous silicon layers (>5 μm). This uneven oxidation characteristic will increase the scattering effect during electron tunneling, thereby causing the field emission performance to deteriorate.

[0032] Based on this, an embodiment of the present invention provides a method for preparing a porous silicon-based cathode electron source 100, comprising: preparing a porous silicon layer by an anodic oxidation method; performing a cathode reduction treatment on the porous silicon layer in a first electrolyte so that specific ions in the first electrolyte passivate the porous silicon layer, which is beneficial to the oxidation of the porous silicon layer; performing electrochemical oxidation on the passivated porous silicon layer so that the passivated porous silicon layer is uniformly and fully oxidized; and performing thermal annealing on the porous silicon layer after the electrochemical oxidation treatment. The preparation method performs a cathode reduction treatment before the electrochemical oxidation treatment of the porous silicon layer, that is, firstly using specific ions to effectively passivate the inner surface of the porous silicon layer, which is conducive to the electrochemical oxidation of the porous silicon layer More complete and more sufficient oxidation, improve the interface and internal electronic defect state density of the porous silicon layer, reduce the random scattering effect caused by defect states of electrons injected into the porous silicon layer by the silicon substrate during the tunneling acceleration process, thereby greatly improving the repeatability and stability of the device current and emission current.

[0033] Please refer to Figure 2 , Figure 2 FIG. 1 is a flow chart of a method for preparing a porous silicon-based cathode electron source 100 according to an embodiment of the present invention. It should be noted that the method disclosed in the present invention is not limited to Figure 2 The complete steps shown may include only one step or multiple steps.

[0034] like Figure 1 and Figure 2 As shown, the method for preparing the porous silicon-based cathode electron source 100 may include steps S210 to S240.

[0035] In step S210, the porous silicon layer 121 is prepared by anodization.

[0036] Specifically, the silicon wafer prepared in advance can be placed in the first electrolyte, and then the silicon wafer is connected to the anode of the electrochemical power source, and the silicon wafer is corroded by the first electrolyte to obtain the porous silicon layer 121. In some embodiments, the silicon wafer can be n-type silicon or p-type silicon; the resistance of the silicon wafer can be less than 10 6 Ω·cm. The first electrolyte can be hydrofluoric acid (HF) or a mixed solution of hydrofluoric acid and ethanol, wherein the proportion of hydrofluoric acid in the mixed solution is not less than 20%. A constant current corrosion method or a pulse corrosion method can be used for anodization. For example, in order to achieve a multi-layer porous silicon structure, the anodization current can adopt a periodic pulse corrosion waveform, and the corrosion current and the number of pulses can be adjusted according to specific needs. Generally speaking, the peak current during anodization is not higher than 200 mA / cm 2 . Then, execute step S220.

[0037] In step S220, the porous silicon layer is subjected to cathode reduction treatment in a first electrolyte so that specific ions in the first electrolyte can passivate the porous silicon layer, thereby facilitating oxidation of the porous silicon layer.

[0038] Specifically, the electrode of the electrochemical power source in step S210 can be reversed, that is, the porous silicon layer 121 is connected to the cathode of the electrochemical power source, and the cathode reduction treatment is continued in the first electrolyte. In other words, step S220 and step S210 can be carried out in the same electrolyte in the same electrolytic cell, without changing the electrolytic cell, the electrolyte, or the electrochemical power source. Only the connection method of the electrodes needs to be adjusted, and the anodic oxidation and cathode reduction can be carried out in sequence. In this way, the time and cost of replacing the electrolyte and the electrochemical power source can be reduced, and the preparation efficiency can be improved. Of course, in some embodiments, according to the actual preparation of the porous silicon-based cathode electron source, an electrochemical power source can also be set up separately in the cathode reduction to provide different currents.

[0039] In some embodiments, the specific ion may be a hydrogen ion (H + ), H + During the cathode reduction treatment, the porous silicon layer 121 is located at the cathode of the electrolyte, which can drive the H + To passivate the inner surface of the porous silicon layer 121, to assist the subsequent electrochemical oxidation to achieve a more uniform oxidation effect, thereby solving the problem that the uneven oxidation characteristics increase the scattering effect of electron tunneling, resulting in the degradation of field emission performance. + The specific content of the passivation porous silicon layer 121 will be further described in conjunction with embodiments below.

