Methods for handling excess antimony during sodium-antimony co-evaporation in the fabrication of super-second generation multi-alkali photocathodes

Abstract

This invention discloses a method for handling excessive antimony during sodium-antimony co-evaporation in the fabrication of a second-generation multi-alkali photocathode. During the fabrication process, the photocurrent is monitored. If the photocurrent is below 1500 nA, it is determined that there is excessive antimony during sodium-antimony co-evaporation of the substrate layer, and the following steps are taken: The sodium evaporation power supply is turned on, and the evaporation current is adjusted to its initial value; the evaporation current is increased incrementally at a rate of 400 mA / min. When an increase or decrease in photocurrent is detected, the increase in the evaporation current is stopped, and the current evaporation current is maintained; after one minute, the antimony evaporation power supply is turned on; the antimony evaporation current is adjusted to its initial value, and the evaporation current is increased incrementally at a rate of 500 mA / min; when an increase or decrease in photocurrent is detected, the antimony evaporation power supply is turned off within 30 seconds; after one minute, the sodium evaporation power supply is turned off, and the process proceeds to the next step. This invention improves the problem of low sensitivity caused by excessive antimony in the substrate layer during the fabrication of a second-generation multi-alkali photocathode, and significantly enhances the sensitivity of the photocathode.

Description

Technical Field

[0001] This invention belongs to the field of photocathode technology, specifically relating to a method for handling excess antimony when sodium-antimony co-evaporization is used in the fabrication of a second-generation multi-alkali photocathode. Background Technology

[0002] Photocathodes are a key component of photoelectric conversion in various low-light image intensifiers, responsible for converting weak photoelectron images into electrons. Photocathode fabrication is a critical technology in image intensifier manufacturing. The sensitivity of the photocathode directly affects various performance indicators of the image intensifier, and the sensitivity after fabrication directly impacts the company's tube selection rate and the manufacturing yield of the image intensifier. As users' performance requirements for image intensifiers become increasingly demanding, improving the sensitivity of the photocathode is urgently needed. Our company's image intensifiers are facing competition from third-generation image intensifiers and CMOS solid-state devices, resulting in high manufacturing costs and declining market competitiveness. Currently, reducing the cost of our image intensifiers is our top priority.

[0003] See Figure 1 The fabrication of multi-alkali photocathodes is carried out in a vacuum environment, and the main vapor deposition components are potassium, sodium, cesium, and antimony. The vapor deposition process is as follows:

[0004] (1) Potassium vapor deposition;

[0005] (2) Sodium vapor deposition;

[0006] (3) Sodium-antimony co-evaporation deposition;

[0007] (4) Potassium, sodium and antimony co-evaporation deposition;

[0008] (5) Surface cesium activation.

[0009] The above steps are usually carried out under the automatic control of the process computer program. During the production process, the photocurrent and leakage current are detected in real time by switching the process lights on and off (the photocurrent is detected when the process lights are on and the leakage current is detected when the process lights are off). The photocurrent is usually detected throughout the entire production process. At the end of each process, the process lights are turned off and the leakage current is detected. Under normal circumstances, the leakage current is considered to be below a certain value (such as below 1000nA).

[0010] It should be noted that during the co-deposition of sodium and antimony in the substrate layer during the fabrication of the photocathode, an excess of antimony may occur when the process is automatically controlled by the computer program (according to the inventor's statistics, this accounts for about 30%). The average sensitivity of the photocathode with excessive antimony is lower than 700μA / lm, which does not meet the general specifications for tube selection of the second-generation image intensifier, leading to the scrapping of the low-light image intensifier. Therefore, it is urgent to provide a solution to this situation. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a method for addressing the issue of low sensitivity caused by excessive antimony during sodium-antimony co-deposition in the fabrication of the above-mentioned second-generation multi-alkali photocathode.

[0012] This invention effectively solves the problem of substandard photocathode sensitivity caused by excessive antimony during the fabrication of multi-alkali photocathodes by controlling the current and time of sodium and antimony vapor deposition. It effectively improves the sensitivity of the second-generation multi-photocathode and also reduces the manufacturing cost of image intensifiers.

