Development of Ferroelectric Cathode Vacuum Diode Test Device for Strong Emission Current

The ferroelectric cathode (also called cold cathode) material is a new type of functional material that obtains pulsed strong current electron emission from ferroelectric material surface under pulsed high voltage or strong laser excitation. The electron beam emitted from the surface of the ferroelectric cathode has the characteristics of excellent quality, electrically controllable, high brightness, and high emission current density.

At the same time, the ferroelectric cathode operates at room temperature, has no harsh requirements for the environment, and its structure is simple and compact, sturdy and durable, and the production cost is low, so it has been highly valued by many countries and research institutions in the world. At present, ferroelectric cathodes have gone through device development and application research through simple material research.

Many people in foreign countries try to encapsulate ferroelectric cathodes into vacuum diodes and conduct electron emission tests to study the properties and applications of electron beams.

As a new high-brightness, high-repetition rate, high-current electron beam source, it is necessary to use a diode to conduct a test simulation test of the emission current density when applied to an electron gun.

The previously designed diodes are shown in the structure and assembly process flow respectively. Ferroelectric cathode has a high working threshold voltage. To ensure that the distance between the two poles is large enough, the volume of the glass bulb must be large. In addition, since the glass bulb can not be used repeatedly, each time a launch test is performed, the glass bulb needs to be re-processed, the test cost is high, and the auxiliary working time is high. Long, does not apply to experimental studies.

d Guo Shuguang 95, female, Sichuan, such as a level 1 engaged in the design of the structure and the electric material research ed. http://ww.cnki.net ferroelectric bright anode anode test is under high voltage negative pulse voltage excitation, from the iron The surface of the electro-cathode material obtains a strong electron emission, and the emitted electrons are collected by the collector. Through the relevant circuit, the charge that reaches the collector is observed and recorded by a high-precision storage oscilloscope. Then the ferroelectric is calculated according to the sample structure size. Current density emitted by the cathode material In the diode tester, due to the glass material used in the housing, the ground current is not adequately shielded so that it couples with the ground current signal, obscuring the actual signal of the sample, but also due to other reasons, Therefore, the relationship between the emission current of the ferroelectric cathode material sample and the pulsed excitation voltage cannot be observed, although this does not hinder the practical application of the ferroelectric body to the diode in the future, it is difficult to provide accurate results for the further development of scientific research work. Test Data.

After many tests and analysis, it was considered that in addition to reusing the DC high-voltage pulse generator with a high-powered hydrogen gate as its working mode, replacing the high-voltage pulse transmitter of the original cold-cathode thyristor, the test device was After a number of improvements in the structure, the emission current density of the ferroelectric cathode material: PZT samples was tested and the results meet the test requirements.

2 dedicated vacuum chamber - tube shell" eight 1 line F past tests are usually conducted in the atmosphere. Since the real electrode (SE) of the ferroelectric cathode material sample and the diode structure diagram have excitation voltage of several kV and the distance between the collector electrode and the gate electrode is only a few millimeters, the charged particles in the air are affected by the high-voltage electric field. There is a large enough kinetic energy in the diode process flow to cause gas molecules to collide and dissociate, resulting in a large conductance, which leads to erroneous determination of the emission current collection of the ferroelectric cathode material sample. When the gas pressure is below 10-3 Pa, the gas release phenomenon can be greatly reduced. Previous tests have found that due to poor shielding, the ground current coupling signal covers the actual signal of the sample itself, making the test inaccurate, so the test system is designed as a vacuum chamber composed of a brass housing. The shell is connected to a large site, and a collector shield is attached to the circular shield connected to the shell. This prevents the influence of ground current on the collection of the sample emission current.

3 Electron collection circuit The electron collection circuit is composed of 20 non-inductive resistors that are uniformly arranged in the graphite collector and in the axial direction. Among them, the main improvement areas are: (1) Using graphite materials instead of the original copper materials as collectors. Because the chemical properties of graphite are inert, and because of its heat resistance, it is not easy to generate oxidation. When the humidity is high, it does not form a solid semi-conductive oxide on the surface like metal. Instead, it generates gas CO or CO2 and evaporates, so this The collecting electrode of the material will have a better effect on the collection of electrons emitted from the product. H. Allrightsreserved, http: // Gold IV Ferroelectric sample holders Schottky and sample assembly tubes Metal welding Heat treatment Vacuum and low temperature (2) Use non-inductive resistors to replace the original ordinary resistors. The lead of the non-inductive resistor should be as short as possible to reduce the inductance of the collector loop lead. Otherwise, the presence of the lead inductance will affect the test of high-frequency electrical signals. At the same time, the 20 non-inductive resistors are evenly distributed in the axial direction to reduce the influence of the distributed inductance of the components on the collection of electrons.

The 8 cable sockets (BNC sockets) and 508 cable are matched with the external high-speed storage oscilloscope to reduce signal attenuation. The waveform relationship between the emission current and the high-voltage pulse excitation voltage is displayed on the high-speed storage oscilloscope, and then the emission current density of the ferroelectric cathode material is calculated according to the structure size of the sample.

4 The composition of the vacuum chamber The vacuum chamber is designed for the circular chip structure: the basic device designed for the electron emission test of the PZT ferroelectric cathode material sample, the structure of which is shown. The vacuum chamber is made of brass and has an outer diameter of 2mm thick vacuum rubber. The upper and lower parts are sealed and connected by screws. Each insulator in the cavity and internal and external electrical connection devices are made of PTFE (its good insulation, dielectric loss is less than 110-4, and the water absorption rate is only 0.01%). The connecting part with the vacuum chamber is sealed and connected with a TLD-704 type silicon rubber liquid at the joint. After the silicone rubber liquid condenses, the connection can be reliably sealed, thereby ensuring a certain degree of vacuum. The graphite collector was made into a pyramid type, and the lower end plane was collected: the electrons emitted from the PZT sample, and the upper end was connected to the cable outlet of the 508. The collector is shielded by a shield that is attached to the housing. Collector and collector: A wire mesh was added between the PZT samples to filter the ferroelectric sample's capacitive effect during launch.

Using the improved high-current ferroelectric cathode vacuum diode tester, emission current densities were measured on three kinds of material samples, namely lead zirconate titanate (PZT), polytetrafluoroethylene, and organic glass. First of all, the vacuum degree reaches 310-3Pa, which satisfies the test conditions. Secondly, under this vacuum degree, when the applied pulse voltage is 8kV, the waveforms of the samples obtained before and after improvement by the high-speed storage test system are as shown.

5 Conclusion Before the improvement of the strong emission current ferroelectric cathode vacuum diode device, three kinds of sample waveform diodes, such as plexiglass, PTFE, and PZT ferroelectric ceramics, were improved before and after waveforms (the abscissa is time, each cell is 100 ris; the ordinate is The voltage, 5V per cell, is almost the same, and the waveform oscillates greatly, making it almost impossible to determine the sample signal. After the improvement, the waveform has almost no oscillation. The ferroelectric sample PZT and the current waveform lag behind the voltage waveform by several tens of nanoseconds. It is completely consistent with the theoretical waveform. The PTFE and Plexiglas are non-ferroelectric samples. Of course, there is no electron emission. . The improved device shields the disturbance of ground current and meets the basic requirements for testing the emission current of ferroelectric cathode materials with strong currents, laying the foundation for the practical application of ferroelectric cathode materials in vacuum diodes.