[0040] In some embodiments, the current density during the cathode reduction treatment of the porous silicon layer does not exceed 100 mA / cm 2 , the cathode reduction treatment time does not exceed 20 min. The specific current waveform can be adjusted as needed. It can be understood that excessive current density and excessive cathode reduction time will affect the passivation effect of specific ions on the porous silicon layer 121, thereby affecting the subsequent electrochemical oxidation treatment effect. Then, step S230 can be performed.

[0041] In step S230, the passivated porous silicon layer 121 is electrochemically oxidized to make the passivated porous silicon layer uniformly and fully oxidized.

[0042] In some embodiments, after replacing the first electrolyte in the electrolytic cell of step S220 with a second electrolyte, the passivated porous silicon layer 121 is placed in the second electrolyte, and then a specific current is passed into the second electrolyte to uniformly and fully oxidize the porous silicon layer 121. That is to say, step S230 and step S220 can be performed in the same electrolytic cell to reduce the number of electrolytic cells. In other embodiments, the passivated porous silicon layer 121 can also be taken out of the electrolytic cell containing the first electrolyte and placed in a separately arranged electrolytic cell containing the second electrolyte for treatment to save time in replacing the electrolyte. The second electrolyte is usually different from the first electrolyte. The second electrolyte can be a sulfuric acid solution, a nitric acid solution or a sodium hydroxide solution, etc., and the solution concentration of the second electrolyte is between 0.1-5 mol / L. The electrochemical oxidation current does not exceed 150 mA / cm 2 , the electrochemical oxidation time is less than 60 min.

[0043] In some embodiments, during the electrochemical oxidation process, a light source can be used to irradiate the sample to provide holes required for the oxidation reaction, thereby increasing the oxidation rate. For example, a tungsten lamp can be used as a light source, with a power not exceeding 1000 W and a distance from the silicon wafer of less than 50 cm. It is understood that the concentration of the second electrolyte, the electrochemical oxidation current and time, the light intensity of the light source and the distance from the sample are appropriately selected by those skilled in the art based on the specific information of the silicon wafer used and the ultimate purpose. Next, step S240 can be performed.

[0044] In step S240 , the porous silicon layer 121 after the electrochemical oxidation treatment is thermally annealed.

[0045] Specifically, the porous silicon layer 121 can be placed in a furnace chamber, and the porous silicon layer 121 can be annealed at a preset temperature and a preset environment and then cooled naturally. In this way, the electrolyte remaining in the pores of the porous silicon layer 121 can be removed, and the quality of the silicon dioxide layer obtained by electrochemical oxidation can be further improved. In some embodiments, the preset temperature (i.e., the annealing temperature) can be selected from 500-1000 ° C; the annealing time does not exceed 120 min. The preset environment may include annealing the porous silicon layer 121 in an inert gas or vacuum environment. The inert gas may be nitrogen or argon. In other words, annealing can be performed under vacuum or in an inert gas atmosphere such as nitrogen or argon.

[0046] Please continue reading Figure 1 and Figure 2In some embodiments, the preparation method of the embodiment of the present invention may further include the preparation process of the top electrode 130 and the bottom electrode 110, that is, depositing the top electrode 130 on the surface of the porous silicon layer 121 and depositing the bottom electrode 110 on the back side of the silicon wafer. The back side of the silicon wafer is also the back side of the silicon substrate 120.

[0047] Specifically, the bottom electrode 110 can be a conventional single-layer metal electrode, such as copper, silver, gold, etc., or a composite metal electrode, such as a nickel / copper / nickel electrode. Considering that a lower metal work function is favorable for electron emission, and it is also required to have good physical adhesion with the porous silicon layer 121, the top electrode 130 used can usually be a gold electrode, and the thickness of the gold electrode is between 5-50 nm. The electrodes 110 and 130 can be prepared by methods such as magnetron sputtering, vacuum evaporation or electron beam evaporation, and the present invention does not make specific limitations. It should be emphasized that when a highly doped silicon substrate 120 is used, the highly doped silicon substrate 120 can also be directly used as the bottom electrode 110 without the need to prepare the bottom electrode 110 separately.