[0013] The technical solution of this invention is as follows:

[0014] A method for handling excessive antimony during sodium-antimony co-evaporation in the fabrication of a second-generation multi-alkali photocathode involves detecting the photocurrent by irradiation with a process lamp during the photocathode fabrication process. If the photocurrent is below a certain value, it is determined that there is excessive antimony during the sodium-antimony co-evaporation of the substrate layer, and the following steps are followed for treatment:

[0015] Step 1: Turn on the sodium evaporation power supply and adjust the sodium evaporation current to the initial value;

[0016] Step 2: Increase the sodium evaporation current at a rate of 400mA / min. When an increase or decrease in photocurrent is detected, stop increasing the sodium evaporation current and maintain the current sodium evaporation current.

[0017] Step 3: Turn on the antimony evaporation power after one minute;

[0018] Step 4: Adjust the antimony evaporation current to the initial value, and increase the antimony evaporation current at a rate of 500mA / min;

[0019] Step 5: When a rise or fall in photocurrent is detected, turn off the antimony evaporation power supply within 30 seconds;

[0020] Step 6: After one minute, turn off the sodium evaporation power supply to complete the treatment of excess antimony in sodium-antimony co-evaporation and proceed to the next step of potassium-sodium-antimony co-evaporation process.

[0021] Furthermore, the term "antimony excess" refers to the detection of photocurrent value after sodium-antimony co-deposition. If the current value is lower than 1500 nA, it is determined that there is an excess of antimony during sodium-antimony co-deposition.

[0022] Furthermore, the initial value of the sodium current in step 1 is 2000-2500mA.

[0023] The mechanism of this invention is as follows:

[0024] The substrate layer of the photocathode is fabricated in a vacuum environment by co-depositing sodium and antimony to form Na3Sb. Na3Sb is a single-crystal semiconductor structure. If there is an excess of antimony, elemental antimony atoms will be deposited and cannot fully react with sodium to form Na3Sb, causing defects in the crystal structure of the photocathode, affecting the emission of photoelectrons, and resulting in low sensitivity of the photocathode after fabrication. This method can fully react the excess antimony with sodium to form Na3Sb.

[0025] The beneficial effects of this invention include:

[0026] (1) During the preparation of multi-alkali photocathodes, the phenomenon of excessive antimony during the co-deposition of sodium and antimony in the substrate layer is obvious and easy to identify.

[0027] (2) The method for treating excess antimony during sodium-antimony co-evaporation of the substrate layer of multi-alkali photocathode is simple and easy to operate, and can be widely promoted and used.

[0028] (3) The average sensitivity of the photocathode after processing by this method reaches 840μA / lm, which effectively improves the sensitivity of the photocathode, increases the selection rate, reduces the manufacturing cost of the image intensifier, and achieves cost savings. Attached Figure Description

[0029] Figure 1 A schematic diagram of the fabrication of the multi-alkali photocathode for this invention.

[0030] Figure 2 A schematic diagram of the process flow for improving the photoelectric sensitivity of the second-generation multi-alkali photoelectric sensor.

[0031] Figure 3 The image shows the imaging effect of the low-light image intensifier after processing using this method. It has a high field of view brightness gain and can meet the tube selection requirements of the general specifications for super second-generation image intensifiers.

[0032] Figure 4 The image shown is of a low-light image intensifier that was not processed using this method. The field of view brightness gain is too low and cannot meet the tube selection requirements of the general specifications for super second-generation image intensifiers.

[0033] Figure 1 In the middle: 1-Process lamp; 2-Substrate; 3-Positive electrode collecting plate; 4-Alkali source evaporation source; 5-Antimony evaporation source; 6-Antimony evaporation source heating wire; 7-Positive electrode collecting terminal; 8-Alkali source heating power cord; 9-Reaction chamber; 10-Vacuum pump pipeline; 11-Heating cover. Detailed Implementation

[0034] This invention aims to find a method for handling excess antimony during sodium-antimony co-evaporation in the fabrication of second-generation multi-alkali photocathodes, thereby improving the sensitivity and selectivity of multi-alkali photocathode fabrication. On a dedicated photocathode fabrication apparatus, the antimony evaporation time during sodium-antimony co-evaporation of the multi-alkali photocathode substrate is controlled. The control group consists of photocathodes that have undergone this treatment and are fabricated using the normal process.

[0035] As an example, the processing method of the present invention includes:

[0036] A method for handling excessive antimony during sodium-antimony co-evaporation in the fabrication of a second-generation multi-alkali photocathode involves detecting the photocurrent by irradiation with a process lamp during the photocathode fabrication process. If the photocurrent is below a certain value, it is determined that there is excessive antimony during the sodium-antimony co-evaporation of the substrate layer, and the following steps are followed for treatment:

[0037] Step 1: Turn on the sodium evaporation power supply and adjust the sodium evaporation current to the initial value;

[0038] Step 2: Increase the sodium evaporation current at a rate of 400mA / min. When an increase or decrease in photocurrent is detected, stop increasing the sodium evaporation current and maintain the current sodium evaporation current.