[0048] For ease of understanding, the preparation method of the silicon-based electron source of the present invention will be described below in conjunction with a specific embodiment, and a comparison group will be set to illustrate the advantages of the preparation method of the porous silicon-based cathode electron source provided by the embodiment of the present invention. The specific embodiment may include the following steps:

[0049] Step S10: Prepare porous silicon by anodizing etching. Select a heavily doped n-type silicon wafer with a resistance of <0.01 Ω·cm and place it in a solution of HF (40%) solution: ethanol (90wt%) = 1:1 for anodization. In order to obtain a periodic multilayer porous silicon layer, a periodic pulse corrosion waveform is used to perform the anodization process, where the number of cycles is 2, and the high and low current densities in the same cycle are 30 mA / cm 2 and 5 mA / cm 2 , the corresponding corrosion times are 54 s and 81 s, and the obtained porous silicon samples are divided into group A and group B.

[0050] Step S20: Perform cathode reduction treatment on the porous silicon obtained in step S10. After the anodic oxidation, Group A reverses the anode and cathode and resets the current to 15 mA / cm 2 The power-on time was 10 min. Group B was the control group and this operation was not performed.

[0051] Step S30: Perform electrochemical oxidation treatment on the porous silicon samples obtained in step S20. Replace the electrolyte in the electrolytic cell with 1 mol / L sulfuric acid, place the samples of group A and group B in the electrolytic cell, and apply a current of 30 mA / cm 2The electrochemical oxidation process of all samples in group A and group B was carried out under the illumination of a 500 W tungsten lamp to provide the holes required for the reaction, and the samples were placed at a distance of 20 cm from the tungsten lamp.

[0052] Step S40: thermally anneal the porous silicon after the electrochemical oxidation treatment in step S30. Both groups of samples were placed in a rapid thermal annealing furnace for annealing at 750°C for 60 mins, with an initial heating rate of 10°C / s to improve the quality of the silicon dioxide layer obtained by electrochemical oxidation. N2 was used as the protective gas for annealing, and the samples cooled to room temperature after annealing.

[0053] Step S50: Electrode preparation is performed on the two groups of samples after thermal annealing in step S40, and a 10 nm Au film is sputtered on one side of the porous silicon as a top electrode using a magnetron sputtering process, and a 90 nm nickel-copper-nickel composite electrode is sputtered on the back silicon substrate.

[0054] Please refer to Figure 3 and Figure 4 , Figure 3 1 is a schematic diagram comparing the test results of electron emission characteristics of two groups of samples (Group A and Group B) according to an embodiment of the present invention and a control example; Figure 4 1 is a schematic diagram comparing the oxidation degree and chemical state of two groups of samples (Group A and Group B) according to an embodiment of the present invention and a control example.

[0055] like Figure 3 As shown, the emission current density J of samples A and B is e and device current density J d Four consecutive tests were conducted, and the results showed that sample A had better repeatability and stability than sample B, especially the emission current J e , the improvement of its repeatability and stability is more significant. In other words, cathodic reduction treatment of the porous silicon layer before electrochemical oxidation can improve the repeatability and stability of the device.

[0056] In order to confirm the effect of cathode reduction treatment on porous silicon, the samples of groups A and B were characterized by Fourier transform infrared spectroscopy (FTIR), and the oxidation degree and chemical state of the porous silicon oxidation products were further analyzed by energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Figure 4 As shown. FTIR spectrum, that is Figure 4 (a) shows that the cathode-treated group A samples have a peak at 2083 cm -1 The transmittance at the Si-H xThe content of (x=1,2,3) has increased significantly, that is, the silicon dangling bonds on the inner surface are saturated with hydrogen bonds. Among them, the appearance of Si-C and OH bands originates from the ethanol in the electrolyte, indicating that some unsaturated Si bonds are also passivated by C and O. The EDS results of the porous silicon surface, namely Figure 4 (b) and (c) show that the oxygen content of the samples in group A treated by cathode reduction is higher, which means that the degree of oxidation is higher, reflecting the Si-H x The presence of accelerated the oxidation process of porous silicon. The asymmetric O 1s signal of the two samples detected by XPS near 530 eV was fitted with two peaks, representing the fully oxidized state ( ) and incompletely oxidized states ( ). The peak separation result is Figure 4 (d) and (e) show that the A group samples pretreated by cathode reduction The higher the content, that is, the higher the content of high-valent oxides in the oxidation product, the higher the content, which indicates that the porous silicon layer can undergo a more complete and sufficient oxidation effect with the assistance of cathode reduction treatment.

[0057] The above results show that cathode oxidation can compensate for the insufficient oxidation effect of single electrochemical oxidation on the porous silicon layer. In the above specific embodiment, in fact, during the cathode reduction treatment, the porous silicon layer is located at the cathode of the electrolytic cell, and the H + The electric field drives the migration to the porous silicon surface, so that a large number of unsaturated silicon dangling bonds on the inner surface of the porous silicon are effectively passivated by hydrogen bonds, especially in the top area of ​​the porous silicon in contact with the electrolyte. Due to the stress of the nanocrystalline silicon and the Si / SiO2 interface on its surface, the Si-H x The formation of a bond will weaken or destroy the Si-Si bond nearby. In the subsequent electrochemical oxidation process, the Si-Si bond will be more easily replaced by the Si-O bond, thereby promoting the complete oxidation of the porous silicon layer, and the nanocrystalline silicon inside it is also fully oxidized, and the interface defect density is effectively suppressed. In addition, the silicon dangling bonds that are not replaced by Si-O bonds are still saturated with hydrogen bonds, the electron defect state density inside the porous silicon layer and the nanocrystal will be greatly reduced, and the structural stability will also be significantly improved. Therefore, under the above-mentioned combined effect, the random scattering effect caused by the defect state of the electrons injected into the porous silicon layer by the silicon substrate during the tunneling acceleration process is curbed, and the phonon scattering effect of the interconnected nanosilicon at the interface will also be weakened, so the stability and repeatability of the device will be significantly improved, and the improvement effect is more significant for the emitted electrons with higher energy.

[0058] Above, a porous silicon-based cathode electron source and its preparation method are introduced. The preparation method of the porous silicon-based cathode electron source provided by the embodiment of the present invention has at least the following beneficial effects: cathode reduction treatment is performed before electrochemical oxidation treatment of the porous silicon layer, that is, cathode reduction is first used to effectively passivate the inner surface of the porous silicon layer, which helps electrochemical oxidation to oxidize the porous silicon layer more completely and fully, helps to improve the density of electron defect states at the interface and inside of the porous silicon layer, and can reduce the random scattering effect caused by defect states during the tunneling acceleration process of electrons injected from the silicon substrate into the porous silicon layer, thereby greatly improving the repeatability and stability of the device current and emission current; the preparation method disclosed in the present invention only involves electrochemical processes, does not require expensive equipment involved in processes such as rapid thermal oxidation and high-temperature water vapor annealing, and the process is simple and convenient, and can be carried out at room temperature, meeting the process requirements of large-area and low-cost processes.

[0059] The porous silicon-based cathode electron source 100 can be manufactured by the manufacturing method disclosed in the above embodiment, and thus has the same or similar characteristics and advantages as the above manufacturing method, and thus will not be described in detail.

[0060] In addition, an embodiment of the present invention further provides a device for preparing a porous silicon-based cathode electron source, including: an anodic oxidation device, a cathode reduction device, an electrochemical oxidation device and a thermal annealing device.

[0061] Anodizing equipment is used to prepare a porous silicon layer by anodizing. In some embodiments, the anodizing equipment can be used to perform step S210 in the above preparation method.

[0062] The cathode reduction device is used to perform cathode reduction treatment on the porous silicon layer in the first electrolyte so that the specific ions in the first electrolyte passivate the porous silicon layer and facilitate oxidation of the porous silicon layer. In some embodiments, the cathode reduction device can be used to perform step S220 in the above preparation method.

[0063] The electrochemical oxidation device is used to electrochemically oxidize the passivated porous silicon layer so that the passivated porous silicon layer is uniformly and fully oxidized. In some embodiments, the electrochemical oxidation device can be used to perform step S230 in the above preparation method.

[0064] The thermal annealing device is used to perform thermal annealing on the porous silicon layer after the electrochemical oxidation treatment. In some embodiments, the thermal annealing device can be used to perform step S240 in the above preparation method.

[0065] As an example, the equipment for preparing the porous silicon-based cathode electron source may specifically include an electrolytic cell, a first electrolyte, a second electrolyte, and an electrochemical power source, but the present invention is not limited thereto. The equipment for preparing the porous silicon-based cathode electron source has the same or similar features and advantages as the above-mentioned preparation method, so it will not be described in detail.