[0039] Step 3: Turn on the antimony evaporation power after one minute;

[0040] Step 4: Adjust the antimony evaporation current to the initial value, and increase the antimony evaporation current at a rate of 500mA / min;

[0041] Step 5: When a rise or fall in photocurrent is detected, turn off the antimony evaporation power supply within 30 seconds;

[0042] Step 6: After one minute, turn off the sodium evaporation power supply to complete the treatment of excess antimony in sodium-antimony co-evaporation and proceed to the next step of potassium-sodium-antimony co-evaporation process.

[0043] As an example, the antimony excess refers to detecting the photocurrent value after sodium-antimony co-deposition. If the current value is lower than 1500 nA, it is determined that there is an excess of antimony during sodium-antimony co-deposition. Excessive antimony leads to a decrease in photoelectron emission efficiency, directly manifested as a photocurrent value below 1500 nA.

[0044] After the photocathodes were treated using the method of this invention, the sensitivity of the two photocathodes was tested using a sensitivity testing device. The results were as follows: the average sensitivity of the treated photocathodes was 841 μA / lm, and the sensitivity test data is shown in Table 1. It can be seen from the data in Table 1 that both meet the tube selection requirements of the general specifications for Super 2 image intensifiers. On the other hand, the average sensitivity of the abnormal photocathodes that were not treated using this method was 662 μA / lm, and the sensitivity test data is shown in Table 2. It can be seen from the data in Table 2 that neither meets the tube selection requirements of the general specifications for Super 2 image intensifiers.

[0045] Table 1 shows the sensitivity and brightness gain of the photocathode processed using this method.

[0046] Pipe number Sensitivity (μA / lm) Brightness gain 5272335 855 12310 5235522 822 11550 5234422 812 12350 5269947 869 11080 5237755 853 13550 5632222 833 12100 5327772 801 11200 5324471 839 12360 5231236 856 13500 5236647 877 13580

[0047] Table 2 shows the sensitivity and brightness gain of photocathodes not processed using this method.

[0048] Pipe number Sensitivity (μA / lm) Brightness gain 4236117 655 7800 4237533 678 7900 5237715 622 7530 5326977 598 7000 5326774 700 8010 5326112 711 8100 5326344 658 7500 4236122 668 7580 4233566 632 7320 4144522 699 7950

[0049] A working voltage was applied to the low-light image intensifier, with the photocathode operating voltage at -200V. The imaging quality of the two image intensifiers—one with an untreated photocathode and the other with the method of this invention—was observed. The results are as follows: The imaging effect after processing with this method is shown in [Figure 1]. Figure 3 As shown, the imaging effect without image intensifier processing is shown below. Figure 4 As shown. The results show that the photocathode, after processing, produces an image ( Figure 3 The image intensifier has a high field-of-view brightness gain, meeting the selection requirements of the general specifications for super-second generation image intensifiers; the untreated image intensifier has a low field-of-view brightness gain. Figure 4 The brightness gain does not meet the general specifications for selecting tubes for Super 2 image intensifiers.

Claims

1. A method for handling excess antimony during sodium-antimony co-evaporation in the fabrication of a second-generation multi-alkali photocathode, characterized in that... During the photocathode fabrication process, the photocurrent is detected by illumination with a process lamp. The photocurrent value is also measured after sodium-antimony co-deposition. If the photocurrent is below 1500 nA, it is determined that there is excessive antimony during the sodium-antimony co-deposition of the substrate layer, and the following steps are taken to address the issue: Step 1: Turn on the sodium evaporation power supply and adjust the sodium evaporation current to the initial value of 2000-2500mA; Step 2: Increase the sodium evaporation current at a rate of 400mA / min. When an increase or decrease in photocurrent is detected, stop increasing the sodium evaporation current and maintain the current sodium evaporation current. Step 3: Turn on the antimony evaporation power after one minute; Step 4: Adjust the antimony evaporation current to the initial value of 1000-1500mA, and increase the antimony evaporation current at a rate of 500mA / min. Step 5: When a rise or fall in photocurrent is detected, turn off the antimony evaporation power supply within 30 seconds; Step 6: After one minute, turn off the sodium distillation power supply to complete the treatment of excess antimony during sodium-antimony co-distillation and proceed to the next process.

Images