[0066] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a porous silicon-based cathode electron source, characterized in that: include: preparing a porous silicon layer by anodization; The method of preparing the porous silicon layer by anodization comprises: connecting a silicon wafer placed in a first electrolyte to an anode of an electrochemical power source, and corroding the silicon wafer to form the porous silicon layer; In a first electrolyte, the porous silicon layer is subjected to a cathode reduction treatment so that specific ions in the first electrolyte passivate the porous silicon layer, which is beneficial to the oxidation of the porous silicon layer; the specific ions include hydrogen ions; in the first electrolyte, the cathode reduction treatment of the porous silicon layer includes: reversing the electrode of the electrochemical power source so that the porous silicon layer is connected to the cathode of the electrochemical power source to drive the hydrogen ions to passivate the porous silicon layer; the first electrolyte includes pure hydrofluoric acid or a mixed solution of hydrofluoric acid and ethanol, wherein the proportion of hydrofluoric acid in the mixed solution is not less than 20%; the silicon wafer includes n-type silicon or p-type silicon, and the resistivity of the silicon wafer is not more than 10 6 Ω·cm; the method of etching the silicon wafer includes a constant current etching method or a pulse etching method, wherein the peak current density of the etching is less than 200 mA / cm 2 The current density of the porous silicon layer during cathode reduction treatment is no more than 100 mA / cm 2 , the cathode reduction treatment time shall not exceed 20 min; Electrochemically oxidizing the passivated porous silicon layer to make the passivated porous silicon layer uniformly and fully oxidized; The porous silicon layer after the electrochemical oxidation treatment is thermally annealed.

2. The preparation method according to claim 1, characterized in that: The electrochemical oxidation of the passivated porous silicon layer comprises: The passivated porous silicon layer is placed in a second electrolyte, and current is passed through the second electrolyte.

3. The preparation method according to claim 2, characterized in that: The second electrolyte includes a sulfuric acid solution, a nitric acid solution or a sodium hydroxide solution, and the concentration of the second electrolyte is between 0.1-5 mol / L; The density of the current does not exceed 150 mA / cm 2 , the electrochemical oxidation time does not exceed 60 min.

4. The preparation method according to claim 2, characterized in that: The electrochemical oxidation of the passivated porous silicon layer further comprises: During the electrochemical oxidation treatment of the porous silicon layer, a light source is used to irradiate the porous silicon layer to provide holes required for oxidation of the porous silicon layer.

5. The preparation method according to any one of claims 1 to 4, characterized in that: After thermally annealing the porous silicon layer after electrochemical oxidation treatment, the preparation method further comprises: A top electrode is deposited on the surface of the porous silicon layer, and a bottom electrode is deposited on the back side of the silicon wafer.

6. A porous silicon-based cathode electron source, comprising a bottom electrode, a silicon substrate, a porous silicon layer and a top electrode stacked in sequence, characterized in that: The porous silicon-based cathode electron source is prepared by the preparation method described in any one of claims 1-5.

7. A device for preparing a porous silicon-based cathode electron source, characterized in that: include: Anodizing equipment, used for preparing a porous silicon layer by anodizing method; the anodizing equipment is also used for connecting a silicon wafer placed in a first electrolyte to an anode of an electrochemical power source, and forming the porous silicon layer after etching the silicon wafer; A cathode reduction device is used to perform cathode reduction treatment on the porous silicon layer in a first electrolyte so that specific ions in the first electrolyte passivate the porous silicon layer and facilitate oxidation of the porous silicon layer; the specific ions include hydrogen ions; the cathode reduction device is also used to reverse the electrode of the electrochemical power source so that the porous silicon layer is connected to the cathode of the electrochemical power source to drive the hydrogen ions to passivate the porous silicon layer; the first electrolyte includes pure hydrofluoric acid or a mixed solution of hydrofluoric acid and ethanol, wherein the proportion of hydrofluoric acid in the mixed solution is not less than 20%; the silicon wafer includes n-type silicon or p-type silicon, and the resistivity of the silicon wafer does not exceed 10 6 Ω·cm; the method of etching the silicon wafer includes a constant current etching method or a pulse etching method, wherein the peak current density of the etching is less than 200 mA / cm 2 The current density of the porous silicon layer during cathode reduction treatment is no more than 100 mA / cm 2 , the cathode reduction treatment time shall not exceed 20 min; An electrochemical oxidation device, used for electrochemically oxidizing the passivated porous silicon layer, so that the passivated porous silicon layer is uniformly and fully oxidized; The thermal annealing equipment is used to perform thermal annealing on the porous silicon layer after the electrochemical oxidation treatment.